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1

Gamma rays from compact binary systems  

NASA Astrophysics Data System (ADS)

Some of the very high energy (VHE) gamma-ray sources detected with the modern generation of Cherenkov telescopes have been identified with previously known X-ray binary systems. These detections demonstrate the richness of non-thermal phenomena in compact galactic objects containing relativistic outflows or winds produced near black holes and neutron stars. Recently, the well-known microquasar Cygnus X-3 seems to be associated with a gamma-ray source detected with AGILE. Here I summarise the main observational results on gamma-ray emission from X-ray binaries, as well as some of the proposed scenarios to explain the production of VHE gamma-rays.

Paredes, Josep M.

2008-12-01

2

A compact gamma ray imager for oncology  

Microsoft Academic Search

A variety of new techniques based on radiopharmaceuticals are showing a valid support for cancer detection and interventional procedures. Axillary lymph nodes status is the most important prognostic factor for determining breast cancer prognosis. The use of dedicated gamma cameras characterized by low costs and weight, could be easily transferred to detection for bioptical procedures. To this aim this paper

R. Pani; A. Soluri; R. Scafč; R. Pellegrini; A. Tati; F. Scopinaro; G De Vincentis; T. Gigliotti; A. Festinesi; F. Garibaldi; A Del Guerra

2002-01-01

3

COMPACT, TUNABLE COMPTON SCATTERING GAMMA-RAY SOURCES  

SciTech Connect

Recent progress in accelerator physics and laser technology have enabled the development of a new class of gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable gamma-ray source driven by a compact, high-gradient X-band linac is currently under development at LLNL. High-brightness, relativistic electron bunches produced by the linac interact with a Joule-class, 10 ps laser pulse to generate tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. The source will be used to excite nuclear resonance fluorescence lines in various isotopes; applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented.

Hartemann, F V; Albert, F; Anderson, G G; Anderson, S G; Bayramian, A J; Betts, S M; Chu, T S; Cross, R R; Ebbers, C A; Fisher, S E; Gibson, D J; Ladran, A S; Marsh, R A; Messerly, M J; O'Neill, K L; Semenov, V A; Shverdin, M Y; Siders, C W; McNabb, D P; Barty, C J; Vlieks, A E; Jongewaard, E N; Tantawi, S G; Raubenheimer, T O

2009-08-20

4

Development of Compact Wide-Angle Imaging Detector for MeV Gamma-Rays using Stacked BGO Scintillator Rods  

Microsoft Academic Search

We are developing a compact wide-angle imaging detector for MeV gamma-rays using stacked BGO scintillator rods to apply to neutron induced prompt gamma-ray analysis (NPGA), which is one of the promising methods for non-destructive detection of hidden explosives by measuring characteristic gamma-rays produced from chemical elements. The gamma-ray imaging in NPGA applications is also necessary to locate them and improve

Kenichi Watanabe; Shinji Mihoya; J. Kawarabayashi; T. Iguchi

2006-01-01

5

ARE ALL SHORT-HARD GAMMA-RAY BURSTS PRODUCED FROM MERGERS OF COMPACT STELLAR OBJECTS?  

SciTech Connect

The origin and progenitors of short-hard gamma-ray bursts (GRBs) remain a puzzle and a highly debated topic. Recent Swift observations suggest that these GRBs may be related to catastrophic explosions in degenerate compact stars, denoted as 'Type I' GRBs. The most popular models include the merger of two compact stellar objects (NS-NS or NS-BH). We utilize a Monte Carlo approach to determine whether a merger progenitor model can self-consistently account for all the observations of short-hard GRBs, including a sample with redshift measurements in the Swift era (z-known sample) and the CGRO/BATSE sample. We apply various merger time delay distributions invoked in compact star merger models to derive the redshift distributions of these Type I GRBs, and then constrain the unknown luminosity function of Type I GRBs using the observed luminosity-redshift (L-z) distributions of the z-known sample. The best luminosity function model, together with the adopted merger delay model, is then applied to confront the peak flux distribution (log N-log P distribution) of the BATSE and Swift samples. We find that for all the merger models invoking a range of merger delay timescales (including those invoking a large fraction of 'prompt mergers'), it is difficult to reconcile the models with all the data. The data are instead statistically consistent with the following two possible scenarios. First, that short/hard GRBs are a superposition of compact-star-merger-origin (Type I) GRBs and a population of GRBs that track the star formation history, which are probably related to the deaths of massive stars (Type II GRBs). Second, the entire short/hard GRB population is consistent with a typical delay of 2 Gyr with respect to the star formation history with modest scatter. This may point toward a different Type I progenitor than the traditional compact star merger models.

Virgili, Francisco J.; Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); O'Brien, Paul [Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH (United Kingdom); Troja, Eleonora, E-mail: virgilif@physics.unlv.edu, E-mail: zhang@physics.unlv.edu [Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2011-02-01

6

Compact Object Coalescence Rate Estimation from Short Gamma-Ray Burst Observations  

NASA Astrophysics Data System (ADS)

Recent observational and theoretical results suggest that short-duration gamma-ray bursts (SGRBs) originate from the merger of compact binary systems of two neutron stars or a neutron star and a black hole. The observation of SGRBs with known redshifts allows astronomers to infer the merger rate of these systems in the local universe. We use data from the SWIFT satellite to estimate this rate to be in the range ~500-1500 Gpc-3 yr-1. This result is consistent with earlier published results which were obtained through alternative approaches. We estimate the number of coincident observations of gravitational-wave signals with SGRBs in the advanced gravitational-wave detector era. By assuming that all SGRBs are created by neutron star-neutron star (neutron star-black hole) mergers, we estimate the expected rate of coincident observations to be in the range ~= 0.2-1 (sime 1-3) yr-1.

Enrico Petrillo, Carlo; Dietz, Alexander; Cavagliŕ, Marco

2013-04-01

7

Prospects for compact high-intensity laser synchrotron x-ray and gamma sources  

SciTech Connect

A laser interacting with a relativistic electron beam behaves like a virtual wiggler of an extremely short period equal to half of the laser wavelength. This approach opens a route to relatively compact, high-brightness x-ray sources alternative or complementary to conventional synchrotron light sources. Although not new, the laser synchrotron source (LSS) concept is still waiting for a convincing demonstration. Available at the BNL Accelerator Test Facility (ATF), a high-brightness electron beam and the high-power CO{sub 2} laser may be used as prototype LSS brick stones. In a feasible demonstration experiment, 10-GW, 100-ps CO{sub 2} laser beam will be brought to a head-on collision with a 10-ps, 0.5-nC, 50 MeV electron bunch. Flashes of collimated 4.7 keV (2.6 {angstrom}) x-rays of 10-ps pulse duration, with a flux of {approximately} 10{sup 19} photons/sec, will be produced via linear Compton backscattering. The x-ray spectrum is tunable proportionally to the e-beam energy. A rational short-term extension of the proposed experiment would be further enhancement of the x-ray flux to the 10{sup 22} photons/sec level, after the ongoing ATF CO{sub 2} laser upgrade to 5 TW peak power and electron bunch shortening to 3 ps is realized. In the future, exploiting the promising approach of a high-gradient laser wake field accelerator, a compact ``table-top`` LSS of monochromatic gamma radiation may become feasible.

Pogorelsky, I.V. [Brookhaven National Lab., Upton, NY (United States). Accelerator Test Facility

1996-11-01

8

Development of a compact 20 MeV gamma-ray source for energy calibration at the Sudbury Neutrino Observatory  

SciTech Connect

The Sudbury Neutrino Observatory (SNO) is a real-time neutrino detector under construction near Sudbury, Ontario, Canada. SNO collaboration is developing various calibration sources in order to determine the detector response completely. This paper describes briefly the calibration sources being developed by the collaboration. One of these, a compact {sup 3}H(p,{gamma}){sup 4}He source, which produces 20-MeV {gamma}-rays, is described.

Poon, A.W.P.; Browne, M.C.; Robertson, R.G.H. [Washington Univ., Seattle, WA (United States). Nuclear Physics Lab.; Waltham, C.E. [British Columbia Univ., Vancouver, BC (Canada). Dept. of Physics; Kherani, N.P. [Ontario Hydro Technologies, Toronto, ON (Canada)

1995-12-31

9

DEVELOPMENT OF A PRECISION TUNABLE GAMMA-RAY SOURCE DRIVEN BY A COMPACT X-BAND LINAC  

SciTech Connect

A precision, tunable gamma-ray source driven by a compact, high-gradient X-band linac is currently under development at LLNL. High-brightness, relativistic electron bunches produced by the linac interact with a Joule-class, 10 ps laser pulse to generate tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. The source will be used to excite nuclear resonance fluorescence lines in various isotopes; applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented.

Hartemann, F V; Albert, F; Anderson, G G; Anderson, S G; Bayramian, A J; Betts, S M; Chu, T S; Cross, R R; Ebbers, C A; Fisher, S E; Gibson, D J; Ladran, A S; Messerly, M J; Semenov, V A; Shverdin, M Y; Siders, C W; McNabb, D P; Barty, C J; Vlieks, A E; Jongewaard, E N; Tantawi, S G

2009-04-30

10

The Locations of Short Gamma-Ray Bursts as Evidence for Compact Object Binary Progenitors  

NASA Astrophysics Data System (ADS)

We present a detailed investigation of Hubble Space Telescope rest-frame UV/optical observations of 22 short gamma-ray burst (GRB) host galaxies and sub-galactic environments. Utilizing the high angular resolution and depth of HST we characterize the host galaxy morphologies, measure precise projected physical and host-normalized offsets between the bursts and host centers, and calculate the locations of the bursts with respect to their host light distributions (rest-frame UV and optical). We calculate a median short GRB projected physical offset of 4.5 kpc, about 3.5 times larger than that for long GRBs, and find that ?25% of short GRBs have offsets of >~ 10 kpc. When compared to their host sizes, the median offset is 1.5 half-light radii (re ), about 1.5 times larger than the values for long GRBs, core-collapse supernovae, and Type Ia supernovae. In addition, ?20% of short GRBs having offsets of >~ 5re , and only ?25% are located within 1re . We further find that short GRBs severely under-represent their hosts' rest-frame optical and UV light, with ?30%-45% of the bursts located in regions of their host galaxies that have no detectable stellar light, and ?55% in the regions with no UV light. Therefore, short GRBs do not occur in regions of star formation or even stellar mass. This demonstrates that the progenitor systems of short GRBs must migrate from their birth sites to their eventual explosion sites, a signature of kicks in compact object binary systems. Utilizing the full sample of offsets, we estimate natal kick velocities of ?20-140 km s–1. These independent lines of evidence provide the strongest support to date that short GRBs result from the merger of compact object binaries (NS-NS/NS-BH).

Fong, W.; Berger, E.

2013-10-01

11

Compact LaBr{sub 3}: Ce Gamma Ray Detector with Si-APD Readout  

SciTech Connect

BrilLanCe 380 (LaBr{sub 3}:Ce) crystal scintillators available from Saint-Gobain Crystals have achieved 2.6% FWHM for 662 keV photons. This is accomplished with PMT light sensors. Attempts to have similarly good results with PIN photo-diodes and APDs have not been successful. PIN photodiodes do not have any gain and the signal to noise ratio is poor at room temperature. Similarly, even though APDs have sufficient gain, they have poor signal to noise at room temperature. Recently there have been improvements in APDs decreasing the internal noise and increasing their sensitivity, making them an excellent light sensor. With the improved APD, it is now possible to achieve performance with a solid state light sensor comparable to that of PMTs. We have measured 2.8% for 662 keV gamma rays at room temperature using an APD for a light sensor on a 20 mm long crystal of 1.6 cc volume. APDs have advantages of compactness, inherent ruggedness and minimal sensitivity to magnetic fields. Such a device is very practical for hand held and portable field measurement applications. (Performance reported in SGC literature.)

Flamanc, Jeremy [Saint-Gobain Crystals, 104 Route de Larchant, 77140 St Pierre les Nemours (France); Rozsa, Csaba [Saint-Gobain Crystals, 17900 Great Lakes Parkway, Hiram, OH 44234 (United States)

2009-03-10

12

Compact LaBr3: Ce Gamma Ray Detector with Si-APD Readout  

NASA Astrophysics Data System (ADS)

BrilLanCe 380™ (LaBr3:Ce) crystal scintillators available from Saint-Gobain Crystals have achieved 2.6% FWHM for 662 keV photons. This is accomplished with PMT light sensors. Attempts to have similarly good results with PIN photo-diodes and APDs have not been successful. PIN photodiodes do not have any gain and the signal to noise ratio is poor at room temperature. Similarly, even though APDs have sufficient gain, they have poor signal to noise at room temperature. Recently there have been improvements in APDs decreasing the internal noise and increasing their sensitivity, making them an excellent light sensor. With the improved APD, it is now possible to achieve performance with a solid state light sensor comparable to that of PMTs. We have measured 2.8% for 662 keV gamma rays at room temperature using an APD for a light sensor on a 20 mm long crystal of 1.6 cc volume. APDs have advantages of compactness, inherent ruggedness and minimal sensitivity to magnetic fields. Such a device is very practical for hand held and portable field measurement applications. (Performance reported in SGC literature.)

Flamanc, Jeremy; Rozsa, Csaba

2009-03-01

13

A compact radio source in the high-redshift soft gamma-ray blazar IGR J12319-0749  

NASA Astrophysics Data System (ADS)

Context. Blazars are powerful active galactic nuclei (AGNs) radiating prominently in the whole electromagnetic spectrum, from the radio to the X-ray and gamma-ray bands. Their emission is dominated by synchrotron and inverse-Compton radiation from a relativistic jet originating from an accreting central supermassive black hole. The object IGR J12319-0749 has recently been identified as a soft gamma-ray source with the IBIS instrument of the INTEGRAL satellite, coincident with a quasar at high redshift (z = 3.12). Aims: We studied the radio structure of IGR J12319-0749 to strengthen its blazar identification by detecting a compact radio jet on the milli-arcsecond (mas) angular scale, and to measure its astrometric position accurate to mas level. Methods: We used the technique of electronic very long baseline interferometry (e-VLBI) to image IGR J12319-0749 with the European VLBI Network (EVN) at 5 GHz on 2012 June 19. Results: IGR J12319-0749 (J1231-0747) is a compact radio source, practically unresolved on interferometric baselines up to ~136 million wavelengths. The estimated brightness temperature (at least 2 × 1011 K) indicates that the radio emission of its jet is Doppler-boosted. The accurate position of the compact radio source is consistent with the positions measured at higher energies.

Frey, S.; Paragi, Z.; Gabányi, K. É.; An, T.

2013-04-01

14

Estimation of compact binary coalescense rates from short gamma-ray burst redshift measurements  

Microsoft Academic Search

Short gamma-ray bursts are believed to originate from the merger of two\\u000acompact objects. If this scenario is correct, these bursts will be accompanied\\u000aby the emission of strong gravitational waves, detectable by current or planned\\u000aGW detectors, such as LIGO and Virgo. No detection of a gravitational wave has\\u000abeen made up to date. In this paper I will

Alexander Dietz; Chemin de Bellevue

2010-01-01

15

Properties of long gamma-ray bursts from massive compact binaries.  

PubMed

We consider the implications of a model for long-duration gamma-ray bursts in which the progenitor is spun up in a close binary by tidal interactions with a massive black-hole companion. We investigate a sample of such binaries produced by a binary population synthesis, and show that the model predicts several common features in the accretion on to the newly formed black hole. In all cases, the accretion rate declines as approximately t(-5/3) until a break at a time of order 10(4)?s. The accretion rate declines steeply thereafter. Subsequently, there is flaring activity, with the flare peaking between 10(4) and 10(5)?s, the peak time being correlated with the flare energy. We show that these times are set by the semi-major axis of the binary, and hence the process of tidal spin-up; furthermore, they are consistent with flares seen in the X-ray light curves of some long gamma-ray bursts. PMID:23630369

Church, Ross P; Levan, Andrew J; Davies, Melvyn B; Kim, Chunglee

2013-04-29

16

Implications of automatic photon quenching on compact gamma-ray sources  

NASA Astrophysics Data System (ADS)

Aims: We investigate photon quenching in compact non-thermal sources. This involves photon-photon annihilation and lepton synchrotron radiation in a network that can become non-linear. As a result the ?-ray luminosity of a source cannot exceed a critical limit that depends only on the radius of the source and on the magnetic field. Methods: We perform analytic and numerical calculations that verify previous results and extend them so that the basic properties of photon quenching are investigated. Results: We apply the above to the 2006 TeV observations of quasar 3C 279 and obtain the parameter space of allowed values for the radius of the emitting source, its magnetic field strength and the Doppler factor of the flow. We argue that the TeV observations favour either a modest Doppler factor and a low magnetic field or a high Doppler factor and a high magnetic field.

Petropoulou, M.; Mastichiadis, A.

2011-08-01

17

SHORT GAMMA-RAY BURSTS FROM DYNAMICALLY ASSEMBLED COMPACT BINARIES IN GLOBULAR CLUSTERS: PATHWAYS, RATES, HYDRODYNAMICS, AND COSMOLOGICAL SETTING  

SciTech Connect

We present a detailed assessment of the various dynamical pathways leading to the coalescence of compact objects in globular clusters (GCs) and Short Gamma-ray Burst (SGRB) production. We consider primordial binaries, dynamically formed binaries (through tidal two-body and three-body exchange interactions), and direct impacts of compact objects (WD/NS/BH). Here, we show that if the primordial binary fraction is small, close encounters dominate the production rate of coalescing compact systems. We find that the two dominant channels are the interaction of field neutron stars (NSs) with dynamically formed binaries and two-body encounters. Under such conditions, we estimate the redshift distribution and host galaxy demographics of SGRB progenitors, and find that GCs can provide a significant contribution to the overall observed rate. Regarding the newly identified channel of close stellar encounters involving WD/NS/BH, we have carried out precise modeling of the hydrodynamical evolution, giving us a detailed description of the resulting merged system. Our calculations show that there is in principle no problem in accounting for the global energy budget of a typical SGRB. The particulars of each encounter, however, are variable in several aspects and can lead to interesting diversity. First and most importantly, the characteristics of the encounter are highly dependent on the impact parameter. This is in contrast to the merger scenario, where the masses of the compact objects dictate a typical length and luminosity scale for SGRB activity. Second, the nature of the compact star itself can produce very different outcomes. Finally, the presence of tidal tails in which material will fall back onto the central object at a later time is a robust feature of the present set of calculations. The mass involved in these structures is considerably larger than for binary mergers. It is thus possible to account generically in this scenario for a prompt episode of energy release, as well as for activity many dynamical time scales later.

Lee, William H. [Instituto de Astronomia, UNAM, Apdo. Postal 70-264, Cd. Universitaria, Mexico DF 04510 (Mexico); Ramirez-Ruiz, Enrico [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Van de Ven, Glenn, E-mail: wlee@astroscu.unam.m, E-mail: enrico@ucolick.or, E-mail: glenn@mpia.d [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany)

2010-09-01

18

Monte-Carlo simulation of a compact gamma-ray detector using wavelength-shifting fibers coupled to a YAP scintillation crystal  

NASA Astrophysics Data System (ADS)

The production and transportation of fluorescent light produced in wavelength-shifting fibers (WSFs) coupled to YAP scintillation crystal is simulated using the GEANT4 codes. An advantage of the wavelength-shifting fiber readout technique over a direct readout with a position-sensitive photo-sensor is the reduced requirement for position sensitive photomultiplier tube photocathode area. With this gamma-ray detector, the gamma camera is small and flexible and has larger effective field of view and low cost. Simulation results show that a) a mean 12 of photons per 59.5 keV gamma ray interaction is produced in the WSF located nearest to the incident gamma ray, and a spatial resolution of 3.6 mm FWHM is obtained, b) a mean 27 of photons per 140 keV gamma ray interaction is produced and a spatial resolution of 3.1 mm FWHM is obtained. Results demonstrate the feasibility of this concept of a compact gamma-ray detector based on wavelength-shifting fibers readout. However, since the very low photoelectron levels, it is very important to use a photon counting device with good single photo-electron response to readout the WSFs. Supported by National Nature Science Foundation of China (10275063)

Zhu, Jie; Ma, Hong-Guang; Ma, Wen-Yan; Zeng, Hui; Wang, Zhao-Min; Xu, Zi-Zong

2008-05-01

19

Galactic Compact Objects Section of the White Paper on the Status and Future of Ground-based TeV Gamma-ray Astronomy  

Microsoft Academic Search

This is a report on the findings of the Galactic compact objects working group for the white paper on the status and future of TeV gamma-ray astronomy. The white paper is an APS commissioned document, and the full version has also been released and can be found on astro-ph. This section of the white paper discusses the potential of future

P. Kaaret; A. A. Abdo; J. Arons; M. Baring; W. Cui; B. Dingus; J. Finley; S. Funk; S. Heinz; B. Gaensler; A. Harding; E. Hays; J. Holder; D. Kieda; A. Konopelko; S. LeBohec; A. Levinson; I. Moskalenko; R. Mukherjee; R. Ong; M. Pohl; K. Ragan; P. Slane; A. Smith; D. Torres

2008-01-01

20

Cosmic gamma-ray bursts  

Microsoft Academic Search

The results of the observation of cosmic gamma-ray bursts are discussed and available theoretical models are presented. Emphasis is placed on a cosmological model in which a gamma burst results from a powerful (? 1051–1053 erg) and very short ( ?10 –100 s) energy release which occurs in a compact ( ? 106–107 cm) region and gives rise to a

Konstantin A Postnov

1999-01-01

21

Relativistic outflows from remnants of compact object mergers and their viability for short gamma-ray bursts  

NASA Astrophysics Data System (ADS)

We present the first general relativistic hydrodynamic models of the launch and evolution of relativistic jets and winds, driven by thermal energy deposition, possibly due to neutrino-antineutrino annihilation, in the close vicinity of black hole-accretion torus systems. The latter are considered to be the remnants of compact object mergers. Our two-dimensional simulations establish the link between models of such mergers and future observations of short gamma-ray bursts by the SWIFT satellite. They show that ultrarelativistic outflow with maximum terminal Lorentz factors around 1000 develops for polar energy deposition rates above some 1048 erg s-1 per steradian, provided the merger environment has a sufficiently low baryon density. By the interaction with the dense accretion torus the ultrarelativistic outflow with Lorentz factors ? above 100 is collimated into a sharp-edged cone that is embedded laterally by a wind with steeply declining Lorentz factor. The typical semi-opening angles of the ? > 100 cone are 5°-10°, corresponding to about 0.4-1.5% of the hemisphere and apparent isotropized energies (kinetic plus internal) up to ?1051 erg although at most 10-30% of the deposited energy is transferred to the outflow with ? > 100. The viability of post-merger black hole-torus systems as engines of short, hard gamma-ray bursts is therefore confirmed. The annihilation of neutrino-antineutrino pairs radiated from the hot accretion torus appears as a suitable energy source for powerful axial outflow even if only ?1049 erg are deposited within a cone of 45° half-opening angle around the system axis. Although the torus lifetimes are expected to be only between some 0.01 s and several 0.1 s, our models can explain the durations of all observed short gamma-ray bursts, because different propagation velocities of the front and rear ends will lead to a radial stretching of the ultrarelativistic fireball before transparency is reached. The ultrarelativistic flow reveals a highly non-uniform structure caused by the action of Kelvin-Helmholtz instabilities that originate at the fireball-torus interface. Large radial variations of the baryon density (up to several orders of magnitude) are uncorrelated with moderate variations of the Lorentz factor (factors of a few) and fluctuations of the gently declining radiation-dominated pressure. In the angular direction the Lorentz factor reveals a nearly flat plateau-like maximum with values of several hundreds, that can be located up to 7° off the symmetry axis, and a steep decrease to less than 10 for polar angles larger than 15°-20°. Lateral expansion of the ultrarelativistic core of the flow is prevented by a subsonic velocity component of about 0.05c towards the symmetry axis, whereas the moderately relativistic wings show a subsonic sideways inflation with less than 0.07c (measured in the frame comoving with the radial flow).

Aloy, M. A.; Janka, H.-T.; Müller, E.

2005-06-01

22

Gamma ray detector shield  

DOEpatents

A gamma ray detector shield comprised of a rigid, lead, cylindrical-shaped vessel having upper and lower portions with an pneumatically driven, sliding top assembly. Disposed inside the lead shield is a gamma ray scintillation crystal detector. Access to the gamma detector is through the sliding top assembly.

Ohlinger, R.D.; Humphrey, H.W.

1985-08-26

23

The Supernovae Associated with Gamma-Ray Bursts  

Microsoft Academic Search

Supernovae were long suspected as possible progenitors of gamma-ray bursts. The arguments relied on circumstantial evidence. Several recent gamma-ray bursts, notably GRB 030329, have provided direct, spectroscopic evidence that supernovae and gamma-ray bursts are related. The supernovae associated with gamma-ray bursts are all of Type Ic, implying a compact progenitor, which has implications for gamma-ray burst models. Other peculiar Type

T. Matheson

2005-01-01

24

Supernovae, hypernovae and gamma ray bursts  

Microsoft Academic Search

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in core collapse supernova explosions (SNe). The result of the event, probably, is not just a compact object plus a spherical ejecta: within a day, a fraction of the parent star falls back to produce a thick accretion disk around the compact

Arnon Dar

2001-01-01

25

Gamma-Ray Burst Environments and Progenitors  

Microsoft Academic Search

Likely progenitors for gamma-ray bursts (GRBs) are the mergers of compact objects or the explosions of massive stars. These two cases have distinctive environments for the GRB afterglow: the compact object explosions occur in the interstellar medium (ISM) and those of massive stars occur in the preburst stellar wind. We calculate the expected afterglow for a burst in a Wolf-Rayet

Roger A. Chevalier; Zhi-Yun Li

1999-01-01

26

Late stages of the evolution of close compact binaries: Type I supernovae, gamma-ray bursts, and supersoft X-ray sources  

Microsoft Academic Search

We consider the evolution of close binaries resulting in the most intensive explosive phenomena in the stellar Universe—Type\\u000a Ia supernovae and gamma-ray bursts. For Type Ia supernovae, which represent thermonuclear explosions of carbon-oxygen dwarfs\\u000a whose masses reach the Chandrasekhar limit during the accretion of matter from the donor star, we derive the conditions for\\u000a the accumulation of the limiting mass

A. V. Tutukov; A. V. Fedorova

2007-01-01

27

Relativistic outflows from remnants of compact object mergers and their viability for short gamma-ray bursts  

Microsoft Academic Search

We present the first general relativistic hydrodynamic models of the launch and evolution of relativistic jets and winds, driven by thermal energy deposition, possibly due to neutrino-antineutrino annihilation, in the close vicinity of black hole-accretion torus systems. The latter are considered to be the remnants of compact object mergers. Our two-dimensional simulations establish the link between models of such mergers

M. A. Aloy; H.-T. Janka; E. Müller

2005-01-01

28

Gamma ray optics  

SciTech Connect

Via refractive or diffractive scattering one can shape {gamma} ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E{sup 2}, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E{sup 2} extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

Jentschel, M.; Guenther, M. M.; Habs, D.; Thirolf, P. G. [Institut Laue-Langevin, F38042 Grenoble (France); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching, Germany and Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany); Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany)

2012-07-09

29

Gamma ray optics  

NASA Astrophysics Data System (ADS)

Via refractive or diffractive scattering one can shape ? ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E2, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E2 extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

Jentschel, M.; Günther, M. M.; Habs, D.; Thirolf, P. G.

2012-07-01

30

Gamma ray astrophysics  

NASA Astrophysics Data System (ADS)

A general review of cosmic energetic gamma particles is given. A discussion on the subject starting with the discovery of the PeV gamma rays by Sammorski and Stamm, passing to the super-nova SN1987A explosion when several groups waited for high energy gamma particles but none has come so far up to the measurements of TeV gamma incoming from the Crab Nebula. The discussion in this paper is a by product of the cosmic ray research done in the Chacaltaya Cosmic Rays Observatory in the past few years. A brief description of the facilities on Mount Chacaltaya (5,200 m above sea level (a.s.l.)) is also given.

Martinic, Nicholas J.

1994-04-01

31

Gamma ray camera  

DOEpatents

A gamma ray camera is disclosed for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array. 6 figs.

Perez-Mendez, V.

1997-01-21

32

Gamma ray camera  

DOEpatents

A gamma ray camera for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array.

Perez-Mendez, Victor (Berkeley, CA)

1997-01-01

33

Delayed gamma Rays from Fission.  

National Technical Information Service (NTIS)

Studies of delayed gamma rays from fission at early times were conducted using the pulsed beams of neutrons and bremsstrahlung x rays from an electron linear accelerator to produce fissions. Measurements of the energy spectrum of isomeric gamma rays from ...

R. B. Walton R. E. Sund

1965-01-01

34

Compact Electronic Gamma Source For Radiotherapy  

SciTech Connect

A compact mono-energetic gamma source is being developed to replace the radiological sources used in radiotherapy and other medical instruments. The electronic gamma source utilizes low-energy nuclear reactions to generate gammas in the 0.5 to 1.0 MeV energy range. Independent control of the ion current and energy is achieved by decoupling the RF-driven ion source and pyroelectric crystal-based acceleration systems The ions are accelerated to voltages above 100 keV and bombard a reaction target to produce gammas. Thermal management of the pyroelectric crystal-based accelerator is achieved by convective dielectric fluid flow around the crystal. This approach provides better temperature uniformity in the crystal and higher dielectric strength for suppressing voltage breakdown and enabling faster thermal cycling rates.

Chen, A. X. [Sandia National Laboratories, PO Box 969, Livermore, CA, 94550 (United States); Department of Mechanical Engineering, University of California, Berkeley, CA 94720 (United States); Antolak, A. J.; Raber, T. N.; Morse, D. H. [Sandia National Laboratories, PO Box 969, Livermore, CA, 94550 (United States); Leung, K.-N. [Department of Nuclear Engineering, University of California, Berkeley, CA 94720 (United States)

2011-06-01

35

Supernova, Hypernova and Gamma Ray Bursts  

Microsoft Academic Search

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows\\u000aare produced by highly relativistic jets emitted in core collapse supernova\\u000aexplosions (SNe). The result of the event, probably, is not just a compact\\u000aobject plus a spherical ejecta: within days, a fraction of the parent star\\u000afalls back to produce a thick accretion disk around the compact object.

Arnon Dar

2001-01-01

36

Accelerating Compact Object Mergers in Triple Systems with the Kozai Resonance: A Mechanism for "Prompt" Type Ia Supernovae, Gamma-Ray Bursts, and Other Exotica  

NASA Astrophysics Data System (ADS)

White dwarf-white dwarf (WD-WD) and neutron star-neutron star (NS-NS) mergers may produce Type Ia supernovae and gamma-ray bursts (GRBs), respectively. A general problem is how to produce binaries with semi-major axes small enough to merge in significantly less than the Hubble time (t H), and thus accommodate the observation that these events closely follow episodes of star formation. I explore the possibility that such systems are not binaries at all, but actually coeval, or dynamical formed, triple systems. The tertiary induces Kozai oscillations in the inner binary, driving it to high eccentricity, and reducing its gravitational wave (GW) merger timescale. This effect significantly increases the allowed range of binary period P such that the merger time is t merge < t H. In principle, Chandrasekhar-mass binaries with P ~ 300 days can merge in <~ t H if they contain a prograde solar-mass tertiary at high enough inclination. For retrograde tertiaries, the maximum P such that t merge <~ t H is yet larger. In contrast, P <~ 0.3 days is required in the absence of a tertiary. I discuss implications of these findings for the production of transients formed via compact object binary mergers. Based on the statistics of solar-type binaries, I argue that many such binaries should be in triple systems affected by the Kozai resonance. If true, expectations for the mHz GW signal from individual sources, the diffuse background, and the foreground for GW experiments like LISA are modified. This work motivates future studies of triples systems of A, B, and O stars, and new types of searches for WD-WD binaries in triple systems.

Thompson, Todd A.

2011-11-01

37

Hypernuclear gamma rays  

SciTech Connect

The observation of hypernuclear ..gamma.. rays pprovides a method of determining the spin dependence of the ..lambda..-nucleon interaction with a sensitivity not approachable by other means in the forseeable future. The transitions of primary interest are those between states that differ only in the orientation of the spin of the ..lambda.. particle with respect to the angular momentum of the nuclear core. The effective ..lambda..-nucleon interaction can be specified by a small number of ..gamma..-ray measurements. A program of experiments directed at this goal is in progress at Brookhaven National Laboratory. This paper reviews the status of the subject with emphasis on the recent experiment to measure ground state doublet splittings using germanium ..gamma..-ray detectors.

May, M.

1985-01-01

38

Scission gamma rays  

SciTech Connect

Gamma rays probably emitted by the fissioning nucleus {sup 236}U* at the instant of the break of the neck or within the time of about 10{sup -21} s after or before this were discovered in the experiment devoted to searches for the effect of rotation of the fissioning nucleus in the process {sup 235}U(n,{gamma}f) and performed in a polarized beam of cold neutrons from the MEPHISTO Guideline at the FRM II Munich reactor. Detailed investigations revealed that the angular distribution of these gamma rays is compatible with the assumption of the dipole character of the radiation and that their energy spectrum differs substantially from the spectrum of prompt fission gamma rays. In the measured interval 250-600 keV, this spectrum can be described by an exponential function at the exponent value of {alpha} = -5 x 10{sup -3} keV{sup -1}. The mechanism of radiation of such gamma rays is not known at the present time. Theoretical models based on the phenomenon of the electric giant dipole resonance in a strongly deformed fissioning nucleus or in a fission fragment predict harder radiation whose spectrum differs substantially from the spectrum measured in the present study.

Danilyan, G. V., E-mail: danilyan@itep.r [Institute of Theoretical and Experimental Physics (Russian Federation); Klenke, J. [Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) (Germany); Krakhotin, V. A.; Kuznetsov, V. L.; Novitsky, V. V.; Pavlov, V. S.; Shatalov, P. B. [Institute of Theoretical and Experimental Physics (Russian Federation)

2009-11-15

39

Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are the brightest transient sources in the gamma-ray sky. Since their discovery in the late 1960s, the investigation of the astrophysical sys- tems in which these phenomena take place, and the physical mechanisms that drive them, has become a vast and prolific area of modern astrophysics. In this work I will briefly describe the most relevant observations of these sources, and the models that describe their nature, emphasizing on the in- vestigations about the progenitor astrophysical systems. FULL TEXT IN SPANISH

Pellizza, L. J.

40

Gamma-ray bursts.  

PubMed

Gamma-ray bursts (GRBs) are bright flashes of gamma rays coming from the cosmos. They occur roughly once per day, typically last for tens of seconds, and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this Review, we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglow. PMID:22923573

Gehrels, Neil; Mészáros, Péter

2012-08-24

41

Prompt Signals of Gamma Ray Bursts.  

National Technical Information Service (NTIS)

We introduce a new model of gamma ray burst (GRB) that explains its observed prompt signals, namely, its primary thermal spectrum and high energy tail. This mechanism can be applied to either assumption of GRB pro-genitor: coalescence of compact objects o...

P. Chen

2001-01-01

42

Accretion Models of Gamma-Ray Bursts  

Microsoft Academic Search

Many models of gamma-ray bursts (GRBs) involve accretion onto a compact object, usually a black hole, at a mass accretion rate on the order of a fraction of a solar mass per second. If the accretion disk is larger than a few tens or hundreds of Schwarzschild radii, the accretion will proceed via a convection-dominated accretion flow (CDAF) in which

Ramesh Narayan; Tsvi Piran; Pawan Kumar

2001-01-01

43

Gamma Ray Observatory survives  

Microsoft Academic Search

Right now the budgetary position of NASA science projects for fiscal year 1982 is shaky, outside of the Space Shuttle Program. Two scientifically crucial missions being planned are the Gamma Ray Observatory (GRO) and the Venus Orbiting Imaging Radar (VOIR). President Reagan's proposed budgetary cuts have left both programs intact but delayed. For FY 1982, GRO will be able to

Peter M. Bell

1981-01-01

44

Gamma-ray bursts  

Microsoft Academic Search

Gamma-ray bursts are the most luminous explosions in the Universe, and their origin and mechanism are the focus of intense research and debate. More than three decades after their discovery, and after pioneering breakthroughs from space and ground experiments, their study is entering a new phase with the recently launched Swift satellite. The interplay between these observations and theoretical models

P. Mészáros

2006-01-01

45

Gamma-Ray Burst Wallsheet  

NSDL National Science Digital Library

The Gamma-ray Burst Wallsheet was developed to illustrate the properties of light emanating from a gamma-ray burst as seen by three distant satellites, including NASA's Swift. The back of the wallsheet has one of the three activities in the accompanying educator guide (Angling for Gamma-ray Bursts).

2005-01-01

46

Massive Binaries as VHE Gamma-ray Sources  

NASA Astrophysics Data System (ADS)

Recent progress in gamma-ray astronomy has established Very High Energy (VHE) gamma-ray binaries as a new class of gamma-ray sources. All of them are massive binaries consisting of an OB star and a compact object. The next generation observing fascilities, such as the Cherenkov Telescope Array, will detect many more massive binaries as VHE gamma-ray sources. Studying VHE gamma-ray binaries is important not only to understand physics at work in individual systems, but also to construct a unified dynamical model for the interaction and the origin of high-energy emission in this class of objects. In this talk, we discuss the interaction between the stellar wind and/or circumstellar disk and the compact object, based on 3-D hydrodynamic simulations of a few VHE gamma-ray binaries.

Okazaki, Atsuo

2013-06-01

47

Compact x-ray source and panel  

DOEpatents

A compact, self-contained x-ray source, and a compact x-ray source panel having a plurality of such x-ray sources arranged in a preferably broad-area pixelized array. Each x-ray source includes an electron source for producing an electron beam, an x-ray conversion target, and a multilayer insulator separating the electron source and the x-ray conversion target from each other. The multi-layer insulator preferably has a cylindrical configuration with a plurality of alternating insulator and conductor layers surrounding an acceleration channel leading from the electron source to the x-ray conversion target. A power source is connected to each x-ray source of the array to produce an accelerating gradient between the electron source and x-ray conversion target in any one or more of the x-ray sources independent of other x-ray sources in the array, so as to accelerate an electron beam towards the x-ray conversion target. The multilayer insulator enables relatively short separation distances between the electron source and the x-ray conversion target so that a thin panel is possible for compactness. This is due to the ability of the plurality of alternating insulator and conductor layers of the multilayer insulators to resist surface flashover when sufficiently high acceleration energies necessary for x-ray generation are supplied by the power source to the x-ray sources.

Sampayon, Stephen E. (Manteca, CA)

2008-02-12

48

Gamma-ray localization of terrestrial gamma-ray flashes.  

PubMed

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of ?5-10° at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space. PMID:20867680

Marisaldi, M; Argan, A; Trois, A; Giuliani, A; Tavani, M; Labanti, C; Fuschino, F; Bulgarelli, A; Longo, F; Barbiellini, G; Del Monte, E; Moretti, E; Trifoglio, M; Costa, E; Caraveo, P; Cattaneo, P W; Chen, A; D'Ammando, F; De Paris, G; Di Cocco, G; Di Persio, G; Donnarumma, I; Evangelista, Y; Feroci, M; Ferrari, A; Fiorini, M; Froysland, T; Galli, M; Gianotti, F; Lapshov, I; Lazzarotto, F; Lipari, P; Mereghetti, S; Morselli, A; Pacciani, L; Pellizzoni, A; Perotti, F; Picozza, P; Piano, G; Pilia, M; Prest, M; Pucella, G; Rapisarda, M; Rappoldi, A; Rubini, A; Sabatini, S; Soffitta, P; Striani, E; Vallazza, E; Vercellone, S; Vittorini, V; Zambra, A; Zanello, D; Antonelli, L A; Colafrancesco, S; Cutini, S; Giommi, P; Lucarelli, F; Pittori, C; Santolamazza, P; Verrecchia, F; Salotti, L

2010-09-14

49

Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes  

SciTech Connect

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of {approx}5-10 deg. at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space.

Marisaldi, M.; Labanti, C.; Fuschino, F.; Bulgarelli, A.; Trifoglio, M.; Di Cocco, G.; Gianotti, F. [INAF-IASF Bologna, Via Gobetti 101, I-40129 Bologna (Italy); Argan, A.; De Paris, G. [INAF, Viale del Parco Mellini 84, Roma (Italy); Trois, A.; Del Monte, E.; Costa, E.; Di Persio, G.; Donnarumma, I.; Evangelista, Y.; Feroci, M.; Lazzarotto, F.; Pacciani, L.; Rubini, A.; Sabatini, S. [INAF-IASF Roma, via del Fosso del Cavaliere 100, I-00133 Roma (Italy)

2010-09-17

50

Gamma-ray luminosity properties of gamma-ray pulsars  

Microsoft Academic Search

Based on a new self-consistent outer gap model, we statistically study luminosity properties of gamma-ray pulsars with ages of <=2× 107 yr in the Galaxy as well as those with ages of <=5× 106 yr in the Gould belt using a Monte Carlo method, where the gamma-ray beaming effect has been included. Generally, the relation between gamma-ray luminosity, Lgamma, and

L. Zhang; Z. X. Han; Z. J. Jiang

2005-01-01

51

The Cannonball Model of Gamma Ray Bursts: Spectral and Temporal Properties of the Gamma Rays  

Microsoft Academic Search

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in supernova explosions. We have proposed that the result of the event is not just a compact object plus the ejecta: within days, a fraction of the parent star falls back to produce a thick accretion disk. The subsequent accretion generates jets

Arnon Dar; Alvaro De Rújula

2000-01-01

52

GRIPS-Gamma-Ray burst Investigation via Polarimetry and Spectroscopy  

SciTech Connect

The primary scientific goal of the GRIPS mission [1] is to revolutionize our understanding of the early universe using {gamma}-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of {gamma}-ray energies (200 keV-50 MeV) and of polarimetry (200-1000 keV). Secondary goals achievable by this mission include direct measurements of supernova interiors through {gamma}-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies.

Greiner, J. [MPE Garching, Giessenbachstr. 1, 85740 Garching (Germany)

2008-05-22

53

Extragalactic Gamma-Rays Gamma Ray Bursts and Blazars  

Microsoft Academic Search

The extragalactic gamma-ray sky is dominated by two classes of sources: Gamma-Ray Bursts (GRBs) and radio loud active galactic nuclei whose jets are pointing at us (blazars). We believe that the radiation we receive from them originates from the transformation of bulk relativistic energy into random energy. Although the mechanisms to produce, collimate and accelerate the jets in these sources

Gabriele Ghisellini

2005-01-01

54

FISSION PRODUCT GAMMA RAY SPECTRA  

Microsoft Academic Search

Uranium-235 fission product gamma spectra were calculated for various ; reactor operating histories. An IBM704 digital computer program was coded to ; compute the gamma energy contributed by each fission product gamma ray and to sum ; these results in energy groups. A representative curve showing the decay of ; various energy groups is presented. Comparisons are made with data

1958-01-01

55

Unsteady outflow models for cosmological gamma-ray bursts  

Microsoft Academic Search

The 'event' that triggers a gamma-ray burst cannot last for more than a few seconds. This is, however, long compared with the dynamical timescale of a compact stellar-mass object (approximately 10 (exp-3) s). Energy is assumed to be released as an outflow with high mean Lorentz factor Gamma. But a compact stellar-mass collapse or merger is, realistically, likely to generate

M. J. Rees; P. Meszaros

1994-01-01

56

The Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D.

1994-06-01

57

Delayed gamma Rays from Fission.  

National Technical Information Service (NTIS)

Measurements of the energy spectrum of delayed gamma rays from the neutron fission of PU239 and U235 were performed with a naI detector at a number of time intervals between 2 and 80 microsec. The data showed three new prominent gamma rays with energies o...

