Investigating the Fraction of Radio-Loud Quasars with High Velocity Broad Emission LInes

NASA Astrophysics Data System (ADS)

Bhattacharjee, Anirban; Gilbert, Miranda; Brotherton, Michael S.

2018-06-01

Quasars show a bimodal distribution in their radio emission, with some having powerful radio-emitting jets (radio-loud), and most having weak or no jets (radio-quiet). Surveys have shown around 10% of of quasars have detectable radio emissions. These quasars are called radio-loud. Several multiwavelength studies have shown that radio-loud quasars have different properties than radio-quiet quasars. This fraction of radio-loud quasars to radio-quiet quasars has been assumed to be constant across all parameter space. In this study, we breakdown the parameter space with respect to the increasing velocity dispersion of broad emission lines. Our sample has been drawn from 2011 Shen et al. catalog of more than 100,000 quasars. In this study, we demonstrate that this fraction varies with respect to the increasing velocity dispersion (FWHM) of broad emission lines. We compare three different emission lines: H-Beta, MgII, and CIV. We observe with increasing FWHM of these three emission lines, fraction of radio-loud quasars within the subset increases. This poster presents our initial results into investigating whether the fraction of RL quasars remains 10% in different parameter space.

MASER: Measuring, Analysing, Simulating low frequency Radio Emissions.

NASA Astrophysics Data System (ADS)

Cecconi, B.; Le Sidaner, P.; Savalle, R.; Bonnin, X.; Zarka, P. M.; Louis, C.; Coffre, A.; Lamy, L.; Denis, L.; Griessmeier, J. M.; Faden, J.; Piker, C.; André, N.; Genot, V. N.; Erard, S.; King, T. A.; Mafi, J. N.; Sharlow, M.; Sky, J.; Demleitner, M.

2017-12-01

The MASER (Measuring, Analysing and Simulating Radio Emissions) project provides a comprehensive infrastructure dedicated to low frequency radio emissions (typically < 50 to 100 MHz). The four main radio sources observed in this frequency are the Earth, the Sun, Jupiter and Saturn. They are observed either from ground (down to 10 MHz) or from space. Ground observatories are more sensitive than space observatories and capture high resolution data streams (up to a few TB per day for modern instruments). Conversely, space-borne instruments can observe below the ionospheric cut-off (10 MHz) and can be placed closer to the studied object. Several tools have been developed in the last decade for sharing space physcis data. Data visualization tools developed by The CDPP (http://cdpp.eu, Centre de Données de la Physique des Plasmas, in Toulouse, France) and the University of Iowa (Autoplot, http://autoplot.org) are available to display and analyse space physics time series and spectrograms. A planetary radio emission simulation software is developed in LESIA (ExPRES: Exoplanetary and Planetary Radio Emission Simulator). The VESPA (Virtual European Solar and Planetary Access) provides a search interface that allows to discover data of interest for scientific users, and is based on IVOA standards (astronomical International Virtual Observatory Alliance). The University of Iowa also develops Das2server that allows to distribute data with adjustable temporal resolution. MASER is making use of all these tools and standards to distribute datasets from space and ground radio instruments available from the Observatoire de Paris, the Station de Radioastronomie de Nançay and the CDPP deep archive. These datasets include Cassini/RPWS, STEREO/Waves, WIND/Waves, Ulysses/URAP, ISEE3/SBH, Voyager/PRA, Nançay Decameter Array (Routine, NewRoutine, JunoN), RadioJove archive, swedish Viking mission, Interball/POLRAD... MASER also includes a Python software library for reading raw data.

The February 15 2011 CME-CME interaction and possibly associated radio emission

NASA Astrophysics Data System (ADS)

Magdalenic, Jasmina; Temmer, Manuela; Krupar, Vratislav; Marque, Christophe; Veronig, Astrid; Eastwood, Jonathan

2017-04-01

On February 15, 2011 a particular, continuum-like radio emission was observed by STEREO WAVES and WIND WAVES spacecraft. The radio event appeared to be associated with the complex interaction of two coronal mass ejections (CMEs) successively launched (February 14 and February 15) from the same active region. Although the CME-CME interaction was widely studied (e.g. Temmer et al., 2014, Maricic et al., 2014, Mishra & Srivastava, 2014) none of the analyses confirmed an association with the continuum-like radio emission. The usual method of establishing temporal coincidence of radio continuum and a CME-CME interaction is not applicable in this event due to a complex and long-lasting interaction of the CMEs. Therefore, we performed radio triangulation studies (see also Magdalenic et al., 2014) which provided us with the 3D source positions of the radio emission. Comparison of the positions of radio sources and the reconstructed positions of the interacting CMEs, shows that the source position of the continuum-like radio emission is about 0.5 AU away from the interacting CMEs. We can therefore concluded that, in this event, the continuum-like emission is not the radio signature of the CME-CME interaction.

Observations of Nonthermal Radio Emission from Early-type Stars

NASA Technical Reports Server (NTRS)

Abbott, D. C.; Bieging, J. H.; Churchwell, E.

1985-01-01

As a part of a wider survey of radio emission from O, B, and Wolf-Rayet (WR) stars, five new stars whose radio emission is dominated by a nonthermal mechanism of unknown origin were discovered. From statistics of distance-limited samples of stars, it is estimated that the minimum fraction of stars which are nonthermal emitters is 25% for the OB stars and 10% for the WR stars. The characteristics of this new class of nonthermal radio emitter are investigated.

LOFAR discovery of radio emission in MACS J0717.5+3745

NASA Astrophysics Data System (ADS)

Bonafede, A.; Brüggen, M.; Rafferty, D.; Zhuravleva, I.; Riseley, C. J.; van Weeren, R. J.; Farnes, J. S.; Vazza, F.; Savini, F.; Wilber, A.; Botteon, A.; Brunetti, G.; Cassano, R.; Ferrari, C.; de Gasperin, F.; Orrú, E.; Pizzo, R. F.; Röttgering, H. J. A.; Shimwell, T. W.

2018-05-01

We present results from LOFAR and GMRT observations of the galaxy cluster MACS J0717.5+3745. The cluster is undergoing a violent merger involving at least four sub-clusters, and it is known to host a radio halo. LOFAR observations reveal new sources of radio emission in the Intra-Cluster Medium: (i) a radio bridge that connects the cluster to a head-tail radio galaxy located along a filament of galaxies falling into the main cluster, (ii) a 1.9 Mpc radio arc, that is located North West of the main mass component, (iii) radio emission along the X-ray bar, that traces the gas in the X-rays South West of the cluster centre. We use deep GMRT observations at 608 MHz to constrain the spectral indices of these new radio sources, and of the emission that was already studied in the literature at higher frequency. We find that the spectrum of the radio halo and of the relic at LOFAR frequency follows the same power law as observed at higher frequencies. The radio bridge, the radio arc, and the radio bar all have steep spectra, which can be used to constrain the particle acceleration mechanisms. We argue that the radio bridge could be caused by the re-acceleration of electrons by shock waves that are injected along the filament during the cluster mass assembly. Despite the sensitivity reached by our observations, the emission from the radio halo does not trace the emission of the gas revealed by X-ray observations. We argue that this could be due to the difference in the ratio of kinetic over thermal energy of the intra-cluster gas, suggested by X-ray observations.

Radio emission from embryonic superluminous supernova remnants

NASA Astrophysics Data System (ADS)

Omand, Conor M. B.; Kashiyama, Kazumi; Murase, Kohta

2018-02-01

It has been widely argued that Type-I superluminous supernovae (SLSNe-I) are driven by powerful central engines with a long-lasting energy injection after the core-collapse of massive progenitors. One of the popular hypotheses is that the hidden engines are fast-rotating pulsars with a magnetic field of B ˜ 1013-1015 G. Murase, Kashiyama & Mészáros proposed that quasi-steady radio/submm emission from non-thermal electron-positron pairs in nascent pulsar wind nebulae can be used as a relevant counterpart of such pulsar-driven supernovae (SNe). In this work, focusing on the nascent SLSN-I remnants, we examine constraints that can be placed by radio emission. We show that the Atacama Large Millimeter/submillimetre Array can detect the radio nebula from SNe at DL ˜ 1 Gpc in a few years after the explosion, while the Jansky Very Large Array can also detect the counterpart in a few decades. The proposed radio follow-up observation could solve the parameter degeneracy in the pulsar-driven SN model for optical/UV light curves, and could also give us clues to young neutron star scenarios for SLSNe-I and fast radio bursts.

Mean and extreme radio properties of quasars and the origin of radio emission

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

Kratzer, Rachael M.; Richards, Gordon T.

2015-02-01

We investigate the evolution of both the radio-loud fraction (RLF) and (using stacking analysis) the mean radio loudness of quasars. We consider how these properties evolve as a function of redshift and luminosity, black hole (BH) mass and accretion rate, and parameters related to the dominance of a wind in the broad emission-line region. We match the FIRST source catalog to samples of luminous quasars (both spectroscopic and photometric), primarily from the Sloan Digital Sky Survey. After accounting for catastrophic errors in BH mass estimates at high redshift, we find that both the RLF and the mean radio luminosity increasemore » for increasing BH mass and decreasing accretion rate. Similarly, both the RLF and mean radio loudness increase for quasars that are argued to have weaker radiation line driven wind components of the broad emission-line region. In agreement with past work, we find that the RLF increases with increasing optical/UV luminosity and decreasing redshift, while the mean radio loudness evolves in the exact opposite manner. This difference in behavior between the mean radio loudness and the RLF in L−z may indicate selection effects that bias our understanding of the evolution of the RLF; deeper surveys in the optical and radio are needed to resolve this discrepancy. Finally, we argue that radio-loud (RL) and radio-quiet (RQ) quasars may be parallel sequences, but where only RQ quasars at one extreme of the distribution are likely to become RL, possibly through slight differences in spin and/or merger history.« less

Diffuse radio emission in the complex merging galaxy cluster Abell2069

NASA Astrophysics Data System (ADS)

Drabent, A.; Hoeft, M.; Pizzo, R. F.; Bonafede, A.; van Weeren, R. J.; Klein, U.

2015-03-01

Context. Galaxy clusters with signs of a recent merger in many cases show extended diffuse radio features. This emission originates from relativistic electrons that suffer synchrotron losses due to the intracluster magnetic field. The mechanisms of particle acceleration and the properties of the magnetic field are still poorly understood. Aims: We search for diffuse radio emission in galaxy clusters. Here, we study the complex galaxy cluster Abell 2069, for which X-ray observations indicate a recent merger. Methods: We investigate the cluster's radio continuum emission by deep Westerbork Synthesis Radio Telescope (WSRT) observations at 346 MHz and Giant Metrewave Radio Telescope (GMRT) observations at 322 MHz. Results: We find an extended diffuse radio feature roughly coinciding with the main component of the cluster. We classify this emission as a radio halo and estimate its lower limit flux density at 25 ± 9 mJy. Moreover, we find a second extended diffuse source located at the cluster's companion and estimate its flux density at 15 ± 2 mJy. We speculate that this is a small halo or a mini-halo. If true, this cluster is the first example of a double-halo in a single galaxy cluster.

Observing the Plasma-Physical Processes of Pulsar Radio Emission with Arecibo

NASA Astrophysics Data System (ADS)

Rankin, Joanna M.

2017-01-01

With their enormous densities and fields, neutron stars entail some of the most exotic physics in the cosmos. Similarly, the physical mechanisms of pulsar radio emission are no less exotic, and we are only now beginning to understand them. The talk will provide an introduction to the phenomenology of radio pulsar emission and focus on those aspects of the exquisite Arecibo observations that bear on their challenging emission physics.The commonalities of the radio beamforms of most slow pulsars (and some millisecond pulsars) argue strongly that their magnetic fields have a nearly dipolar structure at the height of their radio emission regions. These heights can often be determined by aberration/retardation analyses. Similarly, measurement of the orientation of the polarized radio emission with respect to the emitting magnetic field facilitates identification of the physical(X/O) emission modes and study of the plasma coupling to the electromagnetic radiation.While the physics of primary plasma generation above the pulsar polar cap is only beginning to be understood, it is clear that the radio pulsars we see are able to generate copious amounts of electron-positron plasma in their emission regions. Within the nearly dipolar field structure of these emission regions, the plasma density is near to that of the Goldreich-Julian model, and so the physical conditions in these regions can be accurately estimated.These conditions show that the plasma frequencies in the emission regions are much higher than the frequency of the emitted radiation, such that the plasma couples most easily to the extraordinary mode as observed. Therefore, the only surviving emission mechanism is curvature radiation from charged solitons, produced by the two-stream instability. Such soliton emission has probably been observed directly in the Crab pulsar; however, a physical theory of charged soliton radiation does not yet exist.

3C 159 - a double emission-line radio galaxy

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

Tytler, D.; Browne, I.

1985-09-01

An optical identification for 3C 159 is reported with a 19-mag emission-line radio galaxy at z = 0.482. Photometric measurements show it to be unusually bright and blue. The emission lines are of exceptionally high luminosity, and are split into two components separated by 598 + or - 13 km/s and 3 kpc along the spectrograph slit. A VLA may show that one of the radio lobes has two hot spots with tails of emission leading to both. 21 references.

Diffuse Interplanetary Radio Emission (DIRE) Accompanying Type II Radio Bursts

NASA Astrophysics Data System (ADS)

Teklu, T. B.; Gopalswamy, N.; Makela, P. A.; Yashiro, S.; Akiyama, S.; Xie, H.

2015-12-01

We report on an unusual drifting feature in the radio dynamic spectra at frequencies below 14 MHz observed by the Radio and Plasma Wave (WAVES) experiment on board the Wind spacecraft. We call this feature as "Diffuse Interplanetary Radio Emission (DIRE)". The DIRE events are generally associated with intense interplanetary type II radio bursts produced by shocks driven by coronal mass ejections (CMEs). DIREs drift like type II bursts in the dynamic spectra, but the drifting feature consist of a series of short-duration spikes (similar to a type I chain). DIREs occur at higher frequencies than the associated type II bursts, with no harmonic relationship with the type II burst. The onset of DIREs is delayed by several hours from the onset of the eruption. Comparing the radio dynamic spectra with white-light observations from the Solar and Heliospheric Observatory (SOHO) mission, we find that the CMEs are generally very energetic (fast and mostly halos). We suggest that the DIRE source is typically located at the flanks of the CME-driven shock that is still at lower heliocentric distances.

Detection of radio emission from the jet in Centaurus A

NASA Technical Reports Server (NTRS)

Schreier, E. J.; Burns, J. O.; Feigelson, E. D.

1981-01-01

The VLA has detected radio emission from the X-ray jet in Centaurus A, at 20 and 6 cm, whose radio morphology is similar to that of the X-ray jet. It is suggested that the same population of relativistic electrons is responsible for both radio and X-ray synchrotron emission, in which case in situ acceleration of electrons in the knots would be mandatory. The relativistic beam may alternatively heat the surrounding gas, resulting in X-ray emission. The static confinement of the knots of the jet seems to be accomplished by the presence of the ambient hot gas in the galaxy. The galaxy's nucleus has an inverted spectrum at radio frequencies, and it is noted that the jet is as bright as the nucleus at low frequencies.

Fast Radio Bursts’ Emission Mechanism: Implication from Localization

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

Lyutikov, Maxim

2017-03-20

We argue that the localization of the repeating fast radio bursts (FRBs) at ∼1 Gpc excludes a rotationally powered type of radio emission (e.g., analogs of Crab’s giant pulses coming from very young energetic pulsars) as the origin of FRBs.

Voyager detection of nonthermal radio emission from Saturn

NASA Technical Reports Server (NTRS)

Kaiser, M. L.; Desch, M. D.; Warwick, J. W.; Pearce, J. B.

1980-01-01

The detection of bursts of nonthermal radio noise from Saturn by the planetary radio astonomy experiment onboard the Voyager spacecraft is discussed. The emissions occur near 200 kHz with a peak flux density comparable to higher frequency Jovian emissions. The radiation is right-hand polarized and is most likely emitted in the extraordinary magnetoionic mode from Saturn's northern hemisphere. Modulation is apparent in the data which is consistent with a planetary rotation period of 10 hr 39.9 min.

Some Aspects of the Radio Emission of EGRET-Detected Blazars

NASA Technical Reports Server (NTRS)

Lin, Y. C.; Bertsch, D. L.; Bloom, S. D.; Esposito, J. A.; Hartman, R. C.; Hunter, S. D.; Kniffen, D. A.; Kanbach, G.; Mayer-Hasselwander, H. A.; Michelson, P. F.

1999-01-01

It has long been recognized that the high-latitude Energetic Gamma Ray Experiment Telescope (EGRET) sources can be identified with blazars of significant radio emission. Many aspects of the relation between high-energy gamma-ray emission and radio emission of EGRET-detected blazars remain uncertain. In this paper, we use the results of the recently published Third EGRET Source Catalog to examine in more detail to what extent the EGRET flux and the radio flux are correlated. In particular we examine the correlation (or the lack of it) in flux level, spectral shape, temporal variation, and detection limit. Many significant previous studies in these areas are also evaluated.

Kinetic Simulations of Type II Radio Burst Emission Processes

NASA Astrophysics Data System (ADS)

Ganse, U.; Spanier, F. A.; Vainio, R. O.

2011-12-01

The fundamental emission process of Type II Radio Bursts has been under discussion for many decades. While analytic deliberations point to three wave interaction as the source for fundamental and harmonic radio emissions, sparse in-situ observational data and high computational demands for kinetic simulations have not allowed for a definite conclusion to be reached. A popular model puts the radio emission into the foreshock region of a coronal mass ejection's shock front, where shock drift acceleration can create eletrcon beam populations in the otherwise quiescent foreshock plasma. Beam-driven instabilities are then assumed to create waves, forming the starting point of three wave interaction processes. Using our kinetic particle-in-cell code, we have studied a number of emission scenarios based on electron beam populations in a CME foreshock, with focus on wave-interaction microphysics on kinetic scales. The self-consistent, fully kinetic simulations with completely physical mass-ratio show fundamental and harmonic emission of transverse electromagnetic waves and allow for detailled statistical analysis of all contributing wavemodes and their couplings.

Dendritic copper phthalocyanine with aggregation induced blue emission and solid-state fluorescence

NASA Astrophysics Data System (ADS)

Wang, Jiayi; Pan, Lin; Zhou, Xuefei; Jia, Kun; Liu, Xiaobo

2016-09-01

In this work, dendritic copper phthalocyanine (CuPc) showing obvious aggregation induced emission (AIE) and strong solid-state fluorescence was synthesized. It was found that synthesized CuPc can be easily solubilized in polar aprotic solvent, where no fluorescence signal was detected. Interestingly, both the CuPc aggregates in solution and solid-state powder exhibited strong fluorescence emission around 480 nm, which should be attributed to the restriction of intramolecular rotation as rationalized in aggregation induced emission framework. Meanwhile the obvious crystalline enhanced solid-state fluorescent emission is observed for CuPc powder.

A search for radio emission from exoplanets around evolved stars

NASA Astrophysics Data System (ADS)

O'Gorman, E.; Coughlan, C. P.; Vlemmings, W.; Varenius, E.; Sirothia, S.; Ray, T. P.; Olofsson, H.

2018-04-01

The majority of searches for radio emission from exoplanets have to date focused on short period planets, i.e., the so-called hot Jupiter type planets. However, these planets are likely to be tidally locked to their host stars and may not generate sufficiently strong magnetic fields to emit electron cyclotron maser emission at the low frequencies used in observations (typically ≥150 MHz). In comparison, the large mass-loss rates of evolved stars could enable exoplanets at larger orbital distances to emit detectable radio emission. Here, we first show that the large ionized mass-loss rates of certain evolved stars relative to the solar value could make them detectable with the LOw Frequency ARray (LOFAR) at 150 MHz (λ = 2 m), provided they have surface magnetic field strengths >50 G. We then report radio observations of three long period (>1 au) planets that orbit the evolved stars β Gem, ι Dra, and β UMi using LOFAR at 150 MHz. We do not detect radio emission from any system but place tight 3σ upper limits of 0.98, 0.87, and 0.57 mJy on the flux density at 150 MHz for β Gem, ι Dra, and β UMi, respectively. Despite our non-detections these stringent upper limits highlight the potential of LOFAR as a tool to search for exoplanetary radio emission at meter wavelengths.

Radio emission of sea surface at centimeter wavelengths and is fluctuations

NASA Technical Reports Server (NTRS)

Tseytlin, N. M.; Shutko, A. M.; Zhislin, G. M.

1981-01-01

The eigen thermal radio emission of the sea was examined as well as the agitated surface of the sea when the reflection (scattering) is similar in nature to diffused scattering. The contribution of this emission to the total emission of the sea is practically constant in time, and the time fluctuations of the radio emissions of the sea are basically determined only by a change in the eigen emission of the sea, connected with the agitation.

Ultraviolet and Radio Emission from the Northern Middle Lobe of Centaurus A

NASA Technical Reports Server (NTRS)

Neff, Susan

2009-01-01

We present deep GALEX ultraviolet (135 - 280 nm) images of the Northern Middle Lobe (NML) of the nearby radio galaxy Centaurus A. We find that the ultraviolet emission appears to have a complex interaction with soft X-ray, H-alpha emission, and radio emission, which should help constrain various models of energy transport in the NML. We also present new 90cm VLA images of the NML. The radio morphology at this wavelength is indicative of a more complex system than either a straightforward flaring jet (Morganti et al. 1999) or a bubble with trailing stem (Saxton et al. 2001). New limits are placed on the lack of radio emission from any corresponding southern counterpart to the NML.

Zebra pattern in decametric radio emission of Jupiter

NASA Astrophysics Data System (ADS)

Panchenko, M.; Rošker, S.; Rucker, H. O.; Brazhenko, A.; Zarka, P.; Litvinenko, G.; Shaposhnikov, V. E.; Konovalenko, A. A.; Melnik, V.; Franzuzenko, A. V.; Schiemel, J.

2018-03-01

We report the systematic analysis of zebra-like fine spectral structures in decametric frequency range of Jovian radio emission. Observations were performed by the large ground-based radio telescope URAN-2 during three observation campaigns between, Sep., 2012, and May, 2015. In total, 51 zebra pattern (ZP) events were detected. These rare fine radio features are observed in frequency range from 12.5 to 29.7 MHz as quasi-harmonically related bands of enhanced brightness. ZPs are strongly polarized radio emission with a duration from 20 s to 290 s and flux densities 105-106 Jy (normalized to 1 AU), that is, 1-2 orders lower than for Io-decametric radio emission (DAM). Occurrence of the events does not depend on the position of Io satellite but is strongly controlled by the Jovian central meridian longitude (CML). ZPs are mainly detected in two active sectors of Jovian CMLs: 100∘ to 160∘ for Northern sources (right-handed polarized) and 300∘ and 60∘ (via 360∘) for the Southern sources (left-handed). The frequency interval between neighboring stripes is from 0.26 to 1.5 MHz and in most cases this interval increases with frequency. We discussed the double plasma resonance with electrons or ions as a possible source of the ZPs. The performed analysis of the observations allows us to conclude that the observed ZPs are a new type of narrow band spectral structures in the Jovian DAM.

The Relationship Between Solar Radio and Hard X-Ray Emission

NASA Technical Reports Server (NTRS)

White, S. M.; Benz, A. O.; Christe, S.; Farnik, F.; Kundu, M. R.; Mann, G.; Ning, Z.; Raulin, J.-P.; Silva-Valio, A. V. R.; Saint-Hilaire, P.;

A multidisciplinary study of planetary, solar and astrophysical radio emissions

NASA Technical Reports Server (NTRS)

Gurnett, D. A.; Calvert, W.; Fielder, R.; Goertz, C.; Grabbe, C.; Kurth, W.; Mutel, R.; Sheerin, J.; Mellott, M.; Spangler, S.

1986-01-01

Combination of the related fields of planetary, solar, and astrophysical radio emissions was attempted in order to more fully understand the radio emission processes. Topics addressed include: remote sensing of astrophysical plasma turbulence; Alfven waves; astrophysical shock waves; surface waves; very long base interferometry results; very large array observations; solar magnetic flux; and magnetohydrodynamic waves as a tool for solar corona diagnostics.

The radio emission from the ultraluminous far-infrared galaxy NGC 6240

NASA Technical Reports Server (NTRS)

Colbert, Edward J. M.; Wilson, Andrew S.; Bland-Hawthorn, Jonathan

1994-01-01

We present new radio observations of the 'prototypical' ultraluminous far-infrared galaxy NGC 6240, obtained using the Very Large Array (VLA) at lambda = 20 cm in B-configuration and at lambda = 3.6 cm in A-configuration. These data, along with those from four previous VLA observations, are used to perform a comprehensive study of the radio emission from NGC 6240. Approximately 70% (approximately 3 x 10(exp 23) W/Hz) of the total radio power at 20 cm originates from the nuclear region (approximately less than 1.5 kpc), of which half is emitted by two unresolved (R approximately less than 36 pc) cores and half by a diffuse component. The radio spectrum of the nuclear emission is relatively flat (alpha approximately equals 0.6; S(sub nu) proportional to nu(exp -alpha). The supernova rate required to power the diffuse component is consistent with that predicted by the stellar evolution models of Rieke et al. (1985). If the radio emission from the two compact cores is powered by supernova remnants, then either the remnants overlap and form hot bubbles in the cores, or they are very young (approximately less than 100 yr.) Nearly all of the remaining 30% of the total radio power comes from an 'armlike' region extending westward from the nuclear region. The western arm emission has a steep spectrum (alpha approximately equals 1.0), suggestive of aging effects from synchrotron or inverse-Compton losses, and is not correlated with starlight; we suggest that it is synchrotron emission from a shell of material driven by a galactic superwind. Inverse Compton scattering of far-infrared photons in the radio sources is expected to produce an X-ray flux of approximately 2 - 6 x 10(exp -14) ergs/s/sq cm in the 2 - 10 keV band. No significant radio emission is detected from or near the possible ultramassive 'dark core'.

Solar radio emission

NASA Technical Reports Server (NTRS)

Goldman, M. V.; Smith, D. F.

1981-01-01

Active areas of both observational and theoretical research in which rapid progress is being made are discussed. These include: (1) the dynamic spectrum or frequency versus time plot; (2) physical mechanisms in the development of various types of bursts; (3) microwave type 1, 2, 3, and moving type 4 bursts; (4) bursts caused by trapped electrons; (5) physics of type 3bursts; (6) the physics of type 2 bursts and their related shocks; (7) the physics of both stationary and moving traps and associated type 1 and moving type 4 bursts; and (8) the status of the field of solar radio emission.

A giant radio flare from Cygnus X-3 with associated γ-ray emission

NASA Astrophysics Data System (ADS)

Corbel, S.; Dubus, G.; Tomsick, J. A.; Szostek, A.; Corbet, R. H. D.; Miller-Jones, J. C. A.; Richards, J. L.; Pooley, G.; Trushkin, S.; Dubois, R.; Hill, A. B.; Kerr, M.; Max-Moerbeck, W.; Readhead, A. C. S.; Bodaghee, A.; Tudose, V.; Parent, D.; Wilms, J.; Pottschmidt, K.

2012-04-01

With frequent flaring activity of its relativistic jets, Cygnus X-3 (Cyg X-3) is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high-energy γ-ray emission, thanks to detections by Fermi Large Area Telescope (Fermi/LAT) and AGILE. In 2011, Cyg X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy γ-ray emission. We present the results of a multiwavelength campaign covering a quenched state, when radio emission from Cyg X-3 is at its weakest and the X-ray spectrum is very soft. A giant (˜20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E≥ 100 MeV) reveal renewed γ-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the γ-ray emission is not exclusively related to the rare giant radio flares. A three-week period of γ-ray emission is also detected when Cyg X-3 was weakly flaring in radio, right before transition to the radio quenched state. No γ-rays are observed during the ˜1-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio-quenched) state trigger γ-ray emission, implying a connection to the accretion process, and also that the γ-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.

A Giant Radio Flare from Cygnus X-3 with Associated Gamma-Ray Emission

NASA Technical Reports Server (NTRS)

Corbel, S.; Dubus, G.; Tomsick, J. A.; Szostek, A.; Corbet, R. H. D.; Miller-Jones, J. C. A.; Richards, J. L.; Pooley, G.; Trushkin, S.; Dubois, R.;

Stochastic Growth Theory of Type 3 Solar Radio Emission

NASA Technical Reports Server (NTRS)

Robinson, P. A.; Carins, I. H.

1993-01-01

The recently developed stochastic growth theory of type 3 radio sources is extended to predict their electromagnetic volume emissivities and brightness temperatures. Predicted emissivities are consistent with spacecraft observations and independent theoretical constraints.

Updated modeling of Io and non-Io Radio Auroral Emissions of Jupiter

NASA Astrophysics Data System (ADS)

Louis, C.; Lamy, L.; Zarka, P.; Cecconi, B.; Hess, S.

2015-10-01

The radio auroral emissions produced by the Jupiter's magnetosphere between a few kHz and 40MHz, the most intense of our Solar System, are known since half a century, but they still drive many questions, and their deepened study is one of the main aim of the JUNO missions (arrival in July 2016). Jovian auroral radio emissions are thought to be produced through the Cyclotron Maser Instability (CMI), from non-maxwellian weakly relativistic electrons gyrating along high-latitude magnetic fields lines (Zarka, 1998). These emissions divide in different spectral components, driven or not by the moon Io. The origin and the relationship between kilometric, hectometric and decametric non-Io emissions in particular remains poorly understood. To investigate these emissions, we simulated numerical dynamic spectra with the most recent version of the ExPRES code - Exoplanetary and Planetary Radio Emission Simulator, available at http://maser.obspm.fr - already used to successfully model Io decametric and Saturn's kilometric arcshaped emissions (Hess et al., 2008, Lamy et al., 2008) and predict exoplanetary radio emissions (Hess et al., 2011). Such simulations bring direct constraints on the locus of active magnetic field lines and on the nature of CMI-unstable electrons (Hess et al., submitted). We validated the new theoretical calculation of the beaming angle used by ExPRES, which now includes refraction at the source. We then built updated simulations of Io and non-Io emissions which were compared to the radio observations acquired by the Cassini spacecraft (Jupiter flyby in 2000) and the Nançay decameter array (routines observations of Jupiter).

Natural radio emission of Jupiter as interferences for radar investigations of the icy satellites of Jupiter

NASA Astrophysics Data System (ADS)

Cecconi, B.; Hess, S.; Hérique, A.; Santovito, M. R.; Santos-Costa, D.; Zarka, P.; Alberti, G.; Blankenship, D.; Bougeret, J.-L.; Bruzzone, L.; Kofman, W.

2012-02-01

Radar instruments are part of the core payload of the two Europa Jupiter System Mission (EJSM) spacecraft: NASA-led Jupiter Europa Orbiter (JEO) and ESA-led Jupiter Ganymede Orbiter (JGO). At this point of the project, several frequency bands are under study for radar, which ranges between 5 and 50 MHz. Part of this frequency range overlaps with that of the natural jovian radio emissions, which are very intense in the decametric range, below 40 MHz. Radio observations above 40 MHz are free of interferences, whereas below this threshold, careful observation strategies have to be investigated. We present a review of spectral intensity, variability and sources of these radio emissions. As the radio emissions are strongly beamed, it is possible to model the visibility of the radio emissions, as seen from the vicinity of Europa or Ganymede. We have investigated Io-related radio emissions as well as radio emissions related to the auroral oval. We also review the radiation belts synchrotron emission characteristics. We present radio sources visibility products (dynamic spectra and radio source location maps, on still frames or movies), which can be used for operation planning. This study clearly shows that a deep understanding of the natural radio emissions at Jupiter is necessary to prepare the future EJSM radar instrumentation. We show that this radio noise has to be taken into account very early in the observation planning and strategies for both JGO and JEO. We also point out possible synergies with RPW (Radio and Plasma Waves) instrumentations.

Natural radio emission of Jupiter as interferences for radar investigations of the icy satellites of Jupiter

NASA Astrophysics Data System (ADS)

Cecconi, B.; Hess, S.; Hérique, A.; Santovito, M. R.; Santos-Costa, D.; Zarka, P.; Alberti, G.; Blankenship, D.; Bougeret, J. L.; Bruzzone, L.; Kofman, W.

2011-10-01

Radar instruments are part of the core payload of the two Europa Jupiter System Mission (EJSM) spacecraft: NASA-led Jupiter Europa Orbiter (JEO) and ESA-led Jupiter Ganymede Orbiter (JGO). At this point of the project, several frequency bands are under study for radar, which ranges between 5MHz and 50MHz. Part of this frequency range overlaps with that of the natural Jovian radio emissions, which are very intense in the decametric range, below 40 MHz. Radio observations above 40 MHz are free of interferences, whereas below this threshold, careful observation strategies have to be investigated. We present a review of spectral intensity, variability and sources of these radio emissions. As the radio emission are strongly beamed, it is possible to model the visibility of the radio emissions, as seen from the vicinity of Europa or Ganymede. We have investigated Io-related radio emissions as well as radio emissions related to the auroral oval. We also review the radiation belts synchrotron emission characteristics. We present radio sources visibility products (dynamic spectra and radio source location maps, on still frames or movies), which can be used for operation planning. This study clearly shows that a deep understanding of the natural radio emissions at Jupiter is necessary to prepare the future EJSM radar instrumentation. We show that this radio noise has to be taken into account very early in the observation planning and strategies for both JGO and JEO. We also point out possible synergies with RPW (Radio and Plasma Waves) instrumentations.

Radio emission from supernova remnants in a cloudy interstellar medium

NASA Technical Reports Server (NTRS)

Blandford, R. D.; Cowie, L. L.

1982-01-01

The van der Laan (1962) theory of SNR radio emission is modified in light of the inhomogeneity of the interstellar medium, and in order to allow for particle acceleration in shock fronts. It is proposed that most of the radio emission in 10-20 pc radius SNRs originates in cold interstellar clouds that have been crushed by the high pressure hot gas within the expanding remnant. Under these circumstances, simple reacceleration of ambient interstellar cosmic ray electrons can account for the surface brightness-diameter distribution of observed remnants, with the additional, relativistic particle energy compensating for the decreased filling factor of the radio-emitting regions. Warm interstellar gas, at about 8000 K, may also be compressed within very large SNRs (of radius of 30-100 pc) and account for both the giant radio loops, when these SNRs are seen individually, and the anomalously bright galactic nonthermal radio background, which may be the superposition of a number of such features.

Study of Ultra-High Energy Cosmic Rays from Extensive Air Showers Radio Emission

NASA Astrophysics Data System (ADS)

Petrov, Igor; Kozlov, Vladimir; Petrov, Zim; Knurenko, Stanislav; Pravdin, Mikhail

The study of cosmic rays with the help of radio detection from extensive air showers may be an alternative to traditional detecting methods, which use a large area array installed with hundreds and thousands of scintillation detectors for charged particles, or the detectors of measuring the emission produced by relativistic particles of EAS in the optical wavelengths. Processes that lead to the emission of electromagnetic radiation are well known and calculations show that the air shower radio emission depends on the processes of development of the electromagnetic cascade, i.e. related with the longitudinal development of the shower, with the magnetic field near sea level etc. In this regard, there is a question to establish the correlation between characteristics of EAS both longitudinal and lateral development and radio emission parameters observed when air shower particles pass through the atmosphere. For this purpose, in Yakutsk, radio array for detecting air shower radio emission was established. The array consists of the antenna field on which crossed antennas are installed; antennas oriented E - W and N - S. Radio emission measurements are conducted at frequency 32 MHz, free from industrial noise. In 2008 - 2013 years, Yakutsk array has measured several seasons of registration of EAS events, including showers with energies above 10 (19) eV. In the course of the data analysis the following results were obtained: a) lateral distribution of the radio signal plotted as a function of distance from the shower axis ; b) a correlation between the amplitude of the radio signal with the energy of the shower, which is determined by measuring the fluxes of charged particles , muons and EAS Cerenkov radiation (energy balance method); c) we made evaluation of the depth of maximum development of the shower using form of radio emission LDF measured in ultra-high energy showers; g) a comparison of the Yakutsk array data with data from other arrays.

Virtual observatory tools and amateur radio observations supporting scientific analysis of Jupiter radio emissions

NASA Astrophysics Data System (ADS)

Cecconi, Baptiste; Hess, Sebastien; Le Sidaner, Pierre; Savalle, Renaud; Stéphane, Erard; Coffre, Andrée; Thétas, Emmanuel; André, Nicolas; Génot, Vincent; Thieman, Jim; Typinski, Dave; Sky, Jim; Higgins, Chuck; Imai, Masafumi

2016-04-01

In the frame of the preparation of the NASA/JUNO and ESA/JUICE (Jupiter Icy Moon Explorer) missions, and the development of a planetary sciences virtual observatory (VO), we are proposing a new set of tools directed to data providers as well as users, in order to ease data sharing and discovery. We will focus on ground based planetary radio observations (thus mainly Jupiter radio emissions), trying for instance to enhance the temporal coverage of jovian decametric emission. The data service we will be using is EPN-TAP, a planetary science data access protocol developed by Europlanet-VESPA (Virtual European Solar and Planetary Access). This protocol is derived from IVOA (International Virtual Observatory Alliance) standards. The Jupiter Routine Observations from the Nancay Decameter Array are already shared on the planetary science VO using this protocol, as well as data from the Iitate Low Frquency Radio Antenna, in Japan. Amateur radio data from the RadioJOVE project is also available. The attached figure shows data from those three providers. We will first introduce the VO tools and concepts of interest for the planetary radioastronomy community. We will then present the various data formats now used for such data services, as well as their associated metadata. We will finally show various prototypical tools that make use of this shared datasets.

Radio emission from an ultraluminous x-ray source.

PubMed

Kaaret, Philip; Corbel, Stephane; Prestwich, Andrea H; Zezas, Andreas

2003-01-17

The physical nature of ultraluminous x-ray sources is uncertain. Stellar-mass black holes with beamed radiation and intermediate black holes with isotropic radiation are two plausible explanations. We discovered radio emission from an ultraluminous x-ray source in the dwarf irregular galaxy NGC 5408. The x-ray, radio, and optical fluxes as well as the x-ray spectral shape are consistent with beamed relativistic jet emission from an accreting stellar black hole. If confirmed, this would suggest that the ultraluminous x-ray sources may be stellar-mass rather than intermediate-mass black holes. However, interpretation of the source as a jet-producing intermediate-mass black hole cannot be ruled out at this time.

Scientists Detect Radio Emission from Rapidly Rotating Cosmic Dust Grains

NASA Astrophysics Data System (ADS)

2001-11-01

Astronomers have made the first tentative observations of a long-speculated, but never before detected, source of natural radio waves in interstellar space. Data from the National Science Foundation's 140 Foot Radio Telescope at the National Radio Astronomy Observatory in Green Bank, W.Va., show the faint, tell-tale signals of what appear to be dust grains spinning billions of times each second. This discovery eventually could yield a powerful new tool for understanding the interstellar medium - the immense clouds of gas and dust that populate interstellar space. The NRAO 140 Foot Radio Telescope The NRAO 140-Foot Radio Telescope "What we believe we have found," said Douglas P. Finkbeiner of Princeton University's Department of Astrophysics, "is the first hard evidence for electric dipole emission from rapidly rotating dust grains. If our studies are confirmed, it will be the first new source of continuum emission to be conclusively identified in the interstellar medium in nearly the past 20 years." Finkbeiner believes that these emissions have the potential in the future of revealing new and exciting information about the interstellar medium; they also may help to refine future studies of the Cosmic Microwave Background Radiation. The results from this study, which took place in spring 1999, were accepted for publication in Astrophysical Journal. Other contributors to this paper include David J. Schlegel, department of astrophysics, Princeton University; Curtis Frank, department of astronomy, University of Maryland; and Carl Heiles, department of astronomy, University of California at Berkeley. "The idea of dust grains emitting radiation by rotating is not new," comments Finkbeiner, "but to date it has been somewhat speculative." Scientists first proposed in 1957 that dust grains could emit radio signals, if they were caused to rotate rapidly enough. It was believed, however, that these radio emissions would be negligibly small - too weak to be of any impact to

The Detectability of Radio Auroral Emission from Proxima b

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

Burkhart, Blakesley; Loeb, Abraham

Magnetically active stars possess stellar winds whose interactions with planetary magnetic fields produce radio auroral emission. We examine the detectability of radio auroral emission from Proxima b, the closest known exosolar planet orbiting our nearest neighboring star, Proxima Centauri. Using the radiometric Bode’s law, we estimate the radio flux produced by the interaction of Proxima Centauri’s stellar wind and Proxima b’s magnetosphere for different planetary magnetic field strengths. For plausible planetary masses, Proxima b could produce radio fluxes of 100 mJy or more in a frequency range of 0.02–3 MHz for planetary magnetic field strengths of 0.007–1 G. According tomore » recent MHD models that vary the orbital parameters of the system, this emission is expected to be highly variable. This variability is due to large fluctuations in the size of Proxima b’s magnetosphere as it crosses the equatorial streamer regions of dense stellar wind and high dynamic pressure. Using the MHD model of Garraffo et al. for the variation of the magnetosphere radius during the orbit, we estimate that the observed radio flux can vary nearly by an order of magnitude over the 11.2-day period of Proxima b. The detailed amplitude variation depends on the stellar wind, orbital, and planetary magnetic field parameters. We discuss observing strategies for proposed future space-based observatories to reach frequencies below the ionospheric cutoff (∼10 MHz), which would be required to detect the signal we investigate.« less

Unknown radio emission at about 3 MHz recorded in Norway

NASA Astrophysics Data System (ADS)

Farges, T.; Blanc, E.; Strand, E.

2012-04-01

A wideband electric field antenna has been installed in Norway (at Hessdalen, 62°41' North and 11°12' East). A signal of 50 ms is automatically recorded every 5 s in order to monitor the spectral variations from 1 kHz to 5 MHz. Signals have been acquired during more than one year from September 2010 to December 2011. The measured electromagnetic spectrum is very similar to other spectra commonly measured in other places in the World. It shows emissions in numerous bands at fixed frequencies corresponding to radio transmissions in VLF, LF, MF and HF bands. However, one emission is quite different and arouses our curiosity. We find a quasi-continuous radio emission at a frequency varying from 2.7 to more than 3.4 MHz with a mean value of 3.0 MHz. The bandwidth is quite large (about 40 kHz) while it is about 9 kHz for all the other radio emissions at frequencies higher than 100 kHz. During the night, the frequency is relatively stable at about 3.1 MHz while during day-time a frequency shift of 200-300 kHz is often observed. These variations can be quick (few tens of minutes) or slow (several hours). Moreover, the emission disappears during day-time, the disappearance duration depending on the daylight duration. From November to the end of March, there is almost no disappearance while in April disappearances are more frequent and longer. From May to July, the emission disappears systematically during day-time from 6:00 UT to 20:00 UT. At the sunrise time the emission frequency suddenly decreases and systematically disappears when it reaches a threshold value (from 2.7 to 2.85 MHz). The emission (frequency and duration) is not influenced by the magnetic storms. We will show in the paper statistical results and some hypothesis on the mechanism which can produce this radio emission.

Discovery of radio emission from the brown dwarf LP944-20.

PubMed

Berger, E; Ball, S; Becker, K M; Clarke, M; Frail, D A; Fukuda, T A; Hoffman, I M; Mellon, R; Momjian, E; Murphy, N W; Teng, S H; Woodruff, T; Zauderer, B A; Zavala, R T

2001-03-15

Brown dwarfs are not massive enough to sustain thermonuclear fusion of hydrogen at their centres, but are distinguished from gas-giant planets by their ability to burn deuterium. Brown dwarfs older than approximately 10 Myr are expected to possess short-lived magnetic fields and to emit radio and X-rays only very weakly from their coronae. An X-ray flare was recently detected on the brown dwarf LP944-20, whereas previous searches for optical activity (and one X-ray search) yielded negative results. Here we report the discovery of quiescent and flaring radio emission from LP944-20, with luminosities several orders of magnitude larger than predicted by the empirical relation between the X-ray and radio luminosities that has been found for many types of stars. Interpreting the radio data within the context of synchrotron emission, we show that LP944-20 has an unusually weak magnetic field in comparison to active M-dwarf stars, which might explain the previous null optical and X-ray results, as well as the strength of the radio emissions compared to those at X-ray wavelengths.

Discovery of Misaligned Radio Emission in Galaxy Cluster Zw CL 2971

NASA Astrophysics Data System (ADS)

Wallack, Nicole; Migliore, C.; Resnick, A.; White, T.; Liu, C.

2014-01-01

In a search for green valley galaxies with radio loud active galactic nuclei (AGN), we found one such object that may be associated with the cluster of galaxies Zw CL 2971 (z = 0.098). Serendipitously, we found in this cluster a strong bent-jet radio source associated with the cluster's central dominant (cD) elliptical galaxy. The center of the cD galaxy is coincident (0.35 arcsecond) with the second brightest spot of radio continuum emission (34.3 mJy as measured by FIRST), but the brightest radio hotspot (66.8 mJy) is offset by 4.6 arcseconds 9 kpc at the redshift of the cluster) and has no visible counterpart. Furthermore, the optical spectrum of the cD galaxy has only weak emission lines, suggesting the absence of a currently active nucleus. It is possible that the counterpart is optically faint (possibly due to a recently completed duty cycle) or is not visible due to movement or position. If the radio source is a distant background object, then the brighter jet is most likely magnified by gravitational lensing. If the radio source is located at the redshift of the cluster, then the brighter radio jet trails backward toward and past the cD galaxy to a distance of ~120 kpc, while the fainter jet is bent at a nearly orthogonal angle, ~40 kpc away from the brightest radio hotspot, in the opposite direction. These geometric offsets could be used to constrain the duty cycle history of the AGN creating the radio emission, as well as the dynamical properties of the intracluster medium.

On the Evolution of the Cores of Radio Sources and Their Extended Radio Emission

NASA Astrophysics Data System (ADS)

Yuan, Zunli; Wang, Jiancheng

2012-01-01

The work in this paper aims at determining the evolution and possible co-evolution of radio-loud active galactic nuclei (AGNs) and their cores via their radio luminosity functions (i.e., total and core RLFs, respectively). Using a large combined sample of 1063 radio-loud AGNs selected at low radio frequency, we investigate the RLF at 408 MHz of steep-spectrum radio sources. Our results support a luminosity-dependent evolution. Using core flux density data of the complete sample 3CRR, we investigate the core RLF at 5.0 GHz. Based on the combined sample with incomplete core flux data, we also estimate the core RLF using a modified factor of completeness. Both results are consistent and show that the comoving number density of radio cores displays a persistent decline with redshift, implying a negative density evolution. We find that the core RLF is obviously different from the total RLF at the 408 MHz band which is mainly contributed by extended lobes, implying that the cores and extended lobes could not be co-evolving at radio emission.

Synthesis and biological evaluation of radio and dye labeled amino functionalized dendritic polyglycerol sulfates as multivalent anti-inflammatory compounds.

PubMed

Gröger, Dominic; Paulus, Florian; Licha, Kai; Welker, Pia; Weinhart, Marie; Holzhausen, Cornelia; Mundhenk, Lars; Gruber, Achim D; Abram, Ulrich; Haag, Rainer

2013-09-18

Herein we describe a platform technology for the synthesis and characterization of partially aminated, (35)S-labeled, dendritic polyglycerol sulfate (dPG(35)S amine) and fluorescent dPGS indocarbocyanine (ICC) dye conjugates. These polymer conjugates, based on a biocompatible dendritic polyglycerol scaffold, exhibit a high affinity to inflamed tissue in vivo and represent promising candidates for therapeutic and diagnostic applications. By utilizing a one-step sequential copolymerization approach, dendritic polyglycerol (Mn ≈ 4.5 kDa) containing 9.4% N-phthalimide protected amine functionalities was prepared on a large scale. Sulfation and simultaneous radio labeling with (35)SO3 pyridine complex, followed by cleavage of the N-phthalimide protecting groups, yielded dPG(35)S amine as a beta emitting, inflammation specific probe with free amino functionalities for conjugation. Furthermore, efficient labeling procedures with ICC via iminothiolane modification and subsequent "Michael" addition of the maleimide functionalized ICC dye, as well as by amide formation via NHS derivatized ICC on a dPGS amine scaffold, are described. The dPGS-ICC conjugates were investigated with respect to their photophysical properties, and both the radiolabeled and fluorescent compounds were comparatively visualized in histological tissue sections (radio detection and fluorescence microscopy) of animals treated with dPGS. Furthermore, cellular uptake of dPGS-ICC was found in endothelial cord blood (HUVEC) and the epithelial lung cells (A549). The presented synthetic routes allow a reproducible, controlled synthesis of dPGS amine on kilogram scale applying a one-pot batch reaction process. dPGS amine can be used for analysis via radioactivity or fluorescence, thereby creating a new platform for inflammation specific, multimodal imaging purposes using other attachable probes or contrast agents.

