Sample records for fermi energy domain

  1. Anisotropy of the Fermi surface, Fermi velocity, many-body enhancement, and superconducting energy gap in Nb

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Crabtree, G.W.; Dye, D.H.; Karim, D.P.

    1987-02-01

    The detailed angular dependence of the Fermi radius k/sub F/, the Fermi velocity v/sub F/(k), the many-body enhancement factor lambda(k), and the superconducting energy gap ..delta..(k), for electrons on the Fermi surface of Nb are derived with use of the de Haas--van Alphen (dHvA) data of Karim, Ketterson, and Crabtree (J. Low Temp. Phys. 30, 389 (1978)), a Korringa-Kohn-Rostoker parametrization scheme, and an empirically adjusted band-structure calculation of Koelling. The parametrization is a nonrelativistic five-parameter fit allowing for cubic rather than spherical symmetry inside the muffin-tin spheres. The parametrized Fermi surface gives a detailed interpretation of the previously unexplained kappa,more » ..cap alpha..', and ..cap alpha..'' orbits in the dHvA data. Comparison of the parametrized Fermi velocities with those of the empirically adjusted band calculation allow the anisotropic many-body enhancement factor lambda(k) to be determined. Theoretical calculations of the electron-phonon interaction based on the tight-binding model agree with our derived values of lambda(k) much better than those based on the rigid-muffin-tin approximation. The anisotropy in the superconducting energy gap ..delta..(k) is estimated from our results for lambda(k), assuming weak anisotropy.« less

  2. Anisotropy of the Fermi surface, Fermi velocity, many-body enhancement, and superconducting energy gap in Nb

    NASA Astrophysics Data System (ADS)

    Crabtree, G. W.; Dye, D. H.; Karim, D. P.; Campbell, S. A.; Ketterson, J. B.

    1987-02-01

    The detailed angular dependence of the Fermi radius kF, the Fermi velocity vF(k), the many-body enhancement factor λ(k), and the superconducting energy gap Δ(k), for electrons on the Fermi surface of Nb are derived with use of the de Haas-van Alphen (dHvA) data of Karim, Ketterson, and Crabtree [J. Low Temp. Phys. 30, 389 (1978)], a Korringa-Kohn-Rostoker parametrization scheme, and an empirically adjusted band-structure calculation of Koelling. The parametrization is a nonrelativistic five-parameter fit allowing for cubic rather than spherical symmetry inside the muffin-tin spheres. The parametrized Fermi surface gives a detailed interpretation of the previously unexplained κ, α', and α'' orbits in the dHvA data. Comparison of the parametrized Fermi velocities with those of the empirically adjusted band calculation allow the anisotropic many-body enhancement factor λ(k) to be determined. Theoretical calculations of the electron-phonon interaction based on the tight-binding model agree with our derived values of λ(k) much better than those based on the rigid-muffin-tin approximation. The anisotropy in the superconducting energy gap Δ(k) is estimated from our results for λ(k), assuming weak anisotropy.

  3. Quasiparticle energy bands and Fermi surfaces of monolayer NbSe2

    NASA Astrophysics Data System (ADS)

    Kim, Sejoong; Son, Young-Woo

    2017-10-01

    A quasiparticle band structure of a single layer 2 H -NbSe2 is reported by using first-principles G W calculation. We show that a self-energy correction increases the width of a partially occupied band and alters its Fermi surface shape when comparing those using conventional mean-field calculation methods. Owing to a broken inversion symmetry in the trigonal prismatic single layer structure, the spin-orbit interaction is included and its impact on the Fermi surface and quasiparticle energy bands are discussed. We also calculate the doping dependent static susceptibilities from the band structures obtained by the mean-field calculation as well as G W calculation with and without spin-orbit interactions. A complete tight-binding model is constructed within the three-band third nearest neighbor hoppings and is shown to reproduce our G W quasiparticle energy bands and Fermi surface very well. Considering variations of the Fermi surface shapes depending on self-energy corrections and spin-orbit interactions, we discuss the formations of charge density wave (CDW) with different dielectric environments and their implications on recent controversial experimental results on CDW transition temperatures.

  4. Solitons as candidates for energy carriers in Fermi-Pasta-Ulam lattices

    NASA Astrophysics Data System (ADS)

    Ming, Yi; Ye, Liu; Chen, Han-Shuang; Mao, Shi-Feng; Li, Hui-Min; Ding, Ze-Jun

    2018-01-01

    Currently, effective phonons (renormalized or interacting phonons) rather than solitary waves (for short, solitons) are regarded as the energy carriers in nonlinear lattices. In this work, by using the approximate soliton solutions of the corresponding equations of motion and adopting the Boltzmann distribution for these solitons, the average velocities of solitons are obtained and are compared with the sound velocities of energy transfer. Excellent agreements with the numerical results and the predictions of other existing theories are shown in both the symmetric Fermi-Pasta-Ulam-β lattices and the asymmetric Fermi-Pasta-Ulam-α β lattices. These clearly indicate that solitons are suitable candidates for energy carriers in Fermi-Pasta-Ulam lattices. In addition, the root-mean-square velocity of solitons can be obtained from the effective phonons theory.

  5. Diagnosing alternative conceptions of Fermi energy among undergraduate students

    NASA Astrophysics Data System (ADS)

    Sharma, Sapna; Ahluwalia, Pardeep Kumar

    2012-07-01

    Physics education researchers have scientifically established the fact that the understanding of new concepts and interpretation of incoming information are strongly influenced by the preexisting knowledge and beliefs of students, called epistemological beliefs. This can lead to a gap between what students actually learn and what the teacher expects them to learn. In a classroom, as a teacher, it is desirable that one tries to bridge this gap at least on the key concepts of a particular field which is being taught. One such key concept which crops up in statistical physics/solid-state physics courses, and around which the behaviour of materials is described, is Fermi energy (εF). In this paper, we present the results which emerged about misconceptions on Fermi energy in the process of administering a diagnostic tool called the Statistical Physics Concept Survey developed by the authors. It deals with eight themes of basic importance in learning undergraduate solid-state physics and statistical physics. The question items of the tool were put through well-established sequential processes: definition of themes, Delphi study, interview with students, drafting questions, administration, validity and reliability of the tool. The tool was administered to a group of undergraduate students and postgraduate students, in a pre-test and post-test design. In this paper, we have taken one of the themes i.e. Fermi energy of the diagnostic tool for our analysis and discussion. Students’ responses and reasoning comments given during interview were analysed. This analysis helped us to identify prevailing misconceptions/learning gaps among students on this topic. How spreadsheets can be effectively used to remove the identified misconceptions and help appreciate the finer nuances while visualizing the behaviour of the system around Fermi energy, normally sidestepped both by the teachers and learners, is also presented in this paper.

  6. Fermi energy dependence of the optical emission in core/shell InAs nanowire homostructures

    NASA Astrophysics Data System (ADS)

    Möller, M.; Oliveira, D. S.; Sahoo, P. K.; Cotta, M. A.; Iikawa, F.; Motisuke, P.; Molina-Sánchez, A.; de Lima, M. M., Jr.; García-Cristóbal, A.; Cantarero, A.

    2017-07-01

    InAs nanowires grown by vapor-liquid-solid (VLS) method are investigated by photoluminescence. We observe that the Fermi energy of all samples is reduced by ˜20 meV when the size of the Au nanoparticle used for catalysis is increased from 5 to 20 nm. Additional capping with a thin InP shell enhances the optical emission and does not affect the Fermi energy. The unexpected behavior of the Fermi energy is attributed to the differences in the residual donor (likely carbon) incorporation in the axial (low) and lateral (high incorporation) growth in the VLS and vapor-solid (VS) methods, respectively. The different impurity incorporation rate in these two regions leads to a core/shell InAs homostructure. In this case, the minority carriers (holes) diffuse to the core due to the built-in electric field created by the radial impurity distribution. As a result, the optical emission is dominated by the core region rather than by the more heavily doped InAs shell. Thus, the photoluminescence spectra and the Fermi energy become sensitive to the core diameter. These results are corroborated by a theoretical model using a self-consistent method to calculate the radial carrier distribution and Fermi energy for distinct diameters of Au nanoparticles.

  7. Fermi energy control of vacancy coalescence and dislocation density in melt-grown GaAs

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Lin, D. G.; Aoyama, T.

    1984-01-01

    A striking effect of the Fermi energy on the dislocation density in melt-grown GaAs has been discovered. Thus, a shift of the Fermi energy from 0.1 eV above to 0.2 eV below its intrinsic value (at high temperature, i.e., near 1100 K) increases the dislocation density by as much as five orders of magnitude. The Fermi energy shift was brought about by n-type and p-type doping at a level of about 10 to the 17th per cu cm (under conditions of optimum partial pressure of As, i.e., under optimum melt stoichiometry). This effect must be associated with the fact that the Fermi energy controls the charge state of vacancies (i.e., the occupancy of the associated electronic states) which in turn must control their tendency to coalesce and thus the dislocation density. It appears most likely that gallium vacancies are the critical species.

  8. Time-Domain Astronomy with the Fermi GBM

    NASA Technical Reports Server (NTRS)

    Hui, C. M.

    2017-01-01

    The Fermi Gamma-ray Burst Monitor (GBM) is an all-sky monitoring instrument sensitive to energies from 8 kiloelectronvolts to 40 megaelectronvolts. Over the past 8 years of operation, the GBM has detected over 240 gamma-ray bursts per year and provided timely GCN (Gamma-ray Coordinates Network) notices with localization to few-degree accuracy for follow-up observations. In addition to GRBs, galactic transients, solar flares, and terrestrial gamma-ray flashes have also been observed. In recent years we have also been searching the continuous GBM data for electromagnetic counterpart to astrophysical neutrinos and gravitational wave events, as these are believed to be associated with gamma-ray bursts. With continuous data downlink every few hours and a temporal resolution of 2 microseconds, GBM is well suited for observing transients and supporting EM followup in the era of multi-messenger astronomy.

  9. Time-Domain Astronomy with the Fermi GBM

    NASA Technical Reports Server (NTRS)

    Hui, C. M.

    2017-01-01

    The Fermi Gamma-ray Burst Monitor (GBM) is an all-sky monitoring instrument sensitive to energies from 8 keV to 40 MeV. Over the past 8 years of operation, the GBM has detected over 240 gamma-ray bursts per year and provided timely GCN notices with localization to few-degree accuracy for follow-up observations. In addition to GRBs, Galactic transients, solar flares, and terrestrial gamma-ray flashes have also been observed. In recent years we have also been searching the continuous GBM data for electromagnetic counterpart to astrophysical neutrinos and gravitational wave events, as these are believed to be associated with gamma-ray bursts. With continuous data downlink every few hours and a temporal resolution of 2 microseconds, GBM is well suited for observing transients and supporting EM follow-up in the era of multi-messenger astronomy.

  10. Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Arimoto, M.; ...

    2009-02-19

    Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. Finally, the known distance of the burstmore » enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.« less

  11. Fermi observations of high-energy gamma-ray emission from GRB 080916C.

    PubMed

    Abdo, A A; Ackermann, M; Arimoto, M; Asano, K; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Band, D L; Barbiellini, G; Baring, M G; Bastieri, D; Battelino, M; Baughman, B M; Bechtol, K; Bellardi, F; Bellazzini, R; Berenji, B; Bhat, P N; Bissaldi, E; Blandford, R D; Bloom, E D; Bogaert, G; Bogart, J R; Bonamente, E; Bonnell, J; Borgland, A W; Bouvier, A; Bregeon, J; Brez, A; Briggs, M S; Brigida, M; Bruel, P; Burnett, T H; Burrows, D; Busetto, G; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Ceccanti, M; Cecchi, C; Celotti, A; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Cominsky, L R; Connaughton, V; Conrad, J; Costamante, L; Cutini, S; Deklotz, M; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; Dingus, B L; do Couto E Silva, E; Drell, P S; Dubois, R; Dumora, D; Edmonds, Y; Evans, P A; Fabiani, D; Farnier, C; Favuzzi, C; Finke, J; Fishman, G; Focke, W B; Frailis, M; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giebels, B; Giglietto, N; Giommi, P; Giordano, F; Glanzman, T; Godfrey, G; Goldstein, A; Granot, J; Greiner, J; Grenier, I A; Grondin, M-H; Grove, J E; Guillemot, L; Guiriec, S; Haller, G; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hernando Morat, J A; Hoover, A; Hughes, R E; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kavelaars, A; Kawai, N; Kelly, H; Kennea, J; Kerr, M; Kippen, R M; Knödlseder, J; Kocevski, D; Kocian, M L; Komin, N; Kouveliotou, C; Kuehn, F; Kuss, M; Lande, J; Landriu, D; Larsson, S; Latronico, L; Lavalley, C; Lee, B; Lee, S-H; Lemoine-Goumard, M; Lichti, G G; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Marangelli, B; Mazziotta, M N; McBreen, S; McEnery, J E; McGlynn, S; Meegan, C; Mészáros, P; Meurer, C; Michelson, P F; Minuti, M; Mirizzi, N; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Moretti, E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Nelson, D; Nolan, P L; Norris, J P; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paciesas, W S; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Perri, M; Pesce-Rollins, M; Petrosian, V; Pinchera, M; Piron, F; Porter, T A; Preece, R; Rainò, S; Ramirez-Ruiz, E; Rando, R; Rapposelli, E; Razzano, M; Razzaque, S; Rea, N; Reimer, A; Reimer, O; Reposeur, T; Reyes, L C; Ritz, S; Rochester, L S; Rodriguez, A Y; Roth, M; Ryde, F; Sadrozinski, H F-W; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Schalk, T L; Segal, K N; Sgrò, C; Shimokawabe, T; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Stamatikos, M; Starck, J-L; Stecker, F W; Steinle, H; Stephens, T E; Strickman, M S; Suson, D J; Tagliaferri, G; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Tenze, A; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Turri, M; Tuvi, S; Usher, T L; van der Horst, A J; Vigiani, L; Vilchez, N; Vitale, V; von Kienlin, A; Waite, A P; Williams, D A; Wilson-Hodge, C; Winer, B L; Wood, K S; Wu, X F; Yamazaki, R; Ylinen, T; Ziegler, M

    2009-03-27

    Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.

  12. FERMI Observations of High-Energy Gamma-Ray Emission from GRB 080825C

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Asano, K.; ...

    2009-11-24

    The Fermi Gamma-ray Space Telescope has opened a new high-energy window in the study of gamma-ray bursts (GRBs). Here in this paper, we present a thorough analysis of GRB 080825C, which triggered the Fermi Gamma-ray Burst Monitor (GBM), and was the first firm detection of a GRB by the Fermi Large Area Telescope (LAT). We discuss the LAT event selections, background estimation, significance calculations, and localization for Fermi GRBs in general and GRB 080825C in particular. We show the results of temporal and time-resolved spectral analysis of the GBM and LAT data. Finally, we also present some theoretical interpretation ofmore » GRB 080825C observations as well as some common features observed in other LAT GRBs.« less

  13. 75 FR 24755 - DTE ENERGY; Enrico Fermi Atomic Power Plant Unit 1; Exemption From Certain Low-Level Waste...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-05

    ... NUCLEAR REGULATORY COMMISSION [Docket No. 50-16; NRC-2009-0073] DTE ENERGY; Enrico Fermi Atomic... License No. DPR-9 issued for Enrico Fermi Atomic Power Plant, Unit 1 (Fermi-1), located in Monroe County... undue hazard to life or property. There are no provisions in the Atomic Energy Act (or in any other...

  14. A connection between domain-averaged Fermi hole orbitals and electron number distribution functions in real space.

    PubMed

    Francisco, E; Martín Pendás, A; Blanco, M A

    2009-09-28

    We show in this article how for single-determinant wave functions the one-electron functions derived from the diagonalization of the Fermi hole, averaged over an arbitrary domain Omega of real space, and expressed in terms of the occupied canonical orbitals, describe coarse-grained statistically independent electrons. With these domain-averaged Fermi hole (DAFH) orbitals, the full electron number distribution function (EDF) is given by a simple product of one-electron events. This useful property follows from the simultaneous orthogonality of the DAFH orbitals in Omega, Omega(')=R(3)-Omega, and R(3). We also show how the interfragment (shared electron) delocalization index, delta(Omega,Omega(')), transforms into a sum of one-electron DAFH contributions. Description of chemical bonding in terms of DAFH orbitals provides a vivid picture relating bonding and delocalization in real space. DAFH and EDF analyses are performed on several test systems to illustrate the close relationship between both concepts. Finally, these analyses clearly prove how DAFH orbitals well localized in Omega or Omega(') can be simply ignored in computing the EDFs and/or delta(Omega,Omega(')), and thus do not contribute to the chemical bonding between the two fragments.

  15. Extended Thomas-Fermi density functional for the unitary Fermi gas

    NASA Astrophysics Data System (ADS)

    Salasnich, Luca; Toigo, Flavio

    2008-11-01

    We determine the energy density ξ(3/5)nɛF and the gradient correction λℏ2(∇n)2/(8mn) of the extended Thomas-Fermi (ETF) density functional, where n is the number density and ɛF is the Fermi energy, for a trapped two-component Fermi gas with infinite scattering length (unitary Fermi gas) on the basis of recent diffusion Monte Carlo (DMC) calculations [Phys. Rev. Lett. 99, 233201 (2007)]. In particular we find that ξ=0.455 and λ=0.13 give the best fit of the DMC data with an even number N of particles. We also study the odd-even splitting γN1/9ℏω of the ground-state energy for the unitary gas in a harmonic trap of frequency ω determining the constant γ . Finally we investigate the effect of the gradient term in the time-dependent ETF model by introducing generalized Galilei-invariant hydrodynamics equations.

  16. Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB6

    NASA Astrophysics Data System (ADS)

    Hartstein, M.; Toews, W. H.; Hsu, Y.-T.; Zeng, B.; Chen, X.; Hatnean, M. Ciomaga; Zhang, Q. R.; Nakamura, S.; Padgett, A. S.; Rodway-Gant, G.; Berk, J.; Kingston, M. K.; Zhang, G. H.; Chan, M. K.; Yamashita, S.; Sakakibara, T.; Takano, Y.; Park, J.-H.; Balicas, L.; Harrison, N.; Shitsevalova, N.; Balakrishnan, G.; Lonzarich, G. G.; Hill, R. W.; Sutherland, M.; Sebastian, Suchitra E.

    2018-02-01

    The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator-metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. Here we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB6 positioned close to the insulator-metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including a sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Thus, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.

  17. Pseudogap-generated a coexistence of Fermi arcs and Fermi pockets in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhao, Huaisong; Gao, Deheng; Feng, Shiping

    2017-03-01

    One of the most intriguing puzzle is why there is a coexistence of Fermi arcs and Fermi pockets in the pseudogap phase of cuprate superconductors? This puzzle is calling for an explanation. Based on the t - J model in the fermion-spin representation, the coexistence of the Fermi arcs and Fermi pockets in cuprate superconductors is studied by taking into account the pseudogap effect. It is shown that the pseudogap induces an energy band splitting, and then the poles of the electron Green's function at zero energy form two contours in momentum space, however, the electron spectral weight on these two contours around the antinodal region is gapped out by the pseudogap, leaving behind the low-energy electron spectral weight only located at the disconnected segments around the nodal region. In particular, the tips of these disconnected segments converge on the hot spots to form the closed Fermi pockets, generating a coexistence of the Fermi arcs and Fermi pockets. Moreover, the single-particle coherent weight is directly related to the pseudogap, and grows linearly with doping. The calculated result of the overall dispersion of the electron excitations is in qualitative agreement with the experimental data. The theory also predicts that the pseudogap-induced peak-dip-hump structure in the electron spectrum is absent from the hot-spot directions.

  18. Fermi surface in the absence of a Fermi liquid in the Kondo insulator SmB 6

    DOE PAGES

    Hartstein, M.; Toews, W. H.; Hsu, Y. -T.; ...

    2017-10-23

    The search for a Fermi surface in the absence of a conventional Fermi liquid has thus far yielded very few potential candidates. Among promising materials are spin-frustrated Mott insulators near the insulator–metal transition, where theory predicts a Fermi surface associated with neutral low-energy excitations. In this paper, we reveal another route to experimentally realize a Fermi surface in the absence of a Fermi liquid by the experimental study of a Kondo insulator SmB 6 positioned close to the insulator–metal transition. We present experimental signatures down to low temperatures (<<1 K) associated with a Fermi surface in the bulk, including amore » sizeable linear specific heat coefficient, and on the application of a finite magnetic field, bulk magnetic quantum oscillations, finite quantum oscillatory entropy, and substantial enhancement in thermal conductivity well below the charge gap energy scale. Finally, the weight of evidence indicates that despite an extreme instance of Fermi liquid breakdown in Kondo insulating SmB 6, a Fermi surface arises from novel itinerant low-energy excitations that couple to magnetic fields, but not weak DC electric fields.« less

  19. Detection potential of the KM3NeT detector for high-energy neutrinos from the Fermi bubbles

    NASA Astrophysics Data System (ADS)

    KM3NeT Collaboration; Adrián-Martínez, S.; Ageron, M.; Aguilar, J. A.; Aharonian, F.; Aiello, S.; Albert, A.; Alexandri, M.; Ameli, F.; Anassontzis, E. G.; Anghinolfi, M.; Anton, G.; Anvar, S.; Ardid, M.; Assis Jesus, A.; Aubert, J.-J.; Bakker, R.; Ball, A. E.; Barbarino, G.; Barbarito, E.; Barbato, F.; Baret, B.; de Bel, M.; Belias, A.; Bellou, N.; Berbee, E.; Berkien, A.; Bersani, A.; Bertin, V.; Beurthey, S.; Biagi, S.; Bigongiari, C.; Bigourdan, B.; Billault, M.; de Boer, R.; Boer Rookhuizen, H.; Bonori, M.; Borghini, M.; Bou-Cabo, M.; Bouhadef, B.; Bourlis, G.; Bouwhuis, M.; Bradbury, S.; Brown, A.; Bruni, F.; Brunner, J.; Brunoldi, M.; Busto, J.; Cacopardo, G.; Caillat, L.; Calvo Díaz-Aldagalán, D.; Calzas, A.; Canals, M.; Capone, A.; Carr, J.; Castorina, E.; Cecchini, S.; Ceres, A.; Cereseto, R.; Chaleil, Th.; Chateau, F.; Chiarusi, T.; Choqueuse, D.; Christopoulou, P. E.; Chronis, G.; Ciaffoni, O.; Circella, M.; Cocimano, R.; Cohen, F.; Colijn, F.; Coniglione, R.; Cordelli, M.; Cosquer, A.; Costa, M.; Coyle, P.; Craig, J.; Creusot, A.; Curtil, C.; D'Amico, A.; Damy, G.; De Asmundis, R.; De Bonis, G.; Decock, G.; Decowski, P.; Delagnes, E.; De Rosa, G.; Distefano, C.; Donzaud, C.; Dornic, D.; Dorosti-Hasankiadeh, Q.; Drogou, J.; Drouhin, D.; Druillole, F.; Drury, L.; Durand, D.; Durand, G. A.; Eberl, T.; Emanuele, U.; Enzenhöfer, A.; Ernenwein, J.-P.; Escoffier, S.; Espinosa, V.; Etiope, G.; Favali, P.; Felea, D.; Ferri, M.; Ferry, S.; Flaminio, V.; Folger, F.; Fotiou, A.; Fritsch, U.; Gajanana, D.; Garaguso, R.; Gasparini, G. P.; Gasparoni, F.; Gautard, V.; Gensolen, F.; Geyer, K.; Giacomelli, G.; Gialas, I.; Giordano, V.; Giraud, J.; Gizani, N.; Gleixner, A.; Gojak, C.; Gómez-González, J. P.; Graf, K.; Grasso, D.; Grimaldi, A.; Groenewegen, R.; Guédé, Z.; Guillard, G.; Guilloux, F.; Habel, R.; Hallewell, G.; van Haren, H.; van Heerwaarden, J.; Heijboer, A.; Heine, E.; Hernández-Rey, J. J.; Herold, B.; Hillebrand, T.; van de Hoek, M.; Hogenbirk, J.; Hößl, J.; Hsu, C. C.; Imbesi, M.; Jamieson, A.; Jansweijer, P.; de Jong, M.; Jouvenot, F.; Kadler, M.; Kalantar-Nayestanaki, N.; Kalekin, O.; Kappes, A.; Karolak, M.; Katz, U. F.; Kavatsyuk, O.; Keller, P.; Kiskiras, Y.; Klein, R.; Kok, H.; Kontoyiannis, H.; Kooijman, P.; Koopstra, J.; Kopper, C.; Korporaal, A.; Koske, P.; Kouchner, A.; Koutsoukos, S.; Kreykenbohm, I.; Kulikovskiy, V.; Laan, M.; La Fratta, C.; Lagier, P.; Lahmann, R.; Lamare, P.; Larosa, G.; Lattuada, D.; Leisos, A.; Lenis, D.; Leonora, E.; Le Provost, H.; Lim, G.; Llorens, C. D.; Lloret, J.; Löhner, H.; Lo Presti, D.; Lotrus, P.; Louis, F.; Lucarelli, F.; Lykousis, V.; Malyshev, D.; Mangano, S.; Marcoulaki, E. C.; Margiotta, A.; Marinaro, G.; Marinelli, A.; Mariş, O.; Markopoulos, E.; Markou, C.; Martínez-Mora, J. A.; Martini, A.; Marvaldi, J.; Masullo, R.; Maurin, G.; Migliozzi, P.; Migneco, E.; Minutoli, S.; Miraglia, A.; Mollo, C. M.; Mongelli, M.; Monmarthe, E.; Morganti, M.; Mos, S.; Motz, H.; Moudden, Y.; Mul, G.; Musico, P.; Musumeci, M.; Naumann, Ch.; Neff, M.; Nicolaou, C.; Orlando, A.; Palioselitis, D.; Papageorgiou, K.; Papaikonomou, A.; Papaleo, R.; Papazoglou, I. A.; Păvălaş, G. E.; Peek, H. Z.; Perkin, J.; Piattelli, P.; Popa, V.; Pradier, T.; Presani, E.; Priede, I. G.; Psallidas, A.; Rabouille, C.; Racca, C.; Radu, A.; Randazzo, N.; Rapidis, P. A.; Razis, P.; Real, D.; Reed, C.; Reito, S.; Resvanis, L. K.; Riccobene, G.; Richter, R.; Roensch, K.; Rolin, J.; Rose, J.; Roux, J.; Rovelli, A.; Russo, A.; Russo, G. V.; Salesa, F.; Samtleben, D.; Sapienza, P.; Schmelling, J.-W.; Schmid, J.; Schnabel, J.; Schroeder, K.; Schuller, J.-P.; Schussler, F.; Sciliberto, D.; Sedita, M.; Seitz, T.; Shanidze, R.; Simeone, F.; Siotis, I.; Sipala, V.; Sollima, C.; Sparnocchia, S.; Spies, A.; Spurio, M.; Staller, T.; Stavrakakis, S.; Stavropoulos, G.; Steijger, J.; Stolarczyk, Th.; Stransky, D.; Taiuti, M.; Taylor, A.; Thompson, L.; Timmer, P.; Tonoiu, D.; Toscano, S.; Touramanis, C.; Trasatti, L.; Traverso, P.; Trovato, A.; Tsirigotis, A.; Tzamarias, S.; Tzamariudaki, E.; Urbano, F.; Vallage, B.; Van Elewyck, V.; Vannoni, G.; Vecchi, M.; Vernin, P.; Viola, S.; Vivolo, D.; Wagner, S.; Werneke, P.; White, R. J.; Wijnker, G.; Wilms, J.; de Wolf, E.; Yepes, H.; Zhukov, V.; Zonca, E.; Zornoza, J. D.; Zúñiga, J.

    2013-02-01

    A recent analysis of the Fermi Large Area Telescope data provided evidence for a high-intensity emission of high-energy gamma rays with a E-2 spectrum from two large areas, spanning 50° above and below the Galactic centre (the "Fermi bubbles"). A hadronic mechanism was proposed for this gamma-ray emission making the Fermi bubbles promising source candidates of high-energy neutrino emission. In this work Monte Carlo simulations regarding the detectability of high-energy neutrinos from the Fermi bubbles with the future multi-km3 neutrino telescope KM3NeT in the Mediterranean Sea are presented. Under the hypothesis that the gamma-ray emission is completely due to hadronic processes, the results indicate that neutrinos from the bubbles could be discovered in about one year of operation, for a neutrino spectrum with a cutoff at 100 TeV and a detector with about 6 km3 of instrumented volume. The effect of a possible lower cutoff is also considered.

  20. The Spectral Energy Distribution of Fermi Bright Blazars

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Ackermann, M.; Agudo, I.; Ajello, M.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Arkharov, A. A.; Axelsson, M.; Bach, U.; hide

    2010-01-01

    We have conducted a detailed investigation of the broadband spectral properties of the gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray /gamma-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log v-log v Fv representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, alpha(sub ro) , and optical to X-ray, alpha(sub ox), spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency (v(sup S) (sub peak)) is positioned between 10(exp 12.5) and 10(exp 14) Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10(exp 13) and 10(exp 17) Hz in featureless BL Lacertae objects. We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than

  1. The Spectral Energy Distribution of Fermi bright blazars

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Agudo, I.; ...

    2010-05-13

    We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν F ν representation, the typical broadband spectral signaturesmore » normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. Here, we have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, α ro, and optical to X-ray, α ox, spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (ν S peak) is positioned between 10 12.5 and 10 14.5 Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10 13 and 10 17 Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked

  2. First Results on the High Energy Cosmic Ray Electron Spectrum from Fermi Lat

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2009-01-01

    This viewgraph presentation addresses energy reconstruction, electron-hadron separation, validation of Monte Carlo with flight data and an assessment of systematic errors from the Fermi Large Area Telescope.

  3. 7th International Fermi Symposium

    NASA Astrophysics Data System (ADS)

    2017-10-01

    The two Fermi instruments have been surveying the high-energy sky since August 2008. The Large Area Telescope (LAT) has discovered more than three thousand gamma-ray sources and many new source classes, bringing the importance of gamma-ray astrophysics to an ever-broadening community. The LAT catalog includes supernova remnants, pulsar wind nebulae, pulsars, binary systems, novae, several classes of active galaxies, starburst galaxies, normal galaxies, and a large number of unidentified sources. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from a wide range of transients. Fermi LAT's study of diffuse gamma-ray emission in our Galaxy revealed giant bubbles, as well as an excess of gamma-rays from the Galactic center region, both observations have become exciting puzzles for the astrophysics community. The direct measurement of a harder-than- expected cosmic-ray electron spectrum may imply the presence of nearby cosmic-ray accelerators. LAT data have provided stringent constraints on new phenomena such as supersymmetric dark-matter annihilations as well as tests of fundamental physics. The full reprocessing of the entire mission dataset with Pass 8 includes improved event reconstruction, a wider energy range, better energy measurements, and significantly increased effective area, all them boosting the discovery potential and the ability to do precision observations with LAT. The Gamma-ray Burst Monitor (GBM) continues to be a prolific detector of gamma-ray transients: magnetars, solar flares, terrestrial gamma-ray flashes and gamma-ray bursts at keV to MeV energies, complementing the higher energy LAT observations of those sources in addition to providing valuable science return in their own right. All gamma-ray data are made immediately available at the Fermi Science Support Center (http://fermi.gsfc.nasa.gov/ssc). These publicly available data and Fermi analysis tools have enabled a large number of important studies. We

  4. A Method for Calculating Fermi Energy and Carrier Concentrations in Semiconducts

    ERIC Educational Resources Information Center

    Gaylord, T. K.; Linxwiler, J. N., Jr.

    1976-01-01

    An efficient numerical method for calculating the Fermi energy, the free electron and free hole concentrations, and the ionized impurity conductors in a semiconductor material is described. The method allows freedom with respect to type of material, temperature, and amount and type of donor and acceptor impurities. (Author/CP)

  5. The Fermi-LAT detection of magnetar-like pulsar PSR J1846-0258 at high-energy gamma-rays

    NASA Astrophysics Data System (ADS)

    Kuiper, L.; Hermsen, W.; Dekker, A.

    2018-03-01

    We report the detection of the pulsed signal of the radio-quiet magnetar-like pulsar PSR J1846-0258 in the high-energy γ-ray data of the Fermi Large Area Telescope (Fermi LAT). We produced phase-coherent timing models exploiting RXTE PCA and Swift XRT monitoring data for the post- (magnetar-like) outburst period from 2007 August 28 to 2016 September 4, with independent verification using INTEGRAL ISGRI and Fermi GBM data. Phase-folding barycentric arrival times of selected Fermi LAT events from PSR J1846-0258 resulted in a 4.2σ detection (30-100 MeV) of a broad pulse consistent in shape and aligned in phase with the profiles that we measured with Swift XRT (2.5-10 keV), INTEGRAL ISGRI (20-150 keV), and Fermi GBM (20-300 keV). The pulsed flux (30-100 MeV) is (3.91 ± 0.97) × 10-9 photons cm-2 s-1 MeV-1. Declining significances of the INTEGRAL ISGRI 20-150 keV pulse profiles suggest fading of the pulsed hard X-ray emission during the post-outburst epochs. We revisited with greatly improved statistics the timing and spectral characteristics of PSR B1509-58 as measured with the Fermi LAT. The broad-band pulsed emission spectra (from 2 keV up to GeV energies) of PSR J1846-0258 and PSR B1509-58 can be accurately described with similarly curved shapes, with maximum luminosities at 3.5 ± 1.1 MeV (PSR J1846-0258) and 2.23 ± 0.11 MeV (PSR B1509-58). We discuss possible explanations for observational differences between Fermi LAT detected pulsars that reach maximum luminosities at GeV energies, like the second magnetar-like pulsar PSR J1119-6127, and pulsars with maximum luminosities at MeV energies, which might be due to geometric differences rather than exotic physics in high-B fields.

  6. Fermi -LAT Observations of High-energy Behind-the-limb Solar Flares

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ackermann, M.; Buehler, R.; Allafort, A.

    2017-02-01

    We report on the Fermi -LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi -LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO . All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwavemore » spectra. We also provide a comparison of the BTL flares detected by Fermi -LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.« less

  7. Fermi-LAT Observations of High-energy Behind-the-limb Solar Flares

    DOE PAGES

    Ackermann, M.; Allafort, A.; Baldini, L.; ...

    2017-01-31

    In this paper, we report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwavemore » spectra. We also provide a comparison of the BTL flares detected by Fermi-LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. In conclusion, the protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.« less

  8. A Method for Localizing Energy Dissipation in Blazars Using Fermi Variability

    NASA Technical Reports Server (NTRS)

    Dotson, Amanda; Georganopoulos, Markos; Kazanas, Demosthenes; Perlman, Eric S.

    2013-01-01

    The distance of the Fermi-detected blazar gamma-ray emission site from the supermassive black hole is a matter of active debate. Here we present a method for testing if the GeV emission of powerful blazars is produced within the sub-pc scale broad line region (BLR) or farther out in the pc-scale molecular torus (MT) environment. If the GeV emission takes place within the BLR, the inverse Compton (IC) scattering of the BLR ultraviolet (UV) seed photons that produces the gamma-rays takes place at the onset of the Klein-Nishina regime. This causes the electron cooling time to become practically energy independent and the variation of the gamma-ray emission to be almost achromatic. If on the other hand the -ray emission is produced farther out in the pc-scale MT, the IC scattering of the infrared (IR) MT seed photons that produces the gamma-rays takes place in the Thomson regime, resulting to energy-dependent electron cooling times, manifested as faster cooling times for higher Fermi energies. We demonstrate these characteristics and discuss the applicability and limitations of our method.

  9. Self-energy behavior away from the Fermi surface in doped Mott insulators.

    PubMed

    Merino, J; Gunnarsson, O; Kotliar, G

    2016-02-03

    We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band ([Formula: see text]) is enhanced with respect to the self-energy magnitude at the bottom of the band ([Formula: see text]). The self-energy behavior at these two [Formula: see text]-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for [Formula: see text], we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, [Formula: see text], at half-filling reproduce the overall self-energy behavior at (0, 0) and [Formula: see text] found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the [Formula: see text] self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.

  10. Energy-absorption spectroscopy of unitary Fermi gases in a uniform potential

    NASA Astrophysics Data System (ADS)

    Zhang, Pengfei; Yu, Zhenhua

    2018-04-01

    We propose to use the energy absorption spectroscopy to measure the kinetic coefficients of unitary Fermi gases in a uniform potential. We show that, in our scheme, the energy absorption spectrum is proportional to the dynamic structure factor of the system. The profile of the spectrum depends on the shear viscosity η , the thermal conductivity κ , and the superfluid bulk viscosity ξ3. We show that extraction of these coefficients from the spectrum is achievable in present experiments.

  11. The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies

    PubMed Central

    Turchinovich, Dmitry; Kläui, Mathias; Hendry, Euan; Polini, Marco

    2018-01-01

    For many of the envisioned optoelectronic applications of graphene, it is crucial to understand the subpicosecond carrier dynamics immediately following photoexcitation and the effect of photoexcitation on the electrical conductivity—the photoconductivity. Whereas these topics have been studied using various ultrafast experiments and theoretical approaches, controversial and incomplete explanations concerning the sign of the photoconductivity, the occurrence and significance of the creation of additional electron-hole pairs, and, in particular, how the relevant processes depend on Fermi energy have been put forward. We present a unified and intuitive physical picture of the ultrafast carrier dynamics and the photoconductivity, combining optical pump–terahertz probe measurements on a gate-tunable graphene device, with numerical calculations using the Boltzmann equation. We distinguish two types of ultrafast photo-induced carrier heating processes: At low (equilibrium) Fermi energy (EF ≲ 0.1 eV for our experiments), broadening of the carrier distribution involves interband transitions (interband heating). At higher Fermi energy (EF ≳ 0.15 eV), broadening of the carrier distribution involves intraband transitions (intraband heating). Under certain conditions, additional electron-hole pairs can be created [carrier multiplication (CM)] for low EF, and hot carriers (hot-CM) for higher EF. The resultant photoconductivity is positive (negative) for low (high) EF, which in our physical picture, is explained using solely electronic effects: It follows from the effect of the heated carrier distributions on the screening of impurities, consistent with the DC conductivity being mostly due to impurity scattering. The importance of these insights is highlighted by a discussion of the implications for graphene photodetector applications. PMID:29756035

  12. Recent Developments in Non-Fermi Liquid Theory

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Sik

    2018-03-01

    Non-Fermi liquids are unconventional metals whose physical properties deviate qualitatively from those of noninteracting fermions due to strong quantum fluctuations near Fermi surfaces. They arise when metals are subject to singular interactions mediated by soft collective modes. In the absence of well-defined quasiparticles, universal physics of non-Fermi liquids is captured by interacting field theories which replace Landau Fermi liquid theory. However, it has been difficult to understand their universal low-energy physics due to a lack of theoretical methods that take into account strong quantum fluctuations in the presence of abundant low-energy degrees of freedom. In this review, we discuss two approaches that have been recently developed for non-Fermi liquid theory with emphasis on two space dimensions. The first is a perturbative scheme based on a dimensional regularization, which achieves a controlled access to the low-energy physics by tuning the codimension of Fermi surface. The second is a nonperturbative approach which treats the interaction ahead of the kinetic term through a non-Gaussian scaling called interaction-driven scaling. Examples of strongly coupled non-Fermi liquids amenable to exact treatments through the interaction-driven scaling are discussed.

  13. On the ground state energy of the delta-function Fermi gas

    NASA Astrophysics Data System (ADS)

    Tracy, Craig A.; Widom, Harold

    2016-10-01

    The weak coupling asymptotics to order γ of the ground state energy of the delta-function Fermi gas, derived heuristically in the literature, is here made rigorous. Further asymptotics are in principle computable. The analysis applies to the Gaudin integral equation, a method previously used by one of the authors for the asymptotics of large Toeplitz matrices.

  14. FermiGrid

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Yocum, D.R.; Berman, E.; Canal, P.

    2007-05-01

    As one of the founding members of the Open Science Grid Consortium (OSG), Fermilab enables coherent access to its production resources through the Grid infrastructure system called FermiGrid. This system successfully provides for centrally managed grid services, opportunistic resource access, development of OSG Interfaces for Fermilab, and an interface to the Fermilab dCache system. FermiGrid supports virtual organizations (VOs) including high energy physics experiments (USCMS, MINOS, D0, CDF, ILC), astrophysics experiments (SDSS, Auger, DES), biology experiments (GADU, Nanohub) and educational activities.

  15. Fermi at Six Months

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    An overview of the Fermi Gamma-ray Space Telescope's first 6 months in operation is provided. The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy rage 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. It contains a Large Area Telescope capable of viewing the entire sky every 3 hours and a Gamma-ray Burst Monitor for viewing the entire unocculted sky. Since its launch on June 11, 2008 Fermi has provided information on pulsars, gamma ray bursts, relativistic jets, the active galactic nucleus, and a globular star cluster. This presentation describes Fermi's development, mission, instruments and recent findings.

  16. Itinerant ferromagnetism in ultracold Fermi gases

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Heiselberg, H.

    2011-05-15

    Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature, a second-order transition is found at ak{sub F}{approx_equal}0.90 compatible with results of quantum-Monte-Carlo (QMC) calculations. Thermodynamic functions and observables, such as the compressibility and spin susceptibility and the resulting fluctuations in number and spin, are calculated. For trapped gases, the resulting cloud radii and kinetic energies are calculated and compared to recent experiments. Spin-polarized systems are recommended for effective separation of large ferromagnetic domains. Collective modes are predicted and tricritical points are calculatedmore » for multicomponent systems.« less

  17. Beam energy spread in FERMI@elettra gun and linac induced by intrabeam scattering

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zholents, Alexander A; Zholents, Alexander A; Zolotorev, Max S.

    Intrabeam scattering (IBS) of electrons in the pre-cathode area in the electron guns know in the literature as Boersh effect is responsible for a growth of the electron beam energy spread there. Albeit most visible within the electron gun where the electron beam density is large and the energy spread is small, the IBS acts all along the entire electron beam pass through the Linac. In this report we calculate the energy spread induced by IBS in the FERMI@elettra electron gun.

  18. Searches for correlation between UHECR events and high-energy gamma-ray Fermi-LAT data

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Álvarez, Ezequiel; Cuoco, Alessandro; Mirabal, Nestor

    The astrophysical sources responsible for ultra high-energy cosmic rays (UHECRs) continue to be one of the most intriguing mysteries in astrophysics. We present a comprehensive search for correlations between high-energy (∼> 1 GeV) gamma-ray events from the Fermi Large Area Telescope (LAT) and UHECRs (∼> 60 EeV) detected by the Telescope Array and the Pierre Auger Observatory. We perform two separate searches. First, we conduct a standard cross-correlation analysis between the arrival directions of 148 UHECRs and 360 gamma-ray sources in the Second Catalog of Hard Fermi-LAT sources (2FHL). Second, we search for a possible correlation between UHECR directions andmore » unresolved Fermi -LAT gamma-ray emission. For the latter, we use three different methods: a stacking technique with both a model-dependent and model-independent background estimate, and a cross-correlation function analysis. We also test for statistically significant excesses in gamma rays from signal regions centered on Cen A and the Telescope Array hotspot. No significant correlation is found in any of the analyses performed, except a weak (∼< 2σ) hint of signal with the correlation function method on scales ∼ 1°. Upper limits on the flux of possible power-law gamma-ray sources of UHECRs are derived.« less

  19. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGES

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; ...

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr 1-xLa x)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  20. Non-Fermi glasses: fractionalizing electrons at finite energy density

    NASA Astrophysics Data System (ADS)

    Parameswaran, Siddharth; Gopalakrishnan, Sarang

    Non-Fermi liquids are metals that cannot be adiabatically deformed into free fermion states. We argue for the existence of ``non-Fermi glasses,'' which are phases of interacting disordered fermions that are fully many-body localized, yet cannot be deformed into an Anderson insulator without an eigenstate phase transition. We explore the properties of such non-Fermi glasses, focusing on a specific solvable example. At high temperature, non-Fermi glasses have qualitatively similar spectral features to Anderson insulators. We identify a diagnostic, based on ratios of correlation functions, that sharply distinguishes between the two phases even at infinite temperature. We argue that our results and diagnostic should generically apply to the high-temperature behavior of the many-body localized descendants of fractionalized phases. S.A.P. is supported by NSF Grant DMR-1455366 and a UC President's Research Catalyst Award CA-15-327861, and S.G. by the Burke Institute at Caltech.

  1. Stochastic Fermi Energization of Coronal Plasma during Explosive Magnetic Energy Release

    NASA Astrophysics Data System (ADS)

    Pisokas, Theophilos; Vlahos, Loukas; Isliker, Heinz; Tsiolis, Vassilis; Anastasiadis, Anastasios

    2017-02-01

    The aim of this study is to analyze the interaction of charged particles (ions and electrons) with randomly formed particle scatterers (e.g., large-scale local “magnetic fluctuations” or “coherent magnetic irregularities”) using the setup proposed initially by Fermi. These scatterers are formed by the explosive magnetic energy release and propagate with the Alfvén speed along the irregular magnetic fields. They are large-scale local fluctuations (δB/B ≈ 1) randomly distributed inside the unstable magnetic topology and will here be called Alfvénic Scatterers (AS). We constructed a 3D grid on which a small fraction of randomly chosen grid points are acting as AS. In particular, we study how a large number of test particles evolves inside a collection of AS, analyzing the evolution of their energy distribution and their escape-time distribution. We use a well-established method to estimate the transport coefficients directly from the trajectories of the particles. Using the estimated transport coefficients and solving the Fokker-Planck equation numerically, we can recover the energy distribution of the particles. We have shown that the stochastic Fermi energization of mildly relativistic and relativistic plasma can heat and accelerate the tail of the ambient particle distribution as predicted by Parker & Tidman and Ramaty. The temperature of the hot plasma and the tail of the energetic particles depend on the mean free path (λsc) of the particles between the scatterers inside the energization volume.

  2. Electrostatic interactions between ions near Thomas-Fermi substrates and the surface energy of ionic crystal at imperfect metals

    PubMed Central

    Kaiser, V.; Comtet, J.; Niguès, A.; Siria, A.; Coasne, B.; Bocquet, L.

    2017-01-01

    The electrostatic interaction between two charged particles is strongly modified in the vicinity of a metal. This situation is usually accounted for by the celebrated image charges approach, which was further extended to account for the electronic screening properties of the metal at the level of the Thomas-Fermi description. In this paper we build upon the approach by [Kornyshev et al. Zh. Eksp. Teor. Fiz., 78(3):1008–1019, 1980] and successive works to calculate the 1-body and 2-body electrostatic energy of ions near a metal in terms of the Thomas-Fermi screening length. We propose workable approximations suitable for molecular simulations of ionic systems close to metallic walls. Furthermore, we use this framework to calculate analytically the electrostatic contribution to the surface energy of a one dimensional crystal at a metallic wall and its dependence on the Thomas-Fermi screening length. These calculations provide a simple interpretation for the surface energy in terms of image charges, which allow for an estimate of interfacial properties in more complex situations of a disordered ionic liquid close to a metal surface. A counterintuitive outcome is that electronic screening, as characterized by a molecular Thomas-Fermi length ℓTF, profoundly affects the wetting of ionic systems close to a metal, in line with the recent experimental observation of capillary freezing of ionic liquids in metallic confinement. PMID:28436506

  3. Fermi's Conundrum: Proliferation and Closed Societies

    NASA Astrophysics Data System (ADS)

    Teller, Wendy; Westfall, Catherine

    2007-04-01

    On January 1, 1946 Emily Taft Douglas, a freshman Representative at Large for Illinois, sent a letter to Enrico Fermi. She wanted to know whether, if atomic energy was used for peaceful purposes, it might be possible to clandestinely divert some material for bombs. Douglas first learned about the bomb not quite five months before when Hiroshima was bombed. Even though she was not a scientist she identified a key problem of the nuclear age. Fermi responded with requirements to allow peaceful uses of atomic energy and still outlaw nuclear weapons. First, free interchange of information between people was required, and second, people who reported possible violations had to be protected. Fermi had lived in Mussolini's Italy and worked under the war time secrecy restrictions of the Manhattan Project. He was not optimistic that these conditions could be met. This paper discusses how Douglas came to recognize the proliferation issue and what led Fermi to his solution and his pessimism about its practicality.

  4. Searches for correlation between UHECR events and high-energy gamma-ray Fermi-LAT data

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Álvarez, Ezequiel; Cuoco, Alessandro; Mirabal, Nestor

    The astrophysical sources responsible for ultra high-energy cosmic rays (UHECRs) continue to be one of the most intriguing mysteries in astrophysics. Here, we present a comprehensive search for correlations between high-energy (≳ 1 GeV) gamma-ray events from the Fermi Large Area Telescope (LAT) and UHECRs (≳ 60 EeV) detected by the Telescope Array and the Pierre Auger Observatory. We perform two separate searches. First, we conduct a standard cross-correlation analysis between the arrival directions of 148 UHECRs and 360 gamma-ray sources in the Second Catalog of Hard Fermi-LAT sources (2FHL). Second, we search for a possible correlation between UHECR directionsmore » and unresolved Fermi-LAT gamma-ray emission. For the latter, we use three different methods: a stacking technique with both a model-dependent and model-independent background estimate, and a cross-correlation function analysis. We also test for statistically significant excesses in gamma rays from signal regions centered on Cen A and the Telescope Array hotspot. There was no significant correlation is found in any of the analyses performed, except a weak (≲ 2σ) hint of signal with the correlation function method on scales ~ 1°. Upper limits on the flux of possible power-law gamma-ray sources of UHECRs are derived.« less

  5. Searches for correlation between UHECR events and high-energy gamma-ray Fermi-LAT data

    DOE PAGES

    Álvarez, Ezequiel; Cuoco, Alessandro; Mirabal, Nestor; ...

    2016-12-13

    The astrophysical sources responsible for ultra high-energy cosmic rays (UHECRs) continue to be one of the most intriguing mysteries in astrophysics. Here, we present a comprehensive search for correlations between high-energy (≳ 1 GeV) gamma-ray events from the Fermi Large Area Telescope (LAT) and UHECRs (≳ 60 EeV) detected by the Telescope Array and the Pierre Auger Observatory. We perform two separate searches. First, we conduct a standard cross-correlation analysis between the arrival directions of 148 UHECRs and 360 gamma-ray sources in the Second Catalog of Hard Fermi-LAT sources (2FHL). Second, we search for a possible correlation between UHECR directionsmore » and unresolved Fermi-LAT gamma-ray emission. For the latter, we use three different methods: a stacking technique with both a model-dependent and model-independent background estimate, and a cross-correlation function analysis. We also test for statistically significant excesses in gamma rays from signal regions centered on Cen A and the Telescope Array hotspot. There was no significant correlation is found in any of the analyses performed, except a weak (≲ 2σ) hint of signal with the correlation function method on scales ~ 1°. Upper limits on the flux of possible power-law gamma-ray sources of UHECRs are derived.« less

  6. Testing the nonlocal kinetic energy functional of an inhomogeneous, two-dimensional degenerate Fermi gas within the average density approximation

    NASA Astrophysics Data System (ADS)

    Towers, J.; van Zyl, B. P.; Kirkby, W.

    2015-08-01

    In a recent paper [B. P. van Zyl et al., Phys. Rev. A 89, 022503 (2014), 10.1103/PhysRevA.89.022503], the average density approximation (ADA) was implemented to develop a parameter-free, nonlocal kinetic energy functional to be used in the orbital-free density functional theory of an inhomogeneous, two-dimensional (2D) Fermi gas. In this work, we provide a detailed comparison of self-consistent calculations within the ADA with the exact results of the Kohn-Sham density functional theory and the elementary Thomas-Fermi (TF) approximation. We demonstrate that the ADA for the 2D kinetic energy functional works very well under a wide variety of confinement potentials, even for relatively small particle numbers. Remarkably, the TF approximation for the kinetic energy functional, without any gradient corrections, also yields good agreement with the exact kinetic energy for all confining potentials considered, although at the expense of the spatial and kinetic energy densities exhibiting poor pointwise agreement, particularly near the TF radius. Our findings illustrate that the ADA kinetic energy functional yields accurate results for both the local and global equilibrium properties of an inhomogeneous 2D Fermi gas, without the need for any fitting parameters.

  7. Fermi Gamma-Ray Space Telescope Science Overview

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2010-01-01

    After more than 2 years of science operations, the Fermi Gamma-ray Space Telescope continues to survey the high-energy sky on a daily basis. In addition to the more than 1400 sources found in the first Fermi Large Area Telescope Catalog (I FGL), new results continue to emerge. Some of these are: (1) Large-scale diffuse emission suggests possible activity from the Galactic Center region in the past; (2) a gamma-ray nova was found, indicating particle acceleration in this binary system; and (3) the Crab Nebula, long thought to be a steady source, has varied in the energy ranges seen by both Fermi instruments.

  8. Electrostatic interactions between ions near Thomas-Fermi substrates and the surface energy of ionic crystals at imperfect metals.

    PubMed

    Kaiser, V; Comtet, J; Niguès, A; Siria, A; Coasne, B; Bocquet, L

    2017-07-01

    The electrostatic interaction between two charged particles is strongly modified in the vicinity of a metal. This situation is usually accounted for by the celebrated image charges approach, which was further extended to account for the electronic screening properties of the metal at the level of the Thomas-Fermi description. In this paper we build upon a previous approach [M. A. Vorotyntsev and A. A. Kornyshev, Zh. Eksp. Teor. Fiz., 1980, 78(3), 1008-1019] and successive works to calculate the 1-body and 2-body electrostatic energy of ions near a metal in terms of the Thomas-Fermi screening length. We propose workable approximations suitable for molecular simulations of ionic systems close to metallic walls. Furthermore, we use this framework to calculate analytically the electrostatic contribution to the surface energy of a one dimensional crystal at a metallic wall and its dependence on the Thomas-Fermi screening length. These calculations provide a simple interpretation for the surface energy in terms of image charges, which allows for an estimation of the interfacial properties in more complex situations of a disordered ionic liquid close to a metal surface. The counter-intuitive outcome is that electronic screening, as characterized by a molecular Thomas-Fermi length l TF , profoundly affects the wetting of ionic systems close to a metal, in line with the recent experimental observation of capillary freezing of ionic liquids in metallic confinement.

  9. Fermi Sees the Gamma Ray Sky

    NASA Image and Video Library

    2009-10-30

    This view of the gamma-ray sky constructed from one year of Fermi LAT observations is the best view of the extreme universe to date. The map shows the rate at which the LAT detects gamma rays with energies above 300 million electron volts -- about 120 million times the energy of visible light -- from different sky directions. Brighter colors equal higher rates. Credit: NASA/DOE/Fermi LAT Collaboration Full story: www.nasa.gov/mission_pages/GLAST/news/first_year.html

  10. Self-energy of an impurity in an ideal Fermi gas to second order in the interaction strength

    NASA Astrophysics Data System (ADS)

    Trefzger, Christian; Castin, Yvan

    2014-09-01

    We study in three dimensions the problem of a spatially homogeneous zero-temperature ideal Fermi gas of spin-polarized particles of mass m perturbed by the presence of a single distinguishable impurity of mass M. The interaction between the impurity and the fermions involves only the partial s wave through the scattering length a and has negligible range b compared to the inverse Fermi wave number 1/kF of the gas. Through the interactions with the Fermi gas the impurity gives birth to a quasiparticle, which will be here a Fermi polaron (or more precisely a monomeron). We consider the general case of an impurity moving with wave vector K ≠0: Then the quasiparticle acquires a finite lifetime in its initial momentum channel because it can radiate particle-hole pairs in the Fermi sea. A description of the system using a variational approach, based on a finite number of particle-hole excitations of the Fermi sea, then becomes inappropriate around K =0. We rely thus upon perturbation theory, where the small and negative parameter kFa→0- excludes any branches other than the monomeronic one in the ground state (as, e.g., the dimeronic one), and allows us a systematic study of the system. We calculate the impurity self-energy Σ(2)(K,ω) up to second order included in a. Remarkably, we obtain an analytical explicit expression for Σ(2)(K,ω), allowing us to study its derivatives in the plane (K,ω). These present interesting singularities, which in general appear in the third-order derivatives ∂3Σ(2)(K,ω). In the special case of equal masses, M =m, singularities appear already in the physically more accessible second-order derivatives ∂2Σ(2)(K,ω); using a self-consistent heuristic approach based on Σ(2) we then regularize the divergence of the second-order derivative ∂K2ΔE(K) of the complex energy of the quasiparticle found in Trefzger and Castin [Europhys. Lett. 104, 50005 (2013), 10.1209/0295-5075/104/50005] at K =kF, and we predict an interesting scaling

  11. Nonlocal Poisson-Fermi model for ionic solvent.

    PubMed

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

  12. Time Domain Astronomy with Fermi GBM in the Multi-messenger Era

    NASA Astrophysics Data System (ADS)

    Wilson-Hodge, Colleen A.; Fermi GBM team, GBM-LIGO team

    2018-01-01

    As the Multi-Messenger era begins with detections of gravitational waves with LIGO/Virgo and neutrinos with IceCube, the Fermi Gamma-ray Burst Monitor (GBM) provides context observations of gamma-ray transients between 8 keV and 40 MeV. Fermi GBM has a wide field of view, high uptime, and both in-orbit triggering and high time resolution continuous data enabling offline searches for weaker transients. GBM detects numerous gamma-ray bursts (GRBs), soft gamma-ray repeaters, X-ray bursters, solar flares and terrestrial gamma-ray flashes. Longer timescale transients, predominantly in our galaxy so far, are detected using the Earth occultation technique and epoch-folding for periodic sources. The GBM team has developed two ground-based searches to enhance detections of faint transients, especially short GRBs. The targeted search uses the time and location of an event detected with another instrument to coherently search the GBM data, increasing the sensitivity to a transient. The untargeted search agnostically searches the GBM data for all directions and times to find weaker transients. This search finds about 80 short GRBs per year, adding to the 40 per year triggered on-orbit. With its large field of view, high duty cycle and increasingly sophisticated detection methods, Fermi GBM is expected to have a major role in the Multi-Messenger era.

  13. Discussion on the energy content of the galactic dark matter Bose-Einstein condensate halo in the Thomas-Fermi approximation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    De Souza, J.C.C.; Pires, M.O.C., E-mail: jose.souza@ufabc.edu.br, E-mail: marcelo.pires@ufabc.edu.br

    We show that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [6] trapped by a self-graviting potential [5], may be stable in the Thomas-Fermi approximation since appropriate choices for the dark matter particle mass and scattering length are made. The demonstration is performed by means of the calculation of the potential, kinetic and self-interaction energy terms of a galactic halo described by a Boehmer-Harko density profile. We discuss the validity of the Thomas-Fermi approximation for the halo system, and show that the kinetic energy contribution is indeed negligible.

  14. Fermi Large Area Telescope

    Science.gov Websites

    Home Mission Instrument Institutions Publications NASA Pictures Internal lock The Fermi Large Area Monitor (GBM). Wikipedia Country Funding Agencies United States NASA; Department of Energy France

  15. Search for Very High-energy Gamma Rays from the Northern Fermi Bubble Region with HAWC

    NASA Astrophysics Data System (ADS)

    Abeysekara, A. U.; Albert, A.; Alfaro, R.; Alvarez, C.; Álvarez, J. D.; Arceo, R.; Arteaga-Velázquez, J. C.; Ayala Solares, H. A.; Barber, A. S.; Bautista-Elivar, N.; Becerril, A.; Belmont-Moreno, E.; BenZvi, S. Y.; Berley, D.; Braun, J.; Brisbois, C.; Caballero-Mora, K. S.; Capistrán, T.; Carramiñana, A.; Casanova, S.; Castillo, M.; Cotti, U.; Cotzomi, J.; Coutiño de León, S.; De León, C.; De la Fuente, E.; Diaz Hernandez, R.; Dingus, B. L.; DuVernois, M. A.; Díaz-Vélez, J. C.; Ellsworth, R. W.; Engel, K.; Fick, B.; Fiorino, D. W.; Fleischhack, H.; Fraija, N.; García-González, J. A.; Garfias, F.; Gerhardt, M.; González Muñoz, A.; González, M. M.; Goodman, J. A.; Hampel-Arias, Z.; Harding, J. P.; Hernandez, S.; Hernandez-Almada, A.; Hinton, J.; Hona, B.; Hui, C. M.; Hüntemeyer, P.; Iriarte, A.; Jardin-Blicq, A.; Joshi, V.; Kaufmann, S.; Kieda, D.; Lara, A.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linnemann, J. T.; Longinotti, A. L.; Raya, G. Luis; Luna-García, R.; López-Coto, R.; Malone, K.; Marinelli, S. S.; Martinez, O.; Martinez-Castellanos, I.; Martínez-Castro, J.; Martínez-Huerta, H.; Matthews, J. A.; Miranda-Romagnoli, P.; Moreno, E.; Mostafá, M.; Nellen, L.; Newbold, M.; Nisa, M. U.; Noriega-Papaqui, R.; Pelayo, R.; Pretz, J.; Pérez-Pérez, E. G.; Ren, Z.; Rho, C. D.; Rivière, C.; Rosa-González, D.; Rosenberg, M.; Ruiz-Velasco, E.; Salazar, H.; Salesa Greus, F.; Sandoval, A.; Schneider, M.; Schoorlemmer, H.; Sinnis, G.; Smith, A. J.; Springer, R. W.; Surajbali, P.; Taboada, I.; Tibolla, O.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Vianello, G.; Weisgarber, T.; Westerhoff, S.; Wisher, I. G.; Wood, J.; Yapici, T.; Yodh, G. B.; Zepeda, A.; Zhou, H.