R. B. Walton R. E. Sund

1966-01-01

58

The gamma-ray cosmos  

NASA Astrophysics Data System (ADS)

NASA's Compton Observatory spacecraft and the Russian/French Granat satellite have yielded vast new knowledge concerning the gamma-ray universe, which is indicative of the most energetic events in existence. A survey is presently conducted of the state of observational and theoretical understanding of gamma-ray sources in active galaxies and within the Galaxy.

Chupp, Edward L.

1992-12-01

59

The Highest Energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are equally likely to occur from any part of the sky, are detected by satellites about once per day, and emit most of their energy in a few seconds. Consequently, a detector with a large field of view and high duty factor is essential to observe gamma-ray bursts. EGRET was the 1st such detector sensitive enough to detect GeV gamma rays from gamma-ray bursts. While only 4 bursts were detected, these were the brightest bursts, as measured at < 1 MeV, in EGRET's field of view. Therefore, GeV emission may be characteristic of many bursts, and several models even predict emission extending to > TeV energies. Recently, a new TeV gamma-ray observatory, Milagro, has begun observing the Northern hemisphere sky. Milagro has > 1 sr field of view and operates 24 hours/day, 7 days/week. Milagrito, a smaller prototype of Milagro, operated for 15 months and 54 bursts were identified by BATSE, a sub-MeV detector in low Earth orbit, to be within Milagrito's field of view. One of the 54 bursts had marginal evidence of TeV gamma-ray emission. The prospect of observing gamma-ray bursts with Milagro will be discussed.

Dingus, Brenda L.

2000-04-01

60

Cosmic Ray Compaction of Porous Interstellar Ices  

NASA Astrophysics Data System (ADS)

We studied the compaction of microporous vapor-deposited ice films under irradiation with different ions in the 80-400 keV energy range. We found that porosity decreases exponentially with irradiation fluence, with a mean compaction area per ion that scales linearly with the stopping power of the projectile S above a threshold St=4 eV Ĺ-1. The experiments roughly follow a universal dependence of ion-induced compaction with restricted dose (eV molecule-1). This behavior can be used to extrapolate our results to conditions of the interstellar medium. Relating our results to ionization rates of interstellar H2, we estimate that porous ice mantles on grains in dense molecular clouds are compacted by cosmic rays in ~10-50 million years.

Raut, U.; Famá, M.; Loeffler, M. J.; Baragiola, R. A.

2008-11-01

61

Gamma-ray burst afterglows  

Microsoft Academic Search

The discovery of counterparts in X-ray and optical to radio wavelengths has revolutionized the study of gamma-ray bursts, until recently the most enigmatic of astrophysical phenomena. We now know that gamma-ray bursts are the biggest explosions in nature, caused by the ejection of ultrarelativistic matter from a powerful energy source and its subsequent collision with its environment. We have just

Paradijs van J. A; Chryssa Kouveliotou; Ralph A. M. J. Wijers

2000-01-01

62

Gamma-ray Astrophysics with AGILE  

SciTech Connect

AGILE will explore the gamma-ray Universe with a very innovative instrument combining for the first time a gamma-ray imager and a hard X-ray imager. AGILE will be operational in spring 2007 and it will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources. Galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. The AGILE instrument is designed to simultaneously detect and image photons in the 30 MeV - 50 GeV and 15 - 45 keV energy bands with excellent imaging and timing capabilities, and a large field of view covering {approx} 1/5 of the entire sky at energies above 30 MeV. A CsI calorimeter is capable of GRB triggering in the energy band 0.3-50 MeV AGILE is now (March 2007) undergoing launcher integration and testing. The PLSV launch is planned in spring 2007. AGILE is then foreseen to be fully operational during the summer of 2007.

Longo, Francesco [Department of Physics, University of Trieste (Italy)]|[INFN, Section of Trieste (Italy); Tavani, M.; Barbiellini, G.; Argan, A.; Basset, M.; Boffelli, F.; Bulgarelli, A.; Caraveo, P.; Cattaneo, P.; Chen, A.; Costa, E.; Del Monte, E.; Di Cocco, G.; Di Persio, G.; Donnarumma, I.; Feroci, M.; Fiorini, M.; Foggetta, L.; Froysland, T.; Frutti, M. (and others)

2007-07-12

63

Spontaneously quenched ?-ray spectra from compact sources  

NASA Astrophysics Data System (ADS)

Aims: We have studied a mechanism for producing intrinsic broken power-law ?-ray spectra in compact sources. This is based on the principles of automatic photon quenching, according to which ?-rays are being absorbed on spontaneously produced soft photons whenever the injected luminosity in ?-rays lies above a certain critical value. Methods: We derived an analytical expression for the critical ?-ray compactness in the case of power-law injection. For the case where automatic photon quenching is relevant, we calculated analytically the emergent steady-state ?-ray spectra. We also performed numerical calculations in order to back up our analytical results. Results: We show that a spontaneously quenched power-law ?-ray spectrum obtains a photon index 3?/2, where ? is the photon index of the power-law at injection. Thus, large spectral breaks of the ?-ray photon spectrum, e.g. ?? ? 1, can be obtained by this mechanism. We also discuss additional features of this mechanism that can be tested observationally. Finally, we fit the multiwavelength spectrum of a newly discovered blazar (PKS 0447-439) by using such parameters to explain the break in the ?-ray spectrum by means of spontaneous photon quenching, under the assumption that its redshift lies in the range 0.1 < z < 0.24.

Petropoulou, M.; Arfani, D.; Mastichiadis, A.

2013-09-01

64

Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes  

Microsoft Academic Search

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by

M. Marisaldi; C. Labanti; F. Fuschino; A. Bulgarelli; M. Trifoglio; G. Di Cocco; F. Gianotti; A. Argan; G. De Paris; A. Trois; E. Del Monte; E. Costa; G. Di Persio; I. Donnarumma; Y. Evangelista; M. Feroci; F. Lazzarotto; L. Pacciani; A. Rubini; S. Sabatini

2010-01-01

65

The Highest Energy Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

Gamma-ray bursts are equally likely to occur from any part of the sky, are detected by satellites about once per day, and emit most of their energy in a few seconds. Consequently, a detector with a large field of view and high duty factor is essential to observe gamma-ray bursts. EGRET was the 1st such detector sensitive enough to detect

Brenda L. Dingus

2000-01-01

66

Cosmic-Rays and Gamma Ray Bursts  

NASA Astrophysics Data System (ADS)

Cosmic-rays are subatomic particles of energies ranging between a few eV to hundreds of TeV. These particles register a power-law spectrum, and it seems that most of them originate from astrophysical galactic and extragalactic sources. The shock acceleration in superalfvenic astrophysical plasmas, is believed to be the main mechanism responsible for the production of the non-thermal cosmic-rays. Especially, the importance of the very high energy cosmic-ray acceleration, with its consequent gamma-ray radiation and neutrino production in the shocks of the relativistic jets of Gamma Ray Bursts, is a favourable theme of study. I will discuss the cosmic-ray shock acceleration mechanism particularly focusing on simulation studies of cosmic-ray acceleration occurring in the relativistic shocks of GRB jets.

Meli, A.

2013-07-01

67

Gamma rays at airplane altitudes  

SciTech Connect

An examination of the gamma ray flux above 1 TeV in the atmosphere is needed to better understand the anomalous showers from point sources. Suggestions are made for future experiments on board airplanes.

Iwai, J.; Koss, T.; Lord, J.; Strausz, S.; Wilkes, J.; Woosley, J. (University of Washington, Seattle, WA 98195 USA (US))

1990-03-20

68

A compact neutron beam generator system designed for prompt gamma nuclear activation analysis.  

PubMed

In this work a compact system was designed for bulk sample analysis using the technique of PGNAA. The system consists of (252)Cf fission neutron source, a moderator/reflector/filter assembly, and a suitable enclosure to delimit the resulting neutron beam. The moderator/reflector/filter arrangement has been optimised to maximise the thermal neutron component useful for samples analysis with a suitably low level of beam contamination. The neutron beam delivered by this compact system is used to irradiate the sample and the prompt gamma rays produced by neutron reactions within the sample elements are detected by appropriate gamma rays detector. Neutron and gamma rays transport calculations have been performed using the Monte Carlo N-Particle transport code (MCNP5). PMID:21129990

Ghassoun, J; Mostacci, D

2010-11-19

69

Gamma-Ray Shielding Studies.  

National Technical Information Service (NTIS)

A monoenergetic beam of gamma rays was used to study the deep penetration of 10-MeV gamma radiation in aluminum. Recently a positron annihilation system was developed at General Atomic for the purpose of making shielding measurements in the energy range f...

J. A. Lonergan E. A. Beaver J. Parez D. F. Herring

1967-01-01

70

The gamma Rays of Uranium  

Microsoft Academic Search

OUR knowledge of the gamma rays of uranium has until now been confined to their discovery by Rutherford (Phys. Zeit., 1902, 517) and to the observations of Eve (ibid., 1907, 185). The latter directed attention to their extraordinary feebleness and to their relatively low penetrating power. Eve found that uranium gives out only about one-tenth as much gamma radiation as

Frederick Soddy; Alexander S. Russell

1909-01-01

71

Gamma-ray Burst Cosmology  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are brief flashes of gamma-rays occurring at cosmological distances. GRB was discovered by Vela satellite in 1967. The discovery of afterglows in 1997 made it possible to measure the GRBs' redshifts and confirmed the cosmological origin. GRB cosmology includes utilizing long GRBs as standard candles to constrain the dark energy and cosmological parameters, measuring the high-redshift star

F. Y. Wang

2011-01-01

72

Underground Gamma-Ray Spectrometry  

Microsoft Academic Search

Gamma-ray spectrometry using high purity Ge detectors has made significant advances in recent years because large crystals have become readily available and the importance of very radiopure materials in the construction of detectors has been understood. The combination of these improvements has made it possible to decrease detection limits in special low-background counting systems. Gamma-ray spectrometry systems located underground are

Mikael Hult; Matthias Köhler; Nova Gorica

73

Swift: Gamma-Ray Bursts  

NSDL National Science Digital Library

In the late 1960s, scientists accidentally discovered gamma-ray bursts, intense flashes of energy that typically last no more than a few seconds or minutes. For decades after the discovery of these powerful bursts, they remained one of the greatest mysteries in astronomy. This video segment discusses the Swift satellite mission, launched in 2004 to investigate gamma-ray bursts, and presents some theories as to their origins. The segment is four minutes fourteen seconds in length.

74

Supernovae and Gamma Ray Bursts  

Microsoft Academic Search

We review the observational status of the Supernova\\/Gamma-Ray Burst connection. Recent (and less recent) observations of long duration Gamma-ray bursts suggest that a significant fraction of them (but not all) are associated with bright SNe of type Ib\\/c. Current estimates of the SN and GRB rates yield a ratio GRB\\/SNe-Ibc in the range ~ 0.4% - 3%. An analysis of

M. Della Valle

2007-01-01

75

Directional detector of gamma rays  

DOEpatents

A directional detector of gamma rays comprises a strip of an electrical cuctor of high atomic number backed with a strip of a second electrical conductor of low atomic number. These elements are enclosed within an electrical conductor that establishes an electrical ground, maintains a vacuum enclosure and screens out low-energy gamma rays. The detector exhibits a directional sensitivity marked by an increased output in the favored direction by a factor of ten over the output in the unfavored direction.

Cox, Samson A. (Downers Grove, IL); Levert, Francis E. (Chicago, IL)

1979-01-01

76

Unveiling the secrets of gamma ray bursts  

Microsoft Academic Search

Gamma Ray Bursts are unpredictable and brief flashes of gamma rays that occur about once a day in random locations in the sky. Since gamma rays do not penetrate the Earth's atmosphere, they are detected by satellites, which automatically trigger ground-based telescopes for follow-up observations at longer wavelengths. In this introduction to Gamma Ray Bursts we review how building a

Andreja Gomboc

2012-01-01

77

The Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory (Compton) was launched by the Space Shuttle Atlantis on 5 April 1991. The spacecraft and instruments are in good health and returning exciting results. The mission provides nearly six orders of magnitude in spectral coverage, from 30 keV to 30 GeV, with sensitivity over the entire range an order of magnitude better than that of previous observations. The 16,000 kilogram observatory contains four instruments on a stabilized platform. The mission began normal operations on 16 May 1991 and is now over half-way through a full-sky survey. The mission duration is expected to be from six to ten years. A Science Support Center has been established at Goddard Space Flight Center for the purpose of supporting a vigorous Guest Investigator Program. New scientific results to date include: (1) the establishment of the isotropy, combined with spatial inhomogeneity, of the distribution of gamma-ray bursts in the sky; (2) the discovery of intense high energy (100 MeV) gamma-ray emission from 3C 279 and other quasars and BL Lac objects, making these the most distant and luminous gamma-ray sources ever detected; (3) one of the first images of a gamma-ray burst; (4) the observation of intense nuclear and position-annihilation gamma-ray lines and neutrons from several large solar flares; and (5) the detection of a third gamma-ray pulsar, plus several other transient and pulsing hard X-ray sources.

Gehrels, N.; Chipman, E.; Kniffen, D. A.

1993-01-01

78

Optical observations of Gamma-Ray Bursts  

Microsoft Academic Search

We briefly review the status and recent progress in the field of optical observations of gamma-ray burst afterglows. We will focus on the fundamental observational evidence for the relationship between gamma-ray bursts and the final evolutionary phases of massive stars. In particular, we will address (i) gamma-ray burst host galaxies, (ii) optically dark gamma-ray burst afterglows, (iii) the gamma-ray burst–supernova

J. Hjorth; E. Pian; J. P. U. Fynbo

2004-01-01

79

PRECURSORS OF SHORT GAMMA-RAY BURSTS  

SciTech Connect

We carried out a systematic search of precursors on the sample of short gamma-ray bursts (GRBs) observed by Swift. We found that {approx}8%-10% of short GRBs display such early episodes of emission. One burst (GRB 090510) shows two precursor events, the former {approx}13 s and the latter {approx}0.5 s before the GRB. We did not find any substantial difference between the precursor and the main GRB emission, and between short GRBs with and without precursors. We discuss possible mechanisms to reproduce the observed precursor emission within the scenario of compact object mergers. The implications of our results on quantum gravity constraints are also discussed.

Troja, E.; Gehrels, N. [NASA, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Rosswog, S. [School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen (Germany)

2010-11-10

80

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

SciTech Connect

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.

Grenier, Isabelle (University Paris Diderot and CEA Saclay, France)

2009-04-01

81

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

ScienceCinema

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.

82

Gamma ray bursts and cosmic ray origin  

Microsoft Academic Search

This paper presents the theoretical basis of the fireball\\/blast wave model, and some implications of recent results on GRB source models and cosmic-ray production from GRBs. BATSE observations of the prompt gamma-ray luminous phase, and Beppo-SAX and long wavelength afterglow observations of GRBs are briefly summarized. Derivation of spectral and temporal indices of an adiabatic blast wave decelerating in a

C. D. Dermer

2001-01-01

83

Gamma Ray Bursts and Cosmic Ray Origin  

Microsoft Academic Search

This paper presents the theoretical basis of the fireball\\/blast wave model, and some implications of recent results on GRB source models and cosmic-ray production from GRBs. BATSE observations of the prompt gamma-ray luminous phase, and Beppo-SAX and long wavelength afterglow observations of GRBs are briefly summarized. Derivation of spectral and temporal indices of an adiabatic blast wave decelerating in a

C. D. Dermer

2002-01-01

84

Gamma Ray Bursts and Cosmic Ray Origin  

Microsoft Academic Search

This paper presents the theoretical basis of the fireball\\/blast wave model,\\u000aand some implications of recent results on GRB source models and cosmic-ray\\u000aproduction from GRBs. BATSE observations of the prompt gamma-ray luminous\\u000aphase, and Beppo-SAX and long wavelength afterglow observations of GRBs are\\u000abriefly summarized. Derivation of spectral and temporal indices of an adiabatic\\u000ablast wave decelerating in a

C. D. Dermer

2002-01-01

85

GeV gamma-rays and TeV neutrinos from very massive compact binary systems: the case of WR 20a  

Microsoft Academic Search

Massive Wolf-Rayet stars in a compact binary system are characterized by very strong winds which collide, creating a shock wave. If the wind nuclei, from helium up to oxygen, accelerated at the shock can reach large enough energies, they suffer disintegration in collisions with soft thermal radiation from the massive stars injecting relativistic protons and neutrons. Protons collide with the

W. Bednarek

2005-01-01

86

Effect of Gamma-Ray Beaming on the Fluxes of Gamma-Ray Pulsars  

Microsoft Academic Search

We study the effect of gamma-ray beaming on gamma-ray emission of the pulsars in a self-sustained outer gap model. In this model, averaged gamma-ray flux is a function of period, magnetic field, magnetic inclination angle and solid angle of gamma-ray beaming for a gamma-ray pulsar. We generate a sample of gamma-ray pulsars with their ages less than 106 years by

Ze-Jun Jiang; Li Zhang

2005-01-01

87

Faint Radio Sources and Gamma Ray Bursts  

Microsoft Academic Search

We calculate the number density of faint radio sources that are expected in radio source surveys due to the isotropic emission of Gamma Ray Burst sources. The calculation assumes the beamed supernovae model for gamma ray burst sources detected in gamma rays, x-rays, optical and radio wavelengths. Since the radio wavelength emission is expected to be more isotropically radiated, the

G. I. Langston; A. H. Minter; T. M. Freismuth

2002-01-01

88

Gamma-ray Imaging Methods  

SciTech Connect

In this document we discuss specific implementations for gamma-ray imaging instruments including the principle of operation and describe systems which have been built and demonstrated as well as systems currently under development. There are several fundamentally different technologies each with specific operational requirements and performance trade offs. We provide an overview of the different gamma-ray imaging techniques and briefly discuss challenges and limitations associated with each modality (in the appendix we give detailed descriptions of specific implementations for many of these technologies). In Section 3 we summarize the performance and operational aspects in tabular form as an aid for comparing technologies and mapping technologies to potential applications.

Vetter, K; Mihailescu, L; Nelson, K; Valentine, J; Wright, D

2006-10-05

89

Cosmological gamma-ray bursts  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Gamma-ray bursts are brief events that dominate the emission from all other gamma-ray objects in the sky, flicker for tens of seconds, and then turn off. Their nature remains uncertain despite years of efforts to understand them. One hypothesis is that the bursts arise within our galaxy albeit in an extended halo of neutron stars. Another hypothesis uses the isotropic distribution of gamma-ray bursts to argue that they come from nearly the edge of the universe. If gamma-ray bursts originate from cosmological distances, then the expansion of the universe should cause the dimmer (and presumably further) bursts to last longer. The authors have developed methods for measuring this time stretching, related the time stretching to the distance to the bursts, determined how the detailed physics causes temporal variations, and found the amount of total energy and peak luminosity that the events must be producing.

Fenimore, E.; Epstein, R.; Ho, C.; Intzand, J.

1996-04-01

90

Periodicities in gamma ray bursts  

SciTech Connect

Gamma ray burst models based on magnetic neutron stars face a problem of account for the scarcity of observed periods. Both this scarcity and the typical period found when any is detected are explained if the neutron stars are accreting in binary systems

Wood, K.S.

1984-05-26

91

On Gamma-Ray Bursts  

Microsoft Academic Search

We show by example how the uncoding of Gamma-Ray Bursts (GRBs) offers unprecedented possibilities to foster new knowledge in fundamental physics and in astrophysics. After recalling some of the classic work on vacuum polarization in uniform electric fields by Klein, Sauter, Heisenberg, Euler and Schwinger, we summarize some of the efforts to observe these effects in heavy ions and high

Remo Ruffini; M. G. Bernardini; C. L. Bianco; Letizia Caito; Pascal Chardonnet; Christian Cherubini; M. G. Dainotti; Federico Fraschetti; Andrea Geralico; Roberto Guida; Barbara Patricelli; Michael Rotondo; J. A. Rueda Hernandez; Gregory Vereshchagin; She-Sheng Xue

2008-01-01

92

Jets from Compact X-ray Sources  

NASA Astrophysics Data System (ADS)

Jets have been observed from both neutron stars and black holes in binary X-ray sources. The neutron star jets are typically 30 times weaker than the black-hole ones. Thus, the second have been studied more extensively. Contrary to common belief, jets from compact X-ray sources are not simply “fireworks” that emit radio waves. I will demonstrate that they play a central role in the observed phenomena in both neutron star and black-hole systems. In particular, for black-hole jets, a simple jet model can explain the very stringent correlations that have been found between the power-law X-ray spectrum and a) the time lag between hard and soft X-rays and b) the characteristic frequencies observed in the power spectra. Up to now, no other model has even attempted to explain these correlations. I will present the weaknesses of the model and the improvements that need to be done to it.

Kylafis, Nick D.

2010-11-01

93

Portable compton gamma-ray detection system  

DOEpatents

A Compton scattered gamma-ray detector system. The system comprises a gamma-ray spectrometer and an annular array of individual scintillators. The scintillators are positioned so that they are arrayed around the gamma-ray spectrometer. The annular array of individual scintillators includes a first scintillator. A radiation shield is positioned around the first scintillator. A multi-channel analyzer is operatively connected to the gamma-ray spectrometer and the annular array of individual scintillators.

Rowland, Mark S. (Alamo, CA); Oldaker, Mark E. (Pleasanton, CA)

2008-03-04

94

Low-level gamma-ray spectrometry  

Microsoft Academic Search

Low-level gamma-ray spectrometry generally equates to high-sensitivity gamma-ray spectrometry that can be attained by background reduction, selective signal identification, or some combination of both. Various methods for selectively identifying gamma-ray events and for reducing the background in gamma ray spectrometers are given. The relative magnitude of each effect on overall sensitivity and the relative 'cost' for implementing them are given

R L Brodzinski

1991-01-01

95

High energy gamma ray balloon instrument  

Microsoft Academic Search

The High Energy Gamma Ray Balloon Instrument was built in part to verify certain subsystems' performance for the Energetic Gamma Ray Experiment Telescope (EGRET) instrument, the high energy telescope to be carried on the Gamma Ray Observatory. This paper describes the instrument, the performance of some subsystems, and some relevant results.

D. J. Thompson; R. G. Baker; D. L. Bertsch; J. R. Chesney; S. M. Derdeyn; C. H. Ehrmann; C. E. Fichtel; S. D. Hunter; J. S. Jacques; N. A. Laubenthal

1985-01-01

96

Monte Carlo calibration of the SMM gamma ray spectrometer for high energy gamma rays and neutrons  

Microsoft Academic Search

The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission spacecraft was primarily designed and calibrated for nuclear gamma ray line measurements, but also has a high energy mode which allows the detection of gamma rays at energies above 10 MeV and solar neutrons above 20 MeV. The GRS response has been extrapolated until now for high energy gamma rays

J. F. Cooper; C. Reppin; D. J. Forrest; E. L. Chupp; G. H. Share; R. L. Kinzer

1985-01-01

97

Determination of the gamma-ray spectrum in a strong neutron\\/gamma-ray mixed field  

Microsoft Academic Search

The knowledge of gamma-ray spectrum highly affects the accuracy of the correspondingly derived gamma-ray dose and the correctness of calculated neutron dose in the neutron\\/gamma-ray mixed field dosimetry when using the paired ionization chambers technique. It is of our interest to develop a method to determine the gamma-ray spectrum in a strong neutron\\/gamma-ray mixed field. The current type detector, Mg(Ar)

Yuan-Hao Liu; Yi-Chun Lin; Sander Nievaart; Wen-Tsae Chou; Hong-Ming Liu; Shiang-Huei Jiang

2011-01-01

98

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst  

Microsoft Academic Search

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the

M. Sommer; D. L. Bertsch; B. L. Dingus; C. E. Fichtel; G. J. Fishman; A. K. Harding; R. C. Hartman; S. D. Hunter; K. Hurley; G. Kanbach; D. A. Kniffen; C. Kouveliotou; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; P. L. Nolan; E. Schneid; P. Sreekumar; D. J. Thompson

1994-01-01

99

Swift Pointing and the Association between Gamma-Ray Bursts and Gravitational Wave Bursts  

Microsoft Academic Search

It is widely believed that gamma-ray bursts originate in relativistic fireballs produced by the merger or collapse of solar-mass compact objects. Gravitational waves should be associated with these violent, relativistic events, and their detection may shed light on the nature of the inner engine that powers the gamma-ray burst. Doing this requires joint observations of gamma-ray burst events with gravitational

Lee Samuel Finn; Badri Krishnan; Patrick J. Sutton

2004-01-01

100

Probing the gamma-ray sky  

NASA Astrophysics Data System (ADS)

The observational results of the NASA's Compton Gamma Ray Observatory (GRO) are reviewed with attention given to the results from solar flares and gamma-ray bursts. The observatory is described emphasizing the Burst and Transient Source Experiment, the Oriented Scintillation Spectrometer Experiment, and the Energetic Gamma Ray Experiment Telescope. Increases in gamma-ray emission are noted in solar observations, and the pulsar in the Crab nebula was studied extensively. More gamma-ray pulsars were observed, and a total of 261 gamma-ray bursts are recorded as a result of the GRO observations. A gamma-ray galaxy was discovered by the GRO instruments, and the source - 3C 279 - is estimated to be 7 billion light years from earth. The GRO is shown to be of use in the characterization of astronomical phenomena that cannot be observed from earth.

Hurley, Kevin

1992-12-01

101

GRETINA: A gamma ray energy tracking array  

Microsoft Academic Search

A gamma-ray energy tracking array (GRETA) is a new concept for the detection of gamma radiation. In such an array, the individual interactions of all the gamma rays are identified by their energies and positions. Then, using tracking algorithms based on the properties of gamma ray interactions, the scattering sequences are reconstructed. GRETA will give high peak efficiency, peak-to-background ratio,

I. Y. Lee; R. M. Clark; M. Cromaz; M. A. Deleplanque; M. Descovich; R. M. Diamond; P. Fallon; A. O. Macchiavelli; F. S. Stephens; D. Ward

2004-01-01

102

Gamma-Ray Lines and High-Energy Sources  

SciTech Connect

Gamma-ray lines may provide diagnostic information on cosmic high energy sources: They originate from the decay of radioactive nucleosynthesis products, from positron annihilations, and from atomic nuclei which have been excited by energetic collisions. Shortlived isotopes such as 56Ni and 44Ti are produced in supernovae, their gamma-ray line intensities and line profiles reflect kinematics and morphology of the exploding star. Long-lived isotopes such as 26Al, and also the positron annihilation gamma-rays, can be used to study propagation processes in the interstellar medium near high-energy sources, complementing observational time scales at the long end of the range of interest. Such annihilation emission and also lines from excited nuclei near accreting compact stars should reflect energetic conditions at environments which are believed to inject suprathermal particles into relativistic accelerators to produce cosmic rays. New INTEGRAL measurements on these frontiers are discussed in this paper.

Diehl, Roland [Max Planck Institut fuer extraterrestrische Physik, D-85741 Garching (Germany)

2005-11-22

103

Black Holes, Supernovae and Gamma Ray Bursts  

NASA Astrophysics Data System (ADS)

We review recent progress in our understanding of the nature of Gamma Ray Bursts (GRBs) and in particular, of the relationship between short GRBs and long GRBs. The first example of a short GRB is described. The coincidental occurrence of a GRB with a supernova (SN) is explained within the induced gravitational collapse (IGC) paradigm, following the sequence: (1) an initial binary system consists of a compact carbon-oxygen (CO) core star and a neutron star (NS); (2) the CO core explodes as a SN, and part of the SN ejecta accretes onto the NS which reaches its critical mass and collapses to a black hole (BH) giving rise to a GRB; (3) a new NS is generated by the SN as a remnant. The observational consequences of this scenario are outlined.

Ruffini, Remo

2013-09-01

104

Gravitational wave: gamma-ray burst connections.  

PubMed

After 35 years of experimental research, we are rapidly approaching the point at which gravitational waves (GWs) from astrophysical sources may be directly detected by the long-baseline detectors LIGO (USA), GEO 600 (Germany/UK), VIRGO (Italy/France) and TAMA 300 (Japan), which are now in or coming into operation.A promising source of GWs is the coalescence of compact binary systems, events which are now believed to be the origin of short gamma-ray bursts (GRBs). In this paper, a brief review of the state of the art in detector development and exploitation will be given, with particular relevance to a search for signals associated with GRBs, and plans for the future will be discussed. PMID:17293333

Hough, Jim

2007-05-15

105

Gamma ray bursts inner engines  

NASA Astrophysics Data System (ADS)

Long gamma ray bursts (GRBs) are brief durations of intense, highly variable gamma radiation coming from point like sources in the Universe. GRBs have been seen in connection with Type 1c supernovae. Their isotropical equivalent energy released in gamma rays is in some cases above 10 54 erg, but the engine creating this energy is unknown. In this thesis several models for the engine are explored. It is shown that cannonballs can in principle form from hyperaccreting disks, however the cannonball model requires almost all supernovae to create cannonballs, and our finding then implies that a hyperaccreting disk is a natural consequence in most supernovae, a notion which remains to be confirmed. General relativistic magnetohydrodynamic simulations of the collapsar model have been performed. Within our setup we found that the duration of the collapsar is too short to explain GRBs, and the energy output is not sufficient. Also the supernova connection could not be explained. I find that the more likely candidate for the GRB engine is an accreting quark star. A quark star has a maximum mass, if the mass increases above this the star will collapse to a black hole. This allows for a two stage engine that might be able to explain features observed in GRBs.

Staff, Jan Erling

106

Observations of the Highest Energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to TeV gamma rays from gamma-ray bursts are beginning operation.

Dingus, Brenda L.

2003-04-01

107

A novel compact gamma camera based on flat panel PMT  

NASA Astrophysics Data System (ADS)

Over the last ten years the strong technological advances in position sensitive detectors have encouraged the scientific community to develop dedicated imagers for new diagnostic techniques in the field of isotope functional imaging. The main feature of the new detectors is the compactness that allows suitable detection geometry fitting the body anatomy. Position sensitive photomultiplier tubes (PSPMTs) have been showing very good features with continuous improvement. In 1997 a novel gamma camera was proposed based on a closely packed array of second generation 1in PSPMTs. The main advantage is the potentially unlimited detection area but with the disadvantage of a relatively large non-active area (30%). The Hamamatsu H8500 Flat Panel PMT represents the last generation of PSPMT. Its extreme compactness allows array assembly with an improved effective area up to 97%. This paper, evaluates the potential improvement of imaging performances of a gamma camera based on the new PSPMT, compared with the two previous generation PSPMTs. To this aim the factors affecting the gamma camera final response, like PSPMT gain anode variation and position resolution, are analyzed and related to the uniformity counting response, energy resolution, position linearity, detection efficiency and intrinsic spatial resolution. The results show that uniformity of pulse height response seems to be the main parameter that provides the best imaging performances. Furthermore an extreme identification of pixels seems to be not effective to a full correction of image uniformity counting and gain response. However, considering the present technological limits, Flat Panel PSPMTs could be the best trade off between gamma camera imaging performances, compactness and large detection area.

Pani, R.; Pellegrini, R.; Cinti, M. N.; Trotta, C.; Trotta, G.; Scafč, R.; Betti, M.; Cusanno, F.; Montani, Livia; Iurlaro, Giorgia; Garibaldi, F.; del Guerra, A.

2003-11-01

108

Recommended standards for gamma ray intensities  

NASA Astrophysics Data System (ADS)

Gamma ray data are used in more and more areas of application, and so over the years the demand for recommended gamma ray energies and intensities has increased. This paper proposes a list of gamma rays whose intensity is sufficiently well-known and they can be used for the calibration of gamma ray spectrometers and other applications; it is based on studies carried out by an international group of evaluators: the Decay Data Evaluation Project. One goal of this paper is to gather this set of data together in order to facilitate and generalize their use. In the first part, a brief description of the methodology followed throughout the evaluations is given, different methods of gamma ray intensity evaluation are presented, some typical examples of evaluations are shown; in the second part, the list of chosen nuclides is given along with their applications, and finally a list of recommended gamma ray intensities is presented.

Bé, Marie-Martine; Chechev, Valery P.

2013-11-01

109

The physics of gamma-ray bursts  

Microsoft Academic Search

Gamma-ray bursts (GRB's), short and intense pulses of low-energy gamma rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last decade, several space missions---BATSE (Burst and Transient Source Experiment) on the Compton Gamma-Ray Observatory, BeppoSAX and now HETE II (High-Energy Transient Explorer)---together with ground-based optical, infrared, and radio observatories have revolutionized our understanding

Tsvi Piran

2004-01-01

110

The Supernovae\\/Gamma-Ray Burst Connection  

Microsoft Academic Search

The correlation of SN 1998bw and GRB 980425 shows that some supernovae produce gamma-ray bursts. SN 1998bw resembled previous Type Ic supernovae in terms of its spectral evolution and finite polarization. A check of correlations between the Asiago supernova catalog and the BATSE catalog of gamma-ray bursts suggests that a correlation of gamma-ray bursts with Type Ic supernovae cannot be

J. C. Wheeler; L. Wang; P. Hoflich

1998-01-01

111

Gamma-ray irradiated polymer optical waveguides  

SciTech Connect

Optical waveguides fabricated by gamma-ray irradiation on polymer through a gold mask are presented. The gamma-ray induced index change is found almost linearly dependent on the dose of the irradiation. And the measured propagation losses are low enough for practical application. Due to the high penetrability of gamma ray, uniform refractive index change in depth can be easily achieved. Moreover, due to large-area printing, the uniformity of waveguide made by gamma-ray irradiation is much better than that by e-beam direct writing.

Lai, C.-C.; Wei, T.-Y.; Chang, C.-Y.; Wang, W.-S.; Wei, Y.-Y. [Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, No. 1, Roosevelt Road Sec. 4, Taipei 10617, Taiwan (China); Nuclear Science and Technology Development Center, National Tsing-Hua University, No. 101, Sec. 2, Kuang-Fu Road, Hsin-Chu 30043, Taiwan (China)

2008-01-14

112

Using Gamma Rays as Intergalactic Magnetometers  

NASA Astrophysics Data System (ADS)

Gamma rays from distant blazars interact with the extragalactic background light, creating electron-positron pairs, and reducing the amount of gamma-rays seen by ground-based atmospheric Cherenkov telescopes. These pairs can Compton-scatter the cosmic microwave background, creating a gamma-ray signature observable by the Fermi Large Area Telesope (LAT). The signature is also dependent on the intergalactic magnetic field (IGMF), since it can deflect the pairs from our line of sight, reducing the gamma-ray emission. We present preliminary constraints on the IGMF using Fermi-LAT and Cherenkov telescope observations, ruling out both very large and very small values of the IGMF strength.

Finke, Justin; Reyes, L. C.; Georganopoulos, M.; Fermi-LAT Collaboration

2013-04-01

113

Low-level gamma-ray spectrometry  

SciTech Connect

Low-level gamma-ray spectrometry generally equates to high-sensitivity gamma-ray spectrometry that can be attained by background reduction, selective signal identification, or some combination of both. Various methods for selectively identifying gamma-ray events and for reducing the background in gamma-ray spectrometers are given. The relative magnitude of each effect on overall sensitivity and the relative cost'' for implementing them are given so that a cost/benefit comparison can be made and a sufficiently sensitive spectrometer system can be designed for any application without going to excessive or unnecessary expense. 10 refs., 8 figs.

Brodzinski, R.L.

1990-10-01

114

Gamma-ray bursts from synchrotron self-Compton emission  

Microsoft Academic Search

The emission mechanism of gamma-ray bursts (GRBs) is still a matter of debate. The standard synchrotron energy spectrum of cooling electrons FE~E-1\\/2 is much too soft to account for the majority of the observed spectral slopes. An alternative in the form of quasi-thermal Comptonization in a high-compactness source has difficulties in reproducing the peak of the observed photon distribution below

Boris E. Stern; Juri Poutanen

2004-01-01

115

The progenitors of short gamma-ray bursts  

Microsoft Academic Search

Recent months have witnessed dramatic progress in our understanding of short gamma-ray burst (SGRB) sources. There is now general agreement that SGRBs---or at least a substantial subset of them---are capable of producing directed outflows of relativistic matter with a kinetic luminosity exceeding by many millions that of active galactic nuclei. Given the twin requirements of energy and compactness, it is

William H. Lee; Enrico Ramirez-Ruiz

2007-01-01

116

Gamma-ray burst models.  

PubMed

I consider various possibilities for making gamma-ray bursts, particularly from close binaries. In addition to the much-studied neutron star+neutron star and black hole+neutron star cases usually considered good candidates for short-duration bursts, there are also other possibilities. In particular, neutron star+massive white dwarf has several desirable features. These systems are likely to produce long-duration gamma-ray bursts (GRBs), in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation and occur close to the host galaxy. However, rare members of the class need not be near star-forming regions and could have any type of host galaxy. Thus, a long-duration burst far from any star-forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts. PMID:17293332

King, Andrew

2007-05-15

117

Very high energy gamma rays from X-ray binaries  

Microsoft Academic Search

We have reported the discovery of VHE gamma ray emission from the X-ray binary Cen X-3. We report further VHE observations of this object taken in 1998 and 1999. While these new data also show VHE gamma ray emission, no evidence of modulation at either the orbital or pulsar periods is found. .

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

2000-01-01

118

Very high energy gamma rays from X-ray binaries  

Microsoft Academic Search

We have reported the discovery of VHE gamma ray emission from the X-ray binary Cen X-3. We report further VHE observations of this object taken in 1998 and 1999. While these new data also show VHE gamma ray emission, no evidence of modulation at either the orbital or pulsar periods is found.

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

2000-01-01

119

Observations of the Highest Energy Gamma-Rays from Gamma-Ray Bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2002-01-01

120

Observations of the Highest Energy Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2003-01-01

121

Observations of the highest energy gamma-rays from gamma-ray bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2001-01-01

122

Telescope for X ray and gamma ray studies in astrophysics  

Microsoft Academic Search

Imaging of x-rays has been achieved by various methods in astrophysics, nuclear physics, medicine, and material science. A new method for imaging x-ray and gamma-ray sources avoids the limitations of previously used imaging devices. Images are formed in optical wavelengths by using mirrors or lenses to reflect and refract the incoming photons. High energy x-ray and gamma-ray photons cannot be

W. D. Weaver; Upendra D. Desai

1993-01-01

123

Gamma-ray generation using laser-accelerated electron beam  

NASA Astrophysics Data System (ADS)

A compact gamma-ray source using laser-accelerated electron beam is being under development at KAERI for nuclear applications, such as, radiography, nuclear activation, photonuclear reaction, and so on. One of two different schemes, Bremsstrahlung radiation and Compton backscattering, may be selected depending on the required specification of photons and/or the energy of electron beams. Compton backscattered gamma-ray source is tunable and quasimonochromatic and requires electron beams with its energy of higher than 100 MeV to produced MeV photons. Bremsstrahlung radiation can generate high energy photons with 20 - 30 MeV electron beams, but its spectrum is continuous. As we know, laser accelerators are good for compact size due to localized shielding at the expense of low average flux, while linear RF accelerators are good for high average flux. We present the design issues for a compact gamma-ray source at KAERI, via either Bremsstrahlung radiation or Compton backscattering, using laser accelerated electron beams for the potential nuclear applications.

Park, Seong Hee; Lee, Ho-Hyung; Lee, Kitae; Cha, Yong-Ho; Lee, Ji-Young; Kim, Kyung-Nam; Jeong, Young Uk

2011-05-01

124

Modeling gamma-ray bursts  

NASA Astrophysics Data System (ADS)

Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies (from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general picture is of a mysterious central engine (CE) probably composed of a black hole or neutron star that ejects relativistic shells of matter into intense magnetic fields. These shells collide and combine, releasing energy in "internal shocks" accounting for the prompt emission and flaring we see and the "external shock" or plowing of the first blastwave into the ambient surrounding medium has well-explained the afterglow radiation. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and follows those shells as they collide, merge and spread, producing prompt emission and X-ray flares. We have also included a blastwave model, which can constrain X-ray flares and explain the origin of high energy (GeV) emission seen by the Fermi telescope. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We pay special attention to the time history of central engine activity, internal shocks, and observed flares. We calculate the gamma-ray (Swift/BAT band) and X-ray (Swift/XRT band) lightcurves for arbitrary central engine activity and compare the model results with the observational data. We show that the observed X-ray flare phenomenology can be explained within the internal shock model. The number, width and occurring time of flares are then used to diagnose the central engine activity, putting constraints on the energy, ejection time, width and number of ejected shells. We find that the observed X-ray flare time history generally reflects the time history of the central engine, which reactivates multiple times after the prompt emission phase with progressively reduced energy. This shell model code can be used to constrain broadband observations of GRB 090926A, which showed two flares in both the Swift UVOT and XRT bands. Using the prompt emission fluence to constrain the total energy contained in the blastwave, the internal shock model requires that Lorentz factors of the shells causing flares must be less than the Lorentz factor of the blastwave when the shells are ejected. Recent observations of Gamma-Ray Bursts (GRBs) by the Fermi Large Area Telescope (LAT) revealed a power law decay feature of the high energy emission (above 100 MeV), which led to the suggestion that it originates from an external shock. We analyze four GRBs (080916C, 090510, 090902B and 090926A) jointly detected by Fermi LAT and Gamma-ray Burst Monitor (GBM), which have high quality lightcurves in both instrument energy bands. Using the MeV prompt emission (GBM) data, we can record the energy output from the central engine as a function of time. Assuming a constant radiative efficiency, we are able to track energy accumulation in the external shock using our internal/external shell model code and show that the late time lightcurves fit well within the external shock model, but the early time lightcurves are dominated by the internal shock component which has a shallow decay phase due to the initial pile-up of shells onto the blast wave.

Maxham, Amanda

125

Gamma rays from the interactions of reactor fast neutrons ordered by increasing gamma-ray energy  

Microsoft Academic Search

Radioactive material handled in nuclear safeguards often emits both gamma rays and neutrons. The gamma rays emitted by the radioactive isotopes are listed in several compilations, which can be used for identification and quantitative analysis of the radioactive isotopes present. Some of the neutrons are moderated and undergo thermal capture. The capture gamma rays are also listed in several compilations

1982-01-01

126

Balloon-Borne Gamma-Ray Polarimeter (PoGO) to Study Black Holes, Pulsars, and AGN.  

National Technical Information Service (NTIS)

Polarization measurements at X-ray and gamma-ray energies can provide crucial information on the emission region around massive compact objects such as black holes and neutron stars. The Polarized Gamma-ray Observer (PoGO) is a new balloon-borne instrumen...

Z. Apte

2005-01-01

127

X-rays and gamma-rays at cosmological distances  

Microsoft Academic Search

Recent work on absorption and reprocessing of gamma-rays at cosmological redshifts as well as the current status of this field of research are discussed. The authors consider Compton scattering and pair production by gamma-rays on cosmic baryonic matter, and photon-photon scattering and photon-photon pair production by gamma-rays and Compton scattering of relativistic pairs on the cosmic blackbody background. The region

A. A. Zdziarski; R. Svensson

1990-01-01

128

The GLAST Gamma-Ray Telescope Mission  

SciTech Connect

The Gamma-ray Large Area Space Telescope, GLAST, is an orbital mission under construction to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its launch in 2007, GLAST will open a new and important window on a wide variety of high energy phenomena, including 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, Lorentz-invariance violation, and exotic relics from the Big Bang. In addition to a short review of the science opportunities, this talk will describe the high-energy gamma-ray telescope and its components and review the mission status.

Johnson, Robert P. [Institute for Particle Physics, University of California, Santa Cruz, CA 95065 (United States)

2006-07-11

129

MAX-a gamma-ray lense for nuclear astrophysics.  