Magnetar-like X-Ray Bursts Suppress Pulsar Radio Emission

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

Archibald, R. F.; Lyutikov, M.; Kaspi, V. M.

Rotation-powered pulsars and magnetars are two different observational manifestations of neutron stars: rotation-powered pulsars are rapidly spinning objects that are mostly observed as pulsating radio sources, while magnetars, neutron stars with the highest known magnetic fields, often emit short-duration X-ray bursts. Here, we report simultaneous observations of the high-magnetic-field radio pulsar PSR J1119−6127 at X-ray, with XMM-Newton and NuSTAR , and at radio energies with the Parkes radio telescope, during a period of magnetar-like bursts. The rotationally powered radio emission shuts off coincident with the occurrence of multiple X-ray bursts and recovers on a timescale of ∼70 s. These observationsmore » of related radio and X-ray phenomena further solidify the connection between radio pulsars and magnetars and suggest that the pair plasma produced in bursts can disrupt the acceleration mechanism of radio-emitting particles.« less

A young source of optical emission from distant radio galaxies.

PubMed

Hammer, F; Fèvre, O Le; Angonin, M C

1993-03-25

DISTANT radio galaxies provide valuable insights into the properties of the young Universe-they are the only known extended optical sources at high redshift and might represent an early stage in the formation and evolution of galaxies in general. This extended optical emission often has very complex morphologies, but the origin of the light is still unclear. Here we report spectroscopic observations for several distant radio galaxies (0.75≤ z ≤ 1.1) in which the rest-frame spectra exhibit featureless continua between 2,500 Å and 5,000 Å. We see no evidence for the break in the spectrum at 4,000 Å expected for an old stellar population 1-3 , and suggest that young stars or scattered emissions from the active nuclei are responsible for most of the observed light. In either case, this implies that the source of the optical emission is com-parable in age to the associated radio source, namely 10 7 years or less.

The Influence of The Galilean Satellites on Radio Emissions From The Jovian System

NASA Technical Reports Server (NTRS)

Kurth, W. S.; Gurnett, D. A.; Menietti, J. D.

2000-01-01

The Galilean satellites influence radio emissions from the Jovian system in a variety of ways. The best and most familiar example of these is the Io control of decametric radiation discovered in 1964 by Bigg. Voyager observations of broadband kilometric radiation revealed a low-latitude shadow zone cast by the Io torus at frequencies between a few tens of kHz and about 1 MHz. Voyager also discovered narrowband kilometric radio emissions emanating from the outer edge of the torus. In this paper we will discuss expansions in the suite of satellite influences based on new observations by Galileo. These include the discovery of Ganymede's magnetosphere and evidence of radio emissions generated via mode conversion from upper hybrid waves in the frequency range of about 20 - 100 kHz. There is evidence that Ganymede may control some of the hectometric or low-frequency decametric radio emissions based on occultation measurements and statistical studies of radio emission occurrence as a function of Ganymede phase. Direction-finding measurements in the vicinity of Io suggest that a portion of the hectometric emissions may be generated near the lo L-shell. A rotationally modulated attenuation band in the hectometric emission appears to be the result of scattering at or near the Io L-shell where the waves propagate nearly parallel to the magnetic field. There is even a tantalizing hint of a Europa connection to the source of narrowband kilometric radiation.

Discovery of radio emission from the symbiotic X-ray binary system GX 1+4

NASA Astrophysics Data System (ADS)

van den Eijnden, J.; Degenaar, N.; Russell, T. D.; Miller-Jones, J. C. A.; Wijnands, R.; Miller, J. M.; King, A. L.; Rupen, M. P.

2018-02-01

We report the discovery of radio emission from the accreting X-ray pulsar and symbiotic X-ray binary GX 1+4 with the Karl G. Jansky Very Large Array. This is the first radio detection of such a system, wherein a strongly magnetized neutron star accretes from the stellar wind of an M-type giant companion. We measure a 9 GHz radio flux density of 105.3 ± 7.3 μJy, but cannot place meaningful constraints on the spectral index due to a limited frequency range. We consider several emission mechanisms that could be responsible for the observed radio source. We conclude that the observed properties are consistent with shocks in the interaction of the accretion flow with the magnetosphere, a synchrotron-emitting jet, or a propeller-driven outflow. The stellar wind from the companion is unlikely to be the origin of the radio emission. If the detected radio emission originates from a jet, it would show that strong magnetic fields (≥1012 G) do not necessarily suppress jet formation.

Observation of hectometric auroral radio emissions in Iceland

NASA Astrophysics Data System (ADS)

Sato, Y.; Ono, T.; Iizima, M.; Sato, N.

2006-12-01

The Earth's auroral region is an active radio source at frequencies from a few hertz to several megahertz. In the hectometric range, it was found that Terrestrial Hectometric Radiation (THR) is related to auroras by observations of the Ohzora satellite [Oya et al.(1985)]. In resent research, Shinbori et al. [2003] showed that occurrence of THR follows SC by several minutes using the Akebono satellite data. On the ground, auroral roar and MF burst were discovered by Kellogg and Monson [1979, 1984] and Weatherwax et al. [1994] in the northern Canada, respectively. Because there is not enough physical and geophysical characterization of these radio emissions, the physical mechanism of these phenomena in the auroral ionosphere has not been fully understood yet. We set up new observation system at Husafell station in Iceland in September, 2005 and have started to observe auroral radio emissions. Radio signals, which are received by the cross loop antennas, are converted into left- and right- handed polarized components within the frequency range from 1 MHz to 5 MHz. Based on the calibration of system, it was found that the possibility of occurence would be smaller than expected due to the low sensitivity because average power spectrum densities of auroral roar and MF burst are 50-100 nV/m/Hz^1/2. So, the system was planed to be upgraded in this September, which makes it possible to detect auroral roar and MF burst. It is expected that the detail physical process will be elucidated by clarifying the spectrum, polarization, dependence on the geomagnetic activity, and so on. In this presentation, we will show the improved points of the new system and preliminary observation results. There is a basic question whether auroral roar and MF burst observed on the ground are generated by the same process as THR observed by satellites. By comparing the results from the ground-based observation and the Akebono satellite observation of THR, it becomes possible to obtain a new

A Link Between X-ray Emission Lines and Radio Jets in 4U 1630-47?

NASA Astrophysics Data System (ADS)

Neilsen, Joseph; Coriat, Mickaël; Fender, Rob; Lee, Julia C.; Ponti, Gabriele; Tzioumis, A.; Edwards, Phillip; Broderick, Jess

2014-06-01

Recently, Díaz Trigo et al. reported an XMM-Newton detection of relativistically Doppler-shifted emission lines associated with steep-spectrum radio emission in the stellar-mass black hole candidate 4U 1630-47 during its 2012 outburst. They interpreted these lines as indicative of a baryonic jet launched by the accretion disk. We present a search for the same lines earlier in the same outburst using high-resolution X-ray spectra from the Chandra HETGS. While our observations (eight months prior to the XMM-Newton campaign) also coincide with detections of steep spectrum radio emission by the Australia Telescope Compact Array, we find a strong disk wind but no evidence for any relativistic X-ray emission lines. Indeed, despite ˜5× brighter radio emission, our Chandra spectra allow us to place an upper limit on the flux in the blueshifted Fe XXVI line that is ˜20× weaker than the line observed by Díaz Trigo et al. Thus we can conclusively say that radio emission is not universally associated with relativistically Doppler-shifted emission lines in 4U 1630-47. We explore several scenarios that could explain our differing results, including variations in the geometry of the jet or a mass-loading process or jet baryon content that evolves with the accretion state of the black hole. We also consider the possibility that the radio emission arises in an interaction between a jet and the nearby ISM, in which case the X-ray emission lines might be unrelated to the radio emission.

A Study of Nonthermal X-Ray and Radio Emission from the O Star 9 Sgr

NASA Technical Reports Server (NTRS)

Waldron, Wayne L.; Corcoran, Michael F.; Drake, Stephen A.

1999-01-01

The observed X-ray and highly variable nonthermal radio emission from OB stars has eluded explanation for more than 18 years. The most favorable model of X-ray production in these stars (shocks) predicts both nonthermal radio and X-ray emission. The nonthermal X-ray emission should occur above 2 keV and the variability of this X-ray component should also be comparable to the observed radio variability. To test this scenario, we proposed an ASC/VLA monitoring program to observe the OB star, 9 Sgr, a well known nonthermal, variable radio source and a strong X-ray source. We requested 625 ks ASCA observations with a temporal spacing of approximately 4 days which corresponds to the time required for a density disturbance to propagate to the 6 cm radio free-free photosphere. The X-ray observations were coordinated with 5 multi-wavelength VLA observations. These observations represent the first systematic attempt to investigate the relationship between the X-ray and radio emission in OB stars.

Mpc-scale diffuse radio emission in two massive cool-core clusters of galaxies

NASA Astrophysics Data System (ADS)

Sommer, Martin W.; Basu, Kaustuv; Intema, Huib; Pacaud, Florian; Bonafede, Annalisa; Babul, Arif; Bertoldi, Frank

2017-04-01

Radio haloes are diffuse synchrotron sources on scales of ˜1 Mpc that are found in merging clusters of galaxies, and are believed to be powered by electrons re-accelerated by merger-driven turbulence. We present measurements of extended radio emission on similarly large scales in two clusters of galaxies hosting cool cores: Abell 2390 and Abell 2261. The analysis is based on interferometric imaging with the Karl G. Jansky Very Large Array, Very Large Array and Giant Metrewave Radio Telescope. We present detailed radio images of the targets, subtract the compact emission components and measure the spectral indices for the diffuse components. The radio emission in A2390 extends beyond a known sloshing-like brightness discontinuity, and has a very steep in-band spectral slope at 1.5 GHz that is similar to some known ultrasteep spectrum radio haloes. The diffuse signal in A2261 is more extended than in A2390 but has lower luminosity. X-ray morphological indicators, derived from XMM-Newton X-ray data, place these clusters in the category of relaxed or regular systems, although some asymmetric features that can indicate past minor mergers are seen in the X-ray brightness images. If these two Mpc-scale radio sources are categorized as giant radio haloes, they question the common assumption of radio haloes occurring exclusively in clusters undergoing violent merging activity, in addition to commonly used criteria for distinguishing between radio haloes and minihaloes.

Solar radio emissions: 2D full PIC simulations

NASA Astrophysics Data System (ADS)

Pierre, H.; Sgattoni, A.; Briand, C.; Amiranoff, F.; Riconda, C.

2016-12-01

Solar radio emissions are electromagnetic waves observed at the local plasma frequency and/or at twice the plasma frequency. To describe their origin a multi-stage model has been proposed by Ginzburg & Zhelezniakov (1958) and further developed by several authors, which consider a succession of non-linear three-wave interaction processes. Electron beams accelerated by solar flares travel in the interplanetary plasma and provide the free energy for the development of plasma instabilities. The model describes how part of the free energy of these beams can be transformed in a succession of plasma waves and eventually into electromagnetic waves. Following the work of Thurgood & Tsiklauri (2015) we performed several 2D Particle In Cell simulations. The simulations follow the entire set of processes from the electron beam propagation in the background plasma to the generation of the electromagnetic waves in particular the 2ωp emission, including the excitation of the low frequency waves. As suggested by Thurgood & Tsiklauri (2015) it is possible to identify regimes where the radiation emission can be directly linked to the electron beams. Our attention was devoted to estimate the conversion efficiency from electron kinetic energy to the em energy, and the growth rate of the several processes which can be identified. We studied the emission angles of the 2ωpradiation and compared them with the theoretical predictions of Willes et. al. (1995). We also show the role played by some numerical parameters i.e. the size and shape of the simulation box. This work is the first step to prepare laser-plasma experiments. V. L. Ginzburg, V. V. Zhelezniakov On the Possible Mechanisms of Sporadic Solar Radio Emission (Radiation in an Isotropic Plasma) Soviet Astronomy, Vol. 2, p.653 (1958) J. O. Thurgood and D. Tsiklauri Self-consistent particle-in-cell simulations of funda- mental and harmonic plasma radio emission mechanisms. Astronomy & Astrophysics 584, A83 (2015). A. Willes, P

Probing the radio emission from air showers with polarization measurements

NASA Astrophysics Data System (ADS)

Aab, A.; Abreu, P.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Albuquerque, I. F. M.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Alves Batista, R.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Antičić, T.; Aramo, C.; Arqueros, F.; Asorey, H.; Assis, P.; Aublin, J.; Ave, M.; Avenier, M.; Avila, G.; Badescu, A. M.; Barber, K. B.; Bardenet, R.; Bäuml, J.; Baus, C.; Beatty, J. J.; Becker, K. H.; Bellido, J. A.; BenZvi, S.; Berat, C.; Bertou, X.; Biermann, P. L.; Billoir, P.; Blanco, F.; Blanco, M.; Bleve, C.; Blümer, H.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Bonino, R.; Borodai, N.; Brack, J.; Brancus, I.; Brogueira, P.; Brown, W. C.; Buchholz, P.; Bueno, A.; Buscemi, M.; Caballero-Mora, K. S.; Caccianiga, B.; Caccianiga, L.; Candusso, M.; Caramete, L.; Caruso, R.; Castellina, A.; Cataldi, G.; Cazon, L.; Cester, R.; Cheng, S. H.; Chiavassa, A.; Chinellato, J. A.; Chudoba, J.; Cilmo, M.; Clay, R. W.; Cocciolo, G.; Colalillo, R.; Collica, L.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cooper, M. J.; Coutu, S.; Covault, C. E.; Criss, A.; Cronin, J.; Curutiu, A.; Dallier, R.; Daniel, B.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; De Domenico, M.; de Jong, S. J.; De La Vega, G.; de Mello Junior, W. J. M.; de Mello Neto, J. R. T.; De Mitri, I.; de Souza, V.; de Vries, K. D.; del Peral, L.; Deligny, O.; Dembinski, H.; Dhital, N.; Di Giulio, C.; Di Matteo, A.; Diaz, J. C.; Díaz Castro, M. L.; Diep, P. N.; Diogo, F.; Dobrigkeit, C.; Docters, W.; D'Olivo, J. C.; Dong, P. N.; Dorofeev, A.; dos Anjos, J. C.; Dova, M. T.; Ebr, J.; Engel, R.; Erdmann, M.; Escobar, C. O.; Espadanal, J.; Etchegoyen, A.; Facal San Luis, P.; Falcke, H.; Fang, K.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Ferguson, A. P.; Fick, B.; Figueira, J. M.; Filevich, A.; Filipčič, A.; Foerster, N.; Fox, B. D.; Fracchiolla, C. E.; Fraenkel, E. D.; Fratu, O.; Fröhlich, U.; Fuchs, B.; Gaior, R.; Gamarra, R. F.; Gambetta, S.; García, B.; Garcia Roca, S. T.; Garcia-Gamez, D.; Garcia-Pinto, D.; Garilli, G.; Gascon Bravo, A.; Gemmeke, H.; Ghia, P. L.; Giammarchi, M.; Giller, M.; Gitto, J.; Glaser, C.; Glass, H.; Gomez Albarracin, F.; Gómez Berisso, M.; Gómez Vitale, P. F.; Gonçalves, P.; Gonzalez, J. G.; Gookin, B.; Gorgi, A.; Gorham, P.; Gouffon, P.; Grebe, S.; Griffith, N.; Grillo, A. F.; Grubb, T. D.; Guardincerri, Y.; Guarino, F.; Guedes, G. P.; Hansen, P.; Harari, D.; Harrison, T. A.; Harton, J. L.; Haungs, A.; Hebbeker, T.; Heck, D.; Herve, A. E.; Hill, G. C.; Hojvat, C.; Hollon, N.; Holt, E.; Homola, P.; Hörandel, J. R.; Horvath, P.; Hrabovský, M.; Huber, D.; Huege, T.; Insolia, A.; Isar, P. G.; Jansen, S.; Jarne, C.; Josebachuili, M.; Kadija, K.; Kambeitz, O.; Kampert, K. H.; Karhan, P.; Kasper, P.; Katkov, I.; Kégl, B.; Keilhauer, B.; Keivani, A.; Kemp, E.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Knapp, J.; Krause, R.; Krohm, N.; Krömer, O.; Kruppke-Hansen, D.; Kuempel, D.; Kunka, N.; La Rosa, G.; LaHurd, D.; Latronico, L.; Lauer, R.; Lauscher, M.; Lautridou, P.; Le Coz, S.; Leão, M. S. A. B.; Lebrun, D.; Lebrun, P.; Leigui de Oliveira, M. A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; López, R.; Lopez Agüera, A.; Louedec, K.; Lozano Bahilo, J.; Lu, L.; Lucero, A.; Ludwig, M.; Lyberis, H.; Maccarone, M. C.; Malacari, M.; Maldera, S.; Maller, J.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Marin, V.; Mariş, I. C.; Marquez Falcon, H. R.; Marsella, G.; Martello, D.; Martin, L.; Martinez, H.; Martínez Bravo, O.; Martraire, D.; Masías Meza, J. J.; Mathes, H. J.; Matthews, J.; Matthews, J. A. J.; Matthiae, G.; Maurel, D.; Maurizio, D.; Mayotte, E.; Mazur, P. O.; Medina, C.; Medina-Tanco, G.; Melissas, M.; Melo, D.; Menichetti, E.; Menshikov, A.; Messina, S.; Meyhandan, R.; Mićanović, S.; Micheletti, M. I.; Middendorf, L.; Minaya, I. A.; Miramonti, L.; Mitrica, B.; Molina-Bueno, L.; Mollerach, S.; Monasor, M.; Monnier Ragaigne, D.; Montanet, F.; Morales, B.; Morello, C.; Moreno, J. C.; Mostafá, M.; Moura, C. A.; Muller, M. A.; Müller, G.; Münchmeyer, M.; Mussa, R.; Navarra, G.; Navarro, J. L.; Navas, S.; Necesal, P.; Nellen, L.; Nelles, A.; Neuser, J.; Nhung, P. T.; Niechciol, M.; Niemietz, L.; Niggemann, T.; Nitz, D.; Nosek, D.; Nožka, L.; Oehlschläger, J.; Olinto, A.; Oliveira, M.; Ortiz, M.; Pacheco, N.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Palmieri, N.; Parente, G.; Parra, A.; Pastor, S.; Paul, T.; Pech, M.; PeÂķala, J.; Pelayo, R.; Pepe, I. M.; Perrone, L.; Pesce, R.; Petermann, E.; Petrera, S.; Petrolini, A.; Petrov, Y.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Plum, M.; Pontz, M.; Porcelli, A.; Preda, T.; Privitera, P.; Prouza, M.; Quel, E. J.; Querchfeld, S.; Quinn, S.; Rautenberg, J.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Riggi, S.; Risse, M.; Ristori, P.; Rivera, H.; Rizi, V.; Roberts, J.; Rodrigues de Carvalho, W.; Rodriguez Cabo, I.; Rodriguez Fernandez, G.; Rodriguez Martino, J.; Rodriguez Rojo, J.; Rodríguez-Frías, M. D.; Ros, G.; Rosado, J.; Rossler, T.; Roth, M.; Rouillé-d'Orfeuil, B.; Roulet, E.; Rovero, A. C.; Rühle, C.; Saffi, S. J.; Saftoiu, A.; Salamida, F.; Salazar, H.; Salesa Greus, F.; Salina, G.; Sánchez, F.; Sanchez-Lucas, P.; Santo, C. E.; Santos, E.; Santos, E. M.; Sarazin, F.; Sarkar, B.; Sarmento, R.; Sato, R.; Scharf, N.; Scherini, V.; Schieler, H.; Schiffer, P.; Schmidt, A.; Scholten, O.; Schoorlemmer, H.; Schovánek, P.; Schröder, F. G.; Schulz, A.; Schulz, J.; Sciutto, S. J.; Scuderi, M.; Segreto, A.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sidelnik, I.; Sigl, G.; Sima, O.; Śmiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sorokin, J.; Spinka, H.; Squartini, R.; Srivastava, Y. N.; Stanič, S.; Stapleton, J.; Stasielak, J.; Stephan, M.; Straub, M.; Stutz, A.; Suarez, F.; Suomijärvi, T.; Supanitsky, A. D.; Šuša, T.; Sutherland, M. S.; Swain, J.; Szadkowski, Z.; Szuba, M.; Tapia, A.; Tartare, M.; Taşcǎu, O.; Thao, N. T.; Tiffenberg, J.; Timmermans, C.; Tkaczyk, W.; Todero Peixoto, C. J.; Toma, G.; Tomankova, L.; Tomé, B.; Tonachini, A.; Torralba Elipe, G.; Torres Machado, D.; Travnicek, P.; Tridapalli, D. B.; Trovato, E.; Tueros, M.; Ulrich, R.; Unger, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van Aar, G.; van den Berg, A. M.; van Velzen, S.; van Vliet, A.; Varela, E.; Vargas Cárdenas, B.; Varner, G.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Verzi, V.; Vicha, J.; Videla, M.; Villaseñor, L.; Wahlberg, H.; Wahrlich, P.; Wainberg, O.; Walz, D.; Watson, A. A.; Weber, M.; Weidenhaupt, K.; Weindl, A.; Werner, F.; Westerhoff, S.; Whelan, B. J.; Widom, A.; Wieczorek, G.; Wiencke, L.; Wilczyńska, B.; Wilczyński, H.; Will, M.; Williams, C.; Winchen, T.; Wundheiler, B.; Wykes, S.; Yamamoto, T.; Yapici, T.; Younk, P.; Yuan, G.; Yushkov, A.; Zamorano, B.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zaw, I.; Zepeda, A.; Zhou, J.; Zhu, Y.; Zimbres Silva, M.; Ziolkowski, M.; Pierre Auger Collaboration

2014-03-01

The emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed that cannot be described by the geomagnetic emission process. The data provide strong evidence that the other electric field component is polarized radially with respect to the shower axis, in agreement with predictions made by Askaryan who described radio emission from particle showers due to a negative charge excess in the front of the shower. Our results are compared to calculations which include the radiation mechanism induced by this charge-excess process.

A giant radio flare from Cygnus X-3 with associated γ-ray emission: The 2011 radio and γ-ray flare of Cyg X-3

DOE PAGES

Corbel, S.; Dubus, G.; Tomsick, J. A.; ...

2012-04-10

With frequent flaring activity of its relativistic jets, Cygnus X-3 (Cyg X-3) is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high-energy γ-ray emission, thanks to detections by Fermi Large Area Telescope (Fermi/LAT) and AGILE. In 2011, we observed Cyg X-3 in order to transit to a soft X-ray state, which is known to be associated with high-energy γ-ray emission. We present the results of a multiwavelength campaign covering a quenched state, when radio emission from Cyg X-3 is at its weakest and the X-ray spectrum is very soft. A giant (~20more » Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E≥ 100 MeV) reveal renewed γ-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the γ-ray emission is not exclusively related to the rare giant radio flares. A three-week period of γ-ray emission is also detected when Cyg X-3 was weakly flaring in radio, right before transition to the radio quenched state. There were no γ-rays observed during the ~1-month long quenched state, when the radio flux is weakest. These results suggest transitions into and out of the ultrasoft X-ray (radio-quenched) state trigger γ-ray emission, implying a connection to the accretion process, and also that the γ-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.« less

Numerical simulations of particle acceleration and low frequency radio emission in stellar environments

NASA Astrophysics Data System (ADS)

Paraskevi Moschou, Sofia; Sokolov, Igor; Cohen, Ofer; Drake, Jeremy J.; Borovikov, Dmitry; Alvarado-Gomez, Julian D.; Garraffo, Cecilia

2018-06-01

Due to their favorable atmospheric window radio waves are a useful tool for ground-based observations of astrophysical systems throughout a plethora of scales, from cosmological down to planetary ones. A wide range of physical mechanisms, from thermal processes to eruptive events linked to magnetic reconnection, can generate emission in radio frequencies. Radio waves have the distinct characteristic that they follow curved paths as they propagate in stratified environments, such as the solar corona, due to their dependence on the refraction index. Low frequency radio rays in particular are affected the most by refraction.Solar radio observations are of particular importance, since it is possible to spatially resolve the Sun and its corona and gain insights on highly dynamic and complex radio-emitting phenomena. The multi-scale problem of particle acceleration and energy partition between CMEs, flares and SEPs requires both MHD and kinetic considerations to account for the emission and mass propagation through the interplanetary space.Radio observations can play a significant role in the rapidly developing area of exoplanetary research and provide insights on the stellar environments of those systems. Even though a large number of flares has been observed for different stellar types, nevertheless there is a lack of stellar CME observations. Currently, the most promising method to incontrovertibly observe stellar CMEs is through Type II radio bursts. Low frequency radio emission can also be produced by the interaction of a magnetized planet with the stellar wind of the host star.The above mentioned characteristics of radio-waves make their integration into numerical simulations imperative for capturing and disentangling the complex radio emitting processes along the actual radio paths and provide the observers with detection limits for future Earth- and space-based missions. Radio synthetic imaging tools incorporated in realistic computational codes are already

NONCOHERENT MECHANISMS OF SPORADIC SOLAR RADIO EMISSION IN THE CASE OF A MAGNETOACTIVE CORONAL PLASMA

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

Ginzburg, V.L.; Zheleznyakov, V.V.

1961-07-01

Noncoherent mechanisms of sporadic solar radiofrequency emission are discussed, with the effect of magnetic field taken into account. The emission is designated conventionally as noncoherent emission when the intensities contributed by discrete particles may be combined additively with reabsorption taken into account, while intensification of waves in the system itself (e.g., in the stream of particles) is negligible. It is shown that noncoherent mechanisms may be held responsible for enhanced radio emission above sunspots, and for type IV and type V solar radio bursts. Solar radio bursts of types I, II, and III cannot be related to noncoherent radio emissionmore » of either the synchrotron radiation or the Cherehkov radiation variety. It is also shown that type II and type III bursts may not be related to the noncoherent emission of plasma waves in an isotropic plasma. (auth)« less

Low-frequency polarization measurements of the diffuse radio emission of the galaxy

NASA Astrophysics Data System (ADS)

Vinyaikin, E. N.; Paseka, A. M.

2015-07-01

Polarization measurements of diffuse Galactic radio emission at 151.5, 198, 217, 237, and 290 MHz have been carried out in the direction of the North Celestial Pole, North Galactic Pole, one region of the North Polar Spur, minimum radio brightness of the Northern sky ( l = 190°, b = 50°), and in the direction l = 147°, b = 9° in the so-called FAN region with enhanced polarization. The results obtained testify to the presence of low spatial frequencies in the angular distribution of the Stokes parameters Q and U of the diffuse Galactic synchrotron emission that are not detectable in interferometric observations. The spectra of the brightness temperature of the polarized component, rotation measures, and intrinsic polarization position angles of the radio emission in the studied regions are presented.

Wavelet Based Characterization of Low Radio Frequency Solar Emissions

NASA Astrophysics Data System (ADS)

Suresh, A.; Sharma, R.; Das, S. B.; Oberoi, D.; Pankratius, V.; Lonsdale, C.

2016-12-01

Low-frequency solar radio observations with the Murchison Widefield Array (MWA) have revealed the presence of numerous short-lived, narrow-band weak radio features, even during quiet solar conditions. In their appearance in in the frequency-time plane, they come closest to the solar type III bursts, but with much shorter spectral spans and flux densities, so much so that they are not detectable with the usual swept frequency radio spectrographs. These features occur at rates of many thousand features per hour in the 30.72 MHz MWA bandwidth, and hence necessarily require an automated approach to determine robust statistical estimates of their properties, e.g., distributions of spectral widths, temporal spans, flux densities, slopes in the time-frequency plane and distribution over frequency. To achieve this, a wavelet decomposition approach has been developed for feature recognition and subsequent parameter extraction from the MWA dynamic spectrum. This work builds on earlier work by the members of this team to achieve a reliable flux calibration in a computationally efficient manner. Preliminary results show that the distribution of spectral span of these features peaks around 3 MHz, most of them last for less than two seconds and are characterized by flux densities of about 60% of the background solar emission. In analogy with the solar type III bursts, this non-thermal emission is envisaged to arise via coherent emission processes. There is also an exciting possibility that these features might correspond to radio signatures of nanoflares, hypothesized (Gold, 1964; Parker, 1972) to explain coronal heating.

A Link between X-Ray Emission Lines and Radio Jets in 4U 1630-47?

NASA Astrophysics Data System (ADS)

Neilsen, Joseph; Coriat, Mickaël; Fender, Rob; Lee, Julia C.; Ponti, Gabriele; Tzioumis, Anastasios K.; Edwards, Philip G.; Broderick, Jess W.

2014-03-01

Recently, Díaz Trigo et al. reported an XMM-Newton detection of relativistically Doppler-shifted emission lines associated with steep-spectrum radio emission in the stellar-mass black hole candidate 4U 1630-47 during its 2012 outburst. They interpreted these lines as indicative of a baryonic jet launched by the accretion disk. Here we present a search for the same lines earlier in the same outburst using high-resolution X-ray spectra from the Chandra HETGS. While our observations (eight months prior to the XMM-Newton campaign) also coincide with detections of steep spectrum radio emission by the Australia Telescope Compact Array, we find no evidence for any relativistic X-ray emission lines. Indeed, despite ~5 × brighter radio emission, our Chandra spectra allow us to place an upper limit on the flux in the blueshifted Fe XXVI line that is >~ 20 × weaker than the line observed by Díaz Trigo et al. We explore several scenarios that could explain our differing results, including variations in the geometry of the jet or a mass-loading process or jet baryon content that evolves with the accretion state of the black hole. We also consider the possibility that the radio emission arises in an interaction between a jet and the nearby interstellar medium, in which case the X-ray emission lines might be unrelated to the radio emission.

Radio imaging of the very-high-energy gamma-ray emission region in the central engine of a radio galaxy.

PubMed

Acciari, V A; Aliu, E; Arlen, T; Bautista, M; Beilicke, M; Benbow, W; Bradbury, S M; Buckley, J H; Bugaev, V; Butt, Y; Byrum, K; Cannon, A; Celik, O; Cesarini, A; Chow, Y C; Ciupik, L; Cogan, P; Cui, W; Dickherber, R; Fegan, S J; Finley, J P; Fortin, P; Fortson, L; Furniss, A; Gall, D; Gillanders, G H; Grube, J; Guenette, R; Gyuk, G; Hanna, D; Holder, J; Horan, D; Hui, C M; Humensky, T B; Imran, A; Kaaret, P; Karlsson, N; Kieda, D; Kildea, J; Konopelko, A; Krawczynski, H; Krennrich, F; Lang, M J; LeBohec, S; Maier, G; McCann, A; McCutcheon, M; Millis, J; Moriarty, P; Ong, R A; Otte, A N; Pandel, D; Perkins, J S; Petry, D; Pohl, M; Quinn, J; Ragan, K; Reyes, L C; Reynolds, P T; Roache, E; Roache, E; Rose, H J; Schroedter, M; Sembroski, G H; Smith, A W; Swordy, S P; Theiling, M; Toner, J A; Varlotta, A; Vincent, S; Wakely, S P; Ward, J E; Weekes, T C; Weinstein, A; Williams, D A; Wissel, S; Wood, M; Walker, R C; Davies, F; Hardee, P E; Junor, W; Ly, C; Aharonian, F; Akhperjanian, A G; Anton, G; Barres de Almeida, U; Bazer-Bachi, A R; Becherini, Y; Behera, B; Bernlöhr, K; Bochow, A; Boisson, C; Bolmont, J; Borrel, V; Brucker, J; Brun, F; Brun, P; Bühler, R; Bulik, T; Büsching, I; Boutelier, T; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Chounet, L-M; Clapson, A C; Coignet, G; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubois, F; Dubus, G; Dyks, J; Dyrda, M; Egberts, K; Emmanoulopoulos, D; Espigat, P; Farnier, C; Feinstein, F; Fiasson, A; Förster, A; Fontaine, G; Füssling, M; Gabici, S; Gallant, Y A; Gérard, L; Gerbig, D; Giebels, B; Glicenstein, J F; Glück, B; Goret, P; Göhring, D; Hauser, D; Hauser, M; Heinz, S; 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; Jahn, C; Jung, I; Katarzyński, K; Katz, U; Kaufmann, S; Kendziorra, E; Kerschhaggl, M; Khangulyan, D; Khélifi, B; Keogh, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Lamanna, G; Lenain, J-P; Lohse, T; Marandon, V; Martin, J M; Martineau-Huynh, O; Marcowith, A; Maurin, D; McComb, T J L; Medina, M C; Moderski, R; Moulin, E; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nicholas, B; Niemiec, J; Nolan, S J; Ohm, S; Olive, J-F; de Oña Wilhelmi, E; Orford, K J; Ostrowski, M; Panter, M; Paz Arribas, M; Pedaletti, G; Pelletier, G; Petrucci, P-O; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raubenheimer, B C; Raue, M; Rayner, S M; Renaud, M; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Ruppel, J; Sahakian, V; Santangelo, A; Schlickeiser, R; Schöck, F M; Schröder, R; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sikora, M; Skilton, J L; Sol, H; Spangler, D; Stawarz, Ł; Steenkamp, R; Stegmann, C; Stinzing, F; Superina, G; Szostek, A; Tam, P H; Tavernet, J-P; Terrier, R; Tibolla, O; Tluczykont, M; van Eldik, C; Vasileiadis, G; Venter, C; Venter, L; Vialle, J P; Vincent, P; Vivier, M; Völk, H J; Volpe, F; Wagner, S J; Ward, M; Zdziarski, A A; Zech, A; Anderhub, H; Antonelli, L A; Antoranz, P; Backes, M; Baixeras, C; Balestra, S; Barrio, J A; Bastieri, D; Becerra González, J; Becker, J K; Bednarek, W; Berger, K; Bernardini, E; Biland, A; Bock, R K; Bonnoli, G; Bordas, P; Borla Tridon, D; Bosch-Ramon, V; Bose, D; Braun, I; Bretz, T; Britvitch, I; Camara, M; Carmona, E; Commichau, S; Contreras, J L; Cortina, J; Costado, M T; Covino, S; Curtef, V; Dazzi, F; De Angelis, A; De Cea del Pozo, E; Delgado Mendez, C; De los Reyes, R; De Lotto, B; De Maria, M; De Sabata, F; Dominguez, A; Dorner, D; Doro, M; Elsaesser, D; Errando, M; Ferenc, D; Fernández, E; Firpo, R; Fonseca, M V; Font, L; Galante, N; García López, R J; Garczarczyk, M; Gaug, M; Goebel, F; Hadasch, D; Hayashida, M; Herrero, A; Hildebrand, D; Höhne-Mönch, D; Hose, J; Hsu, C C; Jogler, T; Kranich, D; La Barbera, A; Laille, A; Leonardo, E; Lindfors, E; Lombardi, S; Longo, F; López, M; Lorenz, E; Majumdar, P; Maneva, G; Mankuzhiyil, N; Mannheim, K; Maraschi, L; Mariotti, M; Martínez, M; Mazin, D; Meucci, M; Miranda, J M; Mirzoyan, R; Miyamoto, H; Moldón, J; Moles, M; Moralejo, A; Nieto, D; Nilsson, K; Ninkovic, J; Oya, I; Paoletti, R; Paredes, J M; Pasanen, M; Pascoli, D; Pauss, F; Pegna, R G; Perez-Torres, M A; Persic, M; Peruzzo, L; Prada, F; Prandini, E; Puchades, N; Reichardt, I; Rhode, W; Ribó, M; Rico, J; Rissi, M; Robert, A; Rügamer, S; Saggion, A; Saito, T Y; Salvati, M; Sanchez-Conde, M; Satalecka, K; Scalzotto, V; Scapin, V; Schweizer, T; Shayduk, M; Shore, S N; Sidro, N; Sierpowska-Bartosik, A; Sillanpää, A; Sitarek, J; Sobczynska, D; Spanier, F; Stamerra, A; Stark, L S; Takalo, L; Tavecchio, F; Temnikov, P; Tescaro, D; Teshima, M; Torres, D F; Turini, N; Vankov, H; Wagner, R M; Zabalza, V; Zandanel, F; Zanin, R; Zapatero, J

2009-07-24

The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.

Periodic Bursts of Jovian Non-Io Decametric Radio Emission

NASA Technical Reports Server (NTRS)

Panchenko, M.; Rucker, H O.; Farrell, W. M.

2013-01-01

During the years 2000-2011 the radio instruments onboard Cassini, Wind and STEREO spacecraft have Recorded a large amount of the Jovian decametric radio emission (DAM). In this paper we report on the analysis of the new type of Jovian periodic radio bursts recently revealed in the decametric frequency range. These bursts, which are non-Io component of DAM, are characterized by a strong periodic reoccurrence over several Jovian days with a period approx. = 1:5% longer than the rotation rate of the planet's magnetosphere (System III). The bursts are typically observed between 4 and 12 MHz and their occurrence probability has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300 deg. and 60 deg. (via 360 deg.). The stereoscopic multispacecraft observations have shown that the radio sources of the periodic bursts radiate in a non-axisymmetric hollow cone-like pattern and sub-corotate with Jupiter remaining active during several planet's rotations. The occurrence of the periodic non-Io DAM bursts is strongly correlated with pulses of the solar wind ram pressure at Jupiter. Moreover the periodic bursts exhibit a tendency to occur in groups every approx. 25 days. The polarization measurements have shown that the periodic bursts are right hand polarized radio emission associated with the Northern magnetic hemisphere of Jupiter. We suggest that periodic non-Io DAM bursts may be connected with the interchange instability in Io plasma torus triggered by the solar wind.

Periodic bursts of Jovian non-Io decametric radio emission

PubMed Central

Panchenko, M.; Rucker, H.O.; Farrell, W.M.

2013-01-01

During the years 2000–2011 the radio instruments onboard Cassini, Wind and STEREO spacecraft have recorded a large amount of the Jovian decametric radio emission (DAM). In this paper we report on the analysis of the new type of Jovian periodic radio bursts recently revealed in the decametric frequency range. These bursts, which are non-Io component of DAM, are characterized by a strong periodic reoccurrence over several Jovian days with a period ≈1.5% longer than the rotation rate of the planet's magnetosphere (System III). The bursts are typically observed between 4 and 12 MHz and their occurrence probability has been found to be significantly higher in the sector of Jovian Central Meridian Longitude between 300° and 60° (via 360°). The stereoscopic multispacecraft observations have shown that the radio sources of the periodic bursts radiate in a non-axisymmetric hollow cone-like pattern and sub-corotate with Jupiter remaining active during several planet's rotations. The occurrence of the periodic non-Io DAM bursts is strongly correlated with pulses of the solar wind ram pressure at Jupiter. Moreover the periodic bursts exhibit a tendency to occur in groups every ∼25 days. The polarization measurements have shown that the periodic bursts are right hand polarized radio emission associated with the Northern magnetic hemisphere of Jupiter. We suggest that periodic non-Io DAM bursts may be connected with the interchange instability in Io plasma torus triggered by the solar wind. PMID:23585696

Bright radio emission from an ultraluminous stellar-mass microquasar in M 31.

PubMed

Middleton, Matthew J; Miller-Jones, James C A; Markoff, Sera; Fender, Rob; Henze, Martin; Hurley-Walker, Natasha; Scaife, Anna M M; Roberts, Timothy P; Walton, Dominic; Carpenter, John; Macquart, Jean-Pierre; Bower, Geoffrey C; Gurwell, Mark; Pietsch, Wolfgang; Haberl, Frank; Harris, Jonathan; Daniel, Michael; Miah, Junayd; Done, Chris; Morgan, John S; Dickinson, Hugh; Charles, Phil; Burwitz, Vadim; Della Valle, Massimo; Freyberg, Michael; Greiner, Jochen; Hernanz, Margarita; Hartmann, Dieter H; Hatzidimitriou, Despina; Riffeser, Arno; Sala, Gloria; Seitz, Stella; Reig, Pablo; Rau, Arne; Orio, Marina; Titterington, David; Grainge, Keith

2013-01-10

A subset of ultraluminous X-ray sources (those with luminosities of less than 10(40) erg s(-1); ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of ∼5-20M cicled dot, probably by means of an accretion disk. The X-ray and radio emission are coupled in such Galactic sources; the radio emission originates in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium hinders the determination of the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source in the nearby galaxy M 31, whose peak luminosity exceeded 10(39) erg s(-1). The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a black hole of stellar mass. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.

From Radio with Love: An Overview of the Role of Radio Observations in Understanding High-Energy Emission from Active Galaxies

NASA Technical Reports Server (NTRS)

Ojha, Roopesh

2012-01-01

The gamma-ray satellite Fermi and the ground based TeV facilities MAGIC, VERITAS and HESS have ushered in a new era in the observation of high-energy emission from active galaxies. The energy budgets of these objects have a major contribution from gamma-rays and it is simply not possible to understand their physics without high-energy observations. Though the exact mechanisms for high-energy production in galaxies remains an open question, gamma-rays typically result from interactions between high-energy particles. Via different interactions these same particles can produce radio emission. Thus the non-thermal nature of gamma-ray emission practically guarantees that high-energy emitters are also radio loud. Aside from their obvious role as a component of multiwavelength analysis, radio observations provide two crucial elements essential to understanding the source structure and physical processes of high-energy emitters: very high timing resolution and very high spatial resolution. A brief overview of the unique role played by radio observations in unraveling the mysteries of the high energy Universe as presented here.

Searching the Nearest Stars for Exoplanetary Radio Emission: VLA and LOFAR Observations

NASA Astrophysics Data System (ADS)

Knapp, Mary; Winterhalter, Daniel; Lazio, Joseph

2016-10-01

Six of the eight solar system planets and one moon (Ganymede) exhibit present-day dynamo magnetic fields. To date, however, there are no conclusive detections of exoplanetary magnetic fields. Low frequency radio emission via the cyclotron maser instability (CMI) from interactions between a planet and the solar/stellar wind is the most direct means of detecting and characterizing planetary/exoplanetary magnetic fields. We have undertaken a survey of the very nearest stars in low frequency radio (30 MHz - 4 GHz) in order to search for yet-undiscovered planets. The closest stars are chosen in order to reduce the attenuation of the magnetospheric radio signal by distance dilution, thereby increasing the chances of making a detection if a planet with a strong magnetic field is present. The VLA telescope (P-band: 230-470 MHz, L-band: 1-2 GHz, S-band: 2-4 GHz) and LOFAR telescope (LBA: 30-75 MHz) have been used to conduct this survey.This work focuses on VLA and LOFAR observations of an M-dwarf binary system: GJ 725. We present upper limits on radio flux as a function of frequency. Since the peak emission frequency of CMI-type emission is the local plasma frequency in the emission region, the peak frequency of planetary radio emission is a direct proxy for the magnetic field strength of the planet. Our spectral irradiance upper limits therefore represent upper limits on the magnetic field strengths of any planets in the GJ 725 system.Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Measurement of radio emission from extensive air showers with LOPES

NASA Astrophysics Data System (ADS)

Hörandel, J. R.; Apel, W. D.; Arteaga, J. C.; Asch, T.; Badea, F.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Brüggemann, M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Ender, M.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Ghia, P. L.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Horneffer, A.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Krömer, O.; Kuijpers, J.; Lafebre, S.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Mayer, H. J.; Melissas, M.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Nigl, A.; Oehlschläger, J.; Over, S.; Palmieri, N.; Petcu, M.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F.; Sima, O.; Singh, K.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.

2011-02-01

A new method is explored to detect extensive air showers: the measurement of radio waves emitted during the propagation of the electromagnetic shower component in the magnetic field of the Earth. Recent results of the pioneering experiment LOPES are discussed. It registers radio signals in the frequency range between 40 and 80 MHz. The intensity of the measured radio emission is investigated as a function of different shower parameters, such as shower energy, angle of incidence, and distance to shower axis. In addition, new antenna types are developed in the framework of LOPESstar and new methods are explored to realize a radio self-trigger algorithm in real time.

The nature of pulsar radio emission

NASA Astrophysics Data System (ADS)

Dyks, J.; Rudak, B.; Demorest, P.

2010-01-01

High-quality averaged radio profiles of some pulsars exhibit double, highly symmetric features both in emission and in absorption. It is shown that both types of feature are produced by a split fan beam of extraordinary-mode curvature radiation that is emitted/absorbed by radially extended streams of magnetospheric plasma. With no emissivity in the plane of the stream, such a beam produces bifurcated emission components (BFCs) when our line of sight passes through the plane. An example of a double component created in this way is present in the averaged profile of the 5-ms pulsar J1012+5307. We show that the component can indeed be very well fitted by the textbook formula for the non-coherent beam of curvature radiation in the polarization state that is orthogonal to the plane of electron trajectory. The observed width of the BFC decreases with increasing frequency at a rate that confirms the curvature origin. Likewise, the double absorption features (double notches) are produced by the same beam of the extraordinary-mode curvature radiation, when it is eclipsed by thin plasma streams. The intrinsic property of curvature radiation to create bifurcated fan beams explains the double features in terms of a very natural geometry and implies the curvature origin of pulsar radio emission. Similarly, the `double conal' profiles of class D result from a cut through a wider stream with finite extent in magnetic azimuth. Therefore, their width reacts very slowly to changes of viewing geometry resulting from geodetic precession. The stream-cut interpretation implies a highly non-orthodox origin of both the famous S-swing of polarization angle and the low-frequency pulse broadening in D profiles. The azimuthal structure of polarization modes in the curvature radiation beam provides an explanation for the polarized `multiple imaging' and the edge depolarization of pulsar profiles.

Radio jets and gamma-ray emission in radio-silent narrow-line Seyfert 1 galaxies

NASA Astrophysics Data System (ADS)

Lähteenmäki, A.; Järvelä, E.; Ramakrishnan, V.; Tornikoski, M.; Tammi, J.; Vera, R. J. C.; Chamani, W.

2018-06-01

We have detected six narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz that were previously classified as radio silent and two that were classified as radio quiet. These detections reveal the presumption that NLS1 galaxies labelled radio quiet or radio silent and hosted by spiral galaxies are unable to launch jets to be incorrect. The detections are a plausible indicator of the presence of a powerful, most likely relativistic jet because this intensity of emission at 37 GHz cannot be explained by, for example, radiation from supernova remnants. Additionally, one of the detected NLS1 galaxies is a newly discovered source of gamma rays and three others are candidates for future detections. 37 GHz data are only available in electronic form at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/L1

RADIO EMISSION FROM RED-GIANT HOT JUPITERS

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

Fujii, Yuka; Spiegel, David S.; Mroczkowski, Tony

2016-04-01

When planet-hosting stars evolve off the main sequence and go through the red-giant branch, the stars become orders of magnitudes more luminous and, at the same time, lose mass at much higher rates than their main-sequence counterparts. Accordingly, if planetary companions exist around these stars at orbital distances of a few au, they will be heated up to the level of canonical hot Jupiters and also be subjected to a dense stellar wind. Given that magnetized planets interacting with stellar winds emit radio waves, such “Red-Giant Hot Jupiters” (RGHJs) may also be candidate radio emitters. We estimate the spectral auroralmore » radio intensity of RGHJs based on the empirical relation with the stellar wind as well as a proposed scaling for planetary magnetic fields. RGHJs might be intrinsically as bright as or brighter than canonical hot Jupiters and about 100 times brighter than equivalent objects around main-sequence stars. We examine the capabilities of low-frequency radio observatories to detect this emission and find that the signal from an RGHJ may be detectable at distances up to a few hundred parsecs with the Square Kilometer Array.« less

Radio Emission from Red-Giant Hot Jupiters

NASA Technical Reports Server (NTRS)

Fujii, Yuka; Spiegel, David S.; Mroczkowski, Tony; Nordhaus, Jason; Zimmerman, Neil T.; Parsons, Aaron R.; Mirbabayi, Mehrdad; Madhusudhan, Nikku

2016-01-01

When planet-hosting stars evolve off the main sequence and go through the red-giant branch, the stars become orders of magnitudes more luminous and, at the same time, lose mass at much higher rates than their main sequence counterparts. Accordingly, if planetary companions exist around these stars at orbital distances of a few au, they will be heated up to the level of canonical hot Jupiters and also be subjected to a dense stellar wind. Given that magnetized planets interacting with stellar winds emit radio waves, such "Red-Giant Hot Jupiters" (RGHJs) may also be candidate radio emitters. We estimate the spectral auroral radio intensity of RGHJs based on the empirical relation with the stellar wind as well as a proposed scaling for planetary magnetic fields. RGHJs might be intrinsically as bright as or brighter than canonical hot Jupiters and about 100 times brighter than equivalent objects around main-sequence stars. We examine the capabilities of low-frequency radio observatories to detect this emission and find that the signal from an RGHJ may be detectable at distances up to a few hundred parsecs with the Square Kilometer Array.