    2017-06-01

    We present a search for very high-energy gamma-ray emission from the Northern Fermi Bubble region using data collected with the High Altitude Water Cherenkov gamma-ray observatory. The size of the data set is 290 days. No significant excess is observed in the Northern Fermi Bubble region, so upper limits above 1 TeV are calculated. The upper limits are between 3× {10}-7 {GeV} {{cm}}-2 {{{s}}}-1 {{sr}}-1 and 4× {10}-8 {GeV} {{cm}}-2 {{{s}}}-1 {{sr}}-1. The upper limits disfavor a proton injection spectrum that extends beyond 100 TeV without being suppressed. They also disfavor a hadronic injection spectrum derived from neutrino measurements.

  16. On the interpretation of domain averaged Fermi hole analyses of correlated wavefunctions.

    PubMed

    Francisco, E; Martín Pendás, A; Costales, Aurora

    2014-03-14

    Few methods allow for a physically sound analysis of chemical bonds in cases where electron correlation may be a relevant factor. The domain averaged Fermi hole (DAFH) analysis, a tool firstly proposed by Robert Ponec in the 1990's to provide interpretations of the chemical bonding existing between two fragments Ω and Ω' that divide the real space exhaustively, is one of them. This method allows for a partition of the delocalization index or bond order between Ω and Ω' into one electron contributions, but the chemical interpretation of its parameters has been firmly established only for single determinant wavefunctions. In this paper we report a general interpretation based on the concept of excluded density that is also valid for correlated descriptions. Both analytical models and actual computations on a set of simple molecules (H2, N2, LiH, and CO) are discussed, and a classification of the possible DAFH situations is presented. Our results show that this kind of analysis may reveal several correlated assisted bonding patterns that might be difficult to detect using other methods. In agreement with previous knowledge, we find that the effective bond order in covalent links decreases due to localization of electrons driven by Coulomb correlation.

  17. Sources of GeV Photons and the Fermi Results

    NASA Astrophysics Data System (ADS)

    Dermer, Charles D.

    This chapter presents the elaborated lecture notes on Sources of GeV Photons and the Fermi Results given by Charles D. Dermer at the 40th Saas-Fee Advanced Course on "Astrophysics at Very High Energies". The Fermi Gamma-ray Space Telescope made important discoveries and established new results in various areas of astrophysics: from our solar system to remote gamma-ray bursts, from pulsar physics to limits on dark matter and Lorentz invariance violations. The author gives a broad overview of these results by discussing GeV instrumentation and the GeV sky as seen by Fermi, the Fermi catalogs on gamma-ray sources, pulsars and active galactic nuclei, relativistic jet physics and blazars, gamma-rays from cosmic rays in the Galaxy, from star-forming galaxies and from clusters of galaxies, the diffuse extra-galactic gamma-ray background, micro-quasars, radio galaxies, the extragalactic background light, gamma-ray bursts, Fermi acceleration, ultra-high energy cosmic rays, and black holes.

  18. Quasiparticles and Fermi liquid behaviour in an organic metal

    PubMed Central

    Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

    2012-01-01

    Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

  19. Quantum chaos on a critical Fermi surface.

    PubMed

    Patel, Aavishkar A; Sachdev, Subir

    2017-02-21

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of [Formula: see text] species of fermions at nonzero density coupled to a [Formula: see text] gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of [Formula: see text], the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

  20. 2FHL: The Second Catalog of Hard Fermi-LAT Sources

    DOE PAGES

    Ackermann, M.; Ajello, M.; Atwood, W. B.; ...

    2016-01-14

    We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass 8 event-level analysis allows the detection and characterization of sources in the 50 GeV–2TeV energy range. In this energy band, Fermi - LAT has detected 360 sources, which constitute the second catalog of hard Fermi -LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (~1.'7 radius at 68 % C. L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associatedmore » with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi -LAT on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.« less

  1. 2FHL- The Second Catalog of Hard Fermi-LAT Sources

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Gonzalez, J. Becerra; Bellazzini, R.; Bissaldi, E.; hide

    2016-01-01

    We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass8 event-level analysis allows the detection and characterization of sources in the 50 GeV-2 TeV energy range. In this energy band, Fermi-LAT has detected 360 sources, which constitute the second catalog of hard Fermi-LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (1.7 radius at 68% C.L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associated with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHLsources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi-LAT on orbit and the observations performed at higher energies byCherenkov telescopes from the ground.

  2. 2FHL: The Second Catalog of Hard Fermi-LAT Sources

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ackermann, M.; Ajello, M.; Atwood, W. B.

    We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass 8 event-level analysis allows the detection and characterization of sources in the 50 GeV–2TeV energy range. In this energy band, Fermi - LAT has detected 360 sources, which constitute the second catalog of hard Fermi -LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (~1.'7 radius at 68 % C. L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associatedmore » with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi -LAT on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.« less

  3. Multiwavelength Optical Switch Based on Controlling the Fermi Energy of Graphene

    NASA Astrophysics Data System (ADS)

    Jiang, Xiangqian; Bao, Jinlin; Sun, Xiudong

    2018-04-01

    We propose a graphene-dielectric-graphene corrugated structure to achieve a multiwavelength optical switch. The transmission and reflection properties of the structure are discussed, and multiultranarrow resonant peaks in the transmission and reflection spectra are found. By adjusting the Fermi energy of graphene, the resonant peaks will shift obviously. Based on this shifting property we present an active multiwavelength optical switch and achieve the on-off of four different wavelengths simultaneously. We also discuss the modulation depths of transmission and reflection. For the transmission of all four wavelengths we can get a very high modulation depth close to 100%.

  4. Energy and contact of the one-dimensional Fermi polaron at zero and finite temperature.

    PubMed

    Doggen, E V H; Kinnunen, J J

    2013-07-12

    We use the T-matrix approach for studying highly polarized homogeneous Fermi gases in one dimension with repulsive or attractive contact interactions. Using this approach, we compute ground state energies and values for the contact parameter that show excellent agreement with exact and other numerical methods at zero temperature, even in the strongly interacting regime. Furthermore, we derive an exact expression for the value of the contact parameter in one dimension at zero temperature. The model is then extended and used for studying the temperature dependence of ground state energies and the contact parameter.

  5. Fermi Spots a Record Flare from Blazar

    NASA Image and Video Library

    2015-07-10

    Blazar 3C 279's historic gamma-ray flare can be seen in this image from the Large Area Telescope (LAT) on NASA's Fermi satellite. Gamma rays with energies from 100 million to 100 billion electron volts (eV) are shown; for comparison, visible light has energies between 2 and 3 eV. The image spans 150 degrees, is shown in a stereographic projection, and represents an exposure from June 11 at 00:28 UT to June 17 at 08:17 UT. Credit: NASA/DOE/Fermi LAT Collaboration

  6. Quantum Monte Carlo studies of superfluid Fermi gases

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chang, S.Y.; Pandharipande, V.R.; Carlson, J.

    2004-10-01

    We report results of quantum Monte Carlo calculations of the ground state of dilute Fermi gases with attractive short-range two-body interactions. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the s-wave scattering length and the Fermi wave vector, ak{sub F}. We report results for the ground-state energy, the pairing gap {delta}, and the quasiparticle spectrum. In the weak-coupling regime, 1/ak{sub F}<-1, we obtain Bardeen-Cooper-Schrieffer (BCS) superfluid and the energy gap {delta} is much smaller than the Fermi gas energy E{sub FG}. When a>0, the interaction is strong enough tomore » form bound molecules with energy E{sub mol}. For 1/ak{sub F} > or approx. 0.5, we find that weakly interacting composite bosons are formed in the superfluid gas with {delta} and gas energy per particle approaching E{sub mol}/2. In this region, we seem to have Bose-Einstein condensation (BEC) of molecules. The behavior of the energy and the gap in the BCS-to-BEC transition region, -0.5<1/ak{sub F}<0.5, is discussed.« less

  7. Tuning the Fano factor of graphene via Fermi velocity modulation

    NASA Astrophysics Data System (ADS)

    Lima, Jonas R. F.; Barbosa, Anderson L. R.; Bezerra, C. G.; Pereira, Luiz Felipe C.

    2018-03-01

    In this work we investigate the influence of a Fermi velocity modulation on the Fano factor of periodic and quasi-periodic graphene superlattices. We consider the continuum model and use the transfer matrix method to solve the Dirac-like equation for graphene where the electrostatic potential, energy gap and Fermi velocity are piecewise constant functions of the position x. We found that in the presence of an energy gap, it is possible to tune the energy of the Fano factor peak and consequently the location of the Dirac point, by a modulation in the Fermi velocity. Hence, the peak of the Fano factor can be used experimentally to identify the Dirac point. We show that for higher values of the Fermi velocity the Fano factor goes below 1/3 at the Dirac point. Furthermore, we show that in periodic superlattices the location of Fano factor peaks is symmetric when the Fermi velocity vA and vB is exchanged, however by introducing quasi-periodicity the symmetry is lost. The Fano factor usually holds a universal value for a specific transport regime, which reveals that the possibility of controlling it in graphene is a notable result.

  8. Quantum mechanical models for the Fermi shuttle

    NASA Astrophysics Data System (ADS)

    Sternberg, James; Ovchinnikov, S. Yu.; Macek, J. H.

    2009-05-01

    Although the Fermi shuttle was originally proposed as an explanation for highly energetic cosmic rays, it is also a mechanism for the production of high energy electrons in atomic collisions [1]. The Fermi shuttle is usually thought of as a classical effect and most models of this process rely on classical or semi-classical approximations. In this work we explore several quantum mechanical models for ion-atom collisions and examine the evidence for the Fermi shuttle in these models. [4pt] [1] B. Sulik, Cs. Koncz, K. Tok'esi, A. Orb'an, and D. Ber'enyi, Phys Rev. Lett. 88 073201 (2002)

  9. Fermi arc mediated entropy transport in topological semimetals

    NASA Astrophysics Data System (ADS)

    McCormick, Timothy M.; Watzman, Sarah J.; Heremans, Joseph P.; Trivedi, Nandini

    2018-05-01

    The low-energy excitations of topological Weyl semimetals are composed of linearly dispersing Weyl fermions that act as monopoles of Berry curvature in the bulk momentum space. Furthermore, on the surface there exist topologically protected Fermi arcs at the projections of these Weyl points. We propose a pathway for entropy transport involving Fermi arcs on one surface connecting to Fermi arcs on the other surface via the bulk Weyl monopoles. We present results for the temperature and magnetic field dependence of the magnetothermal conductance of this conveyor belt channel. The circulating currents result in a net entropy transport without any net charge transport. We provide results for the Fermi arc mediated magnetothermal conductivity in the low-field semiclassical limit as well as in the high-field ultraquantum limit, where only chiral Landau levels are involved. Our work provides a proposed signature of Fermi arc mediated magnetothermal transport and sets the stage for utilizing and manipulating the topological Fermi arcs in thermal applications.

  10. Effective field theories for superconducting systems with multiple Fermi surfaces

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Braga, P.R., E-mail: pedro.rangel.braga@gmail.com; Granado, D.R., E-mail: diegorochagrana@uerj.br; Department of Physics and Astronomy, Ghent University, Krijgslaan 281-S9, 9000 Gent

    2016-11-15

    In this work we investigate the description of superconducting systems with multiple Fermi surfaces. For the case of one Fermi surface we re-obtain the result that the superconductor is more precisely described as a topological state of matter. Studying the case of more than one Fermi surface, we obtain the effective theory describing a time reversal symmetric topological superconductor. These results are obtained by employing a general procedure to construct effective low energy actions describing states of electromagnetic systems interacting with charges and defects. The procedure consists in taking into account the proliferation or dilution of these charges and defectsmore » and its consequences for the low energy description of the electromagnetic response of the system. We find that the main ingredient entering the low energy characterization of the system with more than one Fermi surface is a non-conservation of the canonical supercurrent triggered by particular vortex configurations.« less

  11. Fermi: The Gamma-Ray Large Area Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2015-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  12. Fermi: The Gamma-Ray Large Area Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10 seconds of gigaelectronvolts from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as super-symmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  13. Leptonic v.s. Hadronic Origin of the Gamma-ray Emission of the Fermi bubbles: Updates from Fermi-LAT and Forecast for Future Gamma-ray Telescopes

    NASA Astrophysics Data System (ADS)

    Su, Meng

    2014-06-01

    Data from the Fermi-LAT revealed two large gamma-ray bubbles, extending 50 degrees above and below the Galactic center, with a width of about 40 degrees in longitude. Such structure has been confirmed with multi-wavelength observations. With the most up to date Fermi-LAT data analysis, I will show that the Fermi bubbles have a spectral cutoff at both low energy < 1 GeV and high energy > 150 GeV. Detailed analysis of the spectral features will help us to distinguish the leptonic origin from hadronic origin of the gamma-ray emission from the bubbles. I will also describe what we expect to learn about the bubbles from future gamma-ray telescopes after Fermi, with an emphasis on Dark Matter Particle Explorer and Pair Production Gamma-ray Unit.

  14. Double-wells and double-layers in dusty Fermi-Dirac plasmas: Comparison with the semiclassical Thomas-Fermi counterpart

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Akbari-Moghanjoughi, M.

    Based on the quantum hydrodynamics (QHD) model, a new relationship between the electrostatic-potential and the electron-density in the ultradense plasma is derived. Propagation of arbitrary amplitude nonlinear ion waves is, then, investigated in a completely degenerate dense dusty electron-ion plasma, using this new energy relation for the relativistic electrons, in the ground of quantum hydrodynamics model and the results are compared to the case of semiclassical Thomas-Fermi dusty plasma. Based on the standard pseudopotential approach, it is remarked that the Fermi-Dirac plasma, in contrast to the Thomas-Fermi counterpart, accommodates a wide variety of nonlinear excitations such as positive/negative-potential ion solitarymore » and periodic waves, double-layers, and double-wells. It is also remarked that the relativistic degeneracy parameter which relates to the mass-density of plasma has significant effects on the allowed matching-speed range in Fermi-Dirac dusty plasmas.« less

  15. Entanglement entropy and the Fermi surface.

    PubMed

    Swingle, Brian

    2010-07-30

    Free fermions with a finite Fermi surface are known to exhibit an anomalously large entanglement entropy. The leading contribution to the entanglement entropy of a region of linear size L in d spatial dimensions is S∼L(d-1)logL, a result that should be contrasted with the usual boundary law S∼L(d-1). This term depends only on the geometry of the Fermi surface and on the boundary of the region in question. I give an intuitive account of this anomalous scaling based on a low energy description of the Fermi surface as a collection of one-dimensional gapless modes. Using this picture, I predict a violation of the boundary law in a number of other strongly correlated systems.

  16. Fermi Large Area Telescope Observations of Markarian 421: The Missing Piece of its Spectral Energy Distribution

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Cannon, A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; de Angelis, A.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Escande, L.; Favuzzi, C.; Fegan, S. J.; Finke, J.; Focke, W. B.; Fortin, P.; Frailis, M.; Fuhrmann, L.; Fukazawa, Y.; Fukuyama, T.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Georganopoulos, M.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kadler, M.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Max-Moerbeck, W.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-Godo, M.; Nishino, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Pavlidou, V.; Pearson, T. J.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Reyes, L. C.; Richards, J. L.; Ritz, S.; Roth, M.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Stevenson, M.; Strickman, M. S.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Wehrle, A. E.; Winer, B. L.; Wood, K. S.; Yang, Z.; Yatsu, Y.; Ylinen, T.; Zensus, J. A.; Ziegler, M.; Fermi LAT Collaboration; Aleksić, J.; Antonelli, L. A.; Antoranz, P.; Backes, M.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berdyugin, A.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnoli, G.; Bordas, P.; Borla Tridon, D.; Bosch-Ramon, V.; Bose, D.; Braun, I.; Bretz, T.; Camara, M.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Dazzi, F.; de Angelis, A.; De Cea del Pozo, E.; Delgado Mendez, C.; De Lotto, B.; De Maria, M.; De Sabata, F.; Diago Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Elsaesser, D.; Ferenc, D.; Fonseca, M. V.; Font, L.; García López, R. J.; Garczarczyk, M.; Gaug, M.; Giavitto, G.; Godinovi, N.; Hadasch, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Hrupec, D.; Jogler, T.; Klepser, S.; Krähenbühl, T.; Kranich, D.; Krause, J.; La Barbera, A.; Leonardo, E.; Lindfors, E.; Lombardi, S.; López, M.; Lorenz, E.; Majumdar, P.; Makariev, E.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Miyamoto, H.; Moldón, J.; Moralejo, A.; Nieto, D.; Nilsson, K.; Orito, R.; Oya, I.; Paoletti, R.; Paredes, J. M.; Partini, S.; Pasanen, M.; Pauss, F.; Pegna, R. G.; Perez-Torres, M. A.; Persic, M.; Peruzzo, J.; Pochon, J.; Prada, F.; Prada Moroni, P. G.; Prandini, E.; Puchades, N.; Puljak, I.; Reichardt, T.; Rhode, W.; Ribó, M.; Rico, J.; Rissi, M.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Salvati, M.; Sánchez-Conde, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shayduk, M.; Shore, S. N.; Sierpowska-Bartosik, A.; Sillanpää, A.; Sitarek, J.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamerra, A.; Steinke, B.; Storz, J.; Strah, N.; Struebig, J. C.; Suric, T.; Takalo, L. O.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Vankov, H.; Wagner, R. M.; Weitzel, Q.; Zabalza, V.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Villata, M.; Raiteri, C.; Aller, H. D.; Aller, M. F.; Chen, W. P.; Jordan, B.; Koptelova, E.; Kurtanidze, O. M.; Lähteenmäki, A.; McBreen, B.; Larionov, V. M.; Lin, C. S.; Nikolashvili, M. G.; Reinthal, R.; Angelakis, E.; Capalbi, M.; Carramiñana, A.; Carrasco, L.; Cassaro, P.; Cesarini, A.; Falcone, A.; Gurwell, M. A.; Hovatta, T.; Kovalev, Yu. A.; Kovalev, Y. Y.; Krichbaum, T. P.; Krimm, H. A.; Lister, M. L.; Moody, J. W.; Maccaferri, G.; Mori, Y.; Nestoras, I.; Orlati, A.; Pace, C.; Pagani, C.; Pearson, R.; Perri, M.; Piner, B. G.; Ros, E.; Sadun, A. C.; Sakamoto, T.; Tammi, J.; Zook, A.

    2011-08-01

    We report on the γ-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Γ = 1.78 ± 0.02 and average photon flux F(> 0.3 GeV) = (7.23 ± 0.16) × 10-8 ph cm-2 s-1. Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor ~3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.

  17. The VELA-X-Pulsar Wind Nebula Revisited with Four Years of Fermi Large Area Telescope Observations

    NASA Technical Reports Server (NTRS)

    Grondin, M. -H.; Romani, R. W.; Lemoine-Goumard, M.; Guillemot, L.; Harding, Alice K.; Reposeur, T.

    2013-01-01

    The Vela supernova remnant (SNR) is the closest SNR to Earth containing an active pulsar, the Vela pulsar (PSR B0833-45). This pulsar is an archetype of the middle-aged pulsar class and powers a bright pulsar wind nebula (PWN), Vela-X, spanning a region of 2deg × 3deg south of the pulsar and observed in the radio, X-ray, and very high energy ?-ray domains. The detection of the Vela-X PWN by the Fermi Large Area Telescope (LAT) was reported in the first year of the mission. Subsequently, we have reinvestigated this complex region and performed a detailed morphological and spectral analysis of this source using 4 yr of Fermi-LAT observations. This study lowers the threshold for morphological analysis of the nebula from 0.8 GeV to 0.3 GeV, allowing for the inspection of distinct energy bands by the LAT for the first time. We describe the recent results obtained on this PWN and discuss the origin of the newly detected spatial features.

  18. The Vela-X pulsar wind nebula revisited with four years of Fermi Large Area Telescope observations

    DOE PAGES

    Grondin, M. -H.; Romani, R. W.; Lemoine-Goumard, M.; ...

    2013-08-21

    Here, the Vela supernova remnant (SNR) is the closest SNR to Earth containing an active pulsar, the Vela pulsar (PSR B0833–45). This pulsar is an archetype of the middle-aged pulsar class and powers a bright pulsar wind nebula (PWN), Vela-X, spanning a region of 2° × 3° south of the pulsar and observed in the radio, X-ray, and very high energy γ-ray domains. The detection of the Vela-X PWN by the Fermi Large Area Telescope (LAT) was reported in the first year of the mission. Subsequently, we have reinvestigated this complex region and performed a detailed morphological and spectral analysismore » of this source using 4 yr of Fermi-LAT observations. This study lowers the threshold for morphological analysis of the nebula from 0.8 GeV to 0.3 GeV, allowing for the inspection of distinct energy bands by the LAT for the first time. We describe the recent results obtained on this PWN and discuss the origin of the newly detected spatial features.« less

  19. Constraining the High-Energy Emission from Gamma-Ray Bursts with Fermi

    NASA Technical Reports Server (NTRS)

    Gehrels, Neil; Harding, A. K.; Hays, E.; Racusin, J. L.; Sonbas, E.; Stamatikos, M.; Guirec, S.

    2012-01-01

    We examine 288 GRBs detected by the Fermi Gamma-ray Space Telescope's Gamma-ray Burst Monitor (GBM) that fell within the field-of-view of Fermi's Large Area Telescope (LAT) during the first 2.5 years of observations, which showed no evidence for emission above 100 MeV. We report the photon flux upper limits in the 0.1-10 GeV range during the prompt emission phase as well as for fixed 30 s and 100 s integrations starting from the trigger time for each burst. We compare these limits with the fluxes that would be expected from extrapolations of spectral fits presented in the first GBM spectral catalog and infer that roughly half of the GBM-detected bursts either require spectral breaks between the GBM and LAT energy bands or have intrinsically steeper spectra above the peak of the nuF(sub v) spectra (E(sub pk)). In order to distinguish between these two scenarios, we perform joint GBM and LAT spectral fits to the 30 brightest GBM-detected bursts and find that a majority of these bursts are indeed softer above E(sub pk) than would be inferred from fitting the GBM data alone. Approximately 20% of this spectroscopic subsample show statistically significant evidence for a cut-off in their high-energy spectra, which if assumed to be due to gamma gamma attenuation, places limits on the maximum Lorentz factor associated with the relativistic outflow producing this emission. All of these latter bursts have maximum Lorentz factor estimates that are well below the minimum Lorentz factors calculated for LAT-detected GRBs, revealing a wide distribution in the bulk Lorentz factor of GRB outflows and indicating that LAT-detected bursts may represent the high end of this distribution.

  20. Constraining the high-energy emission from gamma-ray bursts with Fermi

    DOE PAGES

    Ackermann, M.; Ajello, M.; Baldini, L.; ...

    2012-07-17

    Here, we examine 288 gamma-ray bursts (GRBs) detected by the Fermi Gamma-ray Space Telescope's Gamma-ray Burst Monitor (GBM) that fell within the field of view of Fermi's Large Area Telescope (LAT) during the first 2.5 years of observations, which showed no evidence for emission above 100 MeV. We report the photon flux upper limits in the 0.1-10 GeV range during the prompt emission phase as well as for fixed 30 s and 100 s integrations starting from the trigger time for each burst. We also compare these limits with the fluxes that would be expected from extrapolations of spectral fitsmore » presented in the first GBM spectral catalog and infer that roughly half of the GBM-detected bursts either require spectral breaks between the GBM and LAT energy bands or have intrinsically steeper spectra above the peak of the νF ν spectra (E pk). In order to distinguish between these two scenarios, we perform joint GBM and LAT spectral fits to the 30 brightest GBM-detected bursts and find that a majority of these bursts are indeed softer above E pk than would be inferred from fitting the GBM data alone. Approximately 20% of this spectroscopic subsample show statistically significant evidence for a cutoff in their high-energy spectra, which if assumed to be due to γγ attenuation, places limits on the maximum Lorentz factor associated with the relativistic outflow producing this emission. Furthermore, all of these latter bursts have maximum Lorentz factor estimates that are well below the minimum Lorentz factors calculated for LAT-detected GRBs, revealing a wide distribution in the bulk Lorentz factor of GRB outflows and indicating that LAT-detected bursts may represent the high end of this distribution.« less

  1. Constraining the High-energy Emission from Gamma-Ray Bursts with Fermi

    NASA Astrophysics Data System (ADS)

    Fermi Large Area Telescope Team; Ackermann, M.; Ajello, M.; Baldini, L.; Barbiellini, G.; Baring, M. G.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Brigida, M.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cutini, S.; D'Ammando, F.; de Palma, F.; Dermer, C. D.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Granot, J.; Grenier, I. A.; Grove, J. E.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hays, E.; Horan, D.; Jóhannesson, G.; Kataoka, J.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McEnery, J.; McGlynn, S.; Michelson, P. F.; Mitthumsiri, W.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Nymark, T.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzaque, S.; Reimer, A.; Reimer, O.; Ritz, S.; Ryde, F.; Sgrò, C.; Siskind, E. J.; Sonbas, E.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Stawarz, Łukasz; Suson, D. J.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Tibaldo, L.; Tinivella, M.; Tosti, G.; Uehara, T.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Fermi Gamma-ray Burst Monitor Team; Connaughton, V.; Briggs, M. S.; Guirec, S.; Goldstein, A.; Burgess, J. M.; Bhat, P. N.; Bissaldi, E.; Camero-Arranz, A.; Fishman, J.; Fitzpatrick, G.; Foley, S.; Gruber, D.; Jenke, P.; Kippen, R. M.; Kouveliotou, C.; McBreen, S.; Meegan, C.; Paciesas, W. S.; Preece, R.; Rau, A.; Tierney, D.; van der Horst, A. J.; von Kienlin, A.; Wilson-Hodge, C.; Xiong, S.

    2012-08-01

    We examine 288 gamma-ray bursts (GRBs) detected by the Fermi Gamma-ray Space Telescope's Gamma-ray Burst Monitor (GBM) that fell within the field of view of Fermi's Large Area Telescope (LAT) during the first 2.5 years of observations, which showed no evidence for emission above 100 MeV. We report the photon flux upper limits in the 0.1-10 GeV range during the prompt emission phase as well as for fixed 30 s and 100 s integrations starting from the trigger time for each burst. We compare these limits with the fluxes that would be expected from extrapolations of spectral fits presented in the first GBM spectral catalog and infer that roughly half of the GBM-detected bursts either require spectral breaks between the GBM and LAT energy bands or have intrinsically steeper spectra above the peak of the νF ν spectra (E pk). In order to distinguish between these two scenarios, we perform joint GBM and LAT spectral fits to the 30 brightest GBM-detected bursts and find that a majority of these bursts are indeed softer above E pk than would be inferred from fitting the GBM data alone. Approximately 20% of this spectroscopic subsample show statistically significant evidence for a cutoff in their high-energy spectra, which if assumed to be due to γγ attenuation, places limits on the maximum Lorentz factor associated with the relativistic outflow producing this emission. All of these latter bursts have maximum Lorentz factor estimates that are well below the minimum Lorentz factors calculated for LAT-detected GRBs, revealing a wide distribution in the bulk Lorentz factor of GRB outflows and indicating that LAT-detected bursts may represent the high end of this distribution.

  2. New Results on High Energy Cosmic Ray Electrons Observed with Fermi LAT and Their Implications on the Origin of Cosmic Rays

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    The Large Area Telescope on-board the Fermi Gamma-Ray Space Telescope has collected more than 10 million cosmic ray electrons with energy above 7 GeV since its science operation on orbit. High energy electrons rapidly lose their energy by synchrotron radiation on Galactic magnetic fields and by inverse Compton scattering on the interstellar radiation field. The typical distance over which a 1 TeV electron loses half its total energy is estimated to be 300-400 pc.This makes them a unique tool for probing nearby Galactic space. Observed spectrum has a harder spectral index than was previously reported and suggests the presence of nearby sources of high energy electrons. One of viable candidates are nearby pulsars, possibly some of recently discovered by Fermi. At the same time the dark matter origin of such sources cannot be ruled out. I will also report our current upper limits on cosmic ray electrons anisotropy which helps to set constraints on their local sources.

  3. Extremely correlated Fermi liquid theory of the t-J model in 2 dimensions: low energy properties

    NASA Astrophysics Data System (ADS)

    Shastry, B. Sriram; Mai, Peizhi

    2018-01-01

    Low energy properties of the metallic state of the two-dimensional t-J model are presented for second neighbor hopping with hole-doping (t\\prime ≤slant 0) and electron-doping (t\\prime > 0), with various superexchange energy J. We use a closed set of equations for the Greens functions obtained from the extremely correlated Fermi liquid theory. These equations reproduce the known low energies features of the large U Hubbard model in infinite dimensions. The density and temperature dependent quasiparticle weight, decay rate and the peak spectral heights over the Brillouin zone are calculated. We also calculate the resistivity, Hall conductivity, Hall number and cotangent Hall angle. The spectral features display high thermal sensitivity at modest T for density n≳ 0.8, implying a suppression of the effective Fermi-liquid temperature by two orders of magnitude relative to the bare bandwidth. The cotangent Hall angle exhibits a T 2 behavior at low T, followed by an interesting kink at higher T. The Hall number exhibits strong renormalization due to correlations. Flipping the sign of t\\prime changes the curvature of the resistivity versus T curves between convex and concave. Our results provide a natural route for understanding the observed difference in the temperature dependent resistivity of strongly correlated electron-doped and hole-doped matter.

  4. Fields in laser-ablated plasmas generalized to degenerate electrons and to Fermi energy in nuclei with change to quark-gluon plasma

    NASA Astrophysics Data System (ADS)

    Hora, Heinrich; Miley, George H.; Osman, Frederick; Hammerling, Peter X.

    2004-09-01

    The studies of laser ablation have lead to a new theory of nuclei, endothermic nuclei generation and quark-gluon plasmas. The surface of ablated plasma expanding into vacuum after high power laser irradiation of targets, contains an electric double layer having the thickness of the Debye length. This led to the discovery of surface tension of plasmas and to the internal dynamic electric fields in all inhomogeneous plasmas. The surface causes stabilization by short length surface waves smoothing the expanding plasma plume. Generalizing this to the degenerate electrons in a metal with the Fermi energy instead of the temperature, resulted in the surface tension of metals in agreement with measurements. Taking then the Fermi energy in the Debye length for nucleons results in a theory of nuclei with stable confinement of protons and neutrons just at the well known nuclear density, and in the Debye length equal to Hofstadter's decay of the nuclear surface. Increasing the nuclear density by a factor of 6 leads to the change of the Fermi energy into its relativistic branch where no surface energy is possible and the particle mass is not defined, permitting the quark-gluon plasma. Expansion of this higher density at the big band or in a supernova results in nucleation and element generation. The Boltzmann equilibrium permits the synthesis of nuclei even in the endothermic range limited to about uranium.

  5. Fermi-Lat Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center

    NASA Technical Reports Server (NTRS)

    Ajello, M.; Albert, A.; Atwood, W.B.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Brandt, T. J.; hide

    2016-01-01

    The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy gamma-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1-100 GeV from a 15 degrees x 15 degrees region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the gamma-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner 1 kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15 degrees x 15 degrees region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point SourceCatalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with gamma-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC areused to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.

  6. FERMI observations of high-energy gamma-ray emission from GRB 090217A

    DOE PAGES

    Ackermann, M.; Ajello, M.; Baldini, L.; ...

    2010-06-22

    The Fermi observatory is advancing our knowledge of gamma-ray bursts (GRBs) through pioneering observations at high energies, covering more than seven decades in energy with the two on-board detectors, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Here, we report on the observation of the long GRB 090217A which triggered the GBM and has been detected by the LAT with a significance greater than 9σ. We present the GBM and LAT observations and on-ground analyses, including the time-resolved spectra and the study of the temporal profile from 8 keV up to ~1 GeV. All spectra are wellmore » reproduced by a Band model. We compare these observations to the first two LAT-detected, long bursts GRB 080825C and GRB 080916C. These bursts were found to have time-dependent spectra and exhibited a delayed onset of the high-energy emission, which are not observed in the case of GRB 090217A. We discuss some theoretical implications for the high-energy emission of GRBs.« less

  7. Fermi: The Gamma-Ray Large Area Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  8. FERMI Observations of TeV-Selected Active Galactic Nuclei

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2009-12-04

    Here, we report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 5.5 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi). In total, 96 AGNs were selected for study, each being either (1) a source detected at TeV energies (28 sources) or (2) an object that has been studied with TeV instruments and for which an upper limit has been reported (68 objects). The Fermi observations show clear detections of 38 of these TeV-selected objects, of which 21 are joint GeV-TeV sources, and 29 were not in the thirdmore » EGRET catalog. For each of the 38 Fermi-detected sources, spectra and light curves are presented. Most can be described with a power law of spectral index harder than 2.0, with a spectral break generally required to accommodate the TeV measurements. Based on an extrapolation of the Fermi spectrum, we identify sources, not previously detected at TeV energies, which are promising targets for TeV instruments. Finally, evidence for systematic evolution of the γ-ray spectrum with redshift is presented and discussed in the context of interaction with the extragalactic background light.« less

  9. Three-component fermions with surface Fermi arcs in tungsten carbide

    NASA Astrophysics Data System (ADS)

    Ma, J.-Z.; He, J.-B.; Xu, Y.-F.; Lv, B. Q.; Chen, D.; Zhu, W.-L.; Zhang, S.; Kong, L.-Y.; Gao, X.; Rong, L.-Y.; Huang, Y.-B.; Richard, P.; Xi, C.-Y.; Choi, E. S.; Shao, Y.; Wang, Y.-L.; Gao, H.-J.; Dai, X.; Fang, C.; Weng, H.-M.; Chen, G.-F.; Qian, T.; Ding, H.

    2018-04-01

    Topological Dirac and Weyl semimetals not only host quasiparticles analogous to the elementary fermionic particles in high-energy physics, but also have a non-trivial band topology manifested by gapless surface states, which induce exotic surface Fermi arcs1,2. Recent advances suggest new types of topological semimetal, in which spatial symmetries protect gapless electronic excitations without high-energy analogues3-11. Here, using angle-resolved photoemission spectroscopy, we observe triply degenerate nodal points near the Fermi level of tungsten carbide with space group P 6 ¯m 2 (no. 187), in which the low-energy quasiparticles are described as three-component fermions distinct from Dirac and Weyl fermions. We further observe topological surface states, whose constant-energy contours constitute pairs of `Fermi arcs' connecting to the surface projections of the triply degenerate nodal points, proving the non-trivial topology of the newly identified semimetal state.

  10. Acoustics of tachyon Fermi gas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Trojan, Ernst; Vlasov, George V.

    2011-06-15

    We consider a Fermi gas of free tachyons as a continuous medium and find whether it satisfies the causality condition. There is no stable tachyon matter with the particle density below critical value n{sub T} and the Fermi momentum k{sub F}<{radical}((3/2))m that depends on the tachyon mass m. The pressure P and energy density E cannot be arbitrary small, but the situation P>E is not forbidden. Existence of shock waves in tachyon gas is also discussed. At low density n{sub T}

  11. Magnetospheric Multiscale Satellite Observations of Parallel Electron Acceleration in Magnetic Field Reconnection by Fermi Reflection from Time Domain Structures

    NASA Technical Reports Server (NTRS)

    Mozer, F. S.; Agapitov, O. A.; Artemyev, A.; Burch, J. L.; Ergun, R. E.; Giles, B. L.; Mourenas, D.; Torbert, R. B.; Phan, T. D.; Vasko, I.

    2016-01-01

    The same time domain structures (TDS) have been observed on two Magnetospheric Multiscale Satellites near Earth's dayside magnetopause. These TDS, traveling away from the X line along the magnetic field at 4000 km/s, accelerated field-aligned approx. 5 eV electrons to approx. 200 eV by a single Fermi reflection of the electrons by these overtaking barriers. Additionally, the TDS contained both positive and negative potentials, so they were a mixture of electron holes and double layers. They evolve in approx.10 km of space or 7 ms of time and their spatial scale size is 10-20 km, which is much larger than the electron gyroradius (less than1km) or the electron inertial length (4 km at the observation point, less nearer the X line).

  12. Millisecond Pulsars at Gamma-Ray Energies: Fermi Detections and Implications

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2011-01-01

    The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the discovery of new populations of radio quiet and millisecond gamma-ray pulsars. The Fermi Large Area Telescope has so far discovered approx.20 new gamma-ray millisecond pulsars (MSPs) by both folding at periods of known radio MSPs or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -30 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. Many of the newly discovered MSPs may be suitable for addition to the collection of very stable MSPs used for gravitational wave detection. Detection of such a large number of MSPs was surprising, given that most have relatively low spin-down luminosity and surface field strength. I will discuss their properties and the implications for pulsar particle acceleration and emission, as well as their potential contribution to gamma-ray backgrounds and Galactic cosmic rays.

  13. Controlling resonant tunneling in graphene via Fermi velocity engineering

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lima, Jonas R. F., E-mail: jonas.lima@ufrpe.br; Pereira, Luiz Felipe C.; Bezerra, C. G.

    We investigate the resonant tunneling in a single layer graphene superlattice with modulated energy gap and Fermi velocity via an effective Dirac-like Hamiltonian. We calculate the transmission coefficient with the transfer matrix method and analyze the effect of a Fermi velocity modulation on the electronic transmission, in the case of normal and oblique incidence. We find it is possible to manipulate the electronic transmission in graphene by Fermi velocity engineering, and show that it is possible to tune the transmitivity from 0 to 1. We also analyze how a Fermi velocity modulation influences the total conductance and the Fano factor.more » Our results are relevant for the development of novel graphene-based electronic devices.« less

  14. FERMI LARGE AREA TELESCOPE OBSERVATIONS OF MARKARIAN 421: THE MISSING PIECE OF ITS SPECTRAL ENERGY DISTRIBUTION

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Abdo, A. A.; Ackermann, M.; Ajello, M.

    We report on the {gamma}-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) {gamma}-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index {Gamma} = 1.78 {+-} 0.02 and average photon flux F(> 0.3 GeV) = (7.23 {+-} 0.16) x 10{sup -8} ph cm{sup -2} s{sup -1}. Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations inmore » the photon flux (up to a factor {approx}3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in {gamma}-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.« less

  15. Fermi Large Area Telescope observations of Markarian 421: The missing piece of its spectral energy distribution

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2011-07-15

    Here, we report on the γ-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Γ = 1.78 ± 0.02 and average photon flux F(> 0.3 GeV) = (7.23 ± 0.16) × 10 –8 ph cm –2 s –1. Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variationsmore » in the photon flux (up to a factor ~3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.« less

  16. Fermi: The Gamma-Ray Large Area Telescope Mission Status

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of an population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  17. Fermi-Level Pinning of Contacted Single-Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Wu, Shi-Yu; Liu, Lei; Jayanthi, Chakram; Guo, Guang-Yu

    2004-03-01

    Experimental evidences suggest that the Fermi-level of a contacted SWCNT with an energy gap is pinned in the vicinity of either the top of the valence band or the bottom of the conduction band, depending on the work function of the metallic leads (see, for example, E. D. Minot, Yuval Yaish,Vera Sazonova, Ji-Yong Park, Markus Brink, and Paul L. McEuen, Phys. Rev. Lett. 90, 156401 (2003)). This pinning of the Fermi-level may be attributed to the finite length of the contacted SWCNT. In this presentation, we report the result of our study of the pinning of the Fermi-level of a finite SWCNT, using the single π-orbital theory modified by the inclusion of a self-consistent scheme for the determination of charge transfer. We will also discuss the effect of the Fermi-level pinning on the transport properties of a SWCNT with a gap, either intrinsic or induced by a mechanical deformation. This work is supported by the NSF (Grant Nos: DMR-0112824 and ECS-0224114), the U.S. Department of Energy (Grant No: DE-FG02-00ER45832), and the National Science Council of Taiwan.

  18. FermiLib v0.1

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    MCCLEAN, JARROD; HANER, THOMAS; STEIGER, DAMIAN

    FermiLib is an open source software package designed to facilitate the development and testing of algorithms for simulations of fermionic systems on quantum computers. Fermionic simulations represent an important application of early quantum devices with a lot of potential high value targets, such as quantum chemistry for the development of new catalysts. This software strives to provide a link between the required domain expertise in specific fermionic applications and quantum computing to enable more users to directly interface with, and develop for, these applications. It is an extensible Python library designed to interface with the high performance quantum simulator, ProjectQ,more » as well as application specific software such as PSI4 from the domain of quantum chemistry. Such software is key to enabling effective user facilities in quantum computation research.« less

  19. New Results on High Energy Cosmic Ray Electrons Observed with Fermi LAT and Their Implications on the Models of Pulsars

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    This viewgraph presentation describes, in detail, the Fermi Large Area Telescope (LAT) and GLAST Burst Monitor (GBM). Observations made from the June 11, 2008 launch and a discussion of observations made of high energy cosmic ray electrons is also presented.

  20. First-principles study of electronic structure and Fermi surface in semimetallic YAs

    DOE PAGES

    Swatek, Przemys?aw Wojciech

    2018-03-23

    In the course of searching for new systems, which exhibit nonsaturating and extremely large positive magnetoresistance, electronic structure, Fermi surface, and de Haas-van Alphen characteristics of the semimetallic YAs compound were studied using the all-electron full-potential linearized augmented-plane wave (FP–LAPW) approach in the framework of the generalized gradient approximation (GGA). In the scalar-relativistic calculation, the cubic symmetry splits fivefold degenerate Y- d orbital into low-energy threefold-degenerate and twofold degenerate doublet states at point around the Fermi energy. Furthermore one of them, together with the threefold degenerate character of As-p orbital, render the YAs semimetal with a topologically trivial band ordermore » and fairly low density of states at the Fermi level. Including spin–orbit (SO) coupling into the calculation leads to pronounced splitting of the state and shifting the bands in the energy scale. Consequently, the determined four different 3-dimensional Fermi surface sheets of YAs consists of three concentric hole-like bands at and one ellipsoidal electron-like sheet centred at the X points. In full accordance with the previous first-principles calculations for isostructural YSb and YBi, the calculated Fermi surface of YAs originates from fairly compensated multi-band electronic structures.« less

  1. First-principles study of electronic structure and Fermi surface in semimetallic YAs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Swatek, Przemys?aw Wojciech

    In the course of searching for new systems, which exhibit nonsaturating and extremely large positive magnetoresistance, electronic structure, Fermi surface, and de Haas-van Alphen characteristics of the semimetallic YAs compound were studied using the all-electron full-potential linearized augmented-plane wave (FP–LAPW) approach in the framework of the generalized gradient approximation (GGA). In the scalar-relativistic calculation, the cubic symmetry splits fivefold degenerate Y- d orbital into low-energy threefold-degenerate and twofold degenerate doublet states at point around the Fermi energy. Furthermore one of them, together with the threefold degenerate character of As-p orbital, render the YAs semimetal with a topologically trivial band ordermore » and fairly low density of states at the Fermi level. Including spin–orbit (SO) coupling into the calculation leads to pronounced splitting of the state and shifting the bands in the energy scale. Consequently, the determined four different 3-dimensional Fermi surface sheets of YAs consists of three concentric hole-like bands at and one ellipsoidal electron-like sheet centred at the X points. In full accordance with the previous first-principles calculations for isostructural YSb and YBi, the calculated Fermi surface of YAs originates from fairly compensated multi-band electronic structures.« less

  2. Fermi large area telescope second source catalog

    DOE PAGES

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; ...

    2012-03-28

    Here, we present the second catalog of high-energy γ-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are fluxmore » measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. Furthermore, we provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. Finally, the 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely γ-ray-producing source classes.« less

  3. Fermi Large Area Telescope Second Source Catalog

    NASA Technical Reports Server (NTRS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M; Allafort, A.; Antolini, E; Bonnell, J.; Cannon, A.; Celik O.; Corbet, R.; hide

    2012-01-01

    We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 11eV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.

  4. FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nolan, P. L.; Ajello, M.; Allafort, A.

    We present the second catalog of high-energy {gamma}-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurementsmore » in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely {gamma}-ray-producing source classes.« less

  5. The fermi paradox is neither Fermi's nor a paradox.

    PubMed

    Gray, Robert H

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox.

  6. VizieR Online Data Catalog: Fermi/non-Fermi blazars jet power and accretion (Chen+, 2015)

    NASA Astrophysics Data System (ADS)

    Chen, Y. Y.; Zhang, X.; Zhang, H. J.; Yu, X. L.

    2017-11-01

    We selected the sample using radio catalogues to get the widest possible sample of blazars based on their radio properties. We split them into Fermi-detected sources and non-Fermi detections. Massaro et al. (2009, J/A+A/495/691) created the "Multifrequency Catalogue of Blazars" (Roma-BZCAT), which classifies blazars into three main groups based on their spectral properties. In total, we have a sample containing 177 clean Fermi blazars (96 Fermi FSRQs and 81 Fermi BL Lacs) and 133 non-Fermi blazars (105 non-Fermi FSRQs and 28 non-Fermi BL Lacs). (2 data files).

  7. Microscopic calculations of heavy-residue formation in quasielastic and deep-inelastic collisions below the Fermi energy.

    NASA Astrophysics Data System (ADS)

    Souliotis, G. A.; Shetty, D. V.; Galanopoulos, S.; Yennello, S. J.

    2007-10-01

    During the last several years we have undertaken a systematic study of heavy residues formed in quasi-elastic and deep- inelastic collisions near and below the Fermi energy [1,2]. Presently, we are exploring the possibility of extracting information on the dynamics by comparing our heavy residue data to calculations using microscopic models based on the quantum molecular dynamics approach (QMD). We have performed detailed calculations of QMD type using the recent version of the constrained molecular dynamics code CoMD of M. Papa [3]. CoMD is especially designed for reactions near the Fermi energy. It implements an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. CoMD imposes a constraint in the phase space occupation for each nucleon, thus restoring the Pauli principle at each time step of the collision. Results of the calculations and comparisons with our residue data will be presented and discussed in detail. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003); Nucl. Instrum. Methods B 204 166 (2003). [2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004). [3] M. Papa et al., Phys. Rev. C 64, 024612 (2001).

  8. Ab initio calculation of the G peak intensity of graphene: Laser-energy and Fermi-energy dependence and importance of quantum interference effects

    NASA Astrophysics Data System (ADS)

    Reichardt, Sven; Wirtz, Ludger

    2017-05-01

    We present the results of a diagrammatic, fully ab initio calculation of the G peak intensity of graphene. The flexibility and generality of our approach enables us to go beyond the previous analytical calculations in the low-energy regime. We study the laser and Fermi energy dependence of the G peak intensity and analyze the contributions from resonant and nonresonant electronic transitions. In particular, we explicitly demonstrate the importance of quantum interference and nonresonant states for the G peak process. Our method of analysis and computational concept is completely general and can easily be applied to study other materials as well.

  9. Nonextensive Thomas-Fermi model

    NASA Astrophysics Data System (ADS)

    Shivamoggi, Bhimsen; Martinenko, Evgeny

    2007-11-01

    Nonextensive Thomas-Fermi model was father investigated in the following directions: Heavy atom in strong magnetic field. following Shivamoggi work on the extension of Kadomtsev equation we applied nonextensive formalism to father generalize TF model for the very strong magnetic fields (of order 10e12 G). The generalized TF equation and the binding energy of atom were calculated which contain a new nonextensive term dominating the classical one. The binding energy of a heavy atom was also evaluated. Thomas-Fermi equations in N dimensions which is technically the same as in Shivamoggi (1998) ,but behavior is different and in interesting 2 D case nonextesivity prevents from becoming linear ODE as in classical case. Effect of nonextensivity on dielectrical screening reveals itself in the reduction of the envelope radius. It was shown that nonextesivity in each case is responsible for new term dominating classical thermal correction term by order of magnitude, which is vanishing in a limit q->1. Therefore it appears that nonextensive term is ubiquitous for a wide range of systems and father work is needed to understand the origin of it.

  10. Fermi Large Area Telescope Second Source Catalog

    NASA Astrophysics Data System (ADS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Belfiore, A.; Bellazzini, R.; Berenji, B.; Bignami, G. F.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Campana, R.; Cañadas, B.; Cannon, A.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Ceccanti, M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Chipaux, R.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Corbet, R.; Cutini, S.; D'Ammando, F.; Davis, D. S.; de Angelis, A.; DeCesar, M. E.; DeKlotz, M.; De Luca, A.; den Hartog, P. R.; de Palma, F.; Dermer, C. D.; Digel, S. W.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Dumora, D.; Enoto, T.; Escande, L.; Fabiani, D.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Iafrate, G.; Itoh, R.; Jóhannesson, G.; Johnson, R. P.; Johnson, T. E.; Johnson, A. S.; Johnson, T. J.; Kamae, T.; Katagiri, H.; Kataoka, J.; Katsuta, J.; Kawai, N.; Kerr, M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Landriu, D.; Latronico, L.; Lemoine-Goumard, M.; Lionetto, A. M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Marelli, M.; Massaro, E.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Minuti, M.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Mongelli, M.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Nymark, T.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Perkins, J. S.; Pesce-Rollins, M.; Pierbattista, M.; Pinchera, M.; Piron, F.; Pivato, G.; Porter, T. A.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Rochester, L. S.; Romani, R. W.; Roth, M.; Rousseau, R.; Ryde, F.; Sadrozinski, H. F.-W.; Salvetti, D.; Sanchez, D. A.; Saz Parkinson, P. M.; Sbarra, C.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Shaw, M. S.; Shrader, C.; Siskind, E. J.; Smith, D. A.; Spandre, G.; Spinelli, P.; Stephens, T. E.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Tinebra, F.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vandenbroucke, J.; Van Etten, A.; Van Klaveren, B.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wallace, E.; Wang, P.; Werner, M.; Winer, B. L.; Wood, D. L.; Wood, K. S.; Wood, M.; Yang, Z.; Zimmer, S.

    2012-04-01

    We present the second catalog of high-energy γ-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely γ-ray-producing source classes. We dedicate this paper to the memory of our colleague Patrick Nolan, who died on 2011 November 6. His career spanned much of the history of high-energy astronomy from space and his work on the Large Area Telescope (LAT) began nearly 20 years ago when it was just a concept. Pat was a central member in the operation of the LAT collaboration and he is greatly missed.

  11. Relativistic Thomas-Fermi treatment of compressed atoms and compressed nuclear matter cores of stellar dimensions

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Rotondo, M.; Rueda, Jorge A.; Xue, S.-S.

    The Feynman-Metropolis-Teller treatment of compressed atoms is extended to the relativistic regimes. Each atomic configuration is confined by a Wigner-Seitz cell and is characterized by a positive electron Fermi energy. The nonrelativistic treatment assumes a pointlike nucleus and infinite values of the electron Fermi energy can be attained. In the relativistic treatment there exists a limiting configuration, reached when the Wigner-Seitz cell radius equals the radius of the nucleus, with a maximum value of the electron Fermi energy (E{sub e}{sup F}){sub max}, here expressed analytically in the ultrarelativistic approximation. The corrections given by the relativistic Thomas-Fermi-Dirac exchange term are alsomore » evaluated and shown to be generally small and negligible in the relativistic high-density regime. The dependence of the relativistic electron Fermi energies by compression for selected nuclei are compared and contrasted to the nonrelativistic ones and to the ones obtained in the uniform approximation. The relativistic Feynman-Metropolis-Teller approach here presented overcomes some difficulties in the Salpeter approximation generally adopted for compressed matter in physics and astrophysics. The treatment is then extrapolated to compressed nuclear matter cores of stellar dimensions with A{approx_equal}(m{sub Planck}/m{sub n}){sup 3}{approx}10{sup 57} or M{sub core}{approx}M{sub {circle_dot}}. A new family of equilibrium configurations exists for selected values of the electron Fermi energy varying in the range 0Fermi energy reaching values much larger than the critical value E{sub c}=m{sub e}{sup 2}c{sup 3}/(e{Dirac_h}) for E{sub e}{sup F}=0. We compare and contrast our results with the ones of Thomas-Fermi model in strange stars.« less

  12. Fermi bubbles as a source of cosmic rays above 1015 eV

    NASA Astrophysics Data System (ADS)

    Chernyshov, D. O.; Cheng, K. S.; Dogiel, V. A.; Ko, C. M.

    2014-11-01

    Fermi bubbles are giant gamma-ray structures extended north and south of the Galactic center with characteristic sizes of order of 10 kpc recently discovered by Fermi Large Area Telescope. Good correlation between radio and gamma-ray emission in the region covered by Fermi bubbles implies the presence of high-energy electrons in this region. Since it is relatively difficult for relativistic electrons of this energy to travel all the way from the Galactic sources toward Fermi bubbles one can assume that they accelerated in-situ. The corresponding acceleration mechanism should also affect the distribution of the relativistic protons in the Galaxy. Since protons have much larger lifetimes the effect may even be observed near the Earth. In our model we suggest that Fermi bubbles are created by acceleration of electrons on series of shocks born due to periodic star accretions by supermassive black hole Sgr A*. We propose that hadronic CR within the 'knee' of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Reacceleration of these particles in the Fermi Bubble produces CRs beyond the knee. This model provides a natural explanation of the observed CR flux, spectral indexes, and matching of spectra at the knee.

  13. NASA's Fermi Telescope Resolves Radio Galaxy Centaurus A

    NASA Image and Video Library

    2017-12-08

    NASA release April 1, 2010 Fermi's Large Area Telescope resolved high-energy gamma rays from an extended region around the active galaxy Centaurus A. The emission corresponds to million-light-year-wide radio-emitting gas thrown out by the galaxy's supersized black hole. This inset shows an optical/gamma-ray composite of the galaxy and its location on the Fermi one-year sky map. Credit: NASA/DOE/Fermi LAT Collaboration, Capella Observatory To learn more about these images go to: www.nasa.gov/mission_pages/GLAST/news/smokestack-plumes.html NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

  14. Multiparticle instability in a spin-imbalanced Fermi gas

    NASA Astrophysics Data System (ADS)

    Whitehead, T. M.; Conduit, G. J.

    2018-01-01

    Weak attractive interactions in a spin-imbalanced Fermi gas induce a multiparticle instability, binding multiple fermions together. The maximum binding energy per particle is achieved when the ratio of the number of up- and down-spin particles in the instability is equal to the ratio of the up- and down-spin densities of states in momentum at the Fermi surfaces, to utilize the variational freedom of all available momentum states. We derive this result using an analytical approach, and verify it using exact diagonalization. The multiparticle instability extends the Cooper pairing instability of balanced Fermi gases to the imbalanced case, and could form the basis of a many-body state, analogously to the construction of the Bardeen-Cooper-Schrieffer theory of superconductivity out of Cooper pairs.

  15. Optical Response of Sr2RuO4 Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory

    NASA Astrophysics Data System (ADS)

    Stricker, D.; Mravlje, J.; Berthod, C.; Fittipaldi, R.; Vecchione, A.; Georges, A.; van der Marel, D.

    2014-08-01

    We report optical measurements demonstrating that the low-energy relaxation rate (1/τ) of the conduction electrons in Sr2RuO4 obeys scaling relations for its frequency (ω) and temperature (T) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/τ∝(ℏω)2+(pπkBT)2 with p=2, and ω/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy.

  16. Fermi observations of the very hard gamma-ray blazar PG 1553+113

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2009-12-22

    Here, we report the observations of PG 1553+113 during the first ~ 200 days of Fermi Gamma-ray Space Telescope science operations, from 2008 August 4 to 2009 February 22 (MJD 54682.7-54884.2). This is the first detailed study of PG 1553+113 in the GeV gamma-ray regime and it allows us to fill a gap of three decades in energy in its spectral energy distribution (SED). We find PG 1553+113 to be a steady source with a hard spectrum that is best fit by a simple power law in the Fermi energy band. We combine the Fermi data with archival radio, optical,more » X-ray, and very high energy (VHE) gamma-ray data to model its broadband SED and find that a simple, one-zone synchrotron self-Compton model provides a reasonable fit. PG 1553+113 has the softest VHE spectrum of all sources detected in that regime and, out of those with significant detections across the Fermi energy bandpass so far, the hardest spectrum in that energy regime. Thus, it has the largest spectral break of any gamma-ray source studied to date, which could be due to the absorption of the intrinsic gamma-ray spectrum by the extragalactic background light (EBL). Assuming this to be the case, we selected a model with a low level of EBL and used it to absorb the power-law spectrum from PG 1553+113 measured with Fermi (200 MeV-157 GeV) to find the redshift, which gave the best fit to the measured VHE data (90 GeV-1.1 TeV) for this parameterization of the EBL. We show that this redshift can be considered an upper limit on the distance to PG 1553+113.« less

  17. Domain wall suppression in trapped mixtures of Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Pepe, Francesco V.; Facchi, Paolo; Florio, Giuseppe; Pascazio, Saverio

    2012-08-01

    The ground-state energy of a binary mixture of Bose-Einstein condensates can be estimated for large atomic samples by making use of suitably regularized Thomas-Fermi density profiles. By exploiting a variational method on the trial densities the energy can be computed by explicitly taking into account the normalization condition. This yields analytical results and provides the basis for further improvement of the approximation. As a case study, we consider a binary mixture of 87Rb atoms in two different hyperfine states in a double-well potential and discuss the energy crossing between density profiles with different numbers of domain walls, as the number of particles and the interspecies interaction vary.

  18. Thermodynamics of inversion-domain boundaries in aluminum nitride: Interplay between interface energy and electric dipole potential energy

    NASA Astrophysics Data System (ADS)

    Zhang, J. Y.; Xie, Y. P.; Guo, H. B.; Chen, Y. G.

    2018-05-01

    Aluminum nitride (AlN) has a polar crystal structure that is susceptible to electric dipolar interactions. The inversion domains in AlN, similar to those in GaN and other wurtzite-structure materials, decrease the energy associated with the electric dipolar interactions at the expense of inversion-domain boundaries, whose interface energy has not been quantified. We study the atomic structures of six different inversion-domain boundaries in AlN, and compare their interface energies from density functional theory calculations. The low-energy interfaces have atomic structures with similar bonding geometry as those in the bulk phase, while the high-energy interfaces contain N-N wrong bonds. We calculate the formation energy of an inversion domain using the interface energy and dipoles' electric-field energy, and find that the distribution of the inversion domains is an important parameter for the microstructures of AlN films. Using this thermodynamic model, it is possible to control the polarity and microstructure of AlN films by tuning the distribution of an inversion-domain nucleus and by selecting the low-energy synthesis methods.

  19. Homogeneous Atomic Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

    2017-03-01

    We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

  20. Fermi: The Gamma-Ray Large Area Space Telescope Mission Status

    NASA Technical Reports Server (NTRS)

    McEnery, Julie E

    2014-01-01

    Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled over 1000 new sources and opened an important and previously unexplored window on a wide variety of phenomena. These have included the discovery of a population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of gigaelectronvolts from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as super-symmetric dark-matter annihilations and exotic relics from the Big Bang. Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory and review the science highlights from Fermi.

  1. Fermi's Motion Produces a Study in Spirograph

    NASA Image and Video Library

    2013-02-27

    Final still from Fermi video [bit.ly/Y2K4LN]. Credit: NASA/DOE/Fermi LAT Collaboration ----- NASA's Fermi Gamma-ray Space Telescope orbits our planet every 95 minutes, building up increasingly deeper views of the universe with every circuit. Its wide-eyed Large Area Telescope (LAT) sweeps across the entire sky every three hours, capturing the highest-energy form of light -- gamma rays -- from sources across the universe. These range from supermassive black holes billions of light-years away to intriguing objects in our own galaxy, such as X-ray binaries, supernova remnants and pulsars. Now a Fermi scientist has transformed LAT data of a famous pulsar into a mesmerizing movie that visually encapsulates the spacecraft's complex motion. Click here to continue reading: 1.usa.gov/WhYwCU NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  2. On the maximum energy achievable in the first order Fermi acceleration at shocks

    NASA Astrophysics Data System (ADS)

    Grozny, I.; Diamond, P.; Malkov, M.

    2002-11-01

    Astrophysical shocks are considered as the sites of cosmic ray (CR) production. The primary mechanism is the diffusive shock (Fermi) acceleration which operates via multiple shock recrossing by a particle. Its efficiency, the rate of energy gain, and the maximum energy are thus determined by the transport mechanisms (confinement to the shock) of these particles in a turbulent shock environment. The turbulence is believed to be generated by accelerated particles themselves. Moreover, in the most interesting case of efficient acceleration the entire MHD shock structure is dominated by their pressure. This makes this problem one of the challenging strongly nonlinear problems of astrophysics. We suggest a physical model that describes particle acceleration, shock structure and the CR driven turbulence on an equal footing. The key new element in this scheme is nonlinear cascading of the MHD turbulence on self-excited (via modulational and Drury instability) sound-like perturbations which gives rise to a significant enrichment of the long wave part of the MHD spectrum. This is critical for the calculation of the maximum energy.