SciTech Connect

The mission concept MAX is a space borne crystal diffraction telescope, featuring a broad-band Laue lens optimized for the observation of compact sources in two wide energy bands of high astrophysical relevance. For the first time in this domain, gamma-rays will be focused from the large collecting area of a crystal diffraction lens onto a very small detector volume. As a consequence, the background noise is extremely low, making possible unprecedented sensitivities. The primary scientific objective of MAX is the study of type Ia supernovae by measuring intensities, shifts and shapes of their nuclear gamma-ray lines. When finally understood and calibrated, these profoundly radioactive events will be crucial in measuring the size, shape, and age of the Universe. Observing the radioactivities from a substantial sample of supernovae and novae will significantly improve our understanding of explosive nucleosynthesis. Moreover, the sensitive gamma-ray line spectroscopy performed with MAX is expected to clarify the nature of galactic microquasars (e{sup +}e{sup -} annihilation radiation from the jets), neutrons stars and pulsars, X-ray Binaries, AGN, solar flares and, last but not least, gamma-ray afterglow from gamma-burst counterparts.

von Ballmoos, P.; Halloin, H.; Skinner, G.; Smither, B.; Paul, J.; Abrosimov, N.; Alvarez, J.; Astier , P.; Bastie, P.; Barrett, D.; Bazzano, A.; Blanchard, A.; Boutonnet, A.; Brousse, P.; Cordier, B.; Courvoisier, T.; DiCocco, G.; Giuliani, A.; Hamelin, B.; Hernanz, M.; Jean, P.; Isern, J.; Knodlseder, J.; Laurent, P.; Lebrun, F.; Experimental Facilities Division (APS); CESR; CEA-Saclay; Inst. fur Kristallzuchtung; IEEC; LPNHE; Inst. Laue-Langevin; IAS; LA-OMP; Alcatel Space Industries; ISDC; TESRE; Univ. Insurbia

2004-01-01

130

X-ray echoes from gamma-ray bursts  

SciTech Connect

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed. 35 refs.

Dermer, C.D.; Hurley, K.C.; Hartmann, D.H. (California Univ., Berkeley (USA) Lawrence Livermore National Laboratory, CA (USA))

1991-03-01

131

Vegetation Density Determinations by Gamma Ray Absorption.  

National Technical Information Service (NTIS)

A method of non-destructive determination of vegetation density in place is presented. This method utilizes a gamma ray absorption technique. The 122 keV gamma rays from Cobalt-57 were used for this work. The determinations are made using the principle of...

C. M. Cialella J. G. Dante

1971-01-01

132

The science of gamma-ray spectroscopy  

Microsoft Academic Search

The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that high amounts of radioactive nuclei are produced during these events, that are expected to be strong gamma-ray emitters. In this paper we investigate the use of gamma-rays as a diagnostic tool. For this purpose we have performed a complete

J. Isern; E. Bravo; A. Hirschmann

2006-01-01

133

A review of gamma ray bursts  

Microsoft Academic Search

Gamma-ray bursts have continued to puzzle astronomers since their discovery thirty years ago. The sources and emission mechanisms are still uncertain. The instruments on the Compton Gamma Ray Observatory, most notably BATSE, have produced a revolution in our understanding of bursts. BATSE found that the burst spatial distribution was isotropic but inhomogeneous, a result inconsistent with any disk population of

Charles Meegan; Kevin Hurley; Alanna Connors; Brenda Dingus; Steven Matz

1997-01-01

134

On The Origin of Gamma Ray Bursts  

Microsoft Academic Search

We propose that repeated photoexcitation\\/ionization of high Z atoms of highly relativistic flows by star light in dense stellar regions followed by emission of decay\\/recombination photons, which are beamed and boosted to gamma ray energies in the observer frame, produce gamma ray bursts (GRBs). We show that this overlooked mechanism, which is able to convert efficiently baryonic kinetic energy release

Nir J. Shaviv; Arnon Dar

1996-01-01

135

Gamma ray observation with emulsion hybrid telescope  

Microsoft Academic Search

A new gamma ray observation project with balloon borne emulsion chambers is presented. A new technique based on the accelerator emulsion experiments was implemented for studying high energy stellar objects with cosmic gamma rays. This paper provides the aim and concept of this project as well as some results of test experiments.

S. Aoki; K. Kodam; J. Kawada; N. Nonaka; A. Suzuki; T. Hara; Y. Watanabe; H. Rokujyo; A. Ariga; M. Kazuyama; H. Kubota; M. Komatsu; T. Sako; O. Sato; Y. Taira; S. Takahashi; N. Naganawa; T. Nakano; M. Nakamura; K. Niwa; Y. Nonoyama; K. Hamada; T. Fukuda; T. Furukawa; K. Hoshino; M. Miyanishi; S. Miyamoto; K. Morishima; T. Yoshioka; J. Yoshida; A. Iyono; Y. Sato; I. Tezuka

2009-01-01

136

The Supernova-Gamma-Ray Burst Connection  

Microsoft Academic Search

SN 1998bw and its corresponding relativistically expanding radio source are coincident with the gamma -ray burst source GRB 980425. We searched for other possible supernova- gamma -ray burst associations among 101 recent Type Ia and 17 Type Ib\\/c supernovae (SNe) for which the dates of optical maximum are relatively well known. We show that Type Ia SNe can be excluded

Lifan Wang; J. Craig Wheeler

1998-01-01

137

Supernova and Gamma-Ray Burst Remnants  

Microsoft Academic Search

The connection between Supernovae and Gamma-Ray Bursts has provided insights to extend our understanding of both these phenomena beyond what was known from studying them separately. A unique window into the connections between the progenitors and mechanisms of supernova and gamma-ray burst explosions is provided by their remnants. This meeting brings together experts of the remnants of both Supernovae and

Roger Chevalier; Una Hwang; Martin Laming

2006-01-01

138

Very high-energy gamma rays from gamma-ray bursts.  

PubMed

Very high-energy (VHE) gamma-ray astronomy has undergone a transformation in the last few years, with telescopes of unprecedented sensitivity having greatly expanded the source catalogue. Such progress makes the detection of a gamma-ray burst at the highest energies much more likely than previously. This paper describes the facilities currently operating and their chances for detecting gamma-ray bursts, and reviews predictions for VHE gamma-ray emission from gamma-ray bursts. Results to date are summarized. PMID:17293337

Chadwick, Paula M

2007-05-15

139

Observations of the highest energy gamma-rays from gamma-ray bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst. .

Dingus, Brenda L.

2001-04-01

140

Observations of the Highest Energy Gamma-Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst.

Dingus, Brenda L.

2002-12-01

141

The MILAGRO Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

MILAGRO will be the first water-\\v{C}erenkov detector specifically built to study extensive air showers. It is being built in an existing man-made pond 60m x 80m by 8m, located in the Jemez mountains near Los Alamos, NM. Unlike conventional air shower detectors, which sample less than 1% of the particles which reach detector level, MILAGRO will be totally sensitive to the electrons, photons, hadrons, and muons in the air shower. The energy threshold of the MILAGRO detector is comparable to atmospheric \\v{C}erenkov detectors, however it has several advantages over these optical detectors. MILAGRO is operational 24 hours a day in all weather conditions and it has an open aperture which allows it to view the entire northern sky every day. These capabilities allow for a systematic all-sky survey to be done for the first time at VHE energies. MILAGRO will measure the Crab spectrum with high significance. In addition, it will detect and measure the spectra from AGN's such as MRK 421. MILAGRO will be the first VHE detector capable of recording Gamma Ray Bursts at energies above 250 GeV. MILAGRO will search for point sources of VHE gamma radiation, both steady and episodic. The scientific merits of this detector together with its design and current status will be discussed.

Shoup, A.; Barwick, S.; Chumney, P.; Yodh, G. B.; Chang, C. Y.; Chen, M. L.; Dion, C.; Goodman, J. A.; Berley, D.; Haines, T. J.; Hoffman, C. M.; Nagle, D. E.; Sandberg, V. D.; Sanders, G.; Schaller, S.; White, D. H.; Schmidt, D. M.; Sinnis, C.; Cavalli-Sforza, M.; Coyne, D.; Dorfan, D.; Kelley, L.; Klein, S.; Schnee, R.; Williams, D. A.; Yang, T.; Mincer, A. I.; Nemethy, P.; Bauer, D.; Caldwell, D.; Lu, A.; Yellin, S.; O'Neill, T. J.; Tumer, O. T.; Zych, A.; Freedman, S. J.; Fujikawa, B. K.; Ellsworth, R. W.; Biller, S.; Dingus, B. L.; Ahulwalia, H. S.

1994-12-01

142

Gamma-ray Emission from HMXBs  

NASA Astrophysics Data System (ADS)

During the last ten years, high-mass X-ray binaries (HMXB) have consolidated their status of gamma-ray sources. Even before the first EGRET detection candidates, HMXB seemed to be interesting sources to look for gamma rays, and study the processes giving rise to such an energetic photons. Presently, there is already a well established population of gamma-ray emittings HMXB found or confirmed by the current GeV and TeV instruments. These objects have turned out to be very efficient as accelerators, and also channelling the available energy budget into relativistic particles. Their emission is strongly variable and typically periodical, with a low-energy counterpart that is intimately related to the processes at the highest energies. In this talk, I will review the main processes associated to the production of gamma-rays in high-mass X-ray binaries.

Bosch-Ramon, Valenti

2012-07-01

143

VHE gamma-ray studies at the Haleakala gamma observatory  

Microsoft Academic Search

Data collected with the Cerenkov telescope at the Haleakala Gamma Observatory have been analyzed in an effort to establish evidence for emission of VHE gamma-rays for a number of candidate sources. Brief episodes of emission from Her X-1 have been detected. The results from searches for emission from other sources, which has not been detected by our group, are discussed.

L. K. Resvanis; A. Szentgyorgyi; M. Kertzman; P. Slane; J. Hudson; J. Kelley; J. G. Learned; C. Sinnis; R. Austin; N. Berezny; J. Gaidos; F. Loeffler; T. Palfrey; G. Sembroski; C. Wilson; G. Zirnstein; U. Camerini; J. P. Finley; W. Fry; J. Jacobsen; M. Jaworski; J. Jennings; A. Kenter; R. Loveless; R. March; R. Morse; D. D. Reeder; M. Skinner

1990-01-01

144

Comets, X-ray bursts, and gamma-ray bursts  

Microsoft Academic Search

The proposal, revived by Tremaine and Zytkow (1985), that accretion of comets by neutron stars may be the origin of gamma-ray bursts is considered. This mechanism has difficulty accounting for the observed gamma-ray spectrum and optical counterparts of the bursts. The survival of comets near supernovae is investigated. Ablation rates and the thermal structure of an ablating surface layer are

J. I. Katz

1986-01-01

145

Gamma photometric redshifts for long gamma-ray bursts  

Microsoft Academic Search

It is known that the soft tail of the gamma-ray bursts' spectra show excesses from the exact power-law dependence. In this article we show that this departure can be detected in the peak flux ratios of different BATSE DISCSC energy channels. This effect allows to estimate the redshift of the bright long gamma-ray bursts in the BATSE Catalog. A verification

Z. Bagoly; I. Csabai; A. Mészáros; P. Mészáros; I. Horváth; L. G. Balázs; R. Vavrek

2003-01-01

146

Swift's 500th Gamma Ray Burst  

NASA Video Gallery

On April 13, 2010, NASA's Swift Gamma-ray Burst Explorer satellite discovered its 500th burst. Swift's main job is to quickly localize each gamma-ray burst (GRB), report its position so that others can immediately conduct follow-up observations, and then study the burst using its X-ray and Ultraviolet/Optical telescopes. Some notable bursts are identified in the video.

Katherine Lewis

2010-04-19

147

Swift gamma-ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well a using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

Neil A. Gehrels

2000-01-01

148

Swift: A gamma ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

2001-01-01

149

The swift gamma-ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

Neil Gehrels

2000-01-01

150

The Prompt Gamma-Ray and Afterglow Energies of Short-Duration Gamma-Ray Bursts  

Microsoft Academic Search

I present an analysis of the gamma-ray and afterglow energies of a complete sample of 16 short-duration GRBs with prompt X-ray follow-up. I find that 80% of the bursts exhibit a linear correlation between their gamma-ray fluence and the afterglow X-ray flux normalized to t=1 day, a proxy for the kinetic energy of the blast wave (FX,1~F1.01+\\/-0.27gamma). An even tighter

E. Berger

2007-01-01

151

Gamma-ray burst reprocessing in an accretion disk  

SciTech Connect

The observational consequences of the reprocessing of gamma-ray burst (GRB) photons by an accretion disk surrounding a neutron star are explored. Reprocessing of gamma rays by cold disks driven by dynamical viscosity of nonrelativistic, degenerate electrons results in an optical/UV fluence relative to the gamma-ray fluence at earth of greater than 0.001, for GRB energies of (1-10) x 10 to the 37th ergs, and distances of 15-250 pc. The spectrum peaks in the optical/UV with a soft X-ray cutoff due to the inner edge of the disk, which lies very near the surface of the neutron star for magnetic fields less than 1 TG. The optical/UV peak is partially due to reprocessing in the outer part of the cold disk, which remains optically thick to gamma rays. At these distances, a positive identification of a quiescent counterpart is expected at an IR (K) sensitivity less than 2 microJy. On the other hand, compact binary systems with standard alpha disks and accretion rates resulting from Roche-lobe overflow must be located at least several hundred pc away in order to have escaped detection down to the current IR sensitivity. The optical/UV fluence resulting from reprocessing in these systems is deficient by at least an order of magnitude compared to the observed values. 35 references.

Melia, F.

1988-01-01

152

Thermal neutron capture gamma-rays  

SciTech Connect

The energy and intensity of gamma rays as seen in thermal neutron capture are presented. Only those (n,..cap alpha..), E = thermal, reactions for which the residual nucleus mass number is greater than or equal to 45 are included. These correspond to evaluations published in Nuclear Data Sheets. The publication source data are contained in the Evaluated Nuclear Structure Data File (ENSDF). The data presented here do not involve any additional evaluation. Appendix I lists all the residual nuclides for which the data are included here. Appendix II gives a cumulated index to A-chain evaluations including the year of publication. The capture gamma ray data are given in two tables - the Table 1 is the list of all gamma rays seen in (n,..gamma..) reaction given in the order of increasing energy; the Table II lists the gamma rays according to the nuclide.

Tuli, J.K.

1983-01-01

153

Gamma-Ray Burst Physics with Glast  

NASA Astrophysics Data System (ADS)

The Gamma-ray Large Area Space Telescope (GLAST) is an international space mission that will study the cosmos in the energy range 10 keV-300 GeV, the upper end of which is one of the last poorly observed region of the celestial electromagnetic spectrum. The ancestor of the GLAST/LAT was the Energetic Gamma Ray Experiment Telescope (EGRET) detector, which flew onboard the Compton Gamma Ray Observatory (CGRO). The amount of information and the step forward that the high energy astrophysics made thanks to its 9 years of observations are impressive. Nevertheless, EGRET uncovered the tip of the iceberg, raising many questions, and it is in the light of EGRET's results that the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope, the Large Area Telescope (LAT) vastly more capable than instruments flown previously, as well as a secondary instrument, the GLAST Bursts Monitor, or GBM, to augment the study of gamma-ray bursts. Gamma-Ray Bursts (GRBs) science is one of the most exciting challenges for the GLAST mission, exploring the high energy emission of one of the most intense phenomena in the sky, shading light on various problems: from the acceleration of particles to the emission processes, to more exotic physics like Quantum Gravity effect. In this paper we report the work done so far in the simulation development as well as the study of the LAT sensitivity to GRB.

Omodei, N.

2006-04-01

154

Gamma-Ray Burst Physics with GLAST  

SciTech Connect

The Gamma-ray Large Area Space Telescope (GLAST) is an international space mission that will study the cosmos in the energy range 10 keV-300 GeV, the upper end of which is one of the last poorly observed region of the celestial electromagnetic spectrum. The ancestor of the GLAST/LAT was the Energetic Gamma Ray Experiment Telescope (EGRET) detector, which flew onboard the Compton Gamma Ray Observatory (CGRO). The amount of information and the step forward that the high energy astrophysics made thanks to its 9 years of observations are impressive. Nevertheless, EGRET uncovered the tip of the iceberg, raising many questions, and it is in the light of EGRET's results that the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope, the Large Area Telescope (LAT) vastly more capable than instruments own previously, as well as a secondary instrument, the GLAST Bursts Monitor, or GBM, to augment the study of gamma-ray bursts. Gamma-Ray Bursts (GRBs) science is one of the most exciting challenges for the GLAST mission, exploring the high energy emission of one of the most intense phenomena in the sky, shading light on various problems: from the acceleration of particles to the emission processes, to more exotic physics like Quantum Gravity effect. In this paper we report the work done so far in the simulation development as well as the study of the LAT sensitivity to GRB.

Omodei, N.; /INFN, Pisa

2006-10-06

155

Absorption of high-energy gamma rays in Cygnus X-3  

NASA Astrophysics Data System (ADS)

Context. The microquasar Cygnus X-3 was detected at high energies by the gamma-ray space telescopes AGILE and Fermi. The gamma-ray emission is transient, modulated with the orbital period and seems related to major radio flares, i.e. to the relativistic jet. The GeV gamma-ray flux can be substantially attenuated by internal absorption with the ambient X-rays. Aims: We examine quantitatively the effect of pair production in Cygnus X-3 and put constraints on the location of the gamma-ray source. Methods: Cygnus X-3 exhibits complex temporal and spectral patterns in X-rays. During gamma-ray flares, the X-ray emission can be approximated by a bright disk black-body component and a non-thermal tail extending in hard X-rays, which is possibly related to a corona above the disk. We calculate numerically the exact optical depth for gamma rays above a standard accretion disk. Emission and absorption in the corona are also investigated. Results: GeV gamma rays are significantly absorbed by soft X-rays emitted from the inner parts of the accretion disk. The absorption pattern is complex and anisotropic. Isotropization of X-rays caused by Thomson scattering in the companion-star wind tends to increase the gamma-ray opacity. Gamma rays from the corona suffer from strong absorption by photons from the disk and cannot explain the observed high-energy emission, unless the corona is unrealistically extended. Conclusions: The lack of an absorption feature in the GeV emission indicates that high-energy gamma rays should be located at a minimum distance ~108-1010 cm from the compact object. The gamma-ray emission is unlikely to have a coronal origin.

Cerutti, B.; Dubus, G.; Malzac, J.; Szostek, A.; Belmont, R.; Zdziarski, A. A.; Henri, G.

2011-05-01

156

Gamma-Ray Pulsar Studies With GLAST  

SciTech Connect

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

Thompson, D.J.; /NASA, Goddard

2011-11-23

157

GRAPE - The Gamma Ray Polarimeter Experiment  

NASA Astrophysics Data System (ADS)

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), has been successfully demonstrated in the lab using partially polarized gamma-ray sources and using fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model was flown on a high altitude balloon flight to demonstrate the design and to collect background data. We are currently working on the development of a much larger balloon payload that would provide a significant level of sensitivity for gamma-ray bursts on a long-duration balloon flight and, if flown near solar max, would also provide significant sensitivity for solar flare polarization measurements. We shall review the history, status and future potential of the GRAPE project and summarize the potential for making polarization measurements of gamma-ray bursts and solar flares.

McConnell, Mark L.; Bloser, P. F.; Legere, J.; Ryan, J. M.; Connor, T.

2009-01-01

158

FLARES IN LONG AND SHORT GAMMA-RAY BURSTS  

SciTech Connect

The many similarities between the prompt emission pulses in gamma-ray bursts (GRBs) and X-ray flares during the fast decay and afterglow (AG) phases of GRBs suggest a common origin. In the cannonball (CB) model of GRBs, this common origin is mass accretion episodes of fall-back matter on a newly born compact object. The prompt emission pulses are produced by a bipolar jet of highly relativistic plasmoids (CBs) ejected in the early, major episodes of mass accretion. As the accretion material is consumed, one may expect the engine's activity to weaken. X-ray flares ending the prompt emission and during the AG phase are produced in such delayed episodes of mass accretion. The common engine, environment, and radiation mechanisms (inverse Compton scattering and synchrotron radiation) produce their observed similarities. Flares in both long GRBs and short hard gamma-ray bursts (SHBs) can also be produced by bipolar ejections of CBs following a phase transition in compact objects due to loss of angular momentum and/or cooling. Optical flares, however, are mostly produced in collisions of CBs with massive stellar winds/ejecta or with density bumps along their path. In this paper, we show that the master formulae of the CB model of GRBs and SHBs, which reproduce very well their prompt emission pulses and their smooth AGs, seem to reproduce also very well the light curves and spectral evolution of the prominent X-ray and optical flares that are well sampled.

Dado, Shlomo; Dar, Arnon, E-mail: dado@phep3.technion.ac.i, E-mail: arnon@physics.technion.ac.i [Physics Department, Technion, Haifa 32000 (Israel)

2010-04-01

159

Gamma-ray Albedo of the Moon  

SciTech Connect

We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma-rays from the Moon is very steep with an effective cutoff around 3 GeV (600 MeV for the inner part of the Moon disc). Since it is the only (almost) black spot in the gamma-ray sky, it provides a unique opportunity for calibration of gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo -rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.

Moskalenko, Igor V.; Porter, Troy A.

2007-06-14

160

How to Make a Gamma-ray  

NASA Video Gallery

Animation showing a proton traveling near the speed of light striking a slower-moving proton. The protons survive the collision, but their interaction creates an unstable particle, a pion, with only 14 percent of the proton's mass. In 10 millionths of a billionth of a second, the pion decays into a pair of gamma-ray photons. Years of data collected by NASA's Fermi Gamma-Ray Space Telescope reveal that the shattered remains of a supernova first observed in 1572 shine in high-energy gamma-rays.

Holly Zell

2011-12-12

161

Detecting Axionlike Particles with Gamma Ray Telescopes  

SciTech Connect

We propose that axionlike particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to a detectable signature in the spectra of high-energy gamma-ray sources. This occurs as a result of gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the 'Hillas criterion', such as jets of active galactic nuclei or hot spots of radio galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV range and by ground-based gamma-ray telescopes in the TeV range.

Hooper, Dan; Serpico, Pasquale D. [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States)

2007-12-07

162

Detecting axionlike particles with gamma ray telescopes.  

PubMed

We propose that axionlike particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to a detectable signature in the spectra of high-energy gamma-ray sources. This occurs as a result of gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the "Hillas criterion", such as jets of active galactic nuclei or hot spots of radio galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV range and by ground-based gamma-ray telescopes in the TeV range. PMID:18233353

Hooper, Dan; Serpico, Pasquale D

2007-12-06

163

Hand-Held Gamma-Ray Imaging Sensors Using Room-Temperature 3Dimensional Position-Sensitive Semiconductor Spectrometers  

Microsoft Academic Search

This paper demonstrates the capability of compact gamma-ray imaging devices using 3-dimensional position sensitive CdZnTe semiconductor gamma-ray spectrometers, developed at the University of Michigan. A prototype imager was constructed and tested using two 1 cm cube 3-dimensional position sensitive CdZnTe detectors. Energy resolutions of 1.5% FWHM for single pixel events at 662 keV gamma-ray energy were obtained on both detectors,

Zhong He; Carolyn Lehner; Feng Zhang; David K. Wehe; Glenn F. Knoll; James Berry; Yanfeng Du

2002-01-01

164

The AGILE Mission and Gamma-Ray Bursts  

SciTech Connect

The AGILE Mission will explore the gamma-ray Universe with a very innovative instrument combining for the first time a gamma-ray imager and a hard X-ray imager. AGILE will be operational at the beginning of 2007 and it will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources, Galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. The AGILE instrument is designed to simultaneously detect and image photons in the 30 MeV - 50 GeV and 15 - 45 keV energy bands with excellent imaging and timing capabilities, and a large field of view covering {approx} 1/5 of the entire sky at energies above 30 MeV. A CsI calorimeter is capable of GRB triggering in the energy band 0.3-50 MeV. The broadband detection of GRBs and the study of implications for particle acceleration and high energy emission are primary goals of the mission. AGILE can image GRBs with 2-3 arcminute error boxes in the hard X-ray range, and provide broadband photon-by photon detection in the 15-45 keV, 03-50 MeV, and 30 MeV-30 GeV energy ranges. Microsecond on-board photon tagging and a {approx} 100 microsecond gamma-ray detection deadtime will be crucial for fast GRB timing. On-board calculated GRB coordinates and energy fluxes will be quickly transmitted to the ground by an ORBCOMM transceiver. AGILE is now (January 2007) undergoing final satellite integration and testing. The PLS V launch is planned in spring 2007. AGILE is then foreseen to be fully operational during the summer of 2007.

Longo, Francesco [Department of Physics, University of Trieste (Italy); INFN, section of Trieste (Italy); Tavani, M.; Barbiellini, G.; Argan, A.; Basset, M.; Boffelli, F.; Bulgarelli, A.; Caraveo, P.; Cattaneo, P.; Chen, A.; Costa, E.; Del Monte, E.; Di Cocco, G.; Di Persio, G.; Donnarumma, I.; Feroci, M.; Fiorini, M.; Foggetta, L.; Froysland, T.; Frutti, M. (and others)

2007-05-01

165

Absorption of gamma-rays in the 5 March 1979 gamma-ray burst source  

Microsoft Academic Search

Absorption of gamma-rays above the source of their burst on March 5, 1979 is considered, in order to measure their distance. The results of a spherical model of the gamma-ray burst shows that unless the photons were collimated during the burst, the gamma-gamma optical thickness above an isotropically emitting burst source would be as high as 10 to the 5th

A. A. Zdziarski

1984-01-01

166

GRI: the gamma-ray imager mission  

NASA Astrophysics Data System (ADS)

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime. With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques hav paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Knödlseder, Jürgen

2006-07-01

167

The Gamma-Ray Imager GRI  

NASA Astrophysics Data System (ADS)

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime. With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Wunderer, Cornelia B.; GRI Collaboration

2006-09-01

168

A General Gamma-Ray Source Catalog  

NASA Astrophysics Data System (ADS)

The past several years have seen unprecedented growth in the field of gamma-ray astronomy. Highly successful missions such as the Compton Gamma-Ray Observatory (CGRO) have led to both a great increase in the number of detected gamma-ray sources and a more fundamental understanding of the basic physical processes involved for those sources. New ground-based observatories, the Rossi X-Ray Timing Explorer (RXTE), and the SIGMA instrument aboard the GRANAT spacecraft have all contributed to this explosion. Detailed observations of active galaxies, pulsars, accreting binaries, and diffuse emission have had a tremendous impact on our view of the universe. Given that new experiments that will provide a similar increase in source numbers are several years away, it is a good time to take inventory of the state of gamma-ray astronomy. To this end, we have developed a general gamma-ray point-source catalog containing 309 objects that summarize the field. Gamma-ray astronomy, as we define it, includes photon energies from 50 keV to about 1 TeV. While many catalogs concentrate on a single type of astronomical object and/or a very restricted energy range, the nature of this catalog is somewhat different. The large variety of objects and the many orders of magnitude in energy space covered by gamma-ray astronomy presents an organizational challenge. We focus on two main types of information: a general listing of the basic characteristics of each source, and detailed tables of a representative sample of high-energy observations. We also summarize the gamma-ray instruments whose observations are included in the catalog.

Macomb, D. J.; Gehrels, N.

1999-02-01

169

Observations of gamma-ray bursts at extreme energies  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs), thought to be produced by the core-collapse of massive stars or merging compact objects, are the most luminous events observed since the Big Bang. GRBs are intrinsically interesting as laboratories to study physical processes at energies much higher than can be produced in the largest particle accelerators on Earth. A better understanding of GRBs may also allow for their use as cosmological tools - backlights for the study of the evolution of the Universe back to the era of the first gravitationally-bound structures. In this work, results from observations of satellite-detected GRBs with the Milagro and VERITAS very high energy (VHE, >100 GeV) gamma-ray telescopes are presented. No significant flux of VHE gamma rays associated with any of the 144 GRBs observed was detected. The limits on VHE gamma-ray emission during the GRB early afterglow phase obtained from the VERITAS observations are among the most constraining to date and the interpretation of these non-detections in the context of GRB emission models is discussed. Results from observation of the "naked-eye burst" GRB 080319B with Milagro are shown to rule out the popular synchrotron self-Compton model of emission over a broad range of energy space. Finally, the prospects for GRB observations with both current and future-generation VHE observatories are examined.

Aune, Taylor

2012-05-01

170

High Energy Gamma Rays from Ultrahigh Energy Cosmic Rays in Gamma Ray Bursts  

Microsoft Academic Search

It has recently been proposed that ultrahigh energy ($\\\\gtrsim 10^{19}$ eV)\\u000acosmic rays (UHECRs) are accelerated by the blast waves associated with GRBs.\\u000aWe calculate the observed synchrotron radiation spectrum from protons and\\u000aenergetic leptons formed in the cascades initiated by photopion production,\\u000ataking into account $\\\\gamma\\\\gamma$ attenuation at the source. Normalizing to\\u000athe emission characteristics of GRB~970508, we predict

M. Boettcher; C. D. Dermer

1998-01-01

171

Gamma-ray bursts from stellar remnants: probing the Universe at high redshift  

Microsoft Academic Search

A gamma-ray burst (GRB) releases an amount of energy similar to that of a\\u000asupernova explosion, which combined with its rapid variability suggests an\\u000aorigin related to neutron stars or black holes. Since these compact stellar\\u000aremnants form from the most massive stars not long after their birth, gamma-ray\\u000abursts should trace the star formation rate in the Universe; we

Ralph A. M. J. Wijers; Joshua S. Bloom; Jasjeet S. Bagla; Priyamvada Natarajan

1997-01-01

172

Simulated Performance of the Nuclear Compton Telescope as a Gamma-Ray Polarimeter  

Microsoft Academic Search

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and gamma-ray polarization. NCT is sensitive to polarization in the range 0.2-1 MeV. NCT consists of 3D position-sensitive germanium strip detectors. The ultra-compact design and new technologies allow NCT to achieve high efficiencies with excellent spectral resolution and

Jau-Shian Liang; E. C. Bellm; S. E. Boggs

2008-01-01

173

Gamma Ray Bursts from Magnetospheric Plasma Oscillations.  

National Technical Information Service (NTIS)

Neutron star Magnetospheric Plasma Oscillations (MPO), can account for the energetics, decay time scale, and spectra of typical Gamma Ray Bursts (GRBs). The soft photon source is likely to be due to backwarming of the reprocessing boundary by the incipien...

F. Melia

1989-01-01

174

Neutron Detection Gamma Ray Sensitivity Criteria  

SciTech Connect

The shortage of 3He has triggered the search for effective alternative neutron detection technologies for national security and safeguards applications. Any new detection technology must satisfy two basic criteria: (1) it must meet a neutron detection efficiency requirement, and (2) it must be insensitive to gamma-ray interference at a prescribed level, while still meeting the neutron detection requirement. It is the purpose of this paper to define measureable gamma ray sensitivity criteria for neutron detectors. Quantitative requirements are specified for: intrinsic gamma ray detection efficiency and gamma ray absolute rejection. The ratio GARRn is defined, and it is proposed that the requirement for neutron detection be 0.9 < GARRn < 1.1 at a 10 mR/h exposure rate. An example of results from a 3He based neutron detector are provided showing that this technology can meet the stated requirements. Results from tests of some alternative technologies are also reported.

Kouzes, Richard T.; Ely, James H.; Lintereur, Azaree T.; Mace, Emily K.; Stephens, Daniel L.; Woodring, Mitchell L.

2011-10-21

175

Do Gamma-ray Burst Sources Repeat.  

National Technical Information Service (NTIS)

The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analy...

C. A. Meegan D. H. Hartmann J. J. Brainerd M. Briggs W. S. Paciesas

1994-01-01

176

Gamma-ray emission from thermonuclear supernovae  

SciTech Connect

The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that high amounts of radioactive nuclei are produced during these events and that they are expected to be strong {gamma}-ray emitters. In this paper we investigate the use of this {gamma}-rays as a diagnostic tool. For this purpose we have performed a complete study of the {gamma}-ray spectra associated with all the different scenarios currently proposed: detonation, deflagration, delayed detonation, and pulsating delayed detonation. Our study shows that the {gamma}-ray emission from SNIa is, effectively, a promising tool but that has to be carefully used since it can lead to misinterpretations. We also show that 3D effects can be relevant in some circumstances and that they can provide important information about the exploding system and the thermonuclear burning front mechanism if high resolution spectra could be obtained.

Isern, J. [Institut de Ciencies de l'Espai (CSIC - IEEC), Campus UAB, Torre C5-parells 2n, 08193 Bellaterra (Spain); Institut d'Estudis Espacials de Catalunya (Spain); Bravo, E.; Hirschmann, A. [Departament de Fisica i Enginyeria Nuclear UPC (Spain); Diagonal 647, 08028 Barcelona (Spain); Institut d'Estudis Espacials de Catalunya (Spain)

2007-08-21

177

Radio counterparts of gamma-ray pulsars  

NASA Astrophysics Data System (ADS)

Observations of pulsars with the Large Area Telescope (LAT) on the Fermi satellite have revolutionized our view of the gamma-ray pulsar population. For the first time, a large number of young gamma-ray pulsars have been discovered in blind searches of the LAT data. More generally, the LAT has discovered many new gamma-ray sources whose properties suggest that they are powered by unknown pulsars. Radio observations of gamma-ray sources have been key to the success of pulsar studies with the LAT. For example, radio observations of LAT-discovered pulsars provide constraints on the relative beaming fractions, which are crucial for pulsar population studies. Also, radio searches of LAT sources with no known counterparts have been very efficient, with the discovery of over forty millisecond pulsars. I review radio follow-up studies of LAT-discovered pulsars and unidentified sources, and discuss some of the implications of the results.

Guillemot, L.

2013-03-01

178

Gamma-ray Burst Predictions for the Fermi Gamma Ray Space Telescope  

Microsoft Academic Search

Results of a phenomenological model to estimate the gamma-ray burst (GRB) detection rate by the Fermi Gamma-Ray Space Telescope are reported. This estimate is based on the Burst and Transient Source Experiment (BATSE) 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV-5 GeV with Energetic Gamma-Ray Experiment Telescope (EGRET) and at 20 keV-2 MeV with BATSE,

Truong Le; Charles D. Dermer

2009-01-01

179

Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation  

Microsoft Academic Search

We develop a general expression for the gamma - gamma absorption coefficient, alphagammagamma, for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray-emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius, R0, and the inner radius, Rms, which is the

Peter A. Becker; Menas Kafatos

1995-01-01

180

Low-State Gamma-Ray Emission from Blazars and the Gamma-Ray Background  

Microsoft Academic Search

We examine the contribution of flat spectrum radio sources (FSRSs), or blazars, to the diffuse gamma-ray background (DGRB), prompted by the association of the extragalactic gamma -ray sources detected by the EGRET instrument aboard the Compton Gamma Ray Observatory (CGRO) with this class of objects by using their well-studied log N--log S distribution. The basic assumption of our study are

Demosthenes Kazanas; Eric Perlman

1997-01-01

181

Gamma-Ray Library and Uncertainty Analysis: Passively Emitted Gamma Rays Used in Safeguards Technology  

Microsoft Academic Search

Non-destructive gamma-ray analysis is a fundamental part of nuclear safeguards, including nuclear energy safeguards technology. Developing safeguards capabilities for nuclear energy will certainly benefit from the advanced use of gamma-ray spectroscopy as well as the ability to model various reactor scenarios. There is currently a wide variety of nuclear data that could be used in computer modeling and gamma-ray spectroscopy

2009-01-01

182

Fermi Gamma-ray Space Telescope Observations of Gamma-ray Pulsars  

Microsoft Academic Search

The Large Area Telescope on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma-ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma-ray pulsars, which in turn

P. M. Saz Parkinson

2009-01-01

183

Pair-Signatures and High-Energy Gamma-Ray Emission from Gamma-Ray Bursts  

Microsoft Academic Search

We discuss high-energy gamma-ray emission from gamma-ray bursts (GRBs). When such high-energy gamma rays are expected, e+\\/- pairs may play an important role both inside and outside the source. e+\\/- pair-signatures inside the source (the pair-annihilation bump and the cutoff due to the pair-creation process) are useful for diagnosing the fireball of GRBs. The recipes for diagnoses are largely model-independent

Kohta Murase; Kunihito Ioka; Shigehiro Nagataki

2008-01-01

184

Constraints on the Luminosity Function of Gamma-Ray Bursts from the Gamma Ray Background  

Microsoft Academic Search

The width of the gamma-ray burst (GRB) luminosity function is presently not well constrained. A wide luminosity function might be expected were GRBs associated with supernovae, for example. The possibility that a large number of undetected GRBs might make a contribution to the diffuse soft gamma-ray background is investigated. If gamma-ray bursts (GRBs) create supernova-like remnants, the width of the

H. Che

1999-01-01

185

Nature of Cosmic gamma Ray Bursts.  

National Technical Information Service (NTIS)

The nature of cosmic gamma ray burst is studied. The sources of the observed gamma bursts are supposed to be presented by the two populations of galactic objects, namely: the old neutron stars concentrated in the galactic disk; and the old degenerated dwa...

N. I. Shakura N. N. Shakura

1990-01-01

186

Study of gamma-ray strength functions  

SciTech Connect

The use of gamma-ray strength function systematics to calculate neutron capture cross sections and capture gamma-ray spectra is discussed. The ratio of the average capture width, GAMMA/sub ..gamma../-bar, to the average level spacing, D/sub obs/, both at the neutron separation energy, can be derived from such systematics with much less uncertainty than from separate systematics for values of GAMMA/sub ..gamma../-bar and D/sub obs/. In particular, the E1 gamma-ray strength function is defined in terms of the giant dipole resonance (GDR). The GDR line shape is modeled with the usual Lorentzian function and also with a new energy-dependent, Breit-Wigner (EDBW) function. This latter form is further parameterized in terms of two overlapping resonances, even for nuclei where photonuclear measurements do not resolve two peaks. In the mass ranges studied, such modeling is successful for all nuclei away from the N = 50 closed neutron shell. Near the N = 50 shell, a one-peak EDBW appears to be more appropriate. Examples of calculated neutron capture excitation functions and capture gamma-ray spectra using the EDBW form are given for target nuclei in the mass-90 region and also in the Ta-Au mass region. 20 figures.

Gardner, D.G.; Gardner, M.A.; Dietrich, F.S.

1980-08-07

187

Solar Two Gamma-Ray Observatory  

Microsoft Academic Search

The field of high energy gamma-ray astronomy grew tremendously in the last decade due to the launch of the EGRET detector on the Compton Gamma-Ray Observatory in 1991 and the proliferation of ground-based air ?herenkov telescopes (ACTs) such as the Whipple 10 meter reflector. Interestingly, the ground-based telescopes only see 4–5 of the over 170 objects detected by EGRET. A

T. Tümer; D. Bhattacharya; U. Mohideen; R. Rieben; V. Souchkov; H. Tom; J. Zweerink

1999-01-01

188

Gamma-Ray Burst Physics with GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in late of 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT), the main instrument of GLAST, will survey the sky in the energy range between 20 MeV to more than 300 GeV, shedding light on many issues left open by its highly

Nicola Omodei

2007-01-01

189

Gamma-Ray Bursts: the Four Crises  

Microsoft Academic Search

We discuss some open problems concerning the origin and the emission\\u000amechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs\\u000aoriginate at extragalactic distances, we are facing four crises: (1) an energy\\u000acrisis, models have to account for more than 10^{53} ergs of energy emitted in\\u000athe gamma-ray energy band; (2) a spectral crisis, emission models have

Marco Tavani

1998-01-01

190

Gamma-Ray Bursts: the Four Crises  

Microsoft Academic Search

We discuss some open problems concerning the origin and the emission mechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs originate at extragalactic distances, we are facing four crises: (1) an energy crisis, models have to account for more than 10^{53} ergs of energy emitted in the gamma-ray energy band; (2) a spectral crisis, emission models have

M. Tavani

1999-01-01

191

Gamma Ray Bursts Cook Book I: Formulation  

Microsoft Academic Search

Since the suggestion of relativistic shocks as the origin of gamma-ray bursts\\u000a(GRBs) in early 90's, the mathematical formulation of this process has stayed\\u000aat phenomenological level. One of the reasons for the slow development of\\u000atheoretical works in this domain has been the simple power-law behaviour of the\\u000aafterglows hours or days after the prompt gamma-ray emission. Nowadays with

Houri Ziaeepour

2008-01-01

192

Classification of Swift's gamma-ray bursts  

Microsoft Academic Search

Context. Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 s. There are, however, some indications for the existence of a third class. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore we reanalyze the durations and their distribution and also the classi-

I. Horváth; L. G. Balázs; Z. Bagoly; P. Veres

2008-01-01

193

First Gamma Ray Burst Observations with Swift  

Microsoft Academic Search

Swift is a NASA Explorer mission that was launched on November 20, 2004. It is a multiwavelength observatory for transient astronomy. The goals of the mission are to determine the origin of gamma-ray bursts and their afterglows and use bursts to probe the early Universe. A wide-field gamma-ray camera will detect more than a hundred GRBs per year to 3

Neil Gehrels

2005-01-01

194

Gamma-ray bursts and Swift  

Microsoft Academic Search

Discovered by accident using satellites monitoring the nuclear test-ban treaty, gamma-ray bursts (GRBs) are the most powerful explosive events in the Universe. Several GRBs per day occur randomly on the sky, typically lasting a few seconds as a gamma-ray source. This abrupt burst is followed by emission across the entire electromagnetic spectrum which can last for several weeks or more.

Paul O'Brien; Julian Osborne; Keith Mason

2005-01-01

195

GeV gamma-ray sources  

NASA Astrophysics Data System (ADS)

We report on the preliminary extension of our work on cataloging the GeV sky to approximately 7 years of CGRO/EGRET observations with special emphasis on a search for transient sources. The search method and significance levels are presented. Our initial results on 13 possible transients indicate that 3 may be new gamma-ray sources. Sixteen new steady GeV sources are also detected, 3 of which have never been reported as gamma-ray sources. .

Lamb, R. C.; Macomb, D. J.

2000-06-01

196

Mining Gamma-Ray Burst Data  

Microsoft Academic Search

Gamma-ray bursts provide what is probably one of the messiest of all astrophysical data sets. Burst class properties are indistinct,\\u000a as overlapping characteristics of individual bursts are convolved with effects of instrumental and sampling biases. Despite\\u000a these complexities, data mining techniques have allowed new insights to be made about gamma-ray burst data. We demonstrate\\u000a how data mining techniques have simultaneously

Jon Hakkila; Richard J. Roiger; David J. Haglin; Robert S. Mallozzi; Geoffrey N. Pendleton; Charles A. Meegan

197

GRI: The Gamma-Ray Imager mission  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe While at lower wavebands the observed emission is generally dominated by thermal processes the gamma-ray sky provides us with a view on the non-thermal Universe Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood and nuclear

Jürgen Knödlseder

2006-01-01

198

The Gamma-Ray Imager GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer

2008-01-01

199

The Gamma-Ray Imager GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer

2006-01-01

200

Gamma-Ray Bursts from Minijets  

Microsoft Academic Search

Striking similarities exist between high-energy gamma-ray emission from active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). They suggest that GRBs are generated by inverse Compton scattering from highly relativistic electrons in transient jets. Such jets may be produced along the axis of an accretion disk formed around stellar black holes (BHs) or neutron stars (NSs) in BH-NS and NS-NS mergers

Nir J. Shaviv; Arnon Dar

1995-01-01

201

Cataclysmic Variables and Gamma-Ray Sources  

NASA Astrophysics Data System (ADS)

The cataclysmic variables are associated with high energy events and probably many of them could be potential gamma-ray sources. Up to now Fermi-LAT detected 3 gamma-ray transients, which belong to CVs and related objects: V407 Cyg, N Sco 2012 and N Mon 2012 = V959 Mon. We present the first multicolour observations of the slow classical nova V959 Mon.

Pavlenko, E.; Malanushenko, V.; Shugarov, S.; Chochol, D.