Very High Frequency Radio Emissions Associated With the Production of Terrestrial Gamma-Ray Flashes

NASA Astrophysics Data System (ADS)

Lyu, Fanchao; Cummer, Steven A.; Krehbiel, Paul R.; Rison, William; Briggs, Michael S.; Cramer, Eric; Roberts, Oliver; Stanbro, Matthew

2018-02-01

Recent studies of the close association between terrestrial gamma-ray flashes (TGFs) production and simultaneous lightning processes have shown that many TGFs are produced during the initial leader of intracloud flashes and that some low-frequency (LF) radio emissions may directly come from TGF itself. Measurements of any simultaneous very high frequency (VHF) radio emissions would give important insight into any lightning leader dynamics that are associated with TGF generation, and thus, such measurements are needed. Here we report on coordinated observations of TGFs detected simultaneously by Fermi Gamma-ray Burst Monitor, two VHF lightning mapping arrays, and Duke ground-based LF radio sensors to investigate more on the close association between TGFs and LF and VHF radio emissions. Three TGFs are analyzed here and confirm previous findings on the close association between TGF generation and lightning processes and, for the first time, provide time-aligned measurements of the VHF radio signature within a few tens of microseconds of TGF generation. Strong VHF emissions were observed essentially simultaneously with two TGFs and within a few tens of microseconds of a third TGF. Equally importantly, the VHF measurement details indicate that the TGF-associated emissions are nonimpulsive and extended in time. We conclude that the TGF-producing process is at least sometimes closely associated with strong VHF emissions, and thus, there may be a link between the generation of TGFs and active lightning streamer dynamics.

Quantifying Weak Nonthermal Solar Radio Emission at Low Radio Frequencies

NASA Astrophysics Data System (ADS)

Sharma, Rohit; Oberoi, Divya; Arjunwadkar, Mihir

2018-01-01

The recent availability of fine-grained high-sensitivity data from the new generation of low radio frequency instruments such as the Murchison Widefield Array (MWA) has opened up opportunities for using novel techniques for characterizing the nature of solar emission at these frequencies. Here we use this opportunity to look for evidence for the presence of weak nonthermal emissions in the 100–240 MHz band, at levels weaker than have been probed so far. The presence of such features is believed to be a necessary consequence of nanoflare-based coronal and chromospheric heating theories. We separate the calibrated MWA solar dynamic spectra into a slowly varying and an impulsive, and hence nonthermal, component. We demonstrate that Gaussian mixture modeling can be used to robustly model the latter, and we estimate the flux density distribution as well as the prevalence of impulsive nonthermal emission in the frequency-time plane. Evidence for the presence of nonthermal emission at levels down to ∼0.2 SFU (1 SFU = 104 Jy) is reported, making them the weakest reported emissions of this nature. Our work shows the fractional occupancy of the nonthermal impulsive emission to lie in the 17%–45% range during a period of medium solar activity. We also find that the flux density radiated in the impulsive nonthermal emission is very similar in strength to that of the slowly varying component, which is dominated by thermal bremsstrahlung. Such significant prevalence and strength of the weak impulsive nonthermal emission has not been appreciated before.

First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster

NASA Astrophysics Data System (ADS)

Savini, F.; Bonafede, A.; Brüggen, M.; van Weeren, R.; Brunetti, G.; Intema, H.; Botteon, A.; Shimwell, T.; Wilber, A.; Rafferty, D.; Giacintucci, S.; Cassano, R.; Cuciti, V.; de Gasperin, F.; Röttgering, H.; Hoeft, M.; White, G.

2018-05-01

Diffuse synchrotron radio emission from cosmic-ray electrons is observed at the center of a number of galaxy clusters. These sources can be classified either as giant radio halos, which occur in merging clusters, or as mini halos, which are found only in cool-core clusters. In this paper, we present the first discovery of a cool-core cluster with an associated mini halo that also shows ultra-steep-spectrum emission extending well beyond the core that resembles radio halo emission. The large-scale component is discovered thanks to LOFAR observations at 144 MHz. We also analyse GMRT observations at 610 MHz to characterise the spectrum of the radio emission. An X-ray analysis reveals that the cluster is slightly disturbed, and we suggest that the steep-spectrum radio emission outside the core could be produced by a minor merger that powers electron re-acceleration without disrupting the cool core. This discovery suggests that, under particular circumstances, both a mini and giant halo could co-exist in a single cluster, opening new perspectives for particle acceleration mechanisms in galaxy clusters.

A search for radio emission from Galactic supersoft X-ray sources

NASA Astrophysics Data System (ADS)

Ogley, R. N.; Chaty, S.; Crocker, M.; Eyres, S. P. S.; Kenworthy, M. A.; Richards, A. M. S.; Rodríguez, L. F.; Stirling, A. M.

2002-03-01

We have made a deep search for radio emission from all the northern hemisphere supersoft X-ray sources using the Very Large Array (VLA) and multi-element radio-linked interferometer network (MERLIN) telescopes, at 5 and 8.4GHz. Three previously undetected sources, T Pyx, V1974 Cygni and RX J0019.8+2156, were imaged in quiescence using the VLA in order to search for any persistent emission. No radio emission was detected in any of the VLA fields down to a typical 1σ rms noise of 20μJybeam-1, however, 17 new point sources were detected in the fields with 5-GHz fluxes between 100 and 1500μJy, giving an average 100-μJy source density of ~200deg-2, comparable to what was found in the MERLIN Hubble Deep Field survey. The persistent source AG Draconis was observed by MERLIN to provide a confirmation of previous VLA observations and to investigate the source at a higher resolution. The core is resolved at the milliarcsec scale into two components that have a combined flux of ~1mJy. It is possible that we are detecting nebulosity, which is becoming resolved out by the higher MERLIN resolution. We have investigated possible causes of radio emission from a wind environment, both directly from the secondary star, and also consequently, of the high X-ray luminosity from the white dwarf. There is an order of magnitude discrepancy between observed and modelled values that can be explained by the uncertainty in fundamental quantities within these systems.

On the Methods of Determining the Radio Emission Geometry in Pulsar Magnetospheres

NASA Technical Reports Server (NTRS)

Dyks, J.; Rudak, B.; Harding, Alice K.

2004-01-01

We present a modification of the relativistic phase shift method of determining the radio emission geometry from pulsar magnetospheres proposed by Gangadhara & Gupta (2001). Our modification provides a method of determining radio emission altitudes which does not depend on the viewing geometry and does not require polarization measurements. We suggest application of the method to the outer edges of averaged radio pulse profiles to identify magnetic field lines associated with'the edges of the pulse and, thereby, to test the geometric method based on the measurement of the pulse width at the lowest intensity level. We show that another relativistic method proposed by Blaskiewicz et al. (1991) provides upper limits for emission altitudes associated with the outer edges of pulse profiles. A comparison of these limits with the altitudes determined with the geometric method may be used to probe the importance of rotational distortions of magnetic field and refraction effects in the pulsar magnetosphere. We provide a comprehensive discussion of the assumptions used in the relativistic methods.

THE ABSENCE OF RADIO EMISSION FROM THE GLOBULAR CLUSTER G1

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

Miller-Jones, J. C. A.; Wrobel, J. M.; Sivakoff, G. R.

2012-08-10

The detections of both X-ray and radio emission from the cluster G1 in M31 have provided strong support for existing dynamical evidence for an intermediate-mass black hole (IMBH) of mass (1.8 {+-} 0.5) Multiplication-Sign 10{sup 4} M{sub Sun} at the cluster center. However, given the relatively low significance and astrometric accuracy of the radio detection, and the non-simultaneity of the X-ray and radio measurements, this identification required further confirmation. Here we present deep, high angular resolution, strictly simultaneous X-ray and radio observations of G1. While the X-ray emission (L{sub X} = 1.74{sup +0.53}{sub -0.44} Multiplication-Sign 10{sup 36} (d/750 kpc){sup 2}more » erg s{sup -1} in the 0.5-10 keV band) remained fully consistent with previous observations, we detected no radio emission from the cluster center down to a 3{sigma} upper limit of 4.7 {mu}Jy beam{sup -1}. Our favored explanation for the previous radio detection is flaring activity from a black hole low-mass X-ray binary (LMXB). We performed a new regression of the 'Fundamental Plane' of black hole activity, valid for determining black hole mass from radio and X-ray observations of sub-Eddington black holes, finding log M{sub BH} = (1.638 {+-} 0.070)log L{sub R} - (1.136 {+-} 0.077)log L{sub X} - (6.863 {+-} 0.790), with an empirically determined uncertainty of 0.44 dex. This constrains the mass of the X-ray source in G1, if a black hole, to be <9.7 Multiplication-Sign 10{sup 3} M{sub Sun} at 95% confidence, suggesting that it is a persistent LMXB. This annuls what was previously the most convincing evidence from radiation for an IMBH in the Local Group, though the evidence for an IMBH in G1 from velocity dispersion measurements remains unaffected by these results.« less

Detection of fundamental and harmonic type III radio emission and the associated Langmuir waves at the source region

NASA Technical Reports Server (NTRS)

Reiner, M. J.; Stone, R. G.; Fainberg, J.

1992-01-01

Type III radio emission generated in the vicinity of the Ulysses spacecraft has been detected at both the fundamental and harmonic of the local plasma frequency. The observations represent the first clear evidence of locally generated type III radio emission. This local emission shows no evidence of frequency drift, exhibits a relatively short rise time, is less intense than the observed remotely generated radio emission, and is temporally correlated with observed in situ Langmuir waves. The observations were made with the unified radio astronomy and wave (URAP) experiment on the Ulysses spacecraft between 1990 November 4 and 1991 April 30, as it traveled from 1 to 3 AU from the sun. During this time period many thousands of bursts were observed. However, only three examples of local emission and associated Langmuir waves were identified. This supports previous suggestions that type III radio emission is generated in localized regions of the interplanetary medium, rather than uniformly along the extent of the electron exciter beam.

A high-sensitivity survey of radio continuum emission from Herbig Ae/Be stars

NASA Technical Reports Server (NTRS)

Skinner, Stephen L.; Brown, Alexander; Stewart, Ron T.

1993-01-01

Results of a high-sensitivity VLA/Australia Telescope survey of radio continuum emission from the 57 Herbig Ae/Be stars and candidates in the 1984 catalog of Finkenzeller and Mundt are presented. Twelve stars were detected at the primary observing wavelength of 3.6 cm, on the basis that not less than 4 sigma radio sources lie within 1 arcsec of the optical positions. It is suggested that the radio emission is predominantly thermal and in many cases wind-related. The unusual eclipsing binary TY CrA is an exception and is classified as a nonthermal radio source on the basis of its decidedly negative spectral index (alpha = -1.2). A simple spherically symmetric free-fall accretion model is used to show that the predicted radio fluxes due to accretion at rates, estimated in the literature, of about 10 exp -6 to 10 exp -5 solar mass/yr are one to four orders of magnitude larger than observed.

Dendritic biomimicry: microenvironmental hydrogen-bonding effects on tryptophan fluorescence.

PubMed

Koenig, S; Müller, L; Smith, D K

2001-03-02

Two series of dendritically modified tryptophan derivatives have been synthesised and their emission spectra measured in a range of different solvents. This paper presents the syntheses of these novel dendritic structures and discusses their emission spectra in terms of both solvent and dendritic effects. In the first series of dendrimers, the NH group of the indole ring is available for hydrogen bonding, whilst in the second series, the indole NH group has been converted to NMe. Direct comparison of the emission wavelengths of analogous NH and NMe derivatives indicates the importance of the Kamlet-Taft solvent beta3 parameter, which reflects the ability of the solvent to accept a hydrogen bond from the NH group, an effect not possible for the NMe series of dendrimers. For the NH dendrimers, the attachment of a dendritic shell to the tryptophan subunit leads to a red shift in emission wavelength. This dendritic effect only operates in non-hydrogen-bonding solvents. For the NMe dendrimers, however, the attachment of a dendritic shell has no effect on the emission spectra of the indole ring. This proves the importance of hydrogen bonding between the branched shell and the indole NH group in causing the dendritic effect. This is the first time a dendritic effect has been unambiguously assigned to individual hydrogen-bonding interactions and indicates that such intramolecular interactions are important in dendrimers, just as they are in proteins. Furthermore, this paper sheds light on the use of tryptophan residues as a probe of the microenvironment within proteins--in particular, it stresses the importance of hydrogen bonds formed by the indole NH group.

Correlated variations of UV and radio emissions during an outstanding Jovian auroral event

NASA Technical Reports Server (NTRS)

Prange, R.; Zarka, P.; Ballester, G. E.; Livengood, T. A.; Denis, L.; Carr, T.; Reyes, F.; Bame, S. J.; Moos, H. W.

1993-01-01

An exceptional Jovian aurora was detected in the FUV on December 21, 1990, by means of Vilspa and Goddard Space Flight Center (GFSC) International Ultraviolet Explorer (IUE) observations. This event included intensification by a factor of three between December 20 and 21, leading to the brightest aurora identified in the IUE data analyzed, and, in the north, to a shift of the emission peak towards larger longitudes. The Jovian radio emission simultaneously recorded at decameter wavelengths in Nancay also exhibits significant changes, from a weak and short-duration emission on December 20 to a very intense one, lasting several hours, on December 21. Confirmation of this intense radio event is also found in the observations at the University of Florida on December 21. The emissions are identified as right-handed Io-independent 'A' (or 'non Io-A') components from the northern hemisphere. The radio source region deduced from the Nancay observations lies, for both days, close to the UV peak emission, exhibiting in particular a similar shift of the source region toward larger longitudes from one day to the next. A significant broadening of the radio source was also observed and it is shown that on both days, the extent of the radio source closely followed the longitude range for which the UV brightness exceeds a given threshold. The correlated variations, both in intensity and longitude, strongly suggest that a common cause triggered the variation of the UV and radio emissions during this exceptional event. On one hand, the variation of the UV aurora could possibly be interpreted according to the Prange and Elkhamsi (1991) model of diffuse multicomponent auroral precipitation (electron and ion): it would arise from an increase in the precipitation rate of ions together with an inward shift of their precipitation locus from L approximately equal 10 to L approximately equal 6. On the other hand, the analysis of Ulysses observations in the upstream solar wind suggests that

X-ray emission associated with radio galaxies in the Perseus cluster

NASA Technical Reports Server (NTRS)

Rhee, George; Burns, Jack O.; Kowalski, Michael P.

1994-01-01

In this paper, we report on new x-ray observations of the Perseus cluster made using four separate pointings of the Roentgen Satellite (ROSAT) Positron Sensitive Proportional Counter (PSPC). We searched for x-ray emission associated with 16 radio galaxies and detected six above 3 sigma. We made use of the PSPC spectra to determine if the x-ray emission associated with radio galaxies in Perseus is thermal or nonthermal in origin (i.e., hot gas or an active galactic nuclei (AGN)). For the head-tail radio galaxy IC 310, we find that the data are best fit by a power law model with an unusually large spectral index alpha = 2.7. This is consistent with its unresolved spatial structure. On the other hand, a second resolved x-ray source associated with another radio galaxy 2.3 Mpc from the Perseus center (V Zw 331) is best fit by a thermal model. For three sources with insufficient flux for a full spectral analysis, we calculated hardness ratios. On this basis, the x-ray emission associated with the well known head-tail source NGC 1265 is consistent with thermal radiation. The x-ray spectra of UGC 2608 and UGC 2654 probably arise from hot gas, although very steep power-law spectra (alpha greater than 3.2) are also possible. The spectrum of NGC 1275 is quite complex due to the presence of an AGN and the galaxy's location at the center of a cluster cooling flow.

Fermi large area telescope detection of extended gamma-ray emission from the radio galaxy fornax A

DOE PAGES

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

2016-07-14

Here, we report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to bemore » $$\\lt 14$$% of the total γ-ray flux. We also demonstrated a preferred alignment of the γ-ray elongation with the radio lobes by rotating the radio lobes template. We found no significant evidence for variability on ~0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. Furthermore, with the extended nature of the $$\\gt 100\\;{\\rm{MeV}}$$ γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ~2–3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton–proton collisions of cosmic rays with thermal plasma within the radio lobes.« less

Fermi Large Area Telescope Detection of Extended Gamma-Ray Emission from the Radio Galaxy Fornax A

NASA Astrophysics Data System (ADS)

Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Cohen, J. M.; Cohen-Tanugi, J.; Costanza, F.; Cutini, S.; D'Ammando, F.; Davis, D. S.; de Angelis, A.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Georganopoulos, M.; Giglietto, N.; Giordano, F.; Giroletti, M.; Godfrey, G.; Green, D.; Grenier, I. A.; Guiriec, S.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Jogler, T.; Jóhannesson, G.; Kensei, S.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Maldera, S.; Manfreda, A.; Mayer, M.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Negro, M.; Nuss, E.; Ohno, M.; Ohsugi, T.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Schmid, J.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Takahashi, H.; Thayer, J. B.; Thompson, D. J.; Torres, D. F.; Tosti, G.; Troja, E.; Vianello, G.; Wood, K. S.; Wood, M.; Zimmer, S.; Fermi LAT Collaboration

2016-07-01

We report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to be < 14% of the total γ-ray flux. A preferred alignment of the γ-ray elongation with the radio lobes was demonstrated by rotating the radio lobes template. We found no significant evidence for variability on ˜0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. With the extended nature of the > 100 MeV γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ˜2-3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton-proton collisions of cosmic rays with thermal plasma within the radio lobes.

Near Earth space sporadic radio emission busts occurring during sunrise

NASA Technical Reports Server (NTRS)

Dudnik, A. V.; Zaljubovsky, I. I.; Kartashev, V. M.; Lasarev, A. V.; Shmatko, E. S.

1985-01-01

During the period of low solar activity at sunrise the effect of sporadic high frequency near Earth space radio emission was experimentally discovered at middle latitudes. The possible mechanism of its origin is discussed.

A search for extended radio emission from selected compact galaxy groups

NASA Astrophysics Data System (ADS)

Nikiel-Wroczyński, B.; Urbanik, M.; Soida, M.; Beck, R.; Bomans, D. J.

2017-07-01

Context. Studies on compact galaxy groups have led to the conclusion that a plenitude of phenomena take place in between galaxies that form them. However, radio data on these objects are extremely scarce and not much is known concerning the existence and role of the magnetic field in intergalactic space. Aims: We aim to study a small sample of galaxy groups that look promising as possible sources of intergalactic magnetic fields; for example data from radio surveys suggest that most of the radio emission is due to extended, diffuse structures in and out of the galaxies. Methods: We used the Effelsberg 100 m radio telescope at 4.85 GHz and NRAO VLA Sky Survey (NVSS) data at 1.40 GHz. After subtraction of compact sources we analysed the maps searching for diffuse, intergalactic radio emission. Spectral index and magnetic field properties were derived. Results: Intergalactic magnetic fields exist in groups HCG 15 and HCG 60, whereas there are no signs of them in HCG 68. There are also hints of an intergalactic bridge in HCG 44 at 4.85 GHz. Conclusions: Intergalactic magnetic fields exist in galaxy groups and their energy density may be comparable to the thermal (X-ray) density, suggesting an important role of the magnetic field in the intra-group medium, wherever it is detected.

Full PIC simulations of solar radio emission

NASA Astrophysics Data System (ADS)

Sgattoni, A.; Henri, P.; Briand, C.; Amiranoff, F.; Riconda, C.

2017-12-01

Solar radio emissions are electromagnetic (EM) waves emitted in the solar wind plasma as a consequence of electron beams accelerated during solar flares or interplanetary shocks such as ICMEs. To describe their origin, a multi-stage model has been proposed in the 60s which considers a succession of non-linear three-wave interaction processes. A good understanding of the process would allow to infer the kinetic energy transfered from the electron beam to EM waves, so that the radio waves recorded by spacecraft can be used as a diagnostic for the electron beam.Even if the electrostatic problem has been extensively studied, full electromagnetic simulations were attempted only recently. Our large scale 2D-3V electromagnetic PIC simulations allow to identify the generation of both electrostatic and EM waves originated by the succession of plasma instabilities. We tested several configurations varying the electron beam density and velocity considering a background plasma of uniform density. For all the tested configurations approximately 105 of the electron-beam kinetic energy is transfered into EM waves emitted in all direction nearly isotropically. With this work we aim to design experiments of laboratory astrophysics to reproduce the electromagnetic emission process and test its efficiency.

The nature of radio emission from distant galaxies

NASA Astrophysics Data System (ADS)

Richards, Eric A.

I describe an observational program aimed at understanding the radio emission from distant, rapidly evolving galaxy populations. These observations were carried out at 1.4 and 8.5 GHz with the VLA centered on the Hubble Deep Field. Further MERLIN observations of the HDF region at 1.4 GHz provided an angular resolution of 0.2'' and when combined with the VLA data produced an image with an unprecedented rms noise of 4 μJy. All radio sources detected in the VLA complete sample are resolved with a median angular size of 1-2''. The differential count of the radio sources is marginally sub-Euclidean (γ = -2.4 +/- 0.1) and fluctuation analysis suggests nearly 60 sources per armin2 are present at the 1 μJy level. A correlation analysis indicates spatial clustering among the 371 radio sources on angular scales of 1-40 arcmin. Optical identifications are made primarily with bright (I = 22) disk systems composed of irregulars, peculiars, interacting/merging galaxies, and a few isolated field spirals. Available redshifts span the range 0.2-3. These clues coupled with the steep spectral index of the 1.4 GHz selected sample are indicative of diffuse synchrotron radiation in distant galactic disks. Thus the evolution in the microjansky radio population is driven principally by star-formation. I have isolated a number of optically faint radio sources (about 25% of the overall sample) which remain unidentified to I = 26-28 in the HDF and flanking optical fields. Several of these objects have extremely red counterparts and constitute a new class of radio sources which are candidate high redshift dusty protogalaxies.

ARCADE 2 Observations of Galactic Radio Emission

NASA Technical Reports Server (NTRS)

Kogut, A.; Fixsen, D. J.; Levin, S. M.; Limon, M.; Lubin, P. M.; Mirel, P.; Seiffert, M.; Singal, J.; Villela, T.; Wollack, E.;

RFID Transponders' RF Emissions in Aircraft Communication and Navigation Radio Bands

NASA Technical Reports Server (NTRS)

Nguyen, Truong X.; Ely, Jay J.; Koppen Sandra V.; Fersch, Mariatheresa S.

2008-01-01

Radiated emission data in aircraft communication and navigation bands are presented for several active radio frequency identification (RFID) tags. The individual tags are different in design, operation and transmitting frequencies. The process for measuring the tags emissions in a reverberation chamber is discussed. Measurement issues dealing with tag interrogation, low level measurement in the presence of strong transmissions, and tags low duty factors are discussed. The results show strong emissions, far exceeding aircraft emission limits and can be of potential interference risks.

A Search for Strong Radio Emission from the Magnetic Interactions of Trappist-1 and its Satellites

NASA Astrophysics Data System (ADS)

Pineda, J. Sebastian; Hallinan, Gregg

2018-06-01

The first nearby very-low mass star planet-host discovered, Trappist-1, presents not only a unique opportunity for studying a system of multiple terrestrial planets, but a means to examine the possibility of significant star-planet magnetic interactions at the end of the main sequence. These very-low mass stars and brown dwarfs have been observationally confirmed as capable of generating strong radio emissions produced by the electron cyclotron maser instability as a consequence of currents coupling the magnetospheric environment to the stellar atmosphere. However, multiple electrodynamic mechanisms have been proposed to power these magnetospheric processes, including a potentially significant role for short-period satellites analogous to the auroral interactions between Jupiter and its moons or the Sun and the solar system planets. With multiple close in terrestrial satellites, the Trappist-1 system is an important test case of these potential theories. We present a search for these radio emissions from the seven-planet Trappist-1 system using the Karl G. Jansky Very Large Array, looking for both highly circularly polarized radio emission and persistent quiescent emissions at GHz frequencies. We place these observations in the context of the possible electrodynamic engines driving radio emissions in very-low mass stars and brown dwarfs, and their relation to magnetic field topology, with implications for future radio surveys of planet-hosts at the end of the main sequence.

Milliarcsecond Imaging of the Radio Emission from the Quasar with the Most Massive Black Hole at Reionization

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

Wang, Ran; Wu, Xue-Bing; Jiang, Linhua

We report Very Long Baseline Array (VLBA) observations of the 1.5 GHz radio continuum emission of the z = 6.326 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802). J0100+2802 is by far the most optically luminous and is a radio-quiet quasar with the most massive black hole known at z > 6. The VLBA observations have a synthesized beam size of 12.10 mas ×5.36 mas (FWHM), and detected the radio continuum emission from this object with a peak surface brightness of 64.6 ± 9.0 μ Jy beam{sup −1} and a total flux density of 88 ± 19 μ Jy. The position of themore » radio peak is consistent with that from SDSS in the optical and Chandra in the X-ray. The radio source is marginally resolved by the VLBA observations. A 2D Gaussian fit to the image constrains the source size to (7.1 ± 3.5) mas × (3.1 ± 1.7) mas. This corresponds to a physical scale of (40 ± 20) pc × (18 ± 10) pc. We estimate the intrinsic brightness temperature of the VLBA source to be T {sub B} = (1.6 ± 1.2) × 10{sup 7} K. This is significantly higher than the maximum value in normal star-forming galaxies, indicating an active galactic nucleus (AGN) origin for the radio continuum emission. However, it is also significantly lower than the brightness temperatures found in highest-redshift radio-loud quasars. J0100+2802 provides a unique example for studying the radio activity in optically luminous and radio-quiet AGNs in the early universe. Further observations at multiple radio frequencies will accurately measure the spectral index and address the dominant radiation mechanism of the radio emission.« less

Chromospheric evaporation and decimetric radio emission in solar flares

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Benz, Arnold O.

1995-01-01

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca XIX soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyze 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Pheonix, hard X-ray data from (BATSE/CGRO) and soft X-ray data from Burst and Transient Source Experiment/Compton Gamma Ray Observatory (GOES) were available.

Observation of radio-wave-induced red hydroxyl emission at low altitude in the ionosphere.

PubMed

Kagan, L M; Nicolls, M J; Kelley, M C; Carlson, H C; Belikovich, V V; Bakhmet'eva, N V; Komrakov, G P; Trondsen, T S; Donovan, E

2005-03-11

We report the discovery of radio-wave-induced red emission of OH Meinel rotation-vibrational bands at 629.79 nm. These are the first measurements of artificial aurora below 100 km. We believe that the 629.79-nm OH emission was due to radio-wave focusing by sporadic ionization clouds near 80-85 km altitude, thus giving a technique to visualize the low-altitude sporadic ionization and providing insight into ionospheric interactions at these low altitudes.

Observations of the auroral hectometric radio emission onboard the INTERBALL-1 satellite

NASA Astrophysics Data System (ADS)

Kuril'Chik, V. N.

2007-06-01

The results of five-year (1995 2000) continuous observations of the auroral radio emission (ARE) in the hectometric wavelength range on the high-apogee INTERBALL-1 satellite are presented. Short intense bursts of the auroral hectometric radio emission (AHR) were observed at frequencies of 1463 and 1501 kHz. The bursts were observed predominantly at times when the terrestrial magnetosphere was undisturbed (in the quiet Sun period), and their number decreased rapidly with increasing solar activity. The bursts demonstrated seasonal dependence in the Northern and Southern hemispheres (dominating in the autumn-winter period). Their appearance probably depends on the observation time (UT). A qualitative explanation of the AHR peculiarities is given.

Interplanetary radio storms. II - Emission levels and solar wind speed in the range 0.05-0.8 AU

NASA Technical Reports Server (NTRS)

Bougeret, J.-L.; Fainberg, J.; Stone, R. G.

1984-01-01

Storms of interplanetary type III radio bursts (IP storms) are commonly observed in the interplanetary medium by the ISEE-3 radio instrument. This instrument has the capability of accurately determining the arrival direction of the radio emission. At each observing frequency, the storm radio sources are tracked as they cross the line-of-sight to the sun. Using a simple model, the emission levels are determined at a number of radio frequencies for four separate storms. The IP storm radiation is found to occur in regions of enhanced density at levels of 0.05 to 0.8 AU. The density in these enhancements falls off faster than R(-2). The solar wind speed in the storm region is also measured. The analysis is consistent with steady conditions in the storm region during a few days around the III storm burst radio emission at the harmonic of the local plasma frequency.

Spectroscopic and polarimetric study of radio-quiet weak emission line quasars

NASA Astrophysics Data System (ADS)

Kumar, Parveen; Chand, Hum; Gopal-Krishna; Srianand, Raghunathan; Stalin, Chelliah Subramonian; Petitjean, Patrick

2018-04-01

A small subset of optically selected radio-quiet QSOs with weak or no emission lines may turn out to be the elusive radio-quiet BL Lac objects, or simply be radio-quiet QSOs with an infant/shielded broad line region (BLR). High polarisation (p > 3-4%), a hallmark of BL Lacs, can be used to test whether some optically selected ‘radio-quiet weak emission line QSOs’ (RQWLQs) show a fractional polarisation high enough to qualify as radio-quiet analogues of BL Lac objects. To check this possibility, we have made optical spectral and polarisation measurements of a sample of 19 RQWLQs. Out of these, only 9 sources show a non-significant proper motion (hence very likely extragalactic) and only two of them are found to have p > 1%. For these two RQWLQs, namely J142505.59+035336.2 and J154515.77+003235.2, we found the highest polarization to be 1.59±0.53%, which is again too low to classify them as (radio-quiet) BL Lacs, although one may recall that even genuine BL Lacs sometimes appear weakly polarised. We also present a statistical comparison of the optical spectral index, for a sample of 45 RQWLQs with redshift-luminosity matched control samples of 900 QSOs and an equivalent sample of 120 blazars, assembled from the literature. The spectral index distribution of RQWLQs is found to differ, at a high significance level, from that of blazars. This, too, is consistent with the common view that the mechanism of the central engine in RQWLQs, as a population, is close to that operating in normal QSOs and the primary difference between them is related to the BLR.

Radio frequency detection assembly and method for detecting radio frequencies

DOEpatents

Cown, Steven H.; Derr, Kurt Warren

2010-03-16

A radio frequency detection assembly is described and which includes a radio frequency detector which detects a radio frequency emission produced by a radio frequency emitter from a given location which is remote relative to the radio frequency detector; a location assembly electrically coupled with the radio frequency detector and which is operable to estimate the location of the radio frequency emitter from the radio frequency emission which has been received; and a radio frequency transmitter electrically coupled with the radio frequency detector and the location assembly, and which transmits a radio frequency signal which reports the presence of the radio frequency emitter.

PULSED GAMMA RAYS FROM THE ORIGINAL MILLISECOND AND BLACK WIDOW PULSARS: A CASE FOR CAUSTIC RADIO EMISSION?

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

Guillemot, L.; Kramer, M.; Freire, P. C. C.

2012-01-01

We report the detection of pulsed gamma-ray emission from the fast millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20 (J1959+2048) using 18 months of survey data recorded by the Fermi Large Area Telescope and timing solutions based on radio observations conducted at the Westerbork and Nancay radio telescopes. In addition, we analyzed archival Rossi X-ray Timing Explorer and XMM-Newton X-ray data for the two MSPs, confirming the X-ray emission properties of PSR B1937+21 and finding evidence ({approx}4{sigma}) for pulsed emission from PSR B1957+20 for the first time. In both cases the gamma-ray emission profile is characterized by twomore » peaks separated by half a rotation and are in close alignment with components observed in radio and X-rays. These two pulsars join PSRs J0034-0534 and J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks in different energy bands. The modeling of the radio and gamma-ray emission profiles suggests co-located emission regions in the outer magnetosphere.« less

Pulsed Gamma Rays From The Original Millisecond And Black Widow Pulsars: A Case For Caustic Radio Emission?

DOE PAGES

Guillemot, L.; Johnson, T. J.; Venter, C.; ...

2011-12-12

We report the detection of pulsed gamma-ray emission from the fast millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20 (J1959+2048) using 18 months of survey data recorded by the Fermi Large Area Telescope (LAT) and timing solutions based on radio observations conducted at the Westerbork and Nancay radio telescopes. In addition, we analyzed archival RXTE and XMM-Newton X-ray data for the two MSPs, con rming the X-ray emission properties of PSR B1937+21 and nding evidence (~ 4σ) for pulsed emission from PSR B1957+20 for the rst time. In both cases the gamma-ray emission pro le is characterized bymore » two peaks separated by half a rotation and are in close alignment with components observed in radio and X-rays. These two pulsars join PSRs J0034-0534 and J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks in different energy bands. The modeling of the radio and gamma-ray emission pro les suggests co-located emission regions in the outer magnetosphere.« less

Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: A Case for Caustic Radio Emission?

NASA Technical Reports Server (NTRS)

Guillemot, L.; Johnson, T. J.; Venter, C.; Kerr, M.; Pancrazi, B.; Livingstone, M.; Janssen, G. H.; Jaroenjittichai, P.; Kramer, M.; Cognard, I.;

Unprecedentedly Strong and Narrow Electromagnetic Emissions Stimulated by High-Frequency Radio Waves in the Ionosphere

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

Norin, L.; Leyser, T. B.; Nordblad, E.

2009-02-13

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

Unprecedentedly strong and narrow electromagnetic emissions stimulated by high-frequency radio waves in the ionosphere.

PubMed

Norin, L; Leyser, T B; Nordblad, E; Thidé, B; McCarrick, M

2009-02-13

Experimental results of secondary electromagnetic radiation, stimulated by high-frequency radio waves irradiating the ionosphere, are reported. We have observed emission peaks, shifted in frequency up to a few tens of Hertz from radio waves transmitted at several megahertz. These emission peaks are by far the strongest spectral features of secondary radiation that have been reported. The emissions are attributed to stimulated Brillouin scattering, long predicted but hitherto never unambiguously identified in high-frequency ionospheric interaction experiments. The experiments were performed at the High-Frequency Active Auroral Research Program (HAARP), Alaska, USA.

Radio emission of energetic cosmic ray air showers: Polarization measurements with LOPES

NASA Astrophysics Data System (ADS)

Lopes Collaboration; Isar, P. G.; Apel, W. D.; Arteaga, J. C.; Asch, T.; Auffenberg, J.; Badea, F.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Brüggemann, M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Ghia, P. L.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huang, X.; Huege, T.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Kolotaev, Y.; Krömer, O.; Kuijpers, J.; Lafebre, S.; Łuczak, P.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Nigl, A.; Oehlschläger, J.; Over, S.; Petcu, M.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F.; Sima, O.; Singh, K.; Stümpert, M.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Walkowiak, W.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.; LOPES Collaboration

2009-06-01

LOPES is a radio antenna array co-located with the Karlsruhe Shower Core and Array DEtector, KASCADE-Grande in Forschungszentrum Karlsruhe, Germany, which provides well-calibrated trigger information and air shower parameters for primary energies up to 10eV. By the end of 2006, the radio antennas were re-configured to perform polarization measurements of the radio signal of cosmic ray air showers, recording in the same time both, the East-West and North-South polarization directions of the radio emission. The main goal of these measurements is to reconstruct the polarization characteristics of the emitted signal. This will allow a detailed comparison with theoretical predictions. The current status of these measurements is reported here.

Modelling of radio emission from cosmic ray air showers

NASA Astrophysics Data System (ADS)

Ludwig, Marianne

2011-06-01

Cosmic rays entering the Earth's atmosphere induce extensive air showers consisting of up to billions of secondary particles. Among them, a multitude of electrons and positrons are generated. These get deflected in the Earth's magnetic field, creating time-varying transverse currents. Thereby, the air shower emits coherent radiation in the MHz frequency range measured by radio antenna arrays on the ground such as LOPES at the KIT. This detection method provides a possibility to study cosmic rays with energies above 1017 eV. At this time, the radio technique undergoes the change from prototype experiments to large scale application. Thus, a detailed understanding of the radio emission process is needed more than ever. Before starting this work, different models made conflicting predictions on the pulse shape and the amplitude of the radio signal. It turned out that a radiation component caused by the variation of the number of charged particles within the air shower was missed in several models. The Monte Carlo code REAS2 superposing the radiation of the individual air shower electrons and positrons was one of those. At this time, it was not known how to take the missing component into account. For REAS3, we developed and implemented the endpoint formalism, a universal approach, to calculate the radiation from each single particle. For the first time, we achieve a good agreement between REAS3 and MGMR, an independent and completely different simulation approach. In contrast to REAS3, MGMR is based on a macroscopic approach and on parametrisations of the air shower. We studied the differences in the underlying air shower models to explain the remaining deviations. For comparisons with LOPES data, we developed a new method which allows "top-down" simulations of air showers. From this, we developed an air shower selection criterion based on the number of muons measured with KASCADE to take shower-to-shower fluctuations for a single event analysis into account. With

Local Group dSph radio survey with ATCA - II. Non-thermal diffuse emission

NASA Astrophysics Data System (ADS)

Regis, Marco; Richter, Laura; Colafrancesco, Sergio; Profumo, Stefano; de Blok, W. J. G.; Massardi, Marcella

2015-04-01

Our closest neighbours, the Local Group dwarf spheroidal (dSph) galaxies, are extremely quiescent and dim objects, where thermal and non-thermal diffuse emissions lack, so far, of detection. In order to possibly study the dSph interstellar medium, deep observations are required. They could reveal non-thermal emissions associated with the very low level of star formation, or to particle dark matter annihilating or decaying in the dSph halo. In this work, we employ radio observations of six dSphs, conducted with the Australia Telescope Compact Array in the frequency band 1.1-3.1 GHz, to test the presence of a diffuse component over typical scales of few arcmin and at an rms sensitivity below 0.05 mJy beam-1. We observed the dSph fields with both a compact array and long baselines. Short spacings led to a synthesized beam of about 1 arcmin and were used for the extended emission search. The high-resolution data mapped background sources, which in turn were subtracted in the short-baseline maps, to reduce their confusion limit. We found no significant detection of a diffuse radio continuum component. After a detailed discussion on the modelling of the cosmic ray (CR) electron distribution and on the dSph magnetic properties, we present bounds on several physical quantities related to the dSphs, such that the total radio flux, the angular shape of the radio emissivity, the equipartition magnetic field, and the injection and equilibrium distributions of CR electrons. Finally, we discuss the connection to far-infrared and X-ray observations.

Source location of the smooth high-frequency radio emissions from Uranus

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Calvert, W.

1989-01-01

The source location of the smooth high-frequency radio emissions from Uranus has been determined. Specifically, by fitting the signal dropouts which occurred as Voyager traversed the hollow center of the emission pattern to a symmetrical cone centered on the source magnetic field direction at the cyclotron frequency, a southern-hemisphere (nightside) source was found at approximately 56 deg S, 219 deg W. The half-angle for the hollow portion of the emission pattern was found to be 13 deg.

Fine Structure of Anomalously Intense Pulses of PSR J0814+7429 Radio Emission in the Decameter Range

NASA Astrophysics Data System (ADS)

Skoryk, A. O.; Ulyanov, O. M.; Zakharenko, V. V.; Shevtsova, A. I.; Vasylieva, I. Y.; Plakhov, M. S.; Kravtsov, I. M.

2017-06-01

Purpose: The fine structure of the anomalously intense pulses of PSR J0814+7429 (B0809+74) has been studied. The pulsar radio emission fine structure is investigated to determine its parameters in the lowest part of spectrum available for groundbased observations. Design/methodology/approach: The scattering measure in the interstellar plasma have been estimated using the spectral and correlation analyses of pulsar data recorded by the UTR-2 radio telescope. Results: Two characteristic time scales of the anomalously intense pulses fine structure of the PSR J0814+7429 radio emission have been found. The strongest pulses of this pulsar in the decameter range can have a duration of about t 2÷3 ms. These pulses are emitted in short series. In some cases, they are emitted over the low-intensity plateau consisting of the “long” subpulse component. Conclusions: The narrowest correlation scale of pulsar J0814+7429 radio emission corresponds to the doubled scattering time constant of the interstellar medium impulse response. Broader scale of the fine structure of its radio emission can be explained by the radiation of a short series of narrow pulses or relatively broad pulses inside this pulsar magnetosphere.

Radio emission in peculiar galaxies

NASA Technical Reports Server (NTRS)

Demellorabaca, Dulia F.; Abraham, Zulema

1990-01-01

During the last decades a number of surveys of peculiar galaxies have been carried out and accurate positions become available. Since peculiarities are a possible evidence of radio emission (Wright, 1974; Sulentic, 1976; Stocke et al., 1978), the authors selected a sample of 24 peculiar galaxies with optical jet-like features or extensions in different optical catalogues, mainly the Catalogue of Southern Peculiar Galaxies and Associations (Arp and Madore, 1987) and the ESO/Uppsala Survey of the ESO(B) Atlas (Lauberts, 1982) for observation at the radio continuum frequency of 22 GHz. The sample is listed in a table. Sol (1987) studied this sample and concluded that the majority of the jet-like features seem to admit an explanation in terms of interactive galaxies with bridges and/or tails due to tidal effects. Only in a few cases do the jets seem to be possibly linked to some nuclear activity of the host galaxy. The observations were made with the 13.7m-radome enclosed Itapetinga Radiotelescope (HPBW of 4.3 arcmin), in Brazil. The receiver was a 1 GHz d.s.b. super-heterodine mixer operated in total-power mode, with a system temperature of approximately 800 K. The observational technique consisted in scans in right ascention, centralized in the optical position of the galaxy. The amplitude of one scan was 43 arcmin, and its duration time was 20 seconds. The integration time was at least 2 hours (12 ten-minute observations) and the sensibility limit adopted was an antenna temperature greater than 3 times the r.m.s. error of the baseline determination. Virgo A was used as the calibrator source. Three galaxies were detected for the first time as radio sources and four other known galaxies at low frequencies had their flux densities measured at 22 GHz. The results for these sources are presented.

A comprehensive study of high-energy gamma-ray and radio emission from Cyg X-3

NASA Astrophysics Data System (ADS)

Zdziarski, Andrzej A.; Malyshev, Denys; Dubus, Guillaume; Pooley, Guy G.; Johnson, Tyrel; Frankowski, Adam; de Marco, Barbara; Chernyakova, Maria; Rao, A. R.

2018-06-01

We study high-energy γ-rays observed from Cyg X-3 by the Fermi Large Area Telescope and the 15-GHz emission observed by the Ryle Telescope and the Arcminute Microkelvin Imager. We measure the γ-ray spectrum averaged over strong flares much more accurately than before, and find it well modelled by Compton scattering of stellar radiation by relativistic electrons with the power law index of ≃3.5 and a low-energy cutoff at the Lorentz factor of ˜103. We find a weaker spectrum in the soft spectral state, but only upper limits in the hard and intermediate states. We measure strong orbital modulation during the flaring state, well modelled by anisotropic Compton scattering of blackbody photons from the donor by jet relativistic electrons. We discover a weaker orbital modulation of the 15 GHz radio emission, which is well modelled by free-free absorption by the stellar wind. We then study cross-correlations between radio, γ-ray and X-ray emissions. We find the cross-correlation between the radio and γ-ray emissions peaks at a lag less than 1 d, while we detect a distinct radio lag of ˜50 d with respect to the soft X-rays in the soft spectral state.

Radio emissions from pulsar companions: a refutable explanation for galactic transients and fast radio bursts

NASA Astrophysics Data System (ADS)

Mottez, F.; Zarka, P.

2014-09-01

Context. The six known highly dispersed fast radio bursts are attributed to extragalactic radio sources that are of unknown origin but extremely energetic. We propose here a new explanation that does not require an extreme release of energy and involves a body (planet, asteroid, white dwarf) orbiting an extragalactic pulsar. Aims: We investigate a theory of radio waves associated with such pulsar-orbiting bodies. We focus our analysis on the waves emitted from the magnetic wake of the body in the pulsar wind. After deriving their properties, we compare them with the observations of various transient radio signals to determine whether they could originate from pulsar-orbiting bodies. Methods: The analysis is based on the theory of Alfvén wings: for a body immersed in a pulsar wind, a system of two stationary Alfvén waves is attached to the body, provided that the wind is highly magnetised. When they are destabilised through plasma instabilities, Alfvén wings can be the locus of strong radio sources that are convected with the pulsar wind. By assuming a cyclotron maser instability operating in the Alfvén wings, we make predictions about the shape, frequencies, and brightness of the resulting radio emissions. Results: Because of the beaming by relativistic aberration, the signal is seen only when the companion is perfectly aligned between its parent pulsar and the observer, as is the case for occultations. For pulsar winds with a high Lorentz factor (≥104), the whole duration of the radio event does not exceed a few seconds, and it is composed of one to four peaks that last a few milliseconds each and are detectable up to distances of several Mpc. The Lorimer burst, the three isolated pulses of PSR J1928+15, and the recently detected fast radio bursts are all compatible with our model. According to it, these transient signals should repeat periodically with the companion's orbital period. Conclusions: The search of pulsar-orbiting bodies could be an exploration

Radio Galaxies.

ERIC Educational Resources Information Center

Downes, Ann

1986-01-01

Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

Ground and space observations of medium frequency auroral radio emissions

NASA Astrophysics Data System (ADS)

Broughton, Matthew C.

The auroral zone is a rich source of natural radio emissions that can be observed in space and at ground-level. By studying these waves, scientists can gain insight into the plasma processes that generate them and use the near-Earth space environment as a large-scale plasma physics laboratory. This thesis uses both ground-level and in situ observations to study two kinds of natural radio emissions. First, we report observations of a new kind of auroral radio emission. The waves have frequencies ranging from 1.3-2.2 MHz, bandwidths ranging from 90-272 kHz, and durations ranging from 16-355 s. Spectral analysis of the waveform data has revealed that the emission has a complex combination of at least three kinds of fine structures. For model auroral electron distributions, calculations indicate that Langmuir waves could be excited at frequencies consistent with observations. The remainder of the thesis discusses auroral medium frequency (MF) burst, an impulsive, broadband natural radio emission observed at ground-level within a few minutes of local substorm onset. LaBelle [2011] proposed that MF burst originates as Langmuir/Z-mode waves on the topside of the ionosphere that subsequently mode convert to L-mode waves and propagate to ground-level. Using continuous waveform measurements and combined observations with the Sondrestrom Incoherent Scatter Radar, we have performed two tests of this mechanism. The results of these tests are consistent with the mechanism described in LaBelle [2011]. A survey of 8,624 half-orbits of the DEMETER spacecraft has revealed 68 observations of bursty MF waves. We have compared the wave properties of these waves to those of MF burst and have found that although it is uncertain, the balance of the evidence suggests that the bursty MF waves observed with DEMETER are the same phenomenon as the ground-level MF burst. Finally, we have used numerical simulations to model both the fine structure of MF burst and to estimate the attenuation the

LSPM J1314+1320: An Oversized Magnetic Star with Constraints on the Radio Emission Mechanism

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

MacDonald, James; Mullan, D. J.

LSPM J1314+1320 (=NLTT 33370) is a binary star system consisting of two nearly identical pre-main-sequence stars of spectral type M7. The system is remarkable among ultracool dwarfs for being the most luminous radio emitter over the widest frequency range. Masses and luminosities are at first sight consistent with the system being coeval at age ∼80 Myr according to standard (nonmagnetic) evolutionary models. However, these models predict an average effective temperature of ∼2950 K, which is 180 K hotter than the empirical value. Thus, the empirical radii are oversized relative to the standard models by ≈13%. We demonstrate that magnetic stellarmore » models can quantitatively account for the oversizing. As a check on our models, we note that the radio emission limits the surface magnetic field strengths: the limits depend on identifying the radio emission mechanism. We find that the field strengths required by our magnetic models are too strong to be consistent with gyrosynchrotron emission but are consistent with electron cyclotron maser emission.« less

SCO X-1: Origin of the radio and hard X-ray emissions

NASA Technical Reports Server (NTRS)

Ramaty, R.; Cheng, C. C.; Tsuruta, S.