  3. Fermi (Formerly GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steven M.

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  4. Fermi (nee GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steve

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  5. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    DOE PAGES

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes amore » phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.« less

  6. 3D Quantum Hall Effect of Fermi Arc in Topological Semimetals

    NASA Astrophysics Data System (ADS)

    Wang, C. M.; Sun, Hai-Peng; Lu, Hai-Zhou; Xie, X. C.

    2017-09-01

    The quantum Hall effect is usually observed in 2D systems. We show that the Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological semimetals. Because of the topological constraint, the Fermi arc at a single surface has an open Fermi surface, which cannot host the quantum Hall effect. Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at opposite surfaces can form a complete Fermi loop and support the quantum Hall effect. The edge states of the Fermi arcs show a unique 3D distribution, giving an example of (d -2 )-dimensional boundary states. This is distinctly different from the surface-state quantum Hall effect from a single surface of topological insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall conductivity evolves from the 1 /B dependence to quantized plateaus at the Weyl nodes. This behavior can be realized by tuning gate voltages in a slab of topological semimetal, such as the TaAs family, Cd3 As2 , or Na3Bi . This work will be instructive not only for searching transport signatures of the Fermi arcs but also for exploring novel electron gases in other topological phases of matter.

  7. In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Barbielini, G; Bastieri, D.; Bechtol, K.; Bellazzini, R.; hide

    2012-01-01

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron- plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between approx. 6 and approx. 13 GeV with an estimated uncertainty of approx. 2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.

  8. In-Flight Measurement of the Absolute Energy Scale of the Fermi Large Area Telescope

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ackermann, M.; /Stanford U., HEPL /SLAC /KIPAC, Menlo Park; Ajello, M.

    The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in themore » Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between {approx}6 and {approx}13 GeV with an estimated uncertainty of {approx}2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.« less

  9. Poisson Noise Removal in Spherical Multichannel Images: Application to Fermi data

    NASA Astrophysics Data System (ADS)

    Schmitt, Jérémy; Starck, Jean-Luc; Fadili, Jalal; Digel, Seth

    2012-03-01

    The Fermi Gamma-ray Space Telescope, which was launched by NASA in June 2008, is a powerful space observatory which studies the high-energy gamma-ray sky [5]. Fermi's main instrument, the Large Area Telescope (LAT), detects photons in an energy range between 20MeV and >300 GeV. The LAT is much more sensitive than its predecessor, the energetic gamma ray experiment telescope (EGRET) telescope on the Compton Gamma-ray Observatory, and is expected to find several thousand gamma-ray point sources, which is an order of magnitude more than its predecessor EGRET [13]. Even with its relatively large acceptance (∼2m2 sr), the number of photons detected by the LAT outside the Galactic plane and away from intense sources is relatively low and the sky overall has a diffuse glow from cosmic-ray interactions with interstellar gas and low energy photons that makes a background against which point sources need to be detected. In addition, the per-photon angular resolution of the LAT is relatively poor and strongly energy dependent, ranging from>10° at 20MeV to ∼0.1° above 100 GeV. Consequently, the spherical photon count images obtained by Fermi are degraded by the fluctuations on the number of detected photons. This kind of noise is strongly signal dependent : on the brightest parts of the image like the galactic plane or the brightest sources, we have a lot of photons per pixel, and so the photon noise is low. Outside the galactic plane, the number of photons per pixel is low, which means that the photon noise is high. Such a signal-dependent noise cannot be accurately modeled by a Gaussian distribution. The basic photon-imaging model assumes that the number of detected photons at each pixel location is Poisson distributed. More specifically, the image is considered as a realization of an inhomogeneous Poisson process. This statistical noise makes the source detection more difficult, consequently it is highly desirable to have an efficient denoising method for spherical

  10. Fermi-edge exciton-polaritons in doped semiconductor microcavities with finite hole mass

    NASA Astrophysics Data System (ADS)

    Pimenov, Dimitri; von Delft, Jan; Glazman, Leonid; Goldstein, Moshe

    2017-10-01

    The coupling between a 2D semiconductor quantum well and an optical cavity gives rise to combined light-matter excitations, the exciton-polaritons. These were usually measured when the conduction band is empty, making the single polariton physics a simple single-body problem. The situation is dramatically different in the presence of a finite conduction-band population, where the creation or annihilation of a single exciton involves a many-body shakeup of the Fermi sea. Recent experiments in this regime revealed a strong modification of the exciton-polariton spectrum. Previous theoretical studies concerned with nonzero Fermi energy mostly relied on the approximation of an immobile valence-band hole with infinite mass, which is appropriate for low-mobility samples only; for high-mobility samples, one needs to consider a mobile hole with large but finite mass. To bridge this gap, we present an analytical diagrammatic approach and tackle a model with short-ranged (screened) electron-hole interaction, studying it in two complementary regimes. We find that the finite hole mass has opposite effects on the exciton-polariton spectra in the two regimes: in the first, where the Fermi energy is much smaller than the exciton binding energy, excitonic features are enhanced by the finite mass. In the second regime, where the Fermi energy is much larger than the exciton binding energy, finite mass effects cut off the excitonic features in the polariton spectra, in qualitative agreement with recent experiments.

  11. There may be Fermi Energy levels in the hollow interiors of Nanotubes that would allow for a type of Quantum

    NASA Astrophysics Data System (ADS)

    Kriske, Richard

    2011-04-01

    There may be Fermi Energy levels that would allow for easy travel by Atoms, Molecules and Particles, in the hollow interior of Nanotubes. This may result in a Quantum Mechanical explaination of Capillary Action, and it may result in devices could take advantage of the idea that it takes no energy to rise in a Capillary tube, only in leaving it. This no-energy conjecture of Capillarity sounds very much like the idea that Electrons in obitals lose no Energy staying in orbit, only in changing orbits.It is this conjecture that may reveal that a Fermi Energy state is essentially in a weak orbital. This weak orbital could be exploited to store Anti-matter for instance. More profoundly it clearly shows how the Quantum Mechanical states meld smoothly into Classical Physics. It also reveals how extremely efficient Classical Machines could be constructed to take advantage of this spontaneous action. Say a tube could be designed to nudge electrons out of a weak obital in one place, sent down the tube (which is another weak orbital) and deposited in a weak orbital of another very distant Atom, apparently with little or perhaps no work being done, as long as the orbitals are the same energy. This may already exist in some Biological systems. Although more experimentation is needed, this would be the breakthrough that is needed to unify Classical and Quantum Mechanics.

  12. High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

    DOE PAGES

    Giroletti, M.; Massaro, F.; D’Abrusco, R.; ...

    2016-04-01

    Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. In this paper, we characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6100 deg 2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detectedmore » by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120–180 MHz) blazar spectral index is (α low) = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Finally, upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.« less

  13. High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Giroletti, M.; Massaro, F.; D’Abrusco, R.

    Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. In this paper, we characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6100 deg 2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detectedmore » by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120–180 MHz) blazar spectral index is (α low) = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Finally, upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.« less

  14. Quasi-Fermi level splitting and sub-bandgap absorptivity from semiconductor photoluminescence

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Katahara, John K.; Hillhouse, Hugh W., E-mail: h2@uw.edu

    A unified model for the direct gap absorption coefficient (band-edge and sub-bandgap) is developed that encompasses the functional forms of the Urbach, Thomas-Fermi, screened Thomas-Fermi, and Franz-Keldysh models of sub-bandgap absorption as specific cases. We combine this model of absorption with an occupation-corrected non-equilibrium Planck law for the spontaneous emission of photons to yield a model of photoluminescence (PL) with broad applicability to band-band photoluminescence from intrinsic, heavily doped, and strongly compensated semiconductors. The utility of the model is that it is amenable to full-spectrum fitting of absolute intensity PL data and yields: (1) the quasi-Fermi level splitting, (2) themore » local lattice temperature, (3) the direct bandgap, (4) the functional form of the sub-bandgap absorption, and (5) the energy broadening parameter (Urbach energy, magnitude of potential fluctuations, etc.). The accuracy of the model is demonstrated by fitting the room temperature PL spectrum of GaAs. It is then applied to Cu(In,Ga)(S,Se){sub 2} (CIGSSe) and Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) to reveal the nature of their tail states. For GaAs, the model fit is excellent, and fitted parameters match literature values for the bandgap (1.42 eV), functional form of the sub-bandgap states (purely Urbach in nature), and energy broadening parameter (Urbach energy of 9.4 meV). For CIGSSe and CZTSSe, the model fits yield quasi-Fermi leveling splittings that match well with the open circuit voltages measured on devices made from the same materials and bandgaps that match well with those extracted from EQE measurements on the devices. The power of the exponential decay of the absorption coefficient into the bandgap is found to be in the range of 1.2 to 1.6, suggesting that tunneling in the presence of local electrostatic potential fluctuations is a dominant factor contributing to the sub-bandgap absorption by either purely electrostatic (screened Thomas-Fermi

  15. Enrico Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Enrico Fermi was, of all the great physicists of the 20th century, among the most respected and admired. He was respected and admired because of his contributions to both theoretical and experimental physics, because of his leadership in discovering for mankind a powerful new source of energy, and above all, because of his personal character. He was always reliable and trustworthy. He had both of his feet on the ground all the time. He had great strength, but never threw his weight around. He did not play to the gallery. He did not practise one-up-manship. He exemplified, I always believe, the perfect Confucian gentleman...

  16. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    PubMed Central

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-01-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier–Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence. PMID:27845342

  17. Energy-efficient writing scheme for magnetic domain-wall motion memory

    NASA Astrophysics Data System (ADS)

    Kim, Kab-Jin; Yoshimura, Yoko; Ham, Woo Seung; Ernst, Rick; Hirata, Yuushou; Li, Tian; Kim, Sanghoon; Moriyama, Takahiro; Nakatani, Yoshinobu; Ono, Teruo

    2017-04-01

    We present an energy-efficient magnetic domain-writing scheme for domain wall (DW) motion-based memory devices. A cross-shaped nanowire is employed to inject a domain into the nanowire through current-induced DW propagation. The energy required for injecting the magnetic domain is more than one order of magnitude lower than that for the conventional field-based writing scheme. The proposed scheme is beneficial for device miniaturization because the threshold current for DW propagation scales with the device size, which cannot be achieved in the conventional field-based technique.

  18. Electron-exchange and quantum screening effects on the Thomson scattering process in quantum Fermi plasmas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Lee, Gyeong Won; Jung, Young-Dae; Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180-3590

    2013-06-15

    The influence of the electron-exchange and quantum screening on the Thomson scattering process is investigated in degenerate quantum Fermi plasmas. The Thomson scattering cross section in quantum plasmas is obtained by the plasma dielectric function and fluctuation-dissipation theorem as a function of the electron-exchange parameter, Fermi energy, plasmon energy, and wave number. It is shown that the electron-exchange effect enhances the Thomson scattering cross section in quantum plasmas. It is also shown that the differential Thomson scattering cross section has a minimum at the scattering angle Θ=π/2. It is also found that the Thomson scattering cross section increases with anmore » increase of the Fermi energy. In addition, the Thomson scattering cross section is found to be decreased with increasing plasmon energy.« less

  19. Gamma-Ray Observations of Tycho’s Supernova Remnant with VERITAS and Fermi

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Archambault, S.; Bourbeau, E.; Feng, Q.

    2017-02-10

    High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho’s SNR is a particularly good target because it is a young, type Ia SNR that has been well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho’s SNR by VERITAS and Fermi -LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho’s SNR with 147 hr of VERITAS and 84 months ofmore » Fermi -LAT observations, which represent about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92 ± 0.42{sub stat} ± 0.20{sub sys}. It is also softer than the spectral index in the GeV energy range, 2.14 ± 0.09{sub stat} ± 0.02{sub sys}, measured in this study using Fermi -LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi -LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously.« less

  20. Gamma-Ray Observations of Tycho’s Supernova Remnant with VERITAS and Fermi

    NASA Astrophysics Data System (ADS)

    Archambault, S.; Archer, A.; Benbow, W.; Bird, R.; Bourbeau, E.; Buchovecky, M.; Buckley, J. H.; Bugaev, V.; Cerruti, M.; Connolly, M. P.; Cui, W.; Dwarkadas, V. V.; Errando, M.; Falcone, A.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Fortson, L.; Furniss, A.; Griffin, S.; Hütten, M.; Hanna, D.; Holder, J.; Johnson, C. A.; Kaaret, P.; Kar, P.; Kelley-Hoskins, N.; Kertzman, M.; Kieda, D.; Krause, M.; Kumar, S.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; Moriarty, P.; Mukherjee, R.; Nieto, D.; O'Brien, S.; Ong, R. A.; Otte, A. N.; Park, N.; Pohl, M.; Popkow, A.; Pueschel, E.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Sadeh, I.; Santander, M.; Sembroski, G. H.; Shahinyan, K.; Slane, P.; Staszak, D.; Telezhinsky, I.; Trepanier, S.; Tyler, J.; Wakely, S. P.; Weinstein, A.; Weisgarber, T.; Wilcox, P.; Wilhelm, A.; Williams, D. A.; Zitzer, B.

    2017-02-01

    High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho’s SNR is a particularly good target because it is a young, type Ia SNR that has been well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho’s SNR by VERITAS and Fermi-LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho’s SNR with 147 hr of VERITAS and 84 months of Fermi-LAT observations, which represent about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92 ± 0.42stat ± 0.20sys. It is also softer than the spectral index in the GeV energy range, 2.14 ± 0.09stat ± 0.02sys, measured in this study using Fermi-LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi-LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously.

  1. Cyclotron resonance mass and Fermi energy pinning in the In(AsN) alloy

    NASA Astrophysics Data System (ADS)

    Drachenko, O.; Patanè, A.; Kozlova, N. V.; Zhuang, Q. D.; Krier, A.; Eaves, L.; Helm, M.

    2011-04-01

    We report cyclotron resonance (CR) experiments on the midinfrared alloy InAs1-xNx grown on GaAs with x from 0% to 1.9%. Using magnetic fields up to 60 T and terahertz photon sources from 3 to 30 THz, we determine the dependence on x of the electron density and CR mass. The increase in the carrier density with increasing x is accompanied by a redshift in the interband photoluminescence emission and is explained in terms of the pinning of the Fermi level to its value at x =0. The high carrier densities (˜1018 cm-3) at x˜1% give rise to a CR mass that is only weakly dependent on the excitation energy, significantly weaker than that in InAs.

  2. Energy Fluctuation of Ideal Fermi Gas Trapped under Generic Power Law Potential U=\\sum_{i=1}^{d} c_i\\vert x_{i}/a_{i}\\vert^{n_{i} } in d Dimensions

    NASA Astrophysics Data System (ADS)

    Mir, Mehedi Faruk; Muktadir Rahman, Md.; Dwaipayan, Debnath; Sakhawat Hossain Himel, Md.

    2016-04-01

    Energy fluctuation of ideal Fermi gas trapped under generic power law potential U=\\sumi=1d ci \\vertxi/ai \\vert n_i has been calculated in arbitrary dimensions. Energy fluctuation is scrutinized further in the degenerate limit μ ≫ KBT with the help of Sommerfeld expansion. The dependence of energy fluctuation on dimensionality and power law potential is studied in detail. Most importantly our general result can not only exactly reproduce the recently published result regarding free and harmonically trapped ideal Fermi gas in d = 3 but also can describe the outcome for any power law potential in arbitrary dimension.

  3. Discrete breathers in a two-dimensional hexagonal Fermi Pasta Ulam lattice

    NASA Astrophysics Data System (ADS)

    Butt, Imran A.; Wattis, Jonathan A. D.

    2007-02-01

    We consider a two-dimensional Fermi-Pasta-Ulam (FPU) lattice with hexagonal symmetry. Using asymptotic methods based on small amplitude ansatz, at third order we obtain a reduction to a cubic nonlinear Schrödinger equation (NLS) for the breather envelope. However, this does not support stable soliton solutions, so we pursue a higher order analysis yielding a generalized NLS, which includes known stabilizing terms. We present numerical results which suggest that long-lived stationary and moving breathers are supported by the lattice. We find breather solutions which move in an arbitrary direction, an ellipticity criterion for the wavenumbers of the carrier wave, asymptotic estimates for the breather energy, and a minimum threshold energy below which breathers cannot be found. This energy threshold is maximized for stationary breathers and becomes vanishingly small near the boundary of the elliptic domain where breathers attain a maximum speed. Several of the results obtained are similar to those obtained for the square FPU lattice (Butt and Wattis 2006 J. Phys. A: Math. Gen. 39 4955), though we find that the square and hexagonal lattices exhibit different properties in regard to the generation of harmonics, and the isotropy of the generalized NLS equation.

  4. High Energy Astrophysics with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    This slide presentation reviews some of the findings of the Large Area Telescope (LAT) aboard the Fermi Observatory. It includes information about the LAT, and the Gamma-Ray Burst Monitor (GBM), detection of the quiet sun and the moon in gamma rays, Pulsars observed by the observatory, Globular Star Clusters, Active Galactic Nucleus, and Gamma-Ray Bursts, with specific information about GRB 080916C.

  5. Applications of Fermi-Lowdin-Orbital Self-Interaction Correction Scheme to Organic Systems

    NASA Astrophysics Data System (ADS)

    Baruah, Tunna; Kao, Der-You; Yamamoto, Yoh

    Recent progress in treating the self-interaction errors by means of local, Lowdin-orthogonalized Fermi Orbitals offers a promising route to study the effect of self-interaction errors in the electronic structure of molecules. The Fermi orbitals depend on the location of the electronic positions, called as Fermi orbital descriptors. One advantage of using the Fermi orbitals is that the corrected Hamiltonian is unitarily invariant. Minimization of the corrected energies leads to an optimized set of centroid positions. Here we discuss the applications of this method to various systems from constituent atoms to several medium size molecules such as Mg-porphyrin, C60, pentacene etc. The applications to the ionic systems will also be discussed. De-SC0002168, NSF-DMR 125302.

  6. Interaction of sodium atoms with stacking faults in silicon with different Fermi levels

    NASA Astrophysics Data System (ADS)

    Ohno, Yutaka; Morito, Haruhiko; Kutsukake, Kentaro; Yonenaga, Ichiro; Yokoi, Tatsuya; Nakamura, Atsutomo; Matsunaga, Katsuyuki

    2018-06-01

    Variation in the formation energy of stacking faults (SFs) with the contamination of Na atoms was examined in Si crystals with different Fermi levels. Na atoms agglomerated at SFs under an electronic interaction, reducing the SF formation energy. The energy decreased with the decrease of the Fermi level: it was reduced by more than 10 mJ/m2 in p-type Si, whereas it was barely reduced in n-type Si. Owing to the energy reduction, Na atoms agglomerating at SFs in p-type Si are stable compared with those in n-type Si, and this hypothesis was supported by ab initio calculations.

  7. Fermi Spots a Record Flare from Blazar

    NASA Image and Video Library

    2015-07-10

    Blazar 3C 279's historic gamma-ray flare can be seen in this image from the Large Area Telescope (LAT) on NASA's Fermi satellite. Gamma rays with energies from 100 million to 100 billion electron volts (eV) are shown; for comparison, visible light has energies between 2 and 3 eV. The image spans 150 degrees, is shown in a stereographic projection, and represents an exposure from June 11 at 00:28 UT to June 17 at 08:17 UT. Read more: go.nasa.gov/1TqBAdJ Credit: NASA/DOE/Fermi LAT Collaboration NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  8. Electrostatic energy and screened charge interaction near the surface of metals with different Fermi surface shape

    NASA Astrophysics Data System (ADS)

    Gabovich, A. M.; Il'chenko, L. G.; Pashitskii, E. A.; Romanov, Yu. A.

    1980-04-01

    Using the Poisson equation Green function for a self-consistent field in a spatially inhomogeneous system, expressions for the electrostatic energy and screened charge interaction near the surface of a semi-infinite metal and a thin quantizing film are derived. It is shown that the decrease law and Friedel oscillation amplitude of adsorbed atom indirect interaction are determined by the electron spectrum character and the Fermi surface shape. The results obtained enable us to explain, in particular, the submonolayer adsorbed film structure on the W and Mo surfaces.

  9. The First FERMI-LAT Gamma-Ray Burst Catalog

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Asano, K.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; hide

    2013-01-01

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy great than (20 MeV) gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above approximately 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

  10. The first Fermi-LAT Gamma-Ray burst catalog

    DOE PAGES

    Ackermann, M.; Ajello, M.; Asano, K.; ...

    2013-10-23

    In three years of observations since the beginning of nominal science operations in 2008 August, the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has observed high-energy (gsim 20 MeV) γ-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above ~20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi andmore » processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for the GRB analysis are provided. Here, we summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared with emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.« less

  11. Fermi LAT Observation of Centaurus a Radio Galaxy

    NASA Astrophysics Data System (ADS)

    Sahakyan, N. V.

    2013-01-01

    The results of analysis of approximately 3 year gamma-ray observations (August 2008-July 2011) of the core of radio galaxy Centaurus A with the Fermi Large Area Telescope (Fermi LAT) are presented. Binned likelihood analysis method applying to the data shows that below several GeV the spectrum can be described by a single power-law with photon index Γ = 2.73 ± 0.06. However, at higher energies the new data show significant excess above the extrapolation of the energy spectrum from low energies. The comparison of the corresponding Spectral Energy Distribution (SED) at GeV energies with the SED in the TeV energy band reported by the H.E.S.S. collaboration shows that we deal with two or perhaps even three components of gamma-radiation originating from different regions located within the central 10 kpc of Centaurus A. The analysis of gamma-ray data of Centaurus A lobe accumulated from the beginning of the operation until November 14, 2011 show extension of the HE gamma-ray emission beyond the WMAP radio image in the case of the Northern lobe [9]. The possible origins of gamma-rays from giant radio lobes of Centaurus A are discussed in the context of hadronic and leptonic scenarios.

  12. Fermi surfaces in Kondo insulators

    NASA Astrophysics Data System (ADS)

    Liu, Hsu; Hartstein, Máté; Wallace, Gregory J.; Davies, Alexander J.; Ciomaga Hatnean, Monica; Johannes, Michelle D.; Shitsevalova, Natalya; Balakrishnan, Geetha; Sebastian, Suchitra E.

    2018-04-01

    We report magnetic quantum oscillations measured using torque magnetisation in the Kondo insulator YbB12 and discuss the potential origin of the underlying Fermi surface. Observed quantum oscillations as well as complementary quantities such as a finite linear specific heat capacity in YbB12 exhibit similarities with the Kondo insulator SmB6, yet also crucial differences. Small heavy Fermi sections are observed in YbB12 with similarities to the neighbouring heavy fermion semimetallic Fermi surface, in contrast to large light Fermi surface sections in SmB6 which are more similar to the conduction electron Fermi surface. A rich spectrum of theoretical models is suggested to explain the origin across different Kondo insulating families of a bulk Fermi surface potentially from novel itinerant quasiparticles that couple to magnetic fields, yet do not couple to weak DC electric fields.

  13. Spin Imbalanced Quasi-Two-Dimensional Fermi Gases

    NASA Astrophysics Data System (ADS)

    Ong, Willie C.

    Spin-imbalanced Fermi gases serve as a testbed for fundamental notions and are efficient table-top emulators of a variety of quantum matter ranging from neutron stars, the quark-gluon plasma, to high critical temperature superconductors. A macroscopic quantum phenomenon which occurs in spin-imbalanced Fermi gases is that of phase separation; in three dimensions, a spin-balanced, fully-paired superfluid core is surrounded by an imbalanced normal-fluid shell, followed by a fully polarized shell. In one dimension, the behavior is reversed; a balanced phase appears outside a spin-imbalanced core. This thesis details the first density profile measurements and studies on spin-imbalanced quasi-2D Fermi gases, accomplished with high-resolution, rapid sequential spin-imaging. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a 2D system. Data for normal-fluid mixtures are well fit by a simple 2D polaron model of the free energy. Not predicted by the model is an observed phase transition to a spin-balanced central core above a critical polarisation.

  14. Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Ruan, John J.; Anderson, Scott F.; MacLeod, Chelsea L.; Becker, Andrew C.; Burnett, T. H.; Davenport, James R. A.; Ivezić, Željko; Kochanek, Christopher S.; Plotkin, Richard M.; Sesar, Branimir; Stuart, J. Scott

    2012-11-01

    We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ~30% of γ-ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ, and driving amplitudes on short timescales \\hat{\\sigma }. Imposing cuts on minimum τ and \\hat{\\sigma } allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several-arcminute error ellipses of γ-ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E >= 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ-ray blazars and is likely to be the γ-ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ~3 years in the rest frame of the jet, in contrast with the ~320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.

  15. Gamma-ray astronomy: From Fermi up to the HAWC high-energy {gamma}-ray observatory in Sierra Negra

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Carraminana, Alberto; Collaboration: HAWC Collaboration

    Gamma-rays represent the most energetic electromagnetic window for the study of the Universe. They are studied both from space at MeV and GeV energies, with instruments like the Fermi{gamma}-ray Space Telescope, and at TeV energies with ground based instruments profiting of particle cascades in the atmosphere and of the Cerenkov radiation of charged particles in the air or in water. The Milagro gamma-ray observatory represented the first instrument to successfully implement the water Cerenkov technique for {gamma}-ray astronomy, opening the ground for the more sensitive HAWC {gamma}-ray observatory, currently under development in the Sierra Negra site and already providing earlymore » science results.« less

  16. Fermi detection of delayed GeV emission from the short gamma-ray burst 081024B

    DOE PAGES

    Abdo, A. A.

    2010-03-03

    Here, we report on the detailed analysis of the high-energy extended emission from the short gamma-ray burst (GRB) 081024B detected by the Fermi Gamma-ray Space Telescope. Historically, this represents the first clear detection of temporal extended emission from a short GRB. Furthermore, the light curve observed by the Fermi Gamma-ray Burst Monitor lasts approximately 0.8 s whereas the emission in the Fermi Large Area Telescope lasts for about 3 s. Evidence of longer lasting high-energy emission associated with long bursts has been already reported by previous experiments. These observations, together with the earlier reported study of the bright short GRBmore » 090510, indicate similarities in the high-energy emission of short and long GRBs and open the path to new interpretations.« less

  17. Theoretical Interpretation of Pass 8 Fermi -LAT e + + e - Data

    DOE PAGES

    Di Mauro, M.; Manconi, S.; Vittino, A.; ...

    2017-08-17

    The flux of positrons and electrons (e + + e -) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. Here, we discuss a number of interpretations of Pass 8 Fermi-LAT e + + e - spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We also found that the Fermi-LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positrons from cataloged PWNe, and amore » secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e + + e - Fermi-LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green's catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e + + e - Fermi-LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e + + e -spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

  18. Theoretical Interpretation of Pass 8 Fermi -LAT e + + e - Data

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Di Mauro, M.; Manconi, S.; Vittino, A.

    The flux of positrons and electrons (e + + e -) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. Here, we discuss a number of interpretations of Pass 8 Fermi-LAT e + + e - spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We also found that the Fermi-LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positrons from cataloged PWNe, and amore » secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e + + e - Fermi-LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green's catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e + + e - Fermi-LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e + + e -spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

  19. The Fermi Science Support Center Data Servers and Archive

    NASA Astrophysics Data System (ADS)

    Reustle, Alexander; Fermi Science Support Center

    2018-01-01

    The Fermi Science Support Center (FSSC) provides the scientific community with access to Fermi data and other products. The Gamma-Ray Burst Monitor (GBM) data is stored at NASA's High Energy Astrophysics Science Archive Research Center (HEASARC) and is accessible through their searchable Browse web interface. The Large Area Telescope (LAT) data is distributed through a custom FSSC interface where users can request all photons detected from a region on the sky over a specified time and energy range. Through its website the FSSC also provides planning and scheduling products, such as long and short term observing timelines, spacecraft position and attitude histories, and exposure maps. We present an overview of the different data products provided by the FSSC, how they can be accessed, and statistics on the archive usage since launch.

  20. Single-Particle Properties of a Strongly Interacting Bose-Fermi Mixture Above the BEC Phase Transition Temperature

    NASA Astrophysics Data System (ADS)

    Kharga, D.; Inotani, D.; Hanai, R.; Ohashi, Y.

    2017-06-01

    We theoretically investigate the normal state properties of a Bose-Fermi mixture with a strong attractive interaction between Fermi and Bose atoms. We extend the ordinary T-matrix approximation (TMA) with respect to Bose-Fermi pairing fluctuations, to include the Hugenholtz-Pines' relation for all Bose Green's functions appearing in TMA self-energy diagrams. This extension is shown to be essentially important to correctly describe the physical properties of the Bose-Fermi mixture, especially near the Bose-Einstein condensation instability. Using this improved TMA, we clarify how the formation of composite fermions affects Bose and Fermi single-particle excitation spectra, over the entire interaction strength.

  1. Momentum-resolved spectroscopy of a Fermi liquid

    PubMed Central

    Doggen, Elmer V. H.; Kinnunen, Jami J.

    2015-01-01

    We consider a recent momentum-resolved radio-frequency spectroscopy experiment, in which Fermi liquid properties of a strongly interacting atomic Fermi gas were studied. Here we show that by extending the Brueckner-Goldstone model, we can formulate a theory that goes beyond basic mean-field theories and that can be used for studying spectroscopies of dilute atomic gases in the strongly interacting regime. The model hosts well-defined quasiparticles and works across a wide range of temperatures and interaction strengths. The theory provides excellent qualitative agreement with the experiment. Comparing the predictions of the present theory with the mean-field Bardeen-Cooper-Schrieffer theory yields insights into the role of pair correlations, Tan's contact, and the Hartree mean-field energy shift. PMID:25941948

  2. High-Energy Gamma-Ray Emission From Solar Flares: Summary of Fermi LAT Detections and Analysis of Two M-Class Flares

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Bissaldi, E.; hide

    2013-01-01

    We present the detections of 19 solar flares detected in high-energy gamma rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its rst four years of operation. Interestingly, all ares are associated with fairly fast Coronal Mass Ejections (CMEs) and are not all powerful X-ray ares. We then describe the detailed temporal, spatial and spectral characteristics of the rst two long-lasting events: the 2011 March 7 are, a moderate (M3.7) impulsive are followed by slowly varying gamma-ray emission over 13 hours, and the 2011 June 7 M2.5 are, which was followed by gamma-ray emission lasting for 2 hours. We compare the Fermi-LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that a hadronic origin of the gamma rays is more likely than a leptonic origin and nd that the energy spectrum of the proton distribution softens after the 2011 March 7 are, favoring a scenario with continuous acceleration at the are site. This work suggests that proton acceleration in solar ares is more common than previously thought, occurring for even modest X-ray ares, and for longer durations.

  3. Seebeck effect on a weak link between Fermi and non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Nguyen, T. K. T.; Kiselev, M. N.

    2018-02-01

    We propose a model describing Seebeck effect on a weak link between two quantum systems with fine-tunable ground states of Fermi and non-Fermi liquid origin. The experimental realization of the model can be achieved by utilizing the quantum devices operating in the integer quantum Hall regime [Z. Iftikhar et al., Nature (London) 526, 233 (2015), 10.1038/nature15384] designed for detection of macroscopic quantum charged states in multichannel Kondo systems. We present a theory of thermoelectric transport through hybrid quantum devices constructed from quantum-dot-quantum-point-contact building blocks. We discuss pronounced effects in the temperature and gate voltage dependence of thermoelectric power associated with a competition between Fermi and non-Fermi liquid behaviors. High controllability of the device allows to fine tune the system to different regimes described by multichannel and multi-impurity Kondo models.

  4. Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices.

    PubMed

    Cramer, M; Eisert, J; Illuminati, F

    2004-11-05

    We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices and parabolic confining potentials. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimension within mean-field and perturbation theory. The results are compared with a new numerical method that is based on a Gutzwiller variational approach for the bosons and an exact treatment for the fermions. The findings can be applied as a guideline for future experiments with trapped atomic Bose-Fermi mixtures in optical lattices.

  5. Fermi/LAT search for counterpart to the IceCube event 67093193 (run 127853)

    NASA Astrophysics Data System (ADS)

    Vianello, G.; Magill, J. D.; Omodei, N.; Kocevski, D.; Ajello, M.; Buson, S.; Krauss, F.; Chiang, J.

    2016-04-01

    on behalf of the Fermi-LAT team: We have searched the Fermi Large Area Telescope data for a high-energy gamma-ray counterpart for the IceCube High Energy Starting Event (HESE) 67093193, detected in run 127853 on 2016-04-27 05:52:32.00 UT (AMON GCN notice rev. 2, http://gcn.gsfc.nasa.gov/notices_amon/67093193_127853.amon . See http://gcn.gsfc.nasa.gov/doc/Public_Doc_AMON_IceCube_GCN_Alerts_v2.pdf for a description of HESE events and related GCN notices).

  6. Spin-imbalanced pairing and Fermi surface deformation in flat bands

    NASA Astrophysics Data System (ADS)

    Huhtinen, Kukka-Emilia; Tylutki, Marek; Kumar, Pramod; Vanhala, Tuomas I.; Peotta, Sebastiano; Törmä, Päivi

    2018-06-01

    We study the attractive Hubbard model with spin imbalance on two lattices featuring a flat band: the Lieb and kagome lattices. We present mean-field phase diagrams featuring exotic superfluid phases, similar to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, whose stability is confirmed by dynamical mean-field theory. The nature of the pairing is found to be richer than just the Fermi surface shift responsible for the usual FFLO state. The presence of a flat band allows for changes in the particle momentum distributions at null energy cost. This facilitates formation of nontrivial superfluid phases via multiband Cooper pair formation: the momentum distribution of the spin component in the flat band deforms to mimic the Fermi surface of the other spin component residing in a dispersive band. The Fermi surface of the unpaired particles that are typical for gapless superfluids becomes deformed as well. The results highlight the profound effect of flat dispersions on Fermi surface instabilities, and provide a potential route for observing spin-imbalanced superfluidity and superconductivity.

  7. Observations of gamma-ray pulsars at the highest energies with the Fermi Large Area Telescope

    NASA Astrophysics Data System (ADS)

    Saz Parkinson, Pablo

    2016-07-01

    One of the most exciting developments in pulsar astrophysics in recent years has been the detection, with ground-based instruments (VERITAS, MAGIC), of pulsed gamma-ray emission from the Crab at very high energies (VHE, E>100 GeV). The Large Area Telescope (LAT) on board the Fermi satellite has detected over 160 pulsars above 100 MeV. Twenty-eight of these have been shown to emit pulsations above 10 GeV and approximately a dozen show emission above 25 GeV. While most gamma-ray pulsars are well-fitted in the GeV range by a power law with an exponential cut-off at around a few GeV, some emission models predict emission at energies above 100 GeV, either through a power-law extrapolation of the low-energy spectrum, or via a new (e.g. Inverse Compton) component. We will present results of our search for high-energy emission from LAT-detected gamma-ray pulsars using the latest Pass 8 data and discuss the prospects of finding the next VHE pulsar, providing a good target (or targets) for follow-up observations with current and future ground-based observatories, like CTA.

  8. Superconductor-insulator transition and Fermi-Bose crossovers

    DOE PAGES

    Loh, Yen Lee; Randeria, Mohit; Trivedi, Nandini; ...

    2016-05-31

    The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is always found to be from a bosonic insulator to a BEC-likemore » SC, with an energy gap for fermions that remains finite across the SIT. Hence, the energy scales that go critical at the SIT are the gap to pair excitations in the insulator and the superfluid stiffness in the SC. In addition to giving insight into important questions about the SIT in solid-state systems, our model should be experimentally realizable using ultracold fermions in optical lattices.« less

  9. Energetics of a strongly correlated Fermi gas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tan, Shina

    2008-12-15

    The energy of the two-component Fermi gas with the s-wave contact interaction is a simple linear functional of its momentum distribution: E{sub internal}=h{sup 2}{omega}C/4{pi}am+{sigma}{sub k{sigma}}(h{sup 2}k{sup 2}/2m)(n{sub k{sigma}}= -C/k{sup 4}) where the external potential energy is not included, a is the scattering length, {omega} is the volume, n{sub k{sigma}} is the average number of fermions with wave vector k and spin {sigma}, and C{identical_to}lim{sub k{yields}}{sub {infinity}}k{sup 4}n{sub k{up_arrow}}=lim{sub k{yields}}{sub {infinity}}k{sup 4}n{sub k{down_arrow}}. This result is a universal identity. Its proof is facilitated by a novel mathematical idea, which might be of utility in dealing with ultraviolet divergences in quantum fieldmore » theories. Other properties of this Fermi system, including pair correlations and the dimer-fermion scattering length, are also studied.« less

  10. Fermi wave vector for the partially spin-polarized composite-fermion Fermi sea

    NASA Astrophysics Data System (ADS)

    Balram, Ajit C.; Jain, J. K.

    2017-12-01

    The fully spin-polarized composite-fermion (CF) Fermi sea at the half-filled lowest Landau level has a Fermi wave vector kF*=√{4 π ρe } , where ρe is the density of electrons or composite fermions, supporting the notion that the interaction between composite fermions can be treated perturbatively. Away from ν =1 /2 , the area is seen to be consistent with kF*=√{4 π ρe } for ν <1 /2 but kF*=√{4 π ρh } for ν >1 /2 , where ρh is the density of holes in the lowest Landau level. This result is consistent with particle-hole symmetry in the lowest Landau level. We investigate in this article the Fermi wave vector of the spin-singlet CF Fermi sea (CFFS) at ν =1 /2 , for which particle-hole symmetry is not a consideration. Using the microscopic CF theory, we find that for the spin-singlet CFFS the Fermi wave vectors for up- and down-spin CFFSs at ν =1 /2 are consistent with kF*↑,↓=√{4 π ρe↑,↓ } , where ρe↑=ρe↓=ρe/2 , which implies that the residual interactions between composite fermions do not cause a nonperturbative correction for spin-singlet CFFS either. Our results suggest the natural conjecture that for arbitrary spin polarization the CF Fermi wave vectors are given by kF*↑=√{4 π ρe↑ } and kF*↓=√{4 π ρe↓ } .

  11. Searches for cosmic-ray electron anisotropies with the Fermi Large Area Telescope

    DOE PAGES

    Ackermann, M.

    2010-11-01

    The Large Area Telescope on board the Fermi satellite (Fermi LAT) detected more than 1.6 × 10 6 cosmic-ray electrons/positrons with energies above 60 GeV during its first year of operation. The arrival directions of these events were searched for anisotropies of angular scale extending from ~ 10 ° up to 90°, and of minimum energy extending from 60 GeV up to 480 GeV. Two independent techniques were used to search for anisotropies, both resulting in null results. Upper limits on the degree of the anisotropy were set that depended on the analyzed energy range and on the anisotropy’s angularmore » scale. The upper limits for a dipole anisotropy ranged from ~ 0.5 % to ~ 10 % .« less

  12. Interaction energy and itinerant ferromagnetism in a strongly interacting Fermi gas in the absence of molecule formation

    DOE PAGES

    He, Lianyi

    2014-11-26

    In this study, we investigate the interaction energy and the possibility of itinerant ferromagnetism in a strongly interacting Fermi gas at zero temperature in the absence of molecule formation. The interaction energy is obtained by summing the perturbative contributions of Galitskii-Feynman type to all orders in the gas parameter. It can be expressed by a simple phase-space integral of an in-medium scattering phase shift. In both three and two dimensions (3D and 2D), the interaction energy shows a maximum before reaching the resonance from the Bose-Einstein condensate side, which provides a possible explanation of the experimental measurements of the interactionmore » energy. This phenomenon can be theoretically explained by the qualitative change of the nature of the binary interaction in the medium. The appearance of an energy maximum has significant effects on the itinerant ferromagnetism. In 3D, the ferromagnetic transition is reentrant and itinerant ferromagnetism exists in a narrow window around the energy maximum. In 2D, the present theoretical approach suggests that itinerant ferromagnetism does not exist, which reflects the fact that the energy maximum becomes much lower than the energy of the fully polarized state.« less

  13. Number of holes contained within the Fermi surface volume in underdoped high-temperature superconductors

    DOE PAGES

    Harrison, Neil

    2016-08-16

    Here, we provide a potential solution to the longstanding problem relating Fermi surface reconstruction to the number of holes contained within the Fermi surface volume in underdoped high T c superconductors. On considering uniaxial and biaxial charge-density wave order, we show that there exists a relationship between the ordering wave vector, the hole doping, and the cross-sectional area of the reconstructed Fermi surface whose precise form depends on the volume of the starting Fermi surface. We consider a “large” starting Fermi surface comprising 1+p hole carriers, as predicted by band structure calculations, and a “small” starting Fermi surface comprising pmore » hole carriers, as proposed in models in which the Coulomb repulsion remains the dominant energy. Using the reconstructed Fermi surface cross-sectional area obtained in quantum oscillation experiments in YBa 2Cu 3O 6+x and HgBa 2CuO 4+x and the established methods for estimating the chemical hole doping, we find the ordering vectors obtained from x-ray scattering measurements to show a close correspondence with those expected for the small starting Fermi surface. We therefore show the quantum oscillation frequency and charge-density wave vectors provide accurate estimates for the number of holes contributing to the Fermi surface volume in the pseudogap regime.« less

  14. Number of holes contained within the Fermi surface volume in underdoped high-temperature superconductors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Harrison, Neil

    Here, we provide a potential solution to the longstanding problem relating Fermi surface reconstruction to the number of holes contained within the Fermi surface volume in underdoped high T c superconductors. On considering uniaxial and biaxial charge-density wave order, we show that there exists a relationship between the ordering wave vector, the hole doping, and the cross-sectional area of the reconstructed Fermi surface whose precise form depends on the volume of the starting Fermi surface. We consider a “large” starting Fermi surface comprising 1+p hole carriers, as predicted by band structure calculations, and a “small” starting Fermi surface comprising pmore » hole carriers, as proposed in models in which the Coulomb repulsion remains the dominant energy. Using the reconstructed Fermi surface cross-sectional area obtained in quantum oscillation experiments in YBa 2Cu 3O 6+x and HgBa 2CuO 4+x and the established methods for estimating the chemical hole doping, we find the ordering vectors obtained from x-ray scattering measurements to show a close correspondence with those expected for the small starting Fermi surface. We therefore show the quantum oscillation frequency and charge-density wave vectors provide accurate estimates for the number of holes contributing to the Fermi surface volume in the pseudogap regime.« less

  15. Thermodynamic properties of ideal Fermi gases in a harmonic potential in an n-dimensional space under the generalized uncertainty principle

    NASA Astrophysics Data System (ADS)

    Li, Heling; Ren, Jinxiu; Wang, Wenwei; Yang, Bin; Shen, Hongjun

    2018-02-01

    Using the semi-classical (Thomas-Fermi) approximation, the thermodynamic properties of ideal Fermi gases in a harmonic potential in an n-dimensional space are studied under the generalized uncertainty principle (GUP). The mean particle number, internal energy, heat capacity and other thermodynamic variables of the Fermi system are calculated analytically. Then, analytical expressions of the mean particle number, internal energy, heat capacity, chemical potential, Fermi energy, ground state energy and amendments of the GUP are obtained at low temperatures. The influence of both the GUP and the harmonic potential on the thermodynamic properties of a copper-electron gas and other systems with higher electron densities are studied numerically at low temperatures. We find: (1) When the GUP is considered, the influence of the harmonic potential is very much larger, and the amendments produced by the GUP increase by eight to nine orders of magnitude compared to when no external potential is applied to the electron gas. (2) The larger the particle density, or the smaller the particle masses, the bigger the influence of the GUP. (3) The effect of the GUP increases with the increase in the spatial dimensions. (4) The amendments of the chemical potential, Fermi energy and ground state energy increase with an increase in temperature, while the heat capacity decreases. T F0 is the Fermi temperature of the ideal Fermi system in a harmonic potential. When the temperature is lower than a certain value (0.22 times T F0 for the copper-electron gas, and this value decreases with increasing electron density), the amendment to the internal energy is positive, however, the amendment decreases with increasing temperature. When the temperature increases to the value, the amendment is zero, and when the temperature is higher than the value, the amendment to the internal energy is negative and the absolute value of the amendment increases with increasing temperature. (5) When electron

  16. Cooling an Optically Trapped Ultracold Fermi Gas by Periodical Driving.

    PubMed

    Li, Jiaming; de Melo, Leonardo F; Luo, Le

    2017-03-30

    We present a cooling method for a cold Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap (ODT). Our method employs the anharmonicity of the ODT, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, we selectively excite the hotter atoms out of the trap while keeping the colder atoms in the trap, generating parametric cooling. This experimental protocol starts with a magneto-optical trap (MOT) that is loaded by a Zeeman slower. The precooled atoms in the MOT are then transferred to an ODT, and a bias magnetic field is applied to create an interacting Fermi gas. We then lower the trapping potential to prepare a cold Fermi gas near the degenerate temperature. After that, we sweep the magnetic field to the noninteracting regime of the Fermi gas, in which the parametric cooling can be manifested by modulating the intensity of the optical trapping beams. We find that the parametric cooling effect strongly depends on the modulation frequencies and amplitudes. With the optimized frequency and amplitude, we measure the dependence of the cloud energy on the modulation time. We observe that the cloud energy is changed in an anisotropic way, where the energy of the axial direction is significantly reduced by parametric driving. The cooling effect is limited to the axial direction because the dominant anharmonicity of the crossed-beam ODT is along the axial direction. Finally, we propose to extend this protocol for the trapping potentials of large anharmonicity in all directions, which provides a promising scheme for cooling quantum gases using external driving.

  17. A New View of the High Energy Gamma-ray Sky with the Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie

    2010-01-01

    This slide presentation reviews some of the findings that have been made possible by the use of the Fermi Gamma-ray Space Telescope. It describes the current status of the Fermi Telescope and reviews some of the science highlights.

  18. Validating simple dynamical simulations of the unitary Fermi gas

    NASA Astrophysics Data System (ADS)

    Forbes, Michael McNeil; Sharma, Rishi

    2014-10-01

    We present a comparison between simulated dynamics of the unitary fermion gas using the superfluid local density approximation (SLDA) and a simplified bosonic model, the extended Thomas-Fermi (ETF) with a unitary equation of state. Small-amplitude fluctuations have similar dynamics in both theories for frequencies far below the pair-breaking threshold and wave vectors much smaller than the Fermi momentum. The low-frequency linear responses in both match well for surprisingly large wave vectors, even up to the Fermi momentum. For nonlinear dynamics such as vortex generation, the ETF provides a semiquantitative description of SLDA dynamics as long as the fluctuations do not have significant power near the pair-breaking threshold; otherwise the dynamics of the ETF cannot be trusted. Nonlinearities in the ETF tend to generate high-frequency fluctuations, and with no normal component to remove this energy from the superfluid, features such as vortex lattices cannot relax and crystallize as they do in the SLDA.

  19. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La) 2CuO 6+δ (Bi2201)

    DOE PAGES

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; ...

    2015-06-18

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

  20. Spin-fluctuation-induced non-Fermi-liquid behavior with suppressed superconductivity in LiFe 1-xCo xAs

    DOE PAGES

    Y. M. Dai; Miao, H.; Xing, L. Y.; ...

    2015-09-15

    A series of LiFe 1–xCo xAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe 1–xCo xAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFemore » 1–xCo xAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.« less

  1. Localization of massless Dirac particles via spatial modulations of the Fermi velocity

    NASA Astrophysics Data System (ADS)

    Downing, C. A.; Portnoi, M. E.

    2017-08-01

    The electrons found in Dirac materials are notorious for being difficult to manipulate due to the Klein phenomenon and absence of backscattering. Here we investigate how spatial modulations of the Fermi velocity in two-dimensional Dirac materials can give rise to localization effects, with either full (zero-dimensional) confinement or partial (one-dimensional) confinement possible depending on the geometry of the velocity modulation. We present several exactly solvable models illustrating the nature of the bound states which arise, revealing how the gradient of the Fermi velocity is crucial for determining fundamental properties of the bound states such as the zero-point energy. We discuss the implications for guiding electronic waves in few-mode waveguides formed by Fermi velocity modulation.

  2. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions

    PubMed Central

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-01-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes. PMID:27551687

  3. Probing topological Fermi-Arcs and bulk boundary correspondence in the Weyl semimetal TaAs

    NASA Astrophysics Data System (ADS)

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    The relation between surface Fermi-arcs and bulk Weyl cones in a Weyl semimetal, uniquely allows to study the notion of bulk to surface correspondence. We visualize these topological Fermi arc states on the surface of the Weyl semi-metal tantalum arsenide using scanning tunneling spectroscopy. Its surface hosts 12 Fermi arcs amongst several other surface bands of non-topological origin. We detect the possible scattering processes of surface bands in which Fermi arcs are involved including intra- and inter arc scatterings and arc-trivial scatterings. Each of the measured scattering processes entails additional information on the unique nature of Fermi arcs in tantalum arsenide: their contour, their energy-momentum dispersion and its relation with the bulk Weyl nodes. We further identify a sharp distinction between the wave function's spatial distribution of topological versus trivial bands. The non-topological surface bands, which are derived from the arsenic dangling bonds, are tightly bound to the arsenic termination layer. In contrast, the Fermi-arc bands reside on the deeper tantalum layer, penetrating into the bulk, which is predominantly derived from tantalum orbitals.

  4. Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie E.; Michelson, Peter F.; Paclesas, William S.; Ritz, Steven

    2012-01-01

    The Fermi Gamma-ray Space Telescope, launched in June 2008, is an observatory designed to survey the high-energy gamma-ray sky. The primary instrument, the Large Area Telescope (LAT), provides observations from 20 MeV to greater than 300 GeV. A second instrument, the Gamma-ray Burst Monitor (GBM), provides observations of transients from less than 10 keV to 40 MeV. We describe the design and performance of the instruments and their subsystems, the spacecraft and the ground system.

  5. Universal Fermi Gas with Two- and Three-Body Resonances

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Nishida, Yusuke; Son, Dam Thanh; Tan, Shina

    2008-03-07

    We consider a Fermi gas with two components of different masses, with the s-wave two-body interaction tuned to unitarity. In the range of mass ratio 8.62energy of a 2 ratio 1 mixture of heavy and light fermions is less than 2% of the energy of a noninteracting gas with the same number densities. Wemore » derive exact relationships between the pressures of the unitary Fermi gases with and without three-body resonance when the mass ratio is close to the critical values of 8.62 and 13.6.« less

  6. Fermi LAT Results and Perspectives in Measurements of High Energy Galactic Cosmic Rays

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    Real breakthrough during last 1-1.5 years in cosmic ray electrons: ATIC, HESS, Pamela, and finally Fermi-LAT. New quality data have made it possible to start quantitative modeling. With the new data more puzzles than before on CR electrons origin. Need "multi-messenger" campaign: electrons, positrons, gammas, X-ray, radio, neutrino... It is viable that we are dealing with at least two distinct mechanisms of "primary" electron (both signs) production: a softer spectrum of negative electrons, and a harder spectrum of both e(+)+e(-). Exotic (e.g. DM) origin is not ruled out. Upper limits on CR electrons anisotropy are set. Good perspectives to have the Fermi LAT results on proton spectrum and positron fraction.

  7. Polaron-to-Polaron Transitions in the Radio-Frequency Spectrum of a Quasi-Two-Dimensional Fermi Gas

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Ong, W.; Arakelyan, I.; Thomas, J. E.

    2012-06-01

    We measure radio-frequency spectra for a two-component mixture of a Li6 atomic Fermi gas in a quasi-two-dimensional regime with the Fermi energy comparable to the energy level spacing in the tightly confining potential. Near the Feshbach resonance, we find that the observed resonances do not correspond to transitions between confinement-induced dimers. The spectral shifts can be fit by assuming transitions between noninteracting polaron states in two dimensions.

  8. Searches for cosmic-ray electron anisotropies with the Fermi Large Area Telescope

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ackermann, M.; Ajello, M.; Bechtol, K.

    The Large Area Telescope on board the Fermi satellite (Fermi LAT) detected more than 1.6x10{sup 6} cosmic-ray electrons/positrons with energies above 60 GeV during its first year of operation. The arrival directions of these events were searched for anisotropies of angular scale extending from {approx}10 deg. up to 90 deg., and of minimum energy extending from 60 GeV up to 480 GeV. Two independent techniques were used to search for anisotropies, both resulting in null results. Upper limits on the degree of the anisotropy were set that depended on the analyzed energy range and on the anisotropy's angular scale. Themore » upper limits for a dipole anisotropy ranged from {approx}0.5% to {approx}10%.« less

  9. Searching for high-energy gamma-ray counterparts to gravitational-wave sources with Fermi-LAT: A needle in a haystack

    DOE PAGES

    Vianello, G.; Omodei, N.; Chiang, J.; ...

    2017-05-20

    At least a fraction of gravitational-wave (GW) progenitors are expected to emit an electromagnetic (EM) signal in the form of a short gamma-ray burst (sGRB). Discovering such a transient EM counterpart is challenging because the LIGO/VIRGO localization region is much larger (several hundreds of square degrees) than the field of view of X-ray, optical, and radio telescopes. The Fermi Large Area Telescope (LAT) has a wide field of view (~2.4 sr) and detects ~2–3 sGRBs per year above 100 MeV. It can detect them not only during the short prompt phase, but also during their long-lasting high-energy afterglow phase. If other wide-field, high-energy instruments such as Fermi-GBM, Swift-BAT, or INTEGRAL-ISGRI cannot detect or localize with enough precision an EM counterpart during the prompt phase, the LAT can potentially pinpoint it withmore » $$\\lesssim 10$$ arcmin accuracy during the afterglow phase. This routinely happens with gamma-ray bursts. Moreover, the LAT will cover the entire localization region within hours of any triggers during normal operations, allowing the γ-ray flux of any EM counterpart to be measured or constrained. As a result, we illustrate two new ad hoc methods to search for EM counterparts with the LAT and their application to the GW candidate LVT151012.« less

  10. Searching for high-energy gamma-ray counterparts to gravitational-wave sources with Fermi-LAT: A needle in a haystack

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Vianello, G.; Omodei, N.; Chiang, J.

    At least a fraction of gravitational-wave (GW) progenitors are expected to emit an electromagnetic (EM) signal in the form of a short gamma-ray burst (sGRB). Discovering such a transient EM counterpart is challenging because the LIGO/VIRGO localization region is much larger (several hundreds of square degrees) than the field of view of X-ray, optical, and radio telescopes. The Fermi Large Area Telescope (LAT) has a wide field of view (~2.4 sr) and detects ~2–3 sGRBs per year above 100 MeV. It can detect them not only during the short prompt phase, but also during their long-lasting high-energy afterglow phase. If other wide-field, high-energy instruments such as Fermi-GBM, Swift-BAT, or INTEGRAL-ISGRI cannot detect or localize with enough precision an EM counterpart during the prompt phase, the LAT can potentially pinpoint it withmore » $$\\lesssim 10$$ arcmin accuracy during the afterglow phase. This routinely happens with gamma-ray bursts. Moreover, the LAT will cover the entire localization region within hours of any triggers during normal operations, allowing the γ-ray flux of any EM counterpart to be measured or constrained. As a result, we illustrate two new ad hoc methods to search for EM counterparts with the LAT and their application to the GW candidate LVT151012.« less

  11. What can Fermi LAT observation of the Galactic Centre tell us about its active past?

    NASA Astrophysics Data System (ADS)

    Zaharijas, Gabrijela; Petrović, Jovana; Serpico, Pasquale

    The Fermi-LAT gamma-ray data in the inner Galaxy region show several prominent features possibly related to the past activity of the Milky Way's super massive black hole. At a large, 50 deg scale, the Fermi LAT revealed symmetric hour glass structures with hard energy spectra extending up to 100 GeV (and dubbed `the Fermi bubbles'). More recently and closer to the Galactic centre, at the 10 deg scale, several groups have claimed evidence for excess gamma-ray emission that appears symmetric around the Galactic center and has an energy spectrum peaking at few GeVs. We explore here the possibility that this emission originates in inverse Compton emission from high-energy electrons produced in a short duration, burst-like event injecting 1052 - 1053 erg, roughly 106 yrs ago. Several lines of evidence suggest that a series of `burst like' events happened in the vicinity of our black hole in the past and gamma-ray observations may offer a new view of that scenario.

  12. Thomas-Fermi approximation for a condensate with higher-order interactions

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Thoegersen, M.; Jensen, A. S.; Zinner, N. T.

    We consider the ground state of a harmonically trapped Bose-Einstein condensate within the Gross-Pitaevskii theory including the effective-range corrections for a two-body zero-range potential. The resulting nonlinear Schroedinger equation is solved analytically in the Thomas-Fermi approximation neglecting the kinetic-energy term. We present results for the chemical potential and the condensate profiles, discuss boundary conditions, and compare to the usual Thomas-Fermi approach. We discuss several ways to increase the influence of effective-range corrections in experiment with magnetically tunable interactions. The level of tuning required could be inside experimental reach in the near future.

  13. Fermi-surface reconstruction and the origin of high-temperature superconductivity.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Norman, M. R.; Materials Science Division

    2010-01-01

    In crystalline lattices, the conduction electrons form waves, known as Bloch states, characterized by a momentum vector k. The defining characteristic of metals is the surface in momentum space that separates occupied from unoccupied states. This 'Fermi' surface may seem like an abstract concept, but it can be measured and its shape can have profound consequences for the thermal, electronic, and magnetic properties of a material. In the presence of an external magnetic field B, electrons in a metal spiral around the field direction, and within a semiclassical momentum-space picture, orbit around the Fermi surface. Physical properties, such as themore » magnetization, involve a sum over these orbits, with extremal orbits on the Fermi surface, i.e., orbits with minimal or maximal area, dominating the sum [Fig. 1(a)]. Upon quantization, the resulting electron energy spectrum consists of Landau levels separated by the cyclotron energy, which is proportional to the magnetic field. As the magnetic field causes subsequent Landau levels to cross through the Fermi energy, physical quantities, such as the magnetization or resistivity, oscillate in response. It turns out that the period of these oscillations, when plotted as a function of 1/B, is proportional to the area of the extremal orbit in a plane perpendicular to the applied field [Fig. 1(b)]. The power of the quantum oscillation technique is obvious: By changing the field direction, one can map out the Fermi surface, much like a blind man feeling an elephant. The nature and topology of the Fermi surface in high-T{sub c} cuprates has been debated for many years. Soon after the materials were discovered by Bednorz and Mueller, it was realized that superconductivity was obtained by doping carriers into a parent insulating state. This insulating state appears to be due to strong electronic correlations, and is known as a Mott insulator. In the case of cuprates, the electronic interactions force the electrons on the

  14. Interplay of short-range correlations and nuclear symmetry energy in hard-photon production from heavy-ion reactions at Fermi energies

    NASA Astrophysics Data System (ADS)

    Yong, Gao-Chan; Li, Bao-An

    2017-12-01

    Within an isospin- and momentum-dependent transport model for nuclear reactions at intermediate energies, we investigate the interplay of the nucleon-nucleon short-range correlations (SRCs) and nuclear symmetry energy Esym(ρ ) on hard-photon spectra in collisions of several Ca isotopes on 112Sn and 124Sn targets at a beam energy of 45 MeV/nucleon. It is found that over the whole spectra of hard photons studied, effects of the SRCs overwhelm those owing to the Esym(ρ ) . The energetic photons come mostly from the high-momentum tails (HMTs) of single-nucleon momentum distributions in the target and projectile. Within the neutron-proton dominance model of SRCs based on the consideration that the tensor force acts mostly in the isosinglet and spin-triplet nucleon-nucleon interaction channel, there are equal numbers of neutrons and protons, thus a zero isospin asymmetry in the HMTs. Therefore, experimental measurements of the energetic photons from heavy-ion collisions at Fermi energies have the great potential to help us better understand the nature of SRCs without any appreciable influence by the uncertain Esym(ρ ) . These measurements will be complementary to but also have some advantages over the ongoing and planned experiments using hadronic messengers from reactions induced by high-energy electrons or protons. Because the underlying physics of SRCs and Esym(ρ ) are closely correlated, a better understanding of the SRCs will, in turn, help constrain the nuclear symmetry energy more precisely in a broad density range.

  15. Discovery of Weyl Fermion Semimetals and Topological Fermi Arc States

    NASA Astrophysics Data System (ADS)

    Hasan, M. Zahid; Xu, Su-Yang; Belopolski, Ilya; Huang, Shin-Ming

    2017-03-01

    Weyl semimetals are conductors whose low-energy bulk excitations are Weyl fermions, whereas their surfaces possess metallic Fermi arc surface states. These Fermi arc surface states are protected by a topological invariant associated with the bulk electronic wave functions of the material. Recently, it has been shown that the TaAs and NbAs classes of materials harbor such a state of topological matter. We review the basic phenomena and experimental history of the discovery of the first Weyl semimetals, starting with the observation of topological Fermi arcs and Weyl nodes in TaAs and NbAs by angle and spin-resolved surface and bulk sensitive photoemission spectroscopy and continuing through magnetotransport measurements reporting the Adler-Bell-Jackiw chiral anomaly. We hope that this article provides a useful introduction to the theory of Weyl semimetals, a summary of recent experimental discoveries, and a guideline to future directions.