2013-07-01

202

Observing Gamma-ray Bursts with GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high-energy gamma-ray sky. The Large Area Telescope, the main instrument, is a pair-conversion telescope which will survey the sky in the energy range 20 MeV to greater than 300 GeV. The LAT's wide field of view (>2; sr), large effective area and low deadtime combine to provide

Julie E. McEnery

2007-01-01

203

Radiation detection system for portable gamma-ray spectroscopy  

DOEpatents

A portable gamma ray detection apparatus having a gamma ray detector encapsulated by a compact isolation structure having at least two volumetrically-nested enclosures where at least one is a thermal shield. The enclosures are suspension-mounted to each other to successively encapsulate the detector without structural penetrations through the thermal shields. A low power cooler is also provided capable of cooling the detector to cryogenic temperatures without consuming cryogens, due to the heat load reduction by the isolation structure and the reduction in the power requirements of the cooler. The apparatus also includes a lightweight portable power source for supplying power to the apparatus, including to the cooler and the processing means, and reducing the weight of the apparatus to enable handheld operation or toting on a user's person.

Rowland, Mark S. (Alamo, CA); Howard, Douglas E. (Livermore, CA); Wong, James L. (Dublin, CA); Jessup, James L. (Tracy, CA); Bianchini, Greg M. (Livermore, CA); Miller, Wayne O. (Livermore, CA)

2006-06-20

204

Optical photometric monitoring of gamma-ray binaries  

NASA Astrophysics Data System (ADS)

Four gamma-ray binaries, namely PSR B1259-63, HESS J0632+057, HD 215227 and LS I +61 303, contain compact objects orbiting around massive Be stars. The nature of the compact object is only known in the case of PSR B1259-63, but the other systems could also contain young non-accreting pulsars with relativistic winds. Around periastron passage the compact objects should produce significant changes in the structure of the Be discs due to gravitational forces and eventually by ram pressure from the putative pulsar wind. Indeed, variability in the Ha emission line has been detected in all these systems, and periodic variability in the optical photometry has been detected in two of them. However, there is lack of a systematic monitoring with accurate photometry, which could be used to constrain the shape of the disc during the periastron passage. This information is important to build accurate physical models to explain the broadband spectral energy distribution of these sources. Here we present an ongoing program to monitor the optical photometry of gamma-ray binaries and we show preliminary results for the case of HD 215227.

Paredes-Fortuny, Xavier; Ribó, Marc; Fors, Octavi; Núńez, Jorge

2012-12-01

205

The Development of GRAPE, a Gamma Ray Polarimeter Experiment  

NASA Astrophysics Data System (ADS)

The measurement of hard X-ray polarization in ?-ray bursts (GRBs) would add yet another piece of information in our effort to resolve the true nature of these enigmatic objects. Here we report on the development of a dedicated polarimeter design with a relatively large FoV that is capable of studying hard X-ray polarization (50-300 keV) from GRBs. This compact design, based on the use of a large area position-sensitive PMT (PSPMT), is referred to as GRAPE (Gamma-RAy Polarimeter Experiment). The feature of GRAPE that is especially attractive for studies of GRBs is the significant off-axis polarization response (at angles greater than 60°). For an array of GRAPE modules, current sensitivity estimates give minimum detectable polarization (MDP) levels of a few percent for the brightest GRBs.

McConnell, M. L.; Ledoux, J. R.; Macri, J. R.; Ryan, J. M.

2003-04-01

206

Observing cosmic nuclei in gamma rays  

NASA Astrophysics Data System (ADS)

Nucleosynthesis events in cosmic objects create new nuclei, admixtures of radioactive isotopes being part of the matter ejected into interstellar space by these events. Gamma rays are emitted in radioactive decays, and can be measured with space-based gamma-ray telescopes. Four mission years of INTEGRAL have led to discoveries of new sources and to detailed astronomical refinements of already-known gamma-ray line emission. As part of the main science objectives of INTEGRAL's spectrometer SPI, diffuse emission from annihilation of positrons has presented a new puzzle, as the Galactic distribution of their presumed sources does not agree with the gamma-ray image. Recent massive-star nucleosynthesis is traced throughout the Galaxy with radioactivites seen in 26Al and now also 60Fe gamma rays; precision line spectroscopy now reveals Doppler shifts for the 26Al line, separately for different parts of the Galaxy. This provides new insights into the dynamics of hot interstellar gas. The processes generating new atomic nuclei in stars and supernovae are reflected in the abundances of the ejected radioactivities. For individual supernovae, measurements of 44Ti with its 85 year decay time probes the symmetry of the supernova interior. Since such gamma-ray measurements probe the generation of new nuclei in cosmic sites through a radiation process which is independent of environmental parameters such as temperature or ionization, it will remain worthwhile to further develop instrumentation in this window to the nuclear-physics universe.

Diehl, Roland

2008-01-01

207

Gamma-ray Emission in GPS Quasars  

NASA Astrophysics Data System (ADS)

In this paper, it is argued that the relativistic jets in gigahertz peaked spectrum (GPS) quasars are oriented at small angle to the line of sight and are powerful gamma-ray sources. Besides luminous hard gamma-ray emission, most of them may have significant soft gamma-ray and X-ray emission due to infrared photons from very dense and dusty nuclear interstellar media in GPS quasars, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than in flat spectrum radio quasars (FSRQs), synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust than in FSRQs, hence most GPS quasars show low optical polarization and small variability. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. The gamma-ray emission in GPS quasars can be tested by the observation of the INTEGRAL and GLAST in the near future.

Bai, Jin-Ming

2005-06-01

208

Light Curves of Swift Gamma-Ray Bursts  

Microsoft Academic Search

Recent observations from the Swift gamma-ray burst mission indicate that a fraction of gamma-ray bursts are characterized by a canonical behavior of the X-ray afterglows. We present an effective theory that allows us to account for X-ray light curves of both (short\\/long) gamma-ray bursts and X-ray-rich flashes. We propose that gamma-ray bursts originate from massive magnetic-powered pulsars.

Paolo Cea; Via G. Amendola

2007-01-01

209

Development of an X-ray photoelectron microscopic system with a compact X-ray source  

Microsoft Academic Search

We have constructed an X-ray photoelectron microscopic system. An X-ray source is a laser-produced plasma in a scheme of an X-ray laser experiment. X rays involving amplified spontaneous emissions (ASE) at 15.47 nm were delivered with a 10-Hz repetition rate from a compact X-ray laser system. X rays were collected and focused by a Schwarzschild optics coated with Mo\\/Si multilayers

Chiemi Fujikawa; Naohiro Yamaguchi; Tadayuki Ohchi; Tamio Hara; Katsumi Watanabe; Ibuki Tanaka; Masami Taguchi

2002-01-01

210

Compact phase-contrast soft X-ray microscopy  

NASA Astrophysics Data System (ADS)

For nearly all elements, the real part, d, of the complex index of refraction n (n = 1 - ? + i?) is larger than the imaginary part, ?, in the x-ray region. Since only ? is used in absorption contrast, phase-contrast imaging techniques which give access to ? are very important. In this paper we present two different implementations of phase contrast in our compact soft x-ray microscope, differential-interference contrast and Zernike phase contrast.

von Hofsten, O.; Bertilson, M.; Lindblom, M.; Holmberg, A.; Hertz, H. M.; Vogt, U.

2009-09-01

211

X-ray astrophysics of compact objects  

Microsoft Academic Search

Seyfert galaxies have long been known to exhibit rapid X- ray variability. As yet, no definitive mechanism for this variability has been identified, but shocks and flare- like events have been suggested as viable possibilities. An ASCA observation of the galaxy NGC 3227 had flares which followed a linear increase and exponential decrease, which is the same pattern followed by

Anna Marishka Krickovich Leroux

2000-01-01

212

The Gamma-Ray Imager GRI  

NASA Astrophysics Data System (ADS)

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are major science themes that are addressed in the gamma-ray regime. ESA's INTEGRAL observatory currently provides the astronomical community with a unique tool to investigate the sky up to MeV energies and hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes have been discovered. NASA's GLAST mission will similarly take the next step in surveying the high-energy ( GeV) sky, and NuSTAR will pioneer focusing observations at hard X-ray energies (to 80 keV). There will be clearly a growing need to perform deeper, more focused investigations of gamma-ray sources in the 100-keV to MeV regime. Recent technological advances in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow the study of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Wunderer, Cornelia B.; GRI Collaboration

2008-03-01

213

Gamma Rays from Heavy Neutralino Dark Matter  

SciTech Connect

We consider the gamma-ray spectrum from neutralino dark matter annihilations and show that internal bremsstrahlung of W pair final states gives a previously neglected source of photons at energies near the mass of the neutralino. For masses larger than about 1 TeV, and for present day detector resolutions, this results in a characteristic signal that may dominate not only over the continuous spectrum from W fragmentation, but also over the {gamma}{gamma} and {gamma}Z line signals which are known to give large rates for heavy neutralinos. Observational prospects thus seem promising.

Bergstroem, Lars; Bringmann, Torsten; Eriksson, Martin; Gustafsson, Michael [Department of Physics, Stockholm University, AlbaNova University Center, SE - 106 91 Stockholm (Sweden)

2005-12-09

214

Prompt gamma rays from thermal-neutron capture  

Microsoft Academic Search

A catalog of ..gamma..-rays emitted following thermal-neutron capture in natural elements is presented. In Table I, ..gamma..-rays are arranged in order of increasing energy. Each line contains the ..gamma..-ray energy, intensity, element identification, thermal-neutron radiative-capture cross section, and the energies and intensities of two of the more abundant ..gamma..-rays associated with that element. In Table II, ..gamma..-rays are arranged by

M. A. Lone; R. A. Leavitt; D. A. Harrison

1981-01-01

215

GRI: The Gamma-Ray Imager mission  

NASA Astrophysics Data System (ADS)

With the INTEGRAL observatory ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction have paved the way towards a new gamma-ray mission, providing major improvements regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow studies of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Knödlseder, Jürgen

216

Development of wide-band X-ray/gamma-ray imagers using reach through APD arrays  

NASA Astrophysics Data System (ADS)

It is quite important to obtain wide band spectra of gamma-ray bursts (GRBs) at the same time in order to probe the emission processes or the structure of GRBs. An avalanche photo diode (APD) is a compact photon sensor with an internal gain of 100. We have developed an X-ray/gamma-ray detector using a back-illuminated reach-through APD (5×5 mm2) optically coupled with a conventional CsI(Tl) scintillator, which covers typically from 1 keV to 1 MeV. Further, we developed a 1-dimensional array of the 8/16 APDs (net 16×20 mm2) for the purpose of an imaging photon detector to be used in future GRB missions. Here we present the current status and performance of our hybrid detector.

Nakamori, T.; Kataoka, J.; Toizumi, T.; Koizumi, M.; Tanaka, S.; Kanai, Y.; Yatsu, Y.; Kawai, N.; Ishikawa, Y.; Kawai, T.; Kawabata, N.; Matsunaga, Y.

2009-05-01

217

Development of wide-band X-ray/gamma-ray imagers using reach through APD arrays  

SciTech Connect

It is quite important to obtain wide band spectra of gamma-ray bursts (GRBs) at the same time in order to probe the emission processes or the structure of GRBs. An avalanche photo diode (APD) is a compact photon sensor with an internal gain of 100. We have developed an X-ray/gamma-ray detector using a back-illuminated reach-through APD (5x5 mm{sup 2}) optically coupled with a conventional CsI(Tl) scintillator, which covers typically from 1 keV to 1 MeV. Further, we developed a 1-dimensional array of the 8/16 APDs (net 16x20 mm{sup 2}) for the purpose of an imaging photon detector to be used in future GRB missions. Here we present the current status and performance of our hybrid detector.

Nakamori, T.; Kataoka, J.; Toizumi, T.; Koizumi, M.; Tanaka, S.; Kanai, Y.; Yatsu, Y.; Kawai, N. [Dept. of Physics, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro, Tokyo (Japan); Ishikawa, Y.; Kawai, T.; Kawabata, N.; Matsunaga, Y. [Solid State Division, Hamamatsu Photonics K. K., 1126-1, Ichino-cho, Hamamatsu, Shizuoka (Japan)

2009-05-25

218

The 1979 March 5 gamma-ray transient: Was it a classic gamma-ray burst?  

Microsoft Academic Search

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the KONUS experiment, the unusual characteristics of the March 5 transient were detectable primarily because it was extremely bright.

E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1996-01-01

219

The 1979 March 5 Gamma-Ray Transient: Was It a Classic Gamma-Ray Burst?  

Microsoft Academic Search

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the KONUS experiment, the unusual characteristics of the March 5 transient were detectable primarily because it was extremely bright.

E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1996-01-01

220

Compact large FoV gamma camera for breast molecular imaging  

NASA Astrophysics Data System (ADS)

The very low sensitivity of scintimammography for tumours under 1 cm in diameter, with current nuclear medicine cameras, is the major limitation in recommending this test modality for screening purposes. To improve this diagnostic technique,a new concept of scintillation gamma camera, which fits the best requirements for functional breast imaging has been developed under “Integrated Mammographic Imaging” (IMI) project. This camera consists of a large detection head (6?×7?),very compact sized and with light weight to be easily positioned in the same X-ray geometry. The detection head consists of matrix of 42 photodetector Hamamatsu 1 in2 square H8520-C12 PSPMTs, which are closely packed and coupled to a NaI(Tl) scintillating array, with individual crystal pixel 2×2×6 mm3 size. Large FoV camera shows a very good pixel identification in the detection dead zones between tubes allowing an accurate LUT correction of the final image reconstruction. Electronic read-out was especially designed to optimize the intrinsic spatial resolution and camera compactness. With respect to Anger camera, the overall spatial resolution is improved up to 40% while the overall energy resolution values is ˜16% at 140 keV. Large FoV dedicated camera was characterized and tested by phantom studies; and clinical trials are currently performed. For all patients, compression views have been acquiring for both breasts in craniocaudal projections, and are compared with standard gamma camera images.

Pani, R.; Cinti, M. N.; Pellegrini, R.; Betti, M.; Devincentis, G.; Bennati, P.; Ridolfi, S.; Iurlaro, G.; Montani, L.; Scafč, R.; Marini, M.; Porfiri, L. M.; Giachetti, G.; Baglini, F.; Salvadori, G.; Madesani, M.; Pieracci, M.; Catarsi, F.; Bigongiari, A.

2006-12-01

221

GAMMA-RAY VARIABILITY FROM WIND CLUMPING IN HIGH-MASS X-RAY BINARIES WITH JETS  

SciTech Connect

In the subclass of high-mass X-ray binaries known as 'microquasars', relativistic hadrons in the jets launched by the compact object can interact with cold protons from the star's radiatively driven wind, producing pions that then quickly decay into gamma rays. Since the resulting gamma-ray emissivity depends on the target density, the detection of rapid variability in microquasars with Gamma-Ray Large Area Space Telescope and the new generation of Cherenkov imaging arrays could be used to probe the clumped structure of the stellar wind. We show here that the fluctuation in gamma rays can be modeled using a 'porosity length' formalism, usually applied to characterize clumping effects. In particular, for a porosity length defined by h {identical_to} l/f, i.e., as the ratio of the characteristic size l of clumps to their volume filling factor f, we find that the relative fluctuation in gamma-ray emission in a binary with orbital separation a scales as {radical}(h/{pi}a) in the 'thin-jet' limit, and is reduced by a factor 1/{radical}(1 +{phi}a/2l) for a jet with a finite opening angle {phi}. For a thin jet and quite moderate porosity length h {approx} 0.03a, this implies a ca. 10% variation in the gamma-ray emission. Moreover, the illumination of individual large clumps might result in isolated flares, as has been recently observed in some massive gamma-ray binaries.

Owocki, S. P.; Townsend, R. H. D. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Romero, G. E.; Araudo, A. T. [Inst. Argentino de RadioastronomIa (CCT La Plata, CONICET), C.C.5, 1894 Villa Elisa, Buenos Aires (Argentina)

2009-05-01

222

Gamma-ray Constraints on Cosmic Rays in Galactic Winds  

NASA Astrophysics Data System (ADS)

Our group is constructing a hybrid thermal gas and cosmic-ray pressure driven wind model. This model is built on past work by Breitschwerdt et al. (1991) and Zirakashvili et al. (1996), and was motivated by unexplained high latitude Galactic X-ray emission observed by ROSAT, and further tested with radio synchrotron observations. In this poster, the role of cosmic-ray protons in generating gamma-ray emission in a Galactic wind is explored. In interacting with the wind plasma, cosmic-ray protons have three mechanisms to generate gamma-rays (pion production, Bremsstrahlung, and inverse Compton scattering), which can be detected by the Fermi Gamma-ray Space Telescope. To test the model, we have calculated the gamma-ray intensity from the wind model of Everett et al (2010), and we compare these predictions to the observed emission in the central Milky Way. Also, we have recently developed a new wind model which includes an azimuthal magnetic field and galactic rotation; we compare the driving in this improved model to the previous one, and report on the gamma-ray emissivity of this model as well. In the future we will apply this model to other galaxies which are observed to have a large scale wind, such as M82 and NGC 253. Understanding the high latitude gamma-ray emission from relativistic particles in galactic winds may help to constrain dark-matter models as well. This work has been supported by NASA through grant NNX10AO50G, and by the NSF through grants NSF AST-0907837 and NSF PHY-0821899 (to the Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas).

Hu, Kaiqi; Everett, J. E.; Zweibel, E. G.

2011-01-01

223

Gamma-ray spectroscopy: An historical perspective  

Microsoft Academic Search

The possibility of MeV-range gamma-rays from extraterrestrial sources had been speculated on by cosmic-ray physicists since the late 1940's. The first definitive detection occurred with balloon-borne cosmic-ray instrumentation during a class 2 solar flare in March 1958, apparently associated with the acceleration of a nonthermal particle population. Following this detection, physicists were motivated to develop instrumentation specific for observation of

Laurence E. Peterson

1988-01-01

224

Gamma-ray spectroscopy: An historical perspective  

Microsoft Academic Search

The possibility of MeV-range gamma-rays from extraterrestrial sources had been speculated on by cosmic-ray physicists since the late 1940’s. The first definitive detection occurred with balloon-borne cosmic-ray instrumentation during a class 2 solar flare in March 1958, apparently associated with the acceleration of a nonthermal particle population. Following this detection, physicists were motivated to develop instrumentation specific for observation of

Laurence E. Peterson

1988-01-01

225

Searching for Gamma-ray Pulsars using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope  

Microsoft Academic Search

The Large Area Telescope (LAT) on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST) has greatly increased the sensitivity to astrophysical gamma-ray sources over previous gamma-ray telescope missions such as the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO). The LAT has a much larger effective area and field of view, helping to increase the

Michael Dormody

2009-01-01

226

OVERVIEW OF MONO-ENERGETIC GAMMA-RAY SOURCES & APPLICATIONS  

SciTech Connect

Recent progress in accelerator physics and laser technology have enabled the development of a new class of tunable gamma-ray light sources based on Compton scattering between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable Mono-Energetic Gamma-ray (MEGa-ray) source driven by a compact, high-gradient X-band linac is currently under development and construction at LLNL. High-brightness, relativistic electron bunches produced by an X-band linac designed in collaboration with SLAC NAL will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. This MEGa-ray source will be used to excite nuclear resonance fluorescence in various isotopes. Applications include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented, along with important applications, including nuclear resonance fluorescence. In conclusion, we have optimized the design of a high brightness Compton scattering gamma-ray source, specifically designed for NRF applications. Two different parameters sets have been considered: one where the number of photons scattered in a single shot reaches approximately 7.5 x 10{sup 8}, with a focal spot size around 8 {micro}m; in the second set, the spectral brightness is optimized by using a 20 {micro}m spot size, with 0.2% relative bandwidth.

Hartemann, F V; Albert, F; Anderson, G G; Anderson, S G; Bayramian, A J; Betts, S M; Chu, T S; Cross, R R; Ebbers, C A; Fisher, S E; Gibson, D J; Ladran, A S; Marsh, R A; Messerly, M J; O'Neill, K L; Semenov, V A; Shverdin, M Y; Siders, C W; McNabb, D P; Barty, C P; Vlieks, A E; Jongewaard, E N; Tantawi, S G; Raubenheimer, T O

2010-05-18

227

Gamma-ray Emission from the gamma-ray-loud BL Lac Objects  

Microsoft Academic Search

Using the HST observation data of BL Lac objects by Urry et al. and gamma-ray observation data, we find that there is a correlation between Fgamma and Fnuclei for gamma-ray-loud BL Lac objects (correlation coefficients: gamma=0.63, p=4.0 × 10-2), but no correlation between Fgamma and FOhost, where FOnuclei and FOhost are the fluxes of nuclei and host galaxy in V-band.

Guang-Zhong Xie; Ben-Zhong Dai; En-Wei Liang; Zhao-Hua Xie

2001-01-01

228

Observations of GRB 990123 by the Compton Gamma Ray Observatory  

Microsoft Academic Search

GRB 990123 was the first burst from which simultaneous optical, X-ray, and gamma-ray emission was detected; its afterglow has been followed by an extensive set of radio, optical, and X-ray observations. We have studied the gamma-ray burst itself as observed by the Compton Gamma Ray Observatory detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations

M. S. Briggs; D. L. Band; R. M. Kippen; R. D. Preece; C. Kouveliotou; J. van Paradijs; G. H. Share; R. J. Murphy; S. M. Matz; A. Connors; C. Winkler; M. L. McConnell; J. M. Ryan; O. R. Williams; C. A. Young; B. Dingus; J. R. Catelli; R. A. M. J. Wijers

1999-01-01

229

Neutron and Gamma-ray Measurements  

SciTech Connect

Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.

Krasilnikov, Anatoly V. [RRC 'Kurchatov Institute', Academician Kurchatov squarel, Moscow, 123182 (Russian Federation); SRC RF TRINITI, Troitsk, 142190 (Russian Federation); Sasao, Mamiko [Tohoku University, Sendai (Japan); Kaschuck, Yuri A. [SRC RF TRINITI, Troitsk, 142190 (Russian Federation); Kiptily, Vasily G.; Popovichev, Sergey V. [UKAEA, Abingdon (United Kingdom); Nishitani, Takeo [Japan Atomic Energy Agency, Tokai (Japan); Bertalot, Luciano [ITER Organization, Cadarach (France)

2008-03-12

230

Neutron and Gamma-ray Measurements  

NASA Astrophysics Data System (ADS)

Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.

Krasilnikov, Anatoly V.; Sasao, Mamiko; Kaschuck, Yuri A.; Kiptily, Vasily G.; Nishitani, Takeo; Popovichev, Sergey V.; Bertalot, Luciano

2008-03-01

231

Luminosity Evolution of Gamma-Ray Pulsars  

NASA Astrophysics Data System (ADS)

We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resulting gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial 10,000 yr, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater, but it increases less rapidly than a light element envelope. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis. The cutoff energy of the primary curvature emission is regulated below several GeV even for young pulsars because the gap thickness, and hence the acceleration electric field, is suppressed by the polarization of the produced pairs.

Hirotani, Kouichi

2013-04-01

232

Inverse compton scattering gamma ray source  

NASA Astrophysics Data System (ADS)

Special Nuclear Materials (SNM) (e.g. U-235, Pu-239) can be detected by active interrogation with gamma rays (>6 MeV) through photofission. For long-range detection (˜1 km), an intense beam of gamma rays (˜1014 per second) is required in order to produce measurable number of neutrons. The production of such fluxes of gamma rays, and in the pulse formats useful for detection, presents many technical challenges, and requires novel approaches to the accelerator and laser technology. RadiaBeam is currently designing a gamma ray source based on Inverse Compton Scattering (ICS) from a high-energy electron beam. To achieve this, improvements in photoinjector, linac, final focus, and laser system are planned. These enhanced sub-systems build on parallel work being performed at RadiaBeam, UCLA, and elsewhere. A high-repetition rate photoinjector, a high-gradient S-band linac, and a laser pulse recirculator will be used. The proposed system will be a transportable source of high-flux, high-energy quasi-monochromatic gamma rays for active interrogation of special nuclear materials.

Boucher, S.; Frigola, P.; Murokh, A.; Ruelas, M.; Jovanovic, I.; Rosenzweig, J. B.; Travish, G.

2009-09-01

233

A determination of neutral pion decay gamma ray spectrum and the spectral shape of gamma rays from cosmic ray sources  

Microsoft Academic Search

Based on the available data on pion production at low energies, a numerical method has been developed to reproduce the total inclusive cross-section for the production of neutral pions in nucleus-nucleus collisions. An attempt is made to utilize this, in the determination of gamma ray production spectrum in interstellar space. Gamma ray spectrum from cosmic ray sources has been investigated

S. A. Stephens

1981-01-01

234

Compact soft X-ray laser  

NASA Astrophysics Data System (ADS)

For the first time, amplified spontaneous emission of Al ions was observed in a recombining plasma produced by a low-power driving laser of only 2 joules. This lasing was achieved by sharply focusing a pumping glass laser (5 ns FWHM) to a line 40 ?m wide and 12 mm long onto a slab target. The spectral lines (time integrated in the 5-50 nm region were recorded on Kodak SWR plates with a flat-field-type grazing incidence spectrograph which axially viewed the plasma at a distance (z) of 0.8 mm from a target surface with a spatial resolution of 200 ?m. The measured gain coefficients are 3.4, 4.5, 3.4 and 3.5 for the 10.57 nm 3d-5f and 15.47 nm 3d-4f transitions in Al XI and for the 12.35 nm 3d-5f and 17.78 nm 3d-4f transitions in Al X, respectively. The gain was observed in large area of 500 ?m ×600 ?m around z=0.8 mm. As Al XI line emissions continue during about 6 ns (FWHM), soft-X-ray laser resonator is expected to be effective. The electron temperatures in the plasma in the neighborhood of the target was estimated by the filter absorption method to be 400+/-100 eV, which is hot enough to produce Al11+ ions with high density. this result can pave the way to a low-power-pumped X-ray laser.

Hara, Tamio; Ando, Kozo; Aoyagi, Yoshinobu; Yashiro, Hidehiko

1990-12-01

235

Cosmic ray nonlinear processes in gamma-ray sources  

Microsoft Academic Search

The interaction of cosmic ray (CR) particles (protons, nuclei and electrons) with matter determine the main processes of high energy gamma-ray (GR) generation through neutral pions decay and bremsstrahlung emission. On the other side, the acceleration and propagation of these particles is mainly determined by nonlinear processes of CR in GR sources: the influence of CR pressure on plasma dynamics;

L. I. Dorman

1996-01-01

236

Gamma-ray Bursts from X-ray Binaries  

NASA Astrophysics Data System (ADS)

In this contribution I review the mechanism proposed earlier for producing a gamma-ray burst from the rapidly spinning neutron star in an X-ray binary (Spruit 1999), with a discussion of some more recent developments and outstanding issues.

Spruit, H. C.

237

Comets, X-ray bursts, and gamma-ray bursts  

NASA Astrophysics Data System (ADS)

The proposal, revived by Tremaine and Zytkow (1985), that accretion of comets by neutron stars may be the origin of gamma-ray bursts is considered. This mechanism has difficulty accounting for the observed gamma-ray spectrum and optical counterparts of the bursts. The survival of comets near supernovae is investigated. Ablation rates and the thermal structure of an ablating surface layer are calculated. In some circumstances, mechanical disruption will erode a comet more rapidly than evaporation. The accretion of comets by neutron stars may produce a class of X-ray burst sources with novel properties.

Katz, J. I.

1986-10-01

238

A Balloon-Borne Gamma-Ray Polarimeter for Gamma-Ray Bursts  

Microsoft Academic Search

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), was successfully demonstrated with partially polarized gamma-ray sources in the lab and fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model flew on a

M. L. McConnell; C. M. Bancroft; P. F. Bloser; T. P. Connor; J. S. Legere; J. R. Macri; J. M. Ryan

2009-01-01

239

Future directions in X-ray\\/gamma-ray observations  

Microsoft Academic Search

Facilities available for X ray and gamma ray astronomical observations in the late 1980s are described, with an emphasis on NASA programs. Current European programs for launching Rosat and Exosat will provide coverage in the 0.4-60 keV energy range. The proposed NASA advanced X ray astrophysics facility is intended to cover the 0.1-8 keV range with higher than 0.5 arcsec

D. A. Kniffen

1982-01-01

240

Insect control with $gamma$ rays  

Microsoft Academic Search

The sterile insect release method (SIRM) for insect pest control with ; gamma radiation uses the insect pest to control itself. It provides the ; following advantages: where a pest insect is able to live or survive, the sterile ; insect will duplicate its behavior, therefore, there is no haven for the pest; ; the insect pest need not, reach

J. E. Simon F; A. M. Srb

1973-01-01

241

Photoneutron spectroscopy using monoenergetic gamma rays for bulk explosives detection  

NASA Astrophysics Data System (ADS)

To date, the most successful nuclear methods to confirm the presence of bulk explosives have been radiative thermal neutron capture (thermal neutron activation) and prompt radiative emission following inelastic fast neutron scattering (fast neutron analysis). This paper proposes an alternative: photoneutron spectroscopy using monoenergetic gamma rays. If monoenergetic gamma rays whose energies exceed the threshold for neutron production are incident on a given isotope, the emitted neutrons have a spectrum consisting of one or more discrete energies and the spectrum can be used as a fingerprint to identify the isotope. A prototype compact gamma-ray generator is proposed as a suitable source and a commercially available 3He ionization chamber is proposed as a suitable spectrometer. Advantages of the method with respect to the previously mentioned ones may include simpler spectra and low inherent natural neutron background. Its drawbacks include a present lack of suitable commercially available photon sources, induced neutron backgrounds and low detection rates. This paper describes the method, including kinematics, sources, detectors and geometries. Simulations using a modified Geant4 Monte Carlo modelling code are described and results are presented to support feasibility. Further experiments are recommended.

McFee, J. E.; Faust, A. A.; Pastor, K. A.

2013-03-01

242

Development of Compton gamma-ray sources at LLNL  

SciTech Connect

Compact Compton scattering gamma-ray sources offer the potential of studying nuclear photonics with new tools. The optimization of such sources depends on the final application, but generally requires maximizing the spectral density (photons/eV) of the gamma-ray beam while simultaneously reducing the overall bandwidth on target to minimize noise. We have developed an advanced design for one such system, comprising the RF drive, photoinjector, accelerator, and electron-generating and electron-scattering laser systems. This system uses a 120 Hz, 250 pC, 2 ps, 0.35 mm mrad electron beam with 250 MeV maximum energy in an X-band accelerator scattering off a 150 mJ, 10 ps, 532 nm laser to generate 5 Multiplication-Sign 10{sup 10} photons/eV/s/Sr at 0.5 MeV with an overall bandwidth of less than 1%. The source will be able to produce photons up to energies of 2.5 MeV. We also discuss Compton scattering gamma-ray source predictions given by numerical codes.

Albert, F.; Anderson, S. G.; Ebbers, C. A.; Gibson, D. J.; Hartemann, F. V.; Marsh, R. A.; Messerly, M. J.; Prantil, M. A.; Wu, S.; Barty, C. P. J. [Lawrence Livermore National Laboratory, NIF and Photon Science, 7000 East avenue, Livermore, CA 94550 (United States)

2012-12-21

243

Multipolarity of gamma-ray Absorption in U238(gamma, f) Reaction produced by F(p, alphagamma) gamma rays  

Microsoft Academic Search

Multipolarity of gamma-ray absorption in U238(gamma, f) reaction, produced by monochromatic gamma rays from F(p, alphagamma) reactions, has been investigated by the analysis of the angular distribution of 1018 tracks of fission fragments in uranium-impregnated nuclear emulsions. It can be explained by mixing two sorts of interaction; electric dipole (E1) and electric quadrupole (E2). The ratio of E2 to E1

Eiko Takekoshi

1960-01-01

244

Emission region of gamma ray bursts  

SciTech Connect

Within the last few years the rapid accumulation of gamma ray burst spectral data, especially those of KONUS and SMM, has made the confrontation between theories of the gamma ray emission mechanisms and observations much more urgent and challenging. At present the most viable model seems to be some combination of inverse Comptonization and synchrotron emission. In this paper we limit the acceptable parameter space of the emission region by taking into account the maximum set of observational constraints. We then apply these to two specific scenarios: surface emission versus magnetospheric emission and consider some observable predictions based on these scenarios.

Liang, E.P.

1985-05-01

245

Photospheric Emission from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

In spite of extensive research over the past decades, a complete physical picture of the origin of the prompt gamma-ray burst emission is still lacking. During recent years, evidence has been accumulating that the jet photosphere plays an important role. In this paper we summarize the lessons learned from Fermi observations regarding the behavior of the photosphere and discuss why photospheric emission does not necessarily appear as blackbody radiation. We concentrate on two strong and important bursts, GRB 090902B and GRB 110721A, which serve as examples of the standard appearance photospheric emission may have in gamma-ray burst spectra.

Axelsson, M.

2013-07-01

246

Gamma ray energy tracking in GRETINA  

NASA Astrophysics Data System (ADS)

The next generation of stable and exotic beam accelerators will provide physics opportunities to study nuclei farther away from the line of stability. However, these experiments will be more demanding on instrumentation performance. These come from the lower production rate for more exotic beams, worse beam impurities, and large beam velocity from the fragmentation and inverse reactions. Gamma-ray spectroscopy will be one of the most effective tools to study exotic nuclei. However, to fully exploit the physics reach provided by these new facilities, better gamma-ray detector will be needed. In the last 10 years, a new concept, gamma-ray energy tracking array, was developed. Tracking arrays will increase the detection sensitivity by factors of several hundred compared to current arrays used in nuclear physics research. Particularly, the capability of reconstructing the position of the interaction with millimeters resolution is needed to correct the Doppler broadening of gamma rays emitted from high velocity nuclei. GRETINA is a gamma-ray tracking array which uses 28 Ge crystals, each with 36 segments, to cover .5ex1 -.1em/ -.15em.25ex4 of the 4? solid angle. The gamma ray tracking technique requires detailed pulse shape information from each of the segments. These pulses are digitized using 14-bit 100 MHz flash ADCs, and digital signal analysis algorithms implemented in the on-board FPGAs provides energy, time and selection of pulse traces. A digital trigger system, provided flexible trigger functions including a fast trigger output, and also allows complicated trigger decisions to be made up to 20 microseconds. Further analyzed, carried out in a computer cluster, determine the energy, time, and three-dimensional positions of all gamma-ray interactions in the array. This information is then utilized, together with the characteristics of Compton scattering and pair-production processes, to track the scattering sequences of the gamma rays. GRETINA construction is completed in March 2011, and extensive engineering runs were carried out using radioactive sources, and beams from the 88-Inch Cyclotron at LBNL. The data obtained will be used to optimize its performance. Then the first scientific campaign will start in March 2012 at NSCL MSU.

Lee, I. Y.

2011-10-01

247

Gamma ray sources using imperfect relativistic mirrors  

SciTech Connect

The collective backscattering of intense laser radiation by energetic electron beams is considered. Exact solutions for the radiation field are obtained, for arbitrary electron pulse shapes and laser intensities. The electron beams act as imperfect nonlinear mirrors on the incident laser radiation. This collective backscattering process can lead to the development of new sources of ultrashort pulse radiation in the gamma-ray domain. Numerical examples show that, for plausible experimental conditions, intense pulses of gamma rays, due to the double Doppler shift of the harmonics of the incident laser radiation, can be produced using the available technology, with durations less than one attosecond.

Mendonca, J. T. [GoLP and CFIF, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Serbeto, A. [Instituto de Fisica, Universidade Federal Fluminense, 24210-340 Rio de Janeiro (Brazil)

2008-11-15

248

A high energy gamma ray survey of Cygnus and Cassiopeia  

Microsoft Academic Search

A gamma-ray telescope was used to search for celestial sources at energies above several hundred MeV. Upper limits for the gamma ray emission of six strong X-ray sources are given. The atmospheric generation rate of secondary gamma rays was also determined. The gamma ray detector is a large balloon-borne gas Cherenkov detector which has been previously described. It has a

M. F. Campbell

1974-01-01

249

Gamma Ray Bursts and Delayed Quark-Deconfinement  

NASA Astrophysics Data System (ADS)

We describe a new model, proposed by Berezhiani et al. (2003), which is able to explain how a gamma-ray burst (GRB) can take place days or years after a supernova explosion. We show that above a threshold value of the gravitational mass a pure hadronic star ("neutron star") is metastable to the conversion into a quark star (hybrid star or strange star), i.e. a star made at least in part of decon-fined quark matter. The stellar conversion process can be delayed if finite size effects at the interface between hadronic and deconfined quark matter phases are taken into account. A huge amount of energy, on the order of 1052 - 1053 ergs, is released during the conversion process and can produce a powerful gammaray burst. The delay between the supernova explosion generating the metastable neutron star and the new collapse can explain the delay inferred in GRB 990705 and in GRB 011211. Next, we explore the consequences of the metastability of "massive" neutron stars and of the existence of stable compact quark stars on the concept of limiting mass of compact stars. Finally, we discuss the implications of the present scenario on the interpretation of the stellar mass and radius extracted from the spectra of several X-ray compact sources.

Bombaci, Ignazio; Parenti, Irene; Vidańa, Isaac

250

Compact soft X-ray source for biological applications  

Microsoft Academic Search

A compact soft X-ray source with carbon nanotubes (CNTs) based field emission electron source is being developed for applications to biological, medical and material technology fields. In the tests using a diode-type source, the maximum current of 13 mA (density of over 50 mA\\/cm2) was extracted from the CNTs emitters (0.26cm2) at electric field of about 6 V\\/?m and 2.5

A. Yamaguchi; N. Kobayashi; N. Aoki; Y. Motoi; Y. Mitsunaka

2003-01-01

251

Optimization of compact synchrotron optics for x-ray lithography  

SciTech Connect

The production of integrated circuits having sub-micron component dimensions has motivated the development of compact electron storage rings to provide synchrotron x-ray radiation. This paper presents considerations for optimizing the optics for small radius rings using superconducting dipole magnets. The key parameters are the sizes and angular divergences of the source points illuminating the different ports. Two ring designs are compared in terms of theoretical beam parameters achievable using idealized optics.

Decker, G.A.; Craft, B.C.

1987-03-01

252

Compact superconducting SR ring for X-ray lithography  

Microsoft Academic Search

A compact synchrotron radiation ring based on a new injection method has been designed as a light source for X-ray lithography, and is now being constructed. This machine consisting of a superconducting weak-focusing single-body magnet is 3 m in outer diameter and 2.2 m in height. The injection method uses half-integer resonance to inject the high-energy and high-intensity electron beams

Noriyuki Takahashi

1987-01-01

253

A compact PC-based X-ray imaging system  

Microsoft Academic Search

A compact, portable PC-based X-ray imaging system has been developed based on a 2D silicon microstrip sensor and particle physics readout electronics. The sensor is housed in a specially built hybrid, which also hosts the front-end electronics. The control and the readout electronics used are based on the standard PCI and PMC architectures and were originally developed for High Energy

A. Asimidis; I. Evangelou; P. Kokkas; N. Manthos; F. Triantis; R. D. Speller; G. Hall; P. F. Van der Stelt

2007-01-01

254

Relativistic fireballs and their impact on external matter - Models for cosmological gamma-ray bursts  

Microsoft Academic Search

We discuss the production of cosmological gamma-ray bursts intense enough to be detected at cosmological distances. Events such as the coalescence of compact binaries can create sufficient energy on time scales much less than 1 s. A short 'primary' burst is expected when the resultant fireball becomes optically thin, but this may be weak because the bulk of the radiative

P. Meszaros; M. J. Rees

1993-01-01

255

X-ray spectral properties of {gamma}-ray bursts  

SciTech Connect

The authors summarize the spectral characteristics of a sample of 22 bright gamma-ray bursts detected with the gamma-ray burst sensors aboard the satellite Ginga. This instrument employed a proportional and scintillation counter to provide sensitivity to photons in the 2--400 keV range, providing a unique opportunity to characterize the largely unexplored X-ray properties of gamma-ray bursts. The photon spectra of the Ginga bursts are well described by a low energy slope, a bend energy, and a high energy slope. In the energy range where they can be compared, this result is consistent with burst spectral analyses obtained from the BATSE experiment aboard the Compton Observatory. However, below 20 keV they find evidence for a positive spectral number index in approximately 40% of their burst sample, with some evidence for a strong rolloff at lower energies in a few events. They find that the distribution of spectral bend energies extends below 10 keV. The observed ratio of energy emitted in the X-rays relative to the gamma-rays can be much larger than a few percent and, in fact, is sometimes larger than unity. The average for their sample is 24%.

Strohmayer, T.E. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center; Fenimore, E.E. [Los Alamos National Lab., NM (United States); Murakami, Toshio [ISAS, Sagamihara, Kanagawa (Japan); Yoshida, Atsumasa [RIKEN, Wako, Saitama (Japan)

1997-09-01

256

Gamma-Ray Bursts During Neutron Star Formation. Gamma-Ray Bursts and Transient X-Ray Sources.  

National Technical Information Service (NTIS)

Discussions are presented of the associations between cosmic gamma ray bursts and transient X-ray sources, and the release of gravitational binding energy during the formation of neutron stars. The model for studying the associations is described along wi...

J. M. Cohen U. D. Desai S. S. Holt

1973-01-01

257

Gamma Ray Bursts, Swift and REM  

Microsoft Academic Search

Relevant information about the physics of Gamma Ray Bursts (GRBs) is hidden in the first phases of the afterglow, i.e. in the multi-wavelength (X-ray to Radio) emission soon after the explosion. Optical and NIR afterglow are particularly important since they allow to measure the redshift of the source and possibly to discover the host galaxies. We present in these pages

G. Chincarini; F. M. Zerbi

2003-01-01

258

Gamma-Ray Bursts and Particle Acceleration  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are possible sources of ultra-high-energy cosmic rays (UHE-CRs). To test the GRB origin of UHECRs, it is essential to search for characteristic, proton-induced signatures of secondary radiation. In this paper we present our recent results of Monte Carlo simulations that model the broadband prompt emission of GRBs including various processes associated with electrons and protons accelerated to

Katsuaki Asano; Katsuaki

2008-01-01

259

The Swift Gamma-Ray Burst Mission  

Microsoft Academic Search

The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr-1 and performing detailed X-ray and UV\\/optical

N. Gehrels; G. Chincarini; P. Giommi; K. O. Mason; J. A. Nousek; A. A. Wells; N. E. White; S. D. Barthelmy; D. N. Burrows; L. R. Cominsky; K. C. Hurley; F. E. Marshall; P. Mészáros; P. W. A. Roming; L. Angelini; L. M. Barbier; T. Belloni; S. Campana; P. A. Caraveo; M. M. Chester; O. Citterio; T. L. Cline; M. S. Cropper; J. R. Cummings; A. J. Dean; E. D. Feigelson; E. E. Fenimore; D. A. Frail; A. S. Fruchter; G. P. Garmire; K. Gendreau; G. Ghisellini; J. Greiner; J. E. Hill; S. D. Hunsberger; H. A. Krimm; S. R. Kulkarni; P. Kumar; F. Lebrun; N. M. Lloyd-Ronning; C. B. Markwardt; B. J. Mattson; R. F. Mushotzky; J. P. Norris; J. Osborne; B. Paczynski; D. M. Palmer; H.-S. Park; A. M. Parsons; J. Paul; M. J. Rees; C. S. Reynolds; J. E. Rhoads; T. P. Sasseen; B. E. Schaefer; A. T. Short; A. P. Smale; I. A. Smith; L. Stella; G. Tagliaferri; T. Takahashi; M. Tashiro; L. K. Townsley; J. Tueller; M. J. L. Turner; M. Vietri; W. Voges; M. J. Ward; R. Willingale; F. M. Zerbi; W. W. Zhang

2004-01-01

260

COMPACT CdZnTe-BASED GAMMA CAMERA FOR PROSTATE CANCER IMAGING  

SciTech Connect

In this paper, we discuss the design of a compact gamma camera for high-resolution prostate cancer imaging using Cadmium Zinc Telluride (CdZnTe or CZT) radiation detectors. Prostate cancer is a common disease in men. Nowadays, a blood test measuring the level of prostate specific antigen (PSA) is widely used for screening for the disease in males over 50, followed by (ultrasound) imaging-guided biopsy. However, PSA tests have a high false-positive rate and ultrasound-guided biopsy has a high likelihood of missing small cancerous tissues. Commercial methods of nuclear medical imaging, e.g. PET and SPECT, can functionally image the organs, and potentially find cancer tissues at early stages, but their applications in diagnosing prostate cancer has been limited by the smallness of the prostate gland and the long working distance between the organ and the detectors comprising these imaging systems. CZT is a semiconductor material with wide band-gap and relatively high electron mobility, and thus can operate at room temperature without additional cooling. CZT detectors are photon-electron direct-conversion devices, thus offering high energy-resolution in detecting gamma rays, enabling energy-resolved imaging, and reducing the background of Compton-scattering events. In addition, CZT material has high stopping power for gamma rays; for medical imaging, a few-mm-thick CZT material provides adequate detection efficiency for many SPECT radiotracers. Because of these advantages, CZT detectors are becoming popular for several SPECT medical-imaging applications. Most recently, we designed a compact gamma camera using CZT detectors coupled to an application-specific-integrated-circuit (ASIC). This camera functions as a trans-rectal probe to image the prostate gland from a distance of only 1-5 cm, thus offering higher detection efficiency and higher spatial resolution. Hence, it potentially can detect prostate cancers at their early stages. The performance tests of this camera have been completed. The results show better than 6-mm resolution at a distance of 1 cm. Details of the test results are discussed in this paper.