1973-01-01

The consequences of models for the central radio source and the hard X-ray ( 30 keV) emitting region in Sco X-1 are examined. It was found that the radio emission could result from noncoherent synchrotron radiation and that the X-rays may be produced by bremsstrahlung. It is shown that both mechanisms require a mass outflow from Sco X-1. The radio source is located at r approximately 3x10 to the 12th power cm from the center of the star, and its linear dimensions do not exceed 3x10 to the 13th power cm. The magnetic field in the radio source is on the order of 1 gauss. If the hard X-rays are produced by thermal bremsstrahlung, their source is located at 10 to the 9th power approximately r approximately 5x10 to the 9th power cm, the temperature is 2x10 to the 9th power K, and the emission measure is 2x10 to the 56th power/cu cm. This hot plasma loses energy inward by conduction and outward by supersonic expansion. The rates of energy loss for both processes are about 10 to the 36th power erg/s, comparable to the total luminosity of Sco X-1.

Interplanetary radio storms. 2: Emission levels and solar wind speed in the range 0.05-0.8 AU

NASA Technical Reports Server (NTRS)

Bougeret, J. L.; Fainberg, J.; Stone, R. G.

1982-01-01

Storms of interplanetary type III radio bursts (IP storms) are commonly observed in the interplanetry medium by the ISEE-3 radio instrument. This instrument has the capability of accurately determining the arrival direction of the radio emission. At each observing frequency, the storm radio sources are tracked as they cross the line-of-sight to the Sun. Usng a simple model, the emission levels are determined at a number of radio frequencies for four separate storms. The IP storm radiation is found to occur in regions of enhanced density at levels of 0.05 to 0.8 AU. The density in these enhancements falls off faster than R(-2). The solar wind speed in the storm region is also measured. The analysis is consistent with steady conditions in the storm region during a few days around the central meridian passage of the storm. The comparison with average in situ density measurements compiled from the HELIOS 1-2 observations favors type III storm burst radio emission at the harmonic of the local plasma frequency.

Theory of Type 3 and Type 2 Solar Radio Emissions

NASA Technical Reports Server (NTRS)

Robinson, P. A.; Cairns, I. H.

2000-01-01

The main features of some current theories of type III and type II bursts are outlined. Among the most common solar radio bursts, type III bursts are produced at frequencies of 10 kHz to a few GHz when electron beams are ejected from solar active regions, entering the corona and solar wind at typical speeds of 0.1c. These beams provide energy to generate Langmuir waves via a streaming instability. In the current stochastic-growth theory, Langmuir waves grow in clumps associated with random low-frequency density fluctuations, leading to the observed spiky waves. Nonlinear wave-wave interactions then lead to secondary emission of observable radio waves near the fundamental and harmonic of the plasma frequency. Subsequent scattering processes modify the dynamic radio spectra, while back-reaction of Langmuir waves on the beam causes it to fluctuate about a state of marginal stability. Theories based on these ideas can account for the observed properties of type III bursts, including the in situ waves and the dynamic spectra of the radiation. Type 11 bursts are associated with shock waves propagating through the corona and interplanetary space and radiating from roughly 30 kHz to 1 GHz. Their basic emission mechanisms are believed to be similar to those of type III events and radiation from Earth's foreshock. However, several sub-classes of type II bursts may exist with different source regions and detailed characteristics. Theoretical models for type II bursts are briefly reviewed, focusing on a model with emission from a foreshock region upstream of the shock for which observational evidence has just been reported.

Comparing LOPES measurements of air-shower radio emission with REAS 3.11 and CoREAS simulations

NASA Astrophysics Data System (ADS)

Apel, W. D.; Arteaga-Velázquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

2013-12-01

Cosmic ray air showers emit radio pulses at MHz frequencies, which can be measured with radio antenna arrays - like LOPES at the Karlsruhe Institute of Technology in Germany. To improve the understanding of the radio emission, we test theoretical descriptions with measured data. The observables used for these tests are the absolute amplitude of the radio signal, and the shape of the radio lateral distribution. We compare lateral distributions of more than 500 LOPES events with two recent and public Monte Carlo simulation codes, REAS 3.11 and CoREAS (v 1.0). The absolute radio amplitudes predicted by REAS 3.11 are in good agreement with the LOPES measurements. The amplitudes predicted by CoREAS are lower by a factor of two, and marginally compatible with the LOPES measurements within the systematic scale uncertainties. In contrast to any previous versions of REAS, REAS 3.11 and CoREAS now reproduce the shape of the measured lateral distributions correctly. This reflects a remarkable progress compared to the situation a few years ago, and it seems that the main processes for the radio emission of air showers are now understood: The emission is mainly due to the geomagnetic deflection of the electrons and positrons in the shower. Less important but not negligible is the Askaryan effect (net charge variation). Moreover, we confirm that the refractive index of the air plays an important role, since it changes the coherence conditions for the emission: Only the new simulations including the refractive index can reproduce rising lateral distributions which we observe in a few LOPES events. Finally, we show that the lateral distribution is sensitive to the energy and the mass of the primary cosmic ray particles.

Radio emission from dusty galaxies observed by AKARI

NASA Astrophysics Data System (ADS)

Pepiak, A.; Pollo, A.; Takeuchi, T. T.; Solarz, A.; Jurusik, W.

2014-10-01

We probe radio-infrared correlation for two samples of extragalactic sources from the local Universe from the AKARI All-Sky Catalogue. The first, smaller sample (1053 objects) was constructed by the cross-correlation of the AKARI/FIS All-Sky Survey Bright Source Catalogue, the AKARI IRC All-Sky Survey Point Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the mid- and far-infrared by AKARI, and at the 1.4 GHz radio frequency by NRAO. The second, larger sample (13,324 objects) was constructed by the cross-correlation of only the AKARI/FIS All-Sky Survey Bright Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the far-infrared and radio, without a condition to be detected in the mid-infrared. Additionally, all objects in both samples were identified as galaxies in the NED and/or SIMBAD databases, and a part of them is known to host active galactic nuclei (AGNs). For the present analysis, we have restricted our samples only to sources with known redshift z. In this paper, we analyse the far-infrared-radio correlation for both of these samples. We compare the ratio of infrared and radio emission from normal star-forming dusty galaxies and AGNs in both samples. For the smaller sample we obtained =2.14 for AGNs and =2.27 for normal galaxies, while for the larger sample =2.15 for AGNs and =2.22 for normal galaxies. An average value of the slope in both samples is ~2.2, which is consistent with the previous measurements from the literature.

X-ray inverse Compton emission from the radio halo of M87

NASA Technical Reports Server (NTRS)

Feigelson, E. D.

1984-01-01

A significant fraction of known galaxies contain an active galactic nucleus (AGN) at their cores, the site of violent activity and non-stellar radiation seen across the entire electromagnetic spectrum. This activity is thought to be due to the accretion of gas onto a massive black hole. A fraction of AGNs also eject collimated beams of energetic material, usually seen by virtue of its synchrotron emission in the radio band. Efforts to study these jets from AGNs in the X-ray band with the Einstein Observatory has led to several detections, most notably the jets in the nearby radio galaxies Centaurus A and Virgo A = M87. In their study of M87, Schreier, Gorenstein and Feigelson (1982) noted that, in addition to the synchrotron jet 10"-20" from the nucleus, X-rays appear to be generated in the diffuse radio halo 2'-5' from the nucleus. This finding may be particularly important as it may constitute the first known case of X-ray inverse Compton emission from AGN ejecta, allowing for the first time direct determination of the magnetic field strengths.

Simultaneous observations of solar sporadic radio emission by the radio telescopes UTR-2, URAN-2 and NDA within the frequency range 8-42 MHz

NASA Astrophysics Data System (ADS)

Melnik, V.; Konovalenko, A.; Brazhenko, A.; Briand, C.; Dorovskyy, V.; Zarka, P.; Denis, L.; Bulatzen, V.; Frantzusenko, A.; Rucker, H.; Stanislavskyy, A.

2012-09-01

From 25 June till 12 August 2011 sporadic solar radio emission was observed simultaneously by three separate radio telescopes: UTR-2 (Kharkov, Ukraine), URAN-2 (Poltava, Ukraine) and NDA (Nancay, France). During these observations some interesting phenomena were observed. Some of them are discussed in this paper.

Radio emission of SN1993J: the complete picture. II. Simultaneous fit of expansion and radio light curves

NASA Astrophysics Data System (ADS)

Martí-Vidal, I.; Marcaide, J. M.; Alberdi, A.; Guirado, J. C.; Pérez-Torres, M. A.; Ros, E.

2011-02-01

We report on a simultaneous modelling of the expansion and radio light curves of the supernova SN1993J. We developed a simulation code capable of generating synthetic expansion and radio light curves of supernovae by taking into consideration the evolution of the expanding shock, magnetic fields, and relativistic electrons, as well as the finite sensitivity of the interferometric arrays used in the observations. Our software successfully fits all the available radio data of SN 1993J with a standard emission model for supernovae, which is extended with some physical considerations, such as an evolution in the opacity of the ejecta material, a radial decline in the magnetic fields within the radiating region, and a changing radial density profile for the circumstellar medium starting from day 3100 after the explosion.

The effect of magnetic topography on high-latitude radio emission at Neptune

NASA Technical Reports Server (NTRS)

Sawyer, C. B.; Warwick, James W.; Romig, J. H.

1992-01-01

Occultation by a local elevation on the surface of constant magnetic field is proposed as a new interpretation for the unusual properties of Neptune high-latitude emission. Abrupt changes in intensity and polarization of this broadband smooth radio emission were observed as the Voyager 2 spacecraft passed near the north magnetic pole before closest approach. The observed sequence of cutoffs with polarization reversal would not occur during descent of the spacecraft through regular surfaces of increasing magnetic field. The sequence can be understood in terms of constant-frequency (constant-field) surfaces that are not only offset from the planet center but are locally highly distorted by an elevation that occults the outgoing extraordinary-mode beam. The required occulter is similar to the field enhancement observed directly by the magnetometer team when Voyager reached lower altitude farther to the west. Evidence is presented that the sources of the high-altitude emission are located near the longitude of the minimum-B anomaly associated with the dipole offset and that the local elevation of constant-B surfaces extends eastward from the longitude where it is directly measured by the magnetometer to the longitude where occultation of the remote radio source is observed. Together, the radio and magnetometer experiments indicate that the constant-frequency surfaces are distorted by an elevation that extends 0.3 rad in the longitudinal direction.

RADIO SYNCHROTRON EMISSION FROM A BOW SHOCK AROUND THE GAS CLOUD G2 HEADING TOWARD THE GALACTIC CENTER

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

Narayan, Ramesh; Sironi, Lorenzo; Oezel, Feryal

2012-10-01

A dense ionized cloud of gas has been recently discovered to be moving directly toward the supermassive black hole, Sgr A*, at the Galactic center. In 2013 June, at the pericenter of its highly eccentric orbit, the cloud will be approximately 3100 Schwarzschild radii from the black hole and will move supersonically through the ambient hot gas with a velocity of v{sub p} Almost-Equal-To 5400 km s{sup -1}. A bow shock is likely to form in front of the cloud and could accelerate electrons to relativistic energies. We estimate via particle-in-cell simulations the energy distribution of the accelerated electrons andmore » show that the non-thermal synchrotron emission from these electrons might exceed the quiescent radio emission from Sgr A* by a factor of several. The enhanced radio emission should be detectable at GHz and higher frequencies around the time of pericentric passage and in the following months. The bow shock emission is expected to be displaced from the quiescent radio emission of Sgr A* by {approx}33 mas. Interferometric observations could resolve potential changes in the radio image of Sgr A* at wavelengths {approx}< 6 cm.« less

EFFECTS OF ALFVEN WAVES ON ELECTRON CYCLOTRON MASER EMISSION IN CORONAL LOOPS AND SOLAR TYPE I RADIO STORMS

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

Zhao, G. Q.; Chen, L.; Wu, D. J.

Solar type I radio storms are long-lived radio emissions from the solar atmosphere. It is believed that these type I storms are produced by energetic electrons trapped within a closed magnetic structure and are characterized by a high ordinary (O) mode polarization. However, the microphysical nature of these emissions is still an open problem. Recently, Wu et al. found that Alfven waves (AWs) can significantly influence the basic physics of wave-particle interactions by modifying the resonant condition. Taking the effects of AWs into account, this work investigates electron cyclotron maser emission driven by power-law energetic electrons with a low-energy cutoffmore » distribution, which are trapped in coronal loops by closed solar magnetic fields. The results show that the emission is dominated by the O mode. It is proposed that this O mode emission may possibly be responsible for solar type I radio storms.« less

An Overview of Saturn Narrowband Radio Emissions Observed by Cassini RPWS

NASA Astrophysics Data System (ADS)

Ye, S.-Y.; Fischer, G.; Menietti, J. D.; Wang, Z.; Gurnett, D. A.; Kurth, W. S.

Saturn narrowband (NB) radio emissions are detected between 3 and 70 kHz, with occurrence probability and wave intensity peaking around 5 kHz and 20 kHz. The emissions usually occur periodically for several days after intensification of Saturn kilometric radiation (SKR). Originally detected by the Voyagers, the extended duration of the Cassini mission and the improved capabilities of the Radio and Plasma Wave Science (RPWS) instrument have significantly advanced our knowledge about them. For example, RPWS measurements of the magnetic component have validated the electromagnetic nature of Saturn NB emissions. Evidences show that the 20 kHz NB emissions are generated by mode conversion of electrostatic upper hybrid waves on the boundary of the plasma torus, whereas direction-finding results point to a source in the auroral zone for the 5 kHz component. Similar to SKR, the 5 kHz NB emissions have a clock-like modulation and display two distinct modulation periods identical to the northern and southern hemisphere periods of SKR. Polarization measurements confirm that most NB emissions are propagating in the L-O mode, with the exception of second harmonic NB emissions. At high latitudes closer to the planet, RPWS detected right hand polarized Z-mode NB emissions below the local electron cyclotron frequency (f_ce), which are believed to be the source of the L-O mode NB emissions detected above the local f_ce. Although the energy source for the generation of the Z-mode waves is still unclear, linear growth rate calculations indicate that the observed plasma distributions are unstable to the growth of electrostatic cyclotron harmonic emission. Alternatively, electromagnetic Z-mode might be directly generated by the cyclotron maser instability. The source Z-mode waves, upon reflection, propagate to the opposite hemisphere before escaping through mode conversion, which could explain the fact that both rotational modulation periods of NB emissions are observable in each

VARIABLE AND POLARIZED RADIO EMISSION FROM THE T6 BROWN DWARF WISEP J112254.73+255021.5

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

Williams, P. K. G.; Berger, E.; Gizis, J. E., E-mail: pwilliams@cfa.harvard.edu

2017-01-10

Route and Wolszczan recently detected five radio bursts from the T6 dwarf WISEP J112254.73+255021.5 and used the timing of these events to propose that this object rotates with an ultra-short period of ∼17.3 minutes. We conducted follow-up observations with the Very Large Array and Gemini-North but found no evidence for this periodicity. We do, however, observe variable, highly circularly polarized radio emission. Assuming that the radio emission of this T dwarf is periodically variable on ∼hour timescales, like other radio-active ultracool dwarfs, we infer a likely period of 116 minutes. However, our observation lasted only 162 minutes and so more data are needed to test thismore » hypothesis. The handedness of the circular polarization switches twice and there is no evidence for any unpolarized emission component, the first time such a phenomenology has been observed in radio studies of very low-mass stars and brown dwarfs. We suggest that the object’s magnetic dipole axis may be highly misaligned relative to its rotation axis.« less

HST FGS1R Results On the Association Between Binary Wolf-Rayet Stars and Non-Thermal Radio Emission

NASA Astrophysics Data System (ADS)

Wallace, D. J.; Gies, D. R.; Nelan, E.; Leitherer, C.

2000-12-01

Two separate models have been proposed to explain the non-thermal emission detected in some Wolf-Rayet (WR) stars. In models based on single WR stars, this emission is proposed to arise via synchrotron radiative processes in the outer (intrinsically unstable) WR wind (e.g. White & Chen 1995). In models based on WR + O systems, this non-thermal radio emission is suggested to arise from the WR wind colliding with the wind of a companion (e.g. Williams et al. 1990). In order to be observed, the colliding winds region is believed to occur in wide binaries where the interaction zone is outside the WR radio photosphere (≈30 AU based on spherically symmetric uniform wind models). HST FGS1R observations of 9 non-thermal and 9, as a control group, purely thermal radio emitting stars attempted to verify the theory that this non-thermal emission is always a result of binary interactions. If the binary model is correct, then most or all of our non-thermal targets should have companions with projected separations of 0.01″ radio positions, while the lower limit comes from the projected radius of the thermal radio photosphere. The absence of non-thermal emission means either that there is no wind interaction with a companion, or that the companion is engulfed in the thermal radio envelope at distances < 10 mas (Dougherty & Williams 2000). With a single exception, WR 48, no companions were found. While this result does not rule out the role of companions in producing the non-thermal radio emission, it does not support the companion hypothesis. These results do strongly suggest that a wind interaction region, if occurring, must lie closer to the WR star than previously believed. Support for this work was provided by NASA through grant number GO-8309 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

Search for low-frequency diffuse radio emission around a shock in the massive galaxy cluster MACS J0744.9+3927

NASA Astrophysics Data System (ADS)

Wilber, A.; Brüggen, M.; Bonafede, A.; Rafferty, D.; Savini, F.; Shimwell, T.; van Weeren, R. J.; Botteon, A.; Cassano, R.; Brunetti, G.; De Gasperin, F.; Wittor, D.; Hoeft, M.; Birzan, L.

2018-05-01

Merging galaxy clusters produce low-Mach-number shocks in the intracluster medium. These shocks can accelerate electrons to relativistic energies that are detectable at radio frequencies. MACS J0744.9+3927 is a massive [M500 = (11.8 ± 2.8) × 1014 M⊙], high-redshift (z = 0.6976) cluster where a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovich maps from MUSTANG indicate that a shock, with Mach number M = 1.0-2.9 and an extension of ˜200 kpc, sits near the centre of the cluster. The shock is also detected as a brightness and temperature discontinuity in X-ray observations. To search for diffuse radio emission associated with the merger, we have imaged the cluster with the LOw Frequency ARray (LOFAR) at 120-165 MHz. Our LOFAR radio images reveal previously undetected AGN emission, but do not show clear cluster-scale diffuse emission in the form of a radio relic nor a radio halo. The region of the shock is on the western edge of AGN lobe emission from the brightest cluster galaxy. Correlating the flux of known shock-induced radio relics versus their size, we find that the radio emission overlapping the shocked region in MACS J0744.9+3927 is likely of AGN origin. We argue against the presence of a relic caused by diffusive shock acceleration and suggest that the shock is too weak to accelerate electrons from the intracluster medium.

Radio emission in ultracool dwarfs: The nearby substellar triple system VHS 1256-1257

NASA Astrophysics Data System (ADS)

Guirado, J. C.; Azulay, R.; Gauza, B.; Pérez-Torres, M. A.; Rebolo, R.; Climent, J. B.; Zapatero Osorio, M. R.

2018-02-01

Aim. With the purpose of investigating the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92-125723.9 (hereafter VHS 1256-1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8 pc. Methods: We observed in phase-reference mode the system VHS 1256-1257 with the Karl G. Jansky Very Large Array at X band and L band and with the European VLBI Network at L band in several epochs during 2015 and 2016. Results: We discovered radio emission at X band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 μJy. We determined a spectral index α = ‑1.1 ± 0.3 between 8 and 12 GHz, suggesting that non-thermal, optically thin, synchrotron, or gyrosynchrotron radiation is responsible for the observed radio emission. Interestingly, no signal is seen at L band where we set a 3σ upper limit of 20 μJy. This might be explained by strong variability of the binary or self-absorption at this frequency. By adopting the latter scenario and gyrosynchrotron radiation, we constrain the turnover frequency to be in the interval 5-8.5 GHz, from which we infer the presence of kG-intense magnetic fields in the M7.5 binary. Our data impose a 3σ upper bound to the radio flux density of the L7 object of 9 μJy at 10 GHz.

Nature of radio feature formed by re-started jet activity in 3C 84 and its relation with γ-ray emissions

NASA Astrophysics Data System (ADS)

Nagai, H.; Chida, H.; Kino, M.; Orienti, M.; D'Ammando, F.; Giovannini, G.; Hiura, K.

2016-02-01

Re-started jet activity occurred in the bright nearby radio source 3C 84 in about 2005. The re-started jet is forming a prominent component (namely C3) at the tip of jet. The component has showed an increase in radio flux density for more than 7 years while the radio spectrum remains optically thin. This suggests that the component is the head of a radio lobe including a hotspot where the particle acceleration occurs. Thus, 3C 84 is a unique laboratory to study the physical properties at the very early stage of radio source evolution. Another important aspect is that high energy and very high energy γ-ray emissions are detected from this source. The quest for the site of γ-ray emission is quite important to obtain a better understanding of γ-ray emission mechanisms in radio galaxies. In this paper, we review the observational results from very long baseline interferometry (VLBI) monitoring of 3C 84 reported in series of our previous papers. We argue the nature of re-started jet/radio lobe and its relation with high-energy emission.

Solar radio continuum storms

NASA Technical Reports Server (NTRS)

1974-01-01

Radio noise continuum emission observed in metric and decametric wave frequencies is discussed. The radio noise is associated with actively varying sunspot groups accompanied by the S-component of microwave radio emissions. It is shown that the S-component emission in microwave frequencies generally occurs several days before the emission of the noise continuum storms of lower frequencies. It is likely that energetic electrons, 10 to 100 Kev, accelerated in association with the variation of sunspot magnetic fields, are the sources of the radio emissions. A model is considered to explain the relation of burst storms on radio noise. An analysis of the role of energetic electrons on the emissions of both noise continuum and type III burst storms is presented. It is shown that instabilities associated with the electrons and their relation to their own stabilizing effects are important in interpreting both of these storms.

X-ray studies of quasars with the Einstein Observatory. IV - X-ray dependence on radio emission

NASA Technical Reports Server (NTRS)

Worrall, D. M.; Tananbaum, H.; Giommi, P.; Zamorani, G.

1987-01-01

The X-ray properties of a sample of 114 radio-loud quasars observed with the Einstein Observatory are examined, and the results are compared with those obtained from a large sample of radio-quiet quasars. The results of statistical analysis of the dependence of X-ray luminosity on combined functions of optical and radio luminosity show that the dependence on both luminosities is important. However, statistically significant differences are found between subsamples of flat radio spectra quasars and steep radio spectra quasars with regard to dependence of X-ray luminosity on only radio luminosity. The data are consistent with radio-loud quasars having a physical component, not directly related to the optical luminosity, which produces the core radio luminosity plus 'extra' X-ray emission.

Chromospheric Evaporation and Decimetric Radio Emission in Solar Flares

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Benz, Arnold O.

1995-01-01

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca xix soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T-(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyzed 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Phoenix, hard X-ray data from BATSE/CGRO, and soft X-ray data from GOES were available. We detected slowly drifting high-frequency cutoffs between 1.1 and 3.0 GHz, with drift rates of -41 +/- 32 MHz/s, extending over time intervals of 24 +/- 23 s. Developing a density model for type III-emitting flare loops based on the statistically observed drift rate of type III bursts by Alvarez & Haddock, we infer velocities of up to

The Nature of Radio Emission from Distant Galaxies: The 1.4 GHZ Observations

NASA Astrophysics Data System (ADS)

Richards, E. A.

2000-04-01

We have conducted a deep radio survey with the Very Large Array at 1.4 GHz of a region containing the Hubble Deep Field (HDF). This survey overlaps previous observations at 8.5 GHz allowing us to investigate the radio spectral properties of microjansky sources to flux densities greater than 40 μJy at 1.4 GHz and greater than 8 μJy at 8.5 GHz. A total of 371 sources have been cataloged at 1.4 GHz as part of a complete sample within 20' of the HDF. The differential source count for this region is only marginally sub-Euclidean and is given by n(S)=(8.3+/-0.4)S-2.4+/-0.1 sr-1 Jy-1. Above about 100 μJy the radio source count is systematically lower in the HDF as compared to other fields. We conclude that there is clustering in our radio sample on size scales of 1'-40'. The 1.4 GHz-selected sample shows that the radio spectral indices are preferentially steep (α1.4=0.85) and that the sources are moderately extended with average angular size θ=1.8". Optical identification with disk-type systems at z~0.1-1 suggests that synchrotron emission, produced by supernovae remnants, is powering the radio emission in the majority of sources. The 8.5 GHz sample contains primarily moderately flat spectrum sources (α8.5=0.35), with less than 15% inverted. We argue that we may be observing an increased fraction of optically thin bremsstrahlung over synchrotron radiation in these distant star-forming galaxies.

Neutral hydrogen in elliptical galaxies with nuclear radio sources and optical emission lines

NASA Technical Reports Server (NTRS)

Dressel, L. L.; Bania, T. M.; Oconnell, R. W.

1982-01-01

An H I detection survey of eleven elliptical galaxies with powerful nuclear radio sources was conducted, using the 305 m antenna of Arecibo Observatory, to test the hypothesis that large H I mass is conductive to the formation of nuclear radio sources in elliptical galaxies. The H I was detected in emission in UGC 09114 and was possibly detected in absorption in UGC 06671. Observations of the remaining galaxies were not sensitive enough to support or refute the hypothesis. Data was combined from other H I surveys and spectroscopic surveys to search for correlations of H I mass with other galactic properties and environmental conditions. Strong correlations of (O II) lambda 3727 emission with H I content and with nuclear radio power were found. The latter two properties may simply indicate, respectively, whether a significant amount of gas is available to be ionized and whether energy is provided by nuclear activity for ionization. No dependence of H I content on optical luminosity or on degree of isolation from other galaxies was found.

Strongly lensed neutral hydrogen emission: detection predictions with current and future radio interferometers

NASA Astrophysics Data System (ADS)

Deane, R. P.; Obreschkow, D.; Heywood, I.

2015-09-01

Strong gravitational lensing provides some of the deepest views of the Universe, enabling studies of high-redshift galaxies only possible with next-generation facilities without the lensing phenomenon. To date, 21-cm radio emission from neutral hydrogen has only been detected directly out to z ˜ 0.2, limited by the sensitivity and instantaneous bandwidth of current radio telescopes. We discuss how current and future radio interferometers such as the Square Kilometre Array (SKA) will detect lensed H I emission in individual galaxies at high redshift. Our calculations rely on a semi-analytic galaxy simulation with realistic H I discs (by size, density profile and rotation), in a cosmological context, combined with general relativistic ray tracing. Wide-field, blind H I surveys with the SKA are predicted to be efficient at discovering lensed H I systems, increasingly so at z ≳ 2. This will be enabled by the combination of the magnification boosts, the steepness of the H I luminosity function at the high-mass end, and the fact that the H I spectral line is relatively isolated in frequency. These surveys will simultaneously provide a new technique for foreground lens selection and yield the highest redshift H I emission detections. More near term (and existing) cm-wave facilities will push the high-redshift H I envelope through targeted surveys of known lenses.

Mulifunctional Dendritic Emitter: Aggregation-Induced Emission Enhanced, Thermally Activated Delayed Fluorescent Material for Solution-Processed Multilayered Organic Light-Emitting Diodes

PubMed Central

Matsuoka, Kenichi; Albrecht, Ken; Yamamoto, Kimihisa; Fujita, Katsuhiko

2017-01-01

Thermally activated delayed fluorescence (TADF) materials emerged as promising light sources in third generation organic light-emitting diodes (OLED). Much effort has been invested for the development of small molecular TADF materials and vacuum process-based efficient TADF-OLEDs. In contrast, a limited number of solution processable high-molecular weight TADF materials toward low cost, large area, and scalable manufacturing of solution processed TADF-OLEDs have been reported so far. In this context, we report benzophenone-core carbazole dendrimers (GnB, n = generation) showing TADF and aggregation-induced emission enhancement (AIEE) properties along with alcohol resistance enabling further solution-based lamination of organic materials. The dendritic structure was found to play an important role for both TADF and AIEE activities in the neat films. By using these multifunctional dendritic emitters as non-doped emissive layers, OLED devices with fully solution processed organic multilayers were successfully fabricated and achieved maximum external quantum efficiency of 5.7%. PMID:28139768

Mulifunctional Dendritic Emitter: Aggregation-Induced Emission Enhanced, Thermally Activated Delayed Fluorescent Material for Solution-Processed Multilayered Organic Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Matsuoka, Kenichi; Albrecht, Ken; Yamamoto, Kimihisa; Fujita, Katsuhiko

2017-01-01

Thermally activated delayed fluorescence (TADF) materials emerged as promising light sources in third generation organic light-emitting diodes (OLED). Much effort has been invested for the development of small molecular TADF materials and vacuum process-based efficient TADF-OLEDs. In contrast, a limited number of solution processable high-molecular weight TADF materials toward low cost, large area, and scalable manufacturing of solution processed TADF-OLEDs have been reported so far. In this context, we report benzophenone-core carbazole dendrimers (GnB, n = generation) showing TADF and aggregation-induced emission enhancement (AIEE) properties along with alcohol resistance enabling further solution-based lamination of organic materials. The dendritic structure was found to play an important role for both TADF and AIEE activities in the neat films. By using these multifunctional dendritic emitters as non-doped emissive layers, OLED devices with fully solution processed organic multilayers were successfully fabricated and achieved maximum external quantum efficiency of 5.7%.

Radio detections of southern ultracool dwarfs

NASA Astrophysics Data System (ADS)

Lynch, C.; Murphy, T.; Ravi, V.; Hobbs, G.; Lo, K.; Ward, C.

2016-04-01

We report the results of a volume-limited survey using the Australia Telescope Compact Array to search for transient and quiescent radio emission from 15 Southern hemisphere ultracool dwarfs. We detect radio emission from 2MASSW J0004348-404405 increasing the number of radio loud ultracool dwarfs to 22. We also observe radio emission from 2MASS J10481463-3956062 and 2MASSI J0339352-352544, two sources with previous radio detections. The radio emission from the three detected sources shows no variability or flare emission. Modelling this quiescent emission we find that it is consistent with optically thin gyrosynchrotron emission from a magnetosphere with an emitting region radius of (1-2)R*, magnetic field inclination 20°-80°, field strength ˜10-200 G, and power-law electron density ˜104-108 cm-3. Additionally, we place upper limits on four ultracool dwarfs with no previous radio observations. This increases the number of ultracool dwarfs studied at radio frequencies to 222. Analysing general trends of the radio emission for this sample of 15 sources, we find that the radio activity increases for later spectral types and more rapidly rotating objects. Furthermore, comparing the ratio of the radio to X-ray luminosities for these sources, we find 2MASS J10481463-3956062 and 2MASSI J0339352-352544 violate the Güdel-Benz relation by more than two orders of magnitude.

Radio emission from supernovae and gamma-ray bursters and the need for the SKA

NASA Astrophysics Data System (ADS)

Weiler, Kurt W.; Van Dyk, Schuyler D.; Sramek, Richard A.; Panagia, Nino

2004-12-01

Study of radio supernovae (SNe) over the past 25 years includes two dozen detected objects and more than 100 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material. Since 1997 the afterglow of γ-ray bursting sources (GRBs) has occasionally been detected in the radio, as well in other wavelength bands. In particular, the interesting and unusual γ-ray burst GRB 980425, almost certainly related to the radio supernova SN 1998bw, and the more recent SN 2003dh/GRB 030329 are links between the two classes of objects. Analyzing the extensive radio emission data available for SN 1998bw, one can describe its time evolution within the well established framework available for the analysis of radio emission from supernovae. This then allows relatively detailed description of a number of physical properties of the object. The radio emission can best be explained as the interaction of a mildly relativistic ( Γ ˜ 1.6) shock with a dense pre-explosion stellar wind-established circumstellar medium that is highly structured both azimuthally, in clumps or filaments, and radially, with observed density enhancements. From this we can support the conclusion that at least some members of the slow-soft class of GRBs are related to type Ib/c SNe and can be attributed to the explosion of a massive star in a dense, highly structured CSM that was presumably established by the pre-explosion stellar system. However, due to the lack of sensitivity of current radio telescopes, most supernovae cannot be studied if they are more

Broad-line radio galaxies observed with Fermi-LAT: The origin of the GeV γ-ray emission

DOE PAGES

Kataoka, J.; Stawarz, Ł.; Takahashi, Y.; ...

2011-09-22

Here, we report on a detailed investigation of the γ-ray emission from 18 broad-line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope data. We confirm the previously reported detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed look at the temporal characteristics of the observed γ-ray emission reveals in addition possible flux variability in both sources. No statistically significant γ-ray detection of the other BLRGs was found, however, in the considered data set. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 frommore » the BLRGs not yet detected in γ-rays is the particularly strong nuclear radio flux. This finding, together with the indications of the γ-ray flux variability and a number of other arguments presented, indicates that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets observed at intermediate viewing angles. In this paper we also analyzed a comparison sample of high-accretion-rate Seyfert 1 galaxies, which can be considered radio-quiet counterparts of BLRGs, and found that none were detected in γ-rays. A simple phenomenological hybrid model applied for the broadband emission of the discussed radio-loud and radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to the accreting matter is ≥ 1% on average for BLRGs, whereas it is ≤ 0.1% for Seyfert 1 galaxies.« less

The search for radio emission from exoplanets using LOFAR low-frequency beam-formed observations

NASA Astrophysics Data System (ADS)

Turner, Jake D.; Griessmeier, Jean-Mathias; Zarka, Philippe

2018-01-01

Detection of radio emission from exoplanets can provide information on the star-planet system that is very difficult or impossible to study otherwise, such as the planet’s magnetic field, magnetosphere, rotation period, orbit inclination, and star-planet interactions. Such a detection in the radio domain would open up a whole new field in the study of exoplanets, however, currently there are no confirmed detections of an exoplanet at radio frequencies. In this study, we discuss our ongoing observational campaign searching for exoplanetary radio emissions using beam-formed observations within the Low Band of the Low-Frequency Array (LOFAR). To date we have observed three exoplanets: 55 Cnc, Upsilon Andromedae, and Tau Boötis. These planets were selected according to theoretical predictions, which indicated them as among the best candidates for an observation. During the observations we usually recorded three beams simultaneously, one on the exoplanet and two on patches of nearby “empty” sky. An automatic pipeline was created to automatically find RFI, calibrate the data due to instrumental effects, and to search for emission in the exoplanet beam. Additionally, we observed Jupiter with LOFAR with the same exact observational setup as the exoplanet observations. The main goals of the Jupiter observations are to train the detection algorithm and to calculate upper limits in the case of a non-detection. Data analysis is currently ongoing. Conclusions reached at the time of the meeting, about detection of or upper limit to the planetary signal, will be presented.

Can Radio Emission From Luminous Obscured AGN Blow Kpc-scale Ionized Outflows?

NASA Astrophysics Data System (ADS)

Goulding, Andy

2017-09-01

We propose joint VLA radio and Chandra X-ray to observe 4 AGN selected from the SDSS-BOSS and the Hyper Suprime-Cam surveys that present spectacular extended outflowing [O III] regions, reaching up to 50kpc in diameter. Our proposed observations allow us to study the mechanical and kinematical output of the AGN through radio and X-ray observations, measure the fraction of the AGN bolometric luminosity that is transferred to the outflow, and to determine the morphology and spectral index (by producing high-res continuum maps) of the radio emission that may be co-spatial with the extended ionized AGN outflow. In turn, our study will determine what role the AGN plays in producing extended outflows, and hence, provide an in-depth understanding of the physical drivers of AGN feedback.

EVLA observations of radio-loud quasars selected to study radio orientation

NASA Astrophysics Data System (ADS)

Maithil, Jaya; Brotherton, Michael S.; Runnoe, Jessie; Wardle, John F. C.; DiPompeo, Michael; De Breuck, Carlos; Wills, Beverley J.

2018-06-01

We present preliminary work to develop an unbiased sample of radio-loud quasars to test orientation indicators. We have obtained radio data of 147 radio-loud quasars using EVLA at 10 GHz and with the A-array. With this high-resolution data we have measured the uncontaminated core flux density to determine orientation indicators based on radio core dominance. The radio cores of quasars have a flat spectrum over a broad range of frequencies, so we expect that the core flux density at the FIRST and the observed frequencies should be the same in the absence of variability. Jackson & Brown (2012) pointed out that the survey measurements of core flux density, like FIRST, often doesn't have the spatial resolution to distinguish cores from extended emission. Our measurements show that at FIRST spatial resolution, core flux measurements are indeed systematically high. Our results establish that orientation studies need high-resolution radio data as compared to survey data, and that the optical emission is a better normalization than the extended radio emission for a core dominance parameter to track orientation.

Collisional quenching of OH radio emission from comet Hale-Bopp

NASA Technical Reports Server (NTRS)

Schloerb, F. P.; Devries, C. H.; Lovell, A. J.; Irvine, W. M.; Senay, M.; Wootten, H. A.; Ferris, J. P. (Principal Investigator)

1997-01-01

Observations of comets in the 18-cm OH transitions offer a means to probe gas production, kinematics, and OH excitation in comets. We present initial results of OH observations of comet Hale-Bopp obtained with the NRAO 43 m antenna located in Greenbank, WV. Maps of the emission provide strong constraints on the amount of quenching of the inversion of the OH ground state A-doublet in the coma. Analysis of the total radio OH flux and maps of its radial brightness distribution indicate a quenched region on the order of approximately 500,000 km during March and April 1997. This large value is generally consistent with previous observations of radio OH quenching in lower production rate comets when the high production rate of comet Hale-Bopp is considered.

Jet-torus connection in radio galaxies. Relativistic hydrodynamics and synthetic emission

NASA Astrophysics Data System (ADS)

Fromm, C. M.; Perucho, M.; Porth, O.; Younsi, Z.; Ros, E.; Mizuno, Y.; Zensus, J. A.; Rezzolla, L.

2018-01-01

Context. High resolution very long baseline interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jets or they may be induced by the different conditions in the surrounding ambient medium, including the obscuring torus, or a combination of the two. Aims: In this paper we investigate the influence of the ambient medium, including the obscuring torus, on the observed properties of jets from radio galaxies. Methods: We performed special-relativistic hydrodynamic (SRHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat, which is based on a second-order accurate finite-volume method and an approximate Riemann solver. Using a newly developed radiative transfer code to compute the electromagnetic radiation, we modelled several jets embedded in various ambient medium and torus configurations and subsequently computed the non-thermal emission produced by the jet and thermal absorption from the torus. To better compare the emission simulations with observations we produced synthetic radio maps, taking into account the properties of the observatory. Results: The detailed analysis of our simulations shows that the observed properties such as core shift could be used to distinguish between over-pressured and pressure matched jets. In addition to the properties of the jets, insights into the extent and density of the obscuring torus can be obtained from analyses of the single-dish spectrum and spectral index maps.

Temporal frequency of radio emissions for the April 25, 1984 flare

NASA Technical Reports Server (NTRS)

Wells, G. D.; Hausman, B. A.; Kroehl, H. W.

1986-01-01

The National Geophysical Data Center archives data of the solar-terrestrial environment. The USAF Radio Solar Telescope Network (RSTN) data allow performance of time series analysis to determine temporal oscillations as low as three seconds. The X13/3B flare which erupted in region 4474 (S12E43) on the 24 to 25 of April 1984, was selected. The soft X-rays, 1 to 8 A, remained above X-levels for 50 minutes and the radio emissions measured at Learmonth Solar Observatory reached a maximum of 3.15 x 10 to the 5th power SFUs at 410 MHz at 0000UT. A power spectral analysis of the fixed frequency RSTN data from Learmonth shows possible quasi-periodic fluctuations in the range two to ten seconds. Repetition rates or quasi-periodicities, in the case of the power spectral analysis, generally showed the same trends as the average solar radio flux at 245 and 8800 MHz. The quasi-periodicities at 1415 MHz showed no such trends.

Discovery of a Time Lag between the Soft X-Ray and Radio Emission of the Tidal Disruption Flare ASASSN-14li: Evidence for Linear Disk–Jet Coupling

NASA Astrophysics Data System (ADS)

Pasham, Dheeraj R.; van Velzen, Sjoert

2018-03-01

The tidal disruption of a star by a supermassive black hole can result in transient radio emission. The electrons producing these synchrotron radio flares could either be accelerated inside a relativistic jet or externally by shocks resulting from an outflow interacting with the circumnuclear medium. Until now, evidence for the internal emission mechanism has been lacking; nearly all tidal disruption flare studies have adopted the external shock model to explain the observed properties of radio flares. Here we report a result that presents a challenge to external emission models: we discovered a cross-correlation between the soft X-ray (0.3–1 keV) and 16 GHz radio flux of the tidal disruption flare ASASSN-14li. Variability features in the X-ray light curve appear again in the radio light curve, but after a time lag of {12}-5+6 days. This demonstrates that the soft X-ray-emitting accretion disk regulates the radio emission. This coupling appears to be inconsistent with all previous external emission models for this source but is naturally explained if the radio emission originates from a freely expanding jet. We show that emission internal to an adiabatically expanding jet can also reproduce the observed evolution of the radio spectral energy distribution. Furthermore, both the correlation between X-ray and radio luminosity as well as our radio spectral modeling imply an approximately linear coupling between the accretion rate and jet power.

Considerations on the radio emission from extended air showers

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

Conti, E.; Sartori, G., E-mail: enrico.conti@pd.infn.it, E-mail: giorgio.sartori@unipd.it

The process of radio emission from extended air showers produced by high energy cosmic rays has reached a good level of comprehension and prediction. It has a coherent nature, so the emitted power scales quadratically with the energy of the primary particle. Recently, a laboratory measurement has revealed that an incoherent radiation mechanism exists, namely, the bremsstrahlung emission. In this paper we expound why bremsstrahlung radiation, that should be present in showers produced by ultra high energy cosmic rays, has escaped detection so far, and why, on the other side, it could be exploited, in the 1–10 GHz frequency range,more » to detect astronomical γ-rays. We propose an experimental scheme to verify such hypothesis, which, if correct, would deeply impact on the observational γ-ray astronomy.« less

Latitudinal beaming of Jupiter's low frequency radio emissions

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

Alexander, J.K.; Desch, M.D.; Kaiser, M.L.

1979-09-01

By comparing Rae 1 and Imp 6 satelite measurements of Jupiter's radio emissions near 1 MHz with recent Voyager 1 and 2 observations in the same frequency range it is now possible to study the properties of the low frequency radiation pattern over a 10/sup 0/ range of latitudes with respect to the Jovian rotation equator. These observations, which cover a wider latitudinal range than is possible from the earth, are consistent with many aspect of earlier ground-based measurements that have been used to infer a sharp beaming pattern for the decameter wavelength emissions. We find marked, systematic changes inmore » the statistical occurrence probability distributions with system III central meridian longitude as the Jovigraphic latitude of the observer changes over this range. Moreover, simultaneous observations by the two Voyager spacecraft, which are separated by up to 3/sup 0/ in Jovigraphic latitude, suggest that the instantaneous beam width may be no more than a few degrees at times. The new hectometer wave results can be interpreted in terms of a narrow, curved sheet at a fixed magnetic latitude into which the emission is beamed to escape the planet.« less

Radio emission from the X-ray pulsar Her X-1: a jet launched by a strong magnetic field neutron star?

NASA Astrophysics Data System (ADS)

van den Eijnden, J.; Degenaar, N.; Russell, T. D.; Miller-Jones, J. C. A.; Wijnands, R.; Miller, J. M.; King, A. L.; Rupen, M. P.

2018-01-01

Her X-1 is an accreting neutron star (NS) in an intermediate-mass X-ray binary. Like low-mass X-ray binaries (LMXBs), it accretes via Roche lobe overflow, but similar to many high-mass X-ray binaries containing a NS; Her X-1 has a strong magnetic field and slow spin. Here, we present the discovery of radio emission from Her X-1 with the Very Large Array. During the radio observation, the central X-ray source was partially obscured by a warped disc. We measure a radio flux density of 38.7 ± 4.8 μJy at 9 GHz but cannot constrain the spectral shape. We discuss possible origins of the radio emission, and conclude that coherent emission, a stellar wind, shocks and a propeller outflow are all unlikely explanations. A jet, as seen in LMXBs, is consistent with the observed radio properties. We consider the implications of the presence of a jet in Her X-1 on jet formation mechanisms and on the launching of jets by NSs with strong magnetic fields.

Portable Wireless LAN Device and Two-way Radio Threat Assessment for Aircraft Navigation Radios

NASA Technical Reports Server (NTRS)

Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Williams, Reuben A.; Smith, Laura J.; Salud, Maria Theresa P.

2003-01-01

Measurement processes, data and analysis are provided to address the concern for Wireless Local Area Network devices and two-way radios to cause electromagnetic interference to aircraft navigation radio systems. A radiated emission measurement process is developed and spurious radiated emissions from various devices are characterized using reverberation chambers. Spurious radiated emissions in aircraft radio frequency bands from several wireless network devices are compared with baseline emissions from standard computer laptops and personal digital assistants. In addition, spurious radiated emission data in aircraft radio frequency bands from seven pairs of two-way radios are provided, A description of the measurement process, device modes of operation and the measurement results are reported. Aircraft interference path loss measurements were conducted on four Boeing 747 and Boeing 737 aircraft for several aircraft radio systems. The measurement approach is described and the path loss results are compared with existing data from reference documents, standards, and NASA partnerships. In-band on-channel interference thresholds are compiled from an existing reference document. Using these data, a risk assessment is provided for interference from wireless network devices and two-way radios to aircraft systems, including Localizer, Glideslope, Very High Frequency Omnidirectional Range, Microwave Landing System and Global Positioning System. The report compares the interference risks associated with emissions from wireless network devices and two-way radios against standard laptops and personal digital assistants. Existing receiver interference threshold references are identified as to require more data for better interference risk assessments.

LOPES-3D: An antenna array for full signal detection of air-shower radio emission

NASA Astrophysics Data System (ADS)

Apel, W. D.; Arteaga, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Buchholz, P.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Finger, M.; Fuchs, B.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.

2012-12-01

To better understand the radio signal emitted by extensive air-showers and to further develop the radio detection technique of high-energy cosmic rays, the LOPES experiment was reconfigured to LOPES-3D. LOPES-3D is able to measure all three vectorial components of the electric field of radio emission from cosmic ray air showers. The additional measurement of the vertical component ought to increase the reconstruction accuracy of primary cosmic ray parameters like direction and energy, provides an improved sensitivity to inclined showers, and will help to validate simulation of the emission mechanisms in the atmosphere. LOPES-3D will evaluate the feasibility of vectorial measurements for large scale applications. In order to measure all three electric field components directly, a tailor-made antenna type (tripoles) was deployed. The change of the antenna type necessitated new pre-amplifiers and an overall recalibration. The reconfiguration and the recalibration procedure are presented and the operationality of LOPES-3D is demonstrated.

Double-peaked Emission Lines Due to a Radio Outflow in KISSR 1219

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

Kharb, P.; Vaddi, S.; Subramanian, S.

We present the results from 1.5 and 5 GHz phase-referenced VLBA and 1.5 GHz Karl G. Jansky Very Large Array (VLA) observations of the Seyfert 2 galaxy KISSR 1219, which exhibits double-peaked emission lines in its optical spectrum. The VLA and VLBA data reveal a one-sided core-jet structure at roughly the same position angles, providing evidence of an active galactic nucleus outflow. The absence of dual parsec-scale radio cores puts the binary black-hole picture in doubt for the case of KISSR 1219. The high brightness temperatures of the parsec-scale core and jet components (>10{sup 6} K) are consistent with thismore » interpretation. Doppler boosting with jet speeds of ≳0.55 c to ≳0.25 c , going from parsec to kiloparsec scales, at a jet inclination ≳50° can explain the jet one-sidedness in this Seyfert 2 galaxy. A blueshifted broad emission line component in [O iii] is also indicative of an outflow in the emission line gas at a velocity of ∼350 km s{sup −1}, while the [O i] doublet lines suggest the presence of shock-heated gas. A detailed line ratio study using the MAPPINGS III code further suggests that a shock+precursor model can explain the line ionization data well. Overall, our data suggest that the radio outflow in KISSR 1219 is pushing the emission line clouds, both ahead of the jet and in a lateral direction, giving rise to the double peak emission line spectra.« less

How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability

NASA Astrophysics Data System (ADS)

Weber, Christof; Lammer, Helmut; Shaikhislamov, Ildar F.; Erkaev, Nikolai; Chadney, Joshua M.; Khodachenko, Maxim L.; Grießmeier, Jean-Mathias; Rucker, Helmut O.; Vocks, Christian; Macher, Wolfgang; Odert, Petra; Kislyakova, Kristina G.