  16. Composite Fermi surface in the half-filled Landau level with anisotropic electron mass

    NASA Astrophysics Data System (ADS)

    Ippoliti, Matteo; Geraedts, Scott; Bhatt, Ravindra

    We study the problem of interacting electrons in the lowest Landau level at half filling in the quantum Hall regime, when the electron dispersion is given by an anisotropic mass tensor. Based on experimental observations and theoretical arguments, the ground state of the system is expected to consist of composite Fermions filling an elliptical Fermi sea, with the anisotropy of the ellipse determined by the competing effects of the isotropic Coulomb interaction and anisotropic electron mass tensor. We test this idea quantitatively by using a numerical density matrix renormalization group method for quantum Hall systems on an infinitely long cylinder. Singularities in the structure factor allow us to map the Fermi surface of the composite Fermions. We compute the composite Fermi surface anisotropy for several values of the electron mass anisotropy which allow us to deduce the functional dependence of the former on the latter. This research was supported by Department of Energy Office of Basic Energy Sciences through Grant No. DE-SC0002140.

  17. Radio-weak BL Lac Objects in the Fermi Era

    NASA Astrophysics Data System (ADS)

    Massaro, F.; Marchesini, E. J.; D'Abrusco, R.; Masetti, N.; Andruchow, I.; Smith, Howard A.

    2017-01-01

    The existence of “radio-weak BL Lac objects” (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]-[4.6]-[12] μm color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.

  18. Strain-Induced Anisotropic Fermi Contour of 2D Holes and Composite Fermions

    NASA Astrophysics Data System (ADS)

    Jo, Insun; Rosales, K. A. V.; Mueed, M. A.; Padmanabhan, M.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Winkler, R.; Shayegan, M.

    We present experimental and theoretical results demonstrating strain-induced Fermi contour anisotropy of two-dimensional (2D) holes and composite fermions (CFs) confined to a (001) GaAs quantum well. We apply a tunable uniaxial strain to a thinned (001) GaAs wafer, glued to a piezoelectric actuator. When the 2D holes are subjected to an in-plane uniaxial strain, their band structure and Fermi contour become anisotropic by about 30% even for a minute amount of strain, on the order of 10-4. Via measurements of commensurability oscillations, we determine the Fermi contour anisotropy for holes near zero magnetic field, and for CFs at high magnetic fields, as a function of uniaxial strain. The measured Fermi contour anisotropy of holes is consistent with the calculation results. The observed CF Fermi contour anisotropy also shows a strong dependence on the applied strain, which we compare quantitatively to that of the low-field holes. Supported by the NSF(Grants DMR-1305691, ECCS-1508925, and MRSEC DMR-1420541), the DOE Basic Energy Sciences (DE-FG02-00-ER45841), the Gordon and Betty Moore Foundation (GBMF4420), and the Keck Foundation. R. W. is supported by the NSF (DMR-1310199).

  19. Non Fermi Liquid Crossovers in a Quasi-One-Dimensional Conductor in an Inclined Magnetic Field

    NASA Astrophysics Data System (ADS)

    Lebed, Andrei

    We consider a theoretical problem of electron-electron scattering time in a quasi-one-dimensional (Q1D) conductor in a magnetic field, perpendicular to its conducting axis. We show that inverse electron-electron scattering time becomes of the order of characteristic electron energy, 1 / τ ~ ɛ ~ T , in a high magnetic field, directed far from the main crystallographic axes, which indicates breakdown of the Fermi liquid theory. In a magnetic field, directed close to one of the main crystallographic axis, inverse electron-electron scattering time becomes much smaller than characteristic electron energy and, thus, applicability of Fermi liquid theory restores. We suggest that there exist crossovers between Fermi liquid and some non Fermi liquid states in a strong enough inclined magnetic field. Application of our results to the Q1D conductor (Per)2Au(mnt)2 shows that it has to be possible to observe the above mentioned phenomenon in feasibly high magnetic fields of the order of H >=H* ~= 25 T . It was partially supported by NFS grant DMR-1104512.

  20. Locality of the Thomas-Fermi-von Weizsäcker Equations

    NASA Astrophysics Data System (ADS)

    Nazar, F. Q.; Ortner, C.

    2017-06-01

    We establish a pointwise stability estimate for the Thomas-Fermi-von Weiz-säcker (TFW) model, which demonstrates that a local perturbation of a nuclear arrangement results also in a local response in the electron density and electrostatic potential. The proof adapts the arguments for existence and uniqueness of solutions to the TFW equations in the thermodynamic limit by Catto et al. (The mathematical theory of thermodynamic limits: Thomas-Fermi type models. Oxford mathematical monographs. The Clarendon Press, Oxford University Press, New York, 1998). To demonstrate the utility of this combined locality and stability result we derive several consequences, including an exponential convergence rate for the thermodynamic limit, partition of total energy into exponentially localised site energies (and consequently, exponential locality of forces), and generalised and strengthened results on the charge neutrality of local defects.

  1. Superfluid transition temperature in a trapped gas of Fermi atoms with a Feshbach resonance

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ohashi, Y.; Institute of Physics, University of Tsukuba, Ibaraki 305; Griffin, A.

    2003-03-01

    We investigate strong-coupling effects on the superfluid phase transition in a gas of Fermi atoms with a Feshbach resonance. The Feshbach resonance describes a composite quasiboson that can give rise to an additional pairing interaction between the Fermi atoms. This attractive interaction becomes stronger as the threshold energy 2{nu} of the Feshbach resonance two-particle bound state is lowered. In a recent paper, we showed that in the uniform Fermi gas, this tunable pairing interaction naturally leads to a crossover from a BCS state to a Bose-Einstein condensate (BEC) of the Nozieres and Schmitt-Rink kind, in which the BCS-type superfluid phasemore » transition continuously changes into the BEC type as the threshold energy is decreased. In this paper, we extend our previous work by including the effect of a harmonic trap potential, treated within the local-density approximation. We also give results for both weak and strong coupling to the Feshbach resonance. We show that the BCS-BEC crossover phenomenon strongly modifies the shape of the atomic density profile at the superfluid phase-transition temperature T{sub c}, reflecting the change of the dominant particles going from Fermi atoms to composite bosons. In the BEC regime, these composite bosons are shown to first appear well above T{sub c}. We also discuss the 'phase diagram' above T{sub c} as a function of the tunable threshold energy 2{nu}. We introduce a characteristic temperature T*(2{nu}) describing the effective crossover in the normal phase from a Fermi gas of atoms to a gas of stable molecules.« less

  2. The Fermi Large Area Telescope on Orbit: Event Classification, Instrument Response Functions, and Calibration

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; hide

    2012-01-01

    The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy -ray telescope, covering the energy range from 20 MeV to more than 300 GeV. During the first years of the mission the LAT team has gained considerable insight into the in-flight performance of the instrument. Accordingly, we have updated the analysis used to reduce LAT data for public release as well as the Instrument Response Functions (IRFs), the description of the instrument performance provided for data analysis. In this paper we describe the effects that motivated these updates. Furthermore, we discuss how we originally derived IRFs from Monte Carlo simulations and later corrected those IRFs for discrepancies observed between flight and simulated data. We also give details of the validations performed using flight data and quantify the residual uncertainties in the IRFs. Finally, we describe techniques the LAT team has developed to propagate those uncertainties into estimates of the systematic errors on common measurements such as fluxes and spectra of astrophysical sources.

  3. The Fermi Large Area Telescope on Orbit: Event Classification, Instrument Response Functions, and Calibration

    DOE PAGES

    Ackermann, M.; Ajello, M.; Albert, A.; ...

    2012-10-12

    The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy γ-ray telescope, covering the energy range from 20 MeV to more than 300 GeV. During the first years of the mission, the LAT team has gained considerable insight into the in-flight performance of the instrument. Accordingly, we have updated the analysis used to reduce LAT data for public release as well as the instrument response functions (IRFs), the description of the instrument performance provided for data analysis. In this study, we describe the effects thatmore » motivated these updates. Furthermore, we discuss how we originally derived IRFs from Monte Carlo simulations and later corrected those IRFs for discrepancies observed between flight and simulated data. We also give details of the validations performed using flight data and quantify the residual uncertainties in the IRFs. In conclusion, we describe techniques the LAT team has developed to propagate those uncertainties into estimates of the systematic errors on common measurements such as fluxes and spectra of astrophysical sources.« less

  4. Cut-off characterisation of energy spectra of bright Fermi sources: Current instrument limits and future possibilities

    NASA Astrophysics Data System (ADS)

    Romoli, Carlo; Taylor, Andrew M.; Aharonian, Felix

    2017-01-01

    The cut-off region of the gamma-ray spectrum of astrophysical sources encodes important information about the acceleration processes producing the parent particle population. For bright AGNs the cut-off happens in an energy range around a few tens of GeV, a region where satellites are limited by their effective area and current ground based telescopes by energy threshold. In the attempt to maximise the statistics, we have looked at two of the brightest AGNs seen by the Fermi-LAT (3C 454.3 and 3C 279) during extremely luminous flares. Our analysis showed the difficulty to obtain good constraints on the cut-off parameters when a power-law with modified exponential cut-off was assumed to fit the SEDs. We discuss the potential of future low-threshold Cherenkov telescope arrays, in particular CTA, showing the impact that a much bigger effective area can have on the determination of spectral parameters in the cut-off region. This preliminary study serves as an example, demonstrating the importance of having good wide-energy coverage around 10 GeV.

  5. Indirect searches for dark matter with the Fermi large area telescope

    DOE PAGES

    Albert, Andrea

    2015-03-24

    There is overwhelming evidence that non-baryonic dark matter constitutes ~ 27% of the energy density of the Universe. Weakly Interacting Massive Particles (WIMPs) are promising dark matter candidates that may produce γ rays via annihilation or decay detectable by the Fermi Large Area Telescope (LAT). A detection of WIMPs would also indicate the existence of physics beyond the Standard Model. We present recent results from the two cleanest indirect WIMP searches by the Fermi-LAT Collaboration: searches for γ-ray spectral lines and γ-ray emission associated with Milky Way dwarf spheroidal satellite galaxies.

  6. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R. D.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; hide

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed 79 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds.

  7. Energy landscape scheme for an intuitive understanding of complex domain dynamics in ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Heon Kim, Tae; Yoon, Jong-Gul; Hyub Baek, Seung; Park, Woong-Kyu; Mo Yang, Sang; Yup Jang, Seung; Min, Taeyuun; Chung, Jin-Seok; Eom, Chang-Beom; Won Noh, Tae

    2015-07-01

    Fundamental understanding of domain dynamics in ferroic materials has been a longstanding issue because of its relevance to many systems and to the design of nanoscale domain-wall devices. Despite many theoretical and experimental studies, a full understanding of domain dynamics still remains incomplete, partly due to complex interactions between domain-walls and disorder. We report domain-shape-preserving deterministic domain-wall motion, which directly confirms microscopic return point memory, by observing domain-wall breathing motion in ferroelectric BiFeO3 thin film using stroboscopic piezoresponse force microscopy. Spatial energy landscape that provides new insights into domain dynamics is also mapped based on the breathing motion of domain walls. The evolution of complex domain structure can be understood by the process of occupying the lowest available energy states of polarization in the energy landscape which is determined by defect-induced internal fields. Our result highlights a pathway for the novel design of ferroelectric domain-wall devices through the engineering of energy landscape using defect-induced internal fields such as flexoelectric fields.

  8. Energy landscape scheme for an intuitive understanding of complex domain dynamics in ferroelectric thin films.

    PubMed

    Kim, Tae Heon; Yoon, Jong-Gul; Baek, Seung Hyub; Park, Woong-kyu; Yang, Sang Mo; Yup Jang, Seung; Min, Taeyuun; Chung, Jin-Seok; Eom, Chang-Beom; Noh, Tae Won

    2015-07-01

    Fundamental understanding of domain dynamics in ferroic materials has been a longstanding issue because of its relevance to many systems and to the design of nanoscale domain-wall devices. Despite many theoretical and experimental studies, a full understanding of domain dynamics still remains incomplete, partly due to complex interactions between domain-walls and disorder. We report domain-shape-preserving deterministic domain-wall motion, which directly confirms microscopic return point memory, by observing domain-wall breathing motion in ferroelectric BiFeO3 thin film using stroboscopic piezoresponse force microscopy. Spatial energy landscape that provides new insights into domain dynamics is also mapped based on the breathing motion of domain walls. The evolution of complex domain structure can be understood by the process of occupying the lowest available energy states of polarization in the energy landscape which is determined by defect-induced internal fields. Our result highlights a pathway for the novel design of ferroelectric domain-wall devices through the engineering of energy landscape using defect-induced internal fields such as flexoelectric fields.

  9. Energy landscape scheme for an intuitive understanding of complex domain dynamics in ferroelectric thin films

    PubMed Central

    Heon Kim, Tae; Yoon, Jong-Gul; Hyub Baek, Seung; Park, Woong-kyu; Mo Yang, Sang; Yup Jang, Seung; Min, Taeyuun; Chung, Jin-Seok; Eom, Chang-Beom; Won Noh, Tae

    2015-01-01

    Fundamental understanding of domain dynamics in ferroic materials has been a longstanding issue because of its relevance to many systems and to the design of nanoscale domain-wall devices. Despite many theoretical and experimental studies, a full understanding of domain dynamics still remains incomplete, partly due to complex interactions between domain-walls and disorder. We report domain-shape-preserving deterministic domain-wall motion, which directly confirms microscopic return point memory, by observing domain-wall breathing motion in ferroelectric BiFeO3 thin film using stroboscopic piezoresponse force microscopy. Spatial energy landscape that provides new insights into domain dynamics is also mapped based on the breathing motion of domain walls. The evolution of complex domain structure can be understood by the process of occupying the lowest available energy states of polarization in the energy landscape which is determined by defect-induced internal fields. Our result highlights a pathway for the novel design of ferroelectric domain-wall devices through the engineering of energy landscape using defect-induced internal fields such as flexoelectric fields. PMID:26130159

  10. High energy transients: The millisecond domain

    NASA Astrophysics Data System (ADS)

    Rao, A. R.

    2018-02-01

    The search for high energy transients in the millisecond domain has come to the focus in recent times due to the detection of gravitational wave events and the identification of fast radio bursts as cosmological sources. Here we highlight the sensitivity limitations in the currently operating hard X-ray telescopes and give some details of the search for millisecond events in the AstroSat CZT Imager data.

  11. The first Fermi LAT supernova remnant catalog

    DOE PAGES

    Acero, F.

    2016-05-16

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude, allows us to determine an upper limit of 22% on the number of GeV candidatesmore » falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. As a result, we model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.« less

  12. Revised Thomas-Fermi approximation for singular potentials

    NASA Astrophysics Data System (ADS)

    Dufty, James W.; Trickey, S. B.

    2016-08-01

    Approximations for the many-fermion free-energy density functional that include the Thomas-Fermi (TF) form for the noninteracting part lead to singular densities for singular external potentials (e.g., attractive Coulomb). This limitation of the TF approximation is addressed here by a formal map of the exact Euler equation for the density onto an equivalent TF form characterized by a modified Kohn-Sham potential. It is shown to be a "regularized" version of the Kohn-Sham potential, tempered by convolution with a finite-temperature response function. The resulting density is nonsingular, with the equilibrium properties obtained from the total free-energy functional evaluated at this density. This new representation is formally exact. Approximate expressions for the regularized potential are given to leading order in a nonlocality parameter, and the limiting behavior at high and low temperatures is described. The noninteracting part of the free energy in this approximation is the usual Thomas-Fermi functional. These results generalize and extend to finite temperatures the ground-state regularization by R. G. Parr and S. Ghosh [Proc. Natl. Acad. Sci. U.S.A. 83, 3577 (1986), 10.1073/pnas.83.11.3577] and by L. R. Pratt, G. G. Hoffman, and R. A. Harris [J. Chem. Phys. 88, 1818 (1988), 10.1063/1.454105] and formally systematize the finite-temperature regularization given by the latter authors.

  13. A Route to Dirac Liquid Theory: A Fermi Liquid Description for Dirac Materials

    NASA Astrophysics Data System (ADS)

    Gochan, Matthew; Bedell, Kevin

    Since the pioneering work developed by L.V. Landau sixty years ago, Fermi Liquid Theory has seen great success in describing interacting Fermi systems. While much interest has been generated over the study of non-Fermi Liquid systems, Fermi Liquid theory serves as a formidable model for many systems and offers a rich amount of of results and insight. The recent classification of Dirac Materials, and the lack of a unifying theoretical framework for them, has motivated our study. Dirac materials are a versatile class of materials in which an abundance of unique physical phenomena can be observed. Such materials are found in all dimensions, with the shared property that their low-energy fermionic excitations behave as massless Dirac fermions and are therefore governed by the Dirac equation. The most popular Dirac material, graphene, is the focus of this work. We present our Fermi Liquid description of Graphene. We find many interesting results, specifically in the transport and dynamics of the system. Additionally, we expand on previous work regarding the Virial Theorem and its impact on the Fermi Liquid parameters in graphene. Finally, we remark on viscoelasticity of Dirac Materials and other unusual results that are consequences of AdS-CFT.

  14. Poisson-Nernst-Planck-Fermi theory for modeling biological ion channels

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Jinn-Liang, E-mail: jinnliu@mail.nhcue.edu.tw; Eisenberg, Bob, E-mail: beisenbe@rush.edu

    2014-12-14

    A Poisson-Nernst-Planck-Fermi (PNPF) theory is developed for studying ionic transport through biological ion channels. Our goal is to deal with the finite size of particle using a Fermi like distribution without calculating the forces between the particles, because they are both expensive and tricky to compute. We include the steric effect of ions and water molecules with nonuniform sizes and interstitial voids, the correlation effect of crowded ions with different valences, and the screening effect of water molecules in an inhomogeneous aqueous electrolyte. Including the finite volume of water and the voids between particles is an important new part ofmore » the theory presented here. Fermi like distributions of all particle species are derived from the volume exclusion of classical particles. Volume exclusion and the resulting saturation phenomena are especially important to describe the binding and permeation mechanisms of ions in a narrow channel pore. The Gibbs free energy of the Fermi distribution reduces to that of a Boltzmann distribution when these effects are not considered. The classical Gibbs entropy is extended to a new entropy form — called Gibbs-Fermi entropy — that describes mixing configurations of all finite size particles and voids in a thermodynamic system where microstates do not have equal probabilities. The PNPF model describes the dynamic flow of ions, water molecules, as well as voids with electric fields and protein charges. The model also provides a quantitative mean-field description of the charge/space competition mechanism of particles within the highly charged and crowded channel pore. The PNPF results are in good accord with experimental currents recorded in a 10{sup 8}-fold range of Ca{sup 2+} concentrations. The results illustrate the anomalous mole fraction effect, a signature of L-type calcium channels. Moreover, numerical results concerning water density, dielectric permittivity, void volume, and steric energy provide

  15. Fermi Gamma-Ray Space Telescope: Science Highlights for the First 8 Months

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2010-01-01

    The Fermi Gamma-ray Space Telescope was launched on June 11, 2008 and since August 2008 has successfully been conducting routine science observations of high energy phenomena in the gamma-ray sky. A number of exciting discoveries have been made during its first year of operation, including blazar flares, high-energy gamma-ray bursts, and numerous new,gamma-ray sources of different types, among them pulsars and Active Galactic Nuclei (AGN). fermi-LAT also performed accurate mea.<;urement of the diffuse gamma-radiation which clarifies the Ge V excess reported by EGRET almost 10 years ago, high precision measurement of the high energy electron spectrum, and other observations. An overview of the observatory status and recent results as of April 30, 2009, are presented. Key words: gamma-ray astronomy, cosmic rays, gamma-ray burst, pulsar, blazar. diffuse gamma-radiation

  16. Galactic Haze seen by Planck and Galactic Bubbles seen by Fermi

    NASA Image and Video Library

    2012-02-13

    This all-sky image shows the distribution of the galactic haze seen by ESA Planck mission at microwave frequencies superimposed over the high-energy sky, as seen by NASA Fermi Gamma-ray Space Telescope.

  17. Determination of the Nucleon-Nucleon Interaction in the ImQMD Model by Nuclear Reactions at Fermi Energy

    NASA Astrophysics Data System (ADS)

    Li, Cheng; Tian, Jun-Long; Wang, Ning

    2013-11-01

    The nucleon-nucleon interaction is investigated by using the ImQMD model with the three sets of parameters IQ1, IQ2 and IQ3 in which the corresponding incompressibility coefficients of nuclear matter are different. Fusion excitation function and the charge distribution of fragments are calculated for reaction systems 40Ca+40Ca at different incident energies. It is found that obvious differences in the charge distribution were observed at the energy region 10-25A MeV by adopting the three sets of parameters, while the results were close to each other at energy region of 30-45A MeV for the reaction system. It indicates that the Fermi energy region is a sensitive energy region to explore the N-N interaction. The fragment multiplicity spectrum for 238U+197Au at 15A MeV are reproduced by the ImQMD model with the set of parameter IQ3. It is concluded that charge distribution of the fragments and the fragment multiplicity spectrum are good observables for studying N-N interaction, and IQ3 is a suitable set of parameters for the ImQMD model.

  18. Quadratic Fermi node in a 3D strongly correlated semimetal

    PubMed Central

    Kondo, Takeshi; Nakayama, M.; Chen, R.; Ishikawa, J. J.; Moon, E.-G.; Yamamoto, T.; Ota, Y.; Malaeb, W.; Kanai, H.; Nakashima, Y.; Ishida, Y.; Yoshida, R.; Yamamoto, H.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Nakatsuji, S.; Balents, L.; Shin, S.

    2015-01-01

    Strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr2Ir2O7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermi liquid behaviour is predicted, for which we observe some evidence. Our discovery implies that Pr2Ir2O7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states. PMID:26640114

  19. Thermal transitions, pseudogap behavior, and BCS-BEC crossover in Fermi-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Karmakar, Madhuparna

    2018-03-01

    We study the mass imbalanced Fermi-Fermi mixture within the framework of a two-dimensional lattice fermion model. Based on the thermodynamic and species-dependent quasiparticle behavior, we map out the finite-temperature phase diagram of this system and show that unlike the balanced Fermi superfluid, there are now two different pseudogap regimes as PG-I and PG-II. While within the PG-I regime both the fermionic species are pseudogapped, PG-II corresponds to the regime where pseudogap feature survives only in the light species. We believe that the single-particle spectral features that we discuss in this paper are observable through the species-resolved radio-frequency spectroscopy and momentum-resolved photoemission spectroscopy measurements on systems such as 6Li-40K mixture. We further investigate the interplay between the population and mass imbalances and report that at a fixed population imbalance, the BCS-BEC crossover in a Fermi-Fermi mixture would require a critical interaction (Uc) for the realization of the uniform superfluid state. The effect of imbalance in mass on the exotic Fulde-Ferrell-Larkin-Ovchinnikov superfluid phase has been probed in detail in terms of the thermodynamic and quasiparticle behavior of this phase. It has been observed that in spite of the s -wave symmetry of the pairing field, a nodal superfluid gap is realized in the Larkin-Ovchinnikov regime. Our results on the various thermal scales and regimes are expected to serve as benchmarks for the experimental observations on 6Li-40K mixture.

  20. Beyond the Fermi liquid paradigm: Hidden Fermi liquids

    PubMed Central

    Jain, J. K.; Anderson, P. W.

    2009-01-01

    An intense investigation of possible non-Fermi liquid states of matter has been inspired by two of the most intriguing phenomena discovered in the past quarter century, namely, high-temperature superconductivity and the fractional quantum Hall effect. Despite enormous conceptual strides, these two fields have developed largely along separate paths. Two widely employed theories are the resonating valence bond theory for high-temperature superconductivity and the composite fermion theory for the fractional quantum Hall effect. The goal of this perspective article is to note that they subscribe to a common underlying paradigm: They both connect these exotic quantum liquids to certain ordinary Fermi liquids residing in unphysical Hilbert spaces. Such a relation yields numerous nontrivial experimental consequences, exposing these theories to rigorous and definitive tests. PMID:19506260

  1. Data cleaning in the energy domain

    NASA Astrophysics Data System (ADS)

    Akouemo Kengmo Kenfack, Hermine N.

    This dissertation addresses the problem of data cleaning in the energy domain, especially for natural gas and electric time series. The detection and imputation of anomalies improves the performance of forecasting models necessary to lower purchasing and storage costs for utilities and plan for peak energy loads or distribution shortages. There are various types of anomalies, each induced by diverse causes and sources depending on the field of study. The definition of false positives also depends on the context. The analysis is focused on energy data because of the availability of data and information to make a theoretical and practical contribution to the field. A probabilistic approach based on hypothesis testing is developed to decide if a data point is anomalous based on the level of significance. Furthermore, the probabilistic approach is combined with statistical regression models to handle time series data. Domain knowledge of energy data and the survey of causes and sources of anomalies in energy are incorporated into the data cleaning algorithm to improve the accuracy of the results. The data cleaning method is evaluated on simulated data sets in which anomalies were artificially inserted and on natural gas and electric data sets. In the simulation study, the performance of the method is evaluated for both detection and imputation on all identified causes of anomalies in energy data. The testing on utilities' data evaluates the percentage of improvement brought to forecasting accuracy by data cleaning. A cross-validation study of the results is also performed to demonstrate the performance of the data cleaning algorithm on smaller data sets and to calculate an interval of confidence for the results. The data cleaning algorithm is able to successfully identify energy time series anomalies. The replacement of those anomalies provides improvement to forecasting models accuracy. The process is automatic, which is important because many data cleaning processes

  2. Fermi Detection Of The Pulsar Wind Nebula Hess J1640–465

    DOE PAGES

    Slane, P.; Castro, D.; Funk, S.; ...

    2010-08-09

    We present observations of HESS J1640–465 with the Fermi-Large Area Telescope. The source is detected with high confidence as an emitter of high-energy gamma-rays. The spectrum lacks any evidence for the characteristic cutoff associated with emission from pulsars, indicating that the emission arises primarily from the pulsar wind nebula (PWN). Broadband modeling implies an evolved nebula with a low magnetic field resulting in a high γ-ray to X-ray flux ratio. The Fermi emission exceeds predictions of the broadband model, and has a steeper spectrum, possibly resulting from a distinct excess of low energy electrons similar to what is inferred formore » both the Vela X and Crab PWNe.« less

  3. Many body effects in a widely tunable Bose-Fermi mixture

    NASA Astrophysics Data System (ADS)

    Ahamdi, Peyman; Wu, Cheng-Hsun; Santiago, Ibon; Park, Jee Woo; Zwierlein, Martin

    2011-05-01

    A Bose-Einstein condensate immersed in the Fermi sea provides a rich platform for the study of many body effects such as polaron physics, boson-induced superfluidity and models of high-tc superconductivity. Few bosonic impurities in a Fermi sea form bosonic polarons, dressed quasi-particles that can condense, while few fermionic impurities in a Bose condensate might dress into heavy fermions with an immense increase of the effective mass. In an atom trap, both extremes of boson-fermion imbalance can in principle be realized in one and the same sample. Recently we have realized a Bose Einstein condensate of 41K immersed in a Fermi sea of 40K at T /TF = 0.3 and detected a wide Feshbach resonance between them. The mixture's lifetime is long enough so that bosonic polarons should form at an expected binding energy of about 0.6 TF. In this talk I will summarize our observations and the progress we have made to detect polaron physics in Bose-Fermi mixtures. This work was supported by the NSF, AFOSR-MURI, AFOSR-YIP, ARO-MURI, a grant from the Army Research Office with funding from the DARPA OLE program, the David and Lucille Packard Foundation and the Alfred P. Sloan Foundation.

  4. Observation of Spin Polarons in a Tunable Fermi Liquid of Ultracold Atoms

    NASA Astrophysics Data System (ADS)

    Zwierlein, Martin

    2009-05-01

    We have observed spin polarons, dressed spin down impurities in a spin up Fermi sea of ultracold atoms via tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom dressed with a spin up cloud constitutes the spin- or Fermi polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The spectra allow us to directly measure the polaron energy and the quasi-particle residue Z. The polarons are found to be only weakly interacting with each other, and can thus be identified with the quasi-particles of Landau's Fermi liquid theory. At a critical interaction strength, we observe a transition from spin one-half polarons to spin zero molecules. At this point the Fermi liquid undergoes a phase transition into a superfluid Bose liquid.

  5. Fermi -Lat Observations Of The Geminga Pulsar

    DOE PAGES

    Abdo, A. A.

    2010-08-09

    We report on the Fermi-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the γ-ray sky and the first example of a radio-quiet γ-ray pulsar. The observations cover one year, from the launch of the Fermi satellite through 2009 June 15. A data sample of over 60,000 photons enabled us to build a timing solution based solely on γ-rays. Timing analysis shows two prominent peaks, separated by Δphgr = 0.497 ± 0.004 in phase, which narrow with increasing energy. Pulsed γ-rays are observed beyond 18 GeV, precluding emission below 2.7 stellar radii because of magnetic absorption.more » The phase-averaged spectrum was fitted with a power law with exponential cutoff of spectral index Γ = (1.30 ± 0.01 ± 0.04), cutoff energy E 0 = (2.46 ± 0.04 ± 0.17) GeV, and an integral photon flux above 0.1 GeV of (4.14 ± 0.02 ± 0.32) × 10 –6 cm –2 s –1. The first uncertainties are statistical and the second ones are systematic. The phase-resolved spectroscopy shows a clear evolution of the spectral parameters, with the spectral index reaching a minimum value just before the leading peak and the cutoff energy having maxima around the peaks. The phase-resolved spectroscopy reveals that pulsar emission is present at all rotational phases. The spectral shape, broad pulse profile, and maximum photon energy favor the outer magnetospheric emission scenarios.« less

  6. RADIO-WEAK BL LAC OBJECTS IN THE FERMI ERA

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Massaro, F.; Marchesini, E. J.; D’Abrusco, R.

    2017-01-10

    The existence of “radio-weak BL Lac objects” (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated bymore » the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]–[4.6]–[12] μ m color–color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.« less

  7. Pseudogap and Fermi-Surface Topology in the Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Wu, Wei; Scheurer, Mathias S.; Chatterjee, Shubhayu; Sachdev, Subir; Georges, Antoine; Ferrero, Michel

    2018-04-01

    One of the distinctive features of hole-doped cuprate superconductors is the onset of a "pseudogap" below a temperature T* . Recent experiments suggest that there may be a connection between the existence of the pseudogap and the topology of the Fermi surface. Here, we address this issue by studying the two-dimensional Hubbard model with two distinct numerical methods. We find that the pseudogap only exists when the Fermi surface is holelike and that, for a broad range of parameters, its opening is concomitant with a Fermi-surface topology change from electronlike to holelike. We identify a common link between these observations: The polelike feature of the electronic self-energy associated with the formation of the pseudogap is found to also control the degree of particle-hole asymmetry, and hence the Fermi-surface topology transition. We interpret our results in the framework of an SU(2) gauge theory of fluctuating antiferromagnetism. We show that a mean-field treatment of this theory in a metallic state with U(1) topological order provides an explanation of this polelike feature and a good description of our numerical results. We discuss the relevance of our results to experiments on cuprates.

  8. Fermi Large Area Telescope First Source Catalog

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2010-05-25

    Here, we present a catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), during the first 11 months of the science phase of the mission, which began on 2008 August 4. The First Fermi-LAT catalog (1FGL) contains 1451 sources detected and characterized in the 100 MeV to 100 GeV range. Source detection was based on the average flux over the 11 month period, and the threshold likelihood Test Statistic is 25, corresponding to a significance of just over 4σ. The 1FGL catalog includes source location regions,more » defined in terms of elliptical fits to the 95% confidence regions and power-law spectral fits as well as flux measurements in five energy bands for each source. In addition, monthly light curves are provided. Using a protocol defined before launch we have tested for several populations of gamma-ray sources among the sources in the catalog. For individual LAT-detected sources we provide firm identifications or plausible associations with sources in other astronomical catalogs. Identifications are based on correlated variability with counterparts at other wavelengths, or on spin or orbital periodicity. For the catalogs and association criteria that we have selected, 630 of the sources are unassociated. In conclusion, care was taken to characterize the sensitivity of the results to the model of interstellar diffuse gamma-ray emission used to model the bright foreground, with the result that 161 sources at low Galactic latitudes and toward bright local interstellar clouds are flagged as having properties that are strongly dependent on the model or as potentially being due to incorrectly modeled structure in the Galactic diffuse emission.« less

  9. Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications

    DOE PAGES

    McConville, W.; Ostorero, L.; Moderski, R.; ...

    2011-08-19

    Here, we report Fermi Large Area Telescope (LAT) observations and broadband spectral modeling of the radio-loud active galaxy 4C +55.17 (z = 0.896), formally classified as a flat-spectrum radio quasar. Using 19 months of all-sky survey Fermi-LAT data, we detect a γ-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of γ-ray variability in the source over its observed history. We illustrate the implications of these results in two different domains. First, we investigate the origin of the steady γ-ray emission, where we re-examine the common classification of 4C +55.17 as amore » quasar-hosted blazar and consider instead its possible nature as a young radio source. We analyze and compare constraints on the source physical parameters in both blazar and young radio source scenarios by means of a detailed multiwavelength analysis and theoretical modeling of its broadband spectrum. Second, we show that the γ-ray spectrum may be formally extrapolated into the very high energy (VHE, ≥100 GeV) range at a flux level detectable by the current generation of ground-based Cherenkov telescopes. This enables us to place constraints on models of extragalactic background light within LAT energies and features the source as a promising candidate for VHE studies of the universe at an unprecedented redshift of z = 0.896.« less

  10. Fermi-LAT Gamma-ray Bursts and Insight from Swift

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.

    2011-01-01

    A new revolution in GRB observation and theory has begun over the last 3 years since the launch of the Fermi gamma-ray space telescope. The new window into high energy gamma-rays opened by the Fermi-LAT is providing insight into prompt emission mechanisms and possibly also afterglow physics. The LAT detected GRBs appear to be a new unique subset of extremely energetic and bright bursts. In this talk I will discuss the context and recent discoveries from these LAT GRBs and the large database of broadband observations collected by Swift over the last 7 years and how through comparisons between the Swift, GBM, and LAT GRB samples, we can learn about the unique characteristics and relationships between each population.

  11. Using experimental data to test an n -body dynamical model coupled with an energy-based clusterization algorithm at low incident energies

    NASA Astrophysics Data System (ADS)

    Kumar, Rohit; Puri, Rajeev K.

    2018-03-01

    Employing the quantum molecular dynamics (QMD) approach for nucleus-nucleus collisions, we test the predictive power of the energy-based clusterization algorithm, i.e., the simulating annealing clusterization algorithm (SACA), to describe the experimental data of charge distribution and various event-by-event correlations among fragments. The calculations are constrained into the Fermi-energy domain and/or mildly excited nuclear matter. Our detailed study spans over different system masses, and system-mass asymmetries of colliding partners show the importance of the energy-based clusterization algorithm for understanding multifragmentation. The present calculations are also compared with the other available calculations, which use one-body models, statistical models, and/or hybrid models.

  12. A Study of Fermi Acceleration of Suprathermal Solar Wind Ions

    NASA Astrophysics Data System (ADS)

    Freeman, Theodore James

    The Wind spacecraft has observed numerous sunward bursts of ~2 MeV ions upstream of the Earth's bow shock. The bursts typically last several minutes at the highest energies, but they can last for tens of minutes at intermediate energies (tens to hundreds of keV). The MeV ions are not protons or alpha particles, and are probably oxygen ions. There are two possible sources of these particles: Fermi acceleration of solar wind ions, and ring current particles which have escaped from the Earth's magnetosphere. In this dissertation, Wind observations and numerical particle simulations of Fermi acceleration are presented which demonstrate that suprathermal solar wind O6+ ions are the most likely source of these bursts. Since the Fermi mechanism accelerates all ions to approximately the same ratio of energy to charge, H+ and He2+ ions are accelerated to much lower energies than O6+ ions. In this model, suprathermal ions are reflected between the bow shock and rotations in the interplanetary magnetic field (IMF) upstream of the shock, gaining energy due to the relative motion of the reflecting magnetic structures. Each burst either coincides with or is closely followed by a large IMF rotation. By using measured magnetic field data, the timing of the bursts detected by Wind is precisely reproduced in the simulation. The energy spectra observed by Wind are also reproduced by adding H+ , He2+ , and O6+ fluxes together, and assuming that there is an increase of ~2 orders of magnitude in the high energy tail of the solar wind oxygen distribution. An enhancement of this order of magnitude in CNO group ions was measured by the ion composition experiment on Wind in association with these bursts. An examination of the magnetospheric escape model shows that while escaping O+ ions can account for some features of the data, such as the longer bursts of intermediate energy ions, it cannot account for the short duration ~2 MeV bursts themselves, because O+ ions scatter diffusively in the

  13. THE FIRST FERMI LAT SUPERNOVA REMNANT CATALOG

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Acero, F.; Ballet, J.; Ackermann, M.

    2016-05-01

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope (LAT). Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude allows us to determine an upper limit of 22% on the number of GeV candidates falsely identifiedmore » as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, we demonstrate the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. We model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.« less

  14. Fermi arc plasmons in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Song, Justin C. W.; Rudner, Mark S.

    2017-11-01

    In the recently discovered Weyl semimetals, the Fermi surface may feature disjoint, open segments—the so-called Fermi arcs—associated with topological states bound to exposed crystal surfaces. Here we show that the collective dynamics of electrons near such surfaces sharply departs from that of a conventional three-dimensional metal. In magnetic systems with broken time reversal symmetry, the resulting Fermi arc plasmons (FAPs) are chiral, with dispersion relations featuring open, hyperbolic constant frequency contours. As a result, a large range of surface plasmon wave vectors can be supported at a given frequency, with corresponding group velocity vectors directed along a few specific collimated directions. Fermi arc plasmons can be probed using near-field photonics techniques, which may be used to launch highly directional, focused surface plasmon beams. The unusual characteristics of FAPs arise from the interplay of bulk and surface Fermi arc carrier dynamics and give a window into the unusual fermiology of Weyl semimetals.

  15. Cooling without contact in bilayer dipolar Fermi gases

    NASA Astrophysics Data System (ADS)

    Tanatar, Bilal; Renklioglu, Basak; Oktel, M. Ozgur

    2016-05-01

    We consider two parallel layers of dipolar ultracold Fermi gases at different temperatures and calculate the heat transfer between them. The effective interactions describing screening and correlation effects between the dipoles in a single layer are modelled within the Euler-Lagrange Fermi-hypernetted chain approximation. The random-phase approximation is employed for the interactions across the layers. We investigate the amount of transferred power between the layers as a function of the temperature difference. Energy transfer proceeds via the long-range dipole-dipole interactions. A simple thermal model is developed to investigate the feasibility of using the contactless sympathetic cooling of the ultracold polar atoms/molecules. Our calculations indicate that dipolar heat transfer is effective for typical polar molecule experiments and may be utilized as a cooling process. Supported by TUBA and TUBITAK (112T974).

  16. Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases

    NASA Astrophysics Data System (ADS)

    Ong, W.; Cheng, Chingyun; Arakelyan, I.; Thomas, J. E.

    2015-03-01

    We measure the density profiles for a Fermi gas of Li 6 containing N1 spin-up atoms and N2 spin-down atoms, confined in a quasi-two-dimensional geometry. The spatial profiles are measured as a function of spin imbalance N2/N1 and interaction strength, which is controlled by means of a collisional (Feshbach) resonance. The measured cloud radii and central densities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory for a true two-dimensional system. We find that the data for normal-fluid mixtures are reasonably well fit by a simple two-dimensional polaron model of the free energy. Not predicted by the model is a phase transition to a spin-balanced central core, which is observed above a critical value of N2/N1. Our observations provide important benchmarks for predictions of the phase structure of quasi-two-dimensional Fermi gases.

  17. Non-Fermi-liquid superconductivity: Eliashberg approach versus the renormalization group

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wang, Huajia; Raghu, Srinivas; Torroba, Gonzalo

    Here, we address the problem of superconductivity for non-Fermi liquids using two commonly adopted, yet apparently distinct, methods: (1) the renormalization group (RG) and (2) Eliashberg theory. The extent to which both methods yield consistent solutions for the low-energy behavior of quantum metals has remained unclear. We show that the perturbative RG beta function for the 4-Fermi coupling can be explicitly derived from the linearized Eliashberg equations, under the assumption that quantum corrections are approximately local across energy scales. We apply our analysis to the test case of phonon-mediated superconductivity and show the consistency of both the Eliashberg and RGmore » treatments. We next study superconductivity near a class of quantum critical points and find a transition between superconductivity and a “naked” metallic quantum critical point with finite, critical BCS couplings. We speculate on the applications of our theory to the phenomenology of unconventional metals.« less

  18. Non-Fermi-liquid superconductivity: Eliashberg approach versus the renormalization group

    DOE PAGES

    Wang, Huajia; Raghu, Srinivas; Torroba, Gonzalo

    2017-04-15

    Here, we address the problem of superconductivity for non-Fermi liquids using two commonly adopted, yet apparently distinct, methods: (1) the renormalization group (RG) and (2) Eliashberg theory. The extent to which both methods yield consistent solutions for the low-energy behavior of quantum metals has remained unclear. We show that the perturbative RG beta function for the 4-Fermi coupling can be explicitly derived from the linearized Eliashberg equations, under the assumption that quantum corrections are approximately local across energy scales. We apply our analysis to the test case of phonon-mediated superconductivity and show the consistency of both the Eliashberg and RGmore » treatments. We next study superconductivity near a class of quantum critical points and find a transition between superconductivity and a “naked” metallic quantum critical point with finite, critical BCS couplings. We speculate on the applications of our theory to the phenomenology of unconventional metals.« less

  19. Intrinsic Correlations for Flaring Blazars Detected by Fermi

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Fan, J. H.; Xiao, H. B.; Lin, C.

    2017-02-01

    Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data.more » Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ -ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi , we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ -ray luminosity is strongly correlated with other intrinsic luminosities.« less

  20. Magnetic and Fermi Surface Properties of EuGa4

    NASA Astrophysics Data System (ADS)

    Nakamura, Ai; Hiranaka, Yuichi; Hedo, Masato; Nakama, Takao; Miura, Yasunao; Tsutsumi, Hiroki; Mori, Akinobu; Ishida, Kazuhiro; Mitamura, Katsuya; Hirose, Yusuke; Sugiyama, Kiyohiro; Honda, Fuminori; Settai, Rikio; Takeuchi, Tetsuya; Hagiwara, Masayuki; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Haga, Yoshinori; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Harima, Hisatomo; Ōnuki, Yoshichika

    2013-10-01

    We grew a high-quality single crystal EuGa4 with the tetragonal structure by the Ga self-flux method, and measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, thermoelectric power and de Haas--van Alphen (dHvA) effect, together with the electrical resistivity and thermoelectric power under pressure. EuGa4 is found to be a Eu-divalent compound without anisotropy of the magnetic susceptibility in the paramagnetic state and to reveal the same magnetization curve between H \\parallel [100] and [001] in the antiferromagnetic state, where the antiferromagnetic easy-axis is oriented along the [100] direction below a Néel temperature TN=16.5 K. The magnetization curve is discussed on the basis of a simple two-sublattice model. The Fermi surface in the paramagnetic state was clarified from the results of a dHvA experiment for EuGa4 and an energy band calculation for a non-4f reference compound SrGa4, which consists of a small ellipsoidal hole--Fermi surface and a compensated cube-like electron--Fermi surface with vacant space in center. We observed an anomaly in the temperature dependence of the electrical resistivity and thermoelectric power at TCDW=150 K under 2 GPa. This might correspond to an emergence of the charge density wave (CDW). The similar phenomenon was also observed in EuAl4 at ambient pressure. We discussed the CDW phenomenon on the basis of the present peculiar Fermi surfaces.

  1. Minimax rational approximation of the Fermi-Dirac distribution.

    PubMed

    Moussa, Jonathan E

    2016-10-28

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ϵ -1 )) poles to achieve an error tolerance ϵ at temperature β -1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δ occ , the occupied energy interval. This is particularly beneficial when Δ ≫ Δ occ , such as in electronic structure calculations that use a large basis set.

  2. Minimax rational approximation of the Fermi-Dirac distribution

    NASA Astrophysics Data System (ADS)

    Moussa, Jonathan E.

    2016-10-01

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ɛ-1)) poles to achieve an error tolerance ɛ at temperature β-1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δocc, the occupied energy interval. This is particularly beneficial when Δ ≫ Δocc, such as in electronic structure calculations that use a large basis set.

  3. SPECTRAL ANALYSIS OF FERMI -LAT BLAZARS ABOVE 50 GEV

    DOE PAGES

    Domínguez, Alberto; Ajello, Marco

    2015-11-04

    We present an analysis of the intrinsic (unattenuated by the extragalactic background light, EBL) power-law spectral indices of 128 extragalactic sources detected up to z ~ 2 with the Fermi-Large Area Telescope (LAT) at very high energies (VHEs, E ≥50 GeV). The median of the intrinsic index distribution is 2.20 (versus 2.54 for the observed distribution). We also analyze the observed spectral breaks (i.e., the difference between the VHE and high energy, HE, 100 MeV ≤ E ≤ 300 GeV, spectral indices). The Fermi-LAT has now provided a large sample of sources detected both at VHE and HE with comparablemore » exposure that allows us to test models of extragalactic γ-ray photon propagation. We find that our data are compatible with simulations that include intrinsic blazar curvature and EBL attenuation. There is also no evidence of evolution with redshift of the physics that drives the photon emission in high-frequency synchrotron peak (HSP) blazars. This makes HSP blazars excellent probes of the EBL.« less

  4. Effect of membrane microheterogeneity and domain size on fluorescence resonance energy transfer.

    PubMed

    Towles, Kevin B; Brown, Angela C; Wrenn, Steven P; Dan, Nily

    2007-07-15

    Studies of multicomponent membranes suggest lateral inhomogeneity in the form of membrane domains, but the size of small (nanoscale) domains in situ cannot be determined with current techniques. In this article, we present a model that enables extraction of membrane domain size from time-resolved fluorescence resonance energy transfer (FRET) data. We expand upon a classic approach to the infinite phase separation limit and formulate a model that accounts for the presence of disklike domains of finite dimensions within a two-dimensional infinite planar bilayer. The model was tested against off-lattice Monte Carlo calculations of a model membrane in the liquid-disordered (l(d)) and liquid-ordered (l(o)) coexistence regime. Simulated domain size was varied from 5 to 50 nm, and two fluorophores, preferentially partitioning into opposite phases, were randomly mixed to obtain the simulated time-resolved FRET data. The Monte Carlo data show clear differences in the efficiency of energy transfer as a function of domain size. The model fit of the data yielded good agreement for the domain size, especially in cases where the domain diameter is <20 nm. Thus, data analysis using the proposed model enables measurement of nanoscale membrane domains using time-resolved FRET.

  5. Fermi problem in disordered systems

    NASA Astrophysics Data System (ADS)

    Menezes, G.; Svaiter, N. F.; de Mello, H. R.; Zarro, C. A. D.

    2017-10-01

    We revisit the Fermi two-atom problem in the framework of disordered systems. In our model, we consider a two-qubit system linearly coupled with a quantum massless scalar field. We analyze the energy transfer between the qubits under different experimental perspectives. In addition, we assume that the coefficients of the Klein-Gordon equation are random functions of the spatial coordinates. The disordered medium is modeled by a centered, stationary, and Gaussian process. We demonstrate that the classical notion of causality emerges only in the wave zone in the presence of random fluctuations of the light cone. Possible repercussions are discussed.

  6. Twelve Years of Education and Public Outreach with the Fermi Gamma-ray Space Telescope

    NASA Astrophysics Data System (ADS)

    Cominsky, Lynn R.; McLin, K. M.; Simonnet, A.; Fermi E/PO Team

    2013-04-01

    During the past twelve years, NASA's Fermi Gamma-ray Space Telescope has supported a wide range of Education and Public Outreach (E/PO) activities, targeting K-14 students and the general public. The purpose of the Fermi E/PO program is to increase student and public understanding of the science of the high-energy Universe, through inspiring, engaging and educational activities linked to the mission’s science objectives. The E/PO program has additional more general goals, including increasing the diversity of students in the Science, Technology, Engineering and Mathematics (STEM) pipeline, and increasing public awareness and understanding of Fermi science and technology. Fermi's multi-faceted E/PO program includes elements in each major outcome category: ● Higher Education: Fermi E/PO promotes STEM careers through the use of NASA data including research experiences for students and teachers (Global Telescope Network), education through STEM curriculum development projects (Cosmology curriculum) and through enrichment activities (Large Area Telescope simulator). ● Elementary and Secondary education: Fermi E/PO links the science objectives of the Fermi mission to well-tested, customer-focused and NASA-approved standards-aligned classroom materials (Black Hole Resources, Active Galaxy Education Unit and Pop-up book, TOPS guides, Supernova Education Unit). These materials have been distributed through (Educator Ambassador and on-line) teacher training workshops and through programs involving under-represented students (after-school clubs and Astro 4 Girls). ● Informal education and public outreach: Fermi E/PO engages the public in sharing the experience of exploration and discovery through high-leverage multi-media experiences (Black Holes planetarium and PBS NOVA shows), through popular websites (Gamma-ray Burst Skymap, Epo's Chronicles), social media (Facebook, MySpace), interactive web-based activities (Space Mysteries, Einstein@Home) and activities by

  7. Observation of Dirac-like energy band and ring-torus Fermi surface associated with the nodal line in topological insulator CaAgAs

    NASA Astrophysics Data System (ADS)

    Takane, Daichi; Nakayama, Kosuke; Souma, Seigo; Wada, Taichi; Okamoto, Yoshihiko; Takenaka, Koshi; Yamakawa, Youichi; Yamakage, Ai; Mitsuhashi, Taichi; Horiba, Koji; Kumigashira, Hiroshi; Takahashi, Takashi; Sato, Takafumi

    2018-01-01

    One of key challenges in current material research is to search for new topological materials with inverted bulk-band structure. In topological insulators, the band inversion caused by strong spin-orbit coupling leads to opening of a band gap in the entire Brillouin zone, whereas an additional crystal symmetry such as point-group and nonsymmorphic symmetries sometimes prohibits the gap opening at/on specific points or line in momentum space, giving rise to topological semimetals. Despite many theoretical predictions of topological insulators/semimetals associated with such crystal symmetries, the experimental realization is still relatively scarce. Here, using angle-resolved photoemission spectroscopy with bulk-sensitive soft-x-ray photons, we experimentally demonstrate that hexagonal pnictide CaAgAs belongs to a new family of topological insulators characterized by the inverted band structure and the mirror reflection symmetry of crystal. We have established the bulk valence-band structure in three-dimensional Brillouin zone, and observed the Dirac-like energy band and ring-torus Fermi surface associated with the line node, where bulk valence and conducting bands cross on a line in the momentum space under negligible spin-orbit coupling. Intriguingly, we found that no other bands cross the Fermi level and therefore the low-energy excitations are solely characterized by the Dirac-like band. CaAgAs provides an excellent platform to study the interplay among low-energy electron dynamics, crystal symmetry, and exotic topological properties.

  8. Detecting superlight dark matter with Fermi-degenerate materials

    DOE PAGES

    Hochberg, Yonit; Pyle, Matt; Zhao, Yue; ...

    2016-08-08

    We examine in greater detail the recent proposal of using superconductors for detecting dark matter as light as the warm dark matter limit of O(keV). Detection of suc light dark matter is possible if the entire kinetic energy of the dark matter is extracted in the scattering, and if the experiment is sensitive to O(meV) energy depositions. This is the case for Fermi-degenerate materials in which the Fermi velocity exceeds the dark matter velocity dispersion in the Milky Way of ~10 –3. We focus on a concrete experimental proposal using a superconducting target with a transition edge sensor in ordermore » to detect the small energy deposits from the dark matter scatterings. Considering a wide variety of constraints, from dark matter self-interactions to the cosmic microwave background, we show that models consistent with cosmological/astrophysical and terrestrial constraints are observable with such detectors. A wider range of viable models with dark matter mass below an MeV is available if dark matter or mediator properties (such as couplings or masses) differ at BBN epoch or in stellar interiors from those in superconductors. We also show that metal targets pay a strong in-medium suppression for kinetically mixed mediators; this suppression is alleviated with insulating targets.« less

  9. VizieR Online Data Catalog: Sample of Fermi Blazars (Chen+, 2016)

    NASA Astrophysics Data System (ADS)

    Chen, Y.-Y.; Zhang, X.; Xiong, D.-R.; Wang, S.-J.; Yu, X.-L.

    2016-04-01

    We tried to select a large number of blazars with reliable redshift, radio core and extended radio luminosity at 1.4GHz. Firstly, we considered the following samples of blazars to get the radio core luminosity and extended luminosity at 1.4GHz: Kharb et al. (2010, J/ApJ/710/764), Antonucci & Ulvestad (1985ApJ...294..158A), Cassaro et al. (1999A&AS..139..601C), Murphy et al. (1993MNRAS.264..298M), Landt & Bignall (2008MNRAS.391..967L), Caccianiga & Marcha (2004, Cat. J/MNRAS/348/973), Giroletti et al. (2004). We cross-correlated these samples with the Fermi LAT Third Source Catalog (3FGL), and we acquired the 3FGL spectral index and energy flux at 0.1-100GeV from clean sources in 3FGL (Fermi-LAT Collaboration 2015, J/ApJS/218/23) Using these catalogs, we compiled 201 Fermi blazars. (1 data file).

  10. Tuning the Fermi velocity in Dirac materials with an electric field.

    PubMed

    Díaz-Fernández, A; Chico, Leonor; González, J W; Domínguez-Adame, F

    2017-08-14

    Dirac materials are characterized by energy-momentum relations that resemble those of relativistic massless particles. Commonly denominated Dirac cones, these dispersion relations are considered to be their essential feature. These materials comprise quite diverse examples, such as graphene and topological insulators. Band-engineering techniques should aim to a full control of the parameter that characterizes the Dirac cones: the Fermi velocity. We propose a general mechanism that enables the fine-tuning of the Fermi velocity in Dirac materials in a readily accessible way for experiments. By embedding the sample in a uniform electric field, the Fermi velocity is substantially modified. We first prove this result analytically, for the surface states of a topological insulator/semiconductor interface, and postulate its universality in other Dirac materials. Then we check its correctness in carbon-based Dirac materials, namely graphene nanoribbons and nanotubes, thus showing the validity of our hypothesis in different Dirac systems by means of continuum, tight-binding and ab-initio calculations.

  11. Twisted Fermi surface of a thin-film Weyl semimetal

    NASA Astrophysics Data System (ADS)

    Bovenzi, N.; Breitkreiz, M.; O'Brien, T. E.; Tworzydło, J.; Beenakker, C. W. J.

    2018-02-01

    The Fermi surface of a conventional two-dimensional electron gas is equivalent to a circle, up to smooth deformations that preserve the orientation of the equi-energy contour. Here we show that a Weyl semimetal confined to a thin film with an in-plane magnetization and broken spatial inversion symmetry can have a topologically distinct Fermi surface that is twisted into a figure-8—opposite orientations are coupled at a crossing which is protected up to an exponentially small gap. The twisted spectral response to a perpendicular magnetic field B is distinct from that of a deformed Fermi circle, because the two lobes of a figure-8 cyclotron orbit give opposite contributions to the Aharonov-Bohm phase. The magnetic edge channels come in two counterpropagating types, a wide channel of width β {l}m2\\propto 1/B and a narrow channel of width {l}m\\propto 1/\\sqrt{B} (with {l}m=\\sqrt{{\\hslash }/{eB}} the magnetic length and β the momentum separation of the Weyl points). Only one of the two is transmitted into a metallic contact, providing unique magnetotransport signatures.

  12. Generalized charge-screening in relativistic Thomas–Fermi model

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Akbari-Moghanjoughi, M.

    In this paper, we study the charge shielding within the relativistic Thomas-Fermi model for a wide range of electron number-densities and the atomic-number of screened ions. A generalized energy-density relation is obtained using the force-balance equation and taking into account the Chandrasekhar's relativistic electron degeneracy pressure. By numerically solving a second-order nonlinear differential equation, the Thomas-Fermi screening length is investigated, and the results are compared for three distinct regimes of the solid-density, warm-dense-matter, and white-dwarfs (WDs). It is revealed that our nonlinear screening theory is compatible with the exponentially decaying Thomas-Fermi-type shielding predicted by the linear response theory. Moreover, themore » variation of relative Thomas-Fermi screening length shows that extremely dense quantum electron fluids are relatively poor charge shielders. Calculation of the total number of screening electrons around a nucleus shows that there is a position of maximum number of screening localized electrons around the screened nucleus, which moves closer to the point-like nucleus by increase in the plasma number density but is unaffected due to increase in the atomic-number value. It is discovered that the total number of screening electrons, (N{sub s}∝r{sub TF}{sup 3}/r{sub d}{sup 3} where r{sub TF} and r{sub d} are the Thomas-Fermi and interparticle distance, respectively) has a distinct limit for extremely dense plasmas such as WD-cores and neutron star crusts, which is unique for all given values of the atomic-number. This is equal to saying that in an ultrarelativistic degeneracy limit of electron-ion plasma, the screening length couples with the system dimensionality and the plasma becomes spherically self-similar. Current analysis can provide useful information on the effects of relativistic correction to the charge screening for a wide range of plasma density, such as the inertial-confined plasmas and compact

  13. Insights Into the High-energy γ-ray Emission of Markarian 501 from Extensive Multifrequency Observations in the Fermi Era

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2011-01-12

    Here, we report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15—August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a sizemore » $$\\lesssim$$0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (~10 44 erg s –1) constitutes only a small fraction (~10 –3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a

  14. Insights into the High-energy γ-ray Emission of Markarian 501 from Extensive Multifrequency Observations in the Fermi Era

    NASA Astrophysics Data System (ADS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Cannon, A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; Dermer, C. D.; de Palma, F.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fuhrmann, L.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guillemot, L.; Guiriec, S.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kadler, M.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Max-Moerbeck, W.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nishino, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Pavlidou, V.; Pearson, T. J.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Readhead, A.; Reimer, A.; Reimer, O.; Richards, J. L.; Ripken, J.; Ritz, S.; Roth, M.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Scargle, J. D.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Stevenson, M.; Strickman, M. S.; Sokolovsky, K. V.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Wehrle, A. E.; Winer, B. L.; Wood, K. S.; Yang, Z.; Ylinen, T.; Zensus, J. A.; Ziegler, M.; Fermi LAT Collaboration; Aleksić, J.; Antonelli, L. A.; Antoranz, P.; Backes, M.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Berdyugin, A.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnoli, G.; Bordas, P.; Borla Tridon, D.; Bosch-Ramon, V.; Bose, D.; Braun, I.; Bretz, T.; Camara, M.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Dazzi, F.; de Angelis, A.; De Cea del Pozo, E.; De Lotto, B.; De Maria, M.; De Sabata, F.; Delgado Mendez, C.; Diago Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Elsaesser, D.; Ferenc, D.; Fonseca, M. V.; Font, L.; García López, R. J.; Garczarczyk, M.; Gaug, M.; Giavitto, G.; Godinovi, N.; Hadasch, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Hrupec, D.; Jogler, T.; Klepser, S.; Krähenbühl, T.; Kranich, D.; Krause, J.; La Barbera, A.; Leonardo, E.; Lindfors, E.; Lombardi, S.; López, M.; Lorenz, E.; Majumdar, P.; Makariev, E.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Miyamoto, H.; Moldón, J.; Moralejo, A.; Nieto, D.; Nilsson, K.; Orito, R.; Oya, I.; Paoletti, R.; Paredes, J. M.; Partini, S.; Pasanen, M.; Pauss, F.; Pegna, R. G.; Perez-Torres, M. A.; Persic, M.; Peruzzo, J.; Pochon, J.; Prada Moroni, P. G.; Prada, F.; Prandini, E.; Puchades, N.; Puljak, I.; Reichardt, T.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rissi, M.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Salvati, M.; Sánchez-Conde, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shayduk, M.; Shore, S. N.; Sierpowska-Bartosik, A.; Sillanpää, A.; Sitarek, J.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamerra, A.; Steinke, B.; Storz, J.; Strah, N.; Struebig, J. C.; Suric, T.; Takalo, L. O.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Vankov, H.; Wagner, R. M.; Weitzel, Q.; Zabalza, V.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Acciari, V. A.; Arlen, T.; Aune, T.; Benbow, W.; Boltuch, D.; Bradbury, S. M.; Buckley, J. H.; Bugaev, V.; Cannon, A.; Cesarini, A.; Ciupik, L.; Cui, W.; Dickherber, R.; Errando, M.; Falcone, A.; Finley, J. P.; Finnegan, G.; Fortson, L.; Furniss, A.; Galante, N.; Gall, D.; Gillanders, G. H.; Godambe, S.; Grube, J.; Guenette, R.; Gyuk, G.; Hanna, D.; Holder, J.; Huang, D.; Hui, C. M.; Humensky, T. B.; Kaaret, P.; Karlsson, N.; Kertzman, M.; Kieda, D.; Konopelko, A.; Krawczynski, H.; Krennrich, F.; Lang, M. J.; Maier, G.; McArthur, S.; McCann, A.; McCutcheon, M.; Moriarty, P.; Mukherjee, R.; Ong, R.; Otte, A. N.; Pandel, D.; Perkins, J. S.; Pichel, A.; Pohl, M.; Quinn, J.; Ragan, K.; Reyes, L. C.; Reynolds, P. T.; Roache, E.; Rose, H. J.; Rovero, A. C.; Schroedter, M.; Sembroski, G. H.; Senturk, G. D.; Steele, D.; Swordy, S. P.; Tešić, G.; Theiling, M.; Thibadeau, S.; Varlotta, A.; Vincent, S.; Wakely, S. P.; Ward, J. E.; Weekes, T. C.; Weinstein, A.; Weisgarber, T.; Williams, D. A.; Wood, M.; Zitzer, B.; VERITAS Collaboration; Villata, M.; Raiteri, C. M.; Aller, H. D.; Aller, M. F.; Arkharov, A. A.; Blinov, D. A.; Calcidese, P.; Chen, W. P.; Efimova, N. V.; Kimeridze, G.; Konstantinova, T. S.; Kopatskaya, E. N.; Koptelova, E.; Kurtanidze, O. M.; Kurtanidze, S. O.; Lähteenmäki, A.; Larionov, V. M.; Larionova, E. G.; Larionova, L. V.; Ligustri, R.; Morozova, D. A.; Nikolashvili, M. G.; Sigua, L. A.; Troitsky, I. S.; Angelakis, E.; Capalbi, M.; Carramiñana, A.; Carrasco, L.; Cassaro, P.; de la Fuente, E.; Gurwell, M. A.; Kovalev, Y. Y.; Kovalev, Yu. A.; Krichbaum, T. P.; Krimm, H. A.; Leto, P.; Lister, M. L.; Maccaferri, G.; Moody, J. W.; Mori, Y.; Nestoras, I.; Orlati, A.; Pagani, C.; Pace, C.; Pearson, R., III; Perri, M.; Piner, B. G.; Pushkarev, A. B.; Ros, E.; Sadun, A. C.; Sakamoto, T.; Tornikoski, M.; Yatsu, Y.; Zook, A.