CUI, Y.; LALL, T.; TSUI, B.; YU, J.; MAHLER, G.; BOLOTNIKOV, A.; VASKA, P.; DeGERONIMO, G.; O'CONNOR, P.; MEINKEN, G.; JOYAL, J.; BARRETT, J.; CAMARDA, G.; HOSSAIN, A.; KIM, K.H.; YANG, G.; POMPER, M.; CHO, S.; WEISMAN, K.; SEO, Y.; BABICH, J.; LaFRANCE, N.; AND JAMES, R.B.

2011-10-23

261

Compact CdZnTe-based gamma camera for prostate cancer imaging  

NASA Astrophysics Data System (ADS)

In this paper, we discuss the design of a compact gamma camera for high-resolution prostate cancer imaging using Cadmium Zinc Telluride (CdZnTe or CZT) radiation detectors. Prostate cancer is a common disease in men. Nowadays, a blood test measuring the level of prostate specific antigen (PSA) is widely used for screening for the disease in males over 50, followed by (ultrasound) imaging-guided biopsy. However, PSA tests have a high falsepositive rate and ultrasound-guided biopsy has a high likelihood of missing small cancerous tissues. Commercial methods of nuclear medical imaging, e.g. PET and SPECT, can functionally image the organs, and potentially find cancer tissues at early stages, but their applications in diagnosing prostate cancer has been limited by the smallness of the prostate gland and the long working distance between the organ and the detectors comprising these imaging systems. CZT is a semiconductor material with wide band-gap and relatively high electron mobility, and thus can operate at room temperature without additional cooling. CZT detectors are photon-electron direct-conversion devices, thus offering high energy-resolution in detecting gamma rays, enabling energy-resolved imaging, and reducing the background of Compton-scattering events. In addition, CZT material has high stopping power for gamma rays; for medical imaging, a few-mm-thick CZT material provides adequate detection efficiency for many SPECT radiotracers. Because of these advantages, CZT detectors are becoming popular for several SPECT medical-imaging applications. Most recently, we designed a compact gamma camera using CZT detectors coupled to an application-specific-integratedcircuit (ASIC). This camera functions as a trans-rectal probe to image the prostate gland from a distance of only 1-5 cm, thus offering higher detection efficiency and higher spatial resolution. Hence, it potentially can detect prostate cancers at their early stages. The performance tests of this camera have been completed. The results show better than 6-mm resolution at a distance of 1 cm. Details of the test results are discussed in this paper.

Cui, Yonggang; Lall, Terry; Tsui, Benjamin; Yu, Jianhua; Mahler, George; Bolotnikov, Aleksey; Vaska, Paul; de Geronimo, Gianluigi; O'Connor, Paul; Meinken, George; Joyal, John; Barrett, John; Camarda, Giuseppe; Hossain, Anwar; Kim, Ki Hyun; Yang, Ge; Pomper, Marty; Cho, Steve; Weisman, Ken; Seo, Youngho; Babich, John; Lafrance, Norman; James, Ralph B.

2011-06-01

262

SUB-LUMINOUS {gamma}-RAY PULSARS  

SciTech Connect

Most pulsars observed by the Fermi Large Area Telescope have {gamma}-ray luminosities scaling with spin-down power E-dot as L{sub {gamma}}{approx}(E-dot x 10{sup 33} erg s{sup -1}){sup 1/2}. However, there exist one detection and several upper limits an order of magnitude or more fainter than this trend. We describe these 'sub-luminous' {gamma}-ray pulsars and discuss the case for this being an orientation effect. Of the 12 known young radio pulsars with E-dot >10{sup 34} erg s{sup -1} and d {<=} 2 kpc several are substantially sub-luminous. The limited available geometrical constraints favor aligned geometries for these pulsars, although no one case for alignment is compelling. In this scenario GeV emission detected from such sub-luminous pulsars can be due to a lower altitude, lower-power accelerator gap.

Romani, R. W.; Kerr, M.; Craig, H. A. [Department of Physics, Stanford University, Stanford, CA 94305 (United States); Johnston, S. [Australia Telescope National Facility, CSIRO, Epping, NSW 1710 (Australia); Cognard, I. [Laboratoire de Physique et Chimie de l'Environnement, LPCE UMR 6115 CNRS, 45071 Orleans Cedex 02 (France); Smith, D. A., E-mail: rwr@astro.stanford.edu [Centre d'Etudes Nucleaires de Bordeaux Gradignan, Universite Bordeaux 1, CNRS/IN2p3, 33175 Gradignan (France)

2011-09-01

263

HYPERNUCLEAR STRUCTURE FROM GAMMA-RAY SPECTROSCOPY.  

SciTech Connect

The energies of p-shell hypernuclear {gamma} rays obtained from recent experiments using the Hyperball at BNL and KEK are used to constrain the YN interaction which enters into shell-model calculations which include both {Lambda} and {Sigma} configurations.

MILLENER,D.J.

2003-10-14

264

Gamma ray activity of neodymium samples  

NASA Astrophysics Data System (ADS)

The gamma ray activity of three samples of natural neodymium has been measured and the concentration of radioactive elements from uranium and thorium chains as well as that from radioactive isotopes of lantanium and lutetium has been quantitatively determined. All the samples show significant contaminations up to p.p.m.

Arpesella, C.; Bellotti, E.; Miramonti, L.; Sverzellati, P. P.

1996-02-01

265

Gamma ray activity of neodymium samples  

Microsoft Academic Search

The gamma ray activity of three samples of natural neodymium has been measured and the concentration of radioactive elements from uranium and thorium chains as well as that from radioactive isotopes of lantanium and lutetium has been quantitatively determined. All the samples show significant contaminations up to p.p.m.

C. Arpesella; E. Bellotti; L. Miramonti; P. P. Sverzellati

1996-01-01

266

Glass as a gamma Ray Dosemeter.  

National Technical Information Service (NTIS)

The advantages of glass as a gamma -rays dosemeter are studied. Experiments have shown that ordinary microscope object glass can be used as a dosemeter, which dose range for linear response extends from about 10 exp 4 -10 exp 6 rads. Heat treatment of the...

Sutrisno Puspodikoro

1978-01-01

267

Gamma-ray Burst Educator Guide  

NSDL National Science Digital Library

This guide accompanies an educational wallsheet that uses Gamma-ray Bursts as an engagement to teach selected topics in physical science and mathematics. It features four curriculum enhancement activities, background information, assessment information, student worksheets, extension and transfer activities, and detailed information about the physical science and mathematics content standards for grades 9-12.

2004-01-01

268

Gamma-ray Burst Science with GLAST  

SciTech Connect

The recent observations of Gamma-ray bursts (GRBs) with Swift have provided unprecedented information about nature of GRBs. The launch of GLAST in late 2007 will unveil the final spectral regime of GRB prompt emission and afterglows. Here we briefly review various theoretical suggestions of producing high energy photons from GRB fireballs, and discuss what observatons are expected from the GLAST observatory.

Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States)

2007-07-12

269

Cosmological aspects of gamma ray bursts  

Microsoft Academic Search

Gamma-ray burst observations provide a great opportunity for cosmography in high redshift. Some tight correlations between different physical properties of GRBs are discovered and used for cosmography. However, data selection, assumptions, systematic uncertainty and some other issues affect most of them. Most importantly, until the physical origin of a relation is understood, one should be cautious to employ the relation

Razieh Behkam

2010-01-01

270

Hypernuclear Structure from Gamma-Ray Spectroscopy.  

National Technical Information Service (NTIS)

The energies of p-shell hypernuclear(gamma) rays obtained from recent experiments using the Hyperball at BNL and KEK are used to constrain the YN interaction which enters into shell-model calculations which include both(Lambda) and(Sigma) configurations.

D. J. Millener

2004-01-01

271

Developments in Mercuric Iodide gamma Ray Imaging.  

National Technical Information Service (NTIS)

A mercuric iodide gamma-ray imaging array and camera system previously described has been characterized for spatial and energy resolution. Based on this data, a new camera is being developed to more fully exploit the potential of the array. Characterizati...

B. E. Patt A. G. Beyerle R. C. Dolin C. Ortale

1987-01-01

272

Gamma Ray Burst Detectives (Elementary School)  

NSDL National Science Digital Library

This interactive resource invites students to join NASA to find the source of gamma ray bursts, the single biggest explosions in the Universe since the Big Bang. The web site features an animation, information on three possible star sources, and a check yes or no for each star with feedback.

Wpsu

2010-04-29

273

Positron Annihilation in gamma-Ray Bursts.  

National Technical Information Service (NTIS)

Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star...

A. K. Harding

1990-01-01

274

Gamma-Ray Bursts The Second Revolution  

Microsoft Academic Search

Gamma-ray bursts GRBs are among the most mysterious astronomical phenomenon ever discovered. Unlike most astronomical discoveries which were explained within weeks or months after their initial discovery, GRBs remain a puzzle for more than thirty years. During the last decade our understanding of GRBs has undergone two major revolutions. First, BATSE discovered that GRBs are distributed isotropically over the sky

Tsvi Piran

1998-01-01

275

Three Types of Gamma-Ray Bursts  

Microsoft Academic Search

A multivariate analysis of gamma-ray burst (GRB) bulk properties is presented to discriminate between distinct classes of GRBs. Several variables representing burst duration, fluence, and spectral hardness are considered. Two multivariate clustering procedures are used on a sample of 797 bursts from the Third BATSE Catalog, a nonparametric average linkage hierarchical agglomerative clustering procedure validated with Wilks' Lambda^* and other

Soma Mukherjee; Eric D. Feigelson; Gutti Jogesh Babu; Fionn Murtagh; Chris Fraley; Adrian Raftery

1998-01-01

276

Theories of Gamma-Ray Bursts  

Microsoft Academic Search

The gamma ray burst phenomenon is reviewed from a theoretical point of view, with emphasis on the fireball shock scenario of the prompt emission and the longer wavelength afterglow. Recent progress and issues are discussed, including spectral-temporal evolution, localizations, jets, spectral lines, environmental and cosmological aspects, as well as some prospects for future experiments in both electromagnetic and nonelectromagnetic channels.

P. Mészáros

2002-01-01

277

Supernovae and gamma-ray bursts†  

Microsoft Academic Search

The observed properties of Supernovae (SNe) and Cosmic Gamma-ray Bursts (GRBs) are briefly summarized. Measurement of SNe distances in cosmology gives important results. It is explained how the acceleration of expansion of Universe was established using SNe. I point out which features of gaseous Supernova Remnants and GRBs (and their afterglows) are common and what is different in those events.

Sergei Blinnikov

2006-01-01

278

The Cosmic Gamma-Ray Bursts  

Microsoft Academic Search

Cosmic gamma-ray bursts are one of the great frontiers of astrophysics today. They are a playground of relativists and observers alike. They may teach us about the death of stars and the birth of black holes, the physics in extreme conditions, and help us probe star formation in the distant and obscured universe. In this review we summarise some of

S. G. Djorgovski; D. A. Frail; S. R. Kulkarni; R. Sari; J. S. Bloom; T. J. Galama; F. A. Harrison; P. A. Price; D. Fox; D. E. Reichart; S. Yost; E. Berger; A. Diercks; R. Goodrich; F. Chaffee

2002-01-01

279

Balloon borne X and gamma ray experiments  

Microsoft Academic Search

A brief history of X and gamma ray astronomy is presented, in order to show the scientific interest in this field of research, and to define the type of work needed for further progress. A general description of the experimental apparatus is given, with a summary of typical detectors and their characteristics. Following this is a discussion of the numerous

K. Hurley

1975-01-01

280

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

There is now clear evidence for Type I supernovae happening in coincidence with two long soft gamma-ray bursts (GRBs) and compelling observations that suggest this may be a common occurrence. At the same time, it is clear that only a small fraction, 1%, of supernovae make GRBs. Why do some stars die one way, and others, another? I will argue

S. E. Woosley

2005-01-01

281

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

This program brought together scientists in both Supernovae and Gamma-Ray Bursts to merge the current progress of both disciplines. We used this combined knowledge to address a range of SN\\/GRB questions such as: Do all long duration GRBs have an underlying SN?, What is special about SNe associated with GRBs?, Where do XRFs, which share several attributes with GRBs, fit

Christopher L. Fryer; Shrinivas R. Kulkarni; Ken'ichi Nomoto; Philip Pinto

2006-01-01

282

First RHESSI terrestrial gamma ray flash catalog  

Microsoft Academic Search

We present a summary of data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flash (TGF) catalog. We describe the RHESSI search algorithm and discuss its limitations due to its design emphasis on cleanliness rather than completeness. This search algorithm has identified 820 TGFs between March of 2002 and February of 2008. Radiation damage to

B. W. Grefenstette; D. M. Smith; B. J. Hazelton; L. I. Lopez

2009-01-01

283

Cosmogenic gamma rays and the composition of cosmic rays  

SciTech Connect

We discuss the prospects of detecting the sources of ultrahigh energy (UHE) cosmic ray (CR) nuclei via their emission of cosmogenic {gamma} rays in the GeV to TeV energy range. These {gamma} rays result from electromagnetic cascades initiated by high energy photons, electrons, and positrons that are emitted by CRs during their propagation in the cosmic radiation background and are independent of the simultaneous emission of {gamma} rays in the vicinity of the source. The corresponding production power by UHE CR nuclei (with mass number A and charge Z) is dominated by pion photo production ({proportional_to}A) and Bethe-Heitler pair production ({proportional_to}Z{sup 2}). We show that the cosmogenic {gamma}-ray signal from a single steady UHE CR source is typically more robust with respect to variations of the source composition and injection spectrum than the accompanying signal of cosmogenic neutrinos. We study the diffuse emission from the sum of extragalactic CR sources as well as the point-source emission of the closest sources.

Ahlers, Markus [C. N. Yang Institute for Theoretical Physics, SUNY at Stony Brook, Stony Brook, New York 11794-3840 (United States); Salvado, Jordi [Departament d'Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos, Universitat de Barcelona, 647 Diagonal, E-08028 Barcelona (Spain)

2011-10-15

284

Conservative Constraints on dark matter annihilation into gamma rays  

Microsoft Academic Search

Using gamma-ray data from observations of the Milky Way, Andromeda (M31), and the cosmic background, we calculate conservative upper limits on the dark matter self-annihilation cross section to monoenergetic gamma rays, _{gamma gamma}, over a wide range of dark matter masses. We focus on the gamma gamma final state, as it would be a very clean signature of dark matter

Thomas Jacques

2008-01-01

285

Gamma Ray Telescope Senses High-Energy Radiation  

NSDL National Science Digital Library

This video from NASA describes the GLAST satellite, which is equipped with a gamma-ray telescope, and shares some background about the kinds of extreme universal phenomena indicated by the presence of gamma rays.

Wnet

2011-11-02

286

Observations of cosmic gamma ray sources and their contribution to the diffuse gamma ray background  

NASA Astrophysics Data System (ADS)

The objective is to study soft gamma ray emission in the 0.1 to 10 MeV energy band for selected active galactic nuclei and explore how much they contribute to the total diffuse gamma ray background. A series of imaging observations of extragalactic objects in the low energy gamma-ray region were carried out by the Coded Aperture Directional Gamma-ray Telescope (DGT). The DGT was successfully flown at stratospheric balloon altitudes, and observations were made of the Crab, NGC 1275, MKN 421, and NGC 4151. The measured Crab spectrum is consistent with a featureless power-law of the form. Significant emission was detected up to 500 keV from the Seyfert galaxy, NGC 4151. To increase the total sky exposure the extragalactic field images were analyzed, including the 3C 273 region, obtained by the DGT.

Bhattacharya, Debadarshi

287

Gamma ray lines from the galactic center and gamma ray transients  

SciTech Connect

The observations and interpretations of cosmic (nonsolar) gamma ray lines are discussed. The most prominent of these lines is the e(+)e(-) annihilation line which was observed from the Galactic Center and from several gamma ray transients. At the Galactic Center the e(+)e(-) pairs are probably produced by an accreting massive black hole (solar mass of approximately one million) and annihilate within the central light year to produce a line at almost exactly 0.511 MeV. In gamma ray transients the annihilation line is redshifted by factors consistent with neutron star surface redshifts. Other observed transient gamma ray lines appear to be due to cyclotron absorption in the strong magnetic fields of neutron stars, and nuclear deexcitations and neutron capture, which could also occur on or around these objects.

Ramaty, R.; Leiter, D.; Lingenfelter, R.E.

1981-04-01

288

Gamma ray lines from the Galactic Center and gamma ray transients  

NASA Astrophysics Data System (ADS)

The observations and interpretations of cosmic (nonsolar) gamma ray lines are discussed. The most prominent of these lines is the e(+)e(-) annihilation line which was observed from the Galactic Center and from several gamma ray transients. At the Galactic Center the e(+)e(-) pairs are probably produced by an accreting massive black hole (solar mass of approximately one million) and annihilate within the central light year to produce a line at almost exactly 0.511 MeV. In gamma ray transients the annihilation line is redshifted by factors consistent with neutron star surface redshifts. Other observed transient gamma ray lines appear to be due to cyclotron absorption in the strong magnetic fields of neutron stars, and nuclear deexcitations and neutron capture, which could also occur on or around these objects.

Ramaty, R.; Leiter, D.; Lingenfelter, R. E.

1981-04-01

289

RHESSI as Gamma Ray Burst Polarimeter  

NASA Astrophysics Data System (ADS)

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) was designed to measure hard X-rays and ?-rays from solar flares. With its big detection area and thin side shielding it also proved to be well suited for studying Gamma Ray Bursts (GRB). Polarization analysis is feasible as well, due to a big modulation factor (MF), though serious constraints on the minimum detectable polarization (MDP) come from detection efficiency of double scattered photons. More constraints are given by background of accidental and real coincidences.

Hajdas, W.; Wigger, C.; Zehnder, A.

2005-07-01

290

Fiber fed x-ray/gamma ray imaging apparatus  

DOEpatents

X-ray/gamma ray imaging apparatus is disclosed for detecting the position, energy, and intensity of x-ray/gamma ray radiation comprising scintillation means disposed in the path of such radiation and capable of generating photons in response to such radiation; first photodetection means optically bonded to the scintillation means and capable of generating an electrical signal indicative of the intensity, and energy of the radiation detected by the scintillation means; second photodetection means capable of generating an electrical signal indicative of the position of the radiation in the radiation pattern; and means for optically coupling the scintillation means to the second photodetection means. The photodetection means are electrically connected to control and storage means which may also be used to screen out noise by rejecting a signal from one photodetection means not synchronized to a signal from the other photodetection means; and also to screen out signals from scattered radiation.

Hailey, C.J.; Ziock, K.P.

1990-08-03

291

Fiber fed x-ray/gamma ray imaging apparatus  

DOEpatents

X-ray/gamma ray imaging apparatus is disclosed for detecting the position, energy, and intensity of x-ray/gamma ray radiation comprising scintillation means disposed in the path of such radiation and capable of generating photons in response to such radiation; first photodetection means optically bonded to the scintillation means and capable of generating an electrical signal indicative of the intensity, and energy of the radiation detected by the scintillation means; second photodetection means capable of generating an electrical signal indicative of the position of the radiation in the radiation pattern; and means for optically coupling the scintillation means to the second photodetection means. The photodetection means are electrically connected to control and storage means which may also be used to screen out noise by rejecting a signal from one photodetection means not synchronized to a signal from the other photodetection means; and also to screen out signals from scattered radiation. 6 figs.

Hailey, C.J.; Ziock, K.P.

1992-06-02

292

Fiber fed x-ray/gamma ray imaging apparatus  

DOEpatents

X-ray/gamma ray imaging apparatus is disclosed for detecting the position, energy, and intensity of x-ray/gamma ray radiation comprising scintillation means disposed in the path of such radiation and capable of generating photons in response to such radiation; first photodetection means optically bonded to the scintillation means and capable of generating an electrical signal indicative of the intensity, and energy of the radiation detected by the scintillation means; second photodetection means capable of generating an electrical signal indicative of the position of the radiation in the radiation pattern; and means for optically coupling the scintillation means to the second photodetection means. The photodetection means are electrically connected to control and storage means which may also be used to screen out noise by rejecting a signal from one photodetection means not synchronized to a signal from the other photodetection means; and also to screen out signals from scattered radiation.

Hailey, Charles J. (San Francisco, CA); Ziock, Klaus-Peter (Livermore, CA)

1992-01-01

293

An Elementary Treatment of Gamma-Ray Heating and Gamma-Ray Dosage in Inhomogeneous Reactors  

Microsoft Academic Search

An analysis is made of the heat produced by the absorption of gamma rays in a sample placed into a reactor. It is clearly shown that enormous local (space) variations in gamma flux exist in current reactors. An application to the Hanford reactors is treated in some detail. Although the estimates obtained may be good to but a factor of

Primak

1952-01-01

294

HIGH-ENERGY GAMMA-RAY AFTERGLOWS FROM LOW-LUMINOSITY GAMMA-RAY BURSTS  

SciTech Connect

The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs-LL-GRBs. The nature of the outflow responsible for them is not yet clear. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of order of GAMMA{sub 0} approx> 10 and the other is a trans-relativistic outflow with GAMMA{sub 0} approx = 1-2. Here, we compare the high-energy gamma-ray afterglow emission from these two different models, taking into account both synchrotron self-inverse Compton (SSC) scattering and the external inverse Compton scattering due to photons from the cooling supernova or hypernova envelope (SNIC). We find that the conventional relativistic outflow model predicts a relatively high gamma-ray flux from SSC at early times (<10{sup 4} s for typical parameters) with a rapidly decaying light curve, while in the trans-relativistic outflow model, one would expect a much flatter light curve of high-energy gamma-ray emission at early times, which could be dominated by both the SSC emission and the SNIC emission, depending on the properties of the underlying supernova and the shock parameter epsilon{sub e} and epsilon{sub B}. The Fermi Gamma-ray Space Telescope should be able to distinguish between the two models in the future.

He Haoning; Wang Xiangyu; Yu Yunwei [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Meszaros, Peter [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)

2009-12-01

295

Muon Detection of TEV Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

Because of the limited size of the satellite-borne instruments, it has not been possible to observe the flux of gamma-ray bursts (GRBs) beyond GeV energy. We here show that it is possible to detect the GRB radiation of TeV energy and above by detecting the muon secondaries produced when the gamma rays shower in Earth's atmosphere. Observation is made possible

J. Alvarez-Muńiz; F. Halzen

1999-01-01

296

Gamma-Ray Lenses for Astrophysics—and the Gamma-Ray Imager Mission GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer; Peter v. Ballmoos; Nicolas Barriere; Angela Bazzano; Steven E. Boggs; Finn Christensen; Filippo Frontera; Margarida Hernanz; Jürgen Knodlseder; Andreas Zoglauer

2009-01-01

297

Medium-Energy Gamma-Ray Astrophysics with the 3DTI Gamma-Ray Telescope  

Microsoft Academic Search

Gamma-ray observations in the medium energy range (0.50-50.0 MeV) are central to unfolding many outstanding questions in astrophysics. The challenges of medium-energy gamma-ray observations, however, are the low photon statistics and large backgrounds. We review these questions, address the telescope technology requirements, and describe our development of the 3-Dimensional Track Imaging (3-DTI) Compton telescope and its performance for a new

Stanley D. Hunter; Robert G. Baker; Louis M. Barbier; Peter F. Bloser; LaVida Cooper; John F. Krizmanic; Jason T. Link; Mark L. McConnell; Georgia A. de Nolfo; James M. Ryan; Satpal Singh; Seunghee Son

2006-01-01

298

The Gamma-ray Large Area Space Telescope and Gamma-Ray Bursts  

Microsoft Academic Search

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high energy gamma-ray sky. The main instrument on GLAST, the Large Area Telescope (LAT) is a pair-conversion telescope that will survey the sky from 20 MeV to greater than 300 GeV With the GLAST launch in 2007, the LAT will open a new and important window on

Julie McEnery

2006-01-01

299

Soft Gamma-Ray Repeaters and Magnetars  

NASA Astrophysics Data System (ADS)

The history and observational properties of the soft gamma repeaters are reviewed in this Chapter. Over the past decades, we have gone from viewing these objects as a special class of cosmic gamma-ray burst, to seeing them as one manifestation of magnetars. There is now a solid body of multiwavelength observations, as well as some more controversial properties. There are still a number of fundamental unanswered questions, which will require better theory, more sensitive observations, and many years to answer. The story of the soft gamma repeaters (SGRs) begins in 1979. On January 7th, a short duration, soft spectrum burst was observed from the direction of the Galactic center [28]. At that time, relatively little was known about cosmic gamma-ray bursts (GRBs), but their energy spectra, as observed up to that point, were clearly “hard,” containing photons up to hundreds of keV and beyond. On the other hand, it was clear that the spectrum of the January 7 event was much softer than that of a GRB, i.e., with little emission beyond 100 keV. The event was called “a gamma-ray burst without the gamma-rays.” Several months later, the most intense gamma-ray transient which had been observed up to that time, the March 5, 1979 burst, was detected. This event had a hard spectrum and a long duration, with a pulsating tail, and it was localized to the N49 supernova remnant in the Large Magellanic Cloud [3,7]. At the distance of the LMC, the intensity of this burst was >103 times the Eddington luminosity. And in the days that followed, smaller bursts were detected from the source [31]. Many theories were proposed to explain this event, which was generally thought to be an unusual GRB. Several weeks later, another repeating source was discovered when it emitted three short duration, soft spectrum bursts in 3 days [32]. Finally, between July and December 1987, yet another repeater was discovered [2]. This object turned out to be the same as the one which had been detected on January 7, 1979. The source was named SGR1806-20, with SGR standing both for the constellation (Sagittarius) and for Soft Gamma Repeater, to distinguish it from the GRBs.

Hurley, Kevin

300

High Energy Gamma-Ray Emission from Gamma-Ray Bursts - Before GLAST  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are short and intense emission of soft -rays, which have fascinated astronomers and astrophysicists since their unexpected discovery in 1960s. The X-ray\\/optical\\/radio afterglow observations confirm the cosmological origin of GRBs, support the fireball model, and imply a long-activity of the central engine. The high-energy -ray emission (> 20 MeV) from GRBs is particularly important because they shed

Yi-Zhong Fan; Tsvi Piran

2011-01-01

301

Gamma-Ray Observatory - The next great observatory in space  

Microsoft Academic Search

The Gamma-Ray Observatory (GRO) which is part of NASA's Great Observatories space program is presented. The GRO is equipped with the Burst and Transient Source Experiment (which detects low-energy gamma-ray photons from 20 keV to 600 keV and locates sources of gamma-ray bursts), the Oriented Scintillation Spectrometer Experiment (which detects celestial gamma rays from 100 keV to 10 MeV and

Valerie Neal; Gerald Fishman; Donald Kniffen

1990-01-01

302

Wide energy range gamma-ray calibration source  

Microsoft Academic Search

Calibration source with monoenergetic gamma-ray lines in wide energy range designed for gamma-ray detector energetic calibration and testing has been built. Gamma-rays are obtained from thermal neutron capture, which is a suitable and cost efficient way how to provide discrete gamma-ray lines with energies above 3 MeV with reasonable intensity. With appropriate and interchangeable targets the source can generate different

M Kroupa; C Granja; Z Janout; M Kralik; F Krejci; A Owens; S Pospisil; F Quarati; J Solc; M Vobecky

2011-01-01

303

Cygnus X-3 and EGRET Gamma-Ray Observations  

Microsoft Academic Search

0!rQ1The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory observed the Cygnus region in 14 different viewing periods during 1991 May to 1994 July. We present here our results on unpulsed and pulsed emissions of gamma rays at E > 50 MeV from Cyg X-3. While we detect a gamma-ray source consistent with the position of

M. Mori; D. L. Bertsch; B. L. Dingus; J. A. Esposito; C. E. Fichtel; S. D. Hunter; G. Kanbach; D. A. Kniffen; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; R. Mukherjee; P. L. Nolan; P. V. Ramanamurthy; E. Schneid; P. Sreekumar; D. J. Thompson

1997-01-01

304

Advanced gamma-ray astronomy telescope experiment: AGATE  

Microsoft Academic Search

In order to continue the achievements in high energy (10 MeV - 100 GeV) gamma-ray astronomy made with the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO), a 'next generation' high energy gamma- ray telescope with a large increase in sensitivity coupled with improved angular resolution will be required. This 'next generation' telescope is envisioned

Brenda L. Dingus; D. L. Bertsch; Rajani Cuddapah; Carl E. Fichtel; Stanley D. Hunter; D. J. Thompson

1993-01-01

305

Gamma-Ray Emission from LS I +61 303  

NASA Astrophysics Data System (ADS)

LS I +61 303 is a high-mass ?-ray binary with known orbital and super-orbital variability in the radio, optical, X-ray, and ?-ray wavelengths. The compact companion is probably a neutron star but remains unconfirmed. Here, we use data from the Fermi Gamma-ray Space Telescope to examine LS I +61 303’s ?-ray emission over both its orbital and its super-orbital period. We find that the emission peaks at orbital phases of 0.3 and 0.5, and that the energy spectrum follows a log parabola model. We also find that there is ?-ray variability in the 1667-day super-orbit, but further investigation will be required to determine the exact parameters of this variability. We interpret these results as possible evidence for a mass stream flowing from the optical star’s circumstellar disk and colliding with a pulsar’s wind, emitting across the electromagnetic spectrum. We are grateful for support provided through NSF grants AST-1109247 and PHY-0849416.

Schaefer, Leigh; McSwain, M. V.

2013-01-01

306

SuperAGILE and Gamma Ray Bursts  

SciTech Connect

The solid-state hard X-ray imager of AGILE gamma-ray mission -- SuperAGILE -- has a six arcmin on-axis angular resolution in the 15-45 keV range, a field of view in excess of 1 steradian. The instrument is very light: 5 kg only. It is equipped with an on-board self triggering logic, image deconvolution, and it is able to transmit the coordinates of a GRB to the ground in real-time through the ORBCOMM constellation of satellites. Photon by photon Scientific Data are sent to the Malindi ground station at every contact. In this paper we review the performance of the SuperAGILE experiment (scheduled for a launch in the middle of 2006), after its first onground calibrations, and show the perspectives for Gamma Ray Bursts.

Pacciani, Luigi; Costa, Enrico; Del Monte, Ettore; Donnarumma, Immacolata; Evangelista, Yuri; Feroci, Marco; Frutti, Massimo; Lazzarotto, Francesco; Lapshov, Igor; Rubini, Alda; Soffitta, Paolo; Tavani, Marco [IASF-INAF Rome (Italy); Barbiellini, Guido [INFN Trieste (Italy); Mastropietro, Marcello [CNR Montelibretti (Italy); Morelli, Ennio [IASF-INAF-Bologna (Italy); Rapisarda, Massimo [ENEA Frascati (Italy)

2006-05-19

307

Gamma-ray imaging probes  

SciTech Connect

External nuclear medicine diagnostic imaging of early primary and metastatic lung cancer tumors is difficult due to the poor sensitivity and resolution of existing gamma cameras. Nonimaging counting detectors used for internal tumor detection give ambiguous results because distant background variations are difficult to discriminate from neighboring tumor sites. This suggests that an internal imaging nuclear medicine probe, particularly an esophageal probe, may be advantageously used to detect small tumors because of the ability to discriminate against background variations and the capability to get close to sites neighboring the esophagus. The design, theory of operation, preliminary bench tests, characterization of noise behavior and optimization of such an imaging probe is the central theme of this work.

Wild, W.J.

1988-01-01

308

Physical constraints on models of gamma-ray bursters  

SciTech Connect

This report deals with the constraints that can be placed on models of gamma-ray burst sources based on only the well-established observational facts and physical principles. The premise is developed that the very hard x-ray and gamma-ray continua spectra are well-established aspects of gamma-ray bursts. Recent theoretical work on gamma-ray bursts are summarized with emphasis on the geometrical properties of the models. Constraints on the source models which are implied by the x-ray and gamma-ray spectra are described. The allowed ranges for the luminosity and characteristic dimension for gamma-ray burst sources are shown. Some of the deductions and inferences about the nature of the gamma-ray burst sources are summarized. 67 refs., 3 figs.

Epstein, R.I.

1985-01-01

309

Modeling of a slanted-hole collimator in a compact endo-cavity gamma camera.  

NASA Astrophysics Data System (ADS)

Having the ability to take an accurate 3D image of a tumor greatly helps doctors diagnose it and then create a treatment plan for a patient. One way to accomplish molecular imaging is to inject a radioactive tracer into a patient and then measure the gamma rays emitted from regions with high-uptake of the tracer, viz., the cancerous tissues. In large, expensive PET- or SPECT-imaging systems, the 3D imaging easily is accomplished by rotating the gamma-ray detectors and then employing software to reconstruct the 3D images from the multiple 2D projections at different angles of view. However, this method is impractical in a very compact imaging system due to anatomical considerations, e.g., the transrectal gamma camera under development at Brookhaven National Laboratory (BNL) for detection of intra-prostatic tumors. The camera uses pixilated cadmium zinc telluride (CdZnTe or CZT) detectors with matched parallel-hole collimator. Our research investigated the possibility of using a collimator with slanted holes to create 3D pictures of a radioactive source. The underlying concept is to take 2D projection images at different angles of view by adjusting the slant angle of the collimator, then using the 2D projection images to reconstruct the 3D image. To do this, we first simulated the response of a pixilated CZT detector to radiation sources placed in the field of view of the camera. Then, we formulated an algorithm to use the simulation results as prior knowledge and estimate the distribution of a shaped source from its 2D projection images. From the results of the simulation, we measured the spatial resolution of the camera as ~7-mm at a depth of 13.85-mm when using a detector with 2.46-mm pixel pitch and a collimator with 60° slant angle.

Kamuda, Mark; Cui, Yonggang; Lall, Terry; Ionson, Jim; Camarda, Giuseppe S.; Hossain, Anwar; Yang, Ge; Roy, Utpal N.; James, Ralph B.

2013-09-01

310

Very High Energy Gamma Ray Extension of GRO Observations.  

National Technical Information Service (NTIS)

This has been an exiciting year for high energy gamma-ray astronomy, both from space and from ground-based observatories. It has been a particularly active period for the Whipple Observatory gamma-ray group. In phase 1 of the Compton Gamma Ray Observatory...

T. C. Weekes

1992-01-01

311

GLAST and Ground-Based gamma-ray Astronomy.  

National Technical Information Service (NTIS)

The launch of the Gamma-ray Large Area Space Telescope (GLAST) in 2007 will open the possibility of combined studies of astrophysical sources with existing ground-based VHE gamma ray experiments such as H.E.S.S., VERITAS and MAGIC. Ground-based gamma ray ...

B. Giebels F. Longo J. E. Carson J. E. McEnery S. Funk

2007-01-01

312

Imaging and background in low-energy gamma ray astronomy  

Microsoft Academic Search

The current status of low energy gamma ray astronomy is reviewed and the conclusion drawn that the next generation of low energy gamma ray telescopes will require high sensitivity, good timing, and spectral resolution. High angular resolution imaging capability is also considered essential. The imaging of low energy gamma rays is hampered by the difficulties encountered in developing high resolution

Fan Lei

1989-01-01

313

The University of Durham Mark 6 Gamma Ray Telescope  

Microsoft Academic Search

The design, construction and operation of the University of Durham ground-based gamma ray telescope is discussed. The telescope has been designed to detect gamma rays in the = 200 GeV region and to achieve good discrimination between gamma ray and hadron initiated showers in the higher energy region (? 300 GeV). The telescope was commissioned in 1995 and a description

P. Armstrong; P. M. Chadwick; P. J. Cottle; J. E. Dickinson; M. R. Dickinson; N. A. Dipper; W. Hogg; J. Holder; T. R. Kendall; T. J. L. McComb; C. M. Moore; K. J. Orford; S. M. Rayner; I. D. Roberts; M. D. Roberts; M. Robertshaw; S. E. Shaw; K. Tindale; S. P. Tummey; K. E. Turver

1999-01-01

314

The University of Durham Mark 6 Gamma Ray Telescope  

Microsoft Academic Search

The design, construction and operation of the University of Durham ground-based gamma ray telescope is discussed. The telescope has been designed to detect gamma rays in the >= 150 GeV region and to achieve good discrimination between gamma ray and hadron initiated showers using conventional imaging and novel fluctuation measures. The telescope was commissioned in 1995 and a description of

P. M. Chadwick; M. R. Dickinson; N. A. Dipper; J. Holder; T. R. Kendall; T. J. L. McComb; K. J. Orford; S. M. Rayner; I. D. Roberts; S. E. Shaw; K. E. Turver; J. E. Dickinson; M. D. Roberts; S. P. Tummey

1997-01-01

315

Gamma-ray burst data from DMSP satellites.  

National Technical Information Service (NTIS)

A number of gamma-ray bursts have been detected by means of gamma-ray detectors aboard three Air Force Defense Meteorological Satellite Program (DMSP) satellites, in polar orbits at 800 km altitude. The gamma-ray data have a 2-second resolving time, and a...

J. Terrell R. W. Klebesadel P. Lee J. W. Griffee

1991-01-01

316

Very High-Energy Gamma-Ray Sources.  

ERIC Educational Resources Information Center

|Discusses topics related to high-energy, gamma-ray astronomy (including cosmic radiation, gamma-ray detectors, high-energy gamma-ray sources, and others). Also considers motivation for the development of this field, the principal results to date, and future prospects. (JN)|

Weekes, Trevor C.

1986-01-01

317

New Gamma-ray flaring activity from NRAO 676  

NASA Astrophysics Data System (ADS)

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a renewed gamma-ray flaring activity from a gamma-ray source not included in any of the Fermi LAT catalogs.

Cutini, Sara

2012-10-01

318

Design and performance of the GAMMA-400 gamma-ray telescope for dark matter searches  

NASA Astrophysics Data System (ADS)

The GAMMA-400 gamma-ray telescope is designed to measure the fluxes of gamma-rays and cosmic-ray electrons + positrons, which can be produced by annihilation or decay of the dark matter particles, as well as to survey the celestial sphere in order to study point and extended sources of gamma-rays, measure energy spectra of Galactic and extragalactic diffuse gamma-ray emission, gamma-ray bursts, and gamma-ray emission from the Sun. GAMMA-400 covers the energy range from 100 MeV to 3000 GeV. Its angular resolution is ~0.01° (E? > 100 GeV), the energy resolution ~1% (E? > 10 GeV), and the proton rejection factor ~106. GAMMA-400 will be installed on the Russian space platform Navigator. The beginning of observations is planned for 2018.

Galper, A. M.; Adriani, O.; Aptekar, R. L.; Arkhangelskaja, I. V.; Arkhangelskiy, A. I.; Boezio, M.; Bonvicini, V.; Boyarchuk, K. A.; Fradkin, M. I.; Gusakov, Yu. V.; Kaplin, V. A.; Kachanov, V. A.; Kheymits, M. D.; Leonov, A. A.; Longo, F.; Mazets, E. P.; Maestro, P.; Marrocchesi, P.; Mereminskiy, I. A.; Mikhailov, V. V.; Moiseev, A. A.; Mocchiutti, E.; Mori, N.; Moskalenko, I. V.; Naumov, P. Yu.; Papini, P.; Picozza, P.; Rodin, V. G.; Runtso, M. F.; Sparvoli, R.; Spillantini, P.; Suchkov, S. I.; Tavani, M.; Topchiev, N. P.; Vacchi, A.; Vannuccini, E.; Yurkin, Yu. T.; Zampa, N.; Zverev, V. G.; Zirakashvili, V. N.

2013-02-01

319

Intrinsic germanium gamma-ray data from the New American Petroleum Institute spectral gamma-ray calibration models  

Microsoft Academic Search

High-resolution gamma-ray spectra have been recorded at the new American Petroleum Institute (API) spectral gamma-ray logging calibration center with a US Department of Energy passive spectral gamma-ray logging unit. These measurements were completed before gamma-ray source concentrations were assigned to the calibration model zones. Analyses of spectra gathered from five of the calibration zones yielded linear relationships between: (1) tentative

C. J. Koizumi; W. H. Ulbricht; J. R. Brodeur

1991-01-01

320

A search for gamma-ray bursts and pulsars, and the application of Kalman filters to gamma-ray reconstruction  

Microsoft Academic Search

High-energy gamma-ray astronomy was revolutionized in 1991 with the launch of the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma-Ray Observatory. In addition to unprecedented instrument effective area and a narrow point-spread function, EGRET provided photon time-tagging to an absolute accuracy of 100 mus. The opportunity to analyze high-quality gamma-ray data requires sophisticated statistical and analytic tools. Part

Brian Butler Jones

1999-01-01

321

A Search for Gamma-Ray Bursts and Pulsars, and the Application of Kalman Filters to Gamma-Ray Reconstruction  

Microsoft Academic Search

Part I describes the analysis of periodic and transient signals in EGRET data. A method to search for the transient flux from gamma-ray bursts independent of triggers from other gamma-ray instruments is developed. Several known gamma-ray bursts were independently detected, and there is evidence for a previously unknown gamma-ray burst candidate. Statistical methods using maximum likelihood and Bayesian inference are

Brian Jones

2002-01-01

322

Detection of high-energy gamma rays from quasar PKS 0528 + 134 by EGRET on the Compton Gamma Ray Observatory  

Microsoft Academic Search

The first several pointing directions of the Compton Gamma Ray Observatory, launched on 1991 April 5, were toward the Galactic anticenter. In addition to the known gamma-ray sources, Crab and Geminga, high-energy gamma-ray emission was observed from the quasar PKS 0528 + 134 by the Energetic Gamma Ray Experiment Telescope (EGRET). A redshift measurement, reported here, of 2.07 confirms the

S. D. Hunter; D. L. Bertsch; B. L. Dingus; C. E. Fichtel; R. C. Hartman; G. Kanbach; D. A. Kniffen; P. W. Kwok; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; P. Moller; C. von Montigny; P. L. Nolan; K. Pinkau; H.-D. Radecke; H. Rothermel; P. Shaver; E. Schneid; M. Sommer; P. Sreekumar; D. J. Thompson

1993-01-01

323

Focusing Soft Gamma-rays: the Challenge and the Promise  

NASA Astrophysics Data System (ADS)

Many science themes would greatly benefit from increased sensitivity in the soft gamma-ray domain. Observation of the light curve and the profile of the 847 keV line from the decay chain of 56Ni synthesized in Type Ia supernovae would place severe constraints on the physical processes at work during these events. This is also true for the observation of the 478 keV line originating in the decay of 7Be synthesized in CO classical novae. In both cases, theoretical models are ready but need observational constraints. In addition, sensitive observations of the 511 keV electron-positron annihilation line would bring new constraints on the origin of the positrons from the Galactic bulge. High significance detection also opens the way for polarization analysis, which is especially interesting in the hard X-ray tails of compact objects. Despite improvements in sensitivity at essentially every other wavelength, the soft gamma-ray domain is lagging behind. Our group at UC Berkeley has been developing a Laue lens: an optic based on diffraction in crystals that enables the concentration of a couple of relatively narrow energy bands in the range from 100 keV to 1.5 MeV. Laue lens telescopes hold the promise of providing at least an order of magnitude improvement in sensitivity with respect to existing instruments, enabling much of the science cited above.