2017-04-01

We present a study of the plasma conditions in the atmospheres of the Hot Jupiters HD 209458b and HD 189733b and for an HD 209458b-like planet at orbit locations between 0.2-1 AU around a Sun-like star. We discuss how these conditions influence the radio emission we expect from their planetary magnetospheres. We find that the environmental conditions for the cyclotron maser instability (CMI), the process which is responsible for the generation of radio waves at magnetic planets in the solar system, most likely will not operate at Hot Jupiters. The reason for that is that hydrodynamically expanding atmospheres possess extended ionospheres whose plasma densities within the magnetosphere are so large that the plasma frequency is much higher than the cyclotron frequency, which contradicts the necessary condition for the production of radio emission and prevents the escape of radio waves from close-in extrasolar planets at distances <0.05 AU from a Sun-like host star. The upper atmosphere structure of Hot Jupiters around stars similar to the Sun changes between 0.2 and 0.5 AU from the hydrodynamic to a hydrostatic regime and this results in conditions similar to solar system planets with a region of depleted plasma between the exobase and the magnetopause where the plasma frequency can be lower than the cyclotron frequency. In such an environment a beam of highly energetic electrons accelerated along the field lines towards the planet can produce radio emission. However, even if the CMI could operate the extended ionospheres of Hot Jupiters are too dense to let the radio emission escape from the planets. We also investigate the possible radio emission of the Hot Jupiter Tau Bootis b by placing it at different orbital distances from the host star, i.e. 0.1 and 0.2 AU. In particular we check if the atmosphere of Tau Bootis b at 0.046 AU is in the hydrostatic or in the hydrodynamic regime. If it is in the hydrodynamic regime it's ionosphere is extended and will constitute

THE VLA SURVEY OF CHANDRA DEEP FIELD SOUTH. V. EVOLUTION AND LUMINOSITY FUNCTIONS OF SUB-MILLIJANSKY RADIO SOURCES AND THE ISSUE OF RADIO EMISSION IN RADIO-QUIET ACTIVE GALACTIC NUCLEI

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

Padovani, P.; Mainieri, V.; Rosati, P.

2011-10-10

We present the evolutionary properties and luminosity functions of the radio sources belonging to the Chandra Deep Field South Very Large Array survey, which reaches a flux density limit at 1.4 GHz of 43 {mu}Jy at the field center and redshift {approx}5 and which includes the first radio-selected complete sample of radio-quiet active galactic nuclei (AGNs). We use a new, comprehensive classification scheme based on radio, far- and near-IR, optical, and X-ray data to disentangle star-forming galaxies (SFGs) from AGNs and radio-quiet from radio-loud AGNs. We confirm our previous result that SFGs become dominant only below 0.1 mJy. The sub-millijanskymore » radio sky turns out to be a complex mix of SFGs and radio-quiet AGNs evolving at a similar, strong rate; non-evolving low-luminosity radio galaxies; and declining radio powerful (P {approx}> 3 x 10{sup 24} W Hz{sup -1}) AGNs. Our results suggest that radio emission from radio-quiet AGNs is closely related to star formation. The detection of compact, high brightness temperature cores in several nearby radio-quiet AGNs can be explained by the coexistence of two components, one non-evolving and AGN related and one evolving and star formation related. Radio-quiet AGNs are an important class of sub-millijansky sources, accounting for {approx}30% of the sample and {approx}60% of all AGNs, and outnumbering radio-loud AGNs at {approx}< 0.1 mJy. This implies that future, large area sub-millijansky surveys, given the appropriate ancillary multiwavelength data, have the potential of being able to assemble vast samples of radio-quiet AGNs, bypassing the problems of obscuration that plague the optical and soft X-ray bands.« less

IRAS observations of radio-quiet and radio-loud quasars

NASA Technical Reports Server (NTRS)

Neugebauer, G.; Soifer, B. T.; Miley, G.; Habing, H. J.; Young, E.; Low, F. J.; Beichman, C. A.; Clegg, P. E.; Harris, S.; Rowan-Robinson, M.

1984-01-01

Observations from 12 to 100 microns are presented of two radio-quiet and three radio-loud quasars. Over this wavelength range, all five have grossly similar continuum energy distributions. The continua of the radio-loud quasars are consistent with synchrotron radiation. There is an indication, however, of excess 100 micron emission in the two radio-quiet quasars.

WISEP J060738.65+242953.4: A NEARBY POLE-ON L8 BROWN DWARF WITH RADIO EMISSION

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

Gizis, John E.; Paudel, Rishi; Williams, Peter K. G.

2016-11-01

We present a simultaneous, multi-wavelength campaign targeting the nearby (7.2 pc) L8/L9 (optical/near-infrared) dwarf WISEP J060738.65+242953.4 in the mid-infrared, radio, and optical. Spitzer Space Telescope observations show no variability at the 0.2% level over 10 hr each in the 3.6 and 4.5 μ m bands. Kepler K2 monitoring over 36 days in Campaign 0 rules out stable periodic signals in the optical with amplitudes greater than 1.5% and periods between 1.5 hr and 2 days. Non-simultaneous Gemini optical spectroscopy detects lithium, constraining this L dwarf to be less than ∼2 Gyr old, but no Balmer emission is observed. The lowmore » measured projected rotation velocity ( v sin i < 6 km s{sup −1}) and lack of variability are very unusual compared to other brown dwarfs, and we argue that this substellar object is likely viewed pole-on. We detect quiescent (non-bursting) radio emission with the Very Large Array. Among radio-detected L and T dwarfs, it has the lowest observed L{sub ν} and the lowest v  sin  i . We discuss the implications of a pole-on detection for various proposed radio emission scenarios.« less

Testing the Young Neutron Star Scenario with Persistent Radio Emission Associated with FRB 121102

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

Kashiyama, Kazumi; Murase, Kohta

Recently a repeating fast radio burst (FRB) 121102 has been confirmed to be an extragalactic event and a persistent radio counterpart has been identified. While other possibilities are not ruled out, the emission properties are broadly consistent with Murase et al. that theoretically proposed quasi-steady radio emission as a counterpart of both FRBs and pulsar-driven supernovae. Here, we constrain the model parameters of such a young neutron star scenario for FRB 121102. If the associated supernova has a conventional ejecta mass of M {sub ej} ≳ a few M {sub ⊙}, a neutron star with an age of t {submore » age} ∼ 10–100 years, an initial spin period of P{sub i} ≲ a few ms, and a dipole magnetic field of B {sub dip} ≲ a few × 10{sup 13} G can be compatible with the observations. However, in this case, the magnetically powered scenario may be favored as an FRB energy source because of the efficiency problem in the rotation-powered scenario. On the other hand, if the associated supernova is an ultra-stripped one or the neutron star is born by the accretion-induced collapse with M {sub ej} ∼ 0.1 M {sub ⊙}, a younger neutron star with t {sub age} ∼ 1–10 years can be the persistent radio source and might produce FRBs with the spin-down power. These possibilities can be distinguished by the decline rate of the quasi-steady radio counterpart.« less

The relationship between the carbon monoxide intensity and the radio continuum emission in spiral galaxies

NASA Technical Reports Server (NTRS)

Adler, David S.; Lo, K. Y.; Allen, Ronald J.

1991-01-01

The relationship between the velocity-integrated CO emission and the nonthermal radio continuum brightness in the disks of normal spiral galaxies is examined on a variety of length scales. On a global scale, the total CO intensity correlates strongly with the total radio continuum flux density for a sample of 31 galaxies. On scales of about 2 kpc or more in the disk of individual galaxies, it is found that the ratio I(CO)/T(20) remains fairly constant over the entire disk as well as from galaxy to galaxy. For the eight spirals in the sample, the disk-averaged values of I(CO)/T(20) range from 0.6-2.4, with the average over all eight galaxies being 1.3 +/- 0.6. It is concluded that what these various length scales actually trace are differences in the primary heating mechanism of the gas in the beam. The observed relationship between CO and nonthermal radio continuum emission can be explained by assuming that molecular gas in galactic disks is heated primarily by cosmic rays. The observed relationship is used to show that the brightness of synchrotron emission is proportional to n(cr) exp 0.4 - 0.9 in galactic disks.

Limits on radio emission from meteors using the MWA

NASA Astrophysics Data System (ADS)

Zhang, X.; Hancock, P.; Devillepoix, H. A. R.; Wayth, R. B.; Beardsley, A.; Crosse, B.; Emrich, D.; Franzen, T. M. O.; Gaensler, B. M.; Horsley, L.; Johnston-Hollitt, M.; Kaplan, D. L.; Kenney, D.; Morales, M. F.; Pallot, D.; Steele, K.; Tingay, S. J.; Trott, C. M.; Walker, M.; Williams, A.; Wu, C.; Ji, Jianghui; Ma, Yuehua

2018-07-01

Recently, low-frequency, broad-band radio emission has been observed accompanying bright meteors by the Long Wavelength Array (LWA). The broad-band spectra between 20 and 60 MHz were captured for several events, while the spectral index (dependence of flux density on frequency, with Sν ∝ να) was estimated to be -4 ± 1 during the peak of meteor afterglows. Here we present a survey of meteor emission and other transient events using the Murchison Wide Field Array (MWA) at 72-103 MHz. In our 322 h survey, down to a 5σ detection threshold of 3.5 Jy beam-1, no transient candidates were identified as intrinsic emission from meteors. We derived an upper limit of -3.7 (95 per cent confidence limit) on the spectral index in our frequency range. We also report detections of other transient events, such as reflected FM broadcast signals from small satellites, conclusively demonstrating the ability of the MWA to detect and track space debris on scales as small as 0.1 m in low Earth orbits.

Limits on radio emission from meteors using the MWA

NASA Astrophysics Data System (ADS)

Zhang, Xiang; Hancock, Paul; Devillepoix, Hadrien A. R.; Wayth, Randall B.; Beardsley, A.; Crosse, B.; Emrich, D.; Franzen, T. M. O.; Gaensler, B. M.; Horsley, L.; Johnston-Hollitt, M.; Kaplan, D. L.; Kenney, D.; Morales, M. F.; Pallot, D.; Steele, K.; Tingay, S. J.; Trott, C. M.; Walker, M.; Williams, A.; Wu, C.; Ji, Jianghui; Ma, Yuehua

2018-04-01

Recently, low frequency, broadband radio emission has been observed accompanying bright meteors by the Long Wavelength Array (LWA). The broadband spectra between 20 and 60 MHz were captured for several events, while the spectral index (dependence of flux density on frequency, with Sν∝να) was estimated to be -4 ± 1 during the peak of meteor afterglows. Here we present a survey of meteor emission and other transient events using the Murchison Widefield Array (MWA) at 72-103 MHz. In our 322-hour survey, down to a 5σ detection threshold of 3.5 Jy/beam, no transient candidates were identified as intrinsic emission from meteors. We derived an upper limit of -3.7 (95% confidence limit) on the spectral index in our frequency range. We also report detections of other transient events, like reflected FM broadcast signals from small satellites, conclusively demonstrating the ability of the MWA to detect and track space debris on scales as small as 0.1 m in low Earth orbits.

GBT Observations of Radio Recombination Line Emission Associated with Supernova Remnants W28 and W44

NASA Astrophysics Data System (ADS)

Hewitt, John W.; Yusef-Zadeh, F.

2006-06-01

Since the 1970's weak radio recombination line(RRL) emission has been observed toward several supernova remnants. It has remained unclear if this emission is in fact associated with these remnants or due to intervening sources such as extended HII envelopes along the line of sight. To explore the origin of this emitting gas we have recently undertaken Green Bank Telescope (GBT) observations of prominent supernova remnants W28 and W44 which are well-known to be interacting with molecular clouds. Eight alpha and beta RRL transitions were mapped at C-Band (4-6 GHz) with 2.5' resolution. Maps cover 0.5 and 0.25 square degrees of W28 and W44, respectively, permitting comparison with the distribution of X-rays, Radio, and H-alpha emission. Both remnants are observed to have a mixed-morphology: a radio-continuum shell centrally-filled by thermal X-rays. We find the observed velocity of RRL emission is near the systemic velocity of both remnants as traced by OH(1720 MHz) masers. Preliminary results are presented exploring the association of the RRL-emitting gas with these interacting supernova remants and implications for the origins of the hot thermal X-ray plasma that fills their centers. Support for this work was provided by the NSF through The GBT Student Support Program from the NRAO.

Radio Emission from Algol. I. Coronal Geometry and Emission Mechanisms Determined from VLBA and Green Bank Interferometer Observations

NASA Astrophysics Data System (ADS)

Mutel, R. L.; Molnar, L. A.; Waltman, E. B.; Ghigo, F. D.

1998-11-01

We report dual circular polarization VLBA observations of Algol made at orbital phases 0.22-0.30 using a differential phase referencing technique. The flux density of Algol varied from 10 to 20 mJy during the observations. The radio maps show a double-lobed source separated by 1.6 mas (1.4 times the K star diameter). Although the total emission is only weakly circularly polarized, the individual lobes are strongly circularly polarized and of opposite helicity. Snapshot VLBI maps made at 3 hour intervals show variations in the flux density of both components, but no significant motions of the centroids. We also analyze Green Bank Interferometer (GBI) synoptic observations of right- and left-circularly polarized (RCP and LCP) flux densities of Algol at 2.3 and 8.3 GHz several times a day from early 1995 to mid-1997. The resulting data set, which consists of more than 2500 observations over 2 years, is by far the most comprehensive available for any stellar system. In addition, we analyzed GBI observations of the very similar (but noneclipsing) binary system HR 1099 over the same time period in order to compare the two systems. We summarize the GBI observations using several statistical descriptions. We find no phase dependence of either the radio luminosity or circular polarization for either system. The luminosity histograms for the two systems are remarkably similar. The distribution functions are not well represented by exponentials as previously suggested, but can be represented by power laws truncated at low luminosity. The cutoff occurs at 20-30 mJy and may represent emission from a slowly varying basal level that is always detected. We confirm several previous results, including the strong dependence of spectral index on luminosity, the decrease of fractional circular polarization with luminosity, and the dependence of fractional circular polarization on orbital inclination angle. We suggest that the radio emission at 8.3 GHz is x-mode gyrosynchrotron emission

The inner radio structure of Centaurus A - Clues to the origin of the jet X-ray emission

NASA Technical Reports Server (NTRS)

Burns, J. O.; Feigelson, E. D.; Schreier, E. J.

1983-01-01

VLA observations at 1.4 and 4.9 GHz of the jet and inner lobes of the nearby radio galaxy Centaurus A have been used to construct maps of total intensity and polarization at resolutions of 31 x 10 and 3.6 x 1.1 arcsec. Surface brightness and pressure distributions in the jet, combined with the apparent X-ray emission from the ISM of NGC 5128, indicate that it is thermally confined. A comparison of the radio structure and the optical galaxy shows that the jet in Cen A emerges nearly along the major axis of the elliptical stellar component that is parallel to the angular momentum vector of the dust lane. The outer radio structure bends toward the galaxy minor axis. Evidence is found for a common synchrotron radiation origin of the full spectrum jet emission.

LOFAR discovery of an ultra-steep radio halo and giant head-tail radio galaxy in Abell 1132

NASA Astrophysics Data System (ADS)

Wilber, A.; Brüggen, M.; Bonafede, A.; Savini, F.; Shimwell, T.; van Weeren, R. J.; Rafferty, D.; Mechev, A. P.; Intema, H.; Andrade-Santos, F.; Clarke, A. O.; Mahony, E. K.; Morganti, R.; Prandoni, I.; Brunetti, G.; Röttgering, H.; Mandal, S.; de Gasperin, F.; Hoeft, M.

2018-01-01

Low-Frequency Array (LOFAR) observations at 144 MHz have revealed large-scale radio sources in the unrelaxed galaxy cluster Abell 1132. The cluster hosts diffuse radio emission on scales of ∼650 kpc near the cluster centre and a head-tail (HT) radio galaxy, extending up to 1 Mpc, south of the cluster centre. The central diffuse radio emission is not seen in NRAO VLA FIRST Survey, Westerbork Northern Sky Survey, nor in C & D array VLA observations at 1.4 GHz, but is detected in our follow-up Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz. Using LOFAR and GMRT data, we determine the spectral index of the central diffuse emission to be α = -1.75 ± 0.19 (S ∝ να). We classify this emission as an ultra-steep spectrum radio halo and discuss the possible implications for the physical origin of radio haloes. The HT radio galaxy shows narrow, collimated emission extending up to 1 Mpc and another 300 kpc of more diffuse, disturbed emission, giving a full projected linear size of 1.3 Mpc - classifying it as a giant radio galaxy (GRG) and making it the longest HT found to date. The head of the GRG coincides with an elliptical galaxy (SDSS J105851.01+564308.5) belonging to Abell 1132. In our LOFAR image, there appears to be a connection between the radio halo and the GRG. The turbulence that may have produced the halo may have also affected the tail of the GRG. In turn, the GRG may have provided seed electrons for the radio halo.

Timing, Emission, and Spectral Studies of Rotating Radio Transients

NASA Astrophysics Data System (ADS)

Cui, Bingyi; McLaughlin, Maura

2018-01-01

Rotating Radio Transients (RRATs) are a class of pulsars with unusually sporadic pulse emissions which were discovered only through their single pulses. We report in new timing solutions, pulse amplitude measurements, and spectral measurements for a number of RRATs. Timing solutions provide derived physical properties of these sources, allowing comparison with other classes of neutron stars. Analyses of single pulse properties also contribute to this study by measuring composite profiles and flux density distributions, which can constrain the RRATs' emission mechanism. We make statistical comparisons between RRATs and canonical pulsars and show that with the same spin period, RRATs are more likely to have larger period derivatives, which may indicate a higher magnetic field. Spectral analyses were also performed in order to compare spectra with those of other source classes. We describe this work and plans for application to much larger numbers of sources in the future.

Radio Emission from Pulsar Wind Nebulae without Surrounding Supernova Ejecta: Application to FRB 121102

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

Dai, Z. G.; Wang, J. S.; Yu, Y. W., E-mail: dzg@nju.edu.cn

2017-03-20

In this paper, we propose a new scenario in which a rapidly rotating strongly magnetized pulsar without any surrounding supernova ejecta repeatedly produces fast radio bursts (FRBs) via a range of possible mechanisms; simultaneously, an ultra-relativistic electron/positron pair wind from the pulsar sweeps up its ambient dense interstellar medium, giving rise to a non-relativistic pulsar wind nebula (PWN). We show that the synchrotron radio emission from such a PWN is bright enough to account for the recently discovered persistent radio source associated with the repeating FRB 121102 within reasonable ranges of the model parameters. Our PWN scenario is consistent withmore » the non-evolution of the dispersion measure inferred from all of the repeating bursts observed in four years.« less

Sco X-1 - A galactic radio source with an extragalactic radio morphology

NASA Technical Reports Server (NTRS)

Geldzahler, B. J.; Corey, B. E.; Fomalont, E. B.; Hilldrup, K.

1981-01-01

VLA observations of radio emissions at 1465 and 4885 MHz, of Sco X-1 confirm the existence of a colinear triple structure. Evidence that the three components of Sco X-1 are physically associated is presented, including the morphology, spectrum, variability, volume emissivity and magnetic field strength. The possibility of a physical phenomenon occurring in Sco X-1 similar to that occurring in extragalactic radio sources is discussed, and two galactic sources are found having extended emission similar to that in extragalactic objects. The extended structure of Sco X-1 is also observed to be similar to that of the hot spots in luminous extragalactic sources, and a radio source 20 arcmin from Sco X-1 is found to lie nearly along the radio axis formed by the components of Sco X-1.

Self-consistent particle-in-cell simulations of fundamental and harmonic radio plasma emission mechanisms

NASA Astrophysics Data System (ADS)

Tsiklauri, D.; Thurgood, J. O.

2015-12-01

first co-author Jonathan O. Thurgood (QMUL) The simulation of three-wave interaction based plasma emission, an underlying mechanism for type III solar radio bursts, is a challenging task requiring fully-kinetic, multi-dimensional models. This paper aims to resolve a contradiction in past attempts, whereby some authors report that no such processes occur and others draw conflicting conclusions, by using 2D, fully kinetic, particle-in-cell simulations of relaxing electron beams. Here we present the results of particle-in-cell simulations which for different physical parameters permit or prohibit the plasma emission. We show that the possibility of plasma emission is contingent upon the frequency of the initial electrostatic waves generated by the bump-in-tail instability, and that these waves may be prohibited from participating in the necessary three-wave interactions due to the frequency beat requirements. We caution against simulating astrophysical radio bursts using unrealistically dense beams (a common approach which reduces run time), as the resulting non-Langmuir characteristics of the initial wave modes significantly suppresses the emission. Comparison of our results indicates that, contrary to the suggestions of previous authors, a plasma emission mechanism based on two counter-propagating beams is unnecessary in astrophysical context. Finally, we also consider the action of the Weibel instability, which generates an electromagnetic beam mode. As this provides a stronger contribution to electromagnetic energy than the emission, we stress that evidence of plasma emission in simulations must disentangle the two contributions and not simply interpret changes in total electromagnetic energy as the evidence of plasma emission. In summary, we present the first self-consistent demonstration of fundamental and harmonic plasma emission from a single-beam system via fully kinetic numerical simulation. Pre-print can be found at http://astro.qmul.ac.uk/~tsiklauri/jtdt1

Outer heliospheric radio emissions. II - Foreshock source models

NASA Technical Reports Server (NTRS)

Cairns, Iver H.; Kurth, William S.; Gurnett, Donald A.

1992-01-01

Observations of LF radio emissions in the range 2-3 kHz by the Voyager spacecraft during the intervals 1983-1987 and 1989 to the present while at heliocentric distances greater than 11 AU are reported. New analyses of the wave data are presented, and the characteristics of the radiation are reviewed and discussed. Two classes of events are distinguished: transient events with varying starting frequencies that drift upward in frequency and a relatively continuous component that remains near 2 kHz. Evidence for multiple transient sources and for extension of the 2-kHz component above the 2.4-kHz interference signal is presented. The transient emissions are interpreted in terms of radiation generated at multiples of the plasma frequency when solar wind density enhancements enter one or more regions of a foreshock sunward of the inner heliospheric shock. Solar wind density enhancements by factors of 4-10 are observed. Propagation effects, the number of radiation sources, and the time variability, frequency drift, and varying starting frequencies of the transient events are discussed in terms of foreshock sources.

On the origins of part-time radio pulsars

NASA Astrophysics Data System (ADS)

Zhang, Bing; Gil, Janusz; Dyks, Jaroslaw

2007-01-01

Growing evidence suggests that some radio pulsars only act sporadically. These `part-time' pulsars include long-term nulls, quasi-periodic radio flares in PSR B1931+24, as well as the so-called Rotating Radio Transients (RRATs). Based on the assumption that these objects are isolated neutron stars similar to conventional radio pulsars, we discuss two possible interpretations to the phenomenon. The first interpretation suggests that these objects are pulsars slightly below the radio emission `death line', which become occasionally active only when the conditions for pair production and coherent emission are satisfied. The second interpretation invokes a radio emission direction reversal in conventional pulsars, as has been introduced to interpret the peculiar mode changing phenomenon in PSR B1822-09. In this picture, our line of sight misses the main radio emission beam of the pulsar but happens to sweep the emission beam when the radio emission direction is reversed. These part-time pulsars are therefore the other half of `nulling' pulsars. We suggest that X-ray observations may provide clues to differentiate between these two possibilities.

Polarized radio emission from extensive air showers measured with LOFAR

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

Schellart, P.; Buitink, S.; Corstanje, A.

2014-10-01

We present LOFAR measurements of radio emission from extensive air showers. We find that this emission is strongly polarized, with a median degree of polarization of nearly 99%, and that the angle between the polarization direction of the electric field and the Lorentz force acting on the particles, depends on the observer location in the shower plane. This can be understood as a superposition of the radially polarized charge-excess emission mechanism, first proposed by Askaryan and the geomagnetic emission mechanism proposed by Kahn and Lerche. We calculate the relative strengths of both contributions, as quantified by the charge-excess fraction, formore » 163 individual air showers. We find that the measured charge-excess fraction is higher for air showers arriving from closer to the zenith. Furthermore, the measured charge-excess fraction also increases with increasing observer distance from the air shower symmetry axis. The measured values range from (3.3± 1.0)% for very inclined air showers at 25 m to (20.3± 1.3)% for almost vertical showers at 225 m. Both dependencies are in qualitative agreement with theoretical predictions.« less

Roles Played by Electrostatic Waves in Producing Radio Emissions

NASA Technical Reports Server (NTRS)

Cairns, Iver H.

2000-01-01

Processes in which electromagnetic radiation is produced directly or indirectly via intermediate waves are reviewed. It is shown that strict theoretical constraints exist for electrons to produce nonthermal levels of radiation directly by the Cerenkov or cyclotron resonances. In contrast, indirect emission processes in which intermediary plasma waves are converted into radiation are often favored on general and specific grounds. Four classes of mechanisms involving the conversion of electrostatic waves into radiation are linear mode conversion, hybrid linear/nonlinear mechanisms, nonlinear wave-wave and wave-particle processes, and radiation from localized wave packets. These processes are reviewed theoretically and observational evidence summarized for their occurrence. Strong evidence exists that specific nonlinear wave processes and mode conversion can explain quantitatively phenomena involving type III solar radio bursts and ionospheric emissions. On the other hand, no convincing evidence exists that magnetospheric continuum radiation is produced by mode conversion instead of nonlinear wave processes. Further research on these processes is needed.

RADIO MONITORING OF THE PERIODICALLY VARIABLE IR SOURCE LRLL 54361: NO DIRECT CORRELATION BETWEEN THE RADIO AND IR EMISSIONS

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

Forbrich, Jan, E-mail: jan.forbrich@univie.ac.at; Rodríguez, Luis F.; Palau, Aina

2015-11-20

LRLL 54361 is an infrared source located in the star-forming region IC 348 SW. Remarkably, its infrared luminosity increases by a factor of 10 over roughly one week every 25.34 days. To understand the origin of these remarkable periodic variations, we obtained sensitive 3.3 cm JVLA radio continuum observations of LRLL 54361 and its surroundings in six different epochs: three of them during the IR-on state and three during the IR-off state. The radio source associated with LRLL 54361 remained steady and did not show a correlation with the IR variations. We suggest that the IR is tracing the resultsmore » of fast (with a timescale of days) pulsed accretion from an unseen binary companion, while the radio traces an ionized outflow with an extent of ∼100 AU that smooths out the variability over a period of the order of a year. The average flux density measured in these 2014 observations, 27 ± 5 μJy, is about a factor of two less than that measured about 1.5 years before, 53 ± 11 μJy, suggesting that variability in the radio is present, but over larger timescales than in the IR. We discuss other sources in the field, in particular two infrared/X-ray stars that show rapidly varying gyrosynchrotron emission.« less

Radio Thermal Emission from Pluto and Charon during the New Horizons Encounter

NASA Astrophysics Data System (ADS)

Bird, Michael; Linscott, Ivan; Hinson, David; Tyler, G. L.; Strobel, Darrell F.; New Horizons Science Team

2017-10-01

As part of the New Horizons Radio-Science Experiment REX, radio thermal emission from Pluto and Charon (wavelength: 4.2 cm) was observed during the encounter on 14 July 2015. The primary REX measurement, a determination of the atmospheric height profile from the surface up to about 100 km, was conducted during an uplink radio occultation at both ingress and egress (Hinson et al., Icarus 290, 96-111, 2017). During the interval between ingress and egress, when the Earth and the REX uplink signals were occulted by the Pluto disk, the spacecraft antenna continued to point toward Earth and thus scanned diametrically across the Pluto nightside. The average diameter of the HGA 3 dB beam was ≈1100 km at the surface during this opportunity, thereby providing crudely resolved measurements of the radio brightness temperature across Pluto. The best resolution for the REX radiometry observations occurred shortly after closest approach, when the HGA was scanned twice across Pluto. These observations will be reported elsewhere (Linscott et al., Icarus, submitted, 2017). In addition to the resolved observations, full disk brightness temperature measurements of both bodies were performed during the approach (dayside) and departure (nightside) phases of the encounter. We present the results of these observations and provide a preliminary interpretation of the measured brightness temperatures.

A Study of the X-Ray Emission from Three Radio Pulsars

NASA Technical Reports Server (NTRS)

Slane, Patrick O. (Principal Investigator)

1996-01-01

The subject grant is for work on a study of x-ray emission from isolated pulsars. The purpose of the study was to: determine whether the pulsars were x-ray sources; and, if so, search for evidence of pulsations at the known radio period; and study the nature of the x-ray emission. Observation of the pulsar PSR 0355+54 were obtained, and the analysis of these data is complete. These results were reported at the 183rd AAS Meeting, and in a paper entitled 'X-Ray Emission from PSR 0355+54' which as published in the The Astrophysical Journal. Also obtained an approx. 3 ks PSPC observations of PSR 1642-03. A summary of the results from these data were reported in a Conference Proceedings for the 'New Horizon of X-ray Astronomy' symposium. In addition, as part of a study with a student from the SAO Summer Intern Program, I incorporated ROSAT archival data in an extended study of pulsar emission. These results were reported at the 185th AAS Meeting, and in a paper entitled 'Soft X-ray Emission from Selected Isolated Pulsars' which was published in The Astrophysical Journal (Letters).

Black Hole Demographics in and Nuclear Properties of Nearby Low Luminosity Radio Galaxies; Connections to Radio Activity?

NASA Technical Reports Server (NTRS)

Baum, S. A.; Kleijn, G. A. Verdoes; Xu, C.; ODea, C. P.; deZeeuw, P. T.

2004-01-01

We combine the results of an HST STIS and WFPC study of a complete sample of 21 nearby UGC low luminosity radio galaxies with the results of a radio VLA and VLBA study of the same sample. We examine the relationship between the stellar and gaseous properties of the galaxies on tens to hundreds of parsec scale with the properties of the radio jets on the same scale. From the VLA and VLBA data we constrain the physics of the outflowing radio plasma from the tens of parsecs to hundreds of kiloparsec scales. From the WFPC2 H alpha and dust images and the STIS kinematics of the near nuclear gas we obtain constraints on the orientation of near nuclear disks of gas and measures of the nuclear stellar, continuum point source, and line emission fluxes. Under the statistically supported assumption that the radio jet issues perpendicular to the disk, we use the orientation of the optical (large scale accretion?) disks to constrain the three-dimensional orientation of the radio ejection. From HST/STIS spectroscopy of the near-nuclear emission line gas we obtain measures/limits on the black hole masses. We examine correlations between the VLBA and VLA-scale radio emission, the nuclear line emission, and the nuclear optical and radio continuum emission. Though our sample is relatively small, it is uniquely well defined, spans a narrow range in redshift and we have a consistent set of high resolution data with which to carefully examine these relationships. We use the combined radio and optical data to: 1) Constrain the orientation, physics, and bulk outflow speed of the radio plasma; 2) Put limits on the mass accretion rate and study the relationship between black hole mass, radio luminosity, and near nuclear gaseous content; 3) Provide insight into the relationship between BL Lac objects and low luminosity radio galaxies.

Polarized radio emission from the edge-on spiral galaxies NGC 891 and NGC 4565

NASA Technical Reports Server (NTRS)

Sukumar, S.; Allen, R. J.

1991-01-01

Results are presented, at a resolution of 20 arcsec, of observations of the distribution of radio continuum intensity and linear polarization with the VLA in two nearby edge-on spiral galaxies, NGC 891 and NGC 4565, at 6 and 20 cm, respectively. A unified model is presented to account for the main features of the radio polarization in these two galaxies. The model geometry is determined from recent observations of face-on galaxies where the polarized emission is found to be strongest in the dark inter-arm and outer parts of the disks. A substantial Z-thickness is ascribed to this polarized emission. It is shown that the exceptionally strong wavelength dependence of this type of Faraday depolarization can result in edge-on galaxies becoming rapidly 'Faraday thick' at decimeter wavelengths, thereby obliterating the polarization from regions on the dark side of the disk. The degree of polarization observed in both galaxies increases strongly with increasing Z-distance from the plane.

LOPES-3D - vectorial measurements of radio emission from cosmic ray induced air showers

NASA Astrophysics Data System (ADS)

Huber, D.; Apel, W. D.; Arteaga-Velázquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

2013-05-01

LOPES-3D is able to measure all three components of the electric field vector of the radio emission from air showers. This allows a better comparison with emission models. The measurement of the vertical component increases the sensitivity to inclined showers. By measuring all three components of the electric field vector LOPES-3D demonstrates by how much the reconstruction accuracy of primary cosmic ray parameters increases. Thus LOPES-3D evaluates the usefulness of vectorial measurements for large scale applications.

Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

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

Kapińska, A. D.; Staveley-Smith, L.; Meurer, G. R.

We present new radio continuum observations of NGC 253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC 253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of a central starburst and extended emission. The central component, corresponding to the inner 500 pc of the starburst region of the galaxy, is best modeled as an internally free–free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the spectrum of NGCmore » 253 is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the southeast halo, and may be indicative of synchrotron self-absorption of shock-reaccelerated electrons or an intrinsic low-energy cutoff of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC 253 in our radio images. At 154–231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ∼8 kpc in the z -direction (from the major axis).« less

Radio monitoring of protoplanetary discs

NASA Astrophysics Data System (ADS)

Ubach, C.; Maddison, S. T.; Wright, C. M.; Wilner, D. J.; Lommen, D. J. P.; Koribalski, B.

2017-04-01

Protoplanetary disc systems observed at radio wavelengths often show excess emission above that expected from a simple extrapolation of thermal dust emission observed at short millimetre wavelengths. Monitoring the emission at radio wavelengths can be used to help disentangle the physical mechanisms responsible for this excess, including free-free emission from a wind or jet, and chromospheric emission associated with stellar activity. We present new results from a radio monitoring survey conducted with Australia Telescope Compact Array over the course of several years with observation intervals spanning days, months and years, where the flux variability of 11 T Tauri stars in the Chamaeleon and Lupus star-forming regions was measured at 7 and 15 mm, and 3 and 6 cm. Results show that most sources are variable to some degree at 7 mm, indicating the presence of emission mechanisms other than thermal dust in some sources. Additionally, evidence of grain growth to centimetre-sized pebbles was found for some sources that also have signs of variable flux at 7 mm. We conclude that multiple processes contributing to the emission are common in T Tauri stars at 7 mm and beyond, and that a detection at a single epoch at radio wavelengths should not be used to determine all processes contributing to the emission.

Synoptic observations of Jupiter's radio emissions: Average Statistical properties observed by Voyager

NASA Technical Reports Server (NTRS)

Alexander, J. K.; Carr, T. D.; Thieman, J. R.; Schauble, J. J.; Riddle, A. C.

1980-01-01

Observations of Jupiter's low frequency radio emissions collected over one month intervals before and after each Voyager encounter were analyzed. Compilations of occurrence probability, average power flux density and average sense of circular polarization are presented as a function of central meridian longitude, phase of Io, and frequency. The results are compared with ground based observations. The necessary geometrical conditions are preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be essentially the same as are observed in Earth based studies. On the other hand, there is a clear local time dependence in the Io-independent decametric emission. Io appears to have an influence on average flux density of the emission down to below 2 MHz. The average power flux density spectrum of Jupiter's emission has a broad peak near 9MHz. Integration of the average spectrum over all frequencies gives a total radiated power for an isotropic source of 4 x 10 to the 11th power W.

Detection of 17 GHz radio emission from X-ray-bright points

NASA Technical Reports Server (NTRS)

Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.

1994-01-01

Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray-bright points (XBPs). This is also the first reported detection of flaring bright points in microwaves. We have detected four BPs at 17 GHz out of eight identified in SXT data on 1992 July 31, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are very similar, and both are long-lasting-about 2 hr in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, the gradual, long-lasting, and unpolarized emission suggests that the 17 GHz emission is thermal.

Radio emission from AM Herculis - The quiescent component and an outburst

NASA Technical Reports Server (NTRS)

Dulk, G. A.; Bastian, T. S.; Chanmugam, G.

1983-01-01

The VLA has been used to search for radio emission from the AM Her-type binaries VV Pup, EF Eri, PG 1550 + 191, CW 1103 + 354, and AN UMa, at 4.9 GHz. A remarkable 10-min outburst was detected from AM Her at 4.9 GHz, which was about 20 times more intense than the quiescent emission and was essentially 100 percent circularly polarized. It is suggested that the quiescent emission of AM Her can be accounted for by 500-keV electrons trapped in the magnetosphere of the white dwarf, provided that the electron energy spectrum is quite hard and that the spectral hardness or number density of energetic electrons increases with radius, while the outburst is probably due to an electron-cyclotron maser operating near the surface of the red dwarf companion. The implied existence of a 1000-gauss localized magnetic field and a corona on the red dwarf has consequences for mass transfer, field line interactions, and variable activity.

Predictions for Uranus from a radiometric Bode's law. [planetary magnetic moment estimated from radio emission flux density

NASA Technical Reports Server (NTRS)

Desch, M. D.; Kaiser, M. L.

1984-01-01

Determinations by spacecraft of the low-frequency radio spectra and radiation beam geometry of the magnetospheres of earth, Jupiter, and Saturn now permit a reliable assessment of the overall efficiency of the solar wind in stimulating intense, nonthermal radio bursts from these magnetospheres. It is found that earlier estimates of how magnetospheric radio output scales with the solar wind energy input must be greatly revised, with the result that, while the efficiency is much lower than previously thought, it is remarkably uniform from planet to planet. A 'radimetric Bode's law' is formulated from which a planet's magnetic moment can be estimated from its radio emission output. This law is applied to estimate the low-frequency radio power likely to be measured for Uranus by Voyager 2. It is shown how measurements of Uranus's radio flux can be used to estimate the planetary magnetic moment and solar wind stand-off distance before the in situ measurements.

Detection of radio continuum emission from Herbig-Haro objects 1 and 2 and from their central exciting source

NASA Technical Reports Server (NTRS)

Pravdo, S. H.; Rodriguez, L. F.; Curiel, S.; Canto, J.; Torrelles, J. M.; Becker, R. H.; Sellgren, K.

1985-01-01

The region in Orion containing HH 1 and HH 2 was observed with the VLA at 20, 6, and 2 cm on several occasions from 1981 to 1984. At lower resolution, four continuum sources were detected. Two of these sources coincide positionally with HH 1 and HH 2. At 6 cm and higher resolution, HH 1 is resolved into at least two components. The emission is probably bremsstrahlung originating in the same region where the visible line emission is produced. This is the first detection of radio continuum from classic Herbig-Haro objects. At a position closely centered between HH 1 and HH 2, an object that can be interpreted as the energy source of the system was detected. The central source spectrum is S(nu) of about nu to the alpha power, where alpha = 0.4 + or - 0.2, suggesting a stellar wind. Finally, the fourth radio continuum source coincides positionally with an H2O maser and is probably excited by an independent star. There is evidence of time variability in its radio flux. No emission was detected from the Cohen-Schwartz (1979) star at the 0.1 mJy level.

Directivity of the radio emission from the K1 dwarf star AB Doradus

NASA Technical Reports Server (NTRS)

Lim, Jeremy; White, Stephen M.; Nelson, Graam J.; Benz, Arnold O.

1994-01-01

We present measurements of the spectrum and polarization of the flaring radio emission from the K1 dwarf star AB Doradus, together with previously reported single frequency measurements (with no polarization information) on 3 other days. On all 4 days spanning a 6 month period, the emission was strong and, when folded with the stellar rotation period, showed similar time variations with two prominant peaks at phase 0.35 and 0.75. These peaks coincide in longitude with two large starspots identified from the stellar optical light curve and have half-powe widths as small as 0.1 rotations and no larger than 0.2 rotations. The modulated emission shows no measurable circular polarization, and its two peaks have different turnover frequencies.

Mystery solved: discovery of extended radio emission in the merging galaxy cluster Abell 2146

NASA Astrophysics Data System (ADS)

Hlavacek-Larrondo, J.; Gendron-Marsolais, M.-L.; Fecteau-Beaucage, D.; van Weeren, R. J.; Russell, H. R.; Edge, A.; Olamaie, M.; Rumsey, C.; King, L.; Fabian, A. C.; McNamara, B.; Hogan, M.; Mezcua, M.; Taylor, G.

2018-04-01

Abell 2146 (z = 0.232) is a massive galaxy cluster currently undergoing a spectacular merger in the plane of the sky with a bullet-like morphology. It was the first system in which both the bow and upstream shock fronts were detected at X-ray wavelengths (Mach ˜2), yet deep Giant MetreWave Telescope 325 MHz observations failed to detect extended radio emission associated with the cluster as is typically seen in such systems. We present new, multiconfiguration 1-2 GHz Karl G. Jansky Very Large Array (VLA) observations of Abell 2146 totalling 16 h of observations. These data reveal for the first time the presence of an extended (≈850 kpc), faint radio structure associated with Abell 2146. The structure appears to harbour multiple components, one associated with the upstream shock that we classify as a radio relic and one associated with the subcluster core that is consisted as being a radio halo bounded by the bow shock. The newly detected structures have some of the lowest radio powers detected thus far in any cluster (P1.4 GHz, halo = 2.4 ± 0.2 × 1023 W Hz-1 and P1.4 GHz, relic = 2.2 ± 0.2 × 1023 W Hz-1). The flux measurement of the halo, as well as its morphology, also suggests that the halo was recently created (≈0.3 Gyr after core passage), consistent with the dynamical state of the cluster. These observations demonstrate the capacity of the upgraded VLA to detect extremely faint and extended radio structures. Based on these observations, we predict that many more radio relics and radio haloes in merging clusters should be detected by future radio facilities such as the Square Kilometre Array.

Planetary radio astronomy: Earth, giant planets, and beyond

NASA Astrophysics Data System (ADS)

Rucker, H. O.; Panchenko, M.; Weber, C.

2014-11-01

The magnetospheric phenomenon of non-thermal radio emission is known since the serendipitous discovery of Jupiter as radio planet in 1955, opening the new field of "Planetary Radio Astronomy". Continuous ground-based observations and, in particular, space-borne measurements have meanwhile produced a comprehensive picture of a fascinating research area. Space missions as the Voyagers to the Giant Planets, specifically Voyager 2 further to Uranus and Neptune, Galileo orbiting Jupiter, and now Cassini in orbit around Saturn since July 2004, provide a huge amount of radio data, well embedded in other experiments monitoring space plasmas and magnetic fields. The present paper as a condensation of a presentation at the Kleinheubacher Tagung 2013 in honour of the 100th anniversary of Prof. Karl Rawer, provides an introduction into the generation mechanism of non-thermal planetary radio waves and highlights some new features of planetary radio emission detected in the recent past. As one of the most sophisticated spacecraft, Cassini, now in space for more than 16 years and still in excellent health, enabled for the first time a seasonal overview of the magnetospheric variations and their implications for the generation of radio emission. Presently most puzzling is the seasonally variable rotational modulation of Saturn kilometric radio emission (SKR) as seen by Cassini, compared with early Voyager observations. The cyclotron maser instability is the fundamental mechanism under which generation and sufficient amplification of non-thermal radio emission is most likely. Considering these physical processes, further theoretical investigations have been started to investigate the conditions and possibilities of non-thermal radio emission from exoplanets, from potential radio planets in extrasolar systems.

A radio monitoring survey of ultra-luminous X-ray sources

NASA Astrophysics Data System (ADS)

Körding, E.; Colbert, E.; Falcke, H.

2005-06-01

We present the results of a radio monitoring campaign to search for radio emission from nearby ultra-luminous X-ray sources (ULXs). These sources are bright off-nuclear X-ray point sources with luminosities exceeding LX > 1039 erg s-1. A well-defined sample of the 9 nearest ULXs has been monitored eight times over 5 months with the Very Large Array in A and B configuration. Our limiting sensitivity is ≈0.15 mJy (4σ) for radio flares and ≈60 μJy for continuous emission. In M 82 two ULXs seem to have coincident compact radio sources, which are probably supernova remnants. No continuous or flaring radio emission has been detected from any other ULX. Thus, ULXs do not generally emit steady-state radio emission above radio powers of 1.5 × 1017 W/Hz. The non-detections of the continuous emission are consistent with beamed or unbeamed radio emission from accreting black holes of ≤ 103 M⊙ based on the radio/X-ray correlation. Other published radio detections (M 82, NGC 5408) are also discussed in this context. Both detections are significantly above our detection limit. If ULXs have flaring radio emission above 4 × 1017 W/Hz we can give an upper limit on the duty cycle of the flares of 6%. This upper limit is in agreement with the observed number of flares in Galactic radio transients. Additionally we present a yet unreported radio double structure in the nearby low-luminosity AGN NGC 4736.

Gamma-ray burster counterparts - Radio

NASA Technical Reports Server (NTRS)

Schaefer, Bradley E.; Cline, Thomas L.; Desai, U. D.; Teegarden, B. J.; Atteia, J.-L.; Barat, C.; Estulin, I. V.; Evans, W. D.; Fenimore, E. E.; Hurley, K.

1989-01-01

Many observers and theorists have suggested that gamma-ray bursters (GRBs) are related to highly magnetized rotating, neutron stars, in which case an analogy with pulsars implies that GRBs would be prodigious emitters of polarized radio emission during quiescence. The paper reports on a survey conducted with the Very Large Array radio telescope of 10 small GRB error regions for quiescent radio emission at wavelengths of 2, 6, and 20 cm. The sensitivity of the survey varied from 0.1 to 0.8 mJy. The observations did indeed reveal four radio sources inside the GRB error regions.

New Chandra observations of the jet in 3C273. 1. Softer X-ray than radio spectra and the X-ray emission mechanism

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

Jester, Sebastian; /Fermilab; Harris, D.E.

2006-05-01

The jet in 3C273 is a high-power quasar jet with radio, optical and X-ray emission whose size and brightness allow a detailed study of the emission processes acting in it. We present deep Chandra observations of this jet and analyze the spectral properties of the jet emission from radio through X-rays. We find that the X-ray spectra are significantly softer than the radio spectra in all regions of the bright part of the jet except for the first bright ''knot A'', ruling out a model in which the X-ray emission from the entire jet arises from beamed inverse-Compton scattering ofmore » cosmic microwave background photons in a single-zone jet flow. Within two-zone jet models, we find that a synchrotron origin for the jet's X-rays requires fewer additional assumptions than an inverse-Compton model, especially if velocity shear leads to efficient particle acceleration in jet flows.« less

POWERFUL RADIO EMISSION FROM LOW-MASS SUPERMASSIVE BLACK HOLES FAVORS DISK-LIKE BULGES

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

Wang, J.; Xu, Y.; Xu, D. W.