    2011-02-01

    We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15—August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size lsim0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (sime1044 erg s-1) constitutes only a small fraction (~10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk

  15. Fermi-edge superfluorescence from a quantum-degenerate electron-hole gas

    NASA Astrophysics Data System (ADS)

    Kim, Ji-Hee; , G. Timothy Noe, II; McGill, Stephen A.; Wang, Yongrui; Wójcik, Aleksander K.; Belyanin, Alexey A.; Kono, Junichiro

    2013-11-01

    Nonequilibrium can be a source of order. This rather counterintuitive statement has been proven to be true through a variety of fluctuation-driven, self-organization behaviors exhibited by out-of-equilibrium, many-body systems in nature (physical, chemical, and biological), resulting in the spontaneous appearance of macroscopic coherence. Here, we report on the observation of spontaneous bursts of coherent radiation from a quantum-degenerate gas of nonequilibrium electron-hole pairs in semiconductor quantum wells. Unlike typical spontaneous emission from semiconductors, which occurs at the band edge, the observed emission occurs at the quasi-Fermi edge of the carrier distribution. As the carriers are consumed by recombination, the quasi-Fermi energy goes down toward the band edge, and we observe a continuously red-shifting streak. We interpret this emission as cooperative spontaneous recombination of electron-hole pairs, or superfluorescence (SF), which is enhanced by Coulomb interactions near the Fermi edge. This novel many-body enhancement allows the magnitude of the spontaneously developed macroscopic polarization to exceed the maximum value for ordinary SF, making electron-hole SF even more ``super'' than atomic SF.

  16. Metastability in the formation of Condon domains

    NASA Astrophysics Data System (ADS)

    Bakaleinikov, L. A.; Gordon, A.

    2018-05-01

    Metastability effects in the formation of Condon non-spin magnetic domains are considered. A possibility for the first-order phase transition occurrence in a three-dimensional electron gas is described in the case of two-frequency de-Haas-van Alphen magnetization oscillations originating from two extremal cross sections of the Fermi surface. The appearance of two additional domains is shown in the metastable region in aluminum. The phase diagram temperature-magnetic field exhibits the presence of second-order and first- order phase transitions in the two-frequency case.

  17. Observation of Dynamical Super-Efimovian Expansion in a Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Deng, Shujin; Diao, Pengpeng; Li, Fang; Yu, Qianli; Yu, Shi; Wu, Haibin

    2018-03-01

    We report an observation of a dynamical super Efimovian expansion in a strongly interacting Fermi gas by engineering time dependent external harmonic trap frequencies. When the trap frequency is tailored as [1 /4 t2+1 /t2λ log2(t /t*)]1/2, where t* and λ are two controllable parameters, and the change is faster than a critical value, the expansion of such a quantum gas shows novel dynamics that share the same characteristics as the super Efimov effect. A clear double-log periodicity with discrete geometric scaling emerges for the cloud size in the expansion. The universality of such scaling dynamics is verified both in the noninteracting and in the unitarity limit of Fermi gas. Moreover, the measured energy scaling reveals that the potential and internal energy also show double-log periodicity with a π /2 phase difference, but the total energy is monotonically decreased. Observing super Efimovian evolution represents a paradigm in probing universal properties and allows us in a new way to study many-body nonequilibrium dynamics with experiments.

  18. Particle scattering by harmonically trapped Bose and Fermi gases

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Ankita; Das, Samir; Biswas, Shyamal

    2018-04-01

    We have analytically explored the quantum phenomenon of particle scattering by harmonically trapped Bose and Fermi gases with the short ranged Fermi–Huang {δ }p3 interactions (Fermi 1936 Ric. Sci. 7 13; Huang and Yang 1957 Phys. Rev. 105 767) interactions among the incident particle and the scatterers. We have predicted differential scattering cross-sections and their temperature dependence in this regard. Coherent scattering even by a single boson or fermion in the finite geometry gives rise to new tool of determining energy eigenstate of the scatterer. Our predictions on the differential scattering cross-sections can be tested within the present day experimental setups, specially, for (i) 3D harmonically trapped interacting Bose–Einstein condensate (BEC), (ii) BECs in a double well, and (iii) BECs in an optical lattice.

  19. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; von Kienlin, A.; Dwyer, J. R.; Smith, D. M.; hide

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed more than 77 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds. The energy spectra of some TGFs have strong 511 keV positron annihilation lines, indicating that these TGFs contain a large fraction of positrons

  20. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph

    2018-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  1. Stability of the two-dimensional Fermi polaron

    NASA Astrophysics Data System (ADS)

    Griesemer, Marcel; Linden, Ulrich

    2018-02-01

    A system composed of an ideal gas of N fermions interacting with an impurity particle in two space dimensions is considered. The interaction between impurity and fermions is given in terms of two-body point interactions whose strength is determined by the two-body binding energy, which is a free parameter of the model. If the mass of the impurity is 1.225 times larger than the mass of a fermion, it is shown that the energy is bounded below uniformly in the number N of fermions. This result improves previous, N-dependent lower bounds, and it complements a recent, similar bound for the Fermi polaron in three space dimensions.

  2. Time-dependent Models for Blazar Emission with the Second-order Fermi Acceleration

    NASA Astrophysics Data System (ADS)

    Asano, Katsuaki; Takahara, Fumio; Kusunose, Masaaki; Toma, Kenji; Kakuwa, Jun

    2014-01-01

    The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101-232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 1038 erg s-1, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

  3. Time-dependent models for blazar emission with the second-order Fermi acceleration

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Asano, Katsuaki; Takahara, Fumio; Toma, Kenji

    The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101–232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range ofmore » Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 10{sup 38} erg s{sup –1}, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.« less

  4. Recent Results on SNRs and PWNe from the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2010-01-01

    Topics include: Fermi LAT Collaboration groups; galactic results from LAT; a GeV, wide-field instrument; the 1FGL catalog, the Fermi LAT 1FGL source catalog, unidentified gamma-ray sources; variability in 1FGL sources; curvature in 1FGL sources; spectral-variability classification; pulsars and their wind nebulae; gamma-ray pulsars and MSPs; GeV PWN search; Crab pulsar and nebula; Vela X nebular of Vela pulsar; MSH 15-52; supernova remnants, resolved GeV sources, galactic transients, LAT unassociated transient detections; gamma rays from a nova; V407 Cyngi - a symbiotic nova; V407 Cygni: a variable star; and March 11 - a nova. Summary slides include pulsars everywhere, blazars, LAT as an electron detector, cosmic ray spectrum, the Large Area Telescope, the Fermi Observatory, LAT sensitivity with time, candidate gamma-ray events, on-orbit energy calibration and rate, a 1 year sky map, LAT automated science processing, reported GeV flares, early activity and spectacular flare, gamma-ray transients near the galactic plane , two early unassociated transients, counter part search - Fermi J0910-5404; counterpart search 3EG J0903-3531, and a new LAT transient - J1057-6027.

  5. Temperature equilibration rate with Fermi-Dirac statistics.

    PubMed

    Brown, Lowell S; Singleton, Robert L

    2007-12-01

    We calculate analytically the electron-ion temperature equilibration rate in a fully ionized, weakly to moderately coupled plasma, using an exact treatment of the Fermi-Dirac electrons. The temperature is sufficiently high so that the quantum-mechanical Born approximation to the scattering is valid. It should be emphasized that we do not build a model of the energy exchange mechanism, but rather, we perform a systematic first principles calculation of the energy exchange. At the heart of this calculation lies the method of dimensional continuation, a technique that we borrow from quantum field theory and use in a different fashion to regulate the kinetic equations in a consistent manner. We can then perform a systematic perturbation expansion and thereby obtain a finite first-principles result to leading and next-to-leading order. Unlike model building, this systematic calculation yields an estimate of its own error and thus prescribes its domain of applicability. The calculational error is small for a weakly to moderately coupled plasma, for which our result is nearly exact. It should also be emphasized that our calculation becomes unreliable for a strongly coupled plasma, where the perturbative expansion that we employ breaks down, and one must then utilize model building and computer simulations. Besides providing different and potentially useful results, we use this calculation as an opportunity to explain the method of dimensional continuation in a pedagogical fashion. Interestingly, in the regime of relevance for many inertial confinement fusion experiments, the degeneracy corrections are comparable in size to the subleading quantum correction below the Born approximation. For consistency, we therefore present this subleading quantum-to-classical transition correction in addition to the degeneracy correction.

  6. Exciting Quantized Vortex Rings in a Superfluid Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Bulgac, Aurel

    2014-03-01

    In a recent article, Yefsah et al., Nature 499, 426 (2013) report the observation of an unusual quantum excitation mode in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe collective oscillations of the superfluid atomic cloud with a period almost an order of magnitude larger than that predicted by any theory of domain walls, which they interpret as a possible new quantum phenomenon dubbed ``a heavy soliton'' with an inertial mass some 50 times larger than one expected for a domain wall. We present compelling evidence that this ``heavy soliton'' is instead a quantized vortex ring by showing that the main aspects of the experiment can be naturally explained within an extension of the time-dependent density functional theory (TDDFT) to superfluid systems. The numerical simulations required the solution of some 260,000 nonlinear coupled time-dependent 3-dimensional partial differential equations and was implemented on 2048 GPUs on the Cray XK7 supercomputer Titan of the Oak Ridge Leadership Computing Facility.

  7. Swift AND Fermi observations of x-ray flares: The case of late internal shock

    DOE PAGES

    Troja, Eleonora; Piro, Luigi; Vasileiou, Vlasios; ...

    2015-04-07

    Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than 10 decades in energy. We present the sample of X-ray flares observed by both Swift and Fermi during the first three years of Fermi operations. While bright in the X-ray band, X-ray flares are often undetected at lower (optical), and higher (MeV to GeV) energies. We show that this disfavors synchrotron self-Compton processes as the origin of the observed X-ray emission. We compare the broadband properties of X-ray flares with the standard late internal shock model, and find thatmore » in this scenario, X-ray flares can be produced by a late-time relativistic (Γ > 50) outflow at radii R ~ 10 13-10 14 cm. As a result, this conclusion holds only if the variability timescale is significantly shorter than the observed flare duration, and implies that X-ray flares can directly probe the activity of the GRB central engine.« less

  8. Swift and Fermi Observations of X-Ray Flares: The Case of Late Internal Shock

    NASA Technical Reports Server (NTRS)

    Troja, E.; Piro, L.; Vasileiou, V.; Omodei, N.; Burgess, J. M.; Cutini, S.; Connaughton, V.; McEnery, J. E.

    2015-01-01

    Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than 10 decades in energy. We present the sample of X-ray flares observed by both Swift and Fermi during the first three years of Fermi operations. While bright in the X-ray band, X-ray flares are often undetected at lower (optical), and higher (MeV to GeV) energies. We show that this disfavors synchrotron self-Compton processes as the origin of the observed X-ray emission. We compare the broadband properties of X-ray flares with the standard late internal shock model, and find that in this scenario, X-ray flares can be produced by a late-time relativistic (gamma greater than 50) outflow at radii R approximately 10(exp 13) - 10(exp 14) cm. This conclusion holds only if the variability timescale is significantly shorter than the observed flare duration, and implies that X-ray flares can directly probe the activity of the GRB central engine.

  9. SWIFT AND FERMI OBSERVATIONS OF X-RAY FLARES: THE CASE OF LATE INTERNAL SHOCK

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Troja, E.; Piro, L.; Vasileiou, V.

    2015-04-10

    Simultaneous Swift and Fermi observations of gamma-ray bursts (GRBs) offer a unique broadband view of their afterglow emission, spanning more than 10 decades in energy. We present the sample of X-ray flares observed by both Swift and Fermi during the first three years of Fermi operations. While bright in the X-ray band, X-ray flares are often undetected at lower (optical), and higher (MeV to GeV) energies. We show that this disfavors synchrotron self-Compton processes as the origin of the observed X-ray emission. We compare the broadband properties of X-ray flares with the standard late internal shock model, and find thatmore » in this scenario, X-ray flares can be produced by a late-time relativistic (Γ > 50) outflow at radii R ∼ 10{sup 13}-10{sup 14} cm. This conclusion holds only if the variability timescale is significantly shorter than the observed flare duration, and implies that X-ray flares can directly probe the activity of the GRB central engine.« less

  10. Theoretical Interpretation of Pass 8 Fermi -LAT e {sup +} + e {sup −} Data

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Di Mauro, M.; Manconi, S.; Donato, F.

    The flux of positrons and electrons ( e {sup +} + e {sup −}) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. We discuss a number of interpretations of Pass 8 Fermi -LAT e {sup +} + e {sup −} spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We find that the Fermi -LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positronsmore » from cataloged PWNe, and a secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e {sup +} + e {sup −} Fermi -LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green’s catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e {sup +} + e {sup −} Fermi -LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e {sup +} + e {sup −} spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

  11. Distinct evolutions of Weyl fermion quasiparticles and Fermi arcs with bulk band topology in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Xu, Nan; Autes, Gabriel; Matt, Christian; Lv, Baiqing; Bisti, Federico; Strocov, Vladimir; Gawryluk, Dariusz; Pomjakushina, Ekaterina; Conder, Kazimierz; Plumb, Nicholas; Radovic, Milan; Qian, Tian; Yazyev, Oleg; Mesot, Joel; Ding, Hong; Shi, Ming

    By performing ARPES and first-principle calculations, we demonstrate that Weyl fermions quasiparticles in bulk and Fermi arc on surface show distinct evolutions with the bulk band topology in transition-metal monophosphides. While Weyl fermion quasiparticles exist only when the chemical potential is located between two saddle points of the Weyl cone features, the Fermi arc states extend in a larger energy scale and are robust across the bulk Lifshitz transitions associated with the recombination of two non-trivial Fermi surfaces enclosing one Weyl point into a single trivial Fermi surface enclosing two Weyl points of opposite chirality. Therefore, in some systems (NbP), Fermi arc states are preserved even if Weyl fermion quasiparticles are absent in the bulk. Our findings not only provide insight into the relationship between the exotic physical phenomena and the intrinsic bulk band topology in Weyl semimetals, but also resolve the apparent puzzle of the different magneto-transport properties observed in TaAs, TaP and NbP, where the Fermi arc states are similar. The Sino-Swiss Science and Technology Cooperation (No. IZLCZ2138954), NCCR-MARVEL funded by the Swiss National Science Foundation.

  12. Fermi's Motion Produces a Study in Spirograph

    NASA Image and Video Library

    2017-12-08

    The LAT's sensitivity to gamma rays is greatest in the center of its wide field of view and decreases toward the edge. LAT scientists regard the effective limit of the instrument's field of view to be 78.5 degrees (red circle) from its center. View a video of this here: bit.ly/Y2K4LN. Credit: NASA/DOE/Fermi LAT Collaboration ----- NASA's Fermi Gamma-ray Space Telescope orbits our planet every 95 minutes, building up increasingly deeper views of the universe with every circuit. Its wide-eyed Large Area Telescope (LAT) sweeps across the entire sky every three hours, capturing the highest-energy form of light -- gamma rays -- from sources across the universe. These range from supermassive black holes billions of light-years away to intriguing objects in our own galaxy, such as X-ray binaries, supernova remnants and pulsars. Now a Fermi scientist has transformed LAT data of a famous pulsar into a mesmerizing movie that visually encapsulates the spacecraft's complex motion. Click here to continue reading: 1.usa.gov/WhYwCU NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  13. The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope

    ScienceCinema

    Isabelle Grenier

    2018-04-17

    The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008.  In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

  14. Search for Extended Sources in the Galactic Plane Using Six Years of Fermi -Large Area Telescope Pass 8 Data above 10 GeV

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ackermann, M.; Buehler, R.; Ajello, M.

    The spatial extension of a γ -ray source is an essential ingredient to determine its spectral properties, as well as its potential multiwavelength counterpart. The capability to spatially resolve γ -ray sources is greatly improved by the newly delivered Fermi -Large Area Telescope (LAT) Pass 8 event-level analysis, which provides a greater acceptance and an improved point-spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7° from the Galactic plane, using 6 yr of Fermi -LAT data above 10 GeV. We find 46 extended sources and providemore » their morphological and spectral characteristics. This constitutes the first catalog of hard Fermi -LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain.« less

  15. Search for Extended Sources in the Galactic Plane Using Six Years of Fermi-Large Area Telescope Pass 8 Data above 10 GeV

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Castro, D.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Cohen, J. M.; Costantin, D.; Costanza, F.; Cutini, S.; D'Ammando, F.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Grenier, I. A.; Grondin, M.-H.; Guillemot, L.; Guiriec, S.; Harding, A. K.; Hays, E.; Hewitt, J. W.; Horan, D.; Hou, X.; Jóhannesson, G.; Kamae, T.; Kuss, M.; La Mura, G.; Larsson, S.; Lemoine-Goumard, M.; Li, J.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Maldera, S.; Malyshev, D.; Manfreda, A.; Mazziotta, M. N.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paliya, V. S.; Paneque, D.; Perkins, J. S.; Persic, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Porter, T. A.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tak, D.; Thayer, J. B.; Thompson, D. J.; Torres, D. F.; Tosti, G.; Troja, E.; Vianello, G.; Wood, K. S.; Wood, M.

    2017-07-01

    The spatial extension of a γ-ray source is an essential ingredient to determine its spectral properties, as well as its potential multiwavelength counterpart. The capability to spatially resolve γ-ray sources is greatly improved by the newly delivered Fermi-Large Area Telescope (LAT) Pass 8 event-level analysis, which provides a greater acceptance and an improved point-spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7° from the Galactic plane, using 6 yr of Fermi-LAT data above 10 GeV. We find 46 extended sources and provide their morphological and spectral characteristics. This constitutes the first catalog of hard Fermi-LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain.

  16. Fermi Gamma-Ray Space Telescope - Science Highlights for the First Two Years on Orbit

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2011-01-01

    Fermi science objectives cover probably everything in high energy astrophysics: How do super massive black holes in Active Galactic Nuclei create powerful jets of material moving at nearly light speed? What are the jets made of? What are the mechanisms that produce Gamma-Ray Burst (GRB) explosions? What is the energy budget? How does the Sun generate high-energy gamma-rays in flares? How do the pulsars operate? How many of them are around and how different are they? What are the unidentified gamma-ray sources found by EGRET? What is the origin of the cosmic rays that pervade the Galaxy? What is the nature of dark matter? Fermi LAT successfully operates on the orbit for more than 2 years and demonstrates excellent performance, which is continuously monitored and calibrated. LAT collected> 100 billion on-orbit triggers

  17. New Fermi-LAT event reconstruction reveals more high-energy gamma rays from gamma-ray bursts

    DOE PAGES

    Atwood, W. B.; Baldini, L.; Bregeon, J.; ...

    2013-08-19

    Here, based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Largemore » Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy (~147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emission mechanism, and the bulk Lorentz factor of the emitting region.« less

  18. The Fermiac or Fermi's Trolley

    NASA Astrophysics Data System (ADS)

    Coccetti, F.

    2016-03-01

    The Fermiac, known also as Fermi's trolley or Monte Carlo trolley, is an analog computer used to determine the change in time of the neutron population in a nuclear device, via the Monte Carlo method. It was invented by Enrico Fermi and constructed by Percy King at Los Alamos in 1947, and used for about two years. A replica of the Fermiac was built at INFN mechanical workshops of Bologna in 2015, on behalf of the Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", thanks to the original drawings made available by Los Alamos National Laboratory (LANL). This reproduction of the Fermiac was put in use, and a simulation was developed.

  19. Looking for blazars in a sample of unidentified high-energy emitting Fermi sources

    NASA Astrophysics Data System (ADS)

    Marchesini, E. J.; Masetti, N.; Chavushyan, V.; Cellone, S. A.; Andruchow, I.; Bassani, L.; Bazzano, A.; Jiménez-Bailón, E.; Landi, R.; Malizia, A.; Palazzi, E.; Patiño-Álvarez, V.; Rodríguez-Castillo, G. A.; Stephen, J. B.; Ubertini, P.

    2016-11-01

    Context. Based on their overwhelming dominance among associated Fermi γ-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified γ-ray sources from the First Fermi Catalog of γ-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional offset. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims: We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods: An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronómico Nacional San Pedro Mártir in Baja California, Mexico. Results: We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions: Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.

  20. Splitting Fermi Surfaces and Heavy Electronic States in Non-Centrosymmetric U3Ni3Sn4

    NASA Astrophysics Data System (ADS)

    Maurya, Arvind; Harima, Hisatomo; Nakamura, Ai; Shimizu, Yusei; Homma, Yoshiya; Li, DeXin; Honda, Fuminori; Sato, Yoshiki J.; Aoki, Dai

    2018-04-01

    We report the single-crystal growth of the non-centrosymmetric paramagnet U3Ni3Sn4 by the Bridgman method and the Fermi surface properties detected by de Haas-van Alphen (dHvA) experiments. We have also investigated single-crystal U3Ni3Sn4 by single-crystal X-ray diffraction, magnetization, electrical resistivity, and heat capacity measurements. The angular dependence of the dHvA frequencies reveals many closed Fermi surfaces, which are nearly spherical in topology. The experimental results are in good agreement with local density approximation (LDA) band structure calculations based on the 5f-itinerant model. The band structure calculation predicts many Fermi surfaces, mostly with spherical shape, derived from 12 bands crossing the Fermi energy. To our knowledge, the splitting of Fermi surfaces due to the non-centrosymmetric crystal in 5f-electron systems is experimentally detected for the first time. The temperature dependence of the dHvA amplitude reveals a large cyclotron effective mass of up to 35 m0, indicating the heavy electronic state of U3Ni3Sn4 due to the proximity of the quantum critical point. From the field dependence of the dHvA amplitude, a mean free path of conduction electrons of up to 1950 Å is detected, reflecting the good quality of the grown crystal. The small splitting energy related to the antisymmetric spin-orbit interaction is most likely due to the large cyclotron effective mass.

  1. Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Debehets, J.; Homm, P.; Menghini, M.

    In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate detector and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-level. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-levelmore » pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs. This work has been funded by J.D.'s PhD fellowship of the Fund of Scientific Research-Flanders (FWO-V) (Dossier No. 11U4516N). P.H. acknowledges support from Becas Chile-CONICYT. This research was also supported by the FWO Odysseus Program, the Belgian Hercules Stichting with the Project No. Her/08/25 and AKUL/13/19 and the KU Leuven project GOA "Fundamental challenges in Semiconductor Research". The authors would also like to thank Bastiaan Opperdoes and Ludwig Henderix for technical support. The work was supported by the U.S. Department of Energy (USDOE), Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and performed in the Environmental Molecular

  2. The many faces of Fermi

    NASA Astrophysics Data System (ADS)

    Delmastro, Marco

    2017-12-01

    When I settled down to read The Last Man Who Knew Everything by Davis Schwartz, I was asking myself whether there was any need for yet another Enrico Fermi biography. While navigating this ambitious book, I realized that maybe I knew less than I thought about Fermi, and that maybe there was still a lot I could learn.

  3. Minimax rational approximation of the Fermi-Dirac distribution

    DOE PAGES

    Moussa, Jonathan E.

    2016-10-27

    Accurate rational approximations of the Fermi-Dirac distribution are a useful component in many numerical algorithms for electronic structure calculations. The best known approximations use O(log(βΔ)log(ϵ –1)) poles to achieve an error tolerance ϵ at temperature β –1 over an energy interval Δ. We apply minimax approximation to reduce the number of poles by a factor of four and replace Δ with Δ occ, the occupied energy interval. Furthermore, this is particularly beneficial when Δ >> Δ occ, such as in electronic structure calculations that use a large basis set.

  4. Thomas-Fermi simulations of dense plasmas without pseudopotentials

    NASA Astrophysics Data System (ADS)

    Starrett, C. E.

    2017-07-01

    The Thomas-Fermi model for warm and hot dense matter is widely used to predict material properties such as the equation of state. However, for practical reasons current implementations use pseudopotentials for the electron-nucleus interaction instead of the bare Coulomb potential. This complicates the calculation and quantities such as free energy cannot be converged with respect to the pseudopotential parameters. We present a method that retains the bare Coulomb potential for the electron-nucleus interaction and does not use pseudopotentials. We demonstrate that accurate free energies are obtained by checking variational consistency. Examples for aluminum and iron plasmas are presented.

  5. A Study of Spatially-Coincident IceCube Neutrinos and Fermi Gamma-Ray Sources

    NASA Astrophysics Data System (ADS)

    Seymour, Hannah; Mukherjee, Reshmi; Shaevitz, Michael; Santander, Marcos

    2016-03-01

    The IceCube neutrino telescope has detected very-high-energy neutrino events with energies between several hundred TeV to a few PeV beginning inside the detector. These events are unlikely to have originated in the atmosphere, and are suspected to come from astrophysical sources, the likes of which can also be observed in gamma rays by the Fermi Gamma-Ray Space Telescope. We present an analysis of archival GeV gamma-ray data collected with the Large Area Telescope onboard the Fermi satellite to search for gamma-ray sources spatially coincident with the locations of high-enery muon neutrinos detected by IceCube. The combined detection of gamma rays and neutrinos from an astrophysical source will allow us to identify cosmic-ray acceleration sites. With gratitude to the Nevis Laboratories REU program.

  6. Diffusion Monte Carlo study of strongly interacting two-dimensional Fermi gases

    DOE PAGES

    Galea, Alexander; Dawkins, Hillary; Gandolfi, Stefano; ...

    2016-02-01

    Ultracold atomic Fermi gases have been a popular topic of research, with attention being paid recently to two-dimensional (2D) gases. In this work, we perform T=0 ab initio diffusion Monte Carlo calculations for a strongly interacting two-component Fermi gas confined to two dimensions. We first go over finite-size systems and the connection to the thermodynamic limit. After that, we illustrate pertinent 2D scattering physics and properties of the wave function. We then show energy results for the strong-coupling crossover, in between the Bose-Einstein condensation (BEC) and Bardeen-Cooper-Schrieffer (BCS) regimes. Our energy results for the BEC-BCS crossover are parametrized to producemore » an equation of state, which is used to determine Tan's contact. We carry out a detailed comparison with other microscopic results. Lastly, we calculate the pairing gap for a range of interaction strengths in the strong coupling regime, following from variationally optimized many-body wave functions.« less

  7. Fermi GBM: Highlights from the First Year

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2009-01-01

    The Fermi Gamma ray Burst Monitor is an all-sky instrument sensitive to photons from about 8 keV to 40 MeV. I will summarize highlights from the first year, including triggered observations of gamma ray bursts, soft gamma ray repeaters, and terrestrial gamma flashes, and observations in the continuous data of X-ray binaries and accreting X-ray pulsars. GBM provides complementary observations to Swift/BAT, observing many of the same sources, but over a wider energy range.

  8. Fermi Gamma-Ray Space Telescope: Highlights of the GeV Sky

    NASA Technical Reports Server (NTRS)

    Thomspon, D. J.

    2011-01-01

    Because high-energy gamma rays can be produced by processes that also produce neutrinos. the gamma-ray survey of the sky by the Fermi Gamma-ray Space Telescope offers a view of potenl ial targds for neutrino observations. Gamma-ray bursts. active galactic nuclei, and supernova remnants are all sites where hadronic, neutrino-producing interactions are plausible. Pulsars, pulsar wind nebulae, and binary sources are all phenomena that reveal leptonic particle acceleration through their gamma-ray emission. \\Vhile important to gamma-ray astrophysics. such sources are of less interest to neutrino studies. This talk will present a broad overview of the constantly changing sky seen with the Large Area Telescope (LAT) on the Fermi spacecraft.

  9. Fermi surface properties of paramagnetic NpCd11 with a large unit cell

    NASA Astrophysics Data System (ADS)

    Homma, Yoshiya; Aoki, Dai; Haga, Yoshinori; Settai, Rikio; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Takeuchi, Tetsuya; Yamagami, Hiroshi; Ōnuki, Yoshichika

    2010-03-01

    We succeeded in growing a high-quality single crystal of NpCd11 with the cubic BaHg11-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 105 to 1.9 x 107 Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd11 is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np3+(5f4) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m0, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K2·mol, revealing no hybridization between the 5f electrons and conduction electrons.

  10. VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars

    NASA Technical Reports Server (NTRS)

    E. Aliu; Archambault, S.; Arlen, T.; Aune, T.; Beilicke, M.; Benbow, W.; Boettcher, M.; Bouvier, A.; Buckley, J. H.; Bugaev, V.; hide

    2012-01-01

    We report on VERITAS very-high-energy (VHE; E >= 100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band, taking gamma-ray absorption by the extragalactic background light into account. This allowed the selection of six bright, hard-spectrum blazars that were good candidate TeV emitters. Spectroscopic redshift measurements were attempted with the Keck Telescope for the targets without Sloan Digital Sky Survey (SDSS) spectroscopic data. No VHE emission is detected during the observations of the six sources described here. Corresponding TeV upper limits are presented, along with contemporaneous Fermi observations and non-concurrent Swift UVOT and XRT data. The blazar broadband spectral energy distributions (SEDs) are assembled and modeled with a single-zone synchrotron self-Compton model. The SED built for each of the six blazars show a synchrotron peak bordering between the intermediate- and high-spectrum-peak classifications, with four of the six resulting in particle-dominated emission region.

  11. Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

    NASA Astrophysics Data System (ADS)

    Debehets, J.; Homm, P.; Menghini, M.; Chambers, S. A.; Marchiori, C.; Heyns, M.; Locquet, J. P.; Seo, J. W.

    2018-05-01

    In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-level pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.

  12. Large optical conductivity of Dirac semimetal Fermi arc surface states

    NASA Astrophysics Data System (ADS)

    Shi, Li-kun; Song, Justin C. W.

    2017-08-01

    Fermi arc surface states, a hallmark of topological Dirac semimetals, can host carriers that exhibit unusual dynamics distinct from that of their parent bulk. Here we find that Fermi arc carriers in intrinsic Dirac semimetals possess a strong and anisotropic light-matter interaction. This is characterized by a large Fermi arc optical conductivity when light is polarized transverse to the Fermi arc; when light is polarized along the Fermi arc, Fermi arc optical conductivity is significantly muted. The large surface spectral weight is locked to the wide separation between Dirac nodes and persists as a large Drude weight of Fermi arc carriers when the system is doped. As a result, large and anisotropic Fermi arc conductivity provides a novel means of optically interrogating the topological surfaces states of Dirac semimetals.

  13. Collapse and revival of the Fermi sea in a Bose-Fermi mixture

    NASA Astrophysics Data System (ADS)

    Iyer, Deepak; Will, Sebastian; Rigol, Marcos

    2014-05-01

    The collapse and revival of quantum fields is one of the most pristine forms of coherent quantum dynamics far from equilibrium. Until now, it has only been observed in the dynamical evolution of bosonic systems. We report on the first observation of the boson mediated collapse and revival of the Fermi sea in a Bose-Fermi mixture. Specifically, we present a simple model which captures the experimental observations shown in the talk titled Observation of Collapse and Revival Dynamics in the Fermionic Component of a Lattice Bose-Fermi Mixture by Sebastian Will. Our theoretical analysis shows why the results are robust to the presence of harmonic traps during the loading or the time evolution phase. It also makes apparent that the fermionic dynamics is independent of whether the bosonic component consists of a coherent state or localized Fock states with random occupation numbers. Because of the robustness of the experimental results, we argue that this kind of collapse and revival experiment can be used to accurately characterize interactions between bosons and fermions in a lattice.

  14. STATISTICS OF GAMMA-RAY POINT SOURCES BELOW THE FERMI DETECTION LIMIT

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Malyshev, Dmitry; Hogg, David W., E-mail: dm137@nyu.edu

    2011-09-10

    An analytic relation between the statistics of photons in pixels and the number counts of multi-photon point sources is used to constrain the distribution of gamma-ray point sources below the Fermi detection limit at energies above 1 GeV and at latitudes below and above 30 deg. The derived source-count distribution is consistent with the distribution found by the Fermi Collaboration based on the first Fermi point-source catalog. In particular, we find that the contribution of resolved and unresolved active galactic nuclei (AGNs) to the total gamma-ray flux is below 20%-25%. In the best-fit model, the AGN-like point-source fraction is 17%more » {+-} 2%. Using the fact that the Galactic emission varies across the sky while the extragalactic diffuse emission is isotropic, we put a lower limit of 51% on Galactic diffuse emission and an upper limit of 32% on the contribution from extragalactic weak sources, such as star-forming galaxies. Possible systematic uncertainties are discussed.« less

  15. Maximizing Iodine Contrast-to-Noise Ratios in Abdominal CT Imaging through Use of Energy Domain Noise Reduction and Virtual Monoenergetic Dual-Energy CT.

    PubMed

    Leng, Shuai; Yu, Lifeng; Fletcher, Joel G; McCollough, Cynthia H

    2015-08-01

    To determine the iodine contrast-to-noise ratio (CNR) for abdominal computed tomography (CT) when using energy domain noise reduction and virtual monoenergetic dual-energy (DE) CT images and to compare the CNR to that attained with single-energy CT at 80, 100, 120, and 140 kV. This HIPAA-compliant study was approved by the institutional review board with waiver of informed consent. A syringe filled with diluted iodine contrast material was placed into 30-, 35-, and 45-cm-wide water phantoms and scanned with a dual-source CT scanner in both DE and single-energy modes with matched scanner output. Virtual monoenergetic images were generated, with energies ranging from 40 to 110 keV in 10-keV steps. A previously developed energy domain noise reduction algorithm was applied to reduce image noise by exploiting information redundancies in the energy domain. Image noise and iodine CNR were calculated. To show the potential clinical benefit of this technique, it was retrospectively applied to a clinical DE CT study of the liver in a 59-year-old male patient by using conventional and iterative reconstruction techniques. Image noise and CNR were compared for virtual monoenergetic images with and without energy domain noise reduction at each virtual monoenergetic energy (in kiloelectron volts) and phantom size by using a paired t test. CNR of virtual monoenergetic images was also compared with that of single-energy images acquired with 80, 100, 120, and 140 kV. Noise reduction of up to 59% (28.7 of 65.7) was achieved for DE virtual monoenergetic images by using an energy domain noise reduction technique. For the commercial virtual monoenergetic images, the maximum iodine CNR was achieved at 70 keV and was 18.6, 16.6, and 10.8 for the 30-, 35-, and 45-cm phantoms. After energy domain noise reduction, maximum iodine CNR was achieved at 40 keV and increased to 30.6, 25.4, and 16.5. These CNRs represented improvement of up to 64% (12.0 of 18.6) with the energy domain noise

  16. The 3-Dimensional Fermi Liquid Description for the Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Misawa, Setsuo

    2018-01-01

    The quasiparticles in the normal state of iron-based superconductors have been shown to behave universally as a 3-dimensional Fermi liquid. Because of interactions and the presence of sharp Fermi surfaces, the quasiparticle energy contains, as a function of the momentum \\varvec{p}, a term of the form ( p - p_0)^3 ln {( |p-p_0|/p_0)} , where p = | \\varvec{p} | and p_0 is the Fermi momentum. The electronic specific heat coefficient, magnetic susceptibility (Knight shift), electrical resistivity, Hall coefficient and thermoelectric power divided by temperature follow, as functions of temperature T, the logarithmic formula a-b T^2 ln {(T/T^*)}, a, b and T^* being constant; these formulae have been shown to explain the observed data for all iron-based superconductors. It is shown that the concept of non-Fermi liquids or anomalous metals which appears in the literature is not needed for descriptions of the present systems. When the superconducting transition temperature TC and the b / a value for the resistivity are plotted as functions of the doping content x, there appear various characteristic diagrams in which regions of positive correlation and those of negative correlation between TC and b / a are interconnected; from these diagrams, we may make speculations about the types of superconductivity and the crossover between them.

  17. Fermi Surface of Sr_{2}RuO_{4}: Spin-Orbit and Anisotropic Coulomb Interaction Effects.

    PubMed

    Zhang, Guoren; Gorelov, Evgeny; Sarvestani, Esmaeel; Pavarini, Eva

    2016-03-11

    The topology of the Fermi surface of Sr_{2}RuO_{4} is well described by local-density approximation calculations with spin-orbit interaction, but the relative size of its different sheets is not. By accounting for many-body effects via dynamical mean-field theory, we show that the standard isotropic Coulomb interaction alone worsens or does not correct this discrepancy. In order to reproduce experiments, it is essential to account for the Coulomb anisotropy. The latter is small but has strong effects; it competes with the Coulomb-enhanced spin-orbit coupling and the isotropic Coulomb term in determining the Fermi surface shape. Its effects are likely sizable in other correlated multiorbital systems. In addition, we find that the low-energy self-energy matrix-responsible for the reshaping of the Fermi surface-sizably differs from the static Hartree-Fock limit. Finally, we find a strong spin-orbital entanglement; this supports the view that the conventional description of Cooper pairs via factorized spin and orbital part might not apply to Sr_{2}RuO_{4}.

  18. Surface effects in the unitary Fermi gas

    NASA Astrophysics Data System (ADS)

    Salasnich, L.; Ancilotto, F.; Toigo, F.

    2010-01-01

    We study the extended Thomas-Fermi (ETF) density functional of the superfluid unitary Fermi gas. This functional includes a gradient term which is essential to describe accurately the surface effects of the system, in particular with a small number of atoms, where the Thomas-Fermi (local density) approximation fails. We find that our ETF functional gives density profiles which are in good agreement with recent Monte Carlo results and also with a more sophisticated superfluid density functional based on Bogoliubov-de Gennes equations. In addition, by using extended hydrodynamics equations of superfluids, we calculate the frequencies of collective surface oscillations of the unitary Fermi gas, showing that quadrupole and octupole modes strongly depend on the number of trapped atoms.

  19. Self-consistent self-interaction corrected density functional theory calculations for atoms using Fermi-Löwdin orbitals: Optimized Fermi-orbital descriptors for Li-Kr

    NASA Astrophysics Data System (ADS)

    Kao, Der-you; Withanage, Kushantha; Hahn, Torsten; Batool, Javaria; Kortus, Jens; Jackson, Koblar

    2017-10-01

    In the Fermi-Löwdin orbital method for implementing self-interaction corrections (FLO-SIC) in density functional theory (DFT), the local orbitals used to make the corrections are generated in a unitary-invariant scheme via the choice of the Fermi orbital descriptors (FODs). These are M positions in 3-d space (for an M-electron system) that can be loosely thought of as classical electron positions. The orbitals that minimize the DFT energy including the SIC are obtained by finding optimal positions for the FODs. In this paper, we present optimized FODs for the atoms from Li-Kr obtained using an unbiased search method and self-consistent FLO-SIC calculations. The FOD arrangements display a clear shell structure that reflects the principal quantum numbers of the orbitals. We describe trends in the FOD arrangements as a function of atomic number. FLO-SIC total energies for the atoms are presented and are shown to be in close agreement with the results of previous SIC calculations that imposed explicit constraints to determine the optimal local orbitals, suggesting that FLO-SIC yields the same solutions for atoms as these computationally demanding earlier methods, without invoking the constraints.

  20. Fermi-LAT observation of nonblazar AGNs

    NASA Astrophysics Data System (ADS)

    Sahakyan, N.; Baghmanyan, V.; Zargaryan, D.

    2018-06-01

    Context. Fermi Large Area Telescope (Fermi-LAT) has recently detected γ-ray emission from active galactic nuclei (AGN) that do not show clear evidence for optical blazar characteristics or have jets pointing away from the observer (nonblazar AGNs). These are interesting γ-ray emitters providing an alternative approach to studying high energy emission processes. Aims: This paper investigates the spectral and temporal properties of γ-ray emission from nonblazar AGNs using the recent Fermi-LAT observational data. Methods: The data collected by Fermi-LAT during 2008-2015, from the observations of 26 nonblazar AGNs, including 11 Fanaroff-Riley Type I (FRI) and ten FRII radio galaxies and steep spectrum radio quasars (SSRQs) and five narrow line seyfert 1s (NLSy1s) are analysed using the new PASS 8 event selection and instrument response function. Possible spectral changes above GeV energies are investigated with a detailed spectral analysis. Light curves generated with normal and adaptive time bins are used to study the γ-ray flux variability. Results: Non-blazar AGNs have a γ-ray photon index in the range of 1.84-2.86 and a flux varying from a few times 10-9 photon cm-2 s-1 to 10-7 photon cm-2 s-1. Over long time periods, the power law provides an adequate description of the γ-ray spectra of almost all sources. Significant curvature is observed in the γ-ray spectra of NGC 1275, NGC 6251, SBS 0846 + 513, and PMN J0948 + 0022 and their spectra are better described by log parabola or by the power law with exponential cut-off models. The γ-ray spectra of PKS 0625-25 and 3C 380 show a possible deviation from a simple power-law shape, indicating a spectral cut-off around the observed photon energy of Ecut = 131.2 ± 88.04 GeV and Ecut = 55.57 ± 50.74 GeV, respectively. Our analysis confirms the previous finding of an unusual spectral turnover in the γ-ray spectrum of Cen A: the photon index changes from Γ = 2.75 ± 0.02 to 2.31 ± 0.1 at 2.35 ± 0.08 GeV. In the

  1. Search for Extended Sources in the Galactic Plane Using Six Years of Fermi-Large Area Telescope Pass 8 Data above 10 GeV

    DOE PAGES

    Ackermann, M.; Ajello, M.; Baldini, L.; ...

    2017-07-10

    The spatial extension of a γ-ray source is an essential ingredient to determine its spectral properties, as well as its potential multiwavelength counterpart. The capability to spatially resolve γ-ray sources is greatly improved by the newly delivered Fermi-Large Area Telescope (LAT) Pass 8 event-level analysis, which provides a greater acceptance and an improved point-spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7° from the Galactic plane, using 6 yr of Fermi-LAT data above 10 GeV. We find 46 extended sources and provide their morphological and spectralmore » characteristics. As a result, this constitutes the first catalog of hard Fermi-LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain.« less

  2. Search for Extended Sources in the Galactic Plane Using Six Years of Fermi-Large Area Telescope Pass 8 Data above 10 GeV

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ackermann, M.; Ajello, M.; Baldini, L.

    The spatial extension of a γ-ray source is an essential ingredient to determine its spectral properties, as well as its potential multiwavelength counterpart. The capability to spatially resolve γ-ray sources is greatly improved by the newly delivered Fermi-Large Area Telescope (LAT) Pass 8 event-level analysis, which provides a greater acceptance and an improved point-spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7° from the Galactic plane, using 6 yr of Fermi-LAT data above 10 GeV. We find 46 extended sources and provide their morphological and spectralmore » characteristics. As a result, this constitutes the first catalog of hard Fermi-LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain.« less

  3. Exploring the Extreme Universe with the Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, David J.; Digel, Seth W.; Racusin, Judith L.

    2012-01-01

    In ways similar to experiments in nuclear and particle physics, high-energy astrophysics usesgamma rays and energetic charged particles toprobe processes that involve large energy transfers.Since its launch in 2008, the international Fermi Gamma-Ray Space Telescope has been exploringnatural particle accelerators and the interactionsof high-energy particles in the universe. Withsources ranging from thunderstorms on Earth to galaxies and exploding stars in distant parts of the cosmos, the telescopes subjects of study are almostas diverse as were those of the scientist whose name it bears.

  4. The First Fermi-LAT Catalog of Sources Above 10 GeV

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Moiseev, Alexander A.

    2013-01-01

    We present a catalog of gamma-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during the first 3 yr of the Fermi Gamma-ray Space Telescope mission. The first Fermi-LAT catalog of >10 GeV sources (1FHL) has 514 sources. For each source we present location, spectrum, a measure of variability, and associations with cataloged sources at other wavelengths. We found that 449 (87%) could be associated with known sources, of which 393 (76% of the 1FHL sources) are active galactic nuclei. Of the 27 sources associated with known pulsars, we find 20 (12) to have significant pulsations in the range >10 GeV (>25 GeV). In this work we also report that, at energies above 10 GeV, unresolved sources account for 27% +/- 8% of the isotropic ? -ray background, while the unresolved Galactic population contributes only at the few percent level to the Galactic diffuse background. We also highlight the subset of the 1FHL sources that are best candidates for detection at energies above 50-100 GeV with current and future ground-based ? -ray observatories.

  5. STEM education and Fermi problems

    NASA Astrophysics Data System (ADS)

    Holubova, Renata

    2017-01-01

    One of the research areas of Physics education is the study of the educational process. Investigations in this area are aimed for example on the teaching and learning process and its results. The conception of STEM education (Science, Technology, Engineering, and Mathematics) is discussed - it is one possible approach to the preparation of the curriculum and the focus on the educational process at basic and secondary schools. At schools in the Czech Republic STEM is much more realized by the application of interdisciplinary relations between subjects Physics-Nature-Technique. In both conceptions the aim is to support pupils' creativity, critical thinking, cross-curricular links. In this context the possibility of using Fermi problems in teaching Physics was discussed (as an interdisciplinary and constructivist activity). The aim of our research was the analysis of Fermi problems solving strategies, the ability of pupils to solve Fermi problems. The outcome of our analysis was to find out methods and teaching strategies which are important to use in teaching - how to solve qualitative and interdisciplinary tasks in physics. In this paper the theoretical basis of STEM education and Fermi problems will be presented. The outcome of our findings based on the research activities will be discussed so as our experiences from 10 years of Fermi problems competition that takes place at the Science Faculty, Palacky University in Olomouc. Changes in competencies of solving tasks by our students (from the point of view in terms of modern, activating teaching methods recommended by theory of Physics education and other science subjects) will be identified.

  6. Non-Equilibrium Dynamics of Fermi Gases Near A Scattering Resonance

    NASA Astrophysics Data System (ADS)

    Trotzky, S.; Luciuk, C.; Smale, S.; Beattie, S.; Taylor, E.; Enss, T.; Zhang, Shizhong; Thywissen, J. H.

    2015-05-01

    We present recent dynamic measurements of fermionic potassium (40K) near Fano-Feshbach scattering resonances. In our experiments, we start with a weakly or non-interacting Fermi gas and initiate strong interactions on a timescale that is fast compared to the equilibration mechanisms in the system quasi-instantaneous quench. Equally fast measurements allow us to follow the non-equilibrium many-body dynamics. First, we discuss time-resolved radio-frequency (rf) spectroscopy, and its use to probe the evolution of the short-range part of the many-body wave function - i.e., the contact. Second, we discuss spin-echo measurements that reveal the nature of transverse spin transport. Most recently, we have studied a Fermi gas with repulsive interactions in the metastable upper branch of the energy spectrum near a s-wave scattering resonance.

  7. High-energy non-thermal and thermal emission from GRB 141207A detected by Fermi

    DOE PAGES

    Arimoto, Makoto; Asano, Katsuaki; Ohno, Masanori; ...

    2016-12-13

    A bright long gamma-ray burst GRB 141207A was observed by the Fermi Gamma-ray Space Telescope and detected by both instruments onboard. The observations show that the spectrum in the prompt phase is not well described by the canonical empirical Band function alone, and that an additional power-law component is needed. In the early phase of the prompt emission, a modified blackbody with a hard low-energy photon index (α = +0.2 to +0.4) is detected, which suggests a photospheric origin. In a finely time-resolved analysis, the spectra are also well fitted by the modified blackbody combined with a power-law function. Heremore » we discuss the physical parameters of the photosphere such as the bulk Lorentz factor of the relativistic flow and the radius. We also discuss the physical origin of the extra power-law component observed during the prompt phase in the context of different models such as leptonic and hadronic scenarios in the internal shock regime and synchrotron emission in the external forward shock. In the afterglow phase, the temporal and spectral behaviors of the temporally extended high-energy emission and the fading X-ray emission detected by the X-Ray Telescope on-board Swift are consistent with synchrotron emission in a radiative external forward shock.« less

  8. Electronic structure Fermi liquid theory of high T(sub c) superconductors: Comparison with experiments

    NASA Astrophysics Data System (ADS)

    Freeman, A. J.; Yu, Jaejun

    1990-04-01

    For years, there has been controversy on whether the normal state of the Cu-oxide superconductors is a Fermi liquid or some other exotic ground state. However, some experimentalists are clarifying the nature of the normal state of the high T(sub c) superconductors by surmounting the experimental difficulties in producing clean, well characterized surfaces so as to obtain meaningful high resolved photoemission data, which agrees with earlier positron-annihilation experiments. The experimental work on high resolution angle resolved photoemission by Campuzano et al. and positron-annihilation studies by Smedskjaer et al. has verified the calculated Fermi surfaces in YBa2Cu3O7 superconductors and has provided evidence for the validity of the energy band approach. Similar good agreement was found for Bi2Sr2CaCu2O8 by Olson et al. As a Fermi liquid (metallic) nature of the normal state of the high T(sub c) superconductors becomes evident, these experimental observations have served to confirm the predictions of the local density functional calculations and hence the energy band approach as a valid natural starting point for further studies of their superconductivity.

  9. Electronic structure Fermi liquid theory of high T(sub c) superconductors: Comparison with experiments

    NASA Technical Reports Server (NTRS)

    Freeman, A. J.; Yu, Jaejun

    1990-01-01

    For years, there has been controversy on whether the normal state of the Cu-oxide superconductors is a Fermi liquid or some other exotic ground state. However, some experimentalists are clarifying the nature of the normal state of the high T(sub c) superconductors by surmounting the experimental difficulties in producing clean, well characterized surfaces so as to obtain meaningful high resolved photoemission data, which agrees with earlier positron-annihilation experiments. The experimental work on high resolution angle resolved photoemission by Campuzano et al. and positron-annihilation studies by Smedskjaer et al. has verified the calculated Fermi surfaces in YBa2Cu3O7 superconductors and has provided evidence for the validity of the energy band approach. Similar good agreement was found for Bi2Sr2CaCu2O8 by Olson et al. As a Fermi liquid (metallic) nature of the normal state of the high T(sub c) superconductors becomes evident, these experimental observations have served to confirm the predictions of the local density functional calculations and hence the energy band approach as a valid natural starting point for further studies of their superconductivity.

  10. Experimental observation of topological Fermi arcs in type-II Weyl semimetal MoTe2

    NASA Astrophysics Data System (ADS)

    Deng, Ke; Wan, Guoliang; Deng, Peng; Zhang, Kenan; Ding, Shijie; Wang, Eryin; Yan, Mingzhe; Huang, Huaqing; Zhang, Hongyun; Xu, Zhilin; Denlinger, Jonathan; Fedorov, Alexei; Yang, Haitao; Duan, Wenhui; Yao, Hong; Wu, Yang; Fan, Shoushan; Zhang, Haijun; Chen, Xi; Zhou, Shuyun

    2016-12-01

    Weyl semimetal is a new quantum state of matter hosting the condensed matter physics counterpart of the relativistic Weyl fermions originally introduced in high-energy physics. The Weyl semimetal phase realized in the TaAs class of materials features multiple Fermi arcs arising from topological surface states and exhibits novel quantum phenomena, such as a chiral anomaly-induced negative magnetoresistance and possibly emergent supersymmetry. Recently it was proposed theoretically that a new type (type-II) of Weyl fermion that arises due to the breaking of Lorentz invariance, which does not have a counterpart in high-energy physics, can emerge as topologically protected touching between electron and hole pockets. Here, we report direct experimental evidence of topological Fermi arcs in the predicted type-II Weyl semimetal MoTe2 (refs ,,). The topological surface states are confirmed by directly observing the surface states using bulk- and surface-sensitive angle-resolved photoemission spectroscopy, and the quasi-particle interference pattern between the putative topological Fermi arcs in scanning tunnelling microscopy. By establishing MoTe2 as an experimental realization of a type-II Weyl semimetal, our work opens up opportunities for probing the physical properties of this exciting new state.

  11. Lifetime of Feshbach dimers in a Fermi-Fermi mixture of 6Li and 40K

    NASA Astrophysics Data System (ADS)

    Jag, M.; Cetina, M.; Lous, R. S.; Grimm, R.; Levinsen, J.; Petrov, D. S.

    2016-12-01

    We present a joint experimental and theoretical investigation of the lifetime of weakly bound dimers formed near narrow interspecies Feshbach resonances in mass-imbalanced Fermi-Fermi systems, considering the specific example of a mixture of 6Li and 40K atoms. Our work addresses the central question of the increase in the stability of the dimers resulting from Pauli suppression of collisional losses, which is a well-known effect in mass-balanced fermionic systems near broad resonances. We present measurements of the spontaneous dissociation of dimers in dilute samples, and of the collisional losses in dense samples arising from both dimer-dimer processes and from atom-dimer processes. We find that all loss processes are suppressed close to the Feshbach resonance. Our general theoretical approach for fermionic mixtures near narrow Feshbach resonances provides predictions for the suppression of collisional decay as a function of the detuning from resonance, and we find excellent agreement with the experimental benchmarks provided by our 40K-6Li system. We finally present model calculations for other Feshbach-resonant Fermi-Fermi systems, which are of interest for experiments in the near future.

  12. Dynamics of atom-atom correlations in the Fermi problem

    NASA Astrophysics Data System (ADS)

    Borrelli, Massimo; Sabín, Carlos; Adesso, Gerardo; Plastina, Francesco; Maniscalco, Sabrina

    2012-10-01

    We present a detailed perturbative study of the dynamics of several types of atom-atom correlations in the famous Fermi problem. This is an archetypal model to study micro-causality in the quantum domain, where two atoms, one initially excited and the other prepared in its ground state, interact with the vacuum electromagnetic field. The excitation can be transferred to the second atom via a flying photon, and various kinds of quantum correlations between the two are generated during this process. Among these, prominent examples are given by entanglement, quantum discord and non-local correlations. The aim of this paper is to analyze the role of the light cone in the emergence of such correlations.

  13. Effects of impurity and Bose-Fermi interactions on the transition temperature of a dilute dipolar Bose-Einstein condensation in trapped Bose-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Yavari, H.; Mokhtari, M.

    2014-03-01

    The effects of impurity and Bose-Fermi interactions on the transition temperature of a dipolar Bose-Einstein condensation in trapped Bose-Fermi mixture, by using the two-fluid model, are investigated. The shift of the transition temperature consists of four contributions due to contact, Bose-Fermi, dipole-dipole, and impurity interactions. We will show that in the presence of an anisotropic trap, the Bose-Fermi correction to the shift of transition temperature due to the excitation spectra of the thermal part is independent of anisotropy factor. Applying our results to trapped Bose-Fermi mixtures shows that, by knowing the impurity effect, the shift of the transition temperature due to Bose-Fermi interaction could be measured for isotropic trap (dipole-dipole contributions is zero) and Feshbach resonance technique (contact potential contribution is negligible).

  14. Superconductivity versus bound-state formation in a two-band superconductor with small Fermi energy: Applications to Fe pnictides/chalcogenides and doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Eremin, Ilya; Efremov, Dmitri V.

    2016-05-01

    We analyze the interplay between superconductivity and the formation of bound pairs of fermions (BCS-BEC crossover) in a 2D model of interacting fermions with small Fermi energy EF and weak attractive interaction, which extends to energies well above EF. The 2D case is special because a two-particle bound state forms at arbitrary weak interaction, and already at weak coupling, one has to distinguish between the bound-state formation and superconductivity. We briefly review the situation in the one-band model and then consider two different two-band models: one with one hole band and one electron band and another with two hole or two electron bands. In each case, we obtain the bound-state energy 2 E0 for two fermions in a vacuum and solve the set of coupled equations for the pairing gaps and the chemical potentials to obtain the onset temperature of the pairing Tins and the quasiparticle dispersion at T =0 . We then compute the superfluid stiffness ρs(T =0 ) and obtain the actual Tc. For definiteness, we set EF in one band to be near zero and consider different ratios of E0 and EF in the other band. We show that at EF≫E0 , the behavior of both two-band models is BCS-like in the sense that Tc≈Tins≪EF and Δ ˜Tc . At EF≪E0 , the two models behave differently: in the model with two hole/two electron bands, Tins˜E0/lnE/0EF , Δ ˜(E0EF) 1 /2 , and Tc˜EF , like in the one-band model. In between Tins and Tc, the system displays a preformed pair behavior. In the model with one hole and one electron bands, Tc remains of order Tins, and both remain finite at EF=0 and of the order of E0. The preformed pair behavior still does exist in this model because Tc is numerically smaller than Tins. For both models, we reexpress Tins in terms of the fully renormalized two-particle scattering amplitude by extending to the two-band case (the method pioneered by Gorkov and Melik-Barkhudarov back in 1961). We apply our results for the model with a hole and an electron band to

  15. Noise of a Chargeless Fermi Liquid

    NASA Astrophysics Data System (ADS)

    Moca, Cǎtǎlin Paşcu; Mora, Christophe; Weymann, Ireneusz; Zaránd, Gergely

    2018-01-01

    We construct a Fermi liquid theory to describe transport in a superconductor-quantum dot-normal metal junction close to the singlet-doublet (parity changing) transition of the dot. Though quasiparticles do not have a definite charge in this chargeless Fermi liquid, in the case of particle-hole symmetry, a mapping to the Anderson model unveils a hidden U(1) symmetry and a corresponding pseudocharge. In contrast to other correlated Fermi liquids, the back scattering noise reveals an effective charge equal to the charge of Cooper pairs, e*=2 e . In addition, we find a strong suppression of noise when the linear conductance is unitary, even for its nonlinear part.

  16. Long lifetimes of ultrahot particles in interacting Fermi systems

    NASA Astrophysics Data System (ADS)

    Bard, M.; Protopopov, I. V.; Mirlin, A. D.

    2018-05-01

    The energy dependence of the relaxation rate of hot electrons due to interaction with the Fermi sea is studied. We consider 2D and 3D systems, quasi-1D quantum wires with multiple transverse bands, as well as single-channel 1D wires. Our analysis includes both spinful and spin-polarized setups, with short-range and Coulomb interactions. We show that, quite generally, the relaxation rate is a nonmonotonic function of the electron energy and decays as a power law at high energies. In other words, ultrahot electrons regain their coherence with increasing energy. Such a behavior was observed in a recent experiment on multiband quantum wires, J. Reiner et al., Phys. Rev. X 7, 021016 (2017)., 10.1103/PhysRevX.7.021016

  17. Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Debehets, J.; Homm, P.; Menghini, M.

    In this study, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-levelmore » pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH 4) 2S-solutions in an inert atmosphere (N 2-gas). Although the (NH 4) 2S-cleaning in N 2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH 4) 2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.« less

  18. Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

    DOE PAGES

    Debehets, J.; Homm, P.; Menghini, M.; ...