Tomsick, John; Barriere, N.; Boggs, S.

2011-09-01

324

Thermonuclear model for. gamma. -ray bursts  

SciTech Connect

The production of ..gamma..-ray bursts by thermonuclear explosions on strongly magnetized nuetron stars is examined. For a neutron star with a magnetic field strength of several times 10/sup 12/ gauss, accretion at approx.10/sup -13/ M/sub sun/ yr/sup -1/ is focused onto kilometer sized regions. The accreted material is confined above the surface by the magnetic field and by a combination of magnetic and crustal stresses below the surface. Stable hydrogen burning leads to a critical helium mass that, depending upon model parameters, explodes either by convective deflagration or detonation, liberating 10/sup 38/--10/sup 40/ ergs km/sup -2/ of thermonuclear energy. Multibillion degree plasma pushed above the surface by the explosion has ..beta..>1 and therefore expands and stresses the magnetic field. Hard emission comes both from the magnetically confined photosphere and from relativistic electrons accelerated by magnetic field recombination. The hard ..gamma..-ray outburst of several seconds is followed by an enduring, softer emission of X-rays, lasting from several minutes to an hour, as the subsurface ashes of the thermonuclear explosion cool. Gamma-ray bursters, at a typical distance of several hundred parsecs, should recur on a time scale of months (low energy) to centuries (high energy). Special attention is given to the spectracular event of 1979 March 5.

Woosley, S.E.; Wallace, R.K.

1982-07-15

325

Nonthermal Gamma-Ray\\/X-Ray Flashes from Shock Breakout in Gamma-Ray Burst-Associated Supernovae  

Microsoft Academic Search

Thermal X-ray emission that is simultaneous with prompt gamma-ray emission has been detected for the first time from a supernova associated with a gamma-ray burst (GRB), namely GRB 060218\\/SN 2006aj. It has been interpreted as arising from the breakout of a mildly relativistic, radiation-dominated shock from a dense stellar wind surrounding the progenitor star. There is also evidence for the

Xiang-Yu Wang; Zhuo Li; Eli Waxman; Peter Mészáros

2007-01-01

326

Gamma rays from cosmic rays in supernova remnants  

NASA Astrophysics Data System (ADS)

Context. Cosmic rays are thought to be accelerated at supernova remnant (SNR) shocks, but obtaining conclusive evidence for this hypothesis is difficult. Aims: New data from ground-based ?-ray telescopes and the Large Area Telescope on the Fermi Gamma-ray Space Telescope are used to test this hypothesis. A simple model for ?-ray production efficiency is compared with measured ?-ray luminosities of SNRs, and the GeV to TeV fluxes ratios of SNRs are examined for correlations with SNR ages. Methods: The supernova explosion is modeled as an expanding spherical shell of material that sweeps up matter from the surrounding interstellar medium (ISM). The accumulated kinetic energy of the shell, which provides the energy available for nonthermal particle acceleration, changes when matter is swept up from the ISM and the SNR shell decelerates. A fraction of this energy is assumed to be converted into the energy of cosmic-ray electrons or protons. Three different particle radiation processes - nuclear pion-production interactions, nonthermal electron bremsstrahlung, and Compton scattering - are considered. Results: The efficiencies for ?-ray production by these three processes are compared with ?-ray luminosities of SNRs. Our results suggest that SNRs become less ?-ray luminous at ?104 yr, and are consistent with the hypothesis that supernova remnants accelerate cosmic rays with an efficiency of ?10% for the dissipation of kinetic energy into nonthermal cosmic rays. Weak evidence for an increasing GeV to TeV flux ratio with SNR age is found.

Dermer, C. D.; Powale, G.

2013-05-01

327

Gamma-ray and X-ray Observations Towards the Gamma-Cygni Supernova Remnant  

NASA Astrophysics Data System (ADS)

We report on observations of the source VER J2019+407 towards the Gamma-Cygni supernova remnant. Very high energy (> 320 GeV) gamma-ray emission from the source was detected by the VERITAS observatory, an array of four 12-meter imaging atmospheric Cherenkov telescopes based near Tucson, Arizona. The proximity of this source to a diffuse region of gamma-ray emission detected by the Fermi Space Telescope increases its significance, and may suggest a connection between the two. To further investigate the properties of VER J2019+407, we have obtained a 50 ks Chandra observation of this region. Analysis of the Chandra data, and implications for the gamma-ray source, will be presented.

Dwarkadas, Vikram; Weinstein, A.; Theiling, M.; VERITAS Collaboration

2013-04-01

328

Search on extraterrestrial gamma-ray lines from Southern Hemisphere sources with high energy resolution gamma-ray telescopes  

Microsoft Academic Search

The scope of the GEL 1 and 2 balloon-borne gamma ray telescope experiments is described. The gamma ray spectrometer to be used on GEL 1 is described. It is designed to study the nature of the Galactic center positron annihilation 511 KeV line. The telescope effect is achieved through the aperture angle formed by the gamma ray spectrometer anticoincidence crystals.

J. M. Dacosta; J. O. D. Jardim; F. Gonzalez-Blanco; D. J. R. Nordemann; I. M. Martin; S. L. G. Dutra; F. Albernhe; G. Vedrenne; D. Boclet; P. Durouchoux

1981-01-01

329

COMPACT OPTICAL COUNTERPARTS OF ULTRALUMINOUS X-RAY SOURCES  

SciTech Connect

Using archival Hubble Space Telescope (HST) imaging data, we report the multiband photometric properties of 13 ultraluminous X-ray sources (ULXs) that have a unique compact optical counterpart. Both magnitude and color variation are detected at timescales of days to years. The optical color, variability, and X-ray to optical flux ratio indicate that the optical emission of most ULXs is dominated by X-ray reprocessing on the disk, similar to that of low-mass X-ray binaries. For most sources, the optical spectrum is a power law, F{sub {nu}}{proportional_to}{nu}{sup {alpha}} with {alpha} in the range 1.0-2.0 and the optically emitting region has a size on the order of 10{sup 12} cm. Exceptions are NGC 2403 X-1 and M83 IXO 82, which show optical spectra consistent with direct emission from a standard thin disk, M101 ULX-1 and M81 ULS1, which have X-ray to optical flux ratios more similar to high-mass X-ray binaries, and IC 342 X-1, in which the optical light may be dominated by the companion star. Inconsistent extinction between the optical counterpart of NGC 5204 X-1 and the nearby optical nebulae suggests that they may be unrelated.

Tao Lian; Feng Hua [Department of Engineering Physics and Center for Astrophysics, Tsinghua University, Beijing 100084 (China); Grise, Fabien; Kaaret, Philip [Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242 (United States)

2011-08-20

330

Gamma-Ray Pulsar Visibility  

NASA Astrophysics Data System (ADS)

PSR J0437-4715 is a millisecond pulsar (MSP) thought to be ``pair formation starved'' (having limited pair cascades due to magnetic photon absorption). Fortunately the general relativistic (GR) electrodynamical model under consideration applicable to this pulsar have few free parameters. We model PSR J0437-4715's visibility, using a 3D model which incorporates the variation of the GR E-field over the polar cap (PC), taking different observer and inclination angles into account. Using this pulsar as a case study, one may generalize to conducting a pulsar population visibility study. We lastly comment on the role of the proposed South African SKA (Square Kilometre Array) prototype, KAT (Karoo Array Telescope), for GLAST ?-ray pulsar identification.

Venter, Christo; de Jager, Ocker C.; Tiplady, Adrian

2005-11-01

331

Gamma-Ray Imaging Probes.  

NASA Astrophysics Data System (ADS)

External nuclear medicine diagnostic imaging of early primary and metastatic lung cancer tumors is difficult due to the poor sensitivity and resolution of existing gamma cameras. Nonimaging counting detectors used for internal tumor detection give ambiguous results because distant background variations are difficult to discriminate from neighboring tumor sites. This suggests that an internal imaging nuclear medicine probe, particularly an esophageal probe, may be advantageously used to detect small tumors because of the ability to discriminate against background variations and the capability to get close to sites neighboring the esophagus. The design, theory of operation, preliminary bench tests, characterization of noise behavior and optimization of such an imaging probe is the central theme of this work. The central concept lies in the representation of the aperture shell by a sequence of binary digits. This, coupled with the mode of operation which is data encoding within an axial slice of space, leads to the fundamental imaging equation in which the coding operation is conveniently described by a circulant matrix operator. The coding/decoding process is a classic coded-aperture problem, and various estimators to achieve decoding are discussed. Some estimators require a priori information about the object (or object class) being imaged; the only unbiased estimator that does not impose this requirement is the simple inverse-matrix operator. The effects of noise on the estimate (or reconstruction) is discussed for general noise models and various codes/decoding operators. The choice of an optimal aperture for detector count times of clinical relevance is examined using a statistical class-separability formalism.

Wild, Walter James

1988-12-01

332

Relativistic Doppler-boosted emission in gamma-ray binaries  

NASA Astrophysics Data System (ADS)

Context. Gamma-ray binaries could be compact pulsar wind nebulae formed when a young pulsar orbits a massive star. The pulsar wind is contained by the stellar wind of the O or Be companion, creating a relativistic comet-like structure accompanying the pulsar along its orbit. Aims: The X-ray and the very high energy (>100 GeV, VHE) gamma-ray emission from the binary LS 5039 are modulated on the orbital period of the system. Maximum and minimum flux occur at the conjunctions of the orbit, suggesting that the explanation is linked to the orbital geometry. The VHE modulation has been proposed to be due to the combined effect of Compton scattering and pair production on stellar photons, both of which depend on orbital phase. The X-ray modulation could be due to relativistic Doppler boosting in the comet tail where both the X-ray and VHE photons would be emitted. Methods: Relativistic aberrations change the seed stellar photon flux in the comoving frame so Doppler boosting affects synchrotron and inverse Compton emission differently. The dependence with orbital phase of relativistic Doppler-boosted (isotropic) synchrotron and (anisotropic) inverse Compton emission is calculated, assuming that the flow is oriented radially away from the star (LS 5039) or tangentially to the orbit (LS I +61°303, PSR B1259-63). Results: Doppler boosting of the synchrotron emission in LS 5039 produces a lightcurve whose shape corresponds to the X-ray modulation. The observations imply an outflow velocity of 0.15-0.33c consistent with the expected flow speed at the pulsar wind termination shock. In LS I +61°303, the calculated Doppler boosted emission peaks in phase with the observed VHE and X-ray maximum. Conclusions: Doppler boosting is not negligible in gamma-ray binaries, even for mildly relativistic speeds. The boosted modulation reproduces the X-ray modulation in LS 5039 and could also provide an explanation for the puzzling phasing of the VHE peak in LS I +61°303.

Dubus, G.; Cerutti, B.; Henri, G.

2010-06-01

333

Mercuric iodide room temperature gamma-ray detectors  

SciTech Connect

High resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis. 3 refs.

Patt, B.E.; Markakis, J.M.; Gerrish, V.M. (EG and G Energy Measurements, Inc., Goleta, CA (USA)); Haymes, R.C. (National Aeronautics and Space Administration, Washington, DC (USA). Astrophysics Div.); Trombka, J.I. (National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center)

1989-01-01

334

Balloon-borne gamma-ray telescope with nuclear emulsion  

Microsoft Academic Search

We are planning to observe cosmic gamma-ray in the energy range 10MeV to 100GeV by balloon-borne gamma-ray telescope with nuclear emulsion. Nuclear emulsion is a precise tracker. By detecting starting point of electron pair, gamma-ray direction can be determined precisely (1.4mrad@1-2GeV). This is much better than Fermi Gamma-ray Space Telescope launched June 2008. Now we are developing the gamma-ray telescope

Satoru Takahashi; Shigeki Aoki; Tsutomu Fukuda; Kaname Hamada; Toshio Hara; Atsushi Iyono; Jiro Kawada; Masashi Kazuyama; Koichi Kodama; Masahiro Komatsu; Shinichiro Koshiba; Hirotaka Kubota; Seigo Miyamoto; Motoaki Miyanishi; Kunihiro Mor-Ishima; Naotaka Naganawa; Tatsuhiro Naka; Mitsuhiro Nakamura; Toshiyuki Nakano; Kimio Niwa; Yoshiaki Nonoyama; Keita Ozaki; Hiroki Rokujo; Takashi Sako; Os-Amu Sato; Yoshihiro Sato; Kazuya Suzuki; Atsumu Suzuki; Ikuo Tezuka; Junya Yoshida; Teppei Yoshioka

2010-01-01

335

Balloon-borne gamma-ray telescope with nuclear emulsion  

NASA Astrophysics Data System (ADS)

We are planning to observe cosmic gamma-ray in the energy range 10MeV to 100GeV by balloon-borne gamma-ray telescope with nuclear emulsion. Nuclear emulsion is a precise tracker. By detecting starting point of electron pair, gamma-ray direction can be determined precisely (1.4mrad@1-2GeV). This is much better than Fermi Gamma-ray Space Telescope launched June 2008. Now we are developing the gamma-ray telescope with nuclear emulsion and are planning to observe by balloon flight. Overview and status of our telescope is introduced in this presentation.

Takahashi, Satoru; Aoki, Shigeki; Fukuda, Tsutomu; Hamada, Kaname; Hara, Toshio; Iyono, Atsushi; Kawada, Jiro; Kazuyama, Masashi; Kodama, Koichi; Komatsu, Masahiro; Koshiba, Shinichiro; Kubota, Hirotaka; Miyamoto, Seigo; Miyanishi, Motoaki; Mor-Ishima, Kunihiro; Naganawa, Naotaka; Naka, Tatsuhiro; Nakamura, Mitsuhiro; Nakano, Toshiyuki; Niwa, Kimio; Nonoyama, Yoshiaki; Ozaki, Keita; Rokujo, Hiroki; Sako, Takashi; Sato, Os-Amu; Sato, Yoshihiro; Suzuki, Kazuya; Suzuki, Atsumu; Takahashi, Satoru; Tezuka, Ikuo; Yoshida, Junya; Yoshioka, Teppei

336

The Calculation of Solar Gamma-rays by TALYS  

NASA Astrophysics Data System (ADS)

Solar gamma-ray lines, produced from nuclear reactions of accelerated particles interacting with solar atmosphere ambient medium, are the most direct diagnosis about the acceleration and transport of electrons and ions in solar flares. Analysis of gamma-ray line spectrum in solar flare has provided information about composition, spectrum and angular distribution of the accelerated ions, as well as elemental abundance of the ambient solar atmosphere. A new gamma-ray calculation program was developed by using an efficient nuclear code - TALYS. The theory of gamma-ray production in solar flares is treated in detail. In addition, the characteristics of gamma-ray spectrum are also presented.

Chen, W.; Gan, W. Q.

2011-05-01

337

The Calculation of Solar Gamma-Rays by TALYS  

NASA Astrophysics Data System (ADS)

Solar gamma-ray lines, produced from nuclear reactions of accelerated particles interacting with the solar atmospheric medium, are the most direct diagnosis for the acceleration and transportation of energetic electrons and ions in solar flares. Much information about composition, spectrum, and angular distribution of the accelerated ions, as well as the elemental abundances of the ambient solar atmosphere can be derived from solar gamma-ray line spectra. A new gamma-ray calculation program has been developed by using an efficient nuclear code - TALYS. The theory of gamma-ray production in solar flares is treated in detail. The characteristics of gamma-ray spectrum are also presented.

Chen, Wei; Gan, Wei-Qun

2012-01-01

338

Real time gamma-ray signature identifier  

SciTech Connect

A real time gamma-ray signature/source identification method and system using principal components analysis (PCA) for transforming and substantially reducing one or more comprehensive spectral libraries of nuclear materials types and configurations into a corresponding concise representation/signature(s) representing and indexing each individual predetermined spectrum in principal component (PC) space, wherein an unknown gamma-ray signature may be compared against the representative signature to find a match or at least characterize the unknown signature from among all the entries in the library with a single regression or simple projection into the PC space, so as to substantially reduce processing time and computing resources and enable real-time characterization and/or identification.

Rowland, Mark (Alamo, CA); Gosnell, Tom B. (Moraga, CA); Ham, Cheryl (Livermore, CA); Perkins, Dwight (Livermore, CA); Wong, James (Dublin, CA)

2012-05-15

339

Gamma-Ray Burst Progenitors: Merger Model  

NASA Astrophysics Data System (ADS)

The mergers of neutron stars and black holes remain a viable model for gamma-ray burst central engines, at least for the class of short bursts: their time scales, occurrence rates and energy output seem to be consistent with observations. We will present results of our latest simulations showing how the orbit of a neutron star around a black hole shrinks due to gravitational radiation, how the neutron star's matter gets accreted by the black hole, and how the tidal forces of the black hole finally shred the neutron star into a thick disk. In this process, huge amounts of energy are radiated away by gravitational waves and by neutrinos emitted from the hot disk. The neutrino luminosities are so large that an appreciable fraction (some few percent!) of neutrinos annihilate with antineutrinos creating the clean fireball necessary to power gamma-ray bursts.

Ruffert, Maximilian

2002-04-01

340

Gamma-ray multiplicity measurements using STEFF  

NASA Astrophysics Data System (ADS)

An ongoing investigation into the angular momentum generated during the fission of 252Cf is currently under way using the SpecTrometer for Exotic Fission Fragments (STEFF). Measurements have been made of the fold distribution (measured multiplicity) with STEFF. These have been compared to a Monte-carlo simulation to determine a value for the average angular momentum Jrms = 6hslash which is comparable to previous measurements [1]. Measurements of the gamma-ray multiplicity were performed whilst gating on different fragment mass regions. The result was compared with a sum of the lowest 2+ energies from both fragment and complementary in the mass gate. The results support the view that gamma-ray multiplicity is largely determined by the decay of the nucleus through near yrast transitions that follow the statistical decay.

Pollitt, A. J.; Smith, A. G.; Tsekhanovich, I.; Dare, J. A.

2012-09-01

341

Gamma-Ray Burst:. Discoveries with Swift  

NASA Astrophysics Data System (ADS)

Gamma Ray Bursts (GRBs) are bright, brief flashes of high energy photons and are the most powerful explosions since the Big Bang, with typical energies up to around 1051 ergs. Their outbursts persist for durations ranging from milliseconds to tens of seconds or more. In these brief moments the explosions radiate more energy than the Sun will release in its entire 10 billion year lifetime. They come in two classes: long (ż2 s), softspectrum bursts and short, hard events. Current theories attribute these phenomena to the final collapse of a massive star, or the coalescence of a binary system induced by gravity wave emission. New results from Swift and related programmes offer fresh understanding of the physics of gamma-ray bursts and of the local environments and host galaxies of burst progenitors. Bursts found at very high red-shifts are new tools for exploring the intergalactic medium, the first stars and the earliest stages of galaxy formation.

Wells, Alan

2007-11-01

342

Neutron-driven gamma-ray laser  

DOEpatents

A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 .ANG. when subjected to an intense neutron flux of about 400 eV neutrons. A 250 .ANG. thick layer of Be is provided between two layers of 100 .ANG. thick layer of .sup.57 Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux .sup.57 Co becomes .sup.58 Co by neutron absorption. The .sup.58 Co then decays to .sup.57 Fe by 1.6 MeV proton emission. .sup.57 Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the .sup.57 Fe from the .sup.57 Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.

Bowman, Charles D. (Los Alamos, NM)

1990-01-01

343

Neutron-driven gamma-ray laser  

DOEpatents

A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 {angstrom} when subjected to an intense neutron flux of about 400 eV neutrons. A 250 {angstrom} thick layer of Be is provided between two layers of 100 {angstrom} thick layer of {sup 57}Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux {sup 57}Co becomes {sup 58}Co by neutron absorption. The {sup 58}Co then decays to {sup 57}Fe by 1.6 MeV proton emission. {sup 57}Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the {sup 57}Fe from the {sup 57}Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.

Bowman, C.D.

1989-03-28

344

The Compton Gamma Ray Observatory: mission status.  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory (Compton) is the second in NASA's series of Great Observatories. Compton has now been operating for over two and a half years, and has given a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made and continue to be made. The authors describe the capabilities of the four scientific instruments and the observing programs for the first three years of the mission. During Phases 2 and 3 of the mission a Guest Investigator program has been in progress with the Guest Observers' time share increasing from 30% to over 50% for the later mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D. A.

345

Gamma ray bursts: a 1983 overview  

SciTech Connect

Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect. Energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all. Burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective. Finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

Cline, T.L.

1983-10-01

346

Plasma Instabilities in Gamma-Ray Bursts  

SciTech Connect

Magnetic fields are important in a variety of astrophysical scenarios, ranging from possible creation mechanisms of cosmological magnetic fields through relativistic jets such as that from Active Galactic Nuclei and gamma-ray bursts to local phenomena in the solar system. Here, the outstanding importance of plasma instabilities to astrophysics is illustrated by applying the so-called neutral point method to gamma-ray bursts (GRBs), which are assumed to have a homogeneous background magnetic field. It is shown how magnetic turbulence, which is a prerequisite for the creation of dissipation and, subsequently, radiation, is created by the highly relativistic particles in the GRB jet. Using the fact that different particle compositions lead to different instability conditions, conclusions can be drawn about the particle composition of the jet, showing that it is more likely of baryonic nature.

Tautz, Robert C. [Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum-und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2008-12-24

347

Gamma-ray polarimetry with Compton Telescope  

NASA Astrophysics Data System (ADS)

Compton telescope is a promising technology to achieve very high sensitivity in the soft gamma-ray band (0.1-10 MeV) by utilizing Compton kinematics. Compton kinematics also enables polarization measurement which will open new windows to study gamma-ray production mechanism in the universe. CdTe and Si semiconductor technologies are key technologies to realize the Compton telescope in which their high energy resolution is crucial for high angular resolution and background rejection capability. We have assembled a prototype module using a double-sided silicon strip detector and CdTe pixel detectors. In this paper, we present expected polarization performance of a proposed mission (NeXT/SGD). We also report results from polarization measurements using polarized synchrotron light and validation of EGS4 MC simulation.

Tajima, Hiroyasu; Madejski, Grzegorz; Mitani, Takefumi; Tanaka, Takaaki; Nakamura, Hidehito; Nakazawa, Kazuhiro; Takahashi, Tadayuki; Fukazawa, Yasushi; Kamae, Tuneyoshi; Kokubun, Motohide; Marlow, Daniel; Nomachi, Masaharu; do Couto e Silva, Eduardo

2004-10-01

348

A Balloon-Borne Gamma-Ray Polarimeter for Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), was successfully demonstrated with partially polarized gamma-ray sources in the lab and fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model flew on a high altitude balloon flight which demonstrated the design and collected background data. A much larger payload is currently under development that will provide a significant level of sensitivity for gamma-ray bursts on a long-duration balloon flight. The first balloon flight of the full GRAPE instrument is currently scheduled to take place in the Fall of 2011 from Ft. Sumner, NM.

McConnell, M. L.; Bancroft, C. M.; Bloser, P. F.; Connor, T. P.; Legere, J. S.; Macri, J. R.; Ryan, J. M.

2009-05-01

349

Gamma Ray Bursts: an Enigma Being Unraveled  

SciTech Connect

The best astrophysical accelerators are quasars and the 'progenitors' of GRBs which, after decades of observations and scores of theories, we still do not understand. But, I shall argue, we now know quite well where GRBs come from, and we understand how their 'beams' behave, as they make short pulses of gamma rays and long-duration X-ray, optical and radio 'afterglows'. I shall argue that our understanding of these phenomena, based on the 'Cannonball Model', is unusually simple, precise and successful. The 'sociology' of GRBs is interesting per se and, in this sense, the avatars of the Cannonball Model in confronting the generally accepted 'fireball models' are also quite revealing.

De Rujula, Alvaro (Boston University and CERN)

2003-05-14

350

Photonuclear Activation by 20.5Mev Gamma Rays  

Microsoft Academic Search

The photonuclear activation cross section of elements whose (gamma, n) cross sections lead to a suitable positron activity has been measured using monochromatic gamma rays from the T3(p, gamma)He4 reaction. The gamma rays were monitored by a 3-in. diam by 4-in. long sodium iodide crystal and calibrated with a 4 1\\/2 ×6 in. crystal whose response curve to the gamma

W. E. del Bianco; W. E. Stephens

1962-01-01

351

Gamma-Ray Emission from Fission of Heavy Nuclei  

Microsoft Academic Search

Average gamma-ray multiplicity , average energy emitted by gamma-rays and average energy per one gamma quantum gamma> as a function of mass and total kinetic energy (TKE) of fission fragments were measured in proton induced reactions p+242Pu->243Am, p+238U->239Np (at proton energy Ep=13, 20 and 55 MeV) and spontaneous fission of 252Cf. Complex structures in , and gamma> (as

L. Krupa; G. N. Kniajeva; A. A. Bogatchev; G. M. Chubarian; O. Dorvaux; I. M. Itkis; M. G. Itkis; S. Khlebnikov; J. Kliman; N. A. Kondratiev; E. M. Kozulin; V. Lyapin; T. Materna; W. Rubchenia; I. V. Pokrovsky; W. Trzaska; D. Vakhtin; V. M. Voskresenski

2003-01-01

352

GAMANAL. Interpretation of Gamma-Ray Spectra  

Microsoft Academic Search

GAMANAL provides a complete qualitative and quantitative analysis of mixtures of radioactive species such as fission products by computer interpretation of high-resolution gamma-ray spectra. The program first determines and removes the background or Compton continuum under the peaks in a spectrum to locate the peak regions. This is done by examining the pulse-height spectrum data for background and peak regions

Gunnink

1986-01-01

353

Common Gamma-ray Glows above Thunderclouds  

NASA Astrophysics Data System (ADS)

Gamma-ray glows are continuous, long duration gamma- and x-ray emission seen coming from thunderclouds. The Airborne for Energetic Lightning Emissions (ADELE) observed 12 gamma-ray glows during its summer 2009 flight campaign over the areas of Colorado and Florida in the United States. For these glows we shall present their spectra, relationship to lightning activity and how their duration and size changes as a function of distance. Gamma-ray glows follow the relativistic runaway electron avalanche (RREA) spectrum and have been previously measured from the ground and inside the cloud. ADELE measured most glows as it flew above the screening layer of the cloud. During the brightest glow on August 21, 2009, we can show that we are flying directly into a downward facing relativistic runaway avalanche, indicative of flying between the upper positive and negative screening layer of the cloud. In order to explain the brightness of this glow, RREA with an electric field approaching the limit for relativistic feedback must be occurring. Using all 12 glows, we show that lightning activity diminishes during the onset of the glow. Using this along with the fact that glows occur as the field approaches the level necessary for feedback, we attempt to distinguish between two possibilities: that glows are evidence that RREA with feedback, rather than lightning, is sometimes the primary channel for discharging the cloud, or else that the overall discharging is still controlled by lightning, with glows simply appearing during times when a subsidence of lightning allows the field to rise above the threshold for RREA.

Kelley, Nicole; Smith, David; Dwyer, Joseph; Hazelton, Bryna; Grefenstette, Brian; Lowell, Alex; Splitt, Michael; Lazarus, Steven; Rassoul, Hamid

2013-04-01

354

Fermi Detects Solar Flare's Gamma Rays  

NASA Video Gallery

During a powerful solar blast in March, NASA's Fermi Gamma-ray Space Telescope detected the highest-energy light ever associated with an eruption on the sun. The discovery heralds Fermi's new role as a solar observatory, a powerful new tool for understanding solar outbursts during the sun's maximum period of activity. Credit: NASA's Goddard Space Flight Center > Related story > Download high-res video

gsfcvideo

2012-06-12

355

Time resolved gamma-ray spectrometry  

Microsoft Academic Search

A new approach is proposed for the measurement of the time-dependent processes in gamma-ray spectrometry. During data acquisition,\\u000a the energy and the detection time of each event are recorded and the data are later analyzed off-line. This separation of\\u000a acquisition and data handling extends the possibilities of the analysis. A series of demonstration experiments was performed\\u000a to show the feasibility

L. Szentmiklósi; T. Belgya; G. L. Molnár; Zs. Révay

2007-01-01

356

Linssi : Database for gamma-ray spectrometry  

Microsoft Academic Search

Linssi is a Structured Query Language (SQL) database for HPGe gamma-ray spectrometry. It covers the whole production chain from\\u000a sample preparation to final analysis results. Static or mobile sampling and measurement and multiple sample types are supported.\\u000a In addition, each sample can be split or combined any number of times. A sample may be measured multiple times and each measurement

P. A. Aarnio; J. J. Ala-Heikkilä; A. Isolankila; A. Kuusi; M. Moring; M. Nikkinen; T. Siiskonen; H. Toivonen; K. Ungar; W. Zhang

2008-01-01

357

Pulsar kicks and gamma-ray burst  

Microsoft Academic Search

Aims:We use the supernova-GRB (gamma-ray burst) association and assume that the GRB asymmetric explosions produce pulsars in order to test the consistency of distributions of modeled and observed pulsar-kick velocities. Methods: The deduced distribution of kick velocity from the model of GRB and the observed kick distribution of radio pulsars are checked by a K-S test. Results: These two distributions

X. H. Cui; H. G. Wang; R. X. Xu; G. J. Qiao

2007-01-01

358

Pulsar's kicks and Gamma-ray bursts  

Microsoft Academic Search

The consistence of the distributions of pulsar's kick velocities from the\\u000amodel of GRB and from the pulsar observations is tested based on the\\u000asupernova-GRB ($\\\\gamma$-ray burst) association and under the assumption that\\u000athe GRB asymmetric explosions produce pulsars. The deduced distribution of kick\\u000avelocity from the model of GRB and the observed kick distribution of radio\\u000apulsars are checked

X. H. Cui; H. G. Wang; R. X. Xu; G. J. Qiao

2007-01-01

359

Kinetics of proposed gamma-ray lasers  

SciTech Connect

Gamma-ray lasers, although proposed for many years, remain undeveloped because pumping can destroy conditions essential for gain. We review many of the solutions (viz, narrowed-line, explosive neutron pump, two-stage pump, two-step pump) proposed so far, with emphasis on kinetics. The most promising approach requires fast interlevel transfer from a separated isomer to initiate a superradiant Borrmann mode in a solid host. However, suitable nuclear transitions and nondestructive transfer mechanisms have yet to be identified.

Baldwin, G.C.

1985-01-01

360

A portable gamma ray spectrometer/computer  

SciTech Connect

A state-of-the-art portable gamma ray spectrometer has been developed commercially. The instrument is available with NaI or hand-held Germanium detectors and can collect and analyze up to 4K channels of PHA or MCS spectra. An integral LCD provides graphic and character readout. Dual microprocessors are operated in a tightly-coupled multi-programming environment providing unique operator interface capability.

Roberts, H.

1984-02-01

361

Nuclear gamma Rays Following K- Capture  

Microsoft Academic Search

It is suggested that the study of the nuclear deexcitation gamma rays emitted following K- capture may help clarify the nature of the capture mechanism. We consider capture in 208Pb and 16O. Capture rates to the various proton or neutron single-hole states in 207Pb, 207Tl, 15O, and 15N are estimated, and the consequences of capture to the isomeric states in

S. D. Bloom; M. S. Weiss; C. M. Shakin

1972-01-01

362

Status of the Milagro Gamma Ray Observatory  

Microsoft Academic Search

The Milagro Gamma Ray Observatory is the world's first large-area water Cherenkov detector capable of continuously monitoring the sky at TeV energies. Located in the mountains of northern New Mexico, Milagro will perform an all sky survey of the Northern Hemisphere at energies between 250 GeV and 50 TeV. With ą a high duty-cycle, large detector area, and wide field-of-view

Joseph McCullough; W. Benbow; D. Berley; M.-L. Chen; D. G. Coyne; R. S. Delay; B. L. Dingus; D. E. Dorfan; R. W. Ellsworth; D. Evans; A. Falcone; L. Fleysher; R. Fleysher; G. Gisler; J. A. Goodman; T. J. Haines; C. M. Hoffman; S. Hugenberger; L. A. Kelley; I. Leonor; J. Macri; M. McConnell; J. E. McEnery; R. S. Miller; A. I. Mincer; M. F. Morales; P. Nemethy; J. M. Ryan; M. Schneider; B. Shen; A. Shoup; G. Sinnis; A. J. Smith; G. W. Sullivan; T. N. Thompson; O. T. Tumer; K. Wang; M. O. Wascko; S. Westerhoff; D. A. Williams; T. Yang; G. B. Yodh

1999-01-01

363

Short-hard gamma-ray bursts  

Microsoft Academic Search

Two types of gamma-ray bursts (GRBs) are observed: short-duration hard spectrum GRBs and long-duration soft spectrum GRBs. For many years long GRBs were the focus of intense research while the lack of observational data limited the study of short-hard GRBs (SHBs). In 2005 a breakthrough occurred following the first detections of SHB afterglows, longer wavelength emission that follows the burst

Ehud Nakar

2007-01-01

364

The Cosmic Gamma-Ray Bursts  

Microsoft Academic Search

Cosmic gamma-ray bursts are one of the great frontiers of astrophysics today.\\u000aThey are a playground of relativists and observers alike. They may teach us\\u000aabout the death of stars and the birth of black holes, the physics in extreme\\u000aconditions, and help us probe star formation in the distant and obscured\\u000auniverse. In this review we summarise some of

S. G. Djorgovski; D. A. Frail; S. R. Kulkarni; R. Sari; J. S. Bloom; T. J. Galama; F. A. Harrison; P. A. Price; D. Fox; D. E. REICHART; S. Yost; E. Berger; A. Diercks; R. Goodrich; F. Chaffee

2001-01-01

365

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

Observations show that at least some gamma-ray bursts (GRBs) happen simultaneously with core-collapse supernovae (SNe), thus linking by a common thread nature's two grandest explosions. We review here the growing evidence for and theoretical implications of this association, and conclude that most long-duration soft-spectrum GRBs are accompanied by massive stellar explosions (GRB-SNe). The kinetic energy and luminosity of well-studied GRB-SNe

S. E. Woosley; J. S. Bloom

2006-01-01

366

Spectral variations in gamma-ray bursts  

Microsoft Academic Search

We report the initial results of an analysis of 19 gamma-ray burst energy spectra recorded by the Venera-13 and 14 SIGNE experiments. The complete data-base includes some 150 events, with 5 channel energy spectra taken in the 50-700 keV range with 0.5 s time resolution, for 64 s. The observed spectra of each event analyzed were fitted with a power

K. Hurley; V. Kargatis; E. Liang; C. Barat; E. Eveno; M. Niel; V. Sh. Dolidze; A. A. Kozlenkov; I. G. Mitrofanov; A. S. Pozanenko

1991-01-01

367

Gamma-rays from massive protostars  

Microsoft Academic Search

Massive protostars have associated bipolar outflows with velocities of\\u000ahundreds of km\\/s. Such outflows produce strong shocks when interact with the\\u000aambient medium leading to regions of non-thermal radio emission. Under certain\\u000aconditions, the population of relativistic particles accelerated at the\\u000aterminal shocks of the protostellar jets can produce significant gamma-ray\\u000aemission. We estimate the conditions necessary for high-energy emission

Gustavo E. Romero; Anabella T. Araudo; Valenti Bosch-Ramon; Josep M. Paredes

2009-01-01

368

Gamma-Rays from Massive Protostars  

Microsoft Academic Search

Massive protostars have associated bipolar outflows with velocities of hundreds of km s-1. Such outflows produce strong shocks when interact with the ambient medium leading to regions of non-thermal radio emission. Under certain conditions, the population of relativistic particles accelerated at the terminal shocks of the protostellar jets can produce significant gamma-ray emission. We estimate the conditions necessary for high-energy

G. E. Romero; A. T. Araudo; V. Bosch-Ramon; J. M. Paredes

2010-01-01

369

Radio search for gamma-ray pulsar counterparts  

NASA Astrophysics Data System (ADS)

The Fermi gamma-ray satellite, launched in June 2008 is already returning remarkable results. In particular, it has discovered a large number of gamma-ray pulsars without any known radio counterpart (where only 1 was known prior to launch) and has detected unknown sources of gamma-ray radiation in the galactic plane with arcmin positional accuracy. Here we request time to (a) search the gamma-ray pulsars for radio pulsations using very deep integrations at 1.4 GHz and (b) search the unidentified galactic plane sources for radio pulsars. Detecting (or not) pulsars in the former case will help to distinguish between models of gamma-ray emission in pulsars. Detection of radio pulsars in the latter case will enable a search for gamma-ray pulsations to be made and/or determine other causes (such as pulsar wind nebulae) for the gamma-ray emission.

Keith, Michael; Johnston, Simon; Romani, Roger W.; Thompson, David J.; Weltevrede, Patrick; Michelson, Peter

2009-04-01

370

Propagation of gamma-rays in massive binary Cen X-3: interaction of cascade gamma-rays with the massive star  

NASA Astrophysics Data System (ADS)

We consider the propagation of very high energy (VHE) gamma-rays in the radiation field of the massive star of binary system Cen X-3. VHE gamma-rays or electrons, injected by the compact object close to the surface of a massive companion, develop inverse Compton e+/- pair (ICS) cascades. Based on the Monte Carlo simulations, we obtain the fraction of secondary cascade photons which collide with the surface of the massive companion in Cen X-3 system. The distribution of photons falling on the surface of the massive star is investigated. These photons interact with the atmosphere of the star and should excite different ?-ray lines (nuclear, e+/- annihilation line). We estimate that these ?-ray lines can be likely detected by the INTEGRAL telescopes.

Bednarek, W.

2001-09-01

371

Solar Two Gamma-Ray Observatory  

NASA Astrophysics Data System (ADS)

The field of high energy gamma-ray astronomy grew tremendously in the last decade due to the launch of the EGRET detector on the Compton Gamma-Ray Observatory in 1991 and the proliferation of ground-based air ?herenkov telescopes (ACTs) such as the Whipple 10 meter reflector. Interestingly, the ground-based telescopes only see 4-5 of the over 170 objects detected by EGRET. A simple extrapolation of the EGRET objects' energy spectra up to the energies which the ACTs are sensitive suggests that many of them should have been detected. The key to resolving this lack of detections is to observe these sources in the previously unobserved 20-250 GeV energy range. The Solar Two Observatory collaboration is developing a secondary optics system on the central tower of the world's largest solar energy pilot plant, Solar Two, to observe gamma-ray sources in this energy range. The progress in building the secondary optics system to be used to image ˜64 heliostats at Solar Two located in Barstow, California, is presented. We hope to design and build this detector over the next 2 years.

Tümer, T.; Bhattacharya, D.; Mohideen, U.; Rieben, R.; Souchkov, V.; Tom, H.; Zweerink, J.

1999-06-01

372

Afterglow Radiation from Gamma Ray Bursts  

SciTech Connect

Gamma-ray bursts (GRB) are huge fluxes of gamma rays that appear randomly in the sky about once a day. It is now commonly accepted that GRBs are caused by a stellar object shooting off a powerful plasma jet along its rotation axis. After the initial outburst of gamma rays, a lower intensity radiation remains, called the afterglow. Using the data from a hydrodynamical numerical simulation that models the dynamics of the jet, we calculated the expected light curve of the afterglow radiation that would be observed on earth. We calculated the light curve and spectrum and compared them to the light curves and spectra predicted by two analytical models of the expansion of the jet (which are based on the Blandford and McKee solution of a relativistic isotropic expansion; see Sari's model [1] and Granot's model [2]). We found that the light curve did not decay as fast as predicted by Sari; the predictions by Granot were largely corroborated. Some results, however, did not match Granot's predictions, and more research is needed to explain these discrepancies.

Desmond, Hugh; /Leuven U. /SLAC

2006-08-28

373

Gamma Ray Burst All-Sky Spectrometer  

NASA Astrophysics Data System (ADS)

The Gamma Ray Burst All-Sky Spectrometer Experiment (GASE) is designed to detect radio emission from gamma ray bursts (GRB's). Radio emission from GRB's could help us better understand the plasma physics of the blast and might also help us measure dark energy. GASE uses short-baseline interferometry with eight dipole antennas located at the MIT Haystack Observatory. These antennas measure the radiofrequency sky at 30 MHz over a 4 MHz bandwidth and are able to collect information from the entire sky. Since the entire sky is surveyed, radio frequency interference occurring at the horizon can be eliminated as a transient source. Along with the SWIFT satellite and the Gamma Ray Burst Coordinate system, we will be able measure blast time, duration and position. We are currently designing techniques to calibrate and image the full sky in radio. In addition to locating and measuring GRB's, GASE may be able to measure dark energy due to the dispersion by the IGM. The pulse of radio emission is delayed as it travels through the intergalactic plasma, with longer wavelengths taking longer to arrive than shorter wavelengths. With the known free electron density (?m) we will use the dispersion measure to calculate the line of sight distance to the GRB and compare to the observed redshift to measure dark energy.

Steger, Arielle

2011-05-01

374

Gamma rays as an indicator of nucleosynthesis  

NASA Astrophysics Data System (ADS)

In 1957 the collaboration of E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle, and the work by A. G. W. Cameron, laid the foundations for understanding the origin of the elements in terms of a few basic processes and astrophysical environments. Half a century after this pioneering work, there is considerable observational evidence for the basic notions of element synthesis during the big-bang, followed by hydrostatic and explosive stellar nucleosynthesis ever since the first population of stars re-illuminated the Universe, and through particle interactions in the turbulent interstellar medium. In 1969 D. D. Clayton, S. A. Colgate, and G. J. Fishman proposed to search for gamma-ray lines from the decay of 56-Ni, freshly synthesized in supernovae. Evidence for these lines was obtained for SN 1987A, and three decades after this pivotal supernova we have ample gamma-ray line evidence for ongoing nucleosynthesis in the Milky Way from surveys for individual sources and unresolved, integrated diffuse emission from an ensemble of such sources. We review the observational evidence for gamma ray lines from various species, and discuss the astrophysical implications of detections and a few puzzles suggested by lack of detections. We reflect on historic developments, assess the accomplishments, and present an outlook on the future of this branch of nuclear astrophysics.

Hartmann, Dieter H.