The origin of spin of low-mass supermassive black holes (SMBHs) is still a puzzle at present. We report here a study on the host galaxies of a sample of radio-selected nearby ( z < 0.05) Seyfert 2 galaxies with a BH mass of 10{sup 6–7} M{sub ⊙}. By modeling the SDSS r -band images of these galaxies through a two-dimensional bulge+disk decomposition, we identify a new dependence of SMBH's radio power on host bulge surface brightness profiles, in which more powerful radio emission comes from an SMBH associated with a more disk-like bulge. This result means low-mass and high-mass SMBHsmore » are spun up by two entirely different modes that correspond to two different evolutionary paths. A low-mass SMBH is spun up by a gas accretion with significant disk-like rotational dynamics of the host galaxy in the secular evolution, while a high-mass one by a BH–BH merger in the merger evolution.« less

X-RAYS FROM A RADIO-LOUD COMPACT BROAD ABSORPTION LINE QUASAR 1045+352 AND THE NATURE OF OUTFLOWS IN RADIO-LOUD BROAD ABSORPTION LINE QUASARS

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

Kunert-Bajraszewska, Magdalena; Katarzynski, Krzysztof; Siemiginowska, Aneta

2009-11-10

We present new results on X-ray properties of radio-loud broad absorption line (BAL) quasars and focus on broadband spectral properties of a high-ionization BAL (HiBAL) compact steep spectrum (CSS) radio-loud quasar 1045+352. This HiBAL quasar has a very complex radio morphology indicating either strong interactions between a radio jet and the surrounding interstellar medium or a possible re-start of the jet activity. We detected 1045+352 quasar in a short 5 ksec Chandra ACIS-S observation. We applied theoretical models to explain spectral energy distribution of 1045+352 and argue that non-thermal, inverse-Compton (IC) emission from the innermost parts of the radio jetmore » can account for a large fraction of the observed X-ray emission. In our analysis, we also consider a scenario in which the observed X-ray emission from radio-loud BAL quasars can be a sum of IC jet X-ray emission and optically thin corona X-ray emission. We compiled a sample of radio-loud BAL quasars that were observed in X-rays to date and report no correlation between their X-ray and radio luminosity. However, the radio-loud BAL quasars show a large range of X-ray luminosities and absorption columns. This is consistent with the results obtained earlier for radio-quiet BAL quasars and may indicate an orientation effect in BAL quasars or more complex dependence between X-ray emission, radio emission, and an orientation based on the radio morphology.« less

Calculations of low-frequency radio emission by cosmic-ray-induced particle showers

NASA Astrophysics Data System (ADS)

García-Fernández, Daniel; Revenu, Benoît; Charrier, Didier; Dallier, Richard; Escudie, Antony; Martin, Lilian

2018-05-01

The radio technique for the detection of high-energy cosmic rays consists in measuring the electric field created by the particle showers created inside a medium by the primary cosmic ray. The electric field is then used to infer the properties of the primary particle. Nowadays, the radio technique is a standard, well-established technique. While most current experiments measure the field at frequencies above 20 MHz, several experiments have reported a large emission at low frequencies, below 10 MHz. The EXTASIS experiment aims at measuring again and understanding this low-frequency electric field. Since at low frequencies the standard far-field approximation for the calculation of the electric field does not necessarily hold, in order to comprehend the low-frequency emission we need to go beyond the far-field approximation. We present in this work a formula for the electric field created by a particle track inside a dielectric medium that is valid for all frequencies. We then implement this formula in the SELFAS Monte Carlo code and calculate the low-frequency electric field of the extensive air shower (EAS). We also study the electric field of a special case of the transition radiation mechanism when the EAS particles cross the air-soil boundary. We introduce the sudden death pulse, the direct emission caused by the coherent deceleration of the shower front at the boundary, as a first approximation to the whole electric field for the air-soil transition, and study its properties. We show that at frequencies larger than 20 MHz and distances larger than 100 m, the standard far-field approximation for the horizontal polarizations of the field is always accurate at the 1% level.

CYGNUS A: Hot Spots, Bow Shocks, Core Emission, and Exclusion of Cluster Gas by Radio Lobes

NASA Technical Reports Server (NTRS)

Harris, Daniel E.

1999-01-01

This report covers work preformed on three ROSAT projects: (1) Monitoring the X-ray Intensity of the Core and Jet of M87; (2) The radio-optical jet in 3C-120 and (3) A search for cluster emission at high redshift.

Characteristics of interplanetary type II radio emission and the relationship to shock and plasma properties

NASA Technical Reports Server (NTRS)

Lengyel-Frey, D.; Stone, R. G.

1989-01-01

A large sample of type II events is the basis of the present study of the properties of interplanetary type II bursts' radio-emission properties. Type II spectra seem to be composed of fundamental and harmonic components of plasma emission, where the intensity of the fundamental component increases relative to the harmonic as the burst evolves with heliocentric distance; burst average flux density increases as a power of the associated shock's average velocity. Solar wind density structures may have a significant influence on type II bandwidths.

Simultaneous observations of changes in coronal bright point emission at the 20 cm radio and He Lambda 10830 wavelengths

NASA Technical Reports Server (NTRS)

Habbal, Shadia R.; Harvey, Karen L.

1986-01-01

Preliminary results of observations of solar coronal bright points acquired simultaneously from ground based observatories at the radio wavelength of 20 cm and in the He I wavelength 10830 line on September 8, 1985, are reported. The impetus for obtaining simultaneous radio and optical data is to identify correlations, if any, in changes of the low transition-coronal signatures of bright points with the evolution of the magnetic field, and to distinguish between intermittent heating and changes in the magnetic field topology. Although simultaneous observations of H alpha emission and the photospheric magnetic field at Big Bear were also made, as well as radio observations from Owen Valley Radio Interferometer and Solar Maximum Mission (SSM) (O VIII line), only the comparison between He 10830 and the Very Large Array (VLA) radio data are presented.

BROADBAND JET EMISSION IN YOUNG AND POWERFUL RADIO SOURCES: THE CASE OF THE COMPACT STEEP SPECTRUM QUASAR 3C 186

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

Migliori, Giulia; Siemiginowska, Aneta; Celotti, Annalisa, E-mail: migliori@cfa.harvard.edu

2012-04-20

We present the X-ray analysis of a deep ({approx}200 ks) Chandra observation of the compact steep spectrum radio-loud quasar 3C 186 (z = 1.06) and investigate the contribution of the unresolved radio jet to the total X-ray emission. The spectral analysis is not conclusive on the origin of the bulk of the X-ray emission. In order to examine the jet contribution to the X-ray flux, we model the quasar spectral energy distribution, adopting several scenarios for the jet emission. For the values of the main physical parameters favored by the observables, a dominant role of the jet emission in themore » X-ray band is ruled out when a single-zone (leptonic) scenario is adopted, even including the contribution of the external photon fields as seed photons for inverse Compton emission. We then consider a structured jet, with the blazar component that-although not directly visible in the X-ray band-provides an intense field of seed synchrotron photons Compton-scattered by electrons in a mildly relativistic knot. In this case, the whole X-ray emission can be accounted for if we assume a blazar luminosity within the range observed from flat spectrum radio quasars. The X-ray radiative efficiency of such a (structured) jet is intimately related to the presence of a complex velocity structure. The jet emission can provide a significant contribution in X-rays if it decelerates within the host galaxy on kiloparsec scales. We discuss the implications of this model in terms of jet dynamics and interaction with the ambient medium.« less

Hard X-ray and radio emission at the onset of great solar flares

NASA Technical Reports Server (NTRS)

Klein, K.-L.; Pick, M.; Magun, A.; Dennis, B. R.

1987-01-01

A study of the onset phase of ten great hard X-ray bursts is presented. It is shown from hard X-ray and radio observations in different wavelength ranges that the energization of the electrons proceeds on a global time-scale for some tens of seconds. In nine of the bursts, two phases of emission can be distinguished during the onset phase: the preflash phase (during which emission up to an energy limit ranging from some tens of keV to 200 keV is observed) followed ten to some tens of seconds later by the flash phase (where the count rate in all detector channels rises simultaneously to within some seconds). For two of the events, strong gamma-ray line emission is observed and is shown to start close to the onset of the flash phase.

Radio Jove: Jupiter Radio Astronomy for Citizens

NASA Astrophysics Data System (ADS)

Higgins, Charles; Thieman, J. R.; Flagg, R.; Reyes, F. J.; Sky, J.; Greenman, W.; Brown, J.; Typinski, D.; Ashcraft, T.; Mount, A.

2014-01-01

Radio JOVE is a hands-on educational activity that brings the radio sounds of the Sun, Jupiter, the Milky Way Galaxy, and terrestrial radio noise to students, teachers, and the general public. Participants may build a simple radio telescope kit, make scientific observations, and interact with professional radio observatories in real-time over the Internet. Our website (http://radiojove.gsfc.nasa.gov) includes science information, construction manuals, observing guides, and education resources for teachers and students. Radio Jove is continually expanding its participants with over 1800 kits sold to more than 70 countries worldwide. Recently some of our most dedicated observers have upgraded their Radio Jove antennas to semi-professional observatories. We have spectrographs and wide band antennas, some with 8 MHz bandwidth and some with dual polarization capabilities. In an effort to add to the science literature, these observers are coordinating their efforts to pursue some basic questions about Jupiter’s radio emissions (radio source locations, spectral structure, long term changes, etc.). We can compare signal and ionosphere variations using the many Radio Jove observers at different locations. Observers are also working with members of the Long Wavelength Array Station 1 (LWA1) radio telescope to coordinate observations of Jupiter; Radio Jove is planning to make coordinated observations while the Juno Mission is active beginning in 2015. The Radio Jove program is overviewed, its hardware and software are highlighted, recent sample observations are shown, and we demonstrate that we are capable of real citizen science.

Simultaneous observations of solar sporadic radio emission by the radio telescopes UTR-2, URAN-2 and NDA within the frequency range 8-41MHz

NASA Astrophysics Data System (ADS)

Melnik, V. N.; Konovalenko, A. A.; Rucker, H. O.; Brazhenko, A. I.; Briand, C.; Dorovskyy, V. V.; Zarka, P.; Denis, L.; Bulatzen, V. G.; Frantzusenko, A. V.; Stanislavskyy, A. A.

2012-04-01

From 25 June till 12 August 2011 sporadic solar radio emission was observed simultaneously by three separate radio telescopes: UTR-2 (Kharkov, Ukraine), URAN-2 (Poltava, Ukraine) and NDA (Nancay, France). During these observations several type II bursts with double and triple harmonics were registered, as well as type II bursts with complex herringbone structure. The events of particular interest were type II bursts registered on 9 and 11 August 2011. These bursts had opposite sign of circular polarization at different parts of their dynamic spectra. In our opinion we registered the emissions, which came from the different parts of the shock propagating through the solar corona. We have observed also groups of type III bursts merged into one burst, type III bursts with triple harmonics and type III bursts with "split" polarization. In addition some unusual solar bursts were registered: storms of strange narrow-band (up to 500kHz) bursts with high polarization degree (about 80%), decameter spikes of extremely short durations (200-300ms), "tadpole-like" bursts with durations of 1-2s and polarization degree up to 60%.

Direction of Arrival Studies of Medium Frequency Burst Radio Emissions at Toolik Lake, AK

NASA Astrophysics Data System (ADS)

Bunch, N.; Labelle, J.; Weatherwax, A.; Lummerzheim, D.; Stenbaek-Nielsen, H.

2008-05-01

MF burst is an impulsive radio emission of auroral origin, which can be detected by ground-based instruments at frequencies between 1,300 and 4,500kHz. MF burst has been shown to be associated with substorm onset, but its exact generation mechanism remains unknown, although it is thought to arise from mode conversion radiation [see review by LaBelle and Treumann, 2002] . In search of the generation mechanism of this emission, Dartmouth College has deployed radio interferometers in Alaska, Northern Canada, Greenland, and Antarctica, including a three-element interferometer deployed to Toolik Field Station in Alaska during the summer of 2006. This instrument measured spectra, amplitudes and directions of arrival (DOA's) of over 47 MF burst events between November 30, 2006 and May 26, 2007. These data represent the first DOA measurements of impulsive MF burst, of which selected case studies were presented at the Fall 2007 AGU conference. Here we present a statistical survey of all 47 events as well as detailed analysis of three events occurring on: Mar 5, Mar 23, and Nov 20, 2007. For the statistical survey, we present distributions of DOA as a function of local time and frequency. In each case study we analyze the direction of arrival of the emissions as a function of both time and frequency within each event. The time variations will be compared with the time variations of optical auroral forms simultaneously measured with all-sky cameras. The dependence of the arrival direction on frequency enables a significant test of the generation mechanism whereby the waves are emitted at the local plasma or upper hybrid frequency in the topside ionosphere, predicting that higher frequencies should originate at lower altitudes. These three events have been selected because All-Sky camera data are available at these times from Toolik Lake and Fort Yukon, Alaska. These are critical both for identifying which optical features are associated with the radio emissions as well as for

Enhanced photoluminescence of Alq3 via patterned array silver dendritic nanostructures

NASA Astrophysics Data System (ADS)

Hsu, Wei-Hsiu; Hsieh, Ming-Hao; Lo, Shih-Shou

2012-04-01

Various silver nanostructures, semi-ball, jungle, and dendritic, are demonstrated by an electrical deposition process. The formation of silver nanostructures with various morphologies is studied by the mechanism of the diffusion limited aggregation (DLA) model. A array pattern of silver nanostructures can be obtained when the conductive substrate was used in a uniform electrical filed. A thickness 500 nm of Alq3 thin-film was covered on the silver nanostructure by thermal evaporation method. The strongest intensity of Alq3 green emission was observed when the pattern-array dendritic silver nanostructure was covered by Alq3. It can be explained with the plasmonic coupling due to the Alq3 and dendritic nanostructure. The result can help us to further application the patterned-array silver dendritic nanostructure for advanced opto-electronic device.

Pre-flare association of magnetic fields and millimeter-wave radio emission

NASA Technical Reports Server (NTRS)

Mayfield, E. B.; White, K. P., III

1976-01-01

Observations of radio emission at 3.3 mm wavelength associated with magnetic fields in active regions are reported. Results of more than 200 regions during the years 1967-1968 show a strong correlation between peak enhanced millimeter emission, total flux of the longitudinal component of photospheric magnetic fields and the number of flares produced during transit of active regions. For magnetic flux greater than (10 to the 21st power) maxwells flares will occur and for flux of (10 to the 23rd power) maxwells the sum of the H-alpha flare importance numbers is about 40. The peak millimeter enhancement increases with magnetic flux for regions which subsequently flared. Estimates of the magnetic energy available and the correlation with flare production indicate that the photospheric fields and probably chromospheric currents are responsible for the observed pre-flare heating and provide the energy of flares.

VLA radio observations of AR Scorpii

NASA Astrophysics Data System (ADS)

Stanway, E. R.; Marsh, T. R.; Chote, P.; Gänsicke, B. T.; Steeghs, D.; Wheatley, P. J.

2018-03-01

Aims: AR Scorpii is unique amongst known white dwarf binaries in showing powerful pulsations extending to radio frequencies. Here we aim to investigate the multi-frequency radio emission of AR Sco in detail, in order to constrain its origin and emission mechanisms. Methods: We present interferometric radio frequency imaging of AR Sco at 1.5, 5 and 9 GHz, analysing the total flux and polarization behaviour of this source at high time resolution (10, 3 and 3 s), across a full 3.6 h orbital period in each band. Results: We find strong modulation of the radio flux on the orbital period and the orbital sideband of the white dwarf's spin period (also known as the "beat" period). This indicates that, like the optical flux, the radio flux arises predominantly from on or near the inner surface of the M-dwarf companion star. The beat-phase pulsations of AR Sco decrease in strength with decreasing frequency. They are strongest at 9 GHz and at an orbital phase 0.5. Unlike the optical emission from this source, radio emission from AR Sco shows weak linear polarization but very strong circular polarization, reaching 30% at an orbital phase 0.8. We infer the probable existence of a non-relativistic cyclotron emission component, which dominates at low radio frequencies. Given the required magnetic fields, this also likely arises from on or near the M-dwarf. A table of the flux time series is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A66

Coherent curvature radiation and fast radio bursts

NASA Astrophysics Data System (ADS)

Ghisellini, Gabriele; Locatelli, Nicola

2018-06-01

Fast radio bursts are extragalactic radio transient events lasting a few milliseconds with a Jy flux at 1 GHz. We propose that these properties suggest a neutron star progenitor, and focus on coherent curvature radiation as the radiation mechanism. We study for which sets of parameters the emission can fulfil the observational constraints. Even if the emission is coherent, we find that self-absorption can limit the produced luminosities at low radio frequencies and that an efficient re-acceleration process is needed to balance the dramatic energy losses of the emitting particles. Self-absorption limits the luminosities at low radio frequency, while coherence favours steep optically thin spectra. Furthermore, the magnetic geometry must have a high degree of order to obtain coherent curvature emission. Particles emit photons along their velocity vectors, thereby greatly reducing the inverse Compton mechanism. In this case we predict that fast radio bursts emit most of their luminosities in the radio band and have no strong counterpart in any other frequency bands.

Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission

DOE PAGES

Max-Moerbeck, W.; Hovatta, T.; Richards, J. L.; ...

2014-09-22

In order to determine the location of the gamma-ray emission site in blazars, we investigate the time-domain relationship between their radio and gamma-ray emission. Light-curves for the brightest detected blazars from the first 3 years of the mission of the Fermi Gamma-ray Space Telescope are cross-correlated with 4 years of 15GHz observations from the OVRO 40-m monitoring program. The large sample and long light-curve duration enable us to carry out a statistically robust analysis of the significance of the cross-correlations, which is investigated using Monte Carlo simulations including the uneven sampling and noise properties of the light-curves. Modeling the light-curvesmore » as red noise processes with power-law power spectral densities, we find that only one of 41 sources with high quality data in both bands shows correlations with significance larger than 3σ (AO0235+164), with only two more larger than even 2.25σ (PKS 1502+106 and B2 2308+34). Additionally, we find correlated variability in Mrk 421 when including a strong flare that occurred in July-September 2012. These results demonstrate very clearly the difficulty of measuring statistically robust multiwavelength correlations and the care needed when comparing light-curves even when many years of data are used. This should be a caution. In all four sources the radio variations lag the gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. Continuous simultaneous monitoring over a longer time period is required to obtain high significance levels in cross-correlations between gamma-ray and radio variability in most blazars.« less

Radio Measurements of Air Showers with LOPES

NASA Astrophysics Data System (ADS)

Schröder, F. G.; Apel, W. D.; Arteaga-Velazquez, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; Di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Fuchs, B.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Zabierowski, J.; Zensus, J. A.

2013-02-01

LOPES is a digital antenna array for the radio measurement of cosmic-ray air showers at energies around 1017 eV. It is triggered by the KASCADE-Grande air-shower array at the Karlsruhe Institute of Technology (KIT), Germany. Because of an absolute amplitude calibration and a sophisticated data analysis, LOPES can test models for the radio emission to an up-to-now unachieved level, thus improving our understanding of the radio emission mechanisms. Recent REAS simulations of the air-shower radio emission come closer to the measurements than any previously tested simulations. We have determined the radio-reconstruction precision of interesting air-shower parameters by comparing LOPES reconstructions to both REAS simulations and KASCADE-Grande measurements, and present our latest results for the angular resolution, the energy and the Xmax reconstruction based on the radio measurement of about 500 air showers. Although the precision of LOPES is limited by the high level of anthropogenic noise at KIT, it opens a promising perspective for next-generation radio arrays in regions with a lower ambient noise level.

Development of solar flares and features of the fine structure of solar radio emission

NASA Astrophysics Data System (ADS)

Chernov, G. P.; Fomichev, V. V.; Yan, Y.; Tan, B.; Tan, Ch.; Fu, Q.

2017-11-01

The reason for the occurrence of different elements of the fine structure of solar radio bursts in the decimeter and centimeter wavelength ranges has been determined based on all available data from terrestrial and satellite observations. In some phenomena, fast pulsations, a zebra structre, fiber bursts, and spikes have been observed almost simultaneously. Two phenomena have been selected to show that the pulsations of radio emission are caused by particles accelerated in the magnetic reconnection region and that the zebra structure is excited in a source, such as a magnetic trap for fast particles. The complex combination of unusual fiber bursts, zebra structure, and spikes in the phenomenon on December 1, 2004, is associated with a single source, a magnetic island formed after a coronal mass ejection.

Sporadic radio emission connected with a definite manifestation of solar activity in the near Earth space

NASA Technical Reports Server (NTRS)

Dudnic, A. V.; Zaljubovski, I. I.; Kartashev, V. M.; Shmatko, E. S.

1985-01-01

Sporadic radio emission of near Earth space at the frequency of 38 MHz is shown to appear in the event of a rapid development of instabilities in the ionospheric plasma. The instabilities are generated due to primary ionospheric disturbances occurring under the influence of solar chromospheric flares.

Project Radio JOVE: Hands-On Radio Astronomy for the Classroom

NASA Astrophysics Data System (ADS)

Thieman, J. R.; Higgins, C. A.

2000-10-01

Radio Jove is a relatively new educational project to involve secondary school students in collecting and analyzing observations of the natural radio emissions of the planet Jupiter and the Sun. Participating students get hands-on experience in gathering and working with space science data. They obtain the data by either building a radio receiver and antenna and making observations with their equipment, or by remotely using professional radio telescopes through the web. They can then compare their results with other schools who had also observed and come to conclusions concerning the nature of the radio sources and how the radio waves propagate to Earth. Thus, they fully follow the method of scientific inquiry used by radio astronomers to study our solar system. (National Science Content Standard A: Science as Inquiry) More than 200 kits have been distributed thus far to schools and individuals as a result of the project. With the coming Cassini flyby of Jupiter we will be advocating a campaign in which many of the schools involved in the project will be observing at times of scientific interest. While Galileo and Cassini are monitoring Jovian radio emissions at lower frequencies, the schools will be observing at frequencies of 20.1 MHz (kit-based observations) or the frequencies available through the professional radio telescopes connected on-line. The aim will be to get a thorough picture of the levels of activity at Jupiter during the flyby period and how the radio signals are received at different observing stations around the world. An archive of observations submitted by the schools will be maintained at Goddard Space Flight Center and there will also be an archive of the professional telescopes data at the University of Florida. We hope that many students will have the feeling of being a part of the planetary exploration program as a result.

The Spectacular Radio-Near-IR-X-Ray Jet of 3C 111: the X-Ray Emission Mechanism and Jet Kinematics

NASA Technical Reports Server (NTRS)

Clautice, Devon; Perlman, Eric S.; Georganopoulos, Markos; Lister, Matthew L.; Tombesi, Francesco; Cara, Mihai; Marshall, Herman L.; Hogan, Brandon M.; Kazanas, Demos

2016-01-01

Relativistic jets are the most energetic manifestation of the active galactic nucleus (AGN) phenomenon. AGN jets are observed from the radio through gamma-rays and carry copious amounts of matter and energy from the subparsec central regions out to the kiloparsec and often megaparsec scale galaxy and cluster environs. While most spatially resolved jets are seen in the radio, an increasing number have been discovered to emit in the optical/near- IR and/or X-ray bands. Here we discuss a spectacular example of this class, the 3C 111 jet, housed in one of the nearest, double-lobed FR II radio galaxies known. We discuss new, deep Chandra and Hubble Space Telescope (HST) observations that reveal both near-IR and X-ray emission from several components of the 3C 111 jet, as well as both the northern and southern hotspots. Important differences are seen between the morphologies in the radio, X-ray, and near-IR bands. The long (over 100 kpc on each side), straight nature of this jet makes it an excellent prototype for future, deep observations, as it is one of the longest such features seen in the radio, near-IR/optical, and X-ray bands. Several independent lines of evidence, including the X-ray and broadband spectral shape as well as the implied velocity of the approaching hotspot, lead us to strongly disfavor the EC/CMB model and instead favor a two-component synchrotron model to explain the observed X-ray emission for several jet components. Future observations with NuSTAR, HST, and Chandra will allow us to further constrain the emission mechanisms.

THE SPECTACULAR RADIO-NEAR-IR-X-RAY JET OF 3C 111: THE X-RAY EMISSION MECHANISM AND JET KINEMATICS

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

Clautice, Devon; Perlman, Eric S.; Georganopoulos, Markos

2016-08-01

Relativistic jets are the most energetic manifestation of the active galactic nucleus (AGN) phenomenon. AGN jets are observed from the radio through gamma-rays and carry copious amounts of matter and energy from the sub-parsec central regions out to the kiloparsec and often megaparsec scale galaxy and cluster environs. While most spatially resolved jets are seen in the radio, an increasing number have been discovered to emit in the optical/near-IR and/or X-ray bands. Here we discuss a spectacular example of this class, the 3C 111 jet, housed in one of the nearest, double-lobed FR II radio galaxies known. We discuss new,more » deep Chandra and Hubble Space Telescope ( HST ) observations that reveal both near-IR and X-ray emission from several components of the 3C 111 jet, as well as both the northern and southern hotspots. Important differences are seen between the morphologies in the radio, X-ray, and near-IR bands. The long (over 100 kpc on each side), straight nature of this jet makes it an excellent prototype for future, deep observations, as it is one of the longest such features seen in the radio, near-IR/optical, and X-ray bands. Several independent lines of evidence, including the X-ray and broadband spectral shape as well as the implied velocity of the approaching hotspot, lead us to strongly disfavor the EC/CMB model and instead favor a two-component synchrotron model to explain the observed X-ray emission for several jet components. Future observations with NuSTAR , HST , and Chandra will allow us to further constrain the emission mechanisms.« less

Low Altitude Solar Magnetic Reconnection, Type III Solar Radio Bursts, and X-ray Emissions.

PubMed

Cairns, I H; Lobzin, V V; Donea, A; Tingay, S J; McCauley, P I; Oberoi, D; Duffin, R T; Reiner, M J; Hurley-Walker, N; Kudryavtseva, N A; Melrose, D B; Harding, J C; Bernardi, G; Bowman, J D; Cappallo, R J; Corey, B E; Deshpande, A; Emrich, D; Goeke, R; Hazelton, B J; Johnston-Hollitt, M; Kaplan, D L; Kasper, J C; Kratzenberg, E; Lonsdale, C J; Lynch, M J; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Ord, S M; Prabu, T; Roshi, A; Shankar, N Udaya; Srivani, K S; Subrahmanyan, R; Wayth, R B; Waterson, M; Webster, R L; Whitney, A R; Williams, A; Williams, C L

2018-01-26

Type III solar radio bursts are the Sun's most intense and frequent nonthermal radio emissions. They involve two critical problems in astrophysics, plasma physics, and space physics: how collective processes produce nonthermal radiation and how magnetic reconnection occurs and changes magnetic energy into kinetic energy. Here magnetic reconnection events are identified definitively in Solar Dynamics Observatory UV-EUV data, with strong upward and downward pairs of jets, current sheets, and cusp-like geometries on top of time-varying magnetic loops, and strong outflows along pairs of open magnetic field lines. Type III bursts imaged by the Murchison Widefield Array and detected by the Learmonth radiospectrograph and STEREO B spacecraft are demonstrated to be in very good temporal and spatial coincidence with specific reconnection events and with bursts of X-rays detected by the RHESSI spacecraft. The reconnection sites are low, near heights of 5-10 Mm. These images and event timings provide the long-desired direct evidence that semi-relativistic electrons energized in magnetic reconnection regions produce type III radio bursts. Not all the observed reconnection events produce X-ray events or coronal or interplanetary type III bursts; thus different special conditions exist for electrons leaving reconnection regions to produce observable radio, EUV, UV, and X-ray bursts.

Voyager planetary radio astronomy studies

NASA Technical Reports Server (NTRS)

Staelin, David H.; Eikenberry, Stephen S.

1993-01-01

Analysis of nonthermal radio emission data obtained by the Planetary Radio Astronomy (PRA) spectrometers on the Voyager 1 and 2 spacecraft was performed. This PRA data provided unique insights into the radio emission characteristics of the outer planets because of PRA's unique spectral response below the terrestrial ionospheric plasma frequency and its unprecedented proximity to the source. Of those results which were documented or published, this final report surveys only the highlights and cites references for more complete discussions. Unpublished results for Uranus, Neptune, and theoretical Ionian current distributions are presented at greater length. The most important conclusion to be drawn from these observations is that banded spectral emission is common to the radio emission below 1-2 MHz observed from all four Jovian planets. In every case multiple spectral features evolve on time scales of seconds to minutes. To the extent these features drift in frequency, they appear never to cross one another. The Neptunian spectral features appear to drift little or not at all, their evolution consisting principally of waxing and waning. Since other evidence strongly suggests that most or all of this radio emission is occurring near the local magnetospheric electron cyclotron frequency, this implies that this emission preferentially occurs at certain continually changing planetary radii. It remains unknown why certain radii might be favored, unless radial electric field components or other means serve to differentiate radially the magnetospheric plasma density, particle energy vectors, or particle coherence. Calculation of the spatial distribution and intensity of the Io-generated magnetospheric currents are also presented; these currents may be limited principally by wave impedance and local field strengths.

The difference between radio-loud and radio-quiet active galaxies

NASA Astrophysics Data System (ADS)

Wilson, A. S.; Colbert, E. J. M.

1995-01-01

The recent development of unified theories of active galactic nuclei (AGNs) has indicated that there are two physically distinct classes of these objects--radio-loud and radio-quiet. Despite differences, the (probable) thermal emissions from the AGNs (continua and lines from X-ray to infrared wavelengths) are quite similar to the two classes of object. We argue that this last result suggests that the black hole masses and mass accretion rates in the two classes are not greatly different, and that the difference between the classes is associated with the spin of the black hole. We assume that the normal process of accretion through a disk does not lead to rapidly spinning holes and propose that galaxies (e.g., spirals) which have not suffered a recent major merger event contain nonrotating or only slowly rotating black holes. When two such galaxies merge, the two black holes are known to form a binary and we assume that they eventually coalesce. The ratio of the number of radio-loud to radio-quiet AGNs at a given thermal (e.g., optical) luminosity is determined by the galaxy merger rate. Comparisons between the predicted and observed radio luminosity functions constrain the efficiencies with which jet power is extracted from the spinning hole and radio emission is produced by the jet.

Herringbone bursts associated with type II solar radio emission

NASA Technical Reports Server (NTRS)

Cairns, I. H.; Robinson, R. D.

1987-01-01

Detailed observations of the herringbone (HB) fine structure on type II solar radio bursts are presented. Data from the Culgoora radiospectrograph, radiometer and radioheliograph are analyzed. The characteristic spectral profiles, frequency drift rates and exciter velocities, fluxes, source sizes, brightness temperatures, and polarizations of individual HB bursts are determined. Correlations between individual bursts within the characteristic groups of bursts and the properties of the associated type II bursts are examined. These data are compatible with HB bursts being radiation at multiples of the plasma frequency generated by electron streams accelerated by the type II shock. HB bursts are physically distinct phenomena from type II and type III bursts, differing significantly in emission processes and/or source conditions; this conclusion indicates that many of the presently available theoretical ideas for HB bursts are incorrect.

Radio Properties of the BAT AGNs: the FIR-radio Relation, the Fundamental Plane, and the Main Sequence of Star Formation

NASA Astrophysics Data System (ADS)

Smith, Krista Lynne; Mushotzky, Richard F.; Vogel, Stuart; Shimizu, Thomas T.; Miller, Neal

2016-12-01

We conducted 22 GHz 1″ JVLA imaging of 70 radio-quiet active galactic nuclei (AGNs) from the Swift-BAT survey. We find radio cores in all but three objects. The radio morphologies of the sample fall into three groups: compact and core-dominated, extended, and jet-like. We spatially decompose each image into core flux and extended flux, and compare the extended radio emission with that predicted from previous Herschel observations using the canonical FIR-radio relation. After removing the AGN contribution to the FIR and radio flux densities, we find that the relation holds remarkably well despite the potentially different star formation physics in the circumnuclear environment. We also compare our core radio flux densities with predictions of coronal models and scale-invariant jet models for the origin of radio emission in radio-quiet AGNs, and find general consistency with both models. However, we find that the L R/L X relation does not distinguish between star formation and non-relativistic AGN-driven outflows as the origin of radio emission in radio-quiet AGNs. Finally, we examine where objects with different radio morphologies fall in relation to the main sequence (MS) of star formation, and conclude that those AGNs that fall below the MS, as X-ray selected AGNs have been found to do, have core-dominated or jet-like 22 GHz morphologies.

A search of the SAS-2 data for pulsed gamma-ray emission from radio pulsars

NASA Technical Reports Server (NTRS)

Ogelman, H.; Fichtel, C. E.; Kniffen, D. A.; Thompson, D. J.

1976-01-01

Data from the SAS-2 high-energy (above 35 MeV) gamma-ray experiment have been examined for pulsed emission from each of 75 radio pulsars which were viewed by the instrument and which have sufficiently well-defined period and period-derivative information from radio observations to allow for gamma-ray periodicity searches. When gamma-ray arrival times were converted to pulsar phase using the radio reference timing information, two pulsars, PSR 1747-46 and PSR 1818-04, showed positive effects, each with a probability of less than 1 part in 10,000 of being a random fluctuation in the data for that pulsar. These are in addition to PSR 0531+21 and PSR 0833-45, previously reported. The results of this study suggest that gamma-ray astronomy has reached the detection threshold for gamma-ray pulsars and that work in the near future should give important new information on the nature of pulsars.

Exploring the connection between radio and GeV-TeV γ-ray emission in the 1FHL and 2FHL AGN samples

NASA Astrophysics Data System (ADS)

Lico, R.; Giroletti, M.; Orienti, M.; Costamante, L.; Pavlidou, V.; D'Ammando, F.; Tavecchio, F.

2017-10-01

Context. With the advent of the Fermi Large Area Telescope (LAT) it was revealed that blazars, representing the most extreme radio-loud active galactic nuclei (AGN) population, dominate the census of the γ-ray sky, and a significant correlation was found between radio and γ-ray emission in the 0.1-100 GeV energy range. However, the possible connection between radio and very high energy (VHE, E> 0.1 TeV) emission still remains elusive, owing to the lack of a homogeneous coverage of the VHE sky. Aims: The main goal of this work is to quantify and assess the significance of a possible connection between the radio emission on parsec scale measured by the very long baseline interferometry (VLBI) and GeV-TeV γ-ray emission in blazars, which is a central issue for understanding blazar physics and the emission processes in these objects. Methods: We investigate the radio VLBI and high energy γ-ray emission by using two large and unbiased AGN samples extracted from the first and second Fermi-LAT catalogs of hard γ-ray sources detected above 10 GeV (1FHL) and 50 GeV (2FHL). For comparison, we perform the same correlation analysis by using the 0.1-300 GeV γ-ray energy flux provided by the third Fermi-LAT source catalog (3FGL). We assess the correlation's statistical significance by means of a method based on permutations of the luminosities, by taking into account the various observational biases, which may apparently enhance or spoil any intrinsic correlation. Results: We find that the correlation strength and significance depend on the γ-ray energy range, with a different behavior among the blazar sub-classes. Overall, the radio and γ-ray emission above 10 GeV turns out to be uncorrelated for the full samples and for all of the blazar sub-classes with the exception of high synchrotron peaked (HSP) objects, which show a strong and significant correlation. On the contrary, when 0.1-300 GeV γ-ray energies are considered, a strong and significant correlation is found

Gamma-Ray Emission from the Broad-Line Radio Galaxy 3C 111

NASA Technical Reports Server (NTRS)

Hartman, Robert C.; Kadler, M.; Tueller, Jack

2008-01-01

The broad-line radio galaxy 3C 111 has been suggested as the counterpart of the y-ray source 3EG J0416+3650. While 3C 111 meets most of the criteria for a high-probability identification, like a bright flat-spectrum radio core and a blazar-like broadband SED, in the Third EGRET Catalog, the large positional offset of about 1.5' put 3C 111 outside the 99% probability region for 3EG J0416+3650, making this association questionable. We present a re-analysis of all available archival data for 3C 111 from the EGRET archives, resulting in detection of variable hard-spectrum high-energy gamma-ray emission above 1000 MeV from a position close to the nominal position of 3C 111, in three separate viewing periods (VPs), at a 3sigma level in each. A second variable hard-spectrum source is present nearby. At >100 MeV, one variable soft-spectrum source seems to account for most of the EGRET-detected emission of 3EG J0416+3650. A follow-up Swift UVOT/XRT observation reveals one moderately bright X-ray source in the error box of 3EG J0416+3650, but because of the large EGRET position uncertainty, it is not certain that the X-ray and gamma-ray sources are associated. Another Swift observation near the second (unidentified) hard gamma-ray source detected no X-ray source nearby.

Radio emission in the directions of cD and related galaxies in poor clusters. III. VLA observations at 20 cm

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

Burns, J.O.; White, R.A.; Hough, D.H.

1981-01-01

VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approx.70%). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approx.25% of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies ismore » seen from rich to poor clusters. We speculate that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. We briefly discuss galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and x-ray emission.« less

Radio emission in the directions of cD and related galaxies in poor clusters. III - VLA observations at 20 cm

NASA Technical Reports Server (NTRS)

Burns, J. O.; White, R. A.; Hough, D. H.

1981-01-01

VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approximately 70 percent). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approximately 25 percent of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies is seen from rich to poor clusters. It is speculated that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. Galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and X-ray emission are discussed

Radio Jove: Citizen Science for Jupiter Radio Astronomy

NASA Astrophysics Data System (ADS)

Higgins, C. A.; Thieman, J.; Reyes, F. J.; Typinski, D.; Flagg, R. F.; Greenman, W.; Brown, J.; Ashcraft, T.; Sky, J.; Cecconi, B.; Garcia, L. N.

2016-12-01

The Radio Jove Project (http://radiojove.gsfc.nasa.gov) has been operating as an educational activity for 18 years to introduce radio astronomy activities to students, teachers, and the general public. Participants may build a simple radio telescope kit, make scientific observations, and interact with radio observatories in real-time over the Internet. Recently some of our dedicated citizen science observers have upgraded their systems to better study radio emission from Jupiter and the Sun by adding dual-polarization spectrographs and wide-band antennas in the frequency range of 15-30 MHz. Some of these observations are being used in conjunction with professional telescopes such as the Long Wavelength Array (LWA), the Nancay Decametric Array, and the Ukrainian URAN2 Radio Telescope. In particular, there is an effort to support the Juno Mission radio waves instrument at Jupiter by using citizen science ground-based data for comparison and polarization verification. These data will be archived through a Virtual European Solar and Planetary Access (VESPA) archive (https://voparis-radiojove.obspm.fr/radiojove/welcome) for use by the amateur and professional radio science community. We overview the program and display recent observations that will be of interest to the science community.

Amateur Planetary Radio Data Archived for Science and Education: Radio Jove

NASA Astrophysics Data System (ADS)

Thieman, J.; Cecconi, B.; Sky, J.; Garcia, L. N.; King, T. A.; Higgins, C. A.; Fung, S. F.

2015-12-01

The Radio Jove Project is a hands-on educational activity in which students, teachers, and the general public build simple radio telescopes, usually from a kit, to observe single frequency decameter wavelength radio emissions from Jupiter, the Sun, the galaxy, and the Earth usually with simple dipole antennas. Some of the amateur observers have upgraded their receivers to spectrographs and their antennas have become more sophisticated as well. The data records compare favorably to more sophisticated professional radio telescopes such as the Long Wavelength Array (LWA) and the Nancay Decametric Array. Since these data are often carefully calibrated and recorded around the clock in widely scattered locations they represent a valuable database useful not only to amateur radio astronomers but to the professional science community as well. Some interesting phenomena have been noted in the data that are of interest to the professionals familiar with such records. The continuous monitoring of radio emissions from Jupiter could serve as useful "ground truth" data during the coming Juno mission's radio observations of Jupiter. Radio Jove has long maintained an archive for thousands of Radio Jove observations, but the database was intended for use by the Radio Jove participants only. Now, increased scientific interest in the use of these data has resulted in several proposals to translate the data into a science community data format standard and store the data in professional archives. Progress is being made in translating Radio Jove data to the Common Data Format (CDF) and also in generating new observations in that format as well. Metadata describing the Radio Jove data would follow the Space Physics Archive Search and Extract (SPASE) standard. The proposed archive to be used for long term preservation would be the Planetary Data System (PDS). Data sharing would be achieved through the PDS and the Paris Astronomical Data Centre (PADC) and the Virtual Wave Observatory (VWO

Detection of radio emission from optically identified supernova remnants in M31

NASA Technical Reports Server (NTRS)

Dickel, J. R.; Dodorico, S.; Felli, M.; Dopita, M.

1982-01-01

The Very Large Array was used to conduct a radio search at a wavelength of 20 cm for ten optically identified supernova remnants (SNRs) in M31. Five SNRs were detected, and for the other objects, upper limits to the emission were determined. On the average, the surface brightness of an SNR in M31 appears to be fainter than that of an SNR in the Galaxy. It is suggested that the median surface brightness at a given diameter is higher in late-type spirals than in Sb systems.

Observations and analysis of lunar radio emission at 3.09 mm wavelength

NASA Technical Reports Server (NTRS)

Ulich, B. L.; Cogdell, J. R.; Davis, J. H.; Calvert, T. A.

1974-01-01

An analysis of data on lunar radio emission at 3.09 mm wavelength is presented. The data were obtained during a single lunation in a manner that facilitates their comparison with a calculated model. Specific regions of the moon (Copernicus, Sea of Serenity, Sea of Tranquillity, Ocean of Storms, and an highland region near the mean center) were studied with enough angular resolution to distinguish between different types of terrain. The data were absolutely calibrated and yield a new measurement of the lunation average brightness temperature of the center of the moon.

Radio Frequency Interference: Radio Astronomy's Biggest Enemy

NASA Astrophysics Data System (ADS)

Acevedo, F.; Ghosh, Tapasi

1997-12-01

As technology progresses, the demand for the usage of the electromagnetic spectrum increases with it. The development is so fast and prolific that clean band space for passive users such as Radio Astronomy is becoming ever so scarce. Even though, several spectral bands have been protected for Radio Astronomy by Federal Communication Commission (in the USA) under the recommendations of the International Telecommunication Union (ITU), pressure for making more spectral space commercially usable is extreme. Although these commercial usages make our modern living at all possible, often the extreme vulnerability of passive users are are not fully appreciated, resulting in unwanted emissions (RFI) in the Radio Astronomy Bands. Another source of RFI is the fact that many of the electronic devices used in the observatories themselves generate radio waves. If proper precautions are not taken, these can be received back through the Radio Telescope itself. This problem is referred to as internal RFI. The focus of this paper is the search and diminution of internal RFI in the Arecibo Observatory in Arecibo, Puerto Rico. Using a simple setup of a log-periodic antenna and a Spectrum Analyzer, spectra spanning a frequency range of 100 - 1800 MHZ were recorded in some areas of the Observatory and the new Visitor Center (AOVEF). The measurements disclosed sources of radio emission among some of the digital electronic equipment in the Equipment room and a few displays in the AOVEF. Most prominent of these was a 2.5 MHz comb spanning the entire range of the measurements emitted from the SRENDIP and AOFTM machines. The respective groups were informed and corrective shielding & isolations were implemented immediately. In AOVEF, three displays, some audio-visual equipment, and video/digital cameras used by the visitors were found to be "leaky". In future, the use of such cameras will be prohibited and the exhibits will be screened appropriately.

Sampling modulation technique in radio-frequency helium glow discharge emission source by use of pulsed laser ablation.

PubMed

Naeem, Tariq Mahmood; Matsuta, Hideyuki; Wagatsuma, Kazuaki

2004-05-01

An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N(2)(+) 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed.

A New Radio Loudness Diagnostic for Active Galaxies: A Radio-to-Mid-Infrared Parameter

NASA Technical Reports Server (NTRS)

Melendez, Marcio B.; Kraemer, S. B.; Schmitt, H. R.

2010-01-01

We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4GHz (3.6cm) and 1.4GHz (20cm), the [O IV) (gamma)25.89 micron, [Ne III] (gamma)l5.56 micron and [Ne II] (gamma)l2.81 micron emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4 GHz/[O IV] ratio, assuming that [0 IV] scales with the luminosity of the active galactic nuclei (AGN). From this we find that Seyfert 1 s (i.e. Seyfert 1.0s, 1.2s and 1.5s) and Seyfert 2s (i.e. Seyfert 1.8s, 1.9s and 2.0s) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne u] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more 'radio loud', by a factor of approx.2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4 GHz/[O IV], or alternatively, 1.4 GHz/[O IV] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables. Key words: Galaxy: stellar content - galaxies: Seyfert - infrared: galaxies

Thunderstorm observations by air-shower radio antenna arrays

NASA Astrophysics Data System (ADS)

Apel, W. D.; Arteaga, J. C.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Ender, M.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huber, D.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Krömer, O.; Kuijpers, J.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Melissas, M.; Morello, C.; Nehls, S.; Oehlschläger, J.; Palmieri, N.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Rühle, C.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F. G.; Sima, O.; Toma, G.; Trinchero, G. C.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.

2011-10-01

Relativistic, charged particles present in extensive air showers (EAS) lead to a coherent emission of radio pulses which are measured to identify the shower initiating high-energy cosmic rays. Especially during thunderstorms, there are additional strong electric fields in the atmosphere, which can lead to further multiplication and acceleration of the charged particles and thus have influence on the form and strength of the radio emission. For a reliable energy reconstruction of the primary cosmic ray by means of the measured radio signal it is very important to understand how electric fields affect the radio emission. In addition, lightning strikes are a prominent source of broadband radio emissions that are visible over very long distances. This, on the one hand, causes difficulties in the detection of the much lower signal of the air shower. On the other hand the recorded signals can be used to study features of the lightning development. The detection of cosmic rays via the radio emission and the influence of strong electric fields on this detection technique is investigated with the LOPES experiment in Karlsruhe, Germany. The important question if a lightning is initiated by the high electron density given at the maximum of a high-energy cosmic-ray air shower is also investigated, but could not be answered by LOPES. But, these investigations exhibit the capabilities of EAS radio antenna arrays for lightning studies. We report about the studies of LOPES measured radio signals of air showers taken during thunderstorms and give a short outlook to new measurements dedicated to search for correlations of lightning and cosmic rays.

Jet-ISM Interaction in the Radio Galaxy 3C 293: Jet-driven Shocks Heat ISM to Power X-Ray and Molecular H2 Emission

NASA Astrophysics Data System (ADS)

Lanz, L.; Ogle, P. M.; Evans, D.; Appleton, P. N.; Guillard, P.; Emonts, B.

2015-03-01

We present a 70 ks Chandra observation of the radio galaxy 3C 293. This galaxy belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have very luminous emission from warm molecular hydrogen. In radio galaxies, the molecular gas appears to be heated by jet-driven shocks, but exactly how this mechanism works is still poorly understood. With Chandra, we observe X-ray emission from the jets within the host galaxy and along the 100 kpc radio jets. We model the X-ray spectra of the nucleus, the inner jets, and the X-ray features along the extended radio jets. Both the nucleus and the inner jets show evidence of 107 K shock-heated gas. The kinetic power of the jets is more than sufficient to heat the X-ray emitting gas within the host galaxy. The thermal X-ray and warm H2 luminosities of 3C 293 are similar, indicating similar masses of X-ray hot gas and warm molecular gas. This is consistent with a picture where both derive from a multiphase, shocked interstellar medium (ISM). We find that radio-loud MOHEGs that are not brightest cluster galaxies (BCGs), like 3C 293, typically have LH2/LX˜ 1 and MH2/MX˜ 1, whereas MOHEGs that are BCGs have LH2/LX˜ 0.01 and MH2/MX˜ 0.01. The more massive, virialized, hot atmosphere in BCGs overwhelms any direct X-ray emission from current jet-ISM interaction. On the other hand, LH2/LX˜ 1 in the Spiderweb BCG at z = 2, which resides in an unvirialized protocluster and hosts a powerful radio source. Over time, jet-ISM interaction may contribute to the establishment of a hot atmosphere in BCGs and other massive elliptical galaxies.

Radio Map of the Andromeda Galaxy.

PubMed

Macleod, J M

1964-07-24

The University of Illinois radio telescope has resolved the 610.5 Mcy/sec disk component of radio emission from the large galaxy M 31 into several discrete concentrations. In two cases, these correspond to the crossing of the optical major axis by spiral arms. A spur of emission extends southeast from the galaxy near the minor axis.

Analytic calculation of radio emission from parametrized extensive air showers: A tool to extract shower parameters

NASA Astrophysics Data System (ADS)

Scholten, O.; Trinh, T. N. G.; de Vries, K. D.; Hare, B. M.

2018-01-01

The radio intensity and polarization footprint of a cosmic-ray induced extensive air shower is determined by the time-dependent structure of the current distribution residing in the plasma cloud at the shower front. In turn, the time dependence of the integrated charge-current distribution in the plasma cloud, the longitudinal shower structure, is determined by interesting physics which one would like to extract, such as the location and multiplicity of the primary cosmic-ray collision or the values of electric fields in the atmosphere during thunderstorms. To extract the structure of a shower from its footprint requires solving a complicated inverse problem. For this purpose we have developed a code that semianalytically calculates the radio footprint of an extensive air shower given an arbitrary longitudinal structure. This code can be used in an optimization procedure to extract the optimal longitudinal shower structure given a radio footprint. On the basis of air-shower universality we propose a simple parametrization of the structure of the plasma cloud. This parametrization is based on the results of Monte Carlo shower simulations. Deriving the parametrization also teaches which aspects of the plasma cloud are important for understanding the features seen in the radio-emission footprint. The calculated radio footprints are compared with microscopic CoREAS simulations.