    2018-01-12

    In this study, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-levelmore » pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH 4) 2S-solutions in an inert atmosphere (N 2-gas). Although the (NH 4) 2S-cleaning in N 2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH 4) 2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.« less

  19. FERMI/LAT Observations of LS 5039

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2009-10-30

    The first results from observations of the high-mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. In this report, our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 ± 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV-300more » GeV) of 4.9 ± 0.5(stat) ± 1.8(syst) ×10 –7 photon cm –2 s –1, with a cutoff at 2.1 ± 0.3(stat) ± 1.1(syst) GeV and photon index Γ = 1.9 ± 0.1(stat) ± 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. Lastly, we suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.« less

  20. Fermi LAT Observations of LS 5039

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Abdo, A.A.; /Naval Research Lab, Wash., D.C. /Federal City Coll.; Ackermann, M.

    The first results from observations of the high-mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. Our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 {+-} 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV-300 GeV) of 4.9more » {+-} 0.5(stat) {+-} 1.8(syst) x 10{sup -7} photon cm{sup -2} s{sup -1}, with a cutoff at 2.1 {+-} 0.3(stat) {+-} 1.1(syst) GeV and photon index {Gamma} = 1.9 {+-} 0.1(stat) {+-} 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. We suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.« less

  1. VizieR Online Data Catalog: Fermi LAT second source catalog (2FGL) (Nolan+, 2012)

    NASA Astrophysics Data System (ADS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Belfiore, A.; Bellazzini, R.; Berenji, B.; Bignami, G. F.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Campana, R.; Canadas, B.; Cannon, A.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Ceccanti, M.; Cecchi, C.; Celik, O.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Chipaux, R.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Corbet, R.; Cutini, S.; D'Ammando, F.; Davis, D. S.; de Angelis, A.; Decesar, M. E.; Deklotz, M.; de Luca A.; den Hartog, P. R.; de Palma, F.; Dermer, C. D.; Digel, S. W.; Do Couto, E. Silva E.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Dumora, D.; Enoto, T.; Escande, L.; Fabiani, D.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Iafrate, G.; Itoh, R.; Johannesson, G.; Johnson, R. P.; Johnson, T. E.; Johnson, A. S.; Johnson, T. J.; Kamae, T.; Katagiri, H.; Kataoka, J.; Katsuta, J.; Kawai, N.; Kerr, M.; Knodlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Landriu, D.; Latronico, L.; Lemoine-Goumard, M.; Lionetto, A. M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Marelli, M.; Massaro, E.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Minuti, M.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Mongelli, M.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-God, O. M.; Norris, J. P.; Nuss, E.; Nymark, T.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Perkins, J. S.; Pesce-Rollins, M.; Pierbattista, M.; Pinchera, M.; Piron, F.; Pivato, G.; Porter, T. A.; Racusin, J. L.; Raino, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Rochester, L. S.; Romani, R. W.; Roth, M.; Rousseau, R.; Ryde, F.; Sadrozinski, H. F.-W.; Salvetti, D.; Sanchez, D. A.; Saz Parkinson, P. M.; Sbarra, C.; Scargle, J. D.; Schalk, T. L.; Sgro, C.; Shaw, M. S.; Shrader, C.; Siskind, E. J.; Smith, D. A.; Spandre, G.; Spinelli, P.; Stephens, T. E.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Tinebra, F.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vandenbroucke, J.; van Etten, A.; van Klaveren, B.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wallace, E.; Wang, P.; Werner, M.; Winer, B. L.; Wood, D. L.; Wood, K. S.; Wood, M.; Yang, Z.; Zimmer, S.

    2012-06-01

    This paper presents a catalog of high-energy γ-ray sources detected, in the 100MeV-100GeV energy range, in the first two years of the Fermi Gamma-ray Space Telescope mission by the Large Area Telescope (LAT), during the period 2008 August 4 (15:43 UTC)-2010 August 1 (01:17 UTC). (4 data files).

  2. Gamma-telescopes Fermi/LAT and GAMMA-400 Trigger Systems Event Recognizing Methods Comparison

    NASA Astrophysics Data System (ADS)

    Arkhangelskaja, I. V.; Murchenko, A. E.; Chasovikov, E. N.; Arkhangelskiy, A. I.; Kheymits, M. D.

    Usually instruments for high-energy γ-quanta registration consists of converter (where γ-quanta produced pairs) and calorimeter for particles energy measurements surrounded by anticoincidence shield used to events identification (whether incident particle was charged or neutral). The influence of pair formation by γ-quanta in shield and the backsplash (moved in the opposite direction particles created due high energy γ-rays interact with calorimeter) should be taken into account. It leads to decrease both effective area and registration efficiency at E>10 GeV. In the presented article the event recognizing methods used in Fermi/LAT trigger system is considered in comparison with the ones applied in counting and triggers signals formation system of gamma-telescope GAMMA-400. The GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) will be the new high-apogee space γ-observatory. The GAMMA-400 consist of converter-tracker based on silicon-strip coordinate detectors interleaved with tungsten foils, imaging calorimeter make of 2 layers of double (x, y) silicon strip coordinate detectors interleaved with planes of CsI(Tl) crystals and the electromagnetic calorimeter CC2 consists only of CsI(Tl) crystals. Several plastics detections systems used as anticoincidence shield, for particles energy and moving direction estimations. The main differences of GAMMA-400 constructions from Fermi/LAT one are using the time-of-flight system with base of 50 cm and double layer structure of plastic detectors provides more effective particles direction definition and backsplash rejection. Also two calorimeters in GAMMA-400 composed the total absorbtion spectrometer with total thickness ∼ 25 X0 or ∼1.2 λ0 for vertical incident particles registration and 54 X0 or 2.5 λ0 for laterally incident ones (where λ0 is nuclear interaction length). It provides energy resolution 1-2% for 10 GeV-3.0×103 GeV events while the Fermi/LAT energy resolution does not reach such a

  3. Fermi Large Area Telescope Constraints On The Gamma-Ray Opacity Of The Universe

    DOE PAGES

    Abdo, A. A.

    2010-10-19

    The extragalactic background light (EBL) includes photons with wavelengths from ultraviolet to infrared, which are effective at attenuating gamma rays with energy above ~10 GeV during propagation from sources at cosmological distances. This results in a redshift- and energy-dependent attenuation of the γ-ray flux of extragalactic sources such as blazars and gamma-ray bursts (GRBs). The Large Area Telescope on board Fermi detects a sample of γ-ray blazars with redshift up to z ~ 3, and GRBs with redshift up to z ~ 4.3. Using photons above 10 GeV collected by Fermi over more than one year of observations for thesemore » sources, we investigate the effect of γ-ray flux attenuation by the EBL. We place upper limits on the γ-ray opacity of the universe at various energies and redshifts and compare this with predictions from well-known EBL models. We find that an EBL intensity in the optical-ultraviolet wavelengths as great as predicted by the "baseline" model of Stecker et al. can be ruled out with high confidence.« less

  4. Shells, orbit bifurcations, and symmetry restorations in Fermi systems

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Magner, A. G., E-mail: magner@kinr.kiev.ua; Koliesnik, M. V.; Arita, K.

    The periodic-orbit theory based on the improved stationary-phase method within the phase-space path integral approach is presented for the semiclassical description of the nuclear shell structure, concerning themain topics of the fruitful activity ofV.G. Soloviev. We apply this theory to study bifurcations and symmetry breaking phenomena in a radial power-law potential which is close to the realistic Woods–Saxon one up to about the Fermi energy. Using the realistic parametrization of nuclear shapes we explain the origin of the double-humped fission barrier and the asymmetry in the fission isomer shapes by the bifurcations of periodic orbits. The semiclassical origin of themore » oblate–prolate shape asymmetry and tetrahedral shapes is also suggested within the improved periodic-orbit approach. The enhancement of shell structures at some surface diffuseness and deformation parameters of such shapes are explained by existence of the simple local bifurcations and new non-local bridge-orbit bifurcations in integrable and partially integrable Fermi-systems. We obtained good agreement between the semiclassical and quantum shell-structure components of the level density and energy for several surface diffuseness and deformation parameters of the potentials, including their symmetry breaking and bifurcation values.« less

  5. Fermi Large Area Telescope third source catalog

    DOE PAGES

    Acero, F.; Ackermann, M.; Ajello, M.; ...

    2015-06-12

    Here, we present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100 MeV–300 GeV range. Based on the first 4 yr of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse γ-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources abovemore » $$4\\sigma $$ significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. As a result, from source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ~3% at 1 GeV.« less

  6. VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars

    DOE PAGES

    Aliu, E.; Archambault, S.; Arlen, T.; ...

    2012-10-25

    In this paper, we report on VERITAS very high energy (VHE; E ≥ 100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band, taking gamma-ray absorption by the extragalactic background light into account. This allowed the selection of six bright, hard-spectrum blazars that were good candidate TeV emitters. Spectroscopic redshift measurements were attempted with the Keck Telescope for the targets without Sloan Digital Sky Survey spectroscopic data. No VHE emission is detected during the observations of the six sources describedmore » here. Corresponding TeV upper limits are presented, along with contemporaneous Fermi observations and non-concurrent Swift UVOT and X-Ray Telescope data. The blazar broadband spectral energy distributions (SEDs) are assembled and modeled with a single-zone synchrotron self-Compton model. Finally, the SED built for each of the six blazars shows a synchrotron peak bordering between the intermediate- and high-spectrum-peak classifications, with four of the six resulting in particle-dominated emission regions.« less

  7. Fermi-LAT upper limits on gamma-ray emission from colliding wind binaries

    DOE PAGES

    Werner, Michael; Reimer, O.; Reimer, A.; ...

    2013-07-09

    Here, colliding wind binaries (CWBs) are thought to give rise to a plethora of physical processes including acceleration and interaction of relativistic particles. Observation of synchrotron radiation in the radio band confirms there is a relativistic electron population in CWBs. Accordingly, CWBs have been suspected sources of high-energy γ-ray emission since the COS-B era. Theoretical models exist that characterize the underlying physical processes leading to particle acceleration and quantitatively predict the non-thermal energy emission observable at Earth. Furthermore, we strive to find evidence of γ-ray emission from a sample of seven CWB systems: WR 11, WR 70, WR 125, WRmore » 137, WR 140, WR 146, and WR 147. Theoretical modelling identified these systems as the most favourable candidates for emitting γ-rays. We make a comparison with existing γ-ray flux predictions and investigate possible constraints. We used 24 months of data from the Large Area Telescope (LAT) on-board the Fermi Gamma Ray Space Telescope to perform a dedicated likelihood analysis of CWBs in the LAT energy range. As a result, we find no evidence of γ-ray emission from any of the studied CWB systems and determine corresponding flux upper limits. For some CWBs the interplay of orbital and stellar parameters renders the Fermi-LAT data not sensitive enough to constrain the parameter space of the emission models. In the cases of WR140 and WR147, the Fermi -LAT upper limits appear to rule out some model predictions entirely and constrain theoretical models over a significant parameter space. A comparison of our findings to the CWB η Car is made.« less

  8. A search for Fermi bursts associated with supernovae and their frequency of occurrence

    NASA Astrophysics Data System (ADS)

    Kovacevic, M.; Izzo, L.; Wang, Y.; Muccino, M.; Della Valle, M.; Amati, L.; Barbarino, C.; Enderli, M.; Pisani, G. B.; Li, L.

    2014-09-01

    Context. Observations suggest that most long duration gamma-ray bursts (GRBs) are connected with broad-line supernovae Ib/c, (SNe-Ibc). The presence of GRB-SNe is revealed by rebrightenings emerging from the optical GRB afterglow 10-15 days, in the rest-frame of the source, after the prompt GRB emission. Aims: Fermi/GBM has a field of view (FoV) about 6.5 times larger than the FoV of Swift, therefore we expect that a number of GRB-SN connections have been missed because of lack of optical and X-ray instruments on board of Fermi, which are essential for revealing SNe associated with GRBs. This has motivated our search in the Fermi catalog for possible GRB-SN events. Methods: The search for possible GRB-SN associations follows two requirements: (1) SNe should fall inside the Fermi/GBM error box of the considered long GRB, and (2) this GRB should occur within 20 days before the SN event. Results: We have found five cases within z< 0.2 fulfilling the above reported requirements. One of them, GRB 130702A-SN 2013dx, was already known to have a GRB-SN association. We have analyzed the remaining four cases and we have concluded that three of them are, very likely, just random coincidences due to the Fermi/GBM large error box associated with each GRB detection. We found one GRB possibly associated with a SN 1998bw-like source, GRB 120121B/SN 2012ba. Conclusions: The very low redshift of GRB 120121B/SN 2012ba (z = 0.017) implies a low isotropic energy of this burst (Eiso = 1.39 × 1048) erg. We then compute the rate of Fermi low-luminosity GRBs connected with SNe to be ρ0,b ≤ 770 Gpc-3 yr-1. We estimate that Fermi/GBM could detect 1-4 GRBs-SNe within z ≤ 0.2 in the next 4 years.

  9. Fermi gamma-ray imaging of a radio galaxy.

    PubMed

    Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Celik, O; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Colafrancesco, S; Cominsky, L R; Conrad, J; Costamante, L; Cutini, S; Davis, D S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Finke, J; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Georganopoulos, M; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sambruna, R; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sgrò, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, Ł; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M; Hardcastle, M J; Kazanas, D

    2010-05-07

    The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.

  10. Holographic non-Fermi-liquid fixed points.

    PubMed

    Faulkner, Tom; Iqbal, Nabil; Liu, Hong; McGreevy, John; Vegh, David

    2011-04-28

    Techniques arising from string theory can be used to study assemblies of strongly interacting fermions. Via this 'holographic duality', various strongly coupled many-body systems are solved using an auxiliary theory of gravity. Simple holographic realizations of finite density exhibit single-particle spectral functions with sharp Fermi surfaces, of a form distinct from those of the Landau theory. The self-energy is given by a correlation function in an infrared (IR) fixed-point theory that is represented by a two-dimensional anti de Sitter space (AdS(2)) region in the dual gravitational description. Here, we describe in detail the gravity calculation of this IR correlation function.

  11. Unitary Fermi gas in a harmonic trap

    NASA Astrophysics Data System (ADS)

    Chang, S. Y.; Bertsch, G. F.

    2007-08-01

    We present an ab initio calculation of small numbers of trapped, strongly interacting fermions using the Green’s function Monte Carlo method. The ground-state energy, density profile, and pairing gap are calculated for particle numbers N=2 22 using the parameter-free “unitary” interaction. Trial wave functions are taken in the form of correlated pairs in a harmonic oscillator basis. We find that the lowest energies are obtained with a minimum explicit pair correlation beyond that needed to exploit the degeneracy of oscillator states. We find that the energies can be well fitted by the expression aTFETF+Δmod(N,2) where ETF is the Thomas-Fermi energy of a noninteracting gas in the trap and Δ is the pairing gap. There is no evidence of a shell correction energy in the systematics, but the density distributions show pronounced shell effects. We find the value Δ=0.7±0.2ω for the pairing gap. This is smaller than the value found for the uniform gas at a density corresponding to the central density of the trapped gas.

  12. The first Fermi-LAT catalog of sources above 10 GeV

    DOE PAGES

    Ackermann, M.; Ajello, M.; Allafort, A.; ...

    2013-11-14

    Here, we present a catalog of γ-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during the first 3 yr of the Fermi Gamma-ray Space Telescope mission. The first Fermi-LAT catalog of >10 GeV sources (1FHL) has 514 sources. For each source we present location, spectrum, a measure of variability, and associations with cataloged sources at other wavelengths. We found that 449 (87%) could be associated with known sources, of which 393 (76% of the 1FHL sources) are active galactic nuclei. Of the 27 sources associated with known pulsars, we find 20more » (12) to have significant pulsations in the range >10 GeV (>25 GeV). In this work we also report that, at energies above 10 GeV, unresolved sources account for 27% ± 8% of the isotropic γ-ray background, while the unresolved Galactic population contributes only at the few percent level to the Galactic diffuse background. We also highlight the subset of the 1FHL sources that are best candidates for detection at energies above 50-100 GeV with current and future ground-based γ-ray observatories.« less

  13. Measurement of the High-Energy Gamma-Ray Emission from the Moon with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; hide

    2016-01-01

    We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first seven years of operation, in the energy range from 30 MeV up to a few GeV. We have also studied the time evolution of the flux, finding a correlation with the solar activity. We have developed a full Monte Carlo simulation describing the interactions of cosmic rays with the lunar surface. The results of the present analysis can be explained in the framework of this model, where the production of gamma rays is due to the interactions of cosmic-ray proton and helium nuclei with the surface of the Moon. Finally, we have used our simulation to derive the cosmic-ray proton and helium spectra near Earth from the Moon gamma-ray data.

  14. On possible interpretations of the high energy electron–positron spectrum measured by the Fermi Large Area Telescope

    DOE PAGES

    Grasso, D.; Profumo, S.; Strong, A. W.; ...

    2009-07-11

    The Fermi-LAT experiment recently reported high precision measurements of the spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV. The spectrum shows no prominent spectral features, and is significantly harder than that inferred from several previous experiments. In this paper, we discuss several interpretations of the Fermi results based either on a single large scale Galactic CRE component or by invoking additional electron–positron primary sources, e.g. nearby pulsars or particle dark matter annihilation. We show that while the reported Fermi-LAT data alone can be interpreted in terms of a single component scenario, when combined with other complementary experimentalmore » results, specifically the CRE spectrum measured by H.E.S.S. and especially the positron fraction reported by PAMELA between 1 and 100 GeV, that class of models fails to provide a consistent interpretation. Rather, we find that several combinations of parameters, involving both the pulsar and dark matter scenarios, allow a consistent description of those results. Finally, we also briefly discuss the possibility of discriminating between the pulsar and dark matter interpretations by looking for a possible anisotropy in the CRE flux.« less

  15. Fermi-LAT detection of increased gamma-ray activity of TXS 0506+056, located inside the IceCube-170922A error region.

    NASA Astrophysics Data System (ADS)

    Tanaka, Yasuyuki T.; Buson, Sara; Kocevski, Daniel

    2017-09-01

    We searched for Fermi-LAT sources inside the extremely high-energy (EHE) IceCube-170922A neutrino event error region (https://gcn.gsfc.nasa.gov/gcn3/21916.gcn3, see also ATels 10773, 10787) with all-sky survey data from the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope.

  16. Fermi-LAT observations of the gamma-ray burst GRB 130427A.

    PubMed

    Ackermann, M; Ajello, M; Asano, K; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Baring, M G; Bastieri, D; Bechtol, K; Bellazzini, R; Bissaldi, E; Bonamente, E; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Burgess, J Michael; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Cecchi, C; Chaplin, V; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Chiaro, G; Ciprini, S; Claus, R; Cleveland, W; Cohen-Tanugi, J; Collazzi, A; Cominsky, L R; Connaughton, V; Conrad, J; Cutini, S; D'Ammando, F; de Angelis, A; DeKlotz, M; de Palma, F; Dermer, C D; Desiante, R; Diekmann, A; Di Venere, L; Drell, P S; Drlica-Wagner, A; Favuzzi, C; Fegan, S J; Ferrara, E C; Finke, J; Fitzpatrick, G; Focke, W B; Franckowiak, A; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gehrels, N; Germani, S; Gibby, M; Giglietto, N; Giles, M; Giordano, F; Giroletti, M; Godfrey, G; Granot, J; Grenier, I A; Grove, J E; Gruber, D; Guiriec, S; Hadasch, D; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Horan, D; Hughes, R E; Inoue, Y; Jogler, T; Jóhannesson, G; Johnson, W N; Kawano, T; Knödlseder, J; Kocevski, D; Kuss, M; Lande, J; Larsson, S; Latronico, L; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Mayer, M; Mazziotta, M N; McEnery, J E; Michelson, P F; Mizuno, T; Moiseev, A A; Monzani, M E; Moretti, E; Morselli, A; Moskalenko, I V; Murgia, S; Nemmen, R; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orienti, M; Paneque, D; Pelassa, V; Perkins, J S; Pesce-Rollins, M; Petrosian, V; Piron, F; Pivato, G; Porter, T A; Racusin, J L; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Ritz, S; Roth, M; Ryde, F; Sartori, A; Parkinson, P M Saz; Scargle, J D; Schulz, A; Sgrò, C; Siskind, E J; Sonbas, E; Spandre, G; Spinelli, P; Tajima, H; Takahashi, H; Thayer, J G; Thayer, J B; Thompson, D J; Tibaldo, L; Tinivella, M; Torres, D F; Tosti, G; Troja, E; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Winer, B L; Wood, K S; Yamazaki, R; Younes, G; Yu, H-F; Zhu, S J; Bhat, P N; Briggs, M S; Byrne, D; Foley, S; Goldstein, A; Jenke, P; Kippen, R M; Kouveliotou, C; McBreen, S; Meegan, C; Paciesas, W S; Preece, R; Rau, A; Tierney, D; van der Horst, A J; von Kienlin, A; Wilson-Hodge, C; Xiong, S; Cusumano, G; La Parola, V; Cummings, J R

    2014-01-03

    The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

  17. Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; hide

    2013-01-01

    The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources. GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest gamma-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

  18. The Spectrum and Morphology of the Fermi Bubbles

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Albert, A.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazini, R.; Bissaldi, E.; Brandt, T. J.; hide

    2014-01-01

    The Fermi bubbles are two large structures in the gamma-ray sky extending to 55 deg above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10 deg in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7 sigma significance. The power law with an exponential cutoff has an index of 1.90+/-0.2 and a cutoff energy of 110+/- 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4(+)2.4(-0.9 ) 10(exp 37) erg s-1. We confirm a significant enhancement of gamma-ray emission in the south-eastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4(+)3.7(-)2.6 deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons t the gamma-ray data well. In the IC scenario, the synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 micro-G.

  19. High-energy gamma-ray emission from solar flares: Summary of Fermi large area telescope detections and analysis of two m-class flares

    DOE PAGES

    Ackermann, M.; Ajello, M.; Albert, A.; ...

    2014-04-29

    Here, we present the detections of 18 solar flares detected in high-energy γ-rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first 4 yr of operation. Our work suggests that particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. Interestingly, all these flares are associated with fairly fast coronal mass ejections (CMEs). We then describe the detailed temporal, spatial, and spectral characteristics of the first two long-lasting events: the 2011 March 7 flare, a moderate (M3.7) impulsive flare followed bymore » slowly varying γ-ray emission over 13 hr, and the 2011 June 7 M2.5 flare, which was followed by γ-ray emission lasting for 2 hr. We compare the Fermi LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that the γ-rays are more likely produced through pion decay than electron bremsstrahlung, and we find that the energy spectrum of the proton distribution softens during the extended emission of the 2011 March 7 flare. Furthermore, this would disfavor a trapping scenario for particles accelerated during the impulsive phase of the flare and point to a continuous acceleration process at play for the duration of the flares. CME shocks are known for accelerating the solar energetic particles (SEPs) observed in situ on similar timescales, but it might be challenging to explain the production of γ-rays at the surface of the Sun while the CME is halfway to the Earth. A stochastic turbulence acceleration process occurring in the solar corona is another likely scenario. Detailed comparison of characteristics of SEPs and γ-ray-emitting particles for several flares will be helpful to distinguish between these two possibilities.« less

  20. All-Sky Earth Occultation Observations with the Fermi Gamma-Ray Burst Monitor

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, C. A.; Beklen, E.; Bhat, P. N.; Briggs, M.; Camero-Arranz, A.; Case, G.; Jenke, P.; Chaplin, V.; Cherry, M.; Connaughton, V.; hide

    2009-01-01

    Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/ soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog is occulted by (or exits occultation by) the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. In addition, to Earth occultations, we have observed numerous occultations with Fermi's solar panels.

  1. Spectral probes of the holographic Fermi ground state: Dialing between the electron star and AdS Dirac hair

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Cubrovic, Mihailo; Liu Yan; Schalm, Koenraad

    2011-10-15

    We argue that the electron star and the anti-de Sitter (AdS) Dirac hair solution are two limits of the free charged Fermi gas in AdS. Spectral functions of holographic duals to probe fermions in the background of electron stars have a free parameter that quantifies the number of constituent fermions that make up the charge and energy density characterizing the electron star solution. The strict electron star limit takes this number to be infinite. The Dirac hair solution is the limit where this number is unity. This is evident in the behavior of the distribution of holographically dual Fermi surfaces.more » As we decrease the number of constituents in a fixed electron star background the number of Fermi surfaces also decreases. An improved holographic Fermi ground state should be a configuration that shares the qualitative properties of both limits.« less

  2. Trial densities for the extended Thomas-Fermi model

    NASA Astrophysics Data System (ADS)

    Yu, An; Jimin, Hu

    1996-02-01

    A new and simplified form of nuclear densities is proposed for the extended Thomas-Fermi method (ETF) and applied to calculate the ground-state properties of several spherical nuclei, with results comparable or even better than other conventional density profiles. With the expectation value method (EVM) for microscopic corrections we checked our new densities for spherical nuclei. The binding energies of ground states almost reproduce the Hartree-Fock (HF) calculations exactly. Further applications to nuclei far away from the β-stability line are discussed.

  3. Terrestrial Gamma-ray Flashes (TGFs) Observed with the Fermi-Gamma-ray Burst Monitor: Temporal and Spectral Properties

    NASA Technical Reports Server (NTRS)

    Fishman, G. J.; Briggs, M. S.; Connaughton, W.; Wilson-Hodge, C.; Bhat, P. N.

    2010-01-01

    The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope Observatory (Fermi) was detecting 2.1 TGFs per week. This rate has increased by a factor of 8 since new flight software was uploaded to the spacecraft in November 2009 in order to increase the sensitivity of GBM to TGFs. Further upgrades to Fermi-GBM to allow observations of weaker TGFs are in progress. The high time resolution (2 s) allows temporal features to be resolved so that some insight may be gained on the origin and transport of the gamma-ray photons through the atmosphere. The absolute time of the TGFs, known to several microseconds, also allows accurate correlations of TGFs with lightning networks and other lightning-related phenomena. The thick bismuth germanate (BGO) scintillation detectors of the GBM system have observed photon energies from TGFs at energies above 40 MeV. New results on the some temporal aspects of TGFs will be presented along with spectral characteristics and properties of several electron-positron TGF events that have been identified.

  4. Fermi Large Area Telescope detection of two very-high-energy ( E > 100 GeV) γ-ray photons from the z = 1.1 blazar PKS 0426–380

    DOE PAGES

    Tanaka, Y. T.; Cheung, C. C.; Inoue, Y.; ...

    2013-10-18

    Here, we report the Fermi Large Area Telescope (LAT) detection of two very-high-energy (VHE, E > 100 GeV) γ-ray photons from the directional vicinity of the distant (redshift, z = 1.1) blazar PKS 0426–380. The null hypothesis that both the 134 and 122 GeV photons originate from unrelated sources can be rejected at the 5.5σ confidence level. We therefore claim that at least one of the two VHE photons is securely associated with PKS 0426–380, making it the most distant VHE emitter known to date. The results are in agreement with recent Fermi-LAT constraints on the extragalactic background light (EBL)more » intensity, which imply a z sime 1 horizon for sime 100 GeV photons. The LAT detection of the two VHE γ-rays coincided roughly with flaring states of the source, although we did not find an exact correspondence between the VHE photon arrival times and the flux maxima at lower γ-ray energies. Modeling the γ-ray continuum of PKS 0426–380 with daily bins revealed a significant spectral hardening around the time of the first VHE event detection (LAT photon index Γ sime 1.4) but on the other hand no pronounced spectral changes near the detection time of the second one. This combination implies a rather complex variability pattern of the source in γ-rays during the flaring epochs. An additional flat component is possibly present above several tens of GeV in the EBL-corrected Fermi-LAT spectrum accumulated over the ~8 month high state.« less

  5. Observation of Fermi arcs in the type-II Weyl semimetal candidate WTe 2

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Wu, Yun; Mou, Daixiang; Jo, Na Hyun

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe 2, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe 2 were proposed to emerge at the crossing points of electron and hole pockets, and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe 2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe 2. Here, we alsomore » find that trivial and topological domains coexist on the same surface of the sample due to the presence of inhomogeneous strain detected by scanning electron microscopy data. This is in agreement with the theoretical prediction that strain can drive this system from topological Weyl to trivial semimetal. WTe 2 therefore provides a tunable playground for studying exotic topological quantum effects.« less

  6. Observation of Fermi arcs in the type-II Weyl semimetal candidate WTe 2

    DOE PAGES

    Wu, Yun; Mou, Daixiang; Jo, Na Hyun; ...

    2016-09-14

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe 2, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe 2 were proposed to emerge at the crossing points of electron and hole pockets, and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe 2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe 2. Here, we alsomore » find that trivial and topological domains coexist on the same surface of the sample due to the presence of inhomogeneous strain detected by scanning electron microscopy data. This is in agreement with the theoretical prediction that strain can drive this system from topological Weyl to trivial semimetal. WTe 2 therefore provides a tunable playground for studying exotic topological quantum effects.« less

  7. FermiGrid—experience and future plans

    NASA Astrophysics Data System (ADS)

    Chadwick, K.; Berman, E.; Canal, P.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Sharma, N.; Timm, S.; Yocum, D. R.

    2008-07-01

    Fermilab supports a scientific program that includes experiments and scientists located across the globe. In order to better serve this community, Fermilab has placed its production computer resources in a Campus Grid infrastructure called 'FermiGrid'. The FermiGrid infrastructure allows the large experiments at Fermilab to have priority access to their own resources, enables sharing of these resources in an opportunistic fashion, and movement of work (jobs, data) between the Campus Grid and National Grids such as Open Science Grid (OSG) and the Worldwide LHC Computing Grid Collaboration (WLCG). FermiGrid resources support multiple Virtual Organizations (VOs), including VOs from the OSG, EGEE, and the WLCG. Fermilab also makes leading contributions to the Open Science Grid in the areas of accounting, batch computing, grid security, job management, resource selection, site infrastructure, storage management, and VO services. Through the FermiGrid interfaces, authenticated and authorized VOs and individuals may access our core grid services, the 10,000+ Fermilab resident CPUs, near-petabyte (including CMS) online disk pools and the multi-petabyte Fermilab Mass Storage System. These core grid services include a site wide Globus gatekeeper, VO management services for several VOs, Fermilab site authorization services, grid user mapping services, as well as job accounting and monitoring, resource selection and data movement services. Access to these services is via standard and well-supported grid interfaces. We will report on the user experience of using the FermiGrid campus infrastructure interfaced to a national cyberinfrastructure - the successes and the problems.

  8. FermiGrid - experience and future plans

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Chadwick, K.; Berman, E.; Canal, P.

    2007-09-01

    Fermilab supports a scientific program that includes experiments and scientists located across the globe. In order to better serve this community, Fermilab has placed its production computer resources in a Campus Grid infrastructure called 'FermiGrid'. The FermiGrid infrastructure allows the large experiments at Fermilab to have priority access to their own resources, enables sharing of these resources in an opportunistic fashion, and movement of work (jobs, data) between the Campus Grid and National Grids such as Open Science Grid and the WLCG. FermiGrid resources support multiple Virtual Organizations (VOs), including VOs from the Open Science Grid (OSG), EGEE and themore » Worldwide LHC Computing Grid Collaboration (WLCG). Fermilab also makes leading contributions to the Open Science Grid in the areas of accounting, batch computing, grid security, job management, resource selection, site infrastructure, storage management, and VO services. Through the FermiGrid interfaces, authenticated and authorized VOs and individuals may access our core grid services, the 10,000+ Fermilab resident CPUs, near-petabyte (including CMS) online disk pools and the multi-petabyte Fermilab Mass Storage System. These core grid services include a site wide Globus gatekeeper, VO management services for several VOs, Fermilab site authorization services, grid user mapping services, as well as job accounting and monitoring, resource selection and data movement services. Access to these services is via standard and well-supported grid interfaces. We will report on the user experience of using the FermiGrid campus infrastructure interfaced to a national cyberinfrastructure--the successes and the problems.« less

  9. Discovery of gamma- and X-ray pulsations from the young and energetic PSR J1357$-$6429 with Fermi and XMM-Newton

    DOE PAGES

    Lemoine-Goumard, M.; Zavlin, V. E.; Grondin, M. -H.; ...

    2011-09-07

    Context. Since the launch of the Fermi satellite, the number of known gamma-ray pulsars has increased tenfold. Most gamma-ray detected pulsars are young and energetic, and many are associated with TeV sources. PSR J1357-6429 is a high spin-down power pulsar (È = 3.1 × 1036 erg s -1), discovered during the Parkes multibeam survey of the Galactic plane, with significant timing noise typical of very young pulsars. In the very-high-energy domain (E > 100 GeV), H.E.S.S. has reported the detection of the extended source HESS J1356-645 (intrinsic Gaussian width of 12') whose centroid lies 7' from PSR J1357-6429. Aims. Wemore » search for gamma- and X-ray pulsations from this pulsar, characterize the neutron star emission and explore the environment of PSR J1357-6429. Methods. Using a rotational ephemeris obtained with 74 observations made with the Parkes telescope at 1.4 GHz, we phase-fold more than two years of gamma-ray data acquired by the Large Area Telescope on-board Fermi as well as those collected with XMM-Newton, and perform gamma-ray spectral modeling. Results. Significant gamma- and X-ray pulsations are detected from PSR J1357-6429. The light curve in both bands shows one broad peak. Gamma-ray spectral analysis of the pulsed emission suggests that it is well described by a simple power-law of index 1.5 ± 0.3 stat ± 0.3 syst with an exponential cut-off at 0.8 ± 0.3 stat ± 0.3 syst GeV and an integral photon flux above 100 MeV of (6.5 ± 1.6 stat ± 2.3 syst) × 10 -8 cm -2 s -1. The X-ray spectra obtained from the new data provide results consistent with previous work. Upper limits on the gamma-ray emission from its potential pulsar wind nebula (PWN) are also reported. Conclusions. Assuming a distance of 2.4 kpc, the Fermi LAT energy flux yields a gamma-ray luminosity for PSR J1357-6429 of L γ = (2.13 ± 0.25 stat ± 0.83 syst) × 1034 erg s -1, consistent with an relationship. The Fermi non-detection of the pulsar wind nebula associated with HESS J1356

  10. Non-Fermi-liquid to Fermi-liquid transports in iron-pnictide Ba(Fe1-x Co x )2As2 and the electronic correlation strength in superconductors newly probed by the normal-state Hall angle

    NASA Astrophysics Data System (ADS)

    Wang, L. M.; Wang, Chih-Yi; Zen, Sha-Min; Chang, Jin-Yuan; Kuo, C. N.; Lue, C. S.; Chang, L. J.; Su, Y.; Wolf, Th; Adelmann, P.

    2017-03-01

    Electrical transports in iron-pnictide Ba(Fe1-x Co x )2As2 (BFCA) single crystals are heavily debated in terms of the hidden Fermi-liquid (HFL) and holographic theories. Both HFL and holographic theories provide consistent physic pictures and propose a universal expression of resistivity to describe the crossover of transports from the non-Fermi-liquid (FL) to FL behavior in these so-called ‘strange metal’ systems. The deduced spin exchange energy J and model-dependent energy scale W in BFCA are almost the same, or are of the same order of several hundred Kelvin for over-doped BFCA, which is in agreement with the HFL theory. Moreover, a drawn line of W/3.5 for BFCA in the higher-doping region up to the right demonstrates the crossover from non-FL-like behavior to FL-like behavior at high doping, and shows a new phase diagram of BFCA. The electronic correlation strength in superconductors has been newly probed by the normal-state Hall angle, which found that, for the first time, correlation strength can be characterized by the ratios of T c to the Fermi temperature T F, J/T F, and the transverse mass to longitudinal mass.

  11. Radio core dominance of Fermi blazars

    NASA Astrophysics Data System (ADS)

    Pei, Zhi-Yuan; Fan, Jun-Hui; Liu, Yi; Yuan, Yi-Hai; Cai, Wei; Xiao, Hu-Bing; Lin, Chao; Yang, Jiang-He

    2016-07-01

    During the first 4 years of mission, Fermi/LAT detected 1444 blazars (3FGL) (Ackermann et al. in Astrophys. J. 810:14, 2015). Fermi/LAT observations of blazars indicate that Fermi blazars are luminous and strongly variable with variability time scales, for some cases, as short as hours. Those observations suggest a strong beaming effect in Fermi/LAT blazars. In the present work, we will investigate the beaming effect in Fermi/LAT blazars using a core-dominance parameter, R = S_{core}/ S_{ext.}, where S_{core} is the core emission, while S_{ext.} is the extended emission. We compiled 1335 blazars with available core-dominance parameter, out of which 169 blazars have γ-ray emission (from 3FGL). We compared the core-dominance parameters, log R, between the 169 Fermi-detected blazars (FDBs) and the rest non-Fermi-detected blazars (non-FDBs), and we found that the averaged values are < log Rrangle = 0.99±0.87 for FDBs and < log Rrangle = -0.62±1.15 for the non-FDBs. A K-S test shows that the probability for the two distributions of FDBs and non-FDBs to come from the same parent distribution is near zero (P =9.12×10^{-52}). Secondly, we also investigated the variability index (V.I.) in the γ-ray band for FDBs, and we found V.I.=(0.12 ±0.07) log R+(2.25±0.10), suggesting that a source with larger log R has larger V.I. value. Thirdly, we compared the mean values of radio spectral index for FDBs and non-FDBs, and we obtained < α_{radio}rangle =0.06±0.35 for FDBs and < α_{radio}rangle =0.57±0.46 for non-FDBs. If γ-rays are composed of two components like radio emission (core and extended components), then we can expect a correlation between log R and the γ-ray spectral index. When we used the radio core-dominance parameter, log R, to investigate the relationship, we found that the spectral index for the core component is α_{γ}|_{core} = 1.11 (a photon spectral index of α_{γ}^{ph}|_{core} = 2.11) and that for the extended component is α_{γ}|_{ext.} = 0

  12. Fermi Gamma-Ray Imaging of a Radio Galaxy

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2010-04-01

    The Fermi Gamma-ray Space Telescope has detected the γ-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved γ-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy γ-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The γ-ray emission from the lobes is interpreted as inverse Compton–scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. In conclusion, these measurements provide γ-raymore » constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.« less

  13. VizieR Online Data Catalog: Fermi-LAT flaring gamma-ray sources from FAVA (Ackermann+, 2013)

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ajello, M.; Albert, A.; Allafort, A.; Antolini, E.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Bottacini, E.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cutini, S.; Dalton, M.; D'Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; di Venere, L.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hewitt, J.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Inoue, Y.; Jackson, M. S.; Jogler, T.; Johannesson, G.; Johnson, W. N.; Kamae, T.; Kataoka, J.; Kawano, T.; Knodlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nemmen, R.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Raino, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Romoli, C.; Roth, M.; Sanchez-Conde, M.; Scargle, J. D.; Schulz, A.; Sgro, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Suson, D. J.; Takahashi, H.; Takeuchi, Y.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Tronconi, V.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Winer, B. L.; Wood, K. S.; Wood, M.; Yang, Z.

    2015-01-01

    We applied FAVA (Fermi All-sky Variability Analysis) to the first 47 months of Fermi/LAT observations (2008 August 4 to 2012 July 16 UTC), in weekly time intervals. The total number of weeks is 206. We considered two ranges of gamma-ray energy, E>100MeV and E>800MeV, to increase the sensitivity for spectrally soft and hard flares, respectively. We generate measured and expected count maps with a resolution of 0.25deg2 per pixel. We found LAT counterparts for 192 of the 215 FAVA sources. Most of the associated sources, 177, are AGNs. (2 data files).

  14. Detection of a Fermi-level crossing in Si(557)-Au with inverse photoemission

    NASA Astrophysics Data System (ADS)

    Lipton-Duffin, J. A.; MacLeod, J. M.; McLean, A. B.

    2006-06-01

    The unoccupied energy bands of the quasi-one-dimensional (1D) Si(557)-Au system have been studied with momentum-resolved inverse photoemission. A band is found that lies (0.4±0.4)eV above the Fermi level at the center of the surface Brillouin zone (Γ¯) . It disperses to higher binding energy, along the Γ Kmacr direction, and crosses the Fermi level at k‖=0.5±0.1Å-1 . The corresponding direction in real space is parallel to both the rows of silicon adatoms and the rows of embedded gold atoms that are distinctive features of this surface reconstruction. The location of the crossing is in good agreement with previously published photoemission data [Altmann , Phys. Rev. B 64, 035406 (2001); Ahn , Phys. Rev. Lett. 91, 196403 (2003)], where two closely spaced bands were found to disperse from the Kmacr zone boundary to lower binding energy and then cross the Fermi level. In addition to the band mentioned above, a band was found that has parabolic dispersion along Γ Kmacr , the direction that is parallel to the rows of embedded gold atoms. The band minimum for the parabolic band lies (0.8±0.4)eV below the vacuum level and it has an effective mass m*=(1.0±0.1)me , where me is the free electron mass. Perpendicular to the rows of gold atoms, as expected for a state with quasi-1D symmetry, it has flat dispersion. This band may be an image state resonance, overlapping the silicon conduction band continuum, and it is spatially localized to the edge of the silicon terraces.

  15. Measurement of the high-energy gamma-ray emission from the Moon with the Fermi Large Area Telescope

    DOE PAGES

    Ackermann, M.; Ajello, M.; Albert, A.; ...

    2016-04-08

    We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first seven years of operation, in the energy range from 30 MeV up to a few GeV. We have also studied the time evolution of the flux, finding a correlation with the solar activity. We have developed a full Monte Carlo simulation describing the interactions of cosmic rays with the lunar surface. The results of the present analysis can be explained in the framework of this model, where the production of gamma rays is duemore » to the interactions of cosmic-ray proton and helium nuclei with the surface of the Moon. Lastly, we have used our simulation to derive the cosmic-ray proton and helium spectra near Earth from the Moon gamma-ray data.« less

  16. Secondary electron emission yield dependence on the Fermi level in Silicon

    NASA Astrophysics Data System (ADS)

    Urrabazo, David; Goeckner, Matthew; Overzet, Lawrence

    2013-09-01

    Secondary Electron Emission (SEE) by ion bombardment plays a key role in determining the properties of many plasmas. As a result, significant efforts have been expended to control the SEE coefficient (increasing or decreasing it) by tailoring the electron work function of surfaces. A few recent publications point to the possibility of controlling the SEE coefficient of semiconductor surfaces in real time through controlling the numbers of electrons in the conduction band near the surface. Large control over the plasma was achieved by injecting electrons into the semiconductor just under the cathode surface via a subsurface PN junction. The hypothesis was that SEE is dependent on the numbers of electrons in the conduction band near the surface (which is related to the position of the Fermi level near the surface). We are testing the validity of this hypothesis. We have begun fundamental ion beam studies to explore this possible dependence of SEE on the Fermi energy level using Si. Various doping levels and dopants are being evaluated and the results of these tests will be presented. This work was supported in part by US Dept. of Energy. Acknowledgement to Dr. L. Raja at UT Austin.

  17. SLAC All Access: Fermi Gamma-ray Space Telescope

    ScienceCinema

    Romani, Roger

    2018-04-16

    Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

  18. Fermi level dependence of hydrogen diffusivity in GaN

    NASA Astrophysics Data System (ADS)

    Polyakov, A. Y.; Smirnov, N. B.; Pearton, S. J.; Ren, F.; Theys, B.; Jomard, F.; Teukam, Z.; Dmitriev, V. A.; Nikolaev, A. E.; Usikov, A. S.; Nikitina, I. P.

    2001-09-01

    Hydrogen diffusion studies were performed in GaN samples with different Fermi level positions. It is shown that, at 350 °C, hydrogen diffusion is quite fast in heavily Mg doped p-type material with the Fermi level close to Ev+0.15 eV, considerably slower in high-resistivity p-GaN(Zn) with the Fermi level Ev+0.9 eV, while for conducting and semi-insulating n-GaN samples with the Fermi level in the upper half of the band gap no measurable hydrogen diffusion could be detected. For these latter samples it is shown that higher diffusion temperature of 500 °C and longer times (50 h) are necessary to incorporate hydrogen to appreciable depth. These findings are in line with previously published theoretical predictions of the dependence of hydrogen interstitials formation in GaN on the Fermi level position.

  19. Observation strategies with the Fermi Gamma-ray Space Telescope

    NASA Astrophysics Data System (ADS)

    McEnery, Julie E.; Fermi mission Teams

    2015-01-01

    During the first few years of the Fermi mission, the default observation mode has been an all-sky survey, optimized to provide relatively uniform coverage of the entire sky every three hours. Over 95% of the mission has been performed in this observation mode. However, Fermi is capable of flexible survey mode patterns, and inertially pointed observations both of which allow increased coverage of selected parts of the sky. In this presentation, we will describe the types of observations that Fermi can make, the relative advantages and disadvantages of various observations, and provide guidelines to help Fermi users plan and evaluate non-standard observations.

  20. Non-Fermi liquids in oxide heterostructures

    NASA Astrophysics Data System (ADS)

    Stemmer, Susanne; Allen, S. James

    2018-06-01

    Understanding the anomalous transport properties of strongly correlated materials is one of the most formidable challenges in condensed matter physics. For example, one encounters metal-insulator transitions, deviations from Landau Fermi liquid behavior, longitudinal and Hall scattering rate separation, a pseudogap phase, and bad metal behavior. These properties have been studied extensively in bulk materials, such as the unconventional superconductors and heavy fermion systems. Oxide heterostructures have recently emerged as new platforms to probe, control, and understand strong correlation phenomena. This article focuses on unconventional transport phenomena in oxide thin film systems. We use specific systems as examples, namely charge carriers in SrTiO3 layers and interfaces with SrTiO3, and strained rare earth nickelate thin films. While doped SrTiO3 layers appear to be a well behaved, though complex, electron gas or Fermi liquid, the rare earth nickelates are a highly correlated electron system that may be classified as a non-Fermi liquid. We discuss insights into the underlying physics that can be gained from studying the emergence of non-Fermi liquid behavior as a function of the heterostructure parameters. We also discuss the role of lattice symmetry and disorder in phenomena such as metal-insulator transitions in strongly correlated heterostructures.

  1. Quadratic Fermi node in a 3D strongly correlated semimetal

    DOE PAGES

    Kondo, Takeshi; Nakayama, M.; Chen, R.; ...

    2015-12-07

    We report that strong spin–orbit coupling fosters exotic electronic states such as topological insulators and superconductors, but the combination of strong spin–orbit and strong electron–electron interactions is just beginning to be understood. Central to this emerging area are the 5d transition metal iridium oxides. Here, in the pyrochlore iridate Pr 2Ir 2O 7, we identify a non-trivial state with a single-point Fermi node protected by cubic and time-reversal symmetries, using a combination of angle-resolved photoemission spectroscopy and first-principles calculations. Owing to its quadratic dispersion, the unique coincidence of four degenerate states at the Fermi energy, and strong Coulomb interactions, non-Fermimore » liquid behaviour is predicted, for which we observe some evidence. Lastly, our discovery implies that Pr 2Ir 2O 7 is a parent state that can be manipulated to produce other strongly correlated topological phases, such as topological Mott insulator, Weyl semimetal, and quantum spin and anomalous Hall states.« less

  2. Enrico Fermi and the Dolomites

    NASA Astrophysics Data System (ADS)

    Battimelli, Giovanni; de Angelis, Alessandro

    2014-11-01

    Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.

  3. Relativistic equation of state at subnuclear densities in the Thomas-Fermi approximation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Zhang, Z. W.; Shen, H., E-mail: shennankai@gmail.com

    We study the non-uniform nuclear matter using the self-consistent Thomas-Fermi approximation with a relativistic mean-field model. The non-uniform matter is assumed to be composed of a lattice of heavy nuclei surrounded by dripped nucleons. At each temperature T, proton fraction Y{sub p} , and baryon mass density ρ {sub B}, we determine the thermodynamically favored state by minimizing the free energy with respect to the radius of the Wigner-Seitz cell, while the nucleon distribution in the cell can be determined self-consistently in the Thomas-Fermi approximation. A detailed comparison is made between the present results and previous calculations in the Thomas-Fermimore » approximation with a parameterized nucleon distribution that has been adopted in the widely used Shen equation of state.« less

  4. Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A

    DOE PAGES

    Ackermann, M.; Ajello, M.; Asano, K.; ...

    2013-11-21

    The Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide constraints on the nature of these unique astrophysical sources using the observations of the exceptionally bright gamma-ray burst (GRB) 130427A. We found that GRB 130427A had the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 hours), and one of the largest isotropic energy releases ever observed from a GRB. Temporal and spectral analyses of GRB 130427A challenge the widely accepted model that the nonthermal high-energy emission in the afterglow phase of GRBs is synchrotron emission radiated by electrons accelerated at an external shock.

  5. THE THIRD FERMI GBM GAMMA-RAY BURST CATALOG: THE FIRST SIX YEARS

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bhat, P. Narayana; Meegan, Charles A.; Briggs, Michael S.

    2016-04-01

    Since its launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has triggered and located on average approximately two γ -ray bursts (GRBs) every three days. Here, we present the third of a series of catalogs of GRBs detected by GBM, extending the second catalog by two more years through the middle of 2014 July. The resulting list includes 1405 triggers identified as GRBs. The intention of the GBM GRB catalog is to provide information to the community on the most important observables of the GBM-detected GRBs. For each GRB, the location and main characteristics of the prompt emission, themore » duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50–300 keV energy band where the maximum energy release of GRBs in the instrument reference system is observed, and also for a broader energy band from 10 to 1000 keV, exploiting the full energy range of GBM's low-energy [Nai[Tl)] detectors. Using statistical methods to assess clustering, we find that the hardness and duration of GRBs are better fit by a two-component model with short-hard and long-soft bursts than by a model with three components. Furthermore, information is provided on the settings and modifications of the triggering criteria and exceptional operational conditions during years five and six in the mission. This third catalog is an official product of the Fermi GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.« less

  6. Hilbert transform evaluation for electron-phonon self-energies

    NASA Astrophysics Data System (ADS)

    Bevilacqua, Giuseppe; Menichetti, Guido; Pastori Parravicini, Giuseppe

    2016-01-01

    The electron tunneling current through nanostructures is considered in the presence of the electron-phonon interactions. In the Keldysh nonequilibrium formalism, the lesser, greater, advanced and retarded self-energies components are expressed by means of appropriate Langreth rules. We discuss the key role played by the entailed Hilbert transforms, and provide an analytic way for their evaluation. Particular attention is given to the current-conserving lowest-order-expansion for the treament of the electron-phonon interaction; by means of an appropriate elaboration of the analytic properties and pole structure of the Green's functions and of the Fermi functions, we arrive at a surprising simple, elegant, fully analytic and easy-to-use expression of the Hilbert transforms and involved integrals in the energy domain.

  7. Quasiparticle lifetime in a mixture of Bose and Fermi superfluids.

    PubMed

    Zheng, Wei; Zhai, Hui

    2014-12-31

    In this Letter, we study the effect of quasiparticle interactions in a Bose-Fermi superfluid mixture. We consider the lifetime of a quasiparticle of the Bose superfluid due to its interaction with quasiparticles in the Fermi superfluid. We find that this damping rate, i.e., the inverse of the lifetime, has quite a different threshold behavior at the BCS and the BEC side of the Fermi superfluid. The damping rate is a constant near the threshold momentum in the BCS side, while it increases rapidly in the BEC side. This is because, in the BCS side, the decay process is restricted by the constraint that the fermion quasiparticle is located near the Fermi surface, while such a restriction does not exist in the BEC side where the damping process is dominated by bosonic quasiparticles of the Fermi superfluid. Our results are related to the collective mode experiment in the recently realized Bose-Fermi superfluid mixture.

  8. Particle localization, spinor two-valuedness, and Fermi quantization of tensor systems

    NASA Technical Reports Server (NTRS)

    Reifler, Frank; Morris, Randall

    1994-01-01

    Recent studies of particle localization shows that square-integrable positive energy bispinor fields in a Minkowski space-time cannot be physically distinguished from constrained tensor fields. In this paper we generalize this result by characterizing all classical tensor systems, which admit Fermi quantization, as those having unitary Lie-Poisson brackets. Examples include Euler's tensor equation for a rigid body and Dirac's equation in tensor form.

  9. The Spectrum And Morphology Of The Fermi Bubbles

    DOE PAGES

    Ackermann, M.

    2014-09-05

    The Fermi bubbles are two large structures in the gamma-ray sky extending to 55° above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10° in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7σ signi cance.more » The power law with an exponential cutoff has an index of 1:9±0:2 and a cutoff energy of 110 ± 50 GeV. We nd that the gamma-ray luminosity of the bubbles is 4:4+2:4 -0:9 X 1037 erg s -1. We confirm a signi cant enhancement of gamma-ray emission in the south-eastern part of the bubbles, but we do not nd signi cant evidence for a jet. No signi cant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3:4+3:7 -2:6 deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons t the gamma-ray data well. In the IC scenario, the synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic eld between 5 and 20 μG.« less

  10. Fermi-LAT Gamma-Ray Bursts and Insights from Swift

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.

    2010-01-01

    A new revolution in Gamma-ray Burst (GRB) observations and theory has begun over the last two years since the launch of the Fermi Gamma-ray Space Telescope. The new window into high energy gamma-rays opened by the Fermi-Large Area Telescope (LAT) is providing insight into prompt emission mechanisms and possibly also afterglow physics. The LAT detected GRBs appear to be a new unique subset of extremely energetic and bright bursts compared to the large sample detected by Swift over the last 6 years. In this talk, I will discuss the context and recent discoveries from these LAT GRBs and the large database of broadband observations collected by the Swift X-ray Telescope (XRT) and UV/Optical Telescope (UVOT). Through comparisons between the GRBs detected by Swift-BAT, G8M, and LAT, we can learn about the unique characteristics, physical differences, and the relationships between each population. These population characteristics provide insight into the different physical parameters that contribute to the diversity of observational GRB properties.

  11. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, J. L.; Oates, S. R.; Schady, P.; Burrows, D. N.; de Pasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; hide

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multiwavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  12. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith I.

    2011-01-01

    The new and extreme population of GRBs detected by Fermi-LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT GRBs and the well studied, fainter, less energetic GRBs detected by Swift-BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi-GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  13. Fermi and Swift Gamma-Ray Burst Afterglow Population Studies

    NASA Technical Reports Server (NTRS)

    Racusin, Judith L.; Oates, S. R.; Schady, P.; Burrows, D. N.; dePasquale, M.; Donato, D.; Gehrels, N.; Koch, S.; McEnery, J.; Piran, T.; hide

    2011-01-01

    The new and extreme population of GRBs detected by Fermi -LAT shows several new features in high energy gamma-rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last 6 years, it has been Swift that has provided the robust dataset of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT detected GRBs and the well studied, fainter, less energetic GRBs detected by Swift -BAT is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and Fermi -GBM, and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties, in order to better understand the nature of the special characteristics of the LAT bursts.

  14. Anisotropies in the diffuse gamma-ray background from dark matter with Fermi LAT: A closer look

    DOE PAGES

    Cuoco, A.; Sellerholm, A.; Conrad, J.; ...

    2011-06-21

    We perform a detailed study of the sensitivity to the anisotropies related to dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) as measured by the Fermi Large Area Telescope ( Fermi LAT). For the first time, we take into account the effects of the Galactic foregrounds and use a realistic representation of the Fermi LAT. We implement an analysis pipeline which simulates Fermi LAT data sets starting from model maps of the Galactic foregrounds, the Fermi-resolved point sources, the extragalactic diffuse emission and the signal from DM annihilation. The effects of the detector are taken into account bymore » convolving the model maps with the Fermi LAT instrumental response. We then use the angular power spectrum to characterize the anisotropy properties of the simulated data and to study the sensitivity to DM. We consider DM anisotropies of extragalactic origin and of Galactic origin (which can be generated through annihilation in the Milky Way substructures) as opposed to a background of anisotropies generated by sources of astrophysical origin, blazars for example. We find that with statistics from 5 yr of observation, Fermi is sensitive to a DM contribution at the level of 1–10 per cent of the measured IGRB depending on the DM mass m χ and annihilation mode. In terms of the thermally averaged cross-section , this corresponds to ~10 –25 cm 3 s –1, i.e. slightly above the typical expectations for a thermal relic, for low values of the DM mass m χ≲ 100 GeV. As a result, the anisotropy method for DM searches has a sensitivity comparable to the usual methods based only on the energy spectrum and thus constitutes an independent and complementary piece of information in the DM puzzle.« less

  15. The Spatially Uniform Spectrum of the Fermi Bubbles: The Leptonic Active Galactic Nucleus Jet Scenario

    NASA Astrophysics Data System (ADS)

    Yang, H.-Y. K.; Ruszkowski, M.

    2017-11-01

    The Fermi bubbles are among the most important findings of the Fermi Gamma-ray Space Telescope; however, their origin is still elusive. One of the unique features of the bubbles is that their gamma-ray spectrum, including a high-energy cutoff at ˜110 GeV and the overall shape of the spectrum, is nearly spatially uniform. The high-energy spectral cutoff is suggestive of a leptonic origin due to synchrotron and inverse-Compton cooling of cosmic-ray (CR) electrons; however, even for a leptonic model, it is not obvious why the spectrum should be spatially uniform. In this work, we investigate the bubble formation in the leptonic active galactic nucleus (AGN) jet scenario using a new CRSPEC module in FLASH that allows us to track the evolution of a CR spectrum during the simulations. We show that the high-energy cutoff is caused by fast electron cooling near the Galactic center (GC) when the jets were launched. Afterwards, the dynamical timescale becomes the shortest among all relevant timescales, and therefore the spectrum is essentially advected with only mild cooling losses. This could explain why the bubble spectrum is nearly spatially uniform: the CRs from different parts of the bubbles as seen today all share the same origin near the GC at an early stage of the bubble expansion. We find that the predicted CR spatial and spectral distribution can simultaneously match the normalization, spectral shape, and high-energy cutoff of the observed gamma-ray spectrum and their spatial uniformity, suggesting that past AGN jet activity is a likely mechanism for the formation of the Fermi bubbles.

  16. Dark lump excitations in superfluid Fermi gases

    NASA Astrophysics Data System (ADS)

    Xu, Yan-Xia; Duan, Wen-Shan

    2012-11-01

    We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev—Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen—Cooper—Schrieffer (BCS) regime, Bose—Einstein condensate (BEC) regime, and unitarity regime. One-lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.

  17. Ground-state properties of trapped Bose-Fermi mixtures: Role of exchange correlation

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Albus, Alexander P.; Wilkens, Martin; Illuminati, Fabrizio

    2003-06-01

    We introduce density-functional theory for inhomogeneous Bose-Fermi mixtures, derive the associated Kohn-Sham equations, and determine the exchange-correlation energy in local-density approximation. We solve numerically the Kohn-Sham system, and determine the boson and fermion density distributions and the ground-state energy of a trapped, dilute mixture beyond mean-field approximation. The importance of the corrections due to exchange correlation is discussed by a comparison with current experiments; in particular, we investigate the effect of the repulsive potential-energy contribution due to exchange correlation on the stability of the mixture against collapse.

  18. Probing and Manipulating Ultracold Fermi Superfluids

    NASA Astrophysics Data System (ADS)

    Jiang, Lei

    Ultracold Fermi gas is an exciting field benefiting from atomic physics, optical physics and condensed matter physics. It covers many aspects of quantum mechanics. Here I introduce some of my work during my graduate study. We proposed an optical spectroscopic method based on electromagnetically-induced transparency (EIT) as a generic probing tool that provides valuable insights into the nature of Fermi paring in ultracold Fermi gases of two hyperfine states. This technique has the capability of allowing spectroscopic response to be determined in a nearly non-destructive manner and the whole spectrum may be obtained by scanning the probe laser frequency faster than the lifetime of the sample without re-preparing the atomic sample repeatedly. Both quasiparticle picture and pseudogap picture are constructed to facilitate the physical explanation of the pairing signature in the EIT spectra. Motivated by the prospect of realizing a Fermi gas of 40K atoms with a synthetic non-Abelian gauge field, we investigated theoretically BEC-HCS crossover physics in the presence of a Rashba spin-orbit coupling in a system of two-component Fermi gas with and without a Zeeman field that breaks the population balance. A new bound state (Rashba pair) emerges because of the spin-orbit interaction. We studied the properties of Rashba pairs using a standard pair fluctuation theory. As the two-fold spin degeneracy is lifted by spin-orbit interaction, bound pairs with mixed singlet and triplet pairings (referred to as rashbons) emerge, leading to an anisotropic superfluid. We discussed in detail the experimental signatures for observing the condensation of Rashba pairs by calculating various physical observables which characterize the properties of the system and can be measured in experiment. The role of impurities as experimental probes in the detection of quantum material properties is well appreciated. Here we studied the effect of a single classical impurity in trapped ultracold Fermi

  19. The Thomas–Fermi quark model: Non-relativistic aspects

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Liu, Quan, E-mail: quan_liu@baylor.edu; Wilcox, Walter, E-mail: walter_wilcox@baylor.edu

    The first numerical investigation of non-relativistic aspects of the Thomas–Fermi (TF) statistical multi-quark model is given. We begin with a review of the traditional TF model without an explicit spin interaction and find that the spin splittings are too small in this approach. An explicit spin interaction is then introduced which entails the definition of a generalized spin “flavor”. We investigate baryonic states in this approach which can be described with two inequivalent wave functions; such states can however apply to multiple degenerate flavors. We find that the model requires a spatial separation of quark flavors, even if completely degenerate.more » Although the TF model is designed to investigate the possibility of many-quark states, we find surprisingly that it may be used to fit the low energy spectrum of almost all ground state octet and decuplet baryons. The charge radii of such states are determined and compared with lattice calculations and other models. The low energy fit obtained allows us to extrapolate to the six-quark doubly strange H-dibaryon state, flavor symmetric strange states of higher quark content and possible six quark nucleon–nucleon resonances. The emphasis here is on the systematics revealed in this approach. We view our model as a versatile and convenient tool for quickly assessing the characteristics of new, possibly bound, particle states of higher quark number content. -- Highlights: • First application of the statistical Thomas–Fermi quark model to baryonic systems. • Novel aspects: spin as generalized flavor; spatial separation of quark flavor phases. • The model is statistical, but the low energy baryonic spectrum is successfully fit. • Numerical applications include the H-dibaryon, strange states and nucleon resonances. • The statistical point of view does not encourage the idea of bound many-quark baryons.« less

  20. A fractional approach to the Fermi-Pasta-Ulam problem

    NASA Astrophysics Data System (ADS)

    Machado, J. A. T.