2007-04-01

375

The Fermi Gamma-Ray Space Telescope Discovers the Pulsar in the Young Galactic Supernova Remnant CTA 1  

Microsoft Academic Search

Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a

A. A. Abdo; M. Ackermann; W. B. Atwood; L. Baldini; J. Ballet; G. Barbiellini; M. G. Baring; D. Bastieri; B. M. Baughman; K. Bechtol; R. Bellazzini; B. Berenji; R. D. Blandford; E. D. Bloom; G. Bogaert; E. Bonamente; A. W. Borgland; J. Bregeon; A. Brez; M. Brigida; P. Bruel; T. H. Burnett; G. A. Caliandro; R. A. Cameron; P. A. Caraveo; P. Carlson; J. M. Casandjian; C. Cecchi; E. Charles; A. Chekhtman; C. C. Cheung; J. Chiang; S. Ciprini; R. Claus; J. Cohen-Tanugi; L. R. Cominsky; J. Conrad; S. Cutini; D. S. Davis; C. D. Dermer; A. de Angelis; F. de Palma; S. W. Digel; M. Dormody; E. do Couto e Silva; P. S. Drell; R. Dubois; D. Dumora; Y. Edmonds; C. Farnier; W. B. Focke; Y. Fukazawa; S. Funk; P. Fusco; F. Gargano; D. Gasparrini; N. Gehrels; S. Germani; B. Giebels; N. Giglietto; F. Giordano; T. Glanzman; G. Godfrey; I. A. Grenier; M.-H. Grondin; J. E. Grove; L. Guillemot; S. Guiriec; A. K. Harding; R. C. Hartman; E. Hays; R. E. Hughes; G. Jóhannesson; A. S. Johnson; R. P. Johnson; T. J. Johnson; W. N. Johnson; T. Kamae; Y. Kanai; G. Kanbach; H. Katagiri; N. Kawai; M. Kerr; T. Kishishita; B. Kiziltan; J. Knödlseder; M. L. Kocian; N. Komin; F. Kuehn; M. Kuss; L. Latronico; M. Lemoine-Goumard; F. Longo; V. Lonjou; F. Loparco; B. Lott; M. N. Lovellette; P. Lubrano; A. Makeev; M. N. Mazziotta; J. E. McEnery; S. McGlynn; C. Meurer; P. F. Michelson; T. Mineo; W. Mitthumsiri; T. Mizuno; A. A. Moiseev; C. Monte; M. E. Monzani; A. Morselli; I. V. Moskalenko; S. Murgia; T. Nakamori; P. L. Nolan; E. Nuss; M. Ohno; T. Ohsugi; A. Okumura; N. Omodei; E. Orlando; J. F. Ormes; M. Ozaki; D. Paneque; J. H. Panetta; D. Parent; V. Pelassa; M. Pesce-Rollins; G. Piano; L. Pieri; F. Piron; T. A. Porter; S. Rainň; R. Rando; P. S. Ray; M. Razzano; A. Reimer; O. Reimer; T. Reposeur; S. Ritz; L. S. Rochester; A. Y. Rodriguez; R. W. Romani; M. Roth; F. Ryde; H. F.-W. Sadrozinski; D. Sanchez; A. Sander; P. M. Saz Parkinson; T. L. Schalk; A. Sellerholm; C. Sgrň; E. J. Siskind; D. A. Smith; P. D. Smith; G. Spandre; P. Spinelli; J.-L. Starck; M. S. Strickman; D. J. Suson; H. Takahashi; T. Takahashi; T. Tanaka; J. B. Thayer; J. G. Thayer; D. J. Thompson; S. E. Thorsett; L. Tibaldo; D. F. Torres; G. Tosti; A. Tramacere; T. L. Usher; A. Van Etten; N. Vilchez; V. Vitale; P. Wang; K. Watters; B. L. Winer; K. S. Wood; H. Yasuda; T. Ylinen; M. Ziegler

2008-01-01

376

Astrophysical Parameters of LS 2883 and Implications for the PSR B1259-63 Gamma-ray Binary  

Microsoft Academic Search

Only a few binary systems with compact objects display TeV emission. The physical properties of the companion stars represent basic input for understanding the physical mechanisms behind the particle acceleration, emission, and absorption processes in these so-called gamma-ray binaries. Here we present high-resolution and high signal-to-noise optical spectra of LS 2883, the Be star forming a gamma-ray binary with the

Ignacio Negueruela; Marc Ribó; Artemio Herrero; Javier Lorenzo; Dmitry Khangulyan; Felix A. Aharonian; Felix A

2011-01-01

377

Compact water-window transmission X-ray microscopy.  

PubMed

We demonstrate sub-100 nm resolution water-window soft X-ray full-field transmission microscopy with a compact system. The microscope operates at lambda = 3.37 nm and is based on a 100 Hz table-top regenerative debris-free droplet-target laser-plasma X-ray source in combination with normal-incidence multilayer condenser optics for sample illumination. High-spatial-resolution imaging is performed with a 7.3% efficiency nickel zone plate and a 1024 x 1024 pixel CCD detector. Images of dry test samples are recorded with exposure times of a few minutes and show features smaller than 60 nm. PMID:10692130

Berglund, M; Rymell, L; Peuker, M; Wilhein, T; Hertz, H M

2000-03-01

378

Numerical simulations of planetary gamma-ray spectra induced by galactic cosmic rays  

SciTech Connect

The fluxes of cosmic-ray-produced gamma rays escaping from Mars were calculated using the LAHET Code System and basic nuclear data for {gamma}-ray production. Both surface water content and atmospheric thickness strongly affect the fluxes of {gamma}-ray lines escaping from Mars.

Masarik, J.; Reedy, R.C.

1994-07-01

379

A NEW CLASSIFICATION METHOD FOR GAMMA-RAY BURSTS  

SciTech Connect

Recent Swift observations suggest that the traditional long versus short gamma-ray burst (GRB) classification scheme does not always associate GRBs to the two physically motivated model types, i.e., Type II (massive star origin) versus Type I (compact star origin). We propose a new phenomenological classification method of GRBs by introducing a new parameter {epsilon} = E{sub {gamma},iso,52}/E {sup 5/3}{sub p,z,2}, where E{sub {gamma},iso} is the isotropic gamma-ray energy (in units of 10{sup 52} erg) and E{sub p,z} is the cosmic rest-frame spectral peak energy (in units of 100 keV). For those short GRBs with 'extended emission', both quantities are defined for the short/hard spike only. With the current complete sample of GRBs with redshift and E{sub p} measurements, the {epsilon} parameter shows a clear bimodal distribution with a separation at {epsilon} {approx} 0.03. The high-{epsilon} region encloses the typical long GRBs with high luminosity, some high-z 'rest-frame-short' GRBs (such as GRB 090423 and GRB 080913), as well as some high-z short GRBs (such as GRB 090426). All these GRBs have been claimed to be of Type II origin based on other observational properties in the literature. All the GRBs that are argued to be of Type I origin are found to be clustered in the low-{epsilon} region. They can be separated from some nearby low-luminosity long GRBs (in 3{sigma}) by an additional T{sub 90} criterion, i.e., T{sub 90,z} {approx}< 5 s in the Swift/BAT band. We suggest that this new classification scheme can better match the physically motivated Type II/I classification scheme.

Lue Houjun; Liang Enwei [Department of Physics, Guangxi University, Nanning 530004 (China); Zhang Binbin; Zhang Bing, E-mail: lew@gxu.edu.c, E-mail: zhang@physics.unlv.ed [Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154 (United States)

2010-12-20

380

Short Gamma-Ray Bursts and Dark Matter Seeding in Neutron Stars  

NASA Astrophysics Data System (ADS)

We present a mechanism based on internal self-annihilation of dark matter accreted from the galactic halo in the inner regions of neutron stars that may trigger full or partial conversion into a quark star. We explain how this effect may induce a gamma-ray burst (GRB) that could be classified as short, according to the usual definition based on time duration of the prompt gamma-ray emission. This mechanism differs in many aspects from the most discussed scenario associating short GRBs with compact object binary mergers. We list possible observational signatures that should help distinguish between these two possible classes of progenitors.

Ángeles Pérez-García, M.; Daigne, F.; Silk, J.

2013-05-01

381

Polarimetry with the Soft Gamma-ray Detector onboard ASTRO-H  

NASA Astrophysics Data System (ADS)

X-ray and gamma-ray polarimetry is a powerful probe to investigate emission mechanisms and geometries of astrophysical sources. It provides vital information on ordered magnetic field and accretion disk around compact objects. The Soft Gamma-ray Detector (SGD) onboard ASTRO-H satellite, scheduled for launch in 2014, is a highly-sensitive spectrometer in the 40-600 keV energy band. Since the SGD employs a Si/CdTe Compton camera surrounded by a thick BGO active shield, it is also sensitive to polarization in the 50-200 keV energy range. We have been developing the SGD through extensive tests in laboratory, detailed Monte-Carlo simulation and verification tests at synchrotron facilities (e.g., Takeda et al. 2010; Tajima et al. 2010). In this contribution, we will present the SGD instrumentation, prototype testing and expected performance as a gamma-ray polarimeter.

Mizuno, Tsunefumi

2012-07-01

382

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts.  

PubMed

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium. PMID:15889084

Vestrand, W T; Wozniak, P R; Wren, J A; Fenimore, E E; Sakamoto, T; White, R R; Casperson, D; Davis, H; Evans, S; Galassi, M; McGowan, K E; Schier, J A; Asa, J W; Barthelmy, S D; Cummings, J R; Gehrels, N; Hullinger, D; Krimm, H A; Markwardt, C B; McLean, K; Palmer, D; Parsons, A; Tueller, J

2005-05-12

383

Short gamma-ray bursts near and far.  

PubMed

Progress in understanding the nature of short gamma-ray bursts (GRBs) has been rapid since the discovery of the first afterglows in mid-2005. The emerging picture appears to be of short GRBs, which originate at moderate redshift (a few tenths) and appear in galaxies of all ages. This discovery has been used to argue for their origin in compact binary mergers. However, this population does not describe all short bursts. Here, I will present results of observations of several short GRBs, which challenge the conclusions drawn from the early observations. The observations show that some short GRBs originate in the very low redshift Universe (below 100Mpc), while some may also lie at redshifts comparable with the long GRBs (i.e. z>2). I will discuss the properties of these bursts and the implications they have for the progenitors of short GRBs. PMID:17293330

Levan, Andrew J

2007-05-15

384

Celestial Gamma Ray Bursts Detector Development and Model Simulations  

NASA Astrophysics Data System (ADS)

Celestial gamma-ray bursts are a poorly understood astrophysical phenomenon. These transient events were discovered over twenty years ago, yet their origin is still an unsolved mystery. At present no quiescent counterpart to a gamma ray burst source has been conclusively identified, partly because the poor angular resolution of gamma ray detectors and the short durations of the bursts make it difficult to determine precise source positions. (A few precise source positions have been determined by analysis of burst arrival times at widely separated detectors.) The High Energy Transient Experiment (HETE), described by Ricker, et al. (1992), is a new gamma ray astronomy satellite designed to overcome these difficulties. It can determine precise source positions by simultaneously observing a gamma ray burst with gamma ray x-ray, and ultraviolet (UV) instruments and utilizing the better angular resolutions available with the x-ray and UV instruments. In the first part of this dissertation I present experimental research which contributes to the development of a UV-sensitive solid-state imaging detector for the HETE satellite. The detector is a thinned, backside-illuminated charge-coupled device (CCD). The UV quantum efficiency (QE) is very sensitive to the results of the back-surface treatment, which stabilizes and protects that surface. As part of the detector development I designed and built an instrument to measure the quantum efficiency of a CCD over the wavelength range of 200--500~nm. With this instrument I measured the QE of seven prototype devices that were manufactured with three different back-surface technologies. I derived a statistical test to measure the mean number of electrons per photon, which increases from unity with increasing photon energy above a threshold of ~3.65~eV (340 nm). This effect is critically important when making photometric measurements at these wavelengths with solid state detectors. I also developed a simple physically-motivated model of the back surface, which provides adequate fits to the measured QE. I find that the best back-surface technology yields CCDs that have stable QEs of >40\\% in the HETE UV band of 220-310 nm. This is significantly better than the QE of 20% required by the HETE UV instrument (Ricker, et al. 1992). This encouraging result enhances the ability of the HETE UV instrument to detect a gamma-ray burst, which will ultimately lead to the discovery of the underlying physical sources. While the origin of gamma-ray bursts is unknown, the rapid variability and hard spectra indicate that the sources are compact objects. Many different models of gamma-ray bursts assume that the bursts originate from neutrons stars. Blaes, et al. (1990) put forth the idea that the natural evolution of a slowly-accreting, isolated neutron star leads to the formation of density inversions which might become unstable and thereby lead to a gamma-ray burst. However, the recent measurements of the gamma-ray burst distribution reported by Meegan, et al. (1992) rule out many galactic models. Recent theoretical work is split between galactic halo models and cosmological models, many of which still associate gamma-ray bursts with neutron stars. In any event, slowly-accreting neutron stars should exist in the galaxy. Their evolution is the focus of the second part of this dissertation. I present computational research on the evolution of this class of slowly accreting neutron stars. I describe an evolution code, which simulates the crust of a slowly accreting neutron star, and report on the evolution of the structure, composition, density inversions, and stored energy of fifteen different models. This evolution code is a version of ASTRA, an evolution code originally developed by Rakavy, et al. (1967). It is based on the version developed by Joss (1978) to simulate thermonuclear flashes in the crust of an accreting neutron star. The major changes are a new set of thermodynamic equations, a new nuclear reaction network, and a new thermal conductivity algorithm. The thermodynamic equations are based on

Mock, Patrick Charles

1993-12-01

385

Can Galactic Gamma-Ray Background be due to Superposition of gamma-Rays from Millisecond Pulsars?  

Microsoft Academic Search

A diffuse background of high energy gamma-rays has been observe in the Galaxy by space probes such as COS B. We make here an attempt to understand this background in terms of the gamma radiation from millisecond pulsars. Because of their large rotational velocities millisecond pulsars could br strong sources of gamma-rays. We calculate the integrated flux of gamma-rays from

V. B. Bhatia; S. Mishra; N. Panchapakesan

1998-01-01

386

The nature of the outflow in gamma-ray bursts  

Microsoft Academic Search

The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt gamma-ray emission, the emission that heralds these bursts, is short lived, and is distinct from

P. Kumar; E. McMahon; A. Panaitescu; R. Willingale; P. O'Brien; D. Burrows; J. Cummings; N. Gehrels; S. Holland; S. B. Pandey; D. vanden Berk; S. Zane

2007-01-01

387

Pulsar searches: From radio to gamma-rays  

Microsoft Academic Search

We report the results of four different pulsar searches, covering radio, X-ray, and gamma-ray wavelengths. These searches targeted pulsars in virtually all of their guises: young and old, long-period and short-period, accretion-powered and rotation-powered. Ten new pulsars were discovered. There are very few known gamma-ray pulsars, all of which were found by folding gamma-ray data with a pulse period known

Adam M. Chandler

2003-01-01

388

EGRET Observations of the Extragalactic Gamma-Ray Emission  

Microsoft Academic Search

The all-sky survey in high-energy gamma rays (E > 30 MeV) carried out by EGRET aboard the Compton Gamma Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, as well as an almost uniformly distributed component

P. Sreekumar; D. L. Bertsch; B. L. Dingus; J. A. Esposito; C. E. Fichtel; R. C. Hartman; S. D. Hunter; G. Kanbach; D. A. Kniffen; Y. C. Lin; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; A. Muecke; R. Mukherjee; P. L. Nolan; M. Pohl; O. Reimer; E. Schneid; J. G. Stacy; F. W. Stecker; D. J. Thompson; T. D. Willis

1998-01-01

389

Gamma-to-electron magnetic spectrometer (GEMS): An energy-resolved {gamma}-ray diagnostic for the National Ignition Facility  

SciTech Connect

The gamma-to-electron magnetic spectrometer, having better than 5% energy resolution, is proposed to resolve {gamma}-rays in the range of E{sub o}{+-} 20% in single shot, where E{sub o} is the central energy and is tunable from 2 to 25 MeV. Gamma-rays from inertial confinement fusion implosions interact with a thin Compton converter (e.g., beryllium) located at approximately 300 cm from the target chamber center (TCC). Scattered electrons out of the Compton converter enter an electromagnet placed outside the NIF chamber (approximately 600 cm from TCC) where energy selection takes place. The electromagnet provides tunable E{sub o} over a broad range in a compact manner. Energy resolved electrons are measured by an array of quartz Cherenkov converters coupled to photomultipliers. Given 100 detectable electrons in the energy bins of interest, 3 Multiplication-Sign 10{sup 14} minimum deuterium/tritium (DT) neutrons will be required to measure the 4.44 MeV {sup 12}C {gamma}-rays assuming 200 mg/cm{sup 2} plastic ablator areal density and 3 Multiplication-Sign 10{sup 15} minimum DT neutrons to measure the 16.75 MeV DT {gamma}-ray line.

Kim, Y.; Herrmann, H. W.; Mack, J. M.; Young, C. S.; Barlow, D. B.; Schillig, J. B.; Sims, J. R. Jr.; Lopez, F. E.; Mares, D.; Oertel, J. A.; Hayes-Sterbenz, A. C. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Hilsabeck, T. J.; Wu, W. [General Atomics, PO Box 85608, San Diego, California 92186 (United States); Moy, K. [National Security Technologies, Special Technologies Laboratory, Santa Barbara, California 93111 (United States); Stoeffl, W. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2012-10-15

390

IDENTIFICATION OF THE EARLY FERMI/LAT GAMMA-RAY BRIGHT OBJECTS WITH EXTRAGALACTIC VLBI SOURCES  

SciTech Connect

A list of 205 gamma-ray strong objects was reported recently as a result of a three-month integration with the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. We attempted identification of these objects, cross-correlating the gamma-ray positions with very long baseline interferometry (VLBI) positions of a large all-sky sample of extragalactic radio sources selected on the basis of their parsec-scale flux density. The original associations reported by the Fermi team are confirmed, and six new identifications are suggested. A Monte Carlo analysis shows that the fraction of chance associations in our analysis is less than 5%, and confirms that the vast majority of gamma-ray bright extragalactic sources are radio-loud blazars with strong parsec-scale jets. A correlation between the parsec-scale radio and gamma-ray flux is supported by our analysis of a complete VLBI flux-density-limited sample of extragalactic jets. The effectiveness of using a VLBI catalog to find associations between gamma-ray detections and compact extragalactic radio sources, especially near the Galactic plane, is demonstrated. It is suggested that VLBI catalogs should be used for future identification of Fermi/LAT objects.

Kovalev, Y. Y., E-mail: yyk@asc.rssi.r [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)

2009-12-10

391

Simulated Performance of the Nuclear Compton Telescope as a Gamma-Ray Polarimeter  

NASA Astrophysics Data System (ADS)

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and gamma-ray polarization. NCT is sensitive to polarization in the range 0.2-1 MeV. NCT consists of 3D position-sensitive germanium strip detectors. The ultra-compact design and new technologies allow NCT to achieve high efficiencies with excellent spectral resolution and background reduction. We are currently preparing a balloon flight of the NCT instrument in New Mexico in September 2008. For studying the gamma-ray polarization capability of NCT during the upcoming balloon flight, detailed Monte Carlo simulations of sources predicted to be polarized in the MeV regime (the Crab nebula, Crab pulsar, and gamma-ray bursts) and of the expected background were performed with the MGGPOD suite. The data analysis, including event reconstruction and polarization analysis, was performed by using the Medium Energy Gamma-ray Astronomy library (MEGAlib). Here we present the results of our Crab and gamma-ray burst simulations and discuss the NCT performance as a polarimeter.

Liang, Jau-Shian; Bellm, E. C.; Boggs, S. E.; NCT Collaboration

2008-03-01

392

Colorado School of Mines fusion gamma ray diagnostic project  

NASA Astrophysics Data System (ADS)

The purpose of our fusion gamma ray project continues to be the development of fusion gamma ray spectrometry as a diagnostic of high temperature fusion plasmas. The three broad areas in support of this purpose are: measurement of gamma ray producing reactions at low energies; development of gamma ray spectrometers capable of measuring the gamma ray yields from current and proposed fusion plasma devices; and determination of appropriate plasma parameters from measured fusion gamma ray yields at present fusion plasma devices. This report summarizes the progress made in these three areas. The recently completed measurement of the radiative capture of protons by the nuclei Li-6, Li-7, Be-9, and B-11 is summarized. Preliminary results of the investigation of the radiative capture of deuterons by Li-6 and B-10 as well as additional data taken on the reaction D(d,gamma)He-4 at very low energies are also presented.

Cecil, F. E.

1991-02-01

393

COMBINED GAMMA-RAY AND NEUTRON DETECTOR FOR MEASURING THE CHEMICAL COMPOSITION OF AIRLESS PLANETARY BODIES.  

SciTech Connect

Galactic cosmic rays (GCR) constant1,y itnpinge all planetary bodies and produce characteristic gamma-ray lines and leakage neutrons as reaction products. Together with gamma-ray lines produced by radioactive decay, these nuclear emissions provide a powerful technique for remotely measuring the chemical composition of airless planetary surfaces. While lunar gamma-ray spectroscopy was first demonstrated with Apollo Gamma-Ray measurements, the full value of combined gamma-ray and neutron spectroscopy was shown for the first time with the Lunar Prospector Gamma-Ray (LP-GRS) and Neutron Spectrometers (LP-NS). Any new planetary mission will likely have the requirement that instrument mass and power be kept to a minimum. To satisfy such requirements, we have been designing a GR/NS instrument which combines all the functionality of the LP-GRS and LP-NS for a fraction of the mass and power. Specifically, our design uses a BGO scintillator crystal to measure gamma-rays from 0.5-10 MeV. A borated plastic scintillator and a lithium gliiss scintillator are used to separately measure thermal, epithermal, and fast neutrons as well as serve as an anticoincidence shield for the BGO. All three scintillators are packaged together in a compact phoswich design. Modifications to this design could include a CdZnTe gamma-ray detector for enhanced energy resolution at low energies (0.5-3 MeV). While care needs to be taken to ensure that an adequate count rate is achieved for specific mission designs, previous mission successes demonstrate that a cornbined GR/NS provides essential information about planetary surfaces.

Lawrence, David J. (David Jeffery),; Barraclough, B. L. (Bruce L.); Feldman, W. C. (William C.); Prettyman, T. H. (Thomas H.); Wiens, R. C. (Roger C.)

2001-01-01

394

Combined gamma-ray and neutron detector for measuring the chemical composition of airless planetary bodies  

NASA Astrophysics Data System (ADS)

Galactic cosmic rays (GCR) constantly impinge all planetary bodies and produce characteristic gamma-ray lines and leakage neutrons as reaction products. Together with gamma-ray lines produced by radioactive decay, these nuclear emissions provide a powerful tool for remotely measuring the chemical composition of planetary surfaces having little or no atmospheres. While lunar gamma-ray spectroscopy was first demonstrated with Apollo Gamma-Ray measurements, the full value of combined gamma-ray and neutron spectroscopy was shown for the first time with the Lunar Prospector Gamma-Ray (LP-GRS) and Neutron Spectrometers (LP-NS). Any new planetary mission will likely have the requirement that instrument mass and power be kept to a minimum. To satisfy such requirements, we have been designing a GR/NS instrument which combines all the functionality of the LP-GRS and LP-NS for a fraction of the mass and power. Specifically, our design uses a BGO scintillator crystal to measure gamma-rays from 0.5 - 10 MeV. A borated plastic scintillator and a lithium glass scintillator are used to separately measure thermal, epithermal, and fast neutrons as well as serve as an anticoincidence shield for the BGO. All three scintillators are packaged together in a compact phoswich design. Modifications to this design could include a CdZnTe gamma-ray detector for enhanced energy resolution at low energies (0.5 - 3 MeV). While care needs to be taken to ensure that an adequate count rate and background suppression is achieved for specific mission designs, previous mission successes demonstrate that a combined GR/NS provides essential information about planetary surfaces.

Lawrence, David J.; Barraclough, Bruce L.; Feldman, William C.; Prettyman, Thomas H.; Wiens, Roger C.

2001-12-01

395

Simulation of prompt gamma-ray emission during proton radiotherapy  

Microsoft Academic Search

The measurement of prompt gamma rays emitted from proton-induced nuclear reactions has been proposed as a method to verify in vivo the range of a clinical proton radiotherapy beam. A good understanding of the prompt gamma-ray emission during proton therapy is key to develop a clinically feasible technique, as it can facilitate accurate simulations and uncertainty analysis of gamma detector

Joost M Verburg; Helen A Shih; Joao Seco

2012-01-01

396

Hand-Held Gamma-Ray Imaging Sensors Using Room-Temperature 3-Dimensional Position-Sensitive Semiconductor Spectrometers  

NASA Astrophysics Data System (ADS)

This paper demonstrates the capability of compact gamma-ray imaging devices using 3-dimensional position sensitive CdZnTe semiconductor gamma-ray spectrometers, developed at the University of Michigan. A prototype imager was constructed and tested using two 1 cm cube 3-dimensional position sensitive CdZnTe detectors. Energy resolutions of 1.5% FWHM for single pixel events at 662 keV gamma-ray energy were obtained on both detectors, and an angular resolution of about 5° FWHM was demonstrated. The capabilities of proposed devices, which can cover a wider energy range up to 2.6 MeV, are discussed.

He, Zhong; Lehner, Carolyn; Zhang, Feng; Wehe, David K.; Knoll, Glenn F.; Berry, James; Du, Yanfeng

2002-10-01

397

X-ray and Gamma-ray Polarimetry of GRBs  

NASA Astrophysics Data System (ADS)

Polarimetry is expected to play a major role as a diagnostic tool for GRBs. Techniques and methods for X/Gamma ray polarimetry are reviewed including the specific problems related to the transient nature of the sources. Optical data do not encourage optimistic predictions on polarimetry of afterglows. I review some of the existing and proposed experiments for the prompt and discuss the existing results.

Costa, E.

2013-07-01

398

CdZnTe gamma ray spectrometer for orbital gamma ray spectroscopy.  

SciTech Connect

We present the design and analysis of a new gamma ray spectrometer for planetary science that uses an array of CdZnTe detectors to achieve the detection efficiency needed for orbital measurements. The use of CdZnTe will provide significantly improved pulse height resolution relative to scintillation-based detectors, with commensurate improvement in the accuracy of elemental abundances determined by gamma ray and neutron spectroscopy. The spectrometer can be flown either on the instrument deck of the spacecraft or on a boom. For deck-mounted systems, a BGO anticoincidence shield is included in the design to suppress the response of the CdZnTe detector to gamma rays that originate in the spacecraft. The BGO shield also serves as a backup spectrometer, providing heritage from earlier planetary science missions and reducing the risk associated with the implementation of new technology.

Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Fuller, K. R. (Kenneth R.); Storms, S. A. (Steven A.); Soldner, S. A.; Lawrence, David J. (David Jeffery),; Browne, M. C. (Michael C.); Moss, C. E. (Calvin E.)

2001-01-01

399

Fundamental Physics with GEV Gamma Rays  

NASA Astrophysics Data System (ADS)

Can we learn about New Physics with astronomical and astro-particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental nature of dark matter. Rapid progress may be within grasp in the context of an approach which combines information from high-energy particle physics with cosmic-ray and traditional astronomical data. I discuss how modifications to the pair annihilation cross section of dark matter with enhanced rates at low relative velocities can lead to a burst of annihilation in the first dark matter halos. I then introduce a novel approach to particle dark matter searches based on the complementarity of astronomical observations across the electromagnetic spectrum, from radio to X-ray and to gamma-ray frequencies.

Profumo, S.

2010-12-01

400

Gamma-ray burst theory after Swift.  

PubMed

Afterglow observations in the pre-Swift era confirmed to a large extend the relativistic blast wave model for gamma-ray bursts (GRBs). Together with the observations of properties of host galaxies and the association with (type Ic) SNe, this has led to the generally accepted collapsar origin of long GRBs. However, most of the afterglow data was collected hours after the burst. The X-ray telescope and the UV/optical telescope onboard Swift are able to slew to the direction of a burst in real time and record the early broadband afterglow light curves. These observations, and in particular the X-ray observations, resulted in many surprises. While we have anticipated a smooth transition from the prompt emission to the afterglow, many observed that early light curves are drastically different. We review here how these observations are changing our understanding of GRBs. PMID:17293324

Piran, Tsvi; Fan, Yi-Zhong

2007-05-15

401

The characteristics of the prompt gamma-rays and early X-ray afterglows of gamma-ray bursts  

Microsoft Academic Search

After the successful launch of NASA's dedicated gamma-ray burst (GRB) mission, Swift, very early X-ray afterglow data for a large sample of GRBs have been recorded by the on board X-ray Telescope (XRT). The data show that the early X-ray afterglow light curves of some GRBs have a shallow decay component, but some have not. The physics mechanisms of this

Y. Q. Lin

2007-01-01

402

Gamma-ray detectors for breast imaging  

NASA Astrophysics Data System (ADS)

Breast cancer is the most common cancer of American women and is the leading cause of cancer-related death among women aged 15 - 54; however recent years have shown that early detection using x-ray mammography can lead to a high probability of cure. However, because of mammography's low positive predictive value, surgical or core biopsy is typically required for diagnosis. In addition, the low radiographic contrast of many nonpalpable breast masses, particularly among women with radiographically dense breasts, results in an overall rate of 10% to 25% for missed tumors. Nuclear imaging of the breast using single gamma emitters (scintimammography) such as (superscript 99m)Tc, or positron emitters such as F-18- fluorodeoxyglucose (FDG) for positron emission tomography (PET), can provide information on functional or metabolic tumor activity that is complementary to the structural information of x-ray mammography, thereby potentially reducing the number of unnecessary biopsies and missed cancers. This paper summarizes recent data on the efficacy of scintimammography using conventional gamma cameras, and describes the development of dedicated detectors for gamma emission breast imaging. The detectors use new, high density crystal scintillators and large area position sensitive photomultiplier tubes (PSPMTs). Detector design, imaging requirements, and preliminary measured imaging performance are discussed.

Williams, Mark B.; Goode, Allen R.; Majewski, Stan; Steinbach, Daniela; Weisenberger, Andrew G.; Wojcik, Randolph F.; Farzanpay, Farzin

1997-07-01

403

PRECISE {gamma}-RAY TIMING AND RADIO OBSERVATIONS OF 17 FERMI {gamma}-RAY PULSARS  

SciTech Connect

We present precise phase-connected pulse timing solutions for 16 {gamma}-ray-selected pulsars recently discovered using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope plus one very faint radio pulsar (PSR J1124-5916) that is more effectively timed with the LAT. We describe the analysis techniques including a maximum likelihood method for determining pulse times of arrival from unbinned photon data. A major result of this work is improved position determinations, which are crucial for multiwavelength follow-up. For most of the pulsars, we overlay the timing localizations on X-ray images from Swift and describe the status of X-ray counterpart associations. We report glitches measured in PSRs J0007+7303, J1124-5916, and J1813-1246. We analyze a new 20 ks Chandra ACIS observation of PSR J0633+0632 that reveals an arcminute-scale X-ray nebula extending to the south of the pulsar. We were also able to precisely localize the X-ray point source counterpart to the pulsar and find a spectrum that can be described by an absorbed blackbody or neutron star atmosphere with a hard power-law component. Another Chandra ACIS image of PSR J1732-3131 reveals a faint X-ray point source at a location consistent with the timing position of the pulsar. Finally, we present a compilation of new and archival searches for radio pulsations from each of the {gamma}-ray-selected pulsars as well as a new Parkes radio observation of PSR J1124-5916 to establish the {gamma}-ray to radio phase offset.

Ray, P. S.; Wolff, M. T.; Grove, J. E.; Gwon, C. [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States); Kerr, M. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Parent, D.; Makeev, A. [Center of Earth Observation and Space Research, College of Science, George Mason University, Fairfax, VA 22030 (United States); Abdo, A. A. [National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001 (United States); Guillemot, L.; Freire, P. C. C.; Kramer, M. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany); Ransom, S. M. [National Radio Astronomy Observatory (NRAO), Charlottesville, VA 22903 (United States); Rea, N. [Institut de Ciencies de l'Espai (IEEC-CSIC), Campus UAB, 08193 Barcelona (Spain); Roberts, M. S. E. [Eureka Scientific, Oakland, CA 94602 (United States); Camilo, F. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Dormody, M. [Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Harding, A. K. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Johnston, S.; Keith, M. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, Epping, NSW 1710 (Australia); Michelson, P. F., E-mail: Paul.Ray@nrl.navy.mil [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)

2011-06-01

404

DETECTION OF VHE {gamma}-RAYS FROM HESS J0632+057 DURING THE 2011 FEBRUARY X-RAY OUTBURST WITH THE MAGIC TELESCOPES  

SciTech Connect

The very high energy (VHE) {gamma}-ray source HESS J0632+057 has recently been confirmed to be a {gamma}-ray binary. The optical counterpart is the Be star MWC 148, and a compact object of unknown nature orbits it every {approx}321 days with a high eccentricity of {approx}0.8. We monitored HESS J0632+057 with the stereoscopic MAGIC telescopes from 2010 October to 2011 March and detected significant VHE {gamma}-ray emission during 2011 February, when the system exhibited an X-ray outburst. We find no {gamma}-ray signal in the other observation periods when the system did not show increased X-ray flux. Thus, HESS J0632+057 exhibits {gamma}-ray variability on timescales of the order of one to two months possibly linked to the X-ray outburst that takes place about 100 days after the periastron passage. Furthermore, our measurements provide for the first time the {gamma}-ray spectrum down to about 140 GeV and indicate no turnover of the spectrum at low energies. We compare the properties of HESS J0632+057 with the similar {gamma}-ray binary LS I +61 Degree-Sign 303 and discuss the possible origin of the multi-wavelength emission of the source.

Aleksic, J.; Blanch, O. [IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra (Spain); Alvarez, E. A.; Asensio, M.; Barrio, J. A. [Grupo de Fisica Altas Energias, Universidad Complutense, E-28040 Madrid (Spain); Antonelli, L. A.; Bonnoli, G. [INAF National Institute for Astrophysics, I-00136 Rome (Italy); Antoranz, P. [Dipartimento di Fisica, Universita di Siena and INFN Pisa, I-53100 Siena (Italy); Backes, M. [Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Barres de Almeida, U.; Bock, R. K.; Borla Tridon, D. [Max-Planck-Institut fuer Physik, D-80805 Muenchen (Germany); Bastieri, D. [Dipartimento di Fisica, Universita di Padova and INFN, I-35131 Padova (Italy); Becerra Gonzalez, J.; Berger, K. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Bednarek, W. [Department of Astrophysics, University of Lodz, PL-90236 Lodz (Poland); Bernardini, E. [Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen (Germany); Biland, A.; Boller, A. [ETH Zurich, CH-8093 Zurich (Switzerland); Bosch-Ramon, V., E-mail: jogler@slac.stanford.edu, E-mail: pmunar@am.ub.es [Facultat de Fisica, Universitat de Barcelona (ICC/IEEC), E-08028 Barcelona (Spain); and others

2012-07-20

405

Very high energy gamma ray astrophysics  

SciTech Connect

The second reflector (project GRANITE) is on schedule. At present (January 1992) it and the 10 m reflector are obtaining stereoscopic views of gamma-ray air showers from the Crab Nebula which verify the expected performance of the twin reflector telescopes. With the additional improvements of the upgrade (a pending DOE proposal) the twin reflectors should reach a limiting intensity of 1% that of the Crab. The astonishing early results from the EGRET detector aboard the Compton Gamma Ray Observatory indicate that distant quasars (powered by supermassive black holes) are active at GeV energies. The Whipple instruments are poised to see if such behavior continues above 100 GeV, as well as perform sensitive observations of previously reported GeV (Geminga) and TeV (Hercules X-1, etc.) sources. In addition to observing sources and identifying their location in the sky to one arcminute, experiments are planned to search for WIMPS in the mass range 0.1 to 1 TeV, and to determine the abundance of anti-protons in the cosmic rays. The successful performance of the stereoscopic reflectors demonstrates the feasibility of the concept of arrays of Cherenkov receivers. Design studies for a much larger array (CASITA) are just beginning.

Lamb, R.C.; Lewis, D.A.

1992-02-01

406

Population III Gamma-Ray Burst  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs) are unique probes of the first generation (Pop III) stars. We show that a relativistic gamma-ray burst (GRB) jet can potentially pierce the envelope of a very massive Pop III star even if the Pop III star has a supergiant hydrogen envelope without mass loss, thanks to the long-lived powerful accretion of the envelope itself. While the Pop III GRB is estimated to be energetic (E ?,iso ~ 1055 erg), the supergiant envelope hides the initial bright phase in the cocoon component, leading to a GRB with a long duration ~1000 (1 + z) s and an ordinary isotropic luminosity ~ 1052 erg s-1 (~ 10-9 erg cm-2 s-1 at redshift z ~ 20), although these quantities are found to be sensitive to the core and envelope mass. We also show that Pop III.2 GRBs (which are primordial but affected by radiation from other stars) occur >100 times more frequently than Pop III.1 GRBs, and thus should be suitable targets for future X-ray and radio missions. The radio transient surveys are already constraining the Pop III GRB rate and promising in the future.

Ioka, Kunihito; Suwa, Yudai; Nagakura, Hiroki; de Souza, Rafael S.; Yoshida, Naoki

2012-09-01

407

Determination of intergalactic magnetic fields from gamma ray data  

Microsoft Academic Search

We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and cosmic rays, the observed spectra are not sensitive to the intrinsic spectrum of the source, because, for a distant blazar, secondary photons produced along

Warren Essey; Shin’ichiro Ando; Alexander Kusenko

2011-01-01

408

Science with the new generation high energy gamma- ray experiments  

Microsoft Academic Search

This Conference is the fifth of a series of Workshops on High Energy Gamma- ray Experiments, following the Conferences held in Perugia 2003, Bari 2004, Cividale del Friuli 2005, Elba Island 2006. This year the focus was on the use of gamma-ray to study the Dark Matter component of the Universe, the origin and propagation of Cosmic Rays, Extra Large

M. Alvarez; D. D'Armiento; G. Agnetta; A. Alberdi; A. Antonelli; A. Argan; P. Assis; E. A. Baltz; C. Bambi; G. Barbiellini; H. Bartko; M. Basset; D. Bastieri; P. Belli; G. Benford; L. Bergstrom; R. Bernabei; G. Bertone; A. Biland; B. Biondo; F. Bocchino; E. Branchini; M. Brigida; T. Bringmann; P. Brogueira; A. Bulgarelli; J. A. Caballero; G. A. Caliandro; P. Camarri; F. Cappella; P. Caraveo; R. Carbone; M. Carvajal; S. Casanova; A. J. Castro-Tirado; O. Catalano; R. Catena; F. Celi; A. Celotti; R. Cerulli; A. Chen; R. Clay; V. Cocco; J. Conrad; E. Costa; A. Cuoco; G. Cusumano; C. J. Dai; B. Dawson; B. De Lotto; G. De Paris; A. de Ugarte Postigo; E. Del Monte; C. Delgado; A. Di Ciaccio; G. Di Cocco; S. Di Falco; G. Di Persio; B. L. Dingus; A. Dominguez; F. Donato; I. Donnarumma; M. Doro; J. Edsjo; J. M. Espino Navas; M. C. Espirito Santo; Y. Evangelista; C. Evoli; D. Fargion; C. Favuzzi; M. Feroci; M. Fiorini; L. Foggetta; N. Fornengo; T. Froysland; M. Frutti; F. Fuschino; J. L. Gomez; M. Gomez; D. Gaggero; N. Galante; M. I. Gallardo; M. Galli; J. E. Garcia; M. Garczarczyk; F. Gargano; M. Gaug; F. Gianotti; S. Giarrusso; B. Giebels; N. Giglietto; P. Giommi; F. Giordano; A. Giuliani; J. Glicenstein; P. Goncalves; D. Grasso; M. Guerriero; H. L. He; A. Incicchitti; J. Kirk; H. H. Kuang; A. La Barbera; G. La Rosa; C. Labanti; G. Lamanna; I. Lapshov; F. Lazzarotto; S. Liberati; F. Liello; P. Lipari; F. Longo; F. Loparco; M. Lozano; P. G. Lucentini De Sanctis; J. M. Ma; M. C. Maccarone; L. Maccione; V. Malvezzi; A. Mangano; M. Mariotti; M. Marisaldi; I. Martel; A. Masiero; E. Massaro; M. Mastropietro; E. Mattaini; F. Mauri; M. N. Mazziotta; S. Mereghetti; T. Mineo; S. Mizobuchi; A. Moiseev; M. Moles; C. Monte; F. Montecchia; E. Morelli; A. Morselli; I. Moskalenko; F. Nozzoli; J. F. Ormes; M. A. Peres-Torres; L. Pacciani; A. Pellizzoni; F. Perez-Bernal; F. Perotti; P. Picozza; L. Pieri; M. Pietroni; M. Pimenta; A. Pina; C. Pittori; C. Pontoni; G. Porrovecchio; F. Prada; M. Prest; D. Prosperi; R. Protheroe; G. Pucella; J. M. Quesada; J. M. Quintana; J. R. Quintero; S. Raino; M. Rapisarda; M. Rissi; J. Rodriguez; E. Rossi; G. Rowell; A. Rubini; F. Russo; M. Sanchez-Conde; B. Sacco; V. Scapin; M. Schelke; A. Segreto; A. Sellerholm; X. D. Sheng; A. Smith; P. Soffitta; R. Sparvoli; P. Spinelli; V. Stamatescu; L. S. Stark; M. Tavani; G. Thornton; L. G. Titarchuk; B. Tome; A. Traci; M. Trifoglio; A. Trois; P. Vallania; E. Vallazza; S. Vercellone; S. Vernetto; V. Vitale; N. Wild; Z. P. Ye; A. Zambra; F. Zandanel; D. Zanello

2007-01-01

409

The measurement of gamma ray induced heating in a mixed neutron and gamma ray environment  

SciTech Connect

The problem of measuring the gamma heating in a mixed DT neutron and gamma ray environment was explored. A new detector technique was developed to make this measurement. Gamma heating measurements were made in a low-Z assembly irradiated with 14-Mev neutrons and (n, n{prime}) gammas produced by a Texas Nuclear Model 9400 neutron generator. Heating measurements were made in the mid-line of the lattice using a proportional counter operating in the Continuously-varied Bias-voltage Acquisition mode. The neutron-induced signal was separated from the gamma-induced signal by exploiting the signal rise-time differences inherent to radiations of different linear energy transfer coefficient, which are observable in a proportional counter. The operating limits of this measurement technique were explored by varying the counter position in the low-Z lattice, hence changing the irradiation spectrum observed. The experiment was modelled numerically to help interpret the measured results. The transport of neutrons and gamma rays in the assembly was modelled using the one- dimensional radiation transport code ANISN/PC. The cross-section set used for these calculations was derived from the ENDF/B-V library using the code MC{sup 2}-2 for the case of DT neutrons slowing down in a low-Z material. The calculated neutron and gamma spectra in the slab and the relevant mass-stopping powers were used to construct weighting factors which relate the energy deposition in the counter fill-gas to that in the counter wall and in the surrounding material. The gamma energy deposition at various positions in the lattice is estimated by applying these weighting factors to the measured gamma energy deposition in the counter at those locations.

Chiu, H.K.