Radio-Frequency Emissions from Streamer Collisions: Implications for High-Energy Processes.

NASA Astrophysics Data System (ADS)

Luque, A.

2017-12-01

The production of energetic particles in a discharge corona is possibly linked to the collision of streamers of opposite polarities [Cooray et al. (2009), Kochkin et al. (2012), Østgaard et al. (2016)]. There is also experimental evidence linking it to radio-frequency emissions in the UHF frequency range (300 MHz-3 GHz) [Montanyà et al. (2015), Petersen and Beasley (2014)]. Here we investigate these two links by modeling the radio-frequency emissions emanating from an encounter between two counter-propagating streamers. Our numerical model combines self-consistently a conservative, high-order Finite-Volume scheme for electron transport with a Finite-Difference Time-Domain (FDTD) method for electromagnetic propagation. We also include the most relevant reactions for streamer propagation: impact ionization, dissociative attachment and photo-ionization. Our implementation benefits from massive parallelization by running on a General-Purpose Graphical Processing Unit (GPGPU). With this code we found that streamer encounters emit electromagnetic waves predominantly in the UHF range, supporting the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges. References Cooray, V., et al., J. Atm. Sol.-Terr. Phys., 71, 1890, doi:10.1016/j.jastp.2009.07.010 (2009). Kochkin, P. O., et al., J. Phys. D, 45, 425202, doi: 10.1088/0022-3727/45/42/425202 (2012). Montanyà, J., et al., J. Atm. Sol.-Terr. Phys., 136, 94, doi:10.1016/j.jastp.2015.06.009, (2015). Østgaard, N., et al., J. Geophys. Res. (Atmos.), 121, 2939, doi:10.1002/2015JD024394 (2016). Petersen, D., and W. Beasley, Atmospheric Research, 135, 314, doi:10.1016/j.atmosres.2013.02.006 (2014).

Identification of a Likely Radio Counterpart to the Rapid Burster

NASA Astrophysics Data System (ADS)

Moore, Christopher B.; Rutledge, Robert E.; Fox, Derek W.; Guerriero, Robert A.; Lewin, Walter H. G.; Fender, Robert; van Paradijs, Jan

2000-04-01

We have identified a likely radio counterpart to the low-mass X-ray binary MXB 1730-335 (the Rapid Burster). The counterpart has shown 8.4 GHz radio on/off behavior correlated with the X-ray on/off behavior as observed by the RXTE/ASM during six VLA observations. The probability of an unrelated, randomly varying background source duplicating this behavior is 1%-3% depending on the correlation timescale. The location of the radio source is R.A. 17h33m24.61s, decl. -33 deg23'19.8" (J2000), +/-0.1". We do not detect 8.4 GHz radio emission coincident with type II (accretion-driven) X-ray bursts. The ratio of radio to X-ray emission during such bursts is constrained to be below the ratio observed during X-ray-persistent emission at the 2.9 σ level. Synchrotron bubble models of the radio emission can provide a reasonable fit to the full data set, collected over several outbursts, assuming that the radio evolution is the same from outburst to outburst but given the physical constraints the emission is more likely to be due to ~1 hr radio flares such as have been observed from the X-ray binary GRS 1915+105.

Jupiter radio bursts and particle acceleration

NASA Technical Reports Server (NTRS)

Desch, Michael D.

1994-01-01

Particle acceleration processes are important in understanding many of the Jovian radio and plasma wave emissions. However, except for the high-energy electrons that generate synchrotron emission following inward diffusion from the outer magnetosphere, acceleration processes in Jupiter's magnetosphere and between Jupiter and Io are poorly understood. We discuss very recent observations from the Ulysses spacecraft of two new Jovian radio and plamas wave emissions in which particle acceleration processes are important and have been addressed directly by complementary investigations. First, radio bursts known as quasi-periodic bursts have been observed in close association with a population of highly energetic electrons. Second, a population of much lower energy (keV range) electrons on auroral field lines can be shown to be responsible for the first observation of a Jovian plasma wave emission known as auroral hiss.

RADIO PROPERTIES OF THE BAT AGNs: THE FIR–RADIO RELATION, THE FUNDAMENTAL PLANE, AND THE MAIN SEQUENCE OF STAR FORMATION

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

Smith, Krista Lynne; Mushotzky, Richard F.; Vogel, Stuart

We conducted 22 GHz 1″ JVLA imaging of 70 radio-quiet active galactic nuclei (AGNs) from the Swift -BAT survey. We find radio cores in all but three objects. The radio morphologies of the sample fall into three groups: compact and core-dominated, extended, and jet-like. We spatially decompose each image into core flux and extended flux, and compare the extended radio emission with that predicted from previous Herschel observations using the canonical FIR–radio relation. After removing the AGN contribution to the FIR and radio flux densities, we find that the relation holds remarkably well despite the potentially different star formation physics inmore » the circumnuclear environment. We also compare our core radio flux densities with predictions of coronal models and scale-invariant jet models for the origin of radio emission in radio-quiet AGNs, and find general consistency with both models. However, we find that the L {sub R}/ L {sub X} relation does not distinguish between star formation and non-relativistic AGN-driven outflows as the origin of radio emission in radio-quiet AGNs. Finally, we examine where objects with different radio morphologies fall in relation to the main sequence (MS) of star formation, and conclude that those AGNs that fall below the MS, as X-ray selected AGNs have been found to do, have core-dominated or jet-like 22 GHz morphologies.« less

Radio Emission and Orbital Motion from the Close-encounter Star-Brown Dwarf Binary WISE J072003.20-084651.2

NASA Astrophysics Data System (ADS)

Burgasser, Adam J.; Melis, Carl; Todd, Jacob; Gelino, Christopher R.; Hallinan, Gregg; Bardalez Gagliuffi, Daniella

2015-12-01

We report the detection of radio emission and orbital motion from the nearby star-brown dwarf binary WISE J072003.20-084651.2AB. Radio observations across the 4.5-6.5 GHz band with the Very Large Array identify at the position of the system quiescent emission with a flux density of 15 ± 3 μJy, and a highly polarized radio source that underwent a 2-3 minute burst with peak flux density 300 ± 90 μJy. The latter emission is likely a low-level magnetic flare similar to optical flares previously observed for this source. No outbursts were detected in separate narrow-band Hα monitoring observations. We report new high-resolution imaging and spectroscopic observations that confirm the presence of a co-moving T5.5 secondary and provide the first indications of three-dimensional orbital motion. We used these data to revise our estimates for the orbital period (4.1{}-1.3+2.7 year) and tightly constrain the orbital inclination to be nearly edge-on (93.°6+1.°6-1.°4), although robust measures of the component and system masses will require further monitoring. The inferred orbital motion does not change the high likelihood that this radio-emitting very low-mass binary made a close pass to the Sun in the past 100 kyr. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

A DISTANT RADIO MINI-HALO IN THE PHOENIX GALAXY CLUSTER

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

Van Weeren, R. J.; Andrade-Santos, F.; Forman, W. R.

We report the discovery of extended radio emission in the Phoenix cluster (SPT-CL J2344-4243, z = 0.596) with the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. The diffuse emission extends over a region of at least 400-500 kpc and surrounds the central radio source of the Brightest Cluster Galaxy, but does not appear to be directly associated with it. We classify the diffuse emission as a radio mini-halo, making it the currently most distant mini-halo known. Radio mini-halos have been explained by synchrotron emitting particles re-accelerated via turbulence, possibly induced by gas sloshing generated from a minor merger event. Chandra observationsmore » show a non-concentric X-ray surface brightness distribution, which is consistent with this sloshing interpretation. The mini-halo has a flux density of 17 ± 5 mJy, resulting in a 1.4 GHz radio power of (10.4 ± 3.5) × 10{sup 24} W Hz{sup –1}. The combined cluster emission, which includes the central compact radio source, is also detected in a shallow GMRT 156 MHz observation and together with the 610 MHz data we compute a spectral index of –0.84 ± 0.12 for the overall cluster radio emission. Given that mini-halos typically have steeper radio spectra than cluster radio galaxies, this spectral index should be taken as an upper limit for the mini-halo.« less

Radio continuum from FU Orionis stars

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

Rodriguez, L.F.; Hartmann, L.W.; Chavira, E.

1990-12-01

Using the very large array a sensitive search is conducted for 3.6-cm continuum emission toward four FU Orionis objects: FU Ori, V1515 Cyg, V1057 Cyg, and Elias 1-12. V1057 Cyg and Elias 1-12 at the level of about 0.1 mJy is detected. The association of radio continuum emission with these FU Ori objects strengthens a possible relation between FU Ori stars and objects like L 1551 IRS 5 and Z CMa that are also sources of radio continuum emission and have been proposed as post-FU Ori objects. Whether the radio continuum emission is caused by free-free emission from ionized ejectamore » or if it is optically thin emission from a dusty disk is discussed. It was determined that, in the archives of the Tonantzintla Observatory, a plate taken in 1957 does not show Elias 1-12. This result significantly narrows the time range for the epoch of the outburst of this source to between 1957 and 1965. 38 refs.« less

The isotropic radio background revisited

NASA Astrophysics Data System (ADS)

Fornengo, Nicolao; Lineros, Roberto A.; Regis, Marco; Taoso, Marco

2014-04-01

We present an extensive analysis on the determination of the isotropic radio background. We consider six different radio maps, ranging from 22 MHz to 2.3 GHz and covering a large fraction of the sky. The large scale emission is modeled as a linear combination of an isotropic component plus the Galactic synchrotron radiation and thermal bremsstrahlung. Point-like and extended sources are either masked or accounted for by means of a template. We find a robust estimate of the isotropic radio background, with limited scatter among different Galactic models. The level of the isotropic background lies significantly above the contribution obtained by integrating the number counts of observed extragalactic sources. Since the isotropic component dominates at high latitudes, thus making the profile of the total emission flat, a Galactic origin for such excess appears unlikely. We conclude that, unless a systematic offset is present in the maps, and provided that our current understanding of the Galactic synchrotron emission is reasonable, extragalactic sources well below the current experimental threshold seem to account for the majority of the brightness of the extragalactic radio sky.

Afterglow model for the radio emission from the jetted tidal disruption candidate Swift J1644+57

NASA Astrophysics Data System (ADS)

Metzger, Brian D.; Giannios, Dimitrios; Mimica, Petar

2012-03-01

The recent transient event Swift J1644+57 has been interpreted as emission from a collimated relativistic jet, powered by the sudden onset of accretion on to a supermassive black hole following the tidal disruption of a star. Here we model the radio-microwave emission as synchrotron radiation produced by the shock interaction between the jet and the gaseous circumnuclear medium (CNM). At early times after the onset of the jet (t≲ 5-10 d) a reverse shock propagates through and decelerates the ejecta, while at later times the outflow approaches the Blandford-McKee self-similar evolution (possibly modified by additional late energy injection). The achromatic break in the radio light curve of Swift J1644+57 is naturally explained as the transition between these phases. We show that the temporal indices of the pre- and post-break light curve are consistent with those predicted if the CNM has a wind-type radial density profile n∝r-2. The observed synchrotron frequencies and self-absorbed flux constrain the fraction of the post-shock thermal energy in relativistic electrons ɛe≈ 0.03-0.1, the CNM density at 1018 cm n18≈ 1-10 cm-3 and the initial Lorentz factor Γj≈ 10-20 and opening angle ? of the jet. Radio modelling thus provides robust independent evidence for a narrowly collimated outflow. Extending our model to the future evolution of Swift J1644+57, we predict that the radio flux at low frequencies (ν≲ few GHz) will begin to brighten more rapidly once the characteristic frequency νm crosses below the radio band after it decreases below the self-absorption frequency on a time-scale of months (indeed, such a transition may already have begun). Our results demonstrate that relativistic outflows from tidal disruption events provide a unique probe of the conditions in distant, previously inactive galactic nuclei, complementing studies of normal active galactic nuclei.

The Millimeter-Radio Emission of BL Lacertae During Two γ-ray Outbursts

NASA Astrophysics Data System (ADS)

Kim, Dae-Won; Trippe, Sascha; Lee, Sang-Sung; Park, Jong-Ho; Kim, Jae-Young; Algaba, Juan-Carlos; Hodgson, Jeffrey A.; Kino, Motoki; Zhao, Guang-Yao; Wajima, Kiyoaki; Kang, Sincheol; Oh, Junghwan; Lee, Taeseok; Byun, Do-Young; Kim, Soon-Wook; Kim, Jeong-Sook

2017-12-01

We present a study of the inexplicit connection between radio jet activity and γ-ray emission of BL Lacertae (BL Lac; 2200+420). We analyze the long-term millimeter activity of BL Lac via interferometric observations with the Korean VLBI Network (KVN) obtained at 22, 43, 86, and 129 GHz simultaneously over three years (from January 2013 to March 2016); during this time, two γ-ray outbursts (in November 2013 and March 2015) can be seen in γ-ray light curves obtained from Fermi observations. The KVN radio core is optically thick at least up to 86 GHz; there is indication that it might be optically thin at higher frequencies. To first order, the radio light curves decay exponentially over the time span covered by our observations, with decay timescales of 411±85 days, 352±79 days, 310±57 days, and 283±55 days at 22, 43, 86, and 129 GHz, respectively. Assuming synchrotron cooling, a cooling time of around one year is consistent with magnetic field strengths B=2 μT and electron Lorentz factors γ=10,000. Taking into account that our formal measurement errors include intrinsic variability and thus over-estimate the statistical uncertainties, we find that the decay timescale τ scales with frequency ν like τ∝ν^{-0.2}. This relation is much shallower than the one expected from opacity effects (core shift), but in agreement with the (sub-)mm radio core being a standing recollimation shock. We do not find convincing radio flux counterparts to the γ-ray outbursts. The spectral evolution is consistent with the 'generalized shock model' of Valtaoja et al. (1992). A temporary increase in the core opacity and the emergence of a knot around the time of the second γ-ray event indicate that this γ-ray outburst might be an 'orphan' flare powered by the 'ring of fire' mechanism.

Radio Flares from Gamma-ray Bursts

NASA Astrophysics Data System (ADS)

Kopač, D.; Mundell, C. G.; Kobayashi, S.; Virgili, F. J.; Harrison, R.; Japelj, J.; Guidorzi, C.; Melandri, A.; Gomboc, A.

2015-06-01

We present predictions of centimeter and millimeter radio emission from reverse shocks (RSs) in the early afterglows of gamma-ray bursts (GRBs) with the goal of determining their detectability with current and future radio facilities. Using a range of GRB properties, such as peak optical brightness and time, isotropic equivalent gamma-ray energy, and redshift, we simulate radio light curves in a framework generalized for any circumburst medium structure and including a parameterization of the shell thickness regime that is more realistic than the simple assumption of thick- or thin-shell approximations. Building on earlier work by Mundell et al. and Melandri et al. in which the typical frequency of the RS was suggested to lie at radio rather than optical wavelengths at early times, we show that the brightest and most distinct RS radio signatures are detectable up to 0.1-1 day after the burst, emphasizing the need for rapid radio follow-up. Detection is easier for bursts with later optical peaks, high isotropic energies, lower circumburst medium densities, and at observing frequencies that are less prone to synchrotron self-absorption effects—typically above a few GHz. Given recent detections of polarized prompt gamma-ray and optical RS emission, we suggest that detection of polarized radio/millimeter emission will unambiguously confirm the presence of low-frequency RSs at early time.

Stacking Searches for Greater Than 100 MeV Gamma Ray Emission from Radio Galaxies and Seyfert Galaxies

NASA Technical Reports Server (NTRS)

Cillis, A. N.; Hartman, R. C.; Bertsch, D. L.

2003-01-01

The EGRET telescope on CGRO detected more than sixty sources of high-energy gamma radiation associated with active galactic nuclei (AGN). All but one of those belong to the blazar subclass; the only exception is the nearby radio galaxy Centaurus A. Since there is no obvious reason other than proximity to expect Cen A to be the only non-blazar AGN emitting in high-energy gamma rays, we have utilized the "stacking" technique to search for $>100$-MeV emission from two non-blazar AGN subclasses, radio galaxies and Seyfert galaxies. Maps of gamma-ray counts, exposure, and diffuse background have been created, then co-added in varying numbers based on sorts by redshift, 5-GHZ flux density, and optical brightness, and finally tested for gamma-ray emission. No detection significance greater than $2\\sigma$ has been found for any subclass, sorting parameter, or number of objects co-added. Monte Carlo simulations have also been performed, to validate the technique and estimate the significance of the results.

Effect of laser intensity on radio frequency emissions from laser induced breakdown of atmospheric air

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

Vinoth Kumar, L.; Manikanta, E.; Leela, Ch.

2016-06-07

The studies on the effect of input laser intensity, through the variation of laser focusing geometry, on radio frequency (RF) emissions, over 30–1000 MHz from nanosecond (ns) and picosecond (ps) laser induced breakdown (LIB) of atmospheric air are presented. The RF emissions from the ns and ps LIB were observed to be decreasing and increasing, respectively, when traversed from tight to loose focusing conditions. The angular and radial intensities of the RF emissions from the ns and ps LIB are found to be consistent with sin{sup 2}θ/r{sup 2} dependence of the electric dipole radiation. The normalized RF emissions were observed tomore » vary with incident laser intensity (Iλ{sup 2}), indicating the increase in the induced dipole moment at moderate input laser intensities and the damping of radiation due to higher recombination rate of plasma at higher input laser intensities.« less

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09

NASA Astrophysics Data System (ADS)

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; Mitra, D.; Rankin, J. M.; Stappers, B. W.; Wright, G. A. E.; Basu, R.; Szary, A.; van Leeuwen, J.

2017-04-01

We report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09 with ESA's XMM-Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2-1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ˜0.15 at 0.3 keV to ˜0.6 at 1 keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ˜0.96 × 106 K, hotspot radius R ˜2.0 km) and a hot component (T ˜2.2 × 106 K, R ˜100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822-09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055-52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822-09, which might be a pulsar wind nebula.

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822$-$09

DOE PAGES

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; ...

2016-12-05

Here, we report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822–09 with ESA's XMM–Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822–09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2–1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1more » keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~0.96 × 10 6 K, hotspot radius R ~2.0 km) and a hot component (T ~2.2 × 10 6 K, R ~100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822–09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055–52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822–09, which might be a pulsar wind nebula.« less

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822$-$09

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

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.

Here, we report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822–09 with ESA's XMM–Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822–09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2–1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1more » keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~0.96 × 10 6 K, hotspot radius R ~2.0 km) and a hot component (T ~2.2 × 10 6 K, R ~100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822–09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055–52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822–09, which might be a pulsar wind nebula.« less

Strange doings on Io. [Jupiter radio emission modification, sodium cloud, ionized sulfur and extreme brightness

NASA Technical Reports Server (NTRS)

Goody, R.

1978-01-01

Some unusual properties of Io are discussed, and possible explanations for these are considered. The properties discussed include Io's ability to modify radio waves emitted by Jupiter in the decametric band, the satellite's ionosphere and sodium cloud, its extraordinary brightness, and the presence of ionized sulfur just inside the satellite's orbit. Io's ability to modulate Jovian decametric radio emission is explained on the basis of the hypothesis that the satellite conducts electricity and interacts with Jupiter's magnetic field. Characteristics of the sodium cloud are reviewed, and the probable mechanism responsible for this cloud is outlined. It is concluded that the only plausible explanation for the brightness of Io is the presence of cat's-eye-type reflectors, possibly composed of crystalline deposits, on the satellite's surface.

Radio Emission from Three-dimensional Relativistic Hydrodynamic Jets: Observational Evidence of Jet Stratification

NASA Astrophysics Data System (ADS)

Aloy, Miguel-Angel; Gómez, José-Luis; Ibáñez, José-María; Martí, José-María; Müller, Ewald

2000-01-01

We present the first radio emission simulations from high-resolution three-dimensional relativistic hydrodynamic jets; these simulations allow us to study the observational implications of the interaction between the jet and the external medium. This interaction gives rise to a stratification of the jet in which a fast spine is surrounded by a slow high-energy shear layer. The stratification (in particular, the large specific internal energy and slow flow in the shear layer) largely determines the emission from the jet. If the magnetic field in the shear layer becomes helical (e.g., resulting from an initial toroidal field and an aligned field component generated by shear), the emission shows a cross section asymmetry, in which either the top or the bottom of the jet dominates the emission. This, as well as limb or spine brightening, is a function of the viewing angle and flow velocity, and the top/bottom jet emission predominance can be reversed if the jet changes direction with respect to the observer or if it presents a change in velocity. The asymmetry is more prominent in the polarized flux because of field cancellation (or amplification) along the line of sight. Recent observations of jet cross section emission asymmetries in the blazar 1055+018 can be explained by assuming the existence of a shear layer with a helical magnetic field.

Direction of Arrival Measurements of Auroral Medium Frequency Burst Radio Emissions at Toolik Lake, AK

NASA Astrophysics Data System (ADS)

Bunch, N. L.; Labelle, J. W.; Hughes, J. M.; Weatherwax, A. T.; Ye, S.; Lummerzheim, D.

2007-12-01

MF burst is an impulsive radio emission of auroral origin detected by ground-based instruments approximately between 1,300 and 3,700 kHz, and associated with substorm onsets. Its exact generation mechanism is unknown, though it has been speculated that it arises from mode conversion radiation. To discover the generation mechanism and the relation of MF burst to auroral processes, Dartmouth has deployed radio interferometers in Alaska, Northern Canada, Greenland, and Antarctica, including a three-element interferometer deployed at Toolik Lake Field Station in Alaska in 2006. This instrument measured spectra, amplitudes, and directions of arrival (DOA's) of over 47 MF burst events occurring between November 30, 2006 and May 26, 2007. These represent the first DOA measurements ever reported for the impulsive MF burst phenomenon. Preliminary analysis shows that the events originated from a wide range of directions in the sky, with all azimuths represented in the distribution of DOA's. The DOA of each individual event is well-defined, however. Many events show apparent motion, with southward motions more common than northward among the subset of events analyzed so far. Some of the events were detected simultaneously on an interferometer deployed at Kaktovik, Alaska, 400 km away. The all-sky imager at Toolik Lake was also operational for some events. Further analysis of these data promises to reveal first information about the locations and motions of MF burst sources, a first step towards discovering the generation mechanism of this mysterious radio emission and its relation to auroral processes.

The Sun Radio Imaging Space Experiment (SunRISE) Mission

NASA Astrophysics Data System (ADS)

Lazio, Joseph; Kasper, Justin; Maksimovic, Milan; Alibay, Farah; Amiri, Nikta; Bastian, Tim; Cohen, Christina; Landi, Enrico; Manchester, Ward; Reinard, Alysha; Schwadron, Nathan; Cecconi, Baptiste; Hallinan, Gregg; Hegedus, Alex; Krupar, Vratislav; Zaslavsky, Arnaud

2017-04-01

Radio emission from coronal mass ejections (CMEs) is a direct tracer of particle acceleration in the inner heliosphere and potential magnetic connections from the lower solar corona to the larger heliosphere. Energized electrons excite Langmuir waves, which then convert into intense radio emission at the local plasma frequency, with the most intense acceleration thought to occur within 20 RS. The radio emission from CMEs is quite strong such that only a relatively small number of antennas is required to detect and map it, but many aspects of this particle acceleration and transport remain poorly constrained. Ground-based arrays would be quite capable of tracking the radio emission associated with CMEs, but absorption by the Earth's ionosphere limits the frequency coverage of ground-based arrays (ν ≳ 15 MHz), which in turn limits the range of solar distances over which they can track the radio emission (≲ 3RS). The state-of-the-art for tracking such emission from space is defined by single antennas (Wind/WAVES, Stereo/SWAVES), in which the tracking is accomplished by assuming a frequency-to-density mapping; there has been some success in triangulating the emission between the spacecraft, but considerable uncertainties remain. We describe the Sun Radio Imaging Space Experiment (SunRISE) mission concept: A constellation of small spacecraft in a geostationary graveyard orbit designed to localize and track radio emissions in the inner heliosphere. Each spacecraft would carry a receiving system for observations below 25 MHz, and SunRISE would produce the first images of CMEs more than a few solar radii from the Sun. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

The Sun Radio Imaging Space Experiment (SunRISE) Mission

NASA Astrophysics Data System (ADS)

Kasper, J. C.; Lazio, J.; Alibay, F.; Amiri, N.; Bastian, T.; Cohen, C.; Landi, E.; Hegedus, A. M.; Maksimovic, M.; Manchester, W.; Reinard, A.; Schwadron, N.; Cecconi, B.; Hallinan, G.; Krupar, V.

2017-12-01

Radio emission from coronal mass ejections (CMEs) is a direct tracer of particle acceleration in the inner heliosphere and potential magnetic connections from the lower solar corona to the larger heliosphere. Energized electrons excite Langmuir waves, which then convert into intense radio emission at the local plasma frequency, with the most intense acceleration thought to occur within 20 R_S. The radio emission from CMEs is quite strong such that only a relatively small number of antennas is required to detect and map it, but many aspects of this particle acceleration and transport remain poorly constrained. Ground-based arrays would be quite capable of tracking the radio emission associated with CMEs, but absorption by the Earth's ionosphere limits the frequency coverage of ground-based arrays (nu > 15 MHz), which in turn limits the range of solar distances over which they can track the radio emission (< 3 R_S). The state-of-the-art for tracking such emission from space is defined by single antennas (Wind/WAVES, Stereo/SWAVES), in which the tracking is accomplished by assuming a frequency-to-density mapping; there has been some success in triangulating the emission between the spacecraft, but considerable uncertainties remain. We describe the Sun Radio Imaging Space Experiment (SunRISE) mission concept: A constellation of small spacecraft in a geostationary graveyard orbit designed to localize and track radio emissions in the inner heliosphere. Each spacecraft would carry a receiving system for observations below 25 MHz, and SunRISE would produce the first images of CMEs more than a few solar radii from the Sun. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Coincident bursts of auroral kilometric radiation and VLF emissions associted with a type 3 solar radio noise event

NASA Technical Reports Server (NTRS)

Rosenberg, T. J.; Singh, S.; Wu, C. S.; Labelle, J.; Treumann, R. A.; Inan, U. S.; Lanzerotti, L. J.

1995-01-01

This paper examines an isolated magnetospheric VLF/radio noise event that is highly suggestive of the triggering of terrestrial auroral kilometric radiation (AKR) bu solar type III radio emission and of a close relation between AKR and broadband hiss. The solar type III burst was measured on polar HF riometers and was coincident with local dayside VLF/LF noise emission bursts at South Pole station. It was also coincident with AKR bursts detected onthe AMPTE/IRM satellite, at the same magnetic local time as South Pole. On the basis of the close association of AKR and VLF bursts, and from geometric considerations relating to wave propagation, it is likely that the AKR source was on the dayside and on field lines near South Pole station. The general level of geomagnetic activity was very low. However, an isolated magnetic impulse event (MIE) accompanied by a riometer absorption pulse was in progress when all of the VLF/radio noise bursts occurred. The very close association of the typew III burst at HF with the AKR is consistent with external stimulation of the AKR, is different, more immediate,triggering process than that implied by Calvert (1981) is invoked. It is suggested here that some of the HF solar radiant energy may decay into waves with frequences comparable to those of the AKR by paraetric excitation or some other process, thus providing the few background photons required for the generation of AKR by the WU and Lee (1979) cyclotron maser instability. The AKR, perhaps by modifying the magnetospheric electron velocity distribution, might have produced the observed VLF emissions. Alternatively, the VLF emissions may have arisen from the same anisotropic and unstable electron distribution function responsible for the AKR.

The ``X component'' of the radio background

NASA Astrophysics Data System (ADS)

Semenova, T. A.; Pariiskii, Yu. N.; Bursov, N. N.

2009-01-01

The recent publication of evidence for a new mechanism producing background radio emission of the Galaxy at centimeter wavelengths (in addition to synchrotron radiation, free—free transitions in ionized gas, and the weak radio emission of standard dust) gave rise to a strong reaction among observers, and requires independent experimental verification. This signal is of special concern in connection with studies of the polarization of the cosmic microwave background (CMB) using new-generation experiments. We have derived independent estimates of the validity of the “spinning-dust” hypothesis (dipole emission of macromolecules) using multi-frequency RATAN-600 observations. Test studies in the Perseus molecular cloud show evidence for anomalous extended emission in the absence of strong radio sources (compact HII regions) that could imitate an anomalous radio spectrum in this region. A statistical analysis at centimeter wavelengths over the Ratan Zenith Field shows that the upper limit for the polarized noise from this new component in the spinning-dust hypothesis is unlikely to exceed 1 µK at wavelengths of 1 cm or shorter on the main scales of the EE mode of Sakharov oscillations. Thus, this emission should not hinder studies of this mode, at least to within several percent of the predicted level of polarization of the CMB emission.

Field emission from ZnS nanorods synthesized by radio frequency magnetron sputtering technique

NASA Astrophysics Data System (ADS)

Ghosh, P. K.; Maiti, U. N.; Jana, S.; Chattopadhyay, K. K.

2006-11-01

The field emission property of zinc sulphides nanorods synthesized in the thin film form on Si substrates has been studied. It is seen that ZnS nanorod thin films showed good field emission properties with a low-macroscopic turn-on field (2.9-6.3 V/μm). ZnS nanorods were synthesized by using radio frequency magnetron sputtering of a polycrystalline prefabricated ZnS target at a relatively higher pressure (10 -1 mbar) and at a lower substrate temperature (233-273 K) without using any catalyst. Transmission electron microscopic image showed the formation of ZnS nanorods with high aspect ratio (>60). The field emission data were analysed using Fowler-Nordhiem theory and the nearly straight-line nature of the F-N plots confirmed cold field emission of electrons. It was also found that the turn-on field decreased with the decrease of nanorod's diameters. The optical properties of the ZnS nanorods were also studied. From the measurements of transmittance of the films deposited on glass substrates, the direct allowed bandgap values have been calculated and they were in the range 3.83-4.03 eV. The thickness of the films was ˜600 nm.

Constraints on the dark matter neutralinos from the radio emissions of galaxy clusters

NASA Astrophysics Data System (ADS)

Kiew, Ching-Yee; Hwang, Chorng-Yuan; Zainal Abibin, Zamri

2017-05-01

By assuming the dark matter to be composed of neutralinos, we used the detection of upper limit on diffuse radio emission in a sample of galaxy clusters to put constraint on the properties of neutralinos. We showed the upper limit constraint on <σv>-mχ space with neutralino annihilation through b\\bar{b} and μ+μ- channels. The best constraint is from the galaxy clusters A2199 and A1367. We showed the uncertainty due to the density profile and cluster magnetic field. The largest uncertainty comes from the uncertainty in dark matter spatial distribution. We also investigated the constraints on minimal Supergravity (mSUGRA) and minimal supersymmetric standard model (MSSM) parameter space by scanning the parameters using the darksusy package. By using the current radio observation, we managed to exclude 40 combinations of mSUGRA parameters. On the other hand, 573 combinations of MSSM parameters can be excluded by current observation.

RADIO MONITORING OF THE TIDAL DISRUPTION EVENT SWIFT J164449.3+573451. II. THE RELATIVISTIC JET SHUTS OFF AND A TRANSITION TO FORWARD SHOCK X-RAY/RADIO EMISSION

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

Zauderer, B. A.; Berger, E.; Margutti, R.

2013-04-20

We present continued multi-frequency radio observations of the relativistic tidal disruption event Swift J164449.3+573451 (Sw 1644+57) extending to t Almost-Equal-To 600 days. The data were obtained with the JVLA and AMI Large Array as part of our on-going study of the jet energetics and the density structure of the parsec-scale environment around the disrupting supermassive black hole. We combine these data with public Swift/XRT and Chandra X-ray observations over the same time-frame to show that the jet has undergone a dramatic transition starting at Almost-Equal-To 500 days, with a sharp decline in the X-ray flux by about a factor ofmore » 170 on a timescale of {delta}t/t {approx}< 0.2 (and by a factor of 15 in {delta}t/t Almost-Equal-To 0.05). The rapid decline rules out a forward shock origin (direct or reprocessing) for the X-ray emission at {approx}< 500 days, and instead points to internal dissipation in the inner jet. On the other hand, our radio data uniquely demonstrate that the low X-ray flux measured by Chandra at Almost-Equal-To 610 days is consistent with emission from the forward shock. Furthermore, the Chandra data are inconsistent with thermal emission from the accretion disk itself since the expected temperature of {approx}30-60 eV and inner radius of {approx}2-10 R{sub s} cannot accommodate the observed flux level or the detected emission at {approx}> 1 keV. We associate the rapid decline with a turn off of the relativistic jet when the mass accretion rate dropped below {approx} M-dot{sub Edd}{approx}0.006 M{sub Sun} yr{sup -1} (for a 3 Multiplication-Sign 10{sup 6} M{sub Sun} black hole and order unity efficiency) indicating that the peak accretion rate was about 330 M-dot{sub Edd}, and the total accreted mass by t Almost-Equal-To 500 days is about 0.15 M{sub Sun }. From the radio data we further find significant flattening in the integrated energy of the forward shock at t {approx}> 250 days with E{sub j,iso} Almost-Equal-To 2 Multiplication

Artificial optical emissions in the thermosphere induced by powerful radio waves: A review

NASA Astrophysics Data System (ADS)

Kosch, M.; Senior, A.; Gustavsson, B.; Grach, S.; Pedersen, T.; Rietveld, M.

High-power high-frequency radio waves beamed into the ionosphere with O-mode polarization cause plasma turbulence which can accelerate electrons These electrons collide with the F-layer neutrals causing artificial optical emissions identical to natural aurora The brightest optical emissions are O 1D 630 nm with a threshold of 2 eV and O 1S 557 7 nm with a threshold of 4 2 eV The optical emissions give direct evidence of electron acceleration by plasma turbulence as well as their non-Maxwellian energy spectrum HF pumping of the ionosphere also causes electron temperature enhancements but these alone are not sufficient to explain the optical emissions EISCAT plasma-line measurements indicate that the enhanced electron temperatures are consistent with the bulk of the electrons having a Maxwellian energy spectrum Novel discoveries include 1 Very large electron temperature enhancements of several 1000 K which maximise along the magnetic field line direction 2 Ion temperature enhancements of a few 100 K 3 Large ion outflows exceeding 200 m s 4 The F-layer optical emission maximizes sharply near the magnetic zenith with clear evidence of self-focusing 5 The optical emission generally appears below the HF pump reflection altitude as well as the upper-hybrid resonance height 6 The optical emission and HF coherent radar backscatter generally minimize when pumping on the third or higher electron gyro-harmonic frequency suggesting upper-hybrid waves as the primary mechanism 7 The optical emissions and HF coherent backscatter are enhanced on the

Direction-Finding Measurements of Heliospheric 2-3 kHz Radio Emissions

NASA Technical Reports Server (NTRS)

Gurnett, Donald A.

1998-01-01

Using data from the Voyager 1 plasma wave instrument, a series of direction-finding measurements is presented for the intense 1992-93 heliospheric 2- to 3-kHz radio emission event, and several weaker events extending into 1994. Direction-finding measurements can only be obtained during roll maneuvers, which are performed about once every three months. Two parameters can be determined from the roll-induced intensity modulation, the azimuthal direction of arrival (measured around the roll axis), and the modulation index (the peak-to-peak amplitude divided by the peak amplitude). Measurements were made at two frequencies, 1.78 and 3.11 kHz. No roll modulation was observed at 1.78 kHz, which is consistent with an isotropic source at this frequency. In most cases an easily measurable roll modulation was detectable at 3.11 kHz. Although the azimuth angles have considerable scatter, the directions of arrival at 3.11 kHz can be organized into three groups, each of which appears to be associated with a separate upward drifting feature in the radio emission spectrum. The first group, which is associated with the main 1992-93 event, is consistent with a source located near the nose of the heliosphere. The remaining two groups, which occur after the main 1992-93 event, have azimuth angles well away from the nose of the heliosphere. The modulation indexes vary over a large range, from 0.06 to 0.61, with no obvious trend. Although the variations in the directions of arrival and modulation indicies appear to reflect changes in the position and angular size of the source, it is also possible that they could be caused by refraction or scattering due to density structures in the solar wind.

A galactic microquasar mimicking winged radio galaxies.

PubMed

Martí, Josep; Luque-Escamilla, Pedro L; Bosch-Ramon, Valentí; Paredes, Josep M

2017-11-24

A subclass of extragalactic radio sources known as winged radio galaxies has puzzled astronomers for many years. The wing features are detected at radio wavelengths as low-surface-brightness radio lobes that are clearly misaligned with respect to the main lobe axis. Different models compete to account for these peculiar structures. Here, we report observational evidence that the parsec-scale radio jets in the Galactic microquasar GRS 1758-258 give rise to a Z-shaped radio emission strongly reminiscent of the X and Z-shaped morphologies found in winged radio galaxies. This is the first time that such extended emission features are observed in a microquasar, providing a new analogy for its extragalactic relatives. From our observations, we can clearly favour the hydrodynamic backflow interpretation against other possible wing formation scenarios. Assuming that physical processes are similar, we can extrapolate this conclusion and suggest that this mechanism could also be at work in many extragalactic cases.

Modelling blazar flaring using a time-dependent fluid jet emission model - an explanation for orphan flares and radio lags

NASA Astrophysics Data System (ADS)

Potter, William J.

2018-01-01

Blazar jets are renowned for their rapid violent variability and multiwavelength flares, however, the physical processes responsible for these flares are not well understood. In this paper, we develop a time-dependent inhomogeneous fluid jet emission model for blazars. We model optically thick radio flares for the first time and show that they are delayed with respect to the prompt optically thin emission by ∼months to decades, with a lag that increases with the jet power and observed wavelength. This lag is caused by a combination of the travel time of the flaring plasma to the optically thin radio emitting sections of the jet and the slow rise time of the radio flare. We predict two types of flares: symmetric flares - with the same rise and decay time, which occur for flares whose duration is shorter than both the radiative lifetime and the geometric path-length delay time-scale; extended flares - whose luminosity tracks the power of particle acceleration in the flare, which occur for flares with a duration longer than both the radiative lifetime and geometric delay. Our model naturally produces orphan X-ray and γ-ray flares. These are caused by flares that are only observable above the quiescent jet emission in a narrow band of frequencies. Our model is able to successfully fit to the observed multiwavelength flaring spectra and light curves of PKS1502+106 across all wavelengths, using a transient flaring front located within the broad-line region.

Wave propagation and earth satellite radio emission studies

NASA Technical Reports Server (NTRS)

Yeh, K. C.; Liu, C. H.; Flaherty, B. J.

1974-01-01

Radio propagation studies of the ionosphere using satellite radio beacons are described. The ionosphere is known as a dispersive, inhomogeneous, irregular and sometimes even nonlinear medium. After traversing through the ionosphere the radio signal bears signatures of these characteristics. A study of these signatures will be helpful in two areas: (1) It will assist in learning the behavior of the medium, in this case the ionosphere. (2) It will provide information of the kind of signal characteristics and statistics to be expected for communication and navigational satellite systems that use the similar geometry.

First limits on the very-high energy gamma-ray afterglow emission of a fast radio burst. H.E.S.S. observations of FRB 150418

NASA Astrophysics Data System (ADS)

H.E.S.S. Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Andersson, T.; Angüner, E. O.; Arakawa, M.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Becker Tjus, J.; Berge, D.; Bernhard, S.; Bernlöhr, K.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Büchele, M.; Bulik, T.; Capasso, M.; Carr, J.; Casanova, S.; Cerruti, M.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Chrétien, M.; Coffaro, M.; Colafrancesco, S.; Cologna, G.; Condon, B.; Conrad, J.; Cui, Y.; Davids, I. D.; Decock, J.; Degrange, B.; Deil, C.; Devin, J.; Dewilt, P.; Dirson, L.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O.'c.; Dutson, K.; Dyks, J.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Hahn, J.; Haupt, M.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Iwasaki, H.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jogler, T.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katsuragawa, M.; Katz, U.; Kerszberg, D.; Khangulyan, D.; Khélifi, B.; Kieffer, M.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lefranc, V.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Lohse, T.; Lorentz, M.; Liu, R.; López-Coto, R.; Lypova, I.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Mohrmann, L.; Morå, K.; Moulin, E.; Murach, T.; Nakashima, S.; de Naurois, M.; Niederwanger, F.; Niemiec, J.; Oakes, L.; O'Brien, P.; Odaka, H.; Öttl, S.; Ohm, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Pekeur, N. W.; Pelletier, G.; Perennes, C.; Petrucci, P.-O.; Peyaud, B.; Piel, Q.; Pita, S.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reimer, A.; Reimer, O.; Renaud, M.; de Los Reyes, R.; Richter, S.; Rieger, F.; Romoli, C.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Saito, S.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seglar-Arroyo, M.; Settimo, M.; Seyffert, A. S.; Shafi, N.; Shilon, I.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stycz, K.; Sushch, I.; Takahashi, T.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tibaldo, L.; Tiziani, D.; Tluczykont, M.; Trichard, C.; Tsuji, N.; Tuffs, R.; Uchiyama, Y.; van der Walt, D. J.; van Eldik, C.; van Rensburg, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zanin, R.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Żywucka, N.; Superb Collaboration; Jankowski, F.; Keane, E. F.; Petroff, E.

2017-01-01

Aims: Following the detection of the fast radio burst FRB150418 by the SUPERB project at the Parkes radio telescope, we aim to search for very-high energy gamma-ray afterglow emission. Methods: Follow-up observations in the very-high energy gamma-ray domain were obtained with the H.E.S.S. imaging atmospheric Cherenkov telescope system within 14.5 h of the radio burst. Results: The obtained 1.4 h of gamma-ray observations are presented and discussed. At the 99% C.L. we obtained an integral upper limit on the gamma-ray flux of Φγ(E > 350 GeV) < 1.33 × 10-8 m-2 s-1. Differential flux upper limits as function of the photon energy were derived and used to constrain the intrinsic high-energy afterglow emission of FRB 150418. Conclusions: No hints for high-energy afterglow emission of FRB 150418 were found. Taking absorption on the extragalactic background light into account and assuming a distance of z = 0.492 based on radio and optical counterpart studies and consistent with the FRB dispersion, we constrain the gamma-ray luminosity at 1 TeV to L < 5.1 × 1047 erg/s at 99% C.L.

Activity-dependent trafficking of lysosomes in dendrites and dendritic spines.

PubMed

Goo, Marisa S; Sancho, Laura; Slepak, Natalia; Boassa, Daniela; Deerinck, Thomas J; Ellisman, Mark H; Bloodgood, Brenda L; Patrick, Gentry N

2017-08-07

In neurons, lysosomes, which degrade membrane and cytoplasmic components, are thought to primarily reside in somatic and axonal compartments, but there is little understanding of their distribution and function in dendrites. Here, we used conventional and two-photon imaging and electron microscopy to show that lysosomes traffic bidirectionally in dendrites and are present in dendritic spines. We find that lysosome inhibition alters their mobility and also decreases dendritic spine number. Furthermore, perturbing microtubule and actin cytoskeletal dynamics has an inverse relationship on the distribution and motility of lysosomes in dendrites. We also find trafficking of lysosomes is correlated with synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors. Strikingly, lysosomes traffic to dendritic spines in an activity-dependent manner and can be recruited to individual spines in response to local activation. These data indicate the position of lysosomes is regulated by synaptic activity and thus plays an instructive role in the turnover of synaptic membrane proteins. © 2017 Goo et al.

Activity-dependent trafficking of lysosomes in dendrites and dendritic spines

PubMed Central

Sancho, Laura; Slepak, Natalia; Boassa, Daniela; Deerinck, Thomas J.; Ellisman, Mark H.

2017-01-01

In neurons, lysosomes, which degrade membrane and cytoplasmic components, are thought to primarily reside in somatic and axonal compartments, but there is little understanding of their distribution and function in dendrites. Here, we used conventional and two-photon imaging and electron microscopy to show that lysosomes traffic bidirectionally in dendrites and are present in dendritic spines. We find that lysosome inhibition alters their mobility and also decreases dendritic spine number. Furthermore, perturbing microtubule and actin cytoskeletal dynamics has an inverse relationship on the distribution and motility of lysosomes in dendrites. We also find trafficking of lysosomes is correlated with synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid–type glutamate receptors. Strikingly, lysosomes traffic to dendritic spines in an activity-dependent manner and can be recruited to individual spines in response to local activation. These data indicate the position of lysosomes is regulated by synaptic activity and thus plays an instructive role in the turnover of synaptic membrane proteins. PMID:28630145

The VLA Nascent Disk And Multiplicity Survey of Perseus Protostars (VANDAM). III. Extended Radio Emission from Protostars in Perseus

NASA Astrophysics Data System (ADS)

Tychoniec, Łukasz; Tobin, John J.; Karska, Agata; Chandler, Claire; Dunham, Michael M.; Li, Zhi-Yun; Looney, Leslie W.; Segura-Cox, Dominique; Harris, Robert J.; Melis, Carl; Sadavoy, Sarah I.

2018-01-01

Centimeter continuum emission from protostars offers insight into the innermost part of the outflows, as shock-ionized gas produces free–free emission. We observed a complete population of Class 0 and I protostars in the Perseus molecular cloud at 4.1 and 6.4 cm with resolution and sensitivity superior to previous surveys. From a total of 71 detections, eight sources exhibit resolved emission at 4.1 cm and/or 6.4 cm. In this paper, we focus on this subsample, analyzing their spectral indices along the jet and their alignment with respect to the large-scale molecular outflow. Spectral indices for fluxes integrated toward the position of the protostar are consistent with free–free thermal emission. The value of the spectral index along a radio jet decreases with distance from the protostar. For six sources, emission is well aligned with the outflow central axis, showing that we observe the ionized base of the jet. This is not the case for two sources, where we note misalignment of the emission with respect to the large-scale outflow. This might indicate that the emission does not originate in the radio jet, but rather in an ionized outflow cavity wall or disk surface. For five of the sources, the spectral indices along the jet decrease well below the thermal free–free limit of ‑0.1 with > 2σ significance. This is indicative of synchrotron emission, meaning that high-energy electrons are being produced in the outflows close to the disk. This result can have far-reaching implications for the chemical composition of the embedded disks.

RESOLVE: A new algorithm for aperture synthesis imaging of extended emission in radio astronomy

NASA Astrophysics Data System (ADS)

Junklewitz, H.; Bell, M. R.; Selig, M.; Enßlin, T. A.

2016-02-01

We present resolve, a new algorithm for radio aperture synthesis imaging of extended and diffuse emission in total intensity. The algorithm is derived using Bayesian statistical inference techniques, estimating the surface brightness in the sky assuming a priori log-normal statistics. resolve estimates the measured sky brightness in total intensity, and the spatial correlation structure in the sky, which is used to guide the algorithm to an optimal reconstruction of extended and diffuse sources. During this process, the algorithm succeeds in deconvolving the effects of the radio interferometric point spread function. Additionally, resolve provides a map with an uncertainty estimate of the reconstructed surface brightness. Furthermore, with resolve we introduce a new, optimal visibility weighting scheme that can be viewed as an extension to robust weighting. In tests using simulated observations, the algorithm shows improved performance against two standard imaging approaches for extended sources, Multiscale-CLEAN and the Maximum Entropy Method.

Portable Wireless Device Threat Assessment for Aircraft Navigation Radios

NASA Technical Reports Server (NTRS)

Nguyen, Truong X.; Koppen, Sandra V.; Ely, Jay J.; Williams, Reuben A.; Smith, Laura J.; Salud, Maria Theresa P.

2004-01-01

This paper addresses the concern for Wireless Local Area Network devices and two-way radios to cause electromagnetic interference to aircraft navigation radio systems. Spurious radiated emissions from various IEEE 802.11a, 802.11b, and Bluetooth devices are characterized using reverberation chambers. The results are compared with baseline emissions from standard laptop computer and personal digital assistants (PDAs) that are currently allowed for use on aircraft. The results indicate that the WLAN devices tested are not more of a threat to aircraft navigation radios than standard laptop computers and PDAs in most aircraft bands. In addition, spurious radiated emission data from seven pairs of two-way radios are provided. These two-way radios emit at much higher levels in the bands considered. A description of the measurement process, device modes of operation and the measurement results are reported.

Plasma and radio waves from Neptune: Source mechanisms and propagation

NASA Astrophysics Data System (ADS)

Wong, H. K.

1994-03-01

This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

Plasma and radio waves from Neptune: Source mechanisms and propagation

NASA Technical Reports Server (NTRS)

Wong, H. K.

1994-01-01

This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

3C 57 as an atypical radio-loud quasar: implications for the radio-loud/radio-quiet dichotomy

NASA Astrophysics Data System (ADS)

Sulentic, J. W.; Martínez-Carballo, M. A.; Marziani, P.; del Olmo, A.; Stirpe, G. M.; Zamfir, S.; Plauchu-Frayn, I.

2015-06-01

Lobe-dominated radio-loud (LD RL) quasars occupy a restricted domain in the 4D Eigenvector 1 (4DE1) parameter space which implies restricted geometry/physics/kinematics for this subclass compared to the radio-quiet (RQ) majority of quasars. We discuss how this restricted domain for the LD RL parent population supports the notion for a RQ-RL dichotomy among type 1 sources. 3C 57 is an atypical RL quasar that shows both uncertain radio morphology and falls in a region of 4DE1 space where RL quasars are rare. We present new radio flux and optical spectroscopic measures designed to verify its atypical optical/UV spectroscopic behaviour and clarify its radio structure. The former data confirms that 3C 57 falls off the 4DE1 quasar `main sequence' with both extreme optical Fe II emission (R_{Fe II} ˜ 1) and a large C IV λ1549 profile blueshift (˜-1500 km s-1). These parameter values are typical of extreme Population A sources which are almost always RQ. New radio measures show no evidence for flux change over a 50+ year time-scale consistent with compact steep-spectrum (or young LD) over core-dominated morphology. In the 4DE1 context where LD RL are usually low L/LEdd quasars, we suggest that 3C 57 is an evolved RL quasar (i.e. large blackhole mass) undergoing a major accretion event leading to a rejuvenation reflected by strong Fe II emission, perhaps indicating significant heavy metal enrichment, high bolometric luminosity for a low-redshift source and resultant unusually high Eddington ratio giving rise to the atypical C IV λ1549.

Suzaku observations of γ-ray bright radio galaxies: Origin of the x-ray emission and broadband modeling

DOE PAGES

Fukazawa, Yasushi; Finke, Justin; Stawarz, Łukasz; ...

2014-12-24

Here, we performed a systematic X-ray study of eight nearby γ-ray bright radio galaxies with Suzaku in order to understand the origins of their X-ray emissions. The Suzaku spectra for five of those have been presented previously, while the remaining three (M87, PKS 0625–354, and 3C 78) are presented here for the first time. Based on the Fe-K line strength, X-ray variability, and X-ray power-law photon indices, and using additional information on the [O III] line emission, we argue for a jet origin of the observed X-ray emission in these three sources. We also analyzed five years of Fermi Largemore » Area Telescope (LAT) GeV gamma-ray data on PKS 0625–354 and 3C 78 to understand these sources within the blazar paradigm. We found significant γ-ray variability in the former object. Overall, we note that the Suzaku spectra for both PKS 0625–354 and 3C 78 are rather soft, while the LAT spectra are unusually hard when compared with other γ-ray detected low-power (FR I) radio galaxies. We demonstrate that the constructed broadband spectral energy distributions of PKS 0625–354 and 3C 78 are well described by a one-zone synchrotron/synchrotron self-Compton model. The results of the modeling indicate lower bulk Lorentz factors compared to those typically found in other BL Lacertae (BL Lac) objects, but consistent with the values inferred from modeling other LAT-detected FR I radio galaxies. Interestingly, the modeling also implies very high peak (~10 16 Hz) synchrotron frequencies in the two analyzed sources, contrary to previously suggested scenarios for Fanaroff-Riley (FR) type I/BL Lac unification. Finally, we discuss the implications of our findings in the context of the FR I/BL Lac unification schemes.« less

ATCA observations of the MACS-Planck Radio Halo Cluster Project. II. Radio observations of an intermediate redshift cluster sample

NASA Astrophysics Data System (ADS)

Martinez Aviles, G.; Johnston-Hollitt, M.; Ferrari, C.; Venturi, T.; Democles, J.; Dallacasa, D.; Cassano, R.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Arnaud, M.; Aghanim, N.; Brown, S.; Douspis, M.; Hurier, J.; Intema, H. T.; Langer, M.; Macario, G.; Pointecouteau, E.

2018-04-01

Aim. A fraction of galaxy clusters host diffuse radio sources whose origins are investigated through multi-wavelength studies of cluster samples. We investigate the presence of diffuse radio emission in a sample of seven galaxy clusters in the largely unexplored intermediate redshift range (0.3 < z < 0.44). Methods: In search of diffuse emission, deep radio imaging of the clusters are presented from wide band (1.1-3.1 GHz), full resolution ( 5 arcsec) observations with the Australia Telescope Compact Array (ATCA). The visibilities were also imaged at lower resolution after point source modelling and subtraction and after a taper was applied to achieve better sensitivity to low surface brightness diffuse radio emission. In case of non-detection of diffuse sources, we set upper limits for the radio power of injected diffuse radio sources in the field of our observations. Furthermore, we discuss the dynamical state of the observed clusters based on an X-ray morphological analysis with XMM-Newton. Results: We detect a giant radio halo in PSZ2 G284.97-23.69 (z = 0.39) and a possible diffuse source in the nearly relaxed cluster PSZ2 G262.73-40.92 (z = 0.421). Our sample contains three highly disturbed massive clusters without clear traces of diffuse emission at the observed frequencies. We were able to inject modelled radio haloes with low values of total flux density to set upper detection limits; however, with our high-frequency observations we cannot exclude the presence of RH in these systems because of the sensitivity of our observations in combination with the high z of the observed clusters. The reduced images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A94

Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers.

PubMed

Schellart, P; Trinh, T N G; Buitink, S; Corstanje, A; Enriquez, J E; Falcke, H; Hörandel, J R; Nelles, A; Rachen, J P; Rossetto, L; Scholten, O; Ter Veen, S; Thoudam, S; Ebert, U; Koehn, C; Rutjes, C; Alexov, A; Anderson, J M; Avruch, I M; Bentum, M J; Bernardi, G; Best, P; Bonafede, A; Breitling, F; Broderick, J W; Brüggen, M; Butcher, H R; Ciardi, B; de Geus, E; de Vos, M; Duscha, S; Eislöffel, J; Fallows, R A; Frieswijk, W; Garrett, M A; Grießmeier, J; Gunst, A W; Heald, G; Hessels, J W T; Hoeft, M; Holties, H A; Juette, E; Kondratiev, V I; Kuniyoshi, M; Kuper, G; Mann, G; McFadden, R; McKay-Bukowski, D; McKean, J P; Mevius, M; Moldon, J; Norden, M J; Orru, E; Paas, H; Pandey-Pommier, M; Pizzo, R; Polatidis, A G; Reich, W; Röttgering, H; Scaife, A M M; Schwarz, D J; Serylak, M; Smirnov, O; Steinmetz, M; Swinbank, J; Tagger, M; Tasse, C; Toribio, M C; van Weeren, R J; Vermeulen, R; Vocks, C; Wise, M W; Wucknitz, O; Zarka, P

2015-04-24

We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.

The relationship of storm severity to directionally resolved radio emissions

NASA Technical Reports Server (NTRS)

Johnson, R. O.; Bushman, M. L.; Sherrill, W. M.

1980-01-01

Directionally resolved atmospheric radio frequency emission data were acquired from thunderstorms occurring in the central and southwestern United States. In addition, RF sferic tracking data were obtained from hurricanes and tropical depressions occurring in the Gulf of Mexico. The data were acquired using a crossed baseline phase interferometer operating at a frequency of 2.001 MHz. The received atmospherics were tested for phase linearity across the array, and azimuth/elevation angles of arrival were computed in real time. A histogram analysis of sferic burst count versus azimuth provided lines of bearing to centers of intense electrical activity. Analysis indicates a consistent capability of the phase linear direction finder to detect severe meteorological activity to distances of 2000 km from the receiving site. The technique evidences the ability to discriminate severe storms from nonsevere storms coexistent in large regional scale thunderstorm activity.

VERITAS Upper Limit on the Very High Energy Emission from the Radio Galaxy NGC 1275

DOE PAGES

Acciari, V. A.; Aliu, E.; Arlen, T.; ...

2009-11-16

We report the recent detection by the Fermi γ-ray space telescope of high-energy γ-rays from the radio galaxy NGC 1275 that makes the observation of the very high energy (VHE: E>100 GeV) part of its broadband spectrum particularly interesting, especially for the understanding of active galactic nuclei with misaligned multi-structured jets. The radio galaxy NGC 1275 was recently observed by VERITAS at energies above 100 GeV for about 8 hr. No VHE γ-ray emission was detected by VERITAS from NGC 1275. Finally, a 99% confidence level upper limit of 2.1% of the Crab Nebula flux level is obtained at themore » decorrelation energy of approximately 340 GeV, corresponding to 19% of the power-law extrapolation of the Fermi Large Area Telescope result.« less

X-ray inverse Compton emission from the radio halo of M87. M.S. Thesis

NASA Technical Reports Server (NTRS)

Wood, P. A. D.

1985-01-01

M87 has been observed in the 0.2-4 KeV X-ray band using the High Resolution Imager on the Einstein Observatory, and at 1.452 GHz using the Very Large Array. The radio map showed that the halo contained prominent asymmetries to the east and southwest. The X-ray map indicated similar asymmetries, but they were imbedded in the diffuse hot gas that surrounds the core out to a radius of several arcminutes. The hot X-ray emitting gas was assumed to be spherically symmetric and could, therefore, be subtracted from the image. The resultant image was asymmetric with major lobes to the east and southwest that coincide approximately with the asymmetries in the radio halo. The data indicates that inverse Compton emission is a plausible model for the X-rays coming from the asymmetric component.

Radio and γ -Ray Variability in the BL Lac PKS 0219−164: Detection of Quasi-periodic Oscillations in the Radio Light Curve

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

Bhatta, Gopal, E-mail: gopalbhatta716@gmail.com; Mt. Suhora Observatory, Pedagogical University, ul. Podchorazych 2, 30-084 Kraków

In this work, we explore the long-term variability properties of the blazar PKS 0219−164 in the radio and the γ -ray regime, utilizing the OVRO 15 GHz and the Fermi /LAT observations from the period 2008–2017. We found that γ -ray emission is more variable than the radio emission implying that γ -ray emission possibly originated in more compact regions while the radio emission represented continuum emission from the large-scale jets. Also, in the γ -ray, the source exhibited spectral variability, characterized by the softer-when-brighter trend, a less frequently observed feature in the high-energy emission by BL Lacs. In radio,more » using Lomb–Scargle periodogram and weighted wavelet z -transform, we detected a strong signal of quasi-periodic oscillation (QPO) with a periodicity of 270 ± 26 days with possible harmonics of 550 ± 42 and 1150 ± 157 day periods. At a time when detections of QPOs in blazars are still under debate, the observed QPO with high statistical significance (∼97%–99% global significance over underlying red-noise processes) and persistent over nearly 10 oscillations could make one of the strongest cases for the detection of QPOs in blazar light curves. We discuss various blazar models that might lead to the γ -ray and radio variability, QPO, and the achromatic behavior seen in the high-energy emission from the source.« less

Long-term radio and X-ray evolution of the tidal disruption event ASASSN-14li

NASA Astrophysics Data System (ADS)

Bright, J. S.; Fender, R. P.; Motta, S. E.; Mooley, K.; Perrott, Y. C.; van Velzen, S.; Carey, S.; Hickish, J.; Razavi-Ghods, N.; Titterington, D.; Scott, P.; Grainge, K.; Scaife, A.; Cantwell, T.; Rumsey, C.

2018-04-01

We report on late time radio and X-ray observations of the tidal disruption event candidate ASASSN-14li, covering the first 1000 d of the decay phase. For the first ˜200 d the radio and X-ray emission fade in concert. This phase is better fitted by an exponential decay at X-ray wavelengths, while the radio emission is well described by either an exponential or the canonical t-5/3 decay assumed for tidal disruption events. The correlation between radio and X-ray emission during this period can be fitted as L_R∝ L_X^{1.9± 0.2}. After 400 d the radio emission at 15.5 GHz has reached a plateau level of 244 ± 8 μJy which it maintains for at least the next 600 d, while the X-ray emission continues to fade exponentially. This steady level of radio emission is likely due to relic radio lobes from the weak AGN-like activity implied by historical radio observations. We note that while most existing models are based upon the evolution of ejecta which are decoupled from the central black hole, the radio-X-ray correlation during the declining phase is also consistent with core-jet emission coupled to a radiatively efficient accretion flow.

A Deep Chandra ACIS Study of NGC 4151. II. The Innermost Emission Line Region and Strong Evidence for Radio Jet-NLR Cloud Collision

NASA Astrophysics Data System (ADS)

Wang, Junfeng; Fabbiano, Giuseppina; Elvis, Martin; Risaliti, Guido; Mundell, Carole G.; Karovska, Margarita; Zezas, Andreas

2011-07-01

We have studied the X-ray emission within the inner ~150 pc radius of NGC 4151 by constructing high spatial resolution emission line images of blended O VII, O VIII, and Ne IX. These maps show extended structures that are spatially correlated with the radio outflow and optical [O III] emission. We find strong evidence for jet-gas cloud interaction, including morphological correspondences with regions of X-ray enhancement, peaks of near-infrared [Fe II] emission, and optical clouds. In these regions, moreover, we find evidence of elevated Ne IX/O VII ratios; the X-ray emission of these regions also exceeds that expected from nuclear photoionization. Spectral fitting reveals the presence of a collisionally ionized component. The thermal energy of the hot gas suggests that >~ 0.1% of the estimated jet power is deposited into the host interstellar medium through interaction between the radio jet and the dense medium of the circumnuclear region. We find possible pressure equilibrium between the collisionally ionized hot gas and the photoionized line-emitting cool clouds. We also obtain constraints on the extended iron and silicon fluorescent emission. Both lines are spatially unresolved. The upper limit on the contribution of an extended emission region to the Fe Kα emission is <~ 5% of the total, in disagreement with a previous claim that 65% of the Fe Kα emission originates in the extended narrow line region.

The importance of Radio Quiet Zone (RQZ) for radio astronomy

NASA Astrophysics Data System (ADS)

Umar, Roslan; Abidin, Zamri Zainal; Ibrahim, Zainol Abidin

2013-05-01

Most of radio observatories are located in isolated areas. Since radio sources from the universe is very weak, astronomer need to avoid radio frequency interference (RFI) from active spectrum users and radio noise produced by human made (telecommunication, mobile phone, microwave user and many more. There are many observatories around the world are surrounded by a Radio Quiet Zone (RQZ), which is it was set up using public or state laws. A Radio Quiet Zone normally consists of two areas: an exclusive area in which totally radio emissions are forbidden, with restrictions for residents and business developments, and a larger (radius up to 100 km above) coordination area where the power of radio transmission limits to threshold levels. Geographical Information System (GIS) can be used as a powerful tool in mapping large areas with varying RQZ profiles. In this paper, we report the initial testing of the usage of this system in order to identify the areas were suitable for Radio Quiet Zone. Among the important parameters used to develop the database for our GIS are population density, information on TV and telecommunication (mobile phones) transmitters, road networks (highway), and contour shielding. We will also use other information gathered from on-site RFI level measurements on selected 'best' areas generated by the GIS. The intention is to find the best site for the purpose of establishing first radio quiet zones for radio telescope in Malaysia.

Radio Transients and their Environments

NASA Astrophysics Data System (ADS)

Rajwade, Kaustubh

The interstellar medium is the principal ingredient for star formation and hence, it is necessary to study the properties of the interstellar medium. Radio sources in our Galaxy and beyond can be used as a probe of the intervening medium. In this dissertation, I present an attempt to use radio transients like pulsars and fast radio bursts and their interactions with the environment around them to study interstellar medium. We show that radio emission from pulsars is absorbed by dense ionized gas in their surroundings, causing a turnover in their flux density spectrum that can be used to reveal information about the absorbing medium. We carried out a multi-wavelength observation campaign of PSR B0611+22. The pulsar shows peculiar emission variability that is broadband in nature. Moreover, we show that the flux density spectrum of B0611+22 is unusual which can be attributed to the environment it lies in. We also present predictions of fast radio burst detections from upcoming low frequency surveys. We show that future surveys with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) will be able to detect 1 radio burst per hour even if the radio burst undergoes significant absorption and scattering. Finally, we present our results of pulsar population synthesis to understand the pulsar population in the Galactic Centre (GC) and place conservative upper limits on the GC pulsar population. We obtain an upper limit of 52 CPs and 10,000 MSPs in the GC. The dense, ionized environment of the GC gives us the opportunity to predict the probability of detection by considering scattering and absorption as the principle sources of flux mitigation. Our results suggest that the optimal frequency range for a pulsar survey in the GC is 9-14 GHz. A larger sample of absorbed spectrum pulsars and fast radio bursts will be beneficial not only for the study of emission processes but also for discerning the properties of the material permeating through space.

Population Studies of Radio and Gamma-Ray Pulsars

NASA Technical Reports Server (NTRS)

Harding, Alice K; Gonthier, Peter; Coltisor, Stefan

2004-01-01

Rotation-powered pulsars are one of the most promising candidates for at least some of the 40-50 EGRET unidentified gamma-ray sources that lie near the Galactic plane. Since the end of the EGRO mission, the more sensitive Parkes Multibeam radio survey has detected mere than two dozen new radio pulsars in or near unidentified EGRET sources, many of which are young and energetic. These results raise an important question about the nature of radio quiescence in gamma-ray pulsars: is the non-detection of radio emission a matter of beaming or of sensitivity? The answer is very dependent on the geometry of the radio and gamma-ray beams. We present results of a population synthesis of pulsars in the Galaxy, including for the first time the full geometry of the radio and gamma-ray beams. We use a recent empirically derived model of the radio emission and luminosity, and a gamma-ray emission geometry and luminosity derived theoretically from pair cascades in the polar slot gap. The simulation includes characteristics of eight radio surveys of the Princeton catalog plus the Parkes MB survey. Our results indicate that EGRET was capable of detecting several dozen pulsars as point sources, with the ratio of radio-loud to radio-quiet gamma-ray pulsars increasing significantly to about ten to one when the Parkes Survey is included. Polar cap models thus predict that many of the unidentified EGRET sources could be radio-loud gamma- ray pulsars, previously undetected as radio pulsars due to distance, large dispersion and lack of sensitivity. If true, this would make gamma-ray telescopes a potentially more sensitive tool for detecting distant young neutron stars in the Galactic plane.

Radio galaxies dominate the high-energy diffuse gamma-ray background

DOE PAGES

Hooper, Dan; Linden, Tim; Lopez, Alejandro

2016-08-09

It has been suggested that unresolved radio galaxies and radio quasars (sometimes referred to as misaligned active galactic nuclei) could be responsible for a significant fraction of the observed diffuse gamma-ray background. In this study, we use the latest data from the Fermi Gamma-Ray Space Telescope to characterize the gamma-ray emission from a sample of 51 radio galaxies. In addition to those sources that had previously been detected using Fermi data, we report here the first statistically significant detection of gamma-ray emission from the radio galaxies 3C 212, 3C 411, and B3 0309+411B. Combining this information with the radio fluxes,more » radio luminosity function, and redshift distribution of this source class, we find that radio galaxies dominate the diffuse gamma-ray background, generating 77.2(+25.4)(-9.4)% of this emission at energies above ~1 GeV . We discuss the implications of this result and point out that it provides support for scenarios in which IceCube's high-energy astrophysical neutrinos also originate from the same population of radio galaxies.« less

DISCOVERY OF γ -RAY EMISSION FROM THE RADIO-INTERMEDIATE QUASAR III ZW 2: VIOLENT JET ACTIVITY WITH INTRADAY γ -RAY VARIABILITY

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

Liao, Neng-Hui; Xin, Yu-Liang; Fan, Yi-Zhong

2016-10-01

III Zw 2 is the prototype of radio-intermediate quasars. Although there is the evidence of possessing strong jet, significant γ -ray emission has not been reported before. In this work, we carry out a detailed analysis of the latest Fermi -LAT Pass  8 data. No significant γ -ray signal has been detected in the time-averaged 7-year Fermi -LAT data of III Zw 2; however, we have identified two distinct γ -ray flares with isotropic luminosities of ∼10{sup 45} erg s{sup −1}. Multiwavelength data analysis (also including the optical photometric observations from Yunnan Observatories) are presented and the main finding ismore » simultaneous optical and γ -ray flares of III Zw 2 appearing in 2009 November. Violent γ -ray variability with a doubling timescale of 2.5 hr was detected in another γ -ray flare in May 2010, for which the 3-hr γ -ray peak flux is ∼250 times of the average flux in 7 years. Rather similar behaviors are observed in blazars and the blazar model can reasonably reproduce the spectral energy distribution of III Zw 2 in a wide energy range, strongly suggesting that its central engine resembles that of blazars. In view of its core, which shares radio similarities with young radio sources, together with weak extended radio lobe emission, we suggest that III Zw 2 harbors a recurrent activity core and thus serves as a valuable target for investigating the fueling and triggering of the activity in radio-loud active galactic nuclei.« less

How Else Can We Detect Fast Radio Bursts?

NASA Astrophysics Data System (ADS)

Lyutikov, Maxim; Lorimer, Duncan R.

2016-06-01

We discuss possible electromagnetic signals accompanying Fast Radio Bursts (FRBs) that are expected in the scenario where FRBs originate in neutron star magnetospheres. For models involving Crab-like giant pulses, no appreciable contemporaneous emission is expected at other wavelengths. However, magnetar giant flares, driven by the reconfiguration of the magnetosphere, can produce both contemporaneous bursts at other wavelengths as well as afterglow-like emission. We conclude that the best chances are: (I) prompt short GRB-like emission, (II) a contemporaneous optical flash that can reach naked eye peak luminosity (but only for a few milliseconds), and (III) a high-energy afterglow emission. Case (I) could be tested by coordinated radio and high-energy experiments. Case (II) could be seen in a coordinated radio-optical surveys, e.g., by the Palomar Transient Factory in a 60 s frame as a transient object of m = 15-20 mag with an expected optical detection rate of about 0.1 hr-1, an order of magnitude higher than in radio. Shallow, but large-area sky surveys such as ASAS-SN and EVRYSCOPE could also detect prompt optical flashes from the more powerful Lorimer-burst clones. The best constraints on the optical to radio power for this kind of emission could be provided by future observations with facilities like Large Synoptic Survey Telescope. Case (III) might be seen in relatively rare cases that the relativistically ejected magnetic blob is moving along the line of sight.

Radio transients from newborn black holes

NASA Astrophysics Data System (ADS)

Kashiyama, Kazumi; Hotokezaka, Kenta; Murase, Kohta

2018-05-01

We consider radio emission from a newborn black hole (BH), which is accompanied by a mini-disk with a mass of ≲ M⊙. Such a disk can be formed from an outer edge of the progenitor's envelope, especially for metal-poor massive stars and/or massive stars in close binaries. The disk accretion rate is typically super-Eddington and an ultrafast outflow with a velocity of ˜0.1-0.3 c will be launched into the circumstellar medium. The outflow forms a collisionless shock, and electrons are accelerated and emit synchrotron emission in radio bands with a flux of ˜ 10^{26-30} erg s^{-1} Hz^{-1} days to decades after the BH formation. The model predicts not only a fast UV/optical transient but also quasi-simultaneous inverse-Compton X-ray emission ˜ a few days after the BH formation, and the discovery of the radio counterpart with coordinated searches will enable us to identify this type of transients. The occurrence rate can be 0.1 - 10 % of the core-collapse supernova rate, which makes them a promising target of dedicated radio observations such as the Jansky VLA Sky Survey.

Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves

NASA Astrophysics Data System (ADS)

Goddard, C. R.; Nisticò, G.; Nakariakov, V. M.; Zimovets, I. V.; White, S. M.

2016-10-01

Aims: Radio emission observations from the Learmonth and Bruny Island radio spectrographs are analysed to determine the nature of a train of discrete, periodic radio "sparks" (finite-bandwidth, short-duration isolated radio features) which precede a type II burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA at multiple wavelengths and identify a series of quasi-periodic rapidly-propagating enhancements, which we interpret as a fast wave train, and link these to the detected radio features. Methods: The speeds and positions of the periodic rapidly propagating fast waves and the coronal mass ejection (CME) were recorded using running-difference images and time-distance analysis. From the frequency of the radio sparks the local electron density at the emission location was estimated for each. Using an empirical model for the scaling of density in the corona, the calculated electron density was used to obtain the height above the surface at which the emission occurs, and the propagation velocity of the emission location. Results: The period of the radio sparks, δtr = 1.78 ± 0.04 min, matches the period of the fast wave train observed at 171 Å, δtEUV = 1.7 ± 0.2 min. The inferred speed of the emission location of the radio sparks, 630 km s-1, is comparable to the measured speed of the CME leading edge, 500 km s-1, and the speeds derived from the drifting of the type II lanes. The calculated height of the radio emission (obtained from the density) matches the observed location of the CME leading edge. From the above evidence we propose that the radio sparks are caused by the quasi-periodic fast waves, and the emission is generated as they catch up and interact with the leading edge of the CME. The movie associated to Fig. 2 is available at http://www.aanda.org

The Compact Radio Sources in the Nucleus of NGC 1068

NASA Astrophysics Data System (ADS)

Roy, A. L.; Colbert, E. J. M.; Wilson, A. S.; Ulvestad, J. S.

1998-09-01

We report VLBA images of the nucleus of the Seyfert galaxy NGC 1068 at 1.7, 5, and 15 GHz, with resolutions between 3 and 10 mas (0.2-0.7 pc) and a sensitivity of ~106 K at all three frequencies. Our goals are to study the morphology of the radio emission at subparsec resolution and to investigate thermal gas in the putative obscuring disk or torus and in the narrow-line region clouds through free-free absorption of the radio emission. All four known radio components in the central arcsecond (S2, S1, C, and NE, from south to north) have been detected at either 1.7 or 5 GHz, or both. No radio emission was detected at 15 GHz. Component S1 is probably associated with the active nucleus, with radio emission originating from the inner edge of the obscuring torus according to Gallimore et al. Our observed flux densities at 1.7 and 5 GHz are in agreement with their thermal bremsstrahlung emission model, and we find that the nuclear radiation may be strong enough to heat the gas in S1 to the required temperature of ~4 × 106 K. The bremsstrahlung power would be 0.15(frefl/0.01) times the bolometric luminosity of the nucleus between 1014.6 and 1018.4 Hz (where frefl is the fraction of radiation reflected into our line of sight by the electron-scattering mirror) and so the model is energetically reasonable. We also discuss two other models for S1 that also match the observed radio spectrum: electron scattering by the torus of radio emission from a compact synchrotron self-absorbed source and synchrotron radiation from the torus itself. Components NE and S2 have spectra consistent with optically thin synchrotron emission, without significant absorption. Both of these components are elongated roughly perpendicular to the larger scale radio jet, suggesting that their synchrotron emission is related to transverse shocks in the jet or to bow shocks in the external medium. Component C has a nonthermal spectrum absorbed at low frequency. This absorption is consistent with free

The Galactic Black Hole Transient H1743-322 During Outburst Decay Connections Between Timing Noise, State Transitions, And Radio Emission

NASA Technical Reports Server (NTRS)

Kalemci, E.; Tomsick, J. A.; Corbel; Kaaret, P.; Rothschild, R. E.; Pottschmidt, K.

2006-01-01

Multiwavelength observations of Galactic black hole transients during outburst decay are instrumental for our understanding of the accretion geometry and the formation of outflows around black hole systems. H1743-322, a black hole transient observed intensely in X-rays and also covered in the radio band during its 2003 decay, provides clues about the changes in accretion geometry during state transitions and also the general properties of X-ray emission during the intermediate and low-hard states. In this work, we report on the evolution of spectral and temporal properties in X-rays and the flux in the radio band, with the goal of understanding the nature of state transitions observed in this source. We concentrate on the transition from the thermal dominant state to the intermediate state that occurs on a timescale of 1 day. We show that the state transition is associated with a sudden increase in power-law flux. We determine that the ratio of the power-law flux to the overall flux in the 3-25 keV band must exceed 0.6 for us to observe strong timing noise. Even after the state transition, once this ratio was below 0.6, the system transited back to the thermal dominant state for 1 day. We show that the emission from the compact radio core does not turn on during the transition from the thermal dominant state to the intermediate state but does turn on when the source reaches the low-hard state, as seen in 4U 1543-47 and GX 339-4. We find that the photon index correlates strongly with the QPO frequency and anticorrelates with the rms amplitude of variability. We also show that the variability is more likely to be associated with the power-law emission than the disk emission.

A Radio Study of the Ultra-luminous FIR Galaxy NGC 6240

NASA Astrophysics Data System (ADS)

Colbert, E.; Wilson, A. S.; Bland-Hawthorn, J.

1993-05-01

A number of galaxies observed in the IRAS mission are noted to emit ~ 99% of their bolometric flux in the FIR, with FIR luminosities in excess of 10(11) Lsun. The interacting galaxy NGC 6240 has often been referred to as the ``proto-typical'' ultra-luminous (L_FIR >~ 10(12) Lsun) FIR galaxy. The origin of the FIR excess remains a disputed subject in the literature. New observations of NGC 6240 were taken with the VLA at 20cm in the B-configuration, and at 3.6cm in the A-configuration. No significant radio emission was detected from or near the possible ultra-massive ``dark core'' hypothesized by Bland-Hawthorn et. al. (1991); however, approximately 30% of Seyfert galaxies have 20 cm radio luminosities weaker than the upper limit derived from the radio maps. The non-thermal radio emission from luminous FIR galaxies is tightly correlated with the FIR emission. Previous radio observations of NGC 6240 revealed two compact, steep-spectrum nuclear sources, nearly coincident with the two nuclear sources seen in optical images. The 2 images from the new VLA observations and 5 images from previous VLA observations are used to identify the morphological and spectral features of the strong, compact components in the nuclear regions (<~ 1.5 kpc; D=100 Mpc) and of the weaker ``clumps'' of diffuse emission south and west (>~ 3 kpc) from the nucleus. Feasible explanations for the radio emission are discussed. The models that have been proposed in the literature for the FIR excess of NGC 6240 are evaluated for consistency with the observed radio emission.

Radio Observations of Ultra-Luminous X-Ray Sources and their Implication for Models

NASA Astrophysics Data System (ADS)

Koerding, E. G.; Colbert, E. J. M.; Falcke, H.

2004-05-01

We present the results of a radio monitoring campaign to search for radio emission from nearby ultra-luminous X-ray sources (ULXs). These intriguing sources are bright off-nuclear X-ray point sources with luminosities exceeding LX > 1039 erg/sec. Assuming isotropic emission the Eddington Limit suggests that they harbor intermediate mass black holes. Due to the problems of this explanation also other possibilities are currently discussed, among them are anisotropic emission, super-Eddington accretion flows or relativistically beamed emission from microquasars. Detections of compact radio cores at the positions of ULXs would be a direct hint to jet-emission. However, as the ULX phenomenom is connected to star formation we have to assume that they are strongly accreting objects. Thus, similar to their nearest Galactic cousins, the very high state X-ray binaries (see e.g., GRS 1915), ULXs may show radio flares. A well-defined sample of the 9 nearest ULXs has been monitored eight times during 5 months with the Very Large Array in A and B configuration. Our limiting sensitivity is 0.15 mJy (4 σ ) for flares and 68 μ Jy for continuous emission. In M82 some ULXs seem to be connected to radio supernova remnants. Besides that no flare or continuous emission has been detected. As the timescales of radio flares in ULXs are highly uncertain, it could well be that we have undersampled the lightcurve. However, upper bounds for the probability to detect a flare can be given. The upper limits for the continuous emission are compared with the emission found in NGC 5408 X-1 and with quasars and microquasars. We show that these limits are well in agreement with the microblazar model using the Radio/X-ray correlation of XRBs and AGN. Thus, it could well be that ULXs are microblazers which may be radio loud.

Planck Early Results. XV. Spectral Energy Distributions and Radio Continuum Spectra of Northern Extragalactic Radio Sources

NASA Technical Reports Server (NTRS)

Aatrokoski, J.; Ade, P. A. R.; Aghanim, N.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Amaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.;

Planck early results. XV. Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources

DOE PAGES

Aatrokoski, J.

2011-12-01

Spectral energy distributions (SEDs) and radio continuum spectra are presented for a northern sample of 104 extragalactic radio sources, based on the Planck Early Release Compact Source Catalogue (ERCSC) and simultaneous multifrequency data. The nine Planck frequencies, from 30 to 857GHz, are complemented by a set of simultaneous observations ranging from radio to gamma-rays. This is the first extensive frequency coverage in the radio and millimetre domains for an essentially complete sample of extragalactic radio sources, and it shows how the individual shocks, each in their own phase of development, shape the radio spectra as they move in the relativisticmore » jet. The SEDs presented in this paper were fitted with second and third degree polynomials to estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and the spectral indices of low and high frequency radio data, including the Planck ERCSC data, were calculated. SED modelling methods are discussed, with an emphasis on proper, physical modelling of the synchrotron bump using multiple components. Planck ERCSC data also suggest that the original accelerated electron energy spectrum could be much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The implications of this are discussed for the acceleration mechanisms effective in blazar shock. Furthermore in many cases the Planck data indicate that gamma-ray emission must originate in the same shocks that produce the radio emission.« less

Plasma and radio waves from Neptune: Source mechamisms and propagation

NASA Technical Reports Server (NTRS)

Menietti, J. Douglas

1994-01-01

The purpose of this project was to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as it flew by Neptune. The study has included data analysis, theoretical and numerical calculations, and ray tracing to determine the possible source mechanisms and locations of the radiation, including the narrowband bursty and smooth components of the Neptune radio emission.

Radio Imaging of Envelopes of Evolved Stars

NASA Astrophysics Data System (ADS)

Cotton, Bill

2018-04-01

This talk will cover imaging of stellar envelopes using radio VLBI techniques; special attention will be paid to the technical differences between radio and optical/IR interferomery. Radio heterodyne receivers allow a straightforward way to derive spectral cubes and full polarization observations. Milliarcsecond resolution of very bright, i.e. non thermal, emission of molecular masers in the envelopes of evolved stars can be achieved using VLBI techniques with baselines of thousands of km. Emission from SiO, H2O and OH masers are commonly seen at increasing distance from the photosphere. The very narrow maser lines allow accurate measurements of the velocity field within the emitting region.

Uncertainties in energy reconstruction of cosmic rays for ANITA III caused by differences in models of radio emission in atmospheric showers

NASA Astrophysics Data System (ADS)

Bugaev, Viatcheslav; Rauch, Brian; Schoorlemmer, Harm; Lam, Joe; Urdaneta, David; Wissel, Stephanie; Belov, Konstantin; Romero-Wolf, Andrew; Anita Collaboration

2015-04-01

The third flight of the high-altitude balloon-borne Antarctic Impulsive Transient Antenna (ANITA III) was launched on a high-altitude balloon from McMurdo, Antarctica on December 17th, 2014 and flew for 22 days. It was optimized for the measurement of impulsive radio signals from the charged component of extensive air showers initiated by ultra-high energy cosmic rays in the frequency range ~ 180 - 1200 MHz. In addition it is designed to detect radio impulses initiated by high-energy neutrinos interacting in the Antarctic ice, which was the primary objective of the first two ANITA flights. Based on an extensive set of Monte Carlo simulations of radio emissions from cosmic rays (CR) with the ZHAireS and CoREAS simulation packages, we estimate uncertainties in the electric fields at the payload due to different models used in the two packages. The uncertainties in the emission are then propagated through an algorithm for energy reconstruction of individual CR showers to assess uncertainties in the energy reconstruction. We also discuss optimization of this algorithm. This research is supported by NASA under Grant # NNX11AC49G.

Very-long-baseline radio interferometry observations of low power radio galaxies.

PubMed Central

Giovannini, G; Cotton, W D; Feretti, L; Lara, L; Venturi, T; Marcaide, J M

1995-01-01

The parsec scale properties of low power radio galaxies are reviewed here, using the available data on 12 Fanaroff-Riley type I galaxies. The most frequent radio structure is an asymmetric parsec-scale morphology--i.e., core and one-sided jet. It is shared by 9 (possibly 10) of the 12 mapped radio galaxies. One (possibly 2) of the other galaxies has a two-sided jet emission. Two sources are known from published data to show a proper motion; we present here evidence for proper motion in two more galaxies. Therefore, in the present sample we have 4 radio galaxies with a measured proper motion. One of these has a very symmetric structure and therefore should be in the plane of the sky. The results discussed here are in agreement with the predictions of the unified scheme models. Moreover, the present data indicate that the parsec scale structure in low and high power radio galaxies is essentially the same. PMID:11607596

Template-free solution approach to synthesize CdS dendrites with SCN based ionic liquid

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

Li, Kangfeng; Li, Jiajia; Cheng, Xianyi

2011-07-15

Highlights: {yields} Template-free solution approach to synthesize CdS hierarchical dendrites. {yields} The 1-butyl-3-methlyimidazole thiocyanate ([BMIM][SCN]) plays doubly functional roles in the progress. {yields} The CdS hierarchical dendrites exhibit a more intense emission at 710 nm belongs to infrared band. -- Abstract: Cadmium sulfide dendrites were synthesized by a facile hydrothermal treatment from CdCl{sub 2} and ionic liquid 1-butyl-3-methlyimidazole thiocyanate acted both as sulfur source and surfactant. The product was characterized by means of X-ray powder diffraction and scanning electron microscopy. X-ray powder diffraction studies indicated that the product was well-crystallized hexagonal phase of CdS, and the scanning electron microscopy imagesmore » showed that the obtained powders consisted of a wealth of well-defined CdS dendritic microstructures with a pronounced trunk and highly ordered branches. The UV-Vis and photoluminescence spectroscopy measurements were taken as well. The possible formation mechanism of CdS dendrites was simply proposed in the end.« less

Characterizing X-Ray and Radio Emission in the Black Hole X-Ray Binary V404 Cygni During Quiescence

NASA Technical Reports Server (NTRS)

Rana, Vikram; Loh, Alan; Corbel, Stephane; Tomsick, John A.; Chakrabarty, Deepto; Walton, Dominic J.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William;

The Berkeley piggyback SETI program - SERENDIP II. [Search for Extraterrestrial Radio Emission from Nearby Developed Intelligent Populations

NASA Technical Reports Server (NTRS)

Bowyer, S.; Werthimer, D.; Lindsay, V.

1988-01-01

The SERENDIP (Search for Extraterrestrial Radio Emission from Nearby Developed Intelligent Populations) II system is currently operating at NRAO's 300-ft telescope in Greenbank, WV. The paper reports on the characteristics of this system in combination with this telescope, as well as elements of an off-line analysis program which are intended to identify signals of special interest. The sensitivity and relative probability of acquisition are evaluated.

LOFAR discovery of a double radio halo system in Abell 1758 and radio/X-ray study of the cluster pair

NASA Astrophysics Data System (ADS)

Botteon, A.; Shimwell, T. W.; Bonafede, A.; Dallacasa, D.; Brunetti, G.; Mandal, S.; van Weeren, R. J.; Brüggen, M.; Cassano, R.; de Gasperin, F.; Hoang, D. N.; Hoeft, M.; Röttgering, H. J. A.; Savini, F.; White, G. J.; Wilber, A.; Venturi, T.

2018-05-01

Radio halos and radio relics are diffuse synchrotron sources that extend over Mpc-scales and are found in a number of merger galaxy clusters. They are believed to form as a consequence of the energy that is dissipated by turbulence and shocks in the intra-cluster medium (ICM). However, the precise physical processes that generate these steep synchrotron spectrum sources are still poorly constrained. We present a new LOFAR observation of the double galaxy cluster Abell 1758. This system is composed of A1758N, a massive cluster hosting a known giant radio halo, and A1758S, which is a less massive cluster whose diffuse radio emission is confirmed here for the first time. Our observations have revealed a radio halo and a candidate radio relic in A1758S, and a suggestion of emission along the bridge connecting the two systems which deserves confirmation. We combined the LOFAR data with archival VLA and GMRT observations to constrain the spectral properties of the diffuse emission. We also analyzed a deep archival Chandra observation and used this to provide evidence that A1758N and A1758S are in a pre-merger phase. The ICM temperature across the bridge that connects the two systems shows a jump which might indicate the presence of a transversal shock generated in the initial stage of the merger.

Somato-dendritic Synaptic Plasticity and Error-backpropagation in Active Dendrites

PubMed Central

Schiess, Mathieu; Urbanczik, Robert; Senn, Walter

2016-01-01

In the last decade dendrites of cortical neurons have been shown to nonlinearly combine synaptic inputs by evoking local dendritic spikes. It has been suggested that these nonlinearities raise the computational power of a single neuron, making it comparable to a 2-layer network of point neurons. But how these nonlinearities can be incorporated into the synaptic plasticity to optimally support learning remains unclear. We present a theoretically derived synaptic plasticity rule for supervised and reinforcement learning that depends on the timing of the presynaptic, the dendritic and the postsynaptic spikes. For supervised learning, the rule can be seen as a biological version of the classical error-backpropagation algorithm applied to the dendritic case. When modulated by a delayed reward signal, the same plasticity is shown to maximize the expected reward in reinforcement learning for various coding scenarios. Our framework makes specific experimental predictions and highlights the unique advantage of active dendrites for implementing powerful synaptic plasticity rules that have access to downstream information via backpropagation of action potentials. PMID:26841235

HOW ELSE CAN WE DETECT FAST RADIO BURSTS?

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

Lyutikov, Maxim; Lorimer, Duncan R., E-mail: lyutikov@purdue.edu

We discuss possible electromagnetic signals accompanying Fast Radio Bursts (FRBs) that are expected in the scenario where FRBs originate in neutron star magnetospheres. For models involving Crab-like giant pulses, no appreciable contemporaneous emission is expected at other wavelengths. However, magnetar giant flares, driven by the reconfiguration of the magnetosphere, can produce both contemporaneous bursts at other wavelengths as well as afterglow-like emission. We conclude that the best chances are: (i) prompt short GRB-like emission, (ii) a contemporaneous optical flash that can reach naked eye peak luminosity (but only for a few milliseconds), and (iii) a high-energy afterglow emission. Case (i)more » could be tested by coordinated radio and high-energy experiments. Case (ii) could be seen in a coordinated radio-optical surveys, e.g., by the Palomar Transient Factory in a 60 s frame as a transient object of m = 15–20 mag with an expected optical detection rate of about 0.1 hr{sup −1}, an order of magnitude higher than in radio. Shallow, but large-area sky surveys such as ASAS-SN and EVRYSCOPE could also detect prompt optical flashes from the more powerful Lorimer-burst clones. The best constraints on the optical to radio power for this kind of emission could be provided by future observations with facilities like Large Synoptic Survey Telescope. Case (iii) might be seen in relatively rare cases that the relativistically ejected magnetic blob is moving along the line of sight.« less

WEAK AND COMPACT RADIO EMISSION IN EARLY HIGH-MASS STAR-FORMING REGIONS. I. VLA OBSERVATIONS

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

Rosero, V.; Hofner, P.; Claussen, M.

2016-12-01

We present a high-sensitivity radio continuum survey at 6 and 1.3 cm using the Karl G. Jansky Very Large Array toward a sample of 58 high-mass star-forming regions. Our sample was chosen from dust clumps within infrared dark clouds with and without IR sources (CMC–IRs and CMCs, respectively), and hot molecular cores (HMCs), with no previous, or relatively weak radio continuum detection at the 1 mJy level. Due to the improvement in the continuum sensitivity of the Very Large Array, this survey achieved map rms levels of ∼3–10  μ Jy beam{sup −1} at sub-arcsecond angular resolution. We extracted 70 continuum sourcesmore » associated with 1.2 mm dust clumps. Most sources are weak, compact, and prime candidates for high-mass protostars. Detection rates of radio sources associated with the millimeter dust clumps for CMCs, CMC–IRs, and HMCs are 6%, 53%, and 100%, respectively. This result is consistent with increasing high-mass star formation activity from CMCs to HMCs. The radio sources located within HMCs and CMC–IRs occur close to the dust clump centers, with a median offset from it of 12,000 au and 4000 au, respectively. We calculated 5–25 GHz spectral indices using power-law fits and obtained a median value of 0.5 (i.e., flux increasing with frequency), suggestive of thermal emission from ionized jets. In this paper we describe the sample, observations, and detections. The analysis and discussion will be presented in Paper II.« less

The Nature of the Stingray Nebula from Radio Observations

NASA Astrophysics Data System (ADS)

Harvey-Smith, Lisa; Hardwick, Jennifer A.; De Marco, Orsola; Parthasarathy, Mudumba; Gonidakis, Ioannis; Akhter, Shaila; Cunningham, Maria; Green, James A.

2018-06-01

We have analysed the full suite of Australia Telescope Compact Array data for the Stingray planetary nebula. Data were taken in the 4- to 23-GHz range of radio frequencies between 1991 and 2016. The radio flux density of the nebula generally declined during that period, but between 2013 and 2016 it shows signs of halting that decline. We produced the first spatially resolved radio images of the Stingray nebula from data taken in 2005. A ring structure, which appears to be associated with the ring seen in HST images, was visible. In addition, we found a narrow extension to the radio emission towards the eastern and western edges of the nebula. We derived the emission measure of the nebula - this decreased between 1992 and 2011, suggesting that the nebula is undergoing recombination. The radio spectral index is broadly consistent with a free-free emission mechanism, however a single data point hints that a steeper spectral index has possibly emerged since 2013, which could indicate the presence of synchrotron emission. If a non-thermal component component has emerged, such as one associated with a region that is launching a jet or outflow, we predict that it would intensify in the years to come.

Galaxy-wide radio-induced feedback in a radio-quiet quasar

NASA Astrophysics Data System (ADS)

Villar-Martín, M.; Emonts, B.; Cabrera Lavers, A.; Tadhunter, C.; Mukherjee, D.; Humphrey, A.; Rodríguez Zaurín, J.; Ramos Almeida, C.; Pérez Torres, M.; Bessiere, P.

2017-12-01

We report the discovery of a radio-quiet type 2 quasar (SDSS J165315.06+234943.0 nicknamed the 'Beetle' at z = 0.103) with unambiguous evidence for active galactic nucleus (AGN) radio-induced feedback acting across a total extension of ∼46 kpc and up to ∼26 kpc from the AGN. To the best of our knowledge, this is the first radio-quiet system where radio-induced feedback has been securely identified at ≫several kpc from the AGN. The morphological, ionization and kinematic properties of the extended ionized gas are correlated with the radio structures. We find along the radio axis (a) enhancement of the optical line emission at the location of the radio hotspots (b) turbulent gas kinematics (FWHM ∼ 380-470 km s-1) across the entire spatial range circumscribed by them (c) ionization minima for the turbulent gas at the location of the hot spots, (d) high temperature Te ≳ 1.9 × 104 K at the NE hotspot. Turbulent gas is also found far from the radio axis, ∼25 kpc in the perpendicular direction. We propose a scenario in which the radio structures have perforated the interstellar medium of the galaxy and escaped into the circumgalactic medium. While advancing, they have interacted with in situ gas modifying its properties. Our results show that jets of modest power can be the dominant feedback mechanism acting across huge volumes in radio-quiet systems, including highly accreting luminous AGNs, where radiative mode feedback may be expected.

Future Trends in Solar Radio Astronomy and Coronal Magnetic-Field Measurements

NASA Astrophysics Data System (ADS)

Fleishman, Gregory; Nita, Gelu; Gary, Dale

Solar radio astronomy has an amazingly rich, but yet largely unexploited, potential for probing the solar corona and chromosphere. Radio emission offers multiple ways of detecting and tracking electron beams, studying chromospheric and coronal thermal structure, plasma processes, particle acceleration, and measuring magnetic fields. To turn the mentioned potential into real routine diagnostics, two major components are needed: (1) well-calibrated observations with high spatial, spectral, and temporal resolutions and (2) accurate and reliable theoretical models and fast numerical tools capable of recovering the emission source parameters from the radio data. This report gives a brief overview of the new, expanded, and planned radio facilities, such as Expanded Owens Valley Solar Array (EOVSA), Jansky Very Large Array (JVLA), Chinese Solar Radio Heliograph (CSRH), Upgraded Siberian Solar Radio Telescope (USSRT), and Frequency