    2013-09-01

    This paper studies the Fermi-Pasta-Ulam problem having in mind the generalization provided by Fractional Calculus (FC). The study starts by addressing the classical formulation, based on the standard integer order differential calculus and evaluates the time and frequency responses. A first generalization to be investigated consists in the direct replacement of the springs by fractional elements of the dissipative type. It is observed that the responses settle rapidly and no relevant phenomena occur. A second approach consists of replacing the springs by a blend of energy extracting and energy inserting elements of symmetrical fractional order with amplitude modulated by quadratic terms. The numerical results reveal a response close to chaotic behaviour.

  1. Conformal Fermi Coordinates

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Dai, Liang; Pajer, Enrico; Schmidt, Fabian, E-mail: ldai@ias.edu, E-mail: Enrico.pajer@gmail.com, E-mail: fabians@mpa-garching.mpg.de

    Fermi Normal Coordinates (FNC) are a useful frame for isolating the locally observable, physical effects of a long-wavelength spacetime perturbation. Their cosmological application, however, is hampered by the fact that they are only valid on scales much smaller than the horizon. We introduce a generalization that we call Conformal Fermi Coordinates (CFC). CFC preserve all the advantages of FNC, but in addition are valid outside the horizon. They allow us to calculate the coupling of long- and short-wavelength modes on all scales larger than the sound horizon of the cosmological fluid, starting from the epoch of inflation until today, bymore » removing the complications of the second order Einstein equations to a large extent, and eliminating all gauge ambiguities. As an application, we present a calculation of the effect of long-wavelength tensor modes on small scale density fluctuations. We recover previous results, but clarify the physical content of the individual contributions in terms of locally measurable effects and ''projection'' terms.« less

  2. Analog Landau-He-McKellar-Wilkens quantization due to noninertial effects of the Fermi-Walker reference frame

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bakke, Knut

    2010-05-15

    We will show that when a neutral particle with permanent electric dipole moment interacts with a specific field configuration when the local reference frames of the observers are Fermi-Walker transported, the Landau quantization analog to the He-McKellar-Wilkens setup arises in the nonrelativistic quantum dynamics of the neutral particle due the noninertial effects of the Fermi-Walker reference frame. We show that the noninertial effects do not break the infinity degeneracy of the energy levels, but in this case, the cyclotron frequency depends on the angular velocity.

  3. NASA Goddard Space Flight Center, on Behalf of the Fermi Large Area Telescope Collaboration

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2010-01-01

    Because high-energy gamma rays can be produced by processes that also produce neutrinos, the gamma-ray survey of the sky by the Fermi (Gamma-ray Space Telescope offers a view of potential targets for neutrino observations. Gamma-ray bursts. Active Galactic Nuclei, and supernova remnants are all sites where hadronic, neutrino-producing interactions are plausible. Pulsars, pulsar wind nebulae, and binary sources are all phenomena that reveal leptonic particle acceleration through their gamma-ray emission. While important to gamma-ray astrophysics, such sources are of less interest to neutrino studies. This talk will present a broad overview of the constantly changing sky seen with the Large Area Telescope (LAT)on the Fermi spacecraft.

  4. Engineering the electronic structure of graphene superlattices via Fermi velocity modulation

    NASA Astrophysics Data System (ADS)

    Lima, Jonas R. F.

    2017-01-01

    Graphene superlattices have attracted much research interest in the last years, since it is possible to manipulate the electronic properties of graphene in these structures. It has been verified that extra Dirac points appear in the electronic structure of the system. The electronic structure in the vicinity of these points has been studied for a gapless and gapped graphene superlattice and for a graphene superlattice with a spatially modulated energy gap. In each case a different behavior was obtained. In this work we show that via Fermi velocity engineering it is possible to tune the electronic properties of a graphene superlattice to match all the previous cases studied. We also obtained new features of the system never observed before, reveling that the electronic structure of graphene is very sensitive to the modulation of the Fermi velocity. The results obtained here are relevant for the development of novel graphene-based electronic devices.

  5. Searching for γ-ray emission from Reticulum II by Fermi-LAT

    NASA Astrophysics Data System (ADS)

    Zhao, Yi; Bi, Xiao-Jun; Yin, Peng-Fei; Zhang, Xinmin

    2018-02-01

    Recently, many new dwarf spheroidal satellites (dSphs) have been discovered by the Dark Energy Survey (DES). These dSphs are ideal candidates for probing for gamma-ray emissions from dark matter (DM) annihilation. However, no significant signature has been found by the Fermi-LAT dSph observations. In this work, we reanalyze the Fermi-LAT Pass 8 data from the direction of Reticulum II, where a slight excess has been reported by some previous studies. We treat Reticulum II (DES J0335.6-5403) as a spatially extended source, and find that no significant gamma-ray signature is observed. Based on this result, we set upper-limits on the DM annihilation cross section. Supported by National Natural Science Foundation of China (11121092, 11033005, 11375202, 11475191, 11475189), the CAS pilot B program (XDB23020000) and the National Key Program for Research and Development (2016YFA0400200)

  6. 3FHL: The Third Catalog of Hard Fermi -LAT Sources

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ajello, M.; Atwood, W. B.; Baldini, L.

    Here, we present a catalog of sources detected above 10 GeV by the Fermi Large Area Telescope (LAT) in the first 7 years of data using the Pass 8 event-level analysis. This is the Third Catalog of Hard Fermi-LAT Sources (3FHL), containing 1556 objects characterized in the 10 GeV–2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog at the same energies (1FHL). The vast majority of detected sources (79%) are associated with extragalactic counterparts at other wavelengths, including 16 sources located at very high redshift (zmore » > 2). Of the sources, 8% have Galactic counterparts and 13% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with a flux sensitivity of 4.4 to 9.5 × 10 -11 ph cm -2 s -1, respectively (this is approximately 0.5% and 1% of the Crab Nebula flux above 10 GeV). The catalog includes 214 new γ-ray sources. The substantial increase in the number of photons (more than 4 times relative to 1FHL and 10 times to 2FHL) also allows us to measure significant spectral curvature for 32 sources and find flux variability for 163 of them. We also estimate that for the same flux limit of 10 -12 erg cm -2 s -1, the energy range above 10 GeV has twice as many sources as the range above 50 GeV, highlighting the importance, for future Cherenkov telescopes, of lowering the energy threshold as much as possible.« less

  7. 3FHL: The Third Catalog of Hard Fermi -LAT Sources

    DOE PAGES

    Ajello, M.; Atwood, W. B.; Baldini, L.; ...

    2017-09-27

    Here, we present a catalog of sources detected above 10 GeV by the Fermi Large Area Telescope (LAT) in the first 7 years of data using the Pass 8 event-level analysis. This is the Third Catalog of Hard Fermi-LAT Sources (3FHL), containing 1556 objects characterized in the 10 GeV–2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog at the same energies (1FHL). The vast majority of detected sources (79%) are associated with extragalactic counterparts at other wavelengths, including 16 sources located at very high redshift (zmore » > 2). Of the sources, 8% have Galactic counterparts and 13% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with a flux sensitivity of 4.4 to 9.5 × 10 -11 ph cm -2 s -1, respectively (this is approximately 0.5% and 1% of the Crab Nebula flux above 10 GeV). The catalog includes 214 new γ-ray sources. The substantial increase in the number of photons (more than 4 times relative to 1FHL and 10 times to 2FHL) also allows us to measure significant spectral curvature for 32 sources and find flux variability for 163 of them. We also estimate that for the same flux limit of 10 -12 erg cm -2 s -1, the energy range above 10 GeV has twice as many sources as the range above 50 GeV, highlighting the importance, for future Cherenkov telescopes, of lowering the energy threshold as much as possible.« less

  8. 3FHL: The Third Catalog of Hard Fermi-LAT Sources

    NASA Astrophysics Data System (ADS)

    Ajello, M.; Atwood, W. B.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Bregeon, J.; Britto, R. J.; Bruel, P.; Buehler, R.; Buson, S.; Cameron, R. A.; Caputo, R.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Cohen, J. M.; Costantin, D.; Costanza, F.; Cuoco, A.; Cutini, S.; D'Ammando, F.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Domínguez, A.; Drell, P. S.; Dumora, D.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Fortin, P.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Green, D.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Harding, A. K.; Hays, E.; Hewitt, J. W.; Horan, D.; Jóhannesson, G.; Kensei, S.; Kuss, M.; La Mura, G.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Li, J.; Longo, F.; Loparco, F.; Lott, B.; Lubrano, P.; Magill, J. D.; Maldera, S.; Manfreda, A.; Mazziotta, M. N.; McEnery, J. E.; Meyer, M.; Michelson, P. F.; Mirabal, N.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Palatiello, M.; Paliya, V. S.; Paneque, D.; Perkins, J. S.; Persic, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Saz Parkinson, P. M.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Stawarz, L.; Suson, D. J.; Takahashi, M.; Tak, D.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Torres, D. F.; Torresi, E.; Troja, E.; Vianello, G.; Wood, K.; Wood, M.

    2017-10-01

    We present a catalog of sources detected above 10 GeV by the Fermi Large Area Telescope (LAT) in the first 7 years of data using the Pass 8 event-level analysis. This is the Third Catalog of Hard Fermi-LAT Sources (3FHL), containing 1556 objects characterized in the 10 GeV-2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog at the same energies (1FHL). The vast majority of detected sources (79%) are associated with extragalactic counterparts at other wavelengths, including 16 sources located at very high redshift (z > 2). Of the sources, 8% have Galactic counterparts and 13% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with a flux sensitivity of 4.4 to 9.5 × 10-11 ph cm-2 s-1, respectively (this is approximately 0.5% and 1% of the Crab Nebula flux above 10 GeV). The catalog includes 214 new γ-ray sources. The substantial increase in the number of photons (more than 4 times relative to 1FHL and 10 times to 2FHL) also allows us to measure significant spectral curvature for 32 sources and find flux variability for 163 of them. Furthermore, we estimate that for the same flux limit of 10-12 erg cm-2 s-1, the energy range above 10 GeV has twice as many sources as the range above 50 GeV, highlighting the importance, for future Cherenkov telescopes, of lowering the energy threshold as much as possible.

  9. Modulational estimate for the maximal Lyapunov exponent in Fermi-Pasta-Ulam chains

    NASA Astrophysics Data System (ADS)

    Dauxois, Thierry; Ruffo, Stefano; Torcini, Alessandro

    1997-12-01

    In the framework of the Fermi-Pasta-Ulam (FPU) model, we show a simple method to give an accurate analytical estimation of the maximal Lyapunov exponent at high energy density. The method is based on the computation of the mean value of the modulational instability growth rates associated to unstable modes. Moreover, we show that the strong stochasticity threshold found in the β-FPU system is closely related to a transition in tangent space, the Lyapunov eigenvector being more localized in space at high energy.

  10. "Where is Everybody?" An Account of Fermi's Question

    DOE R&D Accomplishments Database

    Jones, E. M.

    1985-03-01

    Enrico Fermi's famous question, now central to debates about the prevalence of extraterrestrial civilizations, arose during a luncheon conversation with Emil Konopinski, Edward Teller, and Herbert York in the summer of 1950. Fermi's companions on that day have provided accounts of the incident.

  11. Vortex Lattices in the Bose-Fermi Superfluid Mixture.

    PubMed

    Jiang, Yuzhu; Qi, Ran; Shi, Zhe-Yu; Zhai, Hui

    2017-02-24

    In this Letter we show that the vortex lattice structure in the Bose-Fermi superfluid mixture can undergo a sequence of structure transitions when the Fermi superfluid is tuned from the BCS regime to the BEC regime. This is due to the difference in the vortex core structure of a Fermi superfluid in the BCS regime and in the BEC regime. In the BCS regime the vortex core is nearly filled, while the density at the vortex core gradually decreases until it empties out in the BEC regime. Therefore, with the density-density interaction between the Bose and the Fermi superfluids, interaction between the two sets of vortex lattices gets stronger in the BEC regime, which yields the structure transition of vortex lattices. In view of the recent realization of this superfluid mixture and vortices therein, our theoretical predication can be verified experimentally in the near future.

  12. The impact of the Fermi-Dirac distribution on charge injection at metal/organic interfaces.

    PubMed

    Wang, Z B; Helander, M G; Greiner, M T; Lu, Z H

    2010-05-07

    The Fermi level has historically been assumed to be the only energy-level from which carriers are injected at metal/semiconductor interfaces. In traditional semiconductor device physics, this approximation is reasonable as the thermal distribution of delocalized states in the semiconductor tends to dominate device characteristics. However, in the case of organic semiconductors the weak intermolecular interactions results in highly localized electronic states, such that the thermal distribution of carriers in the metal may also influence device characteristics. In this work we demonstrate that the Fermi-Dirac distribution of carriers in the metal has a much more significant impact on charge injection at metal/organic interfaces than has previously been assumed. An injection model which includes the effect of the Fermi-Dirac electron distribution was proposed. This model has been tested against experimental data and was found to provide a better physical description of charge injection. This finding indicates that the thermal distribution of electronic states in the metal should, in general, be considered in the study of metal/organic interfaces.

  13. Eternity in six hours: Intergalactic spreading of intelligent life and sharpening the Fermi paradox

    NASA Astrophysics Data System (ADS)

    Armstrong, Stuart; Sandberg, Anders

    2013-08-01

    The Fermi paradox is the discrepancy between the strong likelihood of alien intelligent life emerging (under a wide variety of assumptions) and the absence of any visible evidence for such emergence. In this paper, we extend the Fermi paradox to not only life in this galaxy, but to other galaxies as well. We do this by demonstrating that travelling between galaxies - indeed even launching a colonisation project for the entire reachable universe - is a relatively simple task for a star-spanning civilisation, requiring modest amounts of energy and resources. We start by demonstrating that humanity itself could likely accomplish such a colonisation project in the foreseeable future, should we want to. Given certain technological assumptions, such as improved automation, the task of constructing Dyson spheres, designing replicating probes, and launching them at distant galaxies, become quite feasible. We extensively analyse the dynamics of such a project, including issues of deceleration and collision with particles in space. Using similar methods, there are millions of galaxies that could have reached us by now. This results in a considerable sharpening of the Fermi paradox.

  14. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.

    PubMed

    Charnukha, A; Evtushinsky, D V; Matt, C E; Xu, N; Shi, M; Büchner, B; Zhigadlo, N D; Batlogg, B; Borisenko, S V

    2015-12-18

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

  15. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

    NASA Astrophysics Data System (ADS)

    Charnukha, A.; Evtushinsky, D. V.; Matt, C. E.; Xu, N.; Shi, M.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Borisenko, S. V.

    2015-12-01

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

  16. First light from the Vela pulsar with the Fermi Gamma-ray Space Telescope

    NASA Astrophysics Data System (ADS)

    Razzano, M.

    2009-04-01

    The Fermi Gamma-ray Space Telescope, launched in June 2008, is an international space mission entirely devoted to the study of the high-energy gamma rays from the Universe. The main instrument aboard Fermi is the Large Area Telescope (LAT), a pair conversion telescope equipped with the state-of-the art in gamma-ray detectors technology. Thanks to its large field of view and effective area, combined with its excellent timing capability, Fermi-LAT is a perfect instrument for probing physics of gamma-ray emission in pulsars. LAT is expected to discover tens of new pulsars, both radio-loud and radio-quiet (Geminga-like). Moreover, LAT will observe with unprecedented statistics the brightest pulsars, investigating the details of magnetospheric emission. The first two months of the mission have been focused on the commissioning and first light, during which the LAT firmly detected the six previously known EGRET gamma-ray pulsars. One of the main sources of interest during our first light observations has been the Vela pulsar, the brightest persistent source in the whole gamma-ray sky. Thanks to its brightness, the Vela pulsar is an ideal candidate for calibrating the LAT and testing its performance. In addition, observations of Vela will help answer many questions related to the physics of pulsar emission processes. We present here some recent results obtained by the LAT on the Vela pulsar, using high-quality timing solutions provided by radio observations carried out within the Fermi pulsar radio timing campaign.

  17. Optical characterization of semi-insulating GaAs - Determination of the Fermi energy, the concentraion of the midgap EL2 level and its occupancy

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Bugajski, M.; Matsui, M.; Gatos, H. C.

    1987-01-01

    The key electronic characteristics of semiinsulating GaAs, i.e., the Fermi energy, concentration, and occupancy of the midgap donor EL2, and the net concentration of ionized acceptors can all be determined from high-resolution measurements of the EL2 intracenter absorption. The procedure is based on the measurement of zero-phonon line intensity before and after the complete transfer of EL2 to its metastable state followed by thermal recovery. The procedure is quantitative, involves no fitting parameters, and unlike existing methods, is applicable even when a significant part of the EL2 is ionized.

  18. Momentum sharing in imbalanced Fermi systems

    NASA Astrophysics Data System (ADS)

    Hen, O.; Sargsian, M.; Weinstein, L. B.; Piasetzky, E.; Hakobyan, H.; Higinbotham, D. W.; Braverman, M.; Brooks, W. K.; Gilad, S.; Adhikari, K. P.; Arrington, J.; Asryan, G.; Avakian, H.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Beck, A.; Beck, S. May-Tal; Bedlinskiy, I.; Bertozzi, W.; Biselli, A.; Burkert, V. D.; Cao, T.; Carman, D. S.; Celentano, A.; Chandavar, S.; Colaneri, L.; Cole, P. L.; Crede, V.; D'Angelo, A.; De Vita, R.; Deur, A.; Djalali, C.; Doughty, D.; Dugger, M.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Fedotov, G.; Fegan, S.; Forest, T.; Garillon, B.; Garcon, M.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G. P.; Girod, F. X.; Goetz, J. T.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guo, L.; Hafidi, K.; Hanretty, C.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkanov, B. I.; Isupov, E. L.; Jiang, H.; Jo, H. S.; Joo, K.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, F. J.; Koirala, S.; Korover, I.; Kuhn, S. E.; Kubarovsky, V.; Lenisa, P.; Levine, W. I.; Livingston, K.; Lowry, M.; Lu, H. Y.; MacGregor, I. J. D.; Markov, N.; Mayer, M.; McKinnon, B.; Mineeva, T.; Mokeev, V.; Movsisyan, A.; Camacho, C. Munoz; Mustapha, B.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Pappalardo, L. L.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Phelps, W.; Pisano, S.; Pogorelko, O.; Price, J. W.; Procureur, S.; Prok, Y.; Protopopescu, D.; Puckett, A. J. R.; Rimal, D.; Ripani, M.; Ritchie, B. G.; Rizzo, A.; Rosner, G.; Roy, P.; Rossi, P.; Sabatié, F.; Schott, D.; Schumacher, R. A.; Sharabian, Y. G.; Smith, G. D.; Shneor, R.; Sokhan, D.; Stepanyan, S. S.; Stepanyan, S.; Stoler, P.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tkachenko, S.; Ungaro, M.; Vlassov, A. V.; Voutier, E.; Walford, N. K.; Wei, X.; Wood, M. H.; Wood, S. A.; Zachariou, N.; Zana, L.; Zhao, Z. W.; Zheng, X.; Zonta, I.; aff16

    2014-10-01

    The atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using 12C, 27Al, 56Fe, and 208Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin-state, ultracold atomic gas systems.

  19. Gamma-ray bursts at high and very high energies

    NASA Astrophysics Data System (ADS)

    Piron, Frédéric

    2016-06-01

    Gamma-Ray Bursts (GRBs) are extra-galactic and extremely energetic transient emissions of gamma rays, which are thought to be associated with the death of massive stars or the merger of compact objects in binary systems. Their huge luminosities involve the presence of a newborn stellar-mass black hole emitting a relativistic collimated outflow, which accelerates particles and produces non-thermal emissions from the radio domain to the highest energies. In this article, I review recent progresses in the understanding of GRB jet physics above 100 MeV, based on Fermi observations of bright GRBs. I discuss the physical implications of these observations and their impact on GRB modeling, and I present some prospects for GRB observation at very high energies in the near future.

  20. Fermi/GBM Results of Magnetars

    NASA Technical Reports Server (NTRS)

    Kouveliotou, chryssa

    2011-01-01

    Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11,2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501 +4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR Jl550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP IEI547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields.

  1. Pairing in a dry Fermi sea

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Maier, Thomas A.; Staar, Peter; Mishra, V.

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

  2. Pairing in a dry Fermi sea

    DOE PAGES

    Maier, Thomas A.; Staar, Peter; Mishra, V.; ...

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

  3. Statistical mechanics of Fermi-Pasta-Ulam chains with the canonical ensemble

    NASA Astrophysics Data System (ADS)

    Demirel, Melik C.; Sayar, Mehmet; Atılgan, Ali R.

    1997-03-01

    Low-energy vibrations of a Fermi-Pasta-Ulam-Β (FPU-Β) chain with 16 repeat units are analyzed with the aid of numerical experiments and the statistical mechanics equations of the canonical ensemble. Constant temperature numerical integrations are performed by employing the cubic coupling scheme of Kusnezov et al. [Ann. Phys. 204, 155 (1990)]. Very good agreement is obtained between numerical results and theoretical predictions for the probability distributions of the generalized coordinates and momenta both of the chain and of the thermal bath. It is also shown that the average energy of the chain scales linearly with the bath temperature.

  4. Periodic box Fermi hypernetted chain calculations of neutron star crustal matter

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Bassan, Nicola; Fantoni, Stefano; Schmidt, Kevin E.

    2011-09-15

    Neutron star crustal matter, whose properties are relevant in many models aimed at explaining observed astrophysical phenomena, has so far always been studied using a mean-field approach. To check the results obtained in this way, a sensible next step is to make use of a realistic nuclear potential. The present paper extends the periodic box Fermi hypernetted chain method to include longitudinal-isospin dependence of the correlations, making feasible a study of asymmetric crustal matter. Results are presented for the symmetry energy, the low-density neutron star equation of state, and the single-particle neutron and proton energies.

  5. Constraints on cosmological dark matter annihilation from the Fermi-LAT isotropic diffuse gamma-ray measurement

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2010-04-01

    The first published Fermi large area telescope (Fermi-LAT) measurement of the isotropic diffuse gamma-ray emission is in good agreement with a single power law, and is not showing any signature of a dominant contribution from dark matter sources in the energy range from 20 to 100 GeV. Here, we use the absolute size and spectral shape of this measured flux to derive cross section limits on three types of generic dark matter candidates: annihilating into quarks, charged leptons and monochromatic photons. Predicted gamma-ray fluxes from annihilating dark matter are strongly affected by the underlying distribution of dark matter, and bymore » using different available results of matter structure formation we assess these uncertainties. We also quantify how the dark matter constraints depend on the assumed conventional backgrounds and on the Universe's transparency to high-energy gamma-rays. In reasonable background and dark matter structure scenarios (but not in all scenarios we consider) it is possible to exclude models proposed to explain the excess of electrons and positrons measured by the Fermi-LAT and PAMELA experiments. Derived limits also start to probe cross sections expected from thermally produced relics (e.g. in minimal supersymmetry models) annihilating predominantly into quarks. Finally, for the monochromatic gamma-ray signature, the current measurement constrains only dark matter scenarios with very strong signals.« less

  6. Constraints on the galactic population of TeV pulsar wind nebulae using Fermi Large Area Telescope observations

    DOE PAGES

    Acero, F.; Ackermann, M.; Ajello, M.; ...

    2013-07-29

    Pulsar wind nebulae (PWNe) have been established as the most populous class of TeV γ-ray emitters. Since launch, the Fermi Large Area Telescope (LAT) has identified five high-energy (100 MeV < E < 100 GeV) γ-ray sources as PWNe and detected a large number of PWN candidates, all powered by young and energetic pulsars. The wealth of multi-wavelength data available and the new results provided by Fermi-LAT give us an opportunity to find new PWNe and to explore the radiative processes taking place in known ones. The TeV γ-ray unidentified (UNID) sources are the best candidates for finding new PWNe.more » Using 45 months of Fermi-LAT data for energies above 10 GeV, an analysis was performed near the position of 58 TeV PWNe and UNIDs within 5° of the Galactic plane to establish new constraints on PWN properties and find new clues on the nature of UNIDs. Of the 58 sources, 30 were detected, and this work provides their γ-ray fluxes for energies above 10 GeV. The spectral energy distributions and upper limits, in the multi-wavelength context, also provide new information on the source nature and can help distinguish between emission scenarios, i.e., between classification as a pulsar candidate or as a PWN candidate. Six new GeV PWN candidates are described in detail and compared with existing models. As a result, a population study of GeV PWN candidates as a function of the pulsar/PWN system characteristics is presented.« less

  7. VizieR Online Data Catalog: Fermi blazars with Doppler factors (Fan+, 2017)

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Yang, J. H.; Xiao, H. B.; Lin, C.; Constantin, D.; Luo, G. Y.; Pei, Z. Y.; Hao, J. M.; Mao, Y. W.

    2017-09-01

    Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ-ray luminosity is strongly correlated with other intrinsic luminosities. (2 data files).

  8. OBSERVATION OF TeV GAMMA RAYS FROM THE FERMI BRIGHT GALACTIC SOURCES WITH THE TIBET AIR SHOWER ARRAY

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Amenomori, M.; Bi, X. J.; Ding, L. K.

    2010-01-20

    Using the Tibet-III air shower array, we search for TeV {gamma}-rays from 27 potential Galactic sources in the early list of bright sources obtained by the Fermi Large Area Telescope at energies above 100 MeV. Among them, we observe seven sources instead of the expected 0.61 sources at a significance of 2{sigma} or more excess. The chance probability from Poisson statistics would be estimated to be 3.8 x 10{sup -6}. If the excess distribution observed by the Tibet-III array has a density gradient toward the Galactic plane, the expected number of sources may be enhanced in chance association. Then, themore » chance probability rises slightly, to 1.2 x 10{sup -5}, based on a simple Monte Carlo simulation. These low chance probabilities clearly show that the Fermi bright Galactic sources have statistically significant correlations with TeV {gamma}-ray excesses. We also find that all seven sources are associated with pulsars, and six of them are coincident with sources detected by the Milagro experiment at a significance of 3{sigma} or more at the representative energy of 35 TeV. The significance maps observed by the Tibet-III air shower array around the Fermi sources, which are coincident with the Milagro {>=}3{sigma} sources, are consistent with the Milagro observations. This is the first result of the northern sky survey of the Fermi bright Galactic sources in the TeV region.« less

  9. Fermi level pinning characterisation on ammonium fluoride-treated surfaces of silicon by energy-filtered doping contrast in the scanning electron microscope

    PubMed Central

    Chee, Augustus K. W.

    2016-01-01

    Two-dimensional dopant profiling using the secondary electron (SE) signal in the scanning electron microscope (SEM) is a technique gaining impulse for its ability to enable rapid and contactless low-cost diagnostics for integrated device manufacturing. The basis is doping contrast from electrical p-n junctions, which can be influenced by wet-chemical processing methods typically adopted in ULSI technology. This paper describes the results of doping contrast studies by energy-filtering in the SEM from silicon p-n junction specimens that were etched in ammonium fluoride solution. Experimental SE micro-spectroscopy and numerical simulations indicate that Fermi level pinning occurred on the surface of the treated-specimen, and that the doping contrast can be explained in terms of the ionisation energy integral for SEs, which is a function of the dopant concentration, and surface band-bending effects that prevail in the mechanism for doping contrast as patch fields from the specimen are suppressed. PMID:27576347

  10. Hidden Fermi liquid; the moral: a good effective low-energy theory is worth all of Monte Carlo with Las Vegas thrown in

    NASA Astrophysics Data System (ADS)

    Anderson, Philip W.; Casey, Philip A.

    2010-04-01

    We present a formalism for dealing directly with the effects of the Gutzwiller projection implicit in the t-J model which is widely believed to underlie the phenomenology of the high-Tc cuprates. We suggest that a true Bardeen-Cooper-Schrieffer condensation from a Fermi liquid state takes place, but in the unphysical space prior to projection. At low doping, however, instead of a hidden Fermi liquid one gets a 'hidden' non-superconducting resonating valence bond state which develops hole pockets upon doping. The theory which results upon projection does not follow conventional rules of diagram theory and in fact in the normal state is a Z = 0 non-Fermi liquid. Anomalous properties of the 'strange metal' normal state are predicted and compared against experimental findings.

  11. Fermi-LAT detection of ongoing gamma-ray activity from the new gamma-ray source Fermi J1654-1055 (PMN J1632-1052)

    NASA Astrophysics Data System (ADS)

    Kocevski, D.; Ajello, M.; Buson, S.; Buehler, R.; Giomi, M.

    2016-02-01

    During the week between February 8 and 15, 2016, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed gamma-ray activity from a new transient source, Fermi J1654-1055.

  12. Gamma-Ray Observations of the Supernova Remnant RX J0852.0-4622 with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Tanaka, T.; Allafort, A.; Ballet, J.; Funk, S.; Giordano, F.; Hewitt, J.; Lemoine-Goumard, M.; Tajima, H.; Tibolla, O.; Uchiyama, Y.

    2011-01-01

    We report on gamma-ray observations of the supernova remnant (SNR) RX J0852.04622 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. In the Fermi-LAT data, we find a spatially extended source at the location of the SNR. The extension is consistent with the SNR size seen in other wavelengths such as X-rays and TeV gamma rays, leading to the identification of the gamma-ray source with the SNR. The spectrum is well described as a power law with a photon index of = 1.85 0.06 (stat)+0.18 0.19 (sys), which smoothly connects to the H.E.S.S. spectrum in the TeV energy band. We discuss the gamma-ray emission mechanism based on multiwavelength data. The broadband data can be fit well by a model in which the gamma rays are of hadronic origin. We also consider a scenario with inverse Compton scattering of electrons as the emission mechanism of the gamma rays. Although the leptonic model predicts a harder spectrum in the Fermi-LAT energy range, the model can fit the data considering the statistical and systematic errors.

  13. Fermi, Szilard and Trinity

    ERIC Educational Resources Information Center

    Anderson, Herbert L.

    1974-01-01

    The final installment of the author's recollections of his work with physicists Enrico Fermi, Leo Szilard and others in developing the first controlled nuclear chain reaction and in preparing the test explosion of the first atomic bomb. (GS)

  14. The vela pulsar: results from the first year of FERMI lat observations

    DOE PAGES

    Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

    2010-03-18

    Here, we report on analysis of timing and spectroscopy of the Vela pulsar using 11 months of observations with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. The intrinsic brightness of Vela at GeV energies combined with the angular resolution and sensitivity of the LAT allows us to make the most detailed study to date of the energy-dependent light curves and phase-resolved spectra, using a LAT-derived timing model. The light curve consists of two peaks (P1 and P2) connected by bridge emission containing a third peak (P3). We have confirmed the strong decrease of the P1/P2 ratiomore » with increasing energy seen with EGRET and previous Fermi LAT data, and observe that P1 disappears above 20 GeV. The increase with energy of the mean phase of the P3 component can be followed with much greater detail, showing that P3 and P2 are present up to the highest energies of pulsation. We find significant pulsed emission at phases outside the main profile, indicating that magnetospheric emission exists over 80% of the pulsar period. With increased high-energy counts the phase-averaged spectrum is seen to depart from a power law with simple exponential cutoff, and is better fit with a more gradual cutoff. The spectra in fixed-count phase bins are well fit with power laws with exponential cutoffs, revealing a strong and complex phase dependence of the cutoff energy, especially in the peaks. Finally, by combining these results with predictions of the outer magnetosphere models that map emission characteristics to phase, it will be possible to probe the particle acceleration and the structure of the pulsar magnetosphere with unprecedented detail.« less

  15. FLaapLUC: A pipeline for the generation of prompt alerts on transient Fermi-LAT γ-ray sources

    NASA Astrophysics Data System (ADS)

    Lenain, J.-P.

    2018-01-01

    The large majority of high energy sources detected with Fermi-LAT are blazars, which are known to be very variable sources. High cadence long-term monitoring simultaneously at different wavelengths being prohibitive, the study of their transient activities can help shedding light on our understanding of these objects. The early detection of such potentially fast transient events is the key for triggering follow-up observations at other wavelengths. A Python tool, FLaapLUC, built on top of the Science Tools provided by the Fermi Science Support Center and the Fermi-LAT collaboration, has been developed using a simple aperture photometry approach. This tool can effectively detect relative flux variations in a set of predefined sources and alert potential users. Such alerts can then be used to trigger target of opportunity observations with other facilities. It is shown that FLaapLUC is an efficient tool to reveal transient events in Fermi-LAT data, providing quick results which can be used to promptly organise follow-up observations. Results from this simple aperture photometry method are also compared to full likelihood analyses. The FLaapLUC package is made available on GitHub and is open to contributions by the community.

  16. Momentum-resolved radio-frequency spectroscopy of a spin-orbit-coupled atomic Fermi gas near a Feshbach resonance in harmonic traps

    NASA Astrophysics Data System (ADS)

    Peng, Shi-Guo; Liu, Xia-Ji; Hu, Hui; Jiang, Kaijun

    2012-12-01

    We theoretically investigate the momentum-resolved radio-frequency spectroscopy of a harmonically trapped atomic Fermi gas near a Feshbach resonance in the presence of equal Rashba and Dresselhaus spin-orbit coupling. The system is qualitatively modeled as an ideal gas mixture of atoms and molecules, in which the properties of molecules, such as the wave function, binding energy, and effective mass, are determined from the two-particle solution of two interacting atoms. We calculate separately the radio-frequency response from atoms and molecules at finite temperatures by using the standard Fermi golden rule and take into account the effect of harmonic traps within local density approximation. The total radio-frequency spectroscopy is discussed as functions of temperature and spin-orbit coupling strength. Our results give a qualitative picture of radio-frequency spectroscopy of a resonantly interacting spin-orbit-coupled Fermi gas and can be directly tested in atomic Fermi gases of 40K atoms at Shanxi University and 6Li atoms at the Massachusetts Institute of Technology.

  17. Towards a complete Fermi surface in underdoped high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    The discovery of magnetic quantum oscillations in underdoped high Tc superconductors raised many questions, and initiated a quest to understand the origin of the Fermi surface the like of which had not been seen since the very first discovery of quantum oscillations in elemental bismuth. While studies of the Fermi surface of materials are today mostly assisted by computer codes for calculating the electronic band structure, this was not the case in the underdoped high Tc materials. The Fermi surface was shown to reconstructed into small pockets, yet there was no hint of a viable order parameter. Crucial clues to understanding the origin of the Fermi surface were provided by the small value of the observed Fermi surface cross-section, the negative Hall coefficient and the small electronic heat capacity at high magnetic fields. We also know that the magnetic fields were likely to be too weak to destroy the pseudogap and that vortex pinning effects could be seen to persist to high magnetic fields at low temperatures. I will show that the Fermi surface that appears to fit best with the experimental observations is a small electron pocket formed by connecting the nodal `Fermi arcs' seen in photoemission experiments, corresponding to a density-wave state with two different orthogonal ordering vectors. The existence of such order has subsequently been detected by x-ray scattering experiments, thereby strengthening the case for charge ordering being responsible for reconstructing the Fermi surface. I will discuss new efforts to understand the relationship between the charge ordering and the pseudogap state, discussing the fate of the quasiparticles in the antinodal region and the dimensionality of the Fermi surface. The author acknowledges contributions from Suchitra Sebastian, Brad Ramshaw, Mun Chan, Yu-Te Hsu, Mate Hartstein, Gil Lonzarich, Beng Tan, Arkady Shekhter, Fedor Balakirev, Ross McDonald, Jon Betts, Moaz Altarawneh, Zengwei Zhu, Chuck Mielke, James Day, Doug

  18. Observation of Spin-Polarons in a strongly interacting Fermi liquid

    NASA Astrophysics Data System (ADS)

    Zwierlein, Martin

    2009-03-01

    We have observed spin-polarons in a highly imbalanced mixture of fermionic atoms using tomographic RF spectroscopy. Feshbach resonances allow to freely tune the interactions between the two spin states involved. A single spin down atom immersed in a Fermi sea of spin up atoms can do one of two things: For strong attraction, it can form a molecule with exactly one spin up partner, but for weaker interaction it will spread its attraction and surround itself with a collection of majority atoms. This spin down atom ``dressed'' with a spin up cloud constitutes the spin-polaron. We have observed a striking spectroscopic signature of this quasi-particle for various interaction strengths, a narrow peak in the spin down spectrum that emerges above a broad background. The narrow width signals a long lifetime of the spin-polaron, much longer than the collision rate with spin up atoms, as it must be for a proper quasi-particle. The peak position allows to directly measure the polaron energy. The broad pedestal at high energies reveals physics at short distances and is thus ``molecule-like'': It is exactly matched by the spin up spectra. The comparison with the area under the polaron peak allows to directly obtain the quasi-particle weight Z. We observe a smooth transition from polarons to molecules. At a critical interaction strength of 1/kFa = 0.7, the polaron peak vanishes and spin up and spin down spectra exactly match, signalling the formation of molecules. This is the same critical interaction strength found earlier to separate a normal Fermi mixture from a superfluid molecular Bose-Einstein condensate. The spin-polarons determine the low-temperature phase diagram of imbalanced Fermi mixtures. In principle, polarons can interact with each other and should, at low enough temperatures, form a superfluid of p-wave pairs. We will present a first indication for interactions between polarons.

  19. 3FHL: The Third Catalog of Hard Fermi -LAT Sources

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ajello, M.; Atwood, W. B.; Baldini, L.

    We present a catalog of sources detected above 10 GeV by the Fermi Large Area Telescope (LAT) in the first 7 years of data using the Pass 8 event-level analysis. This is the Third Catalog of Hard Fermi -LAT Sources (3FHL), containing 1556 objects characterized in the 10 GeV–2 TeV energy range. The sensitivity and angular resolution are improved by factors of 3 and 2 relative to the previous LAT catalog at the same energies (1FHL). The vast majority of detected sources (79%) are associated with extragalactic counterparts at other wavelengths, including 16 sources located at very high redshift (more » z > 2). Of the sources, 8% have Galactic counterparts and 13% are unassociated (or associated with a source of unknown nature). The high-latitude sky and the Galactic plane are observed with a flux sensitivity of 4.4 to 9.5 × 10{sup −11} ph cm{sup −2} s{sup −1}, respectively (this is approximately 0.5% and 1% of the Crab Nebula flux above 10 GeV). The catalog includes 214 new γ -ray sources. The substantial increase in the number of photons (more than 4 times relative to 1FHL and 10 times to 2FHL) also allows us to measure significant spectral curvature for 32 sources and find flux variability for 163 of them. Furthermore, we estimate that for the same flux limit of 10{sup −12} erg cm{sup −2} s{sup −1}, the energy range above 10 GeV has twice as many sources as the range above 50 GeV, highlighting the importance, for future Cherenkov telescopes, of lowering the energy threshold as much as possible.« less

  20. Giant energy density and high efficiency achieved in bismuth ferrite-based film capacitors via domain engineering.

    PubMed

    Pan, Hao; Ma, Jing; Ma, Ji; Zhang, Qinghua; Liu, Xiaozhi; Guan, Bo; Gu, Lin; Zhang, Xin; Zhang, Yu-Jun; Li, Liangliang; Shen, Yang; Lin, Yuan-Hua; Nan, Ce-Wen

    2018-05-08

    Developing high-performance film dielectrics for capacitive energy storage has been a great challenge for modern electrical devices. Despite good results obtained in lead titanate-based dielectrics, lead-free alternatives are strongly desirable due to environmental concerns. Here we demonstrate that giant energy densities of ~70 J cm -3 , together with high efficiency as well as excellent cycling and thermal stability, can be achieved in lead-free bismuth ferrite-strontium titanate solid-solution films through domain engineering. It is revealed that the incorporation of strontium titanate transforms the ferroelectric micro-domains of bismuth ferrite into highly-dynamic polar nano-regions, resulting in a ferroelectric to relaxor-ferroelectric transition with concurrently improved energy density and efficiency. Additionally, the introduction of strontium titanate greatly improves the electrical insulation and breakdown strength of the films by suppressing the formation of oxygen vacancies. This work opens up a feasible and propagable route, i.e., domain engineering, to systematically develop new lead-free dielectrics for energy storage.

  1. Magnetar Observations with Fermi/GBM

    NASA Technical Reports Server (NTRS)

    Kouveliotou, Chryssa

    2009-01-01

    NASA's Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. In the first year of operations we recorded emission from four magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other three detections were: SGR J0501+4516, newly discovered with Swift and extensively monitored with both Swift and GBM, SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP) and a very recently discovered new source, SGR 0418+5729. I report below on the current status of the analyses efforts of the GBM data.

  2. Chandra and Swift Observations of Unidentified Fermi-LAT Objects

    NASA Astrophysics Data System (ADS)

    Donato, Davide; Cheung, T.; Gehrels, N.

    2010-03-01

    In the last year we targeted some of the unidentified Fermi-LAT objects (UFOs) at high Galactic latitude with Chandra and Swift in order to determine the basic properties (positions, fluxes, hardness ratios) of all X-ray sources within the Fermi-LAT localization circles. These satellites enable us to detect the X-ray conterparts with a flux limit that is at least an order of magnitude lower than achieved in extant RASS data and to further follow-up at other wavelengths, with the ultimate goal to reveal the nature of these enigmatic gamma-ray sources. Here we present the results obtained with 5 Chandra pointings of high Galactic latitude UFOs in the Fermi-LAT 3-months bright source list. The association of detected X-ray sources within the improved 11-months Fermi-LAT localization circles with available optical and radio observations is discussed.

  3. Two-color Fermi-liquid theory for transport through a multilevel Kondo impurity

    NASA Astrophysics Data System (ADS)

    Karki, D. B.; Mora, Christophe; von Delft, Jan; Kiselev, Mikhail N.

    2018-05-01

    We consider a quantum dot with K ≥2 orbital levels occupied by two electrons connected to two electric terminals. The generic model is given by a multilevel Anderson Hamiltonian. The weak-coupling theory at the particle-hole symmetric point is governed by a two-channel S =1 Kondo model characterized by intrinsic channels asymmetry. Based on a conformal field theory approach we derived an effective Hamiltonian at a strong-coupling fixed point. The Hamiltonian capturing the low-energy physics of a two-stage Kondo screening represents the quantum impurity by a two-color local Fermi liquid. Using nonequilibrium (Keldysh) perturbation theory around the strong-coupling fixed point we analyze the transport properties of the model at finite temperature, Zeeman magnetic field, and source-drain voltage applied across the quantum dot. We compute the Fermi-liquid transport constants and discuss different universality classes associated with emergent symmetries.

  4. Origins of Fermi-level pinning on GaN and InN polar and nonpolar surfaces

    NASA Astrophysics Data System (ADS)

    Segev, D.; Van de Walle, C. G.

    2006-10-01

    Using band structure and total energy methods, we study the atomic and electronic structures of the polar (+c and - c plane) and nonpolar (a and m plane) surfaces of GaN and InN. We identify two distinct microscopic origins for Fermi-level pinning on GaN and InN, depending on surface stoichiometry and surface polarity. At moderate Ga/N ratios unoccupied gallium dangling bonds pin the Fermi level on n-type GaN at 0.5 0.7 eV below the conduction-band minimum. Under highly Ga-rich conditions metallic Ga adlayers lead to Fermi-level pinning at 1.8 eV above the valence-band maximum. We also explain the source of the intrinsic electron accumulation that has been universally observed on polar InN surfaces. It is caused by In-In bonds leading to occupied surface states above the conduction-band minimum. We predict that such a charge accumulation will be absent on the nonpolar surfaces of InN, when prepared under specific conditions.

  5. Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Casandjian, Jean -Marc

    Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope ( Fermi) restricted to absolute latitudesmore » $$10^\\circ \\lt | b| \\lt 70^\\circ $$. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor $${X}_{\\mathrm{CO}}=(0.902\\pm 0.007)\\times {10}^{20}$$ cm–2 (K km s–1)–1, and the dust-to-gas ratio $${X}_{\\mathrm{DUST}}=(41.4\\pm 0.3)\\times {10}^{20}$$ cm–2 mag–1. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through the anticorrelation between CR fluxes and solar activity. Lastly, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.« less

  6. Local H i emissivity measured with FERMI-LAT and implications for Cosmic-ray spectra

    DOE PAGES

    Casandjian, Jean -Marc

    2015-06-20

    Cosmic-ray (CR) electrons and nuclei interact with the Galactic interstellar gas and produce high-energy γ-rays. The γ-ray emission rate per hydrogen atom, called emissivity, provides a unique indirect probe of the CR flux. We present the measurement and the interpretation of the emissivity in the solar neighborhood for γ-ray energy from 50 MeV to 50 GeV. We analyzed a subset of 4 yr of observations from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope ( Fermi) restricted to absolute latitudesmore » $$10^\\circ \\lt | b| \\lt 70^\\circ $$. From a fit to the LAT data including atomic, molecular, and ionized hydrogen column density templates, as well as a dust optical depth map, we derived the emissivities, the molecular hydrogen–to–CO conversion factor $${X}_{\\mathrm{CO}}=(0.902\\pm 0.007)\\times {10}^{20}$$ cm–2 (K km s–1)–1, and the dust-to-gas ratio $${X}_{\\mathrm{DUST}}=(41.4\\pm 0.3)\\times {10}^{20}$$ cm–2 mag–1. Moreover, we detected for the first time γ-ray emission from ionized hydrogen. We compared the extracted emissivities to those calculated from γ-ray production cross sections and to CR spectra measured in the heliosphere. We observed that the experimental emissivities are reproduced only if the solar modulation is accounted for. This provides a direct detection of solar modulation observed previously through the anticorrelation between CR fluxes and solar activity. Lastly, we fitted a parameterized spectral form to the heliospheric CR observations and to the Fermi-LAT emissivity and obtained compatible local interstellar spectra for proton and helium kinetic energy per nucleon between between 1 and 100 GeV and for electron–positrons between 0.1 and 100 GeV.« less

  7. Momentum sharing in imbalanced Fermi systems

    DOE PAGES

    Hen, O.; Sargsian, M.; Weinstein, L. B.; ...

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron starsmore » and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.« less

  8. Cinema, Fermi problems and general education

    NASA Astrophysics Data System (ADS)

    Efthimiou, C. J.; Llewellyn, R. A.

    2007-05-01

    During the past few years the authors have developed a new approach to the teaching of physical science, a general education course typically found in the curricula of nearly every college and university. This approach, called Physics in Films (Efthimiou and Llewellyn 2006 Phys. Teach. 44 28-33), uses scenes from popular films to illustrate physical principles and has excited student interest and improved student performance. A similar approach at the senior/high-school level, nicknamed Hollywood Physics, has been developed by Chandler (2006 Phys. Teach. 44 290-2 2002 Phys. Teach. 40 420-4). The two approaches may be considered complementary as they target different student groups. The analyses of many of the scenes in Physics in Films are a direct application of Fermi calculations—estimates and approximations designed to make solutions of complex and seemingly intractable problems understandable to the student non-specialist. The intent of this paper is to provide instructors with examples they can use to develop skill in recognizing Fermi problems and making Fermi calculations in their own courses.

  9. HESS and Fermi-LAT discovery of γ-rays from the blazar 1ES 1312-423

    DOE PAGES

    Abramowski, A.; Acero, F.; Aharonian, F.; ...

    2013-08-01

    In this study, a deep observation campaign carried out by the High Energy Stereoscopic System (HESS) on Centaurus A enabled the discovery of γ-rays from the blazar 1ES 1312-423, 2° away from the radio galaxy. With a differential flux at 1 TeV of (Φ1 TeV) = (1.9 ± 0.6stat ± 0.4sys) × 10 -13 cm -2 s -1 TeV -1 corresponding to 0.5 percent of the Crab nebula differential flux and a spectral index Γ = 2.9 ± 0.5stat ± 0.2sys, 1ES 1312-423 is one of the faintest sources ever detected in the very high energy (E > 100 GeV)more » extragalactic sky. A careful analysis using three and a half years of Fermi Large Area Telescope (Fermi-LAT) data allows the discovery at high energies (E > 100 MeV) of a hard spectrum (Γ = 1.4 ± 0.4stat ± 0.2sys) source coincident with 1ES 1312-423. Radio, optical, UV and X-ray observations complete the spectral energy distribution of this blazar, now covering 16 decades in energy. Lastly, the emission is successfully fitted with a synchrotron self-Compton model for the non-thermal component, combined with a blackbody spectrum for the optical emission from the host galaxy.« less

  10. Enrico Fermi Awards Ceremony for Dr. Mildred S. Dresselhaus and Dr. Burton Richter, May 2012 (Presentations, including remarks by Energy Secretary, Dr. Steven Chu)

    ScienceCinema

    Chu, Steven [Dept. of Energy (DOE), Washington DC (United States)

    2018-06-12

    The Fermi Award is a Presidential award and is one of the oldest and most prestigious science and technology honors bestowed by the U.S. Government. On May 7, 2012 it was conferred upon two exceptional scientists: Dr. Mildred Dresselhaus, 'for her scientific leadership, her major contributions to science and energy policy, her selfless work in science education and the advancement of diversity in the scientific workplace, and her highly original and impactful research,' and Dr. Burton Richter, 'for the breadth of his influence in the multiple disciplines of accelerator physics and particle physics, his profound scientific discoveries, his visionary leadership as SLAC Director, his leadership of science, and his notable contributions in energy and public policy.' Dr. John Holder, Director of the White House Office of Science and Technology Policy, opened the ceremony, and Dr. Bill Brinkman, Director of DOE's Office of Science introduced the main speaker, Dr. Steven Chu, U.S. Energy Secretary.

  11. Use of Fermi-Dirac statistics for defects in solids

    NASA Astrophysics Data System (ADS)

    Johnson, R. A.

    1981-12-01

    The Fermi-Dirac distribution function is an approximation describing a special case of Boltzmann statistics. A general occupation probability formula is derived and a criterion given for the use of Fermi-Dirac statistics. Application to classical problems of defects in solids is discussed.

  12. Exploring the Extreme Universe with the Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2010-01-01

    Because high-energy gamma rays are produced by powerful sources, the Fermi Gamma-ray Space Telescope provides a window on extreme conditions in the Universe. Some key observations of the constantly changing gamma-ray sky include: (1) Gamma-rays from pulsars appear to come from a region well above the surface of the neutron star; (2) Multiwavelength studies of blazars show that simple models of jet emission are not always adequate to explain what is seen; (3) Gamma-ray bursts can constrain models of quantum gravity; (4) Cosmic-ray electrons at energies approaching 1 TeV suggest a local source for some of these particles.

  13. New Theoretical Estimates of the Contribution of Unresolved Star-Forming Galaxies to the Extragalactic Gamma-Ray Background (EGB) as Measured by EGRET and the Fermi-LAT

    NASA Technical Reports Server (NTRS)

    Venters, Tonia M.

    2011-01-01

    We present new theoretical estimates of the contribution of unresolved star-forming galaxies to the extragalactic gamma-ray background (EGB) as measured by EGRET and the Fermi-LAT. We employ several methods for determining the star-forming galaxy contribution the the EGB, including a method positing a correlation between the gamma-ray luminosity of a galaxy and its rate of star formation as calculated from the total infrared luminosity, and a method that makes use of a model of the evolution of the galaxy gas mass with cosmic time. We find that depending on the model, unresolved star-forming galaxies could contribute significantly to the EGB as measured by the Fermi-LAT at energies between approx. 300 MeV and approx. few GeV. However, the overall spectrum of unresolved star-forming galaxies can explain neither the EGRET EGB spectrum at energies between 50 and 200 MeV nor the Fermi-LAT EGB spectrum at energies above approx. few GeV.

  14. Constraints on the nuclear equation of state from nuclear masses and radii in a Thomas-Fermi meta-modeling approach

    NASA Astrophysics Data System (ADS)

    Chatterjee, D.; Gulminelli, F.; Raduta, Ad. R.; Margueron, J.

    2017-12-01

    The question of correlations among empirical equation of state (EoS) parameters constrained by nuclear observables is addressed in a Thomas-Fermi meta-modeling approach. A recently proposed meta-modeling for the nuclear EoS in nuclear matter is augmented with a single finite size term to produce a minimal unified EoS functional able to describe the smooth part of the nuclear ground state properties. This meta-model can reproduce the predictions of a large variety of models, and interpolate continuously between them. An analytical approximation to the full Thomas-Fermi integrals is further proposed giving a fully analytical meta-model for nuclear masses. The parameter space is sampled and filtered through the constraint of nuclear mass reproduction with Bayesian statistical tools. We show that this simple analytical meta-modeling has a predictive power on masses, radii, and skins comparable to full Hartree-Fock or extended Thomas-Fermi calculations with realistic energy functionals. The covariance analysis on the posterior distribution shows that no physical correlation is present between the different EoS parameters. Concerning nuclear observables, a strong correlation between the slope of the symmetry energy and the neutron skin is observed, in agreement with previous studies.

  15. Constraints on Lorentz Invariance Violation from Fermi -Large Area Telescope Observations of Gamma-Ray Bursts

    NASA Technical Reports Server (NTRS)

    Vasileiou, V.; Jacholkowska, A.; Piron, F.; Bolmont, J.; Courturier, C.; Granot, J.; Stecker, Floyd William; Cohen-Tanugi, J.; Longo, F.

    2013-01-01

    We analyze the MeV/GeV emission from four bright Gamma-Ray Bursts (GRBs) observed by the Fermi-Large Area Telescope to produce robust, stringent constraints on a dependence of the speed of light in vacuo on the photon energy (vacuum dispersion), a form of Lorentz invariance violation (LIV) allowed by some Quantum Gravity (QG) theories. First, we use three different and complementary techniques to constrain the total degree of dispersion observed in the data. Additionally, using a maximally conservative set of assumptions on possible source-intrinsic spectral-evolution effects, we constrain any vacuum dispersion solely attributed to LIV. We then derive limits on the "QG energy scale" (the energy scale that LIV-inducing QG effects become important, E(sub QG)) and the coefficients of the Standard Model Extension. For the subluminal case (where high energy photons propagate more slowly than lower energy photons) and without taking into account any source-intrinsic dispersion, our most stringent limits (at 95% CL) are obtained from GRB 090510 and are E(sub QG,1) > 7.6 times the Planck energy (E(sub Pl)) and E(sub QG,2) > 1.3×10(exp 11) GeV for linear and quadratic leading order LIV-induced vacuum dispersion, respectively. These limits improve the latest constraints by Fermi and H.E.S.S. by a factor of approx. 2. Our results disfavor any class of models requiring E(sub QG,1) < or approx. E(sub Pl)

  16. Constraints on Lorentz invariance violation from Fermi -Large Area Telescope observations of gamma-ray bursts

    DOE PAGES

    Vasileiou, V.; Jacholkowska, A.; Piron, F.; ...

    2013-06-04

    For this research, we analyze the MeV/GeV emission from four bright gamma-ray bursts (GRBs) observed by the Fermi Large Area Telescope to produce robust, stringent constraints on a dependence of the speed of light in vacuo on the photon energy (vacuum dispersion), a form of Lorentz invariance violation (LIV) allowed by some quantum gravity (QG) theories. First, we use three different and complementary techniques to constrain the total degree of dispersion observed in the data. Additionally, using a maximally conservative set of assumptions on possible source-intrinsic, spectral-evolution effects, we constrain any vacuum dispersion solely attributed to LIV. We then derivemore » limits on the QG energy scale (the energy scale where LIV-inducing QG effects become strong, E QG) and the coefficients of the Standard Model Extension. For the subluminal case (where high-energy photons propagate more slowly than lower-energy photons) and without taking into account any source-intrinsic dispersion, our most stringent limits (at 95% C.L.) are obtained from GRB 090510 and are E QG,1 > 7.6 times the Planck energy (E Pl) and E QG,2 > 1.3 × 10 11 GeV for linear and quadratic leading-order LIV-induced vacuum dispersion, respectively. In conclusion, these limits improve the latest constraints by Fermi and H.E.S.S. by a factor of ~2 . Our results disfavor any class of models requiring E QG,1 ≲ E Pl .« less

  17. Large momentum part of a strongly correlated Fermi gas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Tan, Shina

    2008-12-15

    It is well known that the momentum distribution of the two-component Fermi gas with large scattering length has a tail proportional to 1/k{sup 4} at large k. We show that the magnitude of this tail is equal to the adiabatic derivative of the energy with respect to the reciprocal of the scattering length, multiplied by a simple constant. This result holds at any temperature (as long as the effective interaction radius is negligible) and any large scattering length; it also applies to few-body cases. We then show some more connections between the 1/k{sup 4} tail and various physical quantities, includingmore » the pressure at thermal equilibrium and the rate of change of energy in a dynamic sweep of the inverse scattering length.« less

  18. Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Ajello, M.; Atwood, W. B.; Baldini, L.

    During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. Here, we derive upper limits on the CRE flux from the Sun’s direction, and use these bounds to constrain two classes ofmore » dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.« less

  19. Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun

    DOE PAGES

    Ajello, M.; Atwood, W. B.; Baldini, L.; ...

    2011-08-15

    During its first year of data taking, the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy cosmic-ray electrons and positrons (CREs). We present the results of a directional analysis of the CRE events, in which we searched for a flux excess correlated with the direction of the Sun. Two different and complementary analysis approaches were implemented, and neither yielded evidence of a significant CRE flux excess from the Sun. Here, we derive upper limits on the CRE flux from the Sun’s direction, and use these bounds to constrain two classes ofmore » dark matter models which predict a solar CRE flux: (1) models in which dark matter annihilates to CREs via a light intermediate state, and (2) inelastic dark matter models in which dark matter annihilates to CREs.« less

  20. Gap Solitons of Superfluid Fermi Gas in FS Optical Lattices

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Zhang, Ke-Zhi; He, Yong-Lin; Liu, Zhen-Lai; Zhu, Liao

    2018-01-01

    By employing the mean-field theory and hydrodynamic scheme, we study the gap solitons of superfluid Fermi gas in Fourier-Synthesized(FS) optical lattices. By means of numerical methods and variational approximation, the atomic interaction, the chemical potential, the potential depth of the lattice and relative phase of the Fermi system are derived along the Bose-Enstein condensation(BEC)side to the Bardeen-Cooper-Schrieffer (BCS)side. It means that the condition exciting gap solitons is obtained. Moreover, we analyze the fundamental gap soltions of the superfluid Fermi gas. It is found that the relative phase α impacts greatly on the properties of fundamental gap solitons for superfluid Fermi gas. Especially, the nonlinearity interaction term g decreases with α. Add, due to Fermi pressure, curvature changes of g in the BEC limit( γ = 1, here, γ is a function of an interaction parameter) is larger than that at unitary ( γ = 2/3). Spatial distribution of gap solitons exhibit very obvious different when the system transit from the BEC side to BCS side.

  1. Fermi-LAT Search for Pulsar Wind Nebulae around gamma-ray Pulsars

    DOE PAGES

    Ackermann, M.; Ajello, M.; Baldini, L.; ...

    2010-12-13

    The high sensitivity of the Fermi-LAT (Large Area Telescope) offers the first opportunity to study faint and extended GeV sources such as pulsar wind nebulae (PWNe). After one year of observation the LAT detected and identified three PWNe: the Crab Nebula, Vela-X, and the PWN inside MSH 15-52. In the meantime, the list of LAT detected pulsars increased steadily. These pulsars are characterized by high energy loss rates (more » $$\\dot{E}$$) from ~3 × 10 33 erg s –1 to 5 × 10 38 erg s –1 and are therefore likely to power a PWN. This paper summarizes the search for PWNe in the off-pulse windows of 54 LAT-detected pulsars using 16 months of survey observations. Ten sources show significant emission, seven of these likely being of magnetospheric origin. The detection of significant emission in the off-pulse interval offers new constraints on the γ-ray emitting regions in pulsar magnetospheres. The three other sources with significant emission are the Crab Nebula, Vela-X, and a new PWN candidate associated with the LAT pulsar PSR J1023–5746, coincident with the TeV source HESS J1023–575. Here, we further explore the association between the HESS and the Fermi source by modeling its spectral energy distribution. Lastly, flux upper limits derived for the 44 remaining sources are used to provide new constraints on famous PWNe that have been detected at keV and/or TeV energies.« less

  2. Application of exergetic sustainability index to a nano-scale irreversible Brayton cycle operating with ideal Bose and Fermi gasses

    NASA Astrophysics Data System (ADS)

    Açıkkalp, Emin; Caner, Necmettin

    2015-09-01

    In this study, a nano-scale irreversible Brayton cycle operating with quantum gasses including Bose and Fermi gasses is researched. Developments in the nano-technology cause searching the nano-scale machines including thermal systems to be unavoidable. Thermodynamic analysis of a nano-scale irreversible Brayton cycle operating with Bose and Fermi gasses was performed (especially using exergetic sustainability index). In addition, thermodynamic analysis involving classical evaluation parameters such as work output, exergy output, entropy generation, energy and exergy efficiencies were conducted. Results are submitted numerically and finally some useful recommendations were conducted. Some important results are: entropy generation and exergetic sustainability index are affected mostly for Bose gas and power output and exergy output are affected mostly for the Fermi gas by x. At the high temperature conditions, work output and entropy generation have high values comparing with other degeneracy conditions.

  3. Universal Pinning Energy Barrier for Driven Domain Walls in Thin Ferromagnetic Films

    NASA Astrophysics Data System (ADS)

    Jeudy, V.; Mougin, A.; Bustingorry, S.; Savero Torres, W.; Gorchon, J.; Kolton, A. B.; Lemaître, A.; Jamet, J.-P.

    2016-07-01

    We report a comparative study of magnetic field driven domain wall motion in thin films made of different magnetic materials for a wide range of field and temperature. The full thermally activated creep motion, observed below the depinning threshold, is shown to be described by a unique universal energy barrier function. Our findings should be relevant for other systems whose dynamics can be modeled by elastic interfaces moving on disordered energy landscapes.

  4. All-Sky Earth Occultation Observations with the Fermi Gamma Ray Burst Monitor

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, C. A.; Beklen, E.; Bhat, P. N.; Briggs, M.; Camero-Arranz, A.; Case, G.; Chaplin, V.; Cherry, M.; Connaughton, V.; Finger, M.; hide

    2010-01-01

    Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog is occulted by (or exits occultation by) the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. New sources are added to our catalog as they become active or upon request. In addition to Earth occultations, we have observed numerous occultations with Fermi's solar panels. We will present early results. Regularly updated results will be found on our website http://gammaray.nsstc.nasa.gov/gbm/science/occultation.

  5. A position-dependent mass model for the Thomas–Fermi potential: Exact solvability and relation to δ-doped semiconductors

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Schulze-Halberg, Axel, E-mail: xbataxel@gmail.com; García-Ravelo, Jesús; Pacheco-García, Christian

    We consider the Schrödinger equation in the Thomas–Fermi field, a model that has been used for describing electron systems in δ-doped semiconductors. It is shown that the problem becomes exactly-solvable if a particular effective (position-dependent) mass distribution is incorporated. Orthogonal sets of normalizable bound state solutions are constructed in explicit form, and the associated energies are determined. We compare our results with the corresponding findings on the constant-mass problem discussed by Ioriatti (1990) [13]. -- Highlights: ► We introduce an exactly solvable, position-dependent mass model for the Thomas–Fermi potential. ► Orthogonal sets of solutions to our model are constructed inmore » closed form. ► Relation to delta-doped semiconductors is discussed. ► Explicit subband bottom energies are calculated and compared to results obtained in a previous study.« less

  6. Fusion reaction cross-sections using the Wong model within Skyrme energy density based semiclassical extended Thomas Fermi approach

    NASA Astrophysics Data System (ADS)

    Kumar, Raj; Sharma, Manoj K.; Gupta, Raj K.

    2011-11-01

    First, the nuclear proximity potential, obtained by using the semiclassical extended Thomas Fermi (ETF) approach in Skyrme energy density formalism (SEDF), is shown to give more realistic barriers in frozen density approximation, as compared to the sudden approximation. Then, taking advantage of the fact that, in ETF method, different Skyrme forces give different barriers (height, position and curvature), we use the ℓ-summed extended-Wong model of Gupta and collaborators (2009) [1] under frozen densities approximation for calculating the cross-sections, where the Skyrme force is chosen with proper barrier characteristics, not-requiring additional "barrier modification" effects (lowering or narrowing, etc.), for a best fit to data at sub-barrier energies. The method is applied to capture cross-section data from 48Ca + 238U, 244Pu, and 248Cm reactions and to fusion-evaporation cross-sections from 58Ni + 58Ni, 64Ni + 64Ni, and 64Ni + 100Mo reactions, with effects of deformations and orientations of nuclei included, wherever required. Interestingly, whereas the capture cross-sections in Ca-induced reactions could be fitted to any force, such as SIII, SV and GSkI, by allowing a small change of couple of units in deduced ℓ-values at below-barrier energies, the near-barrier data point of 48Ca + 248Cm reaction could not be fitted to ℓ-values deduced for below-barrier energies, calling for a check of data. On the other hand, the fusion-evaporation cross-sections in Ni-induced reactions at sub-barrier energies required different Skyrme forces, representing "modifications of the barrier", for the best fit to data at all incident center-of-mass energies E's, displaying a kind of fusion hindrance at sub-barrier energies. This barrier modification effect is taken into care here by using different Skyrme forces for reactions belonging to different regions of the periodic table. Note that more than one Skyrme force (with identical barrier characteristics) could equally well

  7. Numerical simulation of the nonlinear dynamics of harmonically driven Riesz-fractional extensions of the Fermi-Pasta-Ulam chains

    NASA Astrophysics Data System (ADS)

    Macías-Díaz, J. E.

    2018-02-01

    In this work, we introduce a spatially discrete model that is a modification of the well-known α-Fermi-Pasta-Ulam chain with damping. The system is perturbed at one end by a harmonic disturbance irradiating at a frequency in the forbidden band-gap of the classical regime, and a nonlocal coupling between the oscillators is considered using discrete Riesz fractional derivatives. We propose fully discrete expressions to approximate an energy functional of the system, and we use them to calculate the total energy of fractional chains over a relatively long period of time [Fract. Diff. Appl. 4 (2004) 153-162]. The approach is thoroughly tested in the case of local couplings against known qualitative results, including simulations of the process of nonlinear recurrence in the traditional chains of anharmonic oscillators. As an application, we provide evidence that the process of supratransmission is present in spatially discrete Fermi-Pasta-Ulam lattices with Riesz fractional derivatives in space. Moreover, we perform numerical experiments for small and large amplitudes of the harmonic disturbance. In either case, we establish the dependency of the critical amplitude at which supratransmission begins as a function of the driving frequency. Our results are in good agreement with the analytic predictions for the classical Fermi-Pasta-Ulam chain.

  8. Single-particle spectral density of the unitary Fermi gas: Novel approach based on the operator product expansion, sum rules and the maximum entropy method

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gubler, Philipp, E-mail: pgubler@riken.jp; RIKEN Nishina Center, Wako, Saitama 351-0198; Yamamoto, Naoki

    2015-05-15

    Making use of the operator product expansion, we derive a general class of sum rules for the imaginary part of the single-particle self-energy of the unitary Fermi gas. The sum rules are analyzed numerically with the help of the maximum entropy method, which allows us to extract the single-particle spectral density as a function of both energy and momentum. These spectral densities contain basic information on the properties of the unitary Fermi gas, such as the dispersion relation and the superfluid pairing gap, for which we obtain reasonable agreement with the available results based on quantum Monte-Carlo simulations.

  9. Exploration of Fermi-Pasta-Ulam Behavior in a Magnetic System

    NASA Astrophysics Data System (ADS)

    Lewis, Jeramy; Camley, Robert E.; Anderson, Nicholas R.

    2018-04-01

    We study nonlinear spin motion in one-dimensional magnetic chains. We find significant differences from the classic Fermi-Pasta-Ulam (FPU) problem examining nonlinear elastic motion in a chain. We find that FPU behavior, the transfer of energy among low order eigenmodes, does not occur in magnetic systems with only exchange and external fields, but does exist if a uniaxial anisotropy is also present. The FPU behavior may be altered or turned off through the magnitude and orientation of an external magnetic field. A realistic micromagnetic model shows such behavior could be measurable.

  10. Non-Fermi-liquid magic angle effects in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Lebed, A. G.

    2016-07-01

    We investigate a theoretical problem of electron-electron interactions in an inclined magnetic field in a quasi-one-dimensional (Q1D) conductor. We show that they result in strong non-Fermi-liquid corrections to a specific heat, provided that the direction of the magnetic field is far from the so-called Lebed's magic angles (LMAs). If magnetic field is directed close to one of the LMAs, the specific heat corrections become small and the Fermi-liquid picture restores. As a result, we predict Fermi-liquid-non-Fermi-liquid angular crossovers in the vicinities of the LMA directions of the field. We suggest to perform the corresponding experiment in the Q1D conductor (Per) 2Au (mnt) 2 under pressure in magnetic fields of the order of H ≃25 T .

  11. Sub-saturation matter in compact stars: Nuclear modelling in the framework of the extended Thomas-Fermi theory

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Aymard, François; Gulminelli, Francesca; Margueron, Jérôme

    A recently introduced analytical model for the nuclear density profile [1] is implemented in the Extended Thomas-Fermi (ETF) energy density functional. This allows to (i) shed a new light on the issue of the sign of surface symmetry energy in nuclear mass formulas, as well as to (ii) show the importance of the in-medium corrections to the nuclear cluster energies in thermodynamic conditions relevant for the description of core-collapse supernovae and (proto)-neutron star crust.

  12. Sub-saturation matter in compact stars: Nuclear modelling in the framework of the extended Thomas-Fermi theory

    NASA Astrophysics Data System (ADS)

    Aymard, François; Gulminelli, Francesca; Margueron, Jérôme

    2015-02-01

    A recently introduced analytical model for the nuclear density profile [1] is implemented in the Extended Thomas-Fermi (ETF) energy density functional. This allows to (i) shed a new light on the issue of the sign of surface symmetry energy in nuclear mass formulas, as well as to (ii) show the importance of the in-medium corrections to the nuclear cluster energies in thermodynamic conditions relevant for the description of core-collapse supernovae and (proto)-neutron star crust.

  13. How Well Does a Funneled Energy Landscape Capture the Folding Mechanism of Spectrin Domains?

    PubMed Central

    2013-01-01

    Three structurally similar domains from α-spectrin have been shown to fold very differently. Firstly, there is a contrast in the folding mechanism, as probed by Φ-value analysis, between the R15 domain and the R16 and R17 domains. Secondly, there are very different contributions from internal friction to folding: the folding rate of the R15 domain was found to be inversely proportional to solvent viscosity, showing no apparent frictional contribution from the protein, but in the other two domains a large internal friction component was evident. Non-native misdocking of helices has been suggested to be responsible for this phenomenon. Here, I study the folding of these three proteins with minimalist coarse-grained models based on a funneled energy landscape. Remarkably, I find that, despite the absence of non-native interactions, the differences in folding mechanism of the domains are well captured by the model, and the agreement of the Φ-values with experiment is fairly good. On the other hand, within the context of this model, there are no significant differences in diffusion coefficient along the chosen folding coordinate, and the model cannot explain the large differences in folding rates between the proteins found experimentally. These results are nonetheless consistent with the expectations from the energy landscape perspective of protein folding: namely, that the folding mechanism is primarily determined by the native-like interactions present in the Gō-like model, with missing non-native interactions being required to explain the differences in “internal friction” seen in experiment. PMID:23947368

  14. The second fermi large area telescope catalog of gamma-ray pulsars

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Abdo, A. A.; Ajello, M.; Allafort, A.

    2013-09-19

    This catalog summarizes 117 high-confidence ≥0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emissionmore » for several young and millisecond pulsars. We compare the gamma-ray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.« less

  15. The second FERMI large area telescope catalog of gamma-ray pulsars

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Abdo, A. A.; Ajello, M.; Allafort, A.

    2013-09-19

    This catalog summarizes 117 high-confidence ≥0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on the Fermi satellite. Half are neutron stars discovered using LAT data through periodicity searches in gamma-ray and radio data around LAT unassociated source positions. The 117 pulsars are evenly divided into three groups: millisecond pulsars, young radio-loud pulsars, and young radio-quiet pulsars. We characterize the pulse profiles and energy spectra and derive luminosities when distance information exists. Spectral analysis of the off-peak phase intervals indicates probable pulsar wind nebula emission for four pulsars, and off-peak magnetospheric emissionmore » for several young and millisecond pulsars. We compare the gamma-ray properties with those in the radio, optical, and X-ray bands. We provide flux limits for pulsars with no observed gamma-ray emission, highlighting a small number of gamma-faint, radio-loud pulsars. The large, varied gamma-ray pulsar sample constrains emission models. Fermi's selection biases complement those of radio surveys, enhancing comparisons with predicted population distributions.« less

  16. Two-Dimensional Homogeneous Fermi Gases

    NASA Astrophysics Data System (ADS)

    Hueck, Klaus; Luick, Niclas; Sobirey, Lennart; Siegl, Jonas; Lompe, Thomas; Moritz, Henning

    2018-02-01

    We report on the experimental realization of homogeneous two-dimensional (2D) Fermi gases trapped in a box potential. In contrast to harmonically trapped gases, these homogeneous 2D systems are ideally suited to probe local as well as nonlocal properties of strongly interacting many-body systems. As a first benchmark experiment, we use a local probe to measure the density of a noninteracting 2D Fermi gas as a function of the chemical potential and find excellent agreement with the corresponding equation of state. We then perform matter wave focusing to extract the momentum distribution of the system and directly observe Pauli blocking in a near unity occupation of momentum states. Finally, we measure the momentum distribution of an interacting homogeneous 2D gas in the crossover between attractively interacting fermions and bosonic dimers.

  17. New Results from Fermi-LAT and Their Implications for the Nature of Dark Matter and the Origin of Cosmic Rays

    NASA Technical Reports Server (NTRS)

    Moiseev, Alexander

    2009-01-01

    The measured spectrum is compatible with a power law within our current systematic errors. The spectral index (-3.04) is harder than expected from previous experiments and simple theoretical considerations. "Pre-Fermi" diffusive model requires a harder electron injection spectrum (by 0.12) to fit the Fermi data, but inconsistent with positron excess reported by Pamela if it extends to higher energy. Additional component of electron flux from local source(s) may solve the problem; its origin, astrophysical or exotic, is still unclear. Valuable contribution to the calculation of IC component of diffuse gamma radiation.

  18. Impact of compressibility and a guide field on Fermi acceleration during magnetic island coalescence

    NASA Astrophysics Data System (ADS)

    Montag, P.; Egedal, J.; Lichko, E.; Wetherton, B.

    2017-06-01

    Previous work has shown that Fermi acceleration can be an effective heating mechanism during magnetic island coalescence, where electrons may undergo repeated reflections as the magnetic field lines contract. This energization has the potential to account for the power-law distributions of particle energy inferred from observations of solar flares. Here, we develop a generalized framework for the analysis of Fermi acceleration that can incorporate the effects of compressibility and non-uniformity along field lines, which have commonly been neglected in previous treatments of the problem. Applying this framework to the simplified case of the uniform flux tube allows us to find both the power-law scaling of the distribution function and the rate at which the power-law behavior develops. We find that a guide magnetic field of order unity effectively suppresses the development of power-law distributions.

  19. Fermi Large Area Telescope Observation Of A Gamma-Ray Source At The Position Of Eta Carinae

    DOE PAGES

    Abdo, A. A,

    2010-10-13

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected a γ-ray source that is spatially consistent with the location of Eta Carinae. This source has been persistently bright since the beginning of the LAT survey observations (from 2008 August to 2009 July, the time interval considered here). The γ-ray signal is detected significantly throughout the LAT energy band (i.e., up to ~100 GeV). The 0.1-100 GeV energy spectrum is well represented by a combination of a cutoff power-law model (<10 GeV) and a hard power-law component (>10 GeV). The total flux (>100 MeV) is 3.7 +0.3more » –0.1 × 10 –7 photons s –1 cm –2, with additional systematic uncertainties of 10%, and consistent with the average flux measured by AGILE. The light curve obtained by Fermi is consistent with steady emission. Our observations do not confirm the presence of a γ-ray flare in 2008 October, as reported by Tavani et al., although we cannot exclude that a flare lasting only a few hours escaped detection by the Fermi LAT. We also do not find any evidence for γ-ray variability that correlates with the large X-ray variability of Eta Carinae observed during 2008 December and 2009 January. We are thus not able to establish an unambiguous identification of the LAT source with Eta Carinae.« less

  20. Cut-off characterisation of energy spectra of bright fermi sources: Current instrument limits and future possibilities

    NASA Astrophysics Data System (ADS)

    Romoli, C.; Taylor, A. M.; Aharonian, F.

    2017-02-01

    In this paper some of the brightest GeV sources observed by the Fermi-LAT were analysed, focusing on their spectral cut-off region. The sources chosen for this investigation were the brightest blazar flares of 3C 454.3 and 3C 279 and the Vela pulsar with a reanalysis with the latest Fermi-LAT software. For the study of the spectral cut-off we first explored the Vela pulsar spectrum, whose statistics in the time interval of the 3FGL catalog allowed strong constraints to be obtained on the parameters. We subsequently performed a new analysis of the flaring blazar SEDs. For these sources we obtained constraints on the cut-off parameters under the assumption that their underlying spectral distribution is described by a power-law with a stretched exponential cut-off. We then highlighted the significant potential improvements on such constraints by observations with next generation ground based Cherenkov telescopes, represented in our study by the Cherenkov Telescope Array (CTA). Adopting currently available simulations for this future observatory, we demonstrate the considerable improvement in cut-off constraints achievable by observations with this new instrument when compared with that achievable by satellite observations.

  1. Observation of the Leggett-Rice Effect in a Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Trotzky, S.; Beattie, S.; Luciuk, C.; Smale, S.; Bardon, A. B.; Enss, T.; Taylor, E.; Zhang, S.; Thywissen, J. H.

    2015-01-01

    We observe that the diffusive spin current in a strongly interacting degenerate Fermi gas of 40K precesses about the local magnetization. As predicted by Leggett and Rice, precession is observed both in the Ramsey phase of a spin-echo sequence, and in the nonlinearity of the magnetization decay. At unitarity, we measure a Leggett-Rice parameter γ =1.08 (9 ) and a bare transverse spin diffusivity D0⊥=2.3 (4 )ℏ/m for a normal-state gas initialized with full polarization and at one-fifth of the Fermi temperature, where m is the atomic mass. One might expect γ =0 at unitarity, where two-body scattering is purely dissipative. We observe γ →0 as temperature is increased towards the Fermi temperature, consistent with calculations that show the degenerate Fermi sea restores a nonzero γ . Tuning the scattering length a , we find that a sign change in γ occurs in the range 0 <(kFa )-1≲1.3 , where kF is the Fermi momentum. We discuss how γ reveals the effective interaction strength of the gas, such that the sign change in γ indicates a switching of branch between a repulsive and an attractive Fermi gas.

  2. A low-latency pipeline for GRB light curve and spectrum using Fermi/GBM near real-time data

    NASA Astrophysics Data System (ADS)

    Zhao, Yi; Zhang, Bin-Bin; Xiong, Shao-Lin; Long, Xi; Zhang, Qiang; Song, Li-Ming; Sun, Jian-Chao; Wang, Yuan-Hao; Li, Han-Cheng; Bu, Qing-Cui; Feng, Min-Zi; Li, Zheng-Heng; Wen, Xing; Wu, Bo-Bing; Zhang, Lai-Yu; Zhang, Yong-Jie; Zhang, Shuang-Nan; Shao, Jian-Xiong

    2018-05-01

    Rapid response and short time latency are very important for Time Domain Astronomy, such as the observations of Gamma-ray Bursts (GRBs) and electromagnetic (EM) counterparts of gravitational waves (GWs). Based on near real-time Fermi/GBM data, we developed a low-latency pipeline to automatically calculate the temporal and spectral properties of GRBs. With this pipeline, some important parameters can be obtained, such as T 90 and fluence, within ∼ 20 min after the GRB trigger. For ∼ 90% of GRBs, T 90 and fluence are consistent with the GBM catalog results within 2σ errors. This pipeline has been used by the Gamma-ray Bursts Polarimeter (POLAR) and the Insight Hard X-ray Modulation Telescope (Insight-HXMT) to follow up the bursts of interest. For GRB 170817A, the first EM counterpart of GW events detected by Fermi/GBM and INTEGRAL/SPI-ACS, the pipeline gave T 90 and spectral information 21 min after the GBM trigger, providing important information for POLAR and Insight-HXMT observations.

  3. MASTER: OT detection during Fermi trigger inspection

    NASA Astrophysics Data System (ADS)

    Popova, E.; Lipunov, V.; Buckley, D.; Gorbovskoy, E.; Tiurina, N.; Balanutsa, P.; Kuznetsov, A.; Kornilov, V.; Chazov, V.; Vlasenko, D.; Vladimirov, V.; Gress, O.; Ivanov, K.; Potter, S.; Gabovich, A.

    2016-11-01

    During inspection of Fermi trigger 501261070 ( (Ra,Dec)=47.190,-47.210; GRB_ERROR_radius=3.27deg, GRB_TIME=2016/11/19 15:11:06.40UT http://gcn.gsfc.nasa.gov/other/501261070.fermi ) MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 03h 22m 52.70s -48d 29m 10.9s on 2016-11-19 21:17:17.878UT with unfiltered m_OT=17.8 (mlim=19.7).

  4. Experimental observation of optical Weyl points and Fermi arcs

    NASA Astrophysics Data System (ADS)

    Rechtsman, Mikael

    We directly observe the presence type-II Weyl points for optical photons in a three-dimensional dielectric structure comprising arrays of evanescently-coupled, single-mode, helical waveguides. We also observe the corresponding Fermi arc surface states emerging from Weyl points (despite the use of the `Fermi arc' terminology, we are referring to bosons rather than fermions). The Weyl points are manifested by the presence of conical diffraction at the Weyl frequency in the photonic band structure, and the Fermi arc states are manifested by the emergence of surface states as we scan in frequency past the Weyl point. We map the Weyl points to Dirac points of the isofrequency surface, and the Fermi arcs to chiral edge states of an anomalous Floquet insulator. In collaboration with: Jiho Noh, Sheng Huang, Daniel Leykam*, Y. D. Chong, Kevin Chen, and Mikael C. Rechtsman M.C.R. acknowledges the National Science Foundation under Award Number ECCS-1509546, the Penn State MRSEC, Center for Nanoscale Science, under Award Number NSF DMR-1420620, and the Alfred P. Sloan Foundation under fellowship number FG-2016-6418.

  5. Terrestrial Gamma-Ray Flashes (TGFs) Observed with the Fermi-Gamma-Ray Burst Monitor: The First Hundred TGFs

    NASA Technical Reports Server (NTRS)

    Fishman, G J.; Briggs, M. S.; Connaughton, V.; Bhat, P. N.

    2010-01-01

    The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope Observatory (Fermi) is now detecting 2.1 TGFs per week. At this rate, nearly a hundred TGFs will have been detected by the time of this Meeting. This rate has increased by a factor of 8 since new flight software was uploaded to the spacecraft in November 2009 in order to increase the sensitivity of GBM to TGFs. The high time resolution (2 microseconds) allows temporal features to be resolved so that some insight may be gained on the origin and transport of the gamma-ray photons through the atmosphere. The absolute time of the TGFs, known to several microseconds, also allows accurate correlations of TGFs with lightning networks and other lightning-related phenomena. The thick bismuth germanate (BGO) scintillation detectors of the GBM system have observed photon energies from TGFs at energies above 40 MeV. New results on the some temporal aspects of TGFs will be presented.

  6. The contact of a homogeneous unitary Fermi gas

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Patel, Parth; Yan, Zhenjie; Fletcher, Richard; Struck, Julian; Zwierlein, Martin

    2017-04-01

    The contact is a fundamental quantity that measures the strength of short-range correlations in quantum gases. As one of its most important implications, it provides a link between the microscopic two-particle correlation function at small distance and the macroscopic thermodynamic properties of the gas. In particular, pairing and superfluidity in a unitary Fermi gas can be expected to leave its mark in behavior of the contact. Here we present measurements on the temperature dependence of the contact of a unitary Fermi gas across the superfluid transition. By trapping ultracold 6Li atoms in a potential that is homogeneous in two directions and harmonic in the third, we obtain radiofrequency spectra of the homogeneous gas at a high signal-to-noise ratio. We compare our data to existing, but often mutually excluding theoretical calculations for the strongly interacting Fermi gas.

  7. Enhanced high-energy gamma-ray emission from the microquasar Cygnus X-3 detected by Fermi/LAT

    NASA Astrophysics Data System (ADS)

    Loh, Alan; Corbel, Stephane

    2017-02-01

    Following the recent decrease of the hard X-ray emission from the high-mass X-ray binary Cygnus X-3 as seen by the Swift/Burst Alert Telescope (https://swift.gsfc.nasa.gov/results/transients/CygX-3/), the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed significant gamma-ray emission originating from the microquasar.

  8. On the validity of the amphoteric-defect model in gallium arsenide and a criterion for Fermi-level pinning by defects

    NASA Astrophysics Data System (ADS)

    Chen, C.-H.; Tan, T. Y.

    1995-10-01

    Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, an amphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancy V {Ga/2-} and the triply positively charged defect complex (ASGa+ V As)3+, with AsGa being the antisite defect of an As atom occupying a Ga site and V As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect system V {Ga/2-}/(AsGa+ V As)3+ is supposed to be able to pin the GaAs Fermi level at approximately the E v +0.6 eV level position, which requires that the net free energy of the V Ga/(AsGa+ V As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about the E v +1.2 eV level position instead of the needed E v +0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future.

  9. Limits on dark matter annihilation signals from the Fermi LAT 4-year measurement of the isotropic gamma-ray background

    DOE PAGES

    Ackermann, M.

    2015-09-02

    We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) measured with 50 months of Fermi Large Area Telescope (LAT) observations. An improved theoretical description of the cosmological DM annihilation signal, based on two complementary techniques and assuming generic weakly interacting massive particle (WIMP) properties, renders more precise predictions compared to previous work. More specifically, we estimate the cosmologically-induced gamma-ray intensity to have an uncertainty of a factor ~ 20 in canonical setups. We consistently include both the Galactic and extragalactic signals under the same theoretical framework, and study the impact of the former onmore » the IGRB spectrum derivation. We find no evidence for a DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our limits are competitive for DM particle masses up to tens of TeV and, indeed, are the strongest limits derived from Fermi LAT data at TeV energies. This is possible thanks to the new Fermi LAT IGRB measurement, which now extends up to an energy of 820 GeV. As a result, we quantify uncertainties in detail and show the potential this type of search offers for testing the WIMP paradigm with a complementary and truly cosmological probe of DM particle signals.« less

  10. Limits on dark matter annihilation signals from the Fermi LAT 4-year measurement of the isotropic gamma-ray background

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Collaboration: Fermi LAT Collaboration

    2015-09-01

    We search for evidence of dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) measured with 50 months of Fermi Large Area Telescope (LAT) observations. An improved theoretical description of the cosmological DM annihilation signal, based on two complementary techniques and assuming generic weakly interacting massive particle (WIMP) properties, renders more precise predictions compared to previous work. More specifically, we estimate the cosmologically-induced gamma-ray intensity to have an uncertainty of a factor ∼ 20 in canonical setups. We consistently include both the Galactic and extragalactic signals under the same theoretical framework, and study the impact of the former on themore » IGRB spectrum derivation. We find no evidence for a DM signal and we set limits on the DM-induced isotropic gamma-ray signal. Our limits are competitive for DM particle masses up to tens of TeV and, indeed, are the strongest limits derived from Fermi LAT data at TeV energies. This is possible thanks to the new Fermi LAT IGRB measurement, which now extends up to an energy of 820 GeV. We quantify uncertainties in detail and show the potential this type of search offers for testing the WIMP paradigm with a complementary and truly cosmological probe of DM particle signals.« less

  11. The Third Fermi LAT Catalog of High-Energy Gamma-ray Sources

    NASA Astrophysics Data System (ADS)

    Thompson, David J.; Ballet, J.; Burnett, T.; Fermi Large Area Telescope Collaboration

    2014-01-01

    The Fermi Gamma-ray Space Telescope Large Area Telescope (LAT) has been gathering science data since August 2008, surveying the full sky every three hours. The second source catalog (2FGL, Nolan et al 2012, ApJS 199, 31) was based on 2 years of data. We are preparing a third source catalog (3FGL) based on 4 years of reprocessed data. The reprocessing introduced a more accurate description of the instrument, which resulted in a narrower point spread function. Both the localization and the detection threshold for hard-spectrum sources have been improved. The new catalog also relies on a refined model of Galactic diffuse emission, particularly important for low-latitude soft-spectrum sources. The process for associating LAT sources with those at other wavelengths has also improved, thanks to dedicated multiwavelength follow-up, new surveys and better ways to extract sources likely to be gamma-ray counterparts. We describe the construction of this new catalog, its characteristics, and its remaining limitations.

  12. The Third Fermi-LAT Catalog of High-Energy Gamma-ray Sources

    NASA Astrophysics Data System (ADS)

    Burnett, Toby

    2014-03-01

    The Fermi Gamma-ray Space Telescope Large Area Telescope (LAT) has been gathering science data since August 2008, surveying the full sky every three hours. The second source catalog (2FGL, Nolan et al. 2012, ApJS 199, 31) was based on 2 years of data. We are preparing a third source catalog (3FGL) based on 4 years of reprocessed data. The reprocessing introduced a more accurate description of the instrument, which resulted in a narrower point spread function. Both the localization and the detection threshold for hard-spectrum sources have been improved. The new catalog also relies on a refined model of Galactic diffuse emission, particularly important for low-latitude soft-spectrum sources. The process for associating LAT sources with those at other wavelengths has also improved, thanks to dedicated multiwavelength follow-up, new surveys and better ways to extract sources likely to be gamma-ray counterparts. We describe the construction of this new catalog, its characteristics, and its remaining limitations.

  13. Generalized Thomas-Fermi equations as the Lampariello class of Emden-Fowler equations

    NASA Astrophysics Data System (ADS)

    Rosu, Haret C.; Mancas, Stefan C.

    2017-04-01

    A one-parameter family of Emden-Fowler equations defined by Lampariello's parameter p which, upon using Thomas-Fermi boundary conditions, turns into a set of generalized Thomas-Fermi equations comprising the standard Thomas-Fermi equation for p = 1 is studied in this paper. The entire family is shown to be non integrable by reduction to the corresponding Abel equations whose invariants do not satisfy a known integrability condition. We also discuss the equivalent dynamical system of equations for the standard Thomas-Fermi equation and perform its phase-plane analysis. The results of the latter analysis are similar for the whole class.

  14. Microscopic calculations of dynamics and N/Z equilibration in peripheral collisions below the Fermi energy.

    NASA Astrophysics Data System (ADS)

    Souliotis, G. A.; Shetty, D. V.; Galanopoulos, S.; Yennello, S. J.

    2008-04-01

    A systematic study of heavy residues formed in peripheral collisions below the Fermi energy has been undertaken at Texas A&M aiming at obtaining information on the mechanism of nucleon exchange and the course towards N/Z equilibration [1,2]. We expect to get insight on the dynamics and the nuclear equation of state by comparing our heavy residue data to detailed calculations using microscopic models of quantum molecular dynamics (QMD) type. We are performing calculations using two codes: the CoMD code of M. Papa, A. Bonasera [3] and the CHIMERA-QMD code of J. Lukasik [4]. Both codes implement an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. CoMD imposes a constraint in the phase space occupation for each nucleon restoring the Pauli principle at each time step of the collision. CHIMERA-QMD uses a Pauli potential term to mimic the Pauli principle. Results of the calculations and comparisons with our residue data will be presented. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003). [2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004). [3] M. Papa et al., Phys. Rev. C 64, 024612 (2001). [4] J. Lukasik, Z. Majka, Acta Phys. Pol. B 24, 1959 (1993).

  15. Fermi-LAT Observations of High-Energy Gamma-Ray Emission Toward the Galactic Center

    DOE PAGES

    Ajello, M.

    2016-02-26

    The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission towards the Galactic centre (GC) in high-energy γ-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1 - 100 GeV from a 15° X15° region about the direction of the GC, and implications for the interstellar emissions produced by cosmic ray (CR) particles interacting with the gas and radiation fields in the inner Galaxy and for the point sources detected. Specialised interstellar emission models (IEMs) are constructed that enable separation ofmore » the γ-ray emission from the inner ~ 1 kpc about the GC from the fore- and background emission from the Galaxy. Based on these models, the interstellar emission from CR electrons interacting with the interstellar radiation field via the inverse Compton (IC) process and CR nuclei inelastically scattering off the gas producing γ-rays via π⁰ decays from the inner ~ 1 kpc is determined. The IC contribution is found to be dominant in the region and strongly enhanced compared to previous studies. A catalog of point sources for the 15 °X 15 °region is self-consistently constructed using these IEMs: the First Fermi–LAT Inner Galaxy point source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with γ-ray point sources over the same region taken from existing catalogs, including the Third Fermi–LAT Source Catalog (3FGL). In general, the spatial density of 1FIG sources differs from those in the 3FGL, which is attributed to the different treatments of the interstellar emission and energy ranges used by the respective analyses. Three 1FIG sources are found to spatially overlap with supernova remnants (SNRs) listed in Green’s SNR catalog; these SNRs have not previously been associated with high-energy γ-ray sources. Most 3FGL sources with known multi-wavelength counterparts are also found

  16. Quantum Space Charge Waves in a Waveguide Filled with Fermi-Dirac Plasmas Including Relativistic Wake Field and Quantum Statistical Pressure Effects

    NASA Astrophysics Data System (ADS)

    Hong, Woo-Pyo; Jung, Young-Dae

    2018-03-01

    The effects of quantum statistical degeneracy pressure on the propagation of the quantum space charge wave are investigated in a cylindrically bounded plasma waveguide filled with relativistically degenerate quantum Fermi-Dirac plasmas and the relativistic ion wake field. The results show that the domain of the degenerate parameter for the resonant beam instability significantly increases with an increase of the scaled beam velocity. It is found that the instability domain of the wave number increases with an increase of the degenerate parameter. It is also found that the growth rate for the resonant beam instability decreases with an increase of the degenerate parameter. In addition, it is shown that the lowest harmonic mode provides the maximum value of the growth rates. Moreover, it is shown that the instability domain of the wave number decreases with an increase of the beam velocity.

  17. Semiclassical Calculations of Peripheral Heavy-Ion Collisions at Fermi Energies and the Nuclear Equation of State

    NASA Astrophysics Data System (ADS)

    Souliotis, G. A.; Shetty, D. V.; Galanopoulos, S.; Yennello, S. J.

    2008-10-01

    A systematic study of quasi-elastic and deep-inelastic collisions at Fermi energies has been undertaken at Texas A&M aiming at obtaining information on the mechanism of nucleon exchange and the course towards N/Z equilibration [1,2]. We expect to get insight in the dynamics and the nuclear equation of state by comparing our experimental heavy residue data to detailed calculations using microscopic models of quantum molecular dynamics (QMD) type. At present, we have performed detailed calculations using the code CoMD (Constrained Molecular Dynamics) of A. Bonasera and M. Papa [3]. The code implements an effective interaction with a nuclear-matter compressibility of K=200 (soft EOS) with several forms of the density dependence of the nucleon-nucleon symmetry potential. CoMD imposes a constraint in the phase space occupation for each nucleon, effectively restoring the Pauli principle at each time step of the collision. Results of the calculations and comparisons with our data will be presented and implications concerning the isospin part of the nuclear equation of state will be discussed. [1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003). [2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004). [3] M. Papa et al., Phys. Rev. C 64, 024612 (2001).

  18. Renormalization Group Theory for the Imbalanced Fermi Gas

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Gubbels, K. B.; Stoof, H. T. C.

    2008-04-11

    We formulate a Wilsonian renormalization group theory for the imbalanced Fermi gas. The theory is able to recover quantitatively well-established results in both the weak-coupling and the strong-coupling (unitarity) limits. We determine for the latter case the line of second-order phase transitions of the imbalanced Fermi gas and, in particular, the location of the tricritical point. We obtain good agreement with the recent experiments of Y. Shin et al. [Nature (London) 451, 689 (2008)].

  19. Bright gamma-ray flares of the quasars 3C 279 and PKS 1222+216 observed at the highest energies with Fermi-LAT and VERITAS

    NASA Astrophysics Data System (ADS)

    Errando, Manel

    2014-08-01

    Flat spectrum radio quasars (FSRQs) are the most powerful sources continuously detected at gamma-ray energies, with luminosities exceeding 1048 erg s-1. The high-energy emission of quasars peaks in the MeV-GeV band, and only a few episodic detections have been reported at very high energies (VHE, E>100 GeV). We will present the first results from an observing campaign on the FSRQ 3C 279 in April 2014 during the brightest gamma-ray outburst ever recorded for this object, with flux exceeding the historic 1991 flare seen by EGRET. Observations include simultaneous coverage with the Fermi-LAT satellite and the VERITAS ground-based array spanning four decades in energy from 100 MeV to 1 TeV with unprecedented sensitivity. We will also report on the detection of persistent VHE emission from the quasar PKS 1222+216 over a week-long period in March 2014. These observations present strong challenges to current models of energy dissipation in relativistic jets. The implications of the absence/presence of VHE emission in connection with flaring activity in the MeV-GeV regime will be discussed, especially concerning the role of ambient photon fields in the radiation mechanisms, and the size and location of the gamma-ray emission region.

  20. Background model systematics for the Fermi GeV excess

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Calore, Francesca; Cholis, Ilias; Weniger, Christoph

    2015-03-01

    The possible gamma-ray excess in the inner Galaxy and the Galactic center (GC) suggested by Fermi-LAT observations has triggered a large number of studies. It has been interpreted as a variety of different phenomena such as a signal from WIMP dark matter annihilation, gamma-ray emission from a population of millisecond pulsars, or emission from cosmic rays injected in a sequence of burst-like events or continuously at the GC. We present the first comprehensive study of model systematics coming from the Galactic diffuse emission in the inner part of our Galaxy and their impact on the inferred properties of the excessmore » emission at Galactic latitudes 2° < |b| < 20° and 300 MeV to 500 GeV. We study both theoretical and empirical model systematics, which we deduce from a large range of Galactic diffuse emission models and a principal component analysis of residuals in numerous test regions along the Galactic plane. We show that the hypothesis of an extended spherical excess emission with a uniform energy spectrum is compatible with the Fermi-LAT data in our region of interest at 95% CL. Assuming that this excess is the extended counterpart of the one seen in the inner few degrees of the Galaxy, we derive a lower limit of 10.0° (95% CL) on its extension away from the GC. We show that, in light of the large correlated uncertainties that affect the subtraction of the Galactic diffuse emission in the relevant regions, the energy spectrum of the excess is equally compatible with both a simple broken power-law of break energy E(break) = 2.1 ± 0.2 GeV, and with spectra predicted by the self-annihilation of dark matter, implying in the case of bar bb final states a dark matter mass of m(χ)=49(+6.4)(-)(5.4)  GeV.« less

  1. Fast trimers in a one-dimensional extended Fermi-Hubbard model

    NASA Astrophysics Data System (ADS)

    Dhar, A.; Törmä, P.; Kinnunen, J. J.

    2018-04-01

    We consider a one-dimensional two-component extended Fermi-Hubbard model with nearest-neighbor interactions and mass imbalance between the two species. We study the binding energy of trimers, various observables for detecting them, and expansion dynamics. We generalize the definition of the trimer gap to include the formation of different types of clusters originating from nearest-neighbor interactions. Expansion dynamics reveal rapidly propagating trimers, with speeds exceeding doublon propagation in the strongly interacting regime. We present a simple model for understanding this unique feature of the movement of the trimers, and we discuss the potential for experimental realization.

  2. Do the surface Fermi arcs in Weyl semimetals survive disorder?

    NASA Astrophysics Data System (ADS)

    Wilson, Justin H.; Pixley, J. H.; Huse, David A.; Refael, Gil; Das Sarma, S.

    2018-06-01

    We theoretically study the topological robustness of the surface physics induced by Weyl Fermi-arc surface states in the presence of short-ranged quenched disorder and surface-bulk hybridization. This is investigated with numerically exact calculations on a lattice model exhibiting Weyl Fermi arcs. We find that the Fermi-arc surface states, in addition to having a finite lifetime from disorder broadening, hybridize with nonperturbative bulk rare states making them no longer bound to the surface (i.e., they lose their purely surface spectral character). Thus, we provide strong numerical evidence that the Weyl Fermi arcs are not topologically protected from disorder. Nonetheless, the surface chiral velocity is robust and survives in the presence of strong disorder, persisting all the way to the Anderson-localized phase by forming localized current loops that live within the localization length of the surface. Thus, the Weyl semimetal is not topologically robust to the presence of disorder, but the surface chiral velocity is.

  3. Five Years of the Fermi LAT Flare Advocate

    NASA Astrophysics Data System (ADS)

    Carpenter, Bryce; Ojha, R.; Gasparrini, D.; Ciprini, S.; Fermi LAT Collaboration; Fermi LAT Flare Advocates

    2014-01-01

    Since the launch of the Fermi satellite, the Fermi Large Area Telescope (LAT) team has run a program that provides a daily review of the the gamma-ray sky as soon as Fermi LAT data becomes available. The Flare Advocate/Gamma-ray Sky Watcher (FA-GSW) program allows a rapid analysis of the Automatic Science Processing (ASP) products and triggers dedicated followup analyses by several LAT science groups such as those studying Galactic transients, extragalactic sources and new gamma-ray sources. Significant gamma-ray detections also trigger rapid communications to the entire astrophysical community via astronomical telegrams and gamma-ray coordination network notices. The FA-GSW program plays a key role in maximizing the science return from Fermi by increasing the rate of multi-frequency observations of sources in an active gamma-ray state. In the past ~5 years blazar flaring activity of varying strength and duty cycles, gravitationally lensed blazars, flares from Galactic sources (like Nova Delphini and the Crab Nebula), unidentified transients near and off the Galactic plane, and emission from the quiet and flaring Sun, represent the range of detections made. Flare Advocates have published about 250 Astronomical Telegrams and they publish a weekly blog. Timely, extensive multi-frequency campaigns have been organized to follow-up on these phenomena leading to some of Fermi’s most interesting results.

  4. Generating Localized Nonlinear Excitations in the Fermi-Pasta-Ulam-Tsingou chains

    NASA Astrophysics Data System (ADS)

    Westley, Alexandra; Sen, Surajit

    Here, we will discuss properties of energy trapping in the decorated Fermi-Pasta-Ulam-Tsingou (FPUT) mass-spring chains with quadratic and quartic coupling terms. It is well-known that the FPUT system admits highly localized nonlinear excitations (LNE) which are stable for long periods of time. We seek to generate these LNEs at will by creating regions in the chain of stiffer or softer springs, or by placing mass impurities throughout. We will show that NLEs tend to coalesce in regions of stiff springs from random perturbations throughout the system. These locations may serve as extremely powerful energy traps or heat sinks in certain materials. Furthermore, we will demonstrate that this process occurs by means of trapping solitary (or anti-solitary) waves into tight spaces.

  5. The novel metallic states of the cuprates: Topological Fermi liquids and strange metals

    NASA Astrophysics Data System (ADS)

    Sachdev, Subir; Chowdhury, Debanjan

    2016-12-01

    We review ideas on the nature of the metallic states of the hole-doped cuprate high temperature superconductors, with an emphasis on the connections between the Luttinger theorem for the size of the Fermi surface, topological quantum field theories (TQFTs), and critical theories involving changes in the size of the Fermi surface. We begin with the derivation of the Luttinger theorem for a Fermi liquid, using momentum balance during a process of flux insertion in a lattice electronic model with toroidal boundary conditions. We then review the TQFT of the ℤ spin liquid, and demonstrate its compatibility with the toroidal momentum balance argument. This discussion leads naturally to a simple construction of "topological" Fermi liquid states: the fractionalized Fermi liquid (FL*) and the algebraic charge liquid (ACL). We present arguments for a description of the pseudogap metal of the cuprates using ℤ-FL* or ℤ-ACL states with Ising-nematic order. These pseudogap metal states are also described as Higgs phases of a SU(2) gauge theory. The Higgs field represents local antiferromagnetism, but the Higgs-condensed phase does not have long-range antiferromagnetic order: the magnitude of the Higgs field determines the pseudogap, the reconstruction of the Fermi surface, and the Ising-nematic order. Finally, we discuss the route to the large Fermi surface Fermi liquid via the critical point where the Higgs condensate and Ising nematic order vanish, and the application of Higgs criticality to the strange metal.

  6. Trapped one-dimensional ideal Fermi gas with a single impurity

    NASA Astrophysics Data System (ADS)

    Astrakharchik, G. E.; Brouzos, I.

    2013-08-01

    Ground-state properties of a single impurity in a one-dimensional Fermi gas are investigated in uniform and trapped geometries. The energy of a trapped system is obtained (i) by generalizing the McGuire expression from a uniform to trapped system (ii) within the local density approximation (iii) using the perturbative approach in the case of a weakly interacting impurity and (iv) diffusion Monte Carlo method. We demonstrate that there is a closed formula based on the exact solution of the homogeneous case which provides a precise estimation for the energy of a trapped system even for a small number of fermions and arbitrary coupling constant of the impurity. Using this expression, we analyze energy contributions from kinetic, interaction, and potential components, as well as spatial properties such as the system size and the pair-correlation function. Finally, we calculate the frequency of the breathing mode. Our analysis is directly connected and applicable to the recent experiments in microtraps.

  7. Single reconstructed Fermi surface pocket in an underdoped single-layer cuprate superconductor

    DOE PAGES

    Chan, Mun Keat; Harrison, Neil; Mcdonald, Ross David; ...

    2016-07-22

    The observation of a reconstructed Fermi surface via quantum oscillations in hole-doped cuprates opened a path towards identifying broken symmetry states in the pseudogap regime. However, such an identification has remained inconclusive due to the multi-frequency quantum oscillation spectra and complications accounting for bilayer effects in most studies. We overcome these impediments with high-resolution measurements on the structurally simpler cuprate HgBa2CuO4+δ (Hg1201), which features one CuO2 plane per primitive unit cell. We find only a single oscillatory component with no signatures of magnetic breakdown tunnelling to additional orbits. Therefore, the Fermi surface comprises a single quasi-two-dimensional pocket. Quantitative modelling ofmore » these results indicates that a biaxial charge density wave within each CuO2 plane is responsible for the reconstruction and rules out criss-crossed charge stripes between layers as a viable alternative in Hg1201. Lastly, we determine that the characteristic gap between reconstructed pockets is a significant fraction of the pseudogap energy« less

  8. Effect of Fermi surface nesting on resonant spin excitations in Ba{<_1-x}K{<_x}Fe{<_2}As{<_2}.

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Castellan, J.-P.; Rosenkranz, S.; Goremychkin, E.A.

    2011-01-01

    We report inelastic neutron scattering measurements of the resonant spin excitations in Ba{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s{sub {+-}}-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.

  9. Fermi Large Area Telescope detection of a break in the gamma-ray spectrum of the supernova remnant Cassiopeia A [ Fermi-LAT detection of a break in the gamma-ray spectrum of the supernova remnant Cassiopeia A

    DOE PAGES

    Yuan, Yajie; Funk, Stefan; Jóhannesson, Gülauger; ...

    2013-12-02

    Here, we report on observations of the supernova remnant Cassiopeia A in the energy range from 100 MeV to 100 GeV using 44 months of observations from the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. We perform a detailed spectral analysis of this source and report on a low-energy break in the spectrum atmore » $$1.72^{+1.35}_{-0.89}$$ GeV. By comparing the results with models for the gamma-ray emission, we find that hadronic emission is preferred for the GeV energy range.« less

  10. Non-Fermi-liquid nature and exotic thermoelectric power in the heavy-fermion superconductor UBe13

    NASA Astrophysics Data System (ADS)

    Shimizu, Yusei; Pourret, Alexandre; Knebel, Georg; Palacio-Morales, Alexandra; Aoki, Dai

    2015-12-01

    We report quite exotic thermoelectric power S in UBe13. At 0 T, the negative S /T continues to strongly enhance down to the superconducting transition temperature with no Fermi-liquid behavior. |S /T | is dramatically suppressed and becomes rather modest with increasing field. We have also obtained precise field dependencies of (i) an anomaly in S due to an exotic Kondo effect and (ii) a field-induced anomaly in S /T associated with the anomalous upward Hc 2(T ) . In contrast to the field-sensitive transport property, the normal-state specific heat is magnetically robust, indicating that the largeness of the 5 f density of states remains in high fields. This unusual behavior in UBe13 can be explained by a considerable change in the energy derivative of the conduction-electron lifetime τc(ɛ ) at the Fermi level under magnetic fields.

  11. New Display-type Analyzer for Three-dimensional Fermi Surface Mapping and Atomic Orbital Analysis

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Takahashi, Nobuaki; Matsuda, Hiroyuki; Shigenai, Shin

    2007-01-19

    We have developed and installed a new Display-type ANAlyzer (DIANA) at Ritsumeikan SR center BL-7. We measured the angle-integrated energy distribution curve of poly-crystal gold and the photoelectron intensity angular distribution (PIAD) of HOPG to estimate the total energy resolution and to check the condition of the analyzer. The total energy resolution ({delta}E/E) is up to 0.78%, which is much higher than the old type. The PIAD of HOPG we obtained was the ring pattern as expected. Therefore, a detailed three-dimensional Fermi surface mapping and an analysis of the atomic orbitals constituting the electron energy bands are possible by combiningmore » them with a linearly polarized synchrotron radiation.« less

  12. Description of atomic burials in compact globular proteins by Fermi-Dirac probability distributions.

    PubMed

    Gomes, Antonio L C; de Rezende, Júlia R; Pereira de Araújo, Antônio F; Shakhnovich, Eugene I

    2007-02-01

    We perform a statistical analysis of atomic distributions as a function of the distance R from the molecular geometrical center in a nonredundant set of compact globular proteins. The number of atoms increases quadratically for small R, indicating a constant average density inside the core, reaches a maximum at a size-dependent distance R(max), and falls rapidly for larger R. The empirical curves turn out to be consistent with the volume increase of spherical concentric solid shells and a Fermi-Dirac distribution in which the distance R plays the role of an effective atomic energy epsilon(R) = R. The effective chemical potential mu governing the distribution increases with the number of residues, reflecting the size of the protein globule, while the temperature parameter beta decreases. Interestingly, betamu is not as strongly dependent on protein size and appears to be tuned to maintain approximately half of the atoms in the high density interior and the other half in the exterior region of rapidly decreasing density. A normalized size-independent distribution was obtained for the atomic probability as a function of the reduced distance, r = R/R(g), where R(g) is the radius of gyration. The global normalized Fermi distribution, F(r), can be reasonably decomposed in Fermi-like subdistributions for different atomic types tau, F(tau)(r), with Sigma(tau)F(tau)(r) = F(r), which depend on two additional parameters mu(tau) and h(tau). The chemical potential mu(tau) affects a scaling prefactor and depends on the overall frequency of the corresponding atomic type, while the maximum position of the subdistribution is determined by h(tau), which appears in a type-dependent atomic effective energy, epsilon(tau)(r) = h(tau)r, and is strongly correlated to available hydrophobicity scales. Better adjustments are obtained when the effective energy is not assumed to be necessarily linear, or epsilon(tau)*(r) = h(tau)*r(alpha,), in which case a correlation with hydrophobicity

  13. Enrico Fermi - And the Revolutions of Modern Physics

    NASA Astrophysics Data System (ADS)

    Cooper, Dan

    1999-02-01

    In 1938, at the age of 37, Enrico Fermi was awarded the Nobel Prize in Physics. That same year he emigrated from Italy to the United States and, in the course of his experiments, discovered nuclear fission--a process which forms the basis of nuclear power and atomic bombs. Soon the brilliant physicist was involved in the top secret race to produce the deadliest weapon on Earth. He created the first self-sustaining chain reaction, devised new methods for purifying plutonium, and eventually participated in the first atomic test. This compelling biography traces Fermis education in Italy, his meteoric career in the scientific world, his escape from fascism to America, and the ingenious experiments he devised and conducted at the University of Rome, Columbia University, and the Los Alamos laboratory. The book also presents a mini-course in quantum and nuclear physics in an accessible, fast-paced narrative that invokes all the dizzying passion of Fermis brilliant discoveries.

  14. Modeling the instability behavior of thin film devices: Fermi Level Pinning

    NASA Astrophysics Data System (ADS)

    Moeini, Iman; Ahmadpour, Mohammad; Gorji, Nima E.

    2018-05-01

    We investigate the underlying physics of degradation/recovery of a metal/n-CdTe Schottcky junction under reverse or forward bias stressing conditions. We used Sah-Noyce-Shockley (SNS) theory to investigate if the swept of Fermi level pinning at different levels (under forward/reverse bias) is the origin of change in current-voltage characteristics of the device. This theory is based on Shockley-Read-Hall recombination within the depletion width and takes into account the interface defect levels. Fermi Level Pinning theory was primarily introduced by Ponpon and developed to thin film solar cells by Dharmadasa's group in Sheffield University-UK. The theory suggests that Fermi level pinning at multiple levels occurs due to high concentration of electron-traps or acceptor-like defects at the interface of a Schottky or pn junction and this re-arranges the recombination rate and charage collection. Shift of these levels under stress conditions determines the change in current-voltage characteristics of the cell. This theory was suggested for several device such as metal/n-CdTe, CdS/CdTe, CIGS/CdS or even GaAs solar cells without a modeling approach to clearly explain it's physics. We have applied the strong SNS modeling approach to shed light on Fermi Level Pinning theory. The modeling confirms that change in position of Fermi Level and it's pining in a lower level close to Valence band increases the recombination and reduces the open-circuit voltage. In contrast, Fermi Level pinning close to conduction band strengthens the electric field at the junction which amplifies the carrier collection and boosts the open-circuit voltage. This theory can well explain the stress effect on device characteristics of various solar cells or Schottky junctions by simply finding the right Fermi level pinning position at every specific stress condition.

  15. Fermi surfaces of the pyrite-type cubic AuSb2 compared with split Fermi surfaces of the ullmannite-type cubic chiral NiSbS and PdBiSe

    NASA Astrophysics Data System (ADS)

    Nishimura, K.; Kakihana, M.; Nakamura, A.; Aoki, D.; Harima, H.; Hedo, M.; Nakama, T.; Ōnuki, Y.

    2018-05-01

    We grew high-quality single crystals of AuSb2 with the pyrite (FeS2)-type cubic structure by the Bridgman method and studied the Fermi surface properties by the de Haas-van Alphen (dHvA) experiment and the full potential LAPW band calculation. The Fermi surfaces of AuSb2 are found to be similar to those of NiSbS and PdBiSe with the ullmannite (NiSbS)-type cubic chiral structure because the crystal structures are similar each other and the number of valence electrons is the same between two different compounds. Note that each Fermi surface splits into two Fermi surfaces in NiSbS and PdBiSe, reflecting the non-centrosymmetric crystal structure.

  16. Lorentz Invariance Violation: the Latest Fermi Results and the GRB-AGN Complementarity

    NASA Technical Reports Server (NTRS)

    Bolmont, J.; Vasileiou, V.; Jacholkowska, A.; Piron, F.; Couturier, C.; Granot, J.; Stecker, F. W.; Cohen-Tanugi, J.; Longo, F.

    2013-01-01

    Because they are bright and distant, Gamma-ray Bursts (GRBs) have been used for more than a decade to test propagation of photons and to constrain relevant Quantum Gravity (QG) models in which the velocity of photons in vacuum can depend on their energy. With its unprecedented sensitivity and energy coverage, the Fermi satellite has provided the most constraining results on the QG energy scale so far. In this talk, the latest results obtained from the analysis of four bright GRBs observed by the Large Area Telescope will be reviewed. These robust results, cross-checked using three different analysis techniques set the limit on QG energy scale at E(sub QG,1) greater than 7.6 times the Planck energy for linear dispersion and E(sub QG,2) greater than 1.3 x 10(exp 11) gigaelectron volts for quadratic dispersion (95% CL). After describing the data and the analysis techniques in use, results will be discussed and confronted to latest constraints obtained with Active Galactic Nuclei.

  17. The Second Catalog of Flaring Gamma-Ray Sources from the Fermi All-sky Variability Analysis

    NASA Astrophysics Data System (ADS)

    Abdollahi, S.; Ackermann, M.; Ajello, M.; Albert, A.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Becerra Gonzalez, J.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Chekhtman, A.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Conrad, J.; Costantin, D.; Costanza, F.; Cutini, S.; D'Ammando, F.; de Palma, F.; Desai, A.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Donaggio, B.; Drell, P. S.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giomi, M.; Giordano, F.; Giroletti, M.; Glanzman, T.; Green, D.; Grenier, I. A.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hays, E.; Horan, D.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Kocevski, D.; Kuss, M.; La Mura, G.; Larsson, S.; Latronico, L.; Li, J.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Magill, J. D.; Maldera, S.; Manfreda, A.; Mayer, M.; Mazziotta, M. N.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Paliya, V. S.; Paneque, D.; Perkins, J. S.; Persic, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Porter, T. A.; Principe, G.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Stawarz, L.; Suson, D. J.; Takahashi, M.; Tanaka, K.; Thayer, J. B.; Thompson, D. J.; Torres, D. F.; Torresi, E.; Tosti, G.; Troja, E.; Vianello, G.; Wood, K. S.

    2017-09-01

    We present the second catalog of flaring gamma-ray sources (2FAV) detected with the Fermi All-sky Variability Analysis (FAVA), a tool that blindly searches for transients over the entire sky observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. With respect to the first FAVA catalog, this catalog benefits from a larger data set, the latest LAT data release (Pass 8), as well as from an improved analysis that includes likelihood techniques for a more precise localization of the transients. Applying this analysis to the first 7.4 years of Fermi observations, and in two separate energy bands 0.1-0.8 GeV and 0.8-300 GeV, a total of 4547 flares were detected with significance greater than 6σ (before trials), on the timescale of one week. Through spatial clustering of these flares, 518 variable gamma-ray sources were identified. Based on positional coincidence, likely counterparts have been found for 441 sources, mostly among the blazar class of active galactic nuclei. For 77 2FAV sources, no likely gamma-ray counterpart has been found. For each source in the catalog, we provide the time, location, and spectrum of each flaring episode. Studying the spectra of the flares, we observe a harder-when-brighter behavior for flares associated with blazars, with the exception of BL Lac flares detected in the low-energy band. The photon indexes of the flares are never significantly smaller than 1.5. For a leptonic model, and under the assumption of isotropy, this limit suggests that the spectrum of freshly accelerated electrons is never harder than p˜ 2.

  18. Second-Order Fermi Acceleration and Emission in Blazar Jets

    NASA Astrophysics Data System (ADS)

    Asano, Katsuaki; Takahara, Fumio; Toma, Kenji; Kusunose, Masaaki; Kakuwa, Jun

    The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations, adopt it for 1ES 1101-232, and Mrk 421. The Fermi-II model with radial evolution of the electron injection rate and/or diffusion coefficient can reproduce the spectra from the radio to the gamma-ray regime. For Mrk 421, an external radio photon field with a luminosity of 4.9 begin{math} {times} 10 (38) erg s (-1) is required to agree with the observed GeV flux. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

  19. Selection and Evaluation of Priority Domains in Global Energy Internet Standard Development Based on Technology Foresight

    NASA Astrophysics Data System (ADS)

    Jin, Yang; Ciwei, Gao; Jing, Zhang; Min, Sun; Jie, Yu

    2017-05-01

    The selection and evaluation of priority domains in Global Energy Internet standard development will help to break through limits of national investment, thus priority will be given to standardizing technical areas with highest urgency and feasibility. Therefore, in this paper, the process of Delphi survey based on technology foresight is put forward, the evaluation index system of priority domains is established, and the index calculation method is determined. Afterwards, statistical method is used to evaluate the alternative domains. Finally the top four priority domains are determined as follows: Interconnected Network Planning and Simulation Analysis, Interconnected Network Safety Control and Protection, Intelligent Power Transmission and Transformation, and Internet of Things.

  20. The Fermi Large Area Telescope Thrid Gamma-ray Source Catalog

    NASA Astrophysics Data System (ADS)

    Stephens, Thomas E.; Ballet, Jean; Burnett, Toby; Cavazzuti, Elisabetta; Digel, Seth William; Fermi LAT Collaboration

    2015-01-01

    We present an overview of the third Fermi Large Area Telescope source catalog (3FGL) of sources in the 100 MeV - 300 GeV range. Based on the first four years of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the 2FGL catalog (Nolan et al. 2012, ApJS 199, 31), the 3FGL catalog incorporates twice as much data as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse gamma-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources, with source location regions, spectral properties, and monthly light curves for each. For approximately one-third of the sources we have not found counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate the contribution of unresolved sources to the Galactic diffuse emission.