1991-10-01

410

The observation of gamma ray bursts and terrestrial gamma-ray flashes with AGILE  

Microsoft Academic Search

Since its early phases of operation, the AGILE mission is successfully observing Gamma Ray Bursts (GRBs) in the hard X-ray band with the SuperAGILE imager and in the MeV range with the Mini-Calorimeter. Up to now, three firm GRB detections were obtained above 25MeV and some bursts were detected with lower statistical confidence in the same energy band. When a

E. Del Monte; G. Barbiellini; F. Fuschino; A. Giuliani; F. Longo; M. Marisaldi; S. Mereghetti; E. Moretti; M. Trifoglio; G. Vianello; E. Costa; I. Donnarumma; Y. Evangelista; M. Feroci; M. Gallil; I. Lapshov; F. Lazzarotto; P. Lipari; L. Pacciani; M. Rapisarda; P. Soffitta; M. Tavani; S. Vercellone; S. Cutini; F. Boffelli; A. Bulgarelli; P. Caraveo; P. W. Cattaneo; A. Chen; G. Di Cocco; F. Gianotti; C. Labanti; A. Morselli; A. Pellizzoni; F. Perotti; G. Piano; P. Picozza; M. Pilia; M. Prest; G. Pucella; A. Rappoldi; S. Sabatini; E. Striani; A. Trois; E. Vallazza; V. Vittorini; L. A. Antonelli; C. Pittori; B. Preger; P. Santolamazza; F. Verrecchia; P. Giommi; L. Salotti

2011-01-01

411

Conservative constraints on dark matter annihilation into gamma rays  

Microsoft Academic Search

Using gamma-ray data from observations of the Milky Way, Andromeda (M31), and\\u000athe cosmic background, we calculate conservative upper limits on the dark\\u000amatter self-annihilation cross section to monoenergetic gamma rays, _{gamma gamma}, over a wide range of dark matter masses. (In fact, over most\\u000aof this range, our results are unchanged if one considers just the branching\\u000aratio

Gregory D. Mack; Thomas D. Jacques; John F. Beacom; Nicole F. Bell; Hasan Yüksel

2008-01-01

412

GRAPE - A Balloon-Borne Gamma-Ray Polarimeter Experiment  

Microsoft Academic Search

This paper reviews the development status of GRAPE (the Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X-rays in the 50–300 keV energy range. We are particularly interested in X-rays that are emitted from solar flares and gamma-ray bursts (GRBs), although GRAPE could also be employed in the study

P. F. Bloser; J. S. Legere; J. R. Macri; M. L. McConnell; T. Narita; J. M. Ryan

2006-01-01

413

GRAPE - A Balloon-Borne Gamma-Ray Polarimeter Experiment  

Microsoft Academic Search

This paper reviews the development status of GRAPE (the Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X-rays in the 50 300 keV energy range. We are particularly interested in X-rays that are emitted from solar flares and gamma-ray bursts (GRBs), although GRAPE could also be employed in the

P. F. Bloser; J. S. Legere; J. R. Macri; M. L. McConnell; T. Narita; J. M. Ryan

2006-01-01

414

High-spin gamma-ray spectroscopy  

SciTech Connect

Nuclei can carry angular momentum by single-particle alignments and by collective motion, as has been well illustrated in discrete-line spectroscopy. From continuum ..gamma..-ray studies in still higher spin regions, it appears that these modes both continue. In favorable cases in rare-earth nuclei, particle alignments from the valence shell separate from proton alignments from the next higher shell. A new generation of Compton-suppressed Ge detector arrays will greatly enhance high-spin studies, both continuum and discrete-line. 17 references.

Diamond, R.M.

1984-03-01

415

Gamma Ray Bursts In Their Historic Context  

NASA Astrophysics Data System (ADS)

Gamma ray bursts remained essentially non-understood or misunderstood from their 1973 discovery (not, I will claim, ``serendipitous'') to the first, 1997, redshift. This is by no means a record. The poster explored some of the examples of longer-standing puzzles and the after-dinner talk some of the details of the GRB case. The most striking feature of the GRB history is probably the unanimity with which ``all we, like sheep, went astray,'' which followed the epoch of ``we have turned everyone to his own way.'' Some of the reasons for this, the range of hypotheses, and how GRBs were presented to the astronomical and larger communities are discussed.

Trimble, Virginia

2004-09-01

416

Gamma rays and matter-antimatter asymmetry.  

NASA Astrophysics Data System (ADS)

It is commonly asserted that although there is a marked asymmetry of matter and antimatter on all scales up to and including clusters of galaxies, on the supercluster scale there could indeed be symmetry, the ensuing annihilation gamma rays being of lower intensity than those observed. The authors argue here that this is not so after making a detailed examination of the manner in which such a supercluster, antisupercluster geometry could be present and allowing for factors which appear not to have been previously considered.

Dudarewicz, A.; Wolfendale, A. W.

417

Material recognition using fission gamma rays  

NASA Astrophysics Data System (ADS)

Material recognition is studied by measuring the transmission spectrum of 252Cf fission gamma rays in the energy range E?=0.1-5.5 MeV for 0.1-MeV-wide energy bins through a number of elementary samples. Each transmitted spectrum is compared with a library of reference spectra for different elements providing the possibility of material identification. In case of elemental samples with known thickness, this procedure allows the identification of the sample Z with uncertainty typically lower than 3 Z-units over a wide range of elements. Applications to composite materials are also reported.

Viesti, G.; Sajo-Bohus, L.; Fabris, D.; Lunardon, M.; Moretto, S.; Nebbia, G.; Pesente, S.

2009-07-01

418

Fermi gamma-ray imaging of a radio galaxy.  

PubMed

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. PMID:20360067

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; Rainň, 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; Sgrň, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, ?; 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

2010-04-01

419

Superluminal blazars and the extragalactic gamma ray background.  

NASA Astrophysics Data System (ADS)

The detection of a few dozen extragalactic gamma ray blazars of extremely high luminosity by the EGRET instrument on board the Compton Gamma Ray Observatory appears to suggest that blazars make the overwhelming contribution to the cosmic gamma ray background in the energy range 100 MeV - 10 GeV. The authors point out that the superluminal effect which boosts and beams the gamma ray emission in the jets of blazars will flatten the source count in the low flux part. Consequently, the unresolved blazars would not be expected to make much contribution to the gamma ray background. From their direct modelling of the source count, they conclude that the contribution of the unresolved blazars to the gamma ray background is only 10% of the latest estimate of the EGRET data. The implication for the cosmological evolution of the blazars is discussed.

Xinyu, Chi; Young, E. C. M.

1997-07-01

420

Superluminal blazars and the extragalactic gamma ray background  

NASA Astrophysics Data System (ADS)

The detection of a few dozen extragalactic gamma ray blazars of extremely high luminosity by the EGRET instrument on board the Compton Gamma Ray Observatory appears to suggest that blazars make the overwhelming contribution to the cosmic gamma ray background in the energy range 100 MeV - 10 GeV. In this paper we point out that the superluminal effect which boosts and beams the gamma ray emission in the jets of blazars will flatten the source count in the low flux part. Consequently, the unresolved blazars would not be expected to make much contribution to the gamma ray background. From our direct modelling of the source count, we conclude that the contribution of the unresolved blazars to the gamma ray background is only 10% of the latest estimate of the EGRET data. The implication for the cosmological evolution of the blazars is discussed.

Chi, Xinyu; Young, Enoch C. M.

1997-07-01

421

Multiwavelength observations of Gamma-Ray Bright Blazars  

NASA Astrophysics Data System (ADS)

We have investigated total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. The blazars with faster apparent speeds, 3C 273, 3C 279, PKS 1510-089, and 3C 66A, exhibit stronger variability of the gamma-ray emission with higher flux density. Only blazars with faster apparent speeds show simultaneous optical and gamma-ray brightness variations during the flares. Our results are consisted with models in which the gamma-ray emission arises in high-relativistic jets.

Morozova, D. A.; Troitskiy, I. S.

2012-05-01

422

Gamma-ray burst data from DMSP satellites  

SciTech Connect

A number of gamma-ray bursts have been detected by means of gamma-ray detectors aboard three Air Force Defense Meteorological Satellite Program (DMSP) satellites, in polar orbits at 800 km altitude. The gamma-ray data have a 2-second resolving time, and are usually telemetered in 5 energy bins in the range 50--1000 keV. Although it is not possible to detect gamma-ray bursts when the DMSP satellites are passing through the radiation belt or the South Atlantic Anomaly, or when the source is obscured by the Earth, a number of gamma-ray bursts have been detected by two or even three of the satellites. The DMSP data may be of considerable, assistance in evaluating time histories, locations, and spectra of gamma-ray bursts.

Terrell, J.; Klebesadel, R.W.; Lee, P. [Los Alamos National Lab., NM (United States); Griffee, J.W. [Sandia National Labs., Albuquerque, NM (United States)

1991-12-31

423

Gamma-ray burst data from DMSP satellites  

SciTech Connect

A number of gamma-ray bursts have been detected by means of gamma-ray detectors aboard three Air Force Defense Meteorological Satellite Program (DMSP) satellites, in polar orbits at 800 km altitude. The gamma-ray data have a 2-second resolving time, and are usually telemetered in 5 energy bins in the range 50--1000 keV. Although it is not possible to detect gamma-ray bursts when the DMSP satellites are passing through the radiation belt or the South Atlantic Anomaly, or when the source is obscured by the Earth, a number of gamma-ray bursts have been detected by two or even three of the satellites. The DMSP data may be of considerable, assistance in evaluating time histories, locations, and spectra of gamma-ray bursts.

Terrell, J.; Klebesadel, R.W.; Lee, P. (Los Alamos National Lab., NM (United States)); Griffee, J.W. (Sandia National Labs., Albuquerque, NM (United States))

1991-01-01

424

Swift pointing and the association between gamma-ray bursts and gravitational wave bursts  

Microsoft Academic Search

It is widely believed that gamma-ray bursts originate in\\u000a\\u0009\\u0009 relativistic fireballs produced by the merger or collapse\\u000a\\u0009\\u0009 of solar-mass compact objects. Gravitational waves should\\u000a\\u0009\\u0009 be associated with these violent, relativistic events, and\\u000a\\u0009\\u0009 their detection may shed light on the nature of the inner\\u000a\\u0009\\u0009 engine that powers the gamma-ray burst. Doing this requires\\u000a\\u0009\\u0009 joint observations of gamma-ray burst events with\\u000a\\u0009\\u0009 gravitational

Lee Samuel Finn; Badri Krishnan; Patrick J. Sutton

2004-01-01

425

Fast variability of tera-electron volt gamma rays from the radio galaxy M87.  

PubMed

The detection of fast variations of the tera-electron volt (TeV) (10(12) eV) gamma-ray flux, on time scales of days, from the nearby radio galaxy M87 is reported. These variations are about 10 times as fast as those observed in any other wave band and imply a very compact emission region with a dimension similar to the Schwarzschild radius of the central black hole. We thus can exclude several other sites and processes of the gamma-ray production. The observations confirm that TeV gamma rays are emitted by extragalactic sources other than blazars, where jets are not relativistically beamed toward the observer. PMID:17068224

Aharonian, F; Akhperjanian, A G; Bazer-Bachi, A R; Beilicke, M; Benbow, W; Berge, D; Bernlöhr, K; Boisson, C; Bolz, O; Borrel, V; Braun, I; Brown, A M; Bühler, R; Büsching, I; Carrigan, S; Chadwick, P M; Chounet, L-M; Coignet, G; Cornils, R; Costamante, L; Degrange, B; Dickinson, H J; Djannati-Ataď, A; Drury, L O'c; Dubus, G; Egberts, K; Emmanoulopoulos, D; Espigat, P; Feinstein, F; Ferrero, E; Fiasson, A; Fontaine, G; Funk, Seb; Funk, S; Füssling, M; Gallant, Y A; Giebels, B; Glicenstein, J F; Goret, P; Hadjichristidis, C; Hauser, D; Hauser, M; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Holleran, M; Hoppe, S; Horns, D; Jacholkowska, A; de Jager, O C; Kendziorra, E; Kerschhaggl, M; Khélifi, B; Komin, Nu; Konopelko, A; Kosack, K; Lamanna, G; Latham, I J; Le Gallou, R; Lemičre, A; Lemoine-Goumard, M; Lenain, J-P; Lohse, T; Martin, J M; Martineau-Huynh, O; Marcowith, A; Masterson, C; Maurin, G; McComb, T J L; Moulin, E; de Naurois, M; Nedbal, D; Nolan, S J; Noutsos, A; Orford, K J; Osborne, J L; Ouchrif, M; Panter, M; Pelletier, G; Pita, S; Pühlhofer, G; Punch, M; Ranchon, S; Raubenheimer, B C; Raue, M; Rayner, S M; Reimer, A; Ripken, J; Rob, L; Rolland, L; Rosier-Lees, S; Rowell, G; Sahakian, V; Santangelo, A; Saugé, L; Schlenker, S; Schlickeiser, R; Schröder, R; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sol, H; Spangler, D; Spanier, F; Steenkamp, R; Stegmann, C; Superina, G; Tam, P H; Tavernet, J-P; Terrier, R; Tluczykont, M; van Eldik, C; Vasileiadis, G; Venter, C; Vialle, J P; Vincent, P; Völk, H J; Wagner, S J; Ward, M

2006-10-26

426

High Energy Gamma-Ray Emission from Gamma-Ray Bursts - Before GLAST  

SciTech Connect

Gamma-ray bursts (GRBs) are short and intense emission of soft {gamma}-rays, which have fascinated astronomers and astrophysicists since their unexpected discovery in 1960s. The X-ray/optical/radio afterglow observations confirm the cosmological origin of GRBs, support the fireball model, and imply a long-activity of the central engine. The high-energy {gamma}-ray emission (> 20 MeV) from GRBs is particularly important because they shed some lights on the radiation mechanisms and can help us to constrain the physical processes giving rise to the early afterglows. In this work, we review observational and theoretical studies of the high-energy emission from GRBs. Special attention is given to the expected high-energy emission signatures accompanying the canonical early-time X-ray afterglow that was observed by the Swift X-ray Telescope. We also discuss the detection prospect of the upcoming GLAST satellite and the current ground-based Cerenkov detectors.

Fan, Yi-Zhong; Piran, Tsvi

2011-11-29

427

High energy gamma-rays from Cygnus X-3  

NASA Astrophysics Data System (ADS)

The maximum entropy method of image analysis has been improved and applied to high-energy gamma-rays from Cygnus X-3 during three periods when the X-ray emission was high. The results show that the 2-12 keV X-rays and 150-5000 MeV gamma rays from Cyg X-3 are negatively correlated. A clear gamma-ray image of Cyg-X-3 can be obtained between June 1977 and June 1980, when the X-ray emission was low. A flux of about 10 to the - 6th/sq cm/s was obtained.

Li, Tipei; Wu, Mei

1989-12-01

428

Propagation of gamma-rays at cosmological redshifts  

Microsoft Academic Search

We discuss absorption and reprocessing of gamma-rays at cosmological redshifts. We consider Compton scattering and pair production by gamma-rays on the cosmic baryonic matter, and photon-photon scattering and photon-photon pair production by gamma-rays and Compton scattering of relativistic pairs on the cosmic blackbody background. We point out the cosmological importance of photon-photon scattering (a process not previously considered in astrophysics).

Andrzej A. Zdziarski; Roland Svensson

1989-01-01

429

Gamma ray polarimetry using a position sensitive germanium detector  

Microsoft Academic Search

Imaging gamma-ray detectors make sensitive polarimeters in the Compton energy regime by measuring the scatter direction of gamma rays. The principle is to capitalize on the angular dependence of the Compton scattering cross section to polarized gamma rays and measure the distribution of scatter directions within the detector. This technique is effective in a double-sided germanium detector between roughly 50keV

R. A Kroeger; W. N Johnson; J. D Kurfess; B. F Phlips

1999-01-01

430

Neutron-Capture gamma Rays from Various Elements  

Microsoft Academic Search

Neutron-capture gamma-ray spectra have been measured in the energy range 0.3 to 3 Mev by means of a two-crystal Compton scintillation spectrometer. The efficiency of the instrument as a function of energy was determined experimentally. The uniqueness of the 2.23-Mev gamma ray following capture of a neutron by hydrogen has been confirmed, and this gamma ray was used as a

T. H. Braid

1956-01-01

431

Gamma Ray Bursts: Explaining the Universe's Biggest Bangs  

NSDL National Science Digital Library

This radio broadcast discusses research into gamma ray bursts, the largest explosions in the universe. Topics include the SWIFT satellite mission and discoveries; the immense energy output of a gamma ray burst, and the causes of long and short gamma ray bursts (long bursts caused by core collapse into a black hole, and the short bursts from binary stellar system mergers, such as a neutron star colliding with a black hole). The broadcast is 28 minutes and 50 seconds in length.

432

Analysis of fissionable material using delayed gamma rays from photofission  

Microsoft Academic Search

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched 235U, natural uranium, and 93% enriched 239Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four

C. L. Hollas; D. A. Close; C. E. Moss

1987-01-01

433

The Solar Maximum Mission Atlas of Gamma?Ray Flares  

Microsoft Academic Search

We present a compilation of data for all 258 gamma-ray —ares detected above 300 keV by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission satellite. This gamma-ray —are sample was collected during the period from 1980 February to 1989 November; covering the latter half of the 21st solar sunspot cycle and the onset of the 22d solar sunspot

W. Thomas Vestrand; Gerald H. Share; Ronald J. Murphy; David J. Forrest; Erich Rieger; Edward L. Chupp; Gottfried Kanbach

1999-01-01

434

VHE gamma rays from PSR B1706-44  

Microsoft Academic Search

Observations made with the University of Durham Mark 6 atmospheric Cerenkov telescope confirm that PSR B1706-44 is a VHE gamma-ray emitter. The gamma-ray flux has been measured at 250 GeV, and suggests a spectral slope that is consistent with extrapolation from the sub-10 GeV region. There is no indication from our dataset that the VHE gamma-rays are pulsed, in contrast

P. M. Chadwick; M. R. Dickinson; N. A. Dipper; J. Holder; T. R. Kendall; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; I. D. Roberts; S. E. Shaw; K. E. Turver

1997-01-01

435

The Uuniversity of Durham Mark 6 Gamma Ray Telescope  

Microsoft Academic Search

The design, construction and operation of the University of Durham\\u000aground-based gamma ray telescope is discussed. The telescope has been designed\\u000ato detect gamma rays in the < 200 GeV region and to achieve good discrimination\\u000abetween gamma ray and hadron initiated showers in the higher energy region (>\\u000a300 GeV). The telescope was commissioned in 1995 and a description

P. Armstrong; P. M. Chadwick; P. J. Cottle; J. E. Dickinson; M. R. Dickinson; N. A. Dipper; S. E. Hilton; W. Hogg; J. Holder; T. R. Kendall; T. J. L. McComb; C. M. Moore; K. J. Orford; S. M. Rayner; I. D. Roberts; M. D. Roberts; M. Robertshaw; S. E. Shaw; K. Tindale; S. P. Tummey; K. E. Turver

1998-01-01

436

Iron and cadmium capture gamma-ray photofission measurements  

Microsoft Academic Search

Photofission measurements have been made in ²³⁸U, ²³²Th, and ²³⁡Np in iron and cadmium capture gamma-ray spectra in cylindrical neutron-driven gamma-ray sources in the thermal column of the National Bureau of Standards (NBS) Reactor. The gamma-ray source strength was measured with neutron activation foils and by direct counting of activations produced in the metal cylinders. Photofission measurements were made with

T. G. Williamson; G. P. Lamaze; D. M. Gilliam; C. M. Eisenhauer

1990-01-01

437

Fermi Discovery of Gamma-ray Emission from NGC 1275  

Microsoft Academic Search

We report the discovery of high-energy (E > 100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope. The positional center of the gamma-ray source is only ≈3' away from the NGC 1275

Aous A. Abdo; M. Ackermann; M. Ajello; K. Asano; L. Baldini; J. Ballet; Guido Barbiellini; Denis Bastieri; B. M. Baughman; K. Bechtol; R. Bellazzini; R. D. Blandford; Elliott D. Bloom; E. Bonamente; A. W. Borgland; J. Bregeon; A. Brez; M. Brigida; P. Bruel; Thompson H. Burnett; G. A. Caliandro; R. A. Cameron; P. A. Caraveo; J. M. Casandjian; E. Cavazzuti; C. Cecchi; A. Celotti; A. Chekhtman; C. C. Cheung; J. Chiang; S. Ciprini; R. Claus; J. Cohen-Tanugi; S. Colafrancesco; L. R. Cominsky; J. Conrad; L. Costamante; C. D. Dermer; A. de Angelis; F. de Palma; S. W. Digel; D. Donato; E. do Couto e Silva; P. S. Drell; R. Dubois; D. Dumora; C. Farnier; C. Favuzzi; J. Finke; W. B. Focke; M. Frailis; Y. Fukazawa; S. Funk; P. Fusco; F. Gargano; M. Georganopoulos; S. Germani; B. Giebels; N. Giglietto; F. Giordano; T. Glanzman; I. A. Grenier; M.-H. Grondin; J. E. Grove; L. Guillemot; S. Guiriec; Y. Hanabata; A. K. Harding; R. C. Hartman; M. Hayashida; E. Hays; R. E. Hughes; G. Jóhannesson; A. S. Johnson; R. P. Johnson; W. N. Johnson; M. Kadler; T. Kamae; Y. Kanai; H. Katagiri; J. Kataoka; N. Kawai; M. Kerr; J. Knödlseder; F. Kuehn; M. Kuss; L. Latronico; M. Lemoine-Goumard; F. Longo; F. Loparco; B. Lott; M. N. Lovellette; P. Lubrano; G. M. Madejski; A. Makeev; M. N. Mazziotta; J. E. McEnery; C. Meurer; P. F. Michelson; W. Mitthumsiri; T. Mizuno; A. A. Moiseev; C. Monte; M. E. Monzani; A. Morselli; I. V. Moskalenko; S. Murgia; T. Nakamori; P. L. Nolan; J. P. Norris; E. Nuss; T. Ohsugi; N. Omodei; E. Orlando; J. F. Ormes; D. Paneque; J. H. Panetta; D. Parent; M. Pepe; M. Pesce-Rollins; F. Piron; T. A. Porter; S. Rainň; M. Razzano; A. Reimer; O. Reimer; T. Reposeur; S. Ritz; A. Y. Rodriguez; R. W. Romani; F. Ryde; H. F.-W. Sadrozinski; R. Sambruna; D. Sanchez; A. Sander; R. Sato; P. M. Saz Parkinson; C. Sgrň; D. A. Smith; P. D. Smith; G. Spandre; P. Spinelli; J.-L. Starck; M. S. Strickman; A. W. Strong; D. J. Suson; H. Tajima; H. Takahashi; T. Takahashi; T. Tanaka; G. B. Taylor; J. G. Thayer; D. J. Thompson; D. F. Torres; G. Tosti; Y. Uchiyama; T. L. Usher; N. Vilchez; V. Vitale; A. P. Waite; K. S. Wood; T. Ylinen; M. Ziegler; H. D. Aller; M. F. Aller; K. I. Kellermann; Y. Y. Kovalev; Yu. A. Kovalev; M. L. Lister; A. B. Pushkarev

2009-01-01

438

Multiwavelength Study of Gamma-Ray Bright Blazars  

Microsoft Academic Search

We investigate total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. We use high-resolution maps obtained by the BU group at 43 GHz with

Daria Morozova; V. M. Larionov; V. A. Hagen-Thorn; S. G. Jorstad; A. P. Marscher; I. S. Troitskii

2011-01-01

439

Nucleonic gamma-ray production in pulsar wind nebulae  

Microsoft Academic Search

Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources.\\u000a Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue\\u000a of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to

D. Horns; F. Aharonian; A. I. D. Hoffmann; A. Santangelo

2007-01-01

440

Simultaneous detection of gamma-ray bundles and air showers  

Microsoft Academic Search

An air shower (EAS) observation system was used with an emulsion chamber, and the correlation between gamma-ray bundles and EAS was studied. It was found that nearly 100% of gamma-ray bundles are accompanied by EAS and about 90% of large EAS with sizes larger than 10 to the 6th power have gamma-ray bundles in their cores. In this experiment a

S. Dake; Y. Hatano; K. Jitsuno; M. Hazama; Y. Nakanishi; K. Nishikawa; M. Sakata; Y. Yamamoto

1979-01-01

441

Evidence for supersymmetric dark matter annihilations into gamma rays  

Microsoft Academic Search

The astrophysical gamma-ray energy spectra measured by balloon-borne emulsion detectors and the Whipple imaging atmospheric Cerenkov telescope are shown to offer possible evidence for the existence of a monoenergetic gamma-ray flux excess over the background centered at 3.5+\\/-0.3 TeV, indicating the annihilation or decay of relic dark matter weakly interacting massive particles. The observed gamma-ray flux is compatible with the

Steven C. Strausz

1997-01-01

442

Probable optical counterpart of a Gamma-ray burster  

Microsoft Academic Search

Sixteen million seconds, or over a half year, of optical monitoring of three Gamma-ray burst positions using the Harvard College Observatory collection of archival plates are described. The probable optical counterpart of the November 19, 1978 Gamma-ray burster has been discovered on a blue emulsion plate exposed in 1928. Optical searches indicate that the absolute magnitude of the Gamma-ray burst

B. E. Schaefer

1981-01-01

443

Prototype TIGRE Compton gamma-ray balloon-borne telescope  

Microsoft Academic Search

A prototype balloon-borne telescope is being constructed for gamma-ray observations in the MeV energy range. The Tracking and Imaging Gamma-Ray Experiment (TIGRE) uses multi-layers of thin silicon detectors to track and measure the energy losses of Compton recoil electrons. When combined with the direction and energy of the Compton scattered gamma-ray a unique incident direction for each photon event is

D. Bhattacharya; T. J. O'Neill; A. Akyüz; J. Samimi; A. D. Zych

2004-01-01

444

Energy spectrum of diffuse component of cosmic soft gamma rays  

Microsoft Academic Search

The new measurements reported take into account gamma rays in the energy range from 0.1 to 4 MeV. A balloon-borne telescope was used in the investigation. The new data are compared with earlier results. The energy spectrum of soft gamma rays is presented in a graph. The approach used in the determination of gamma ray intensity is discussed along with

Y. Fukada; S. Hayakawa; I. Kasahara; F. Makino; Y. Tanakay; B. V. Sreekantan

1975-01-01

445

Wolf-Rayet Stars and Cosmic Gamma-ray Bursts  

Microsoft Academic Search

The observational properties of cosmic gamma-ray bursts and of Wolf-Rayet (WR) stars and their CO cores at the end of their evolution are analyzed. WR stars do not have hydrogen envelopes, facilitating the transformation of the energy of collapse into observable gamma rays. Of the ≈90 well-localized gamma-ray bursts, 21 have optical identifications, of which 16 have measured redshifts (z=0.4

K. A. Postnov; A. M. Cherepashchuk

2001-01-01

446

Supernovae and Gamma-ray Bursts: Flashy and Somber Explosions  

Microsoft Academic Search

We review the observational status of the Supernova\\/Gamma-Ray Burst connection. Several lines of evidence suggest that long duration Gamma-ray Bursts are associated with bright SNe-Ic. However recent observations of GRB 060614 puzzle this scenario, pointing out the existence of long-duration Gamma-ray Burst not accompanied by a bright supernova. An analysis of the association GRB 060218\\/SN 2006aj and X081009\\/SN 2008D finds

Massimo Della Valle

2009-01-01

447

Nuclear criticality as a contributor to gamma ray burst events  

NASA Astrophysics Data System (ADS)

Most gamma ray bursts are able to be explained using supernovae related phenomenon. Some measured results still lack compelling explanations and a contributory cause from nuclear criticality is proposed. This is shown to have general properties consistent with various known gamma ray burst properties. The galactic origin of fast rise exponential decay gamma ray bursts is considered a strong candidate for these types of events.

Hayes, Robert B.

2013-05-01

448

Estimation methods for semiconductor gamma-ray detectors  

Microsoft Academic Search

Gamma-ray detectors based on high-density semiconductors, such as cadmium zinc telluride, are being developed for applications in nuclear medicine, astronomy and the monitoring of nuclear weapons material. In contrast to the more commonly used scintillators, which convert gamma-ray energy into light, semiconductors directly convert the energy of a gamma ray into electrical current. This direct conversion often leads to the

Daniel George Marks

2000-01-01

449

Supernovae and Gamma-ray Bursts  

NASA Astrophysics Data System (ADS)

The properties of the Supernovae discovered in coincidence with long-duration Gamma-ray Bursts and X-Ray Flashes are reviewed, and compared to those of SNe for which GRBs are not observed. The SNe associated with GRBs are of Type Ic, they are brighter than the norm, and show very broad absorption lines in their spectra, indicative of high expansion velocities and hence of large explosion kinetic energies. This points to a massive star origin, and to the birth of a black hole at the time of core collapse. There is strong evidence for gross asymmetries in the SN ejecta. The observational evidence seems to suggest that GRB/SNe are more massive and energetic than XRF/SNe, and come from more massive stars. While for GRB/SNe the collapsar model is favoured, XRF/SNe may host magnetars.

Mazzali, Paolo A.

2012-09-01

450

The Gamma-Ray Burst - Supernova Connection  

NASA Astrophysics Data System (ADS)

A preponderance of evidence links long-duration, soft-spectrum gamma-ray bursts (GRBs) with the death of massive stars. The observations of the GRB-supernova (SN) connection present the most direct evidence of this physical link. We summarize 30 GRB-SN associations and focus on five ironclad cases, highlighting the subsequent insight into the progenitors enabled by detailed observations. We also address the SN association (or lack thereof) with several sub-classes of GRBs, finding that the X-ray Flash (XRF) population is likely associated with massive stellar death whereas short-duration events likely arise from an older population not readily capable of producing a SN concurrent with a GRB. Interestingly, a minority population of seemingly long-duration, soft-spectrum GRBs show no evidence for SN-like activity; this may be a natural consequence of the range of Ni-56 production expected in stellar deaths.

Hjorth, Jens; Bloom, Joshua S.

2012-11-01

451

POPULATION III GAMMA-RAY BURSTS  

SciTech Connect

We discuss a model of Poynting-dominated gamma-ray bursts from the collapse of very massive first generation (Pop. III) stars. From redshifts of order 20, the resulting relativistic jets would radiate in the hard X-ray range around 50 keV and above, followed after roughly a day by an external shock component peaking around a few keV. On the same timescales an inverse Compton component around 75 GeV may be expected, as well as a possible infrared flash. The fluences of these components would be above the threshold for detectors such as Swift and Fermi, providing potentially valuable information on the formation and properties of what may be the first luminous objects and their black holes in the high redshift universe.

Meszaros, P. [Department of Astronomy and Astrophysics, Department of Physics and Center for Particle Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Rees, M. J. [Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA (United Kingdom)

2010-06-01

452

The radio Aftreglows of Gamma Ray Bursts  

NASA Astrophysics Data System (ADS)

The best cosmic accelerators are quasars and the GRB projenitors. After decades of observations and scores of theories, we still do not know how they work. But, I shall argue, we now know quite well where GRBs come from and we understand how, their ``beams'' behave, as they make short pulses of gamma rays and long-duration X- ray, optical and radio ``afterglows''. For the afterglows ---on which I shall concentrate--- our understanding, based on the ``Cannonball Model'', is extraordinarily simple, precise and successful. Standard candles live and die and, since GRBs are being understood and are very distant, they may be about to be incarnated as such. The ``sociology'' of GRBs is interesting per se, the avatars of the Cannonball Model are also significant in this sense.

Dado, S.; Dar, A.; de Rujula, A.

453

Soft gamma-ray polarimetry using a Laue lens telescope: The Gamma Ray Imager  

Microsoft Academic Search

The Gamma Ray Imager (GRI) mission is a concept that was elaborated by a large international consortium and proposed to ESA in the framework of the Cosmic Vision first announcement of opportunity in 2007. The aim was simple: to beat the instrumental background in order to get a sensitivity improvement of at least one order of magnitude with respect to

Nicolas Barričre; Lorenzo Natalucci; Pietro Ubertini

454

Improved Gamma-Ray Flux Monitoring at the High Intensity Gamma-Ray Source (HIGS)  

NASA Astrophysics Data System (ADS)

An improved gamma-ray beam flux monitor has been built for use at the High Intensity Gamma-Ray Source at the Duke University Free Electron Laser Laboratories. It is important to know precisely the gamma-ray flux of this beam. It is also important to limit beam attenuation to a minimum while making an accurate flux measurement. The improvements from a more accurate gamma-ray intensity monitor will allow for more precise cross-section measurements and will be valuable to many of the experiments conducted at HIGS. The detector consists of a thin scintillator optically coupled to two photomultiplier tubes, a thin foil, and then another thin scintillator attached to two photomultiplier tubes. The front scintillator is used to veto counts from charged particles emitted upstream in the beam-line. The preliminary tests of the monitor show very promising results and after slight adjustments and calibrations, the detector will be ready to acquire accurate beam intensity measurements while contributing very little to beam attenuation.

Reynolds, Robert

2002-10-01

455

The distance indicators in gamma-ray pulsars  

NASA Astrophysics Data System (ADS)

Distance measurements of gamma-ray pulsars are challenging questions in present pulsar studies. The Large Area Telescope (LAT) aboard the Fermi gamma-ray observatory discovered more than 100 gamma-ray pulsars, including 34 new gamma-selected pulsars which nearly have no distance information. We study the relation between gamma-ray emission efficiency (?=L ?/?) and pulsar parameters, for young radio-selected gamma-ray pulsars with known distance information. We have introduced three generation order parameters to describe gamma-ray emission properties of pulsars, and find a strong correlation between ? and ?3, the generation order parameter which reflects ?-ray photon generations in pair cascade processes induced by magnetic field absorption in pulsar magnetosphere. A good correlation between ? and B LC, the magnetic field at the light cylinder radius, is also found. These correlations can serve as distance indicators in gamma-ray pulsars, to evaluate distances for gamma-selected pulsars. Distances of 35 gamma-selected pulsars are estimated, which could be tested by other distance measurement methods. The physical origin of the correlations may be also interesting for pulsar studies.

Wang, Wei

2013-03-01

456

Nonthermal gamma-ray and X-ray flashes from shock breakout in gamma-ray bursts\\/supernovae  

Microsoft Academic Search

Thermal X-ray emission which is simultaneous with the prompt gamma-rays has\\u000abeen detected for the first time from a supernova connected with a gamma-ray\\u000aburst (GRB), namely GRB060218\\/SN2006aj. It has been interpreted as arising from\\u000athe breakout of a mildly relativistic, radiation-dominated shock from a dense\\u000astellar wind surrounding the progenitor star. There is also evidence for the\\u000apresence of

Xiang-Yu Wang; Zhuo Li; Eli Waxman; Peter Meszaros

2006-01-01

457

Gamma-ray emission from massive young stellar objects  

NASA Astrophysics Data System (ADS)

Context: Massive stars form in dense and massive molecular cores. The exact formation mechanism is unclear, but it is possible that some massive stars are formed by processes similar to those that produce the low-mass stars, with accretion/ejection phenomena occurring at some point of the evolution of the protostar. This picture seems to be supported by the detection of a collimated stellar wind emanating from the massive protostar IRAS 16547-4247. A triple radio source is associated with the protostar: a compact core and two radio lobes. The emission of the southern lobe is clearly non-thermal. Such emission is interpreted as synchrotron radiation produced by relativistic electrons locally accelerated at the termination point of a thermal jet. Since the ambient medium is determined by the properties of the molecular cloud in which the whole system is embedded, we can expect high densities of particles and infrared photons. Because of the confirmed presence of relativistic electrons, inverse Compton and relativistic Bremsstrahlung interactions are unavoidable. Aims: We aim to make quantitative predictions of the spectral energy distribution of the non-thermal spots generated by massive young stellar objects, with emphasis on the particular case of IRAS 16547-4247. Methods: We study the high-energy emission generated by the relativistic electrons which produce the non-thermal radio source in IRAS 16547-4247. We also study the result of proton acceleration at the terminal shock of the thermal jet and make estimates of the secondary gamma rays and electron-positron pairs produced by pion decay. Results: We present spectral energy distributions for the southern lobe of IRAS 16547-4247, for a variety of conditions. We show that high-energy emission might be detectable from this object in the gamma-ray domain. The source may also be detectable in X-rays through long exposures with current X-ray instruments. Conclusions: Gamma-ray telescopes such as GLAST, and even ground-based Cherenkov arrays of new generation can be used to study non-thermal processes occurring during the formation of massive stars.

Araudo, A. T.; Romero, G. E.; Bosch-Ramon, V.; Paredes, J. M.

2007-12-01

458

Experiment on gamma-ray generation and application  

NASA Astrophysics Data System (ADS)

An experimental setup of gamma-ray generation through laser Compton scattering has been built on the NewSUBARU storage ring. The aim is to study nuclear transmutation, which is regarded as the first stage to explore the feasibility of developing a nuclear waste disposal system based on the concept of irradiating long-lived fission products by laser Compton scattering gamma ray. In this paper, the gamma-ray generation facility is presented, and some experimental results such as gamma-ray energy spectrum, intensity distribution, and the coupling efficiency of nuclear transmutation, are given. The experimental data is in good agreement with the analytic calculation or simulation analysis.

Li, D.; Imasaki, K.; Aoki, M.; Miyamoto, S.; Amano, S.; Aoki, K.; Hosono, K.; Mochizuki, T.

2004-08-01

459

Fermi Large Area Telescope Bright Gamma-ray Source List  

SciTech Connect

Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /KIPAC, Menlo Park /SLAC; Ajello, M.; /KIPAC, Menlo Park /SLAC; Atwood, W.B.; /UC, Santa Cruz; Axelsson, M.; /Stockholm U., OKC /Stockholm U.; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Band, D.L.; /NASA, Goddard /NASA, Goddard; Barbiellini, Guido; /INFN, Trieste /Trieste U.; Bastieri, Denis; /INFN, Padua /Padua U.; Bechtol, K.; /KIPAC, Menlo Park /SLAC; Bellazzini, R.; /INFN, Pisa; Berenji, B.; /KIPAC, Menlo Park /SLAC; Bignami, G.F.; /Pavia U.; Bloom, Elliott D.; /KIPAC, Menlo Park /SLAC; Bonamente, E.; /INFN, Perugia /Perugia U.; Borgland, A.W.; /KIPAC, Menlo Park /SLAC; Bregeon, J.; /INFN, Pisa; Brigida, M.; /Bari U. /INFN, Bari; Bruel, P.; /Ecole Polytechnique; Burnett, Thompson H.; /Washington U., Seattle /Bari U. /INFN, Bari /KIPAC, Menlo Park /SLAC /IASF, Milan /IASF, Milan /DAPNIA, Saclay /ASDC, Frascati /INFN, Perugia /Perugia U. /KIPAC, Menlo Park /SLAC /George Mason U. /Naval Research Lab, Wash., D.C. /NASA, Goddard /KIPAC, Menlo Park /SLAC /INFN, Perugia /Perugia U. /KIPAC, Menlo Park /SLAC /Montpellier U. /Sonoma State U. /Stockholm U., OKC /Royal Inst. Tech., Stockholm /Stockholm U. /KIPAC, Menlo Park /SLAC /ASDC, Frascati /NASA, Goddard /Maryland U. /Naval Research Lab, Wash., D.C. /INFN, Trieste /Pavia U. /Bari U. /INFN, Bari /KIPAC, Menlo Park /SLAC /UC, Santa Cruz /KIPAC, Menlo Park /SLAC /KIPAC, Menlo Park /SLAC /KIPAC, Menlo Park /SLAC /Montpellier U. /Bari U. /INFN, Bari /Ecole Polytechnique /NASA, Goddard; /more authors..

2009-05-15

460

Measurement of Disintegration Rates and Absolute {gamma}-ray Intensities  

SciTech Connect

The majority of practical radioactive materials decay by modes that include {gamma}-ray emission. For questions of 'how much' or 'how pure', one must know the absolute intensities of the major radiations. We are using liquid scintillation counting (LSC) to measurements of disintegration rates, coupled with {gamma}-ray spectroscopy to measure absolute {gamma}-ray emission probabilities. Described is a study of the 227Th chain yielding absolute {gamma}-ray intensities with {approx}0.5% accuracy and information on LSC efficiencies.

DeVries, Daniel J.; Griffin, Henry C. [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109 (United States)

2006-03-13

461

Nonrelativistic phase in gamma-ray burst afterglows  

Microsoft Academic Search

The discovery of multiband afterglows definitely shows that most $\\\\gamma$-ray\\u000abursts are of cosmological origin. $\\\\gamma$-ray bursts are found to be one of\\u000athe most violent explosive phenomena in the Universe, in which astonishing\\u000aultra-relativistic motions are involved. In this article, the multiband\\u000aobservational characteristics of $\\\\gamma$-ray bursts and their afterglows are\\u000abriefly reviewed. The standard model of $\\\\gamma$-ray bursts,

HUANG Yongfeng; T. Lu; K. S. Cheng

2007-01-01

462

Inelastic cross sections from gamma-ray measurements  

SciTech Connect

Measurements of gamma rays following neutron induced reactions have been studied with the Germanium Array for Neutron-induced Excitations (GEANIE) at the Los Alamos Neutron Science Center (LANSCE) for many years. Gamma-ray excitation functions and coincidence studies provide insight into nuclear reaction mechanisms as well as expanding our knowledge of energy levels and gamma-rays. Samples studied with Ge detectors at LANSCE range from Be to Pu. Fe, Cr and Ti have been considered for use as reference cross sections. An overview of the measurements and efforts to create a reliable neutron-induced gamma-ray reference cross section will be presented.

Nelson, Ronald Owen [Los Alamos National Laboratory

2010-12-06

463

Portable high energy gamma ray imagers  

NASA Astrophysics Data System (ADS)

To satisfy the needs of high energy gamma ray imagers for industrial nuclear imaging applications, three high energy gamma cameras are presented. The RMD-Pinhole camera uses a lead pinhole collimator and a segmented BGO detector viewed by a 3 in. square position sensitive photomultiplier tube (PSPMT). This pinhole gamma camera displayed an energy resolution of 25.0% FWHM at the center of the camera at 662 keV and an angular resolution of 6.2° FWHM at 412 keV. The fixed multiple hole collimated camera (FMCC), used a multiple hole collimator and a continuous slab of NaI(Tl) detector viewed by the same PSPMT. The FMCC displayed an energy resolution of 12.4% FWHM at 662 keV at the center of the camera and an angular resolution of 6.0° FWHM at 412 keV. The rotating multiple hole collimated camera (RMCC) used a 180° antisymmetric rotation modulation collimator and CsI(Tl) detectors coupled to PIN silicon photodiodes. The RMCC displayed an energy resolution of 7.1% FWHM at 662 keV and an angular resolution of 4.0° FWHM at 810 keV. The performance of these imagers is discussed in this paper.

Guru, S. V.; He, Z.; Wehe, D. K.; Knoll, G. F.; Redus, R. H.; Squillante, M. R.

1996-02-01

464

Integral observations of gamma-ray polarized sources: from the Crab pulsar to Cygnus X-1  

NASA Astrophysics Data System (ADS)

In complement to spectro-imaging observations, gamma-ray polarimetry provides a unique insight into the geometry and magnetic configuration of compact gamma-ray sources, such as neutron stars or black holes. These measurements were unsuccessful up to now because of intrinsic asymmetries in the detector response and of non-uniformities in the background dominated signals, which induce pseudo polarimetric signals, even from an unpolarized source. Due to the unprecedented spectral and timing capabilities of Integral, and thanks to its coded mask imaging technics, which efficiently suppresses most of the background contribution, we have measured linearly polarized emission from the brightest cosmic high energy sources. We were able to measure for the first time, at energies above 200 keV, a clear signal from several gamma-ray sources such as the Crab pulsar, the black hole candidate Cygnus X-1, and a Gamma-Ray Burst, GRB 041219A. These observations have enabled us to put strong constraints on the physical process at work in these sources, and, after a short review of Compton polarimeter principles, I will describe these Integral results and their implication on our knowledge of compact objects.

Laurent, Philippe

2012-07-01

465

Very high energy gamma-ray emission from X-ray transients during major outbursts  

Microsoft Academic Search

Context: Some high mass X-ray binaries (HMXB) have been recently confirmed as gamma-ray sources by ground based Cherenkov telescopes. In this work, we discuss the gamma-ray emission from X-ray transient sources formed by a Be star and a highly magnetized neutron star. This kind of systems can produce variable hadronic gamma-ray emission through the mechanism proposed by Cheng and Ruderman,

M. Orellana; G. E. Romero; L. J. Pellizza; S. Vidrih

2007-01-01

466

On the Time Evolution of Gamma-Ray Burst Pulses: A Self-Consistent Description  

Microsoft Academic Search

For the first time, the consequences of combining two well-established empirical relations that describe different aspects of the spectral evolution of observed gamma-ray burst (GRB) pulses are explored. These empirical relations are (1) the hardness-intensity correlation and (2) the hardness-photon fluence correlation. From these we find a self-consistent, quantitative, and compact description for the temporal evolution of pulse decay phases

Felix Ryde; Roland Svensson

2000-01-01

467

The PoGOLite balloon-borne soft gamma-ray polarimeter  

Microsoft Academic Search

PoGOLite is a balloon-borne experiment that will measure the polarization of soft gamma-rays between 25 keV and 80 keV through detection of coincident Compton scattering and absorption in a close-packed array of 217 well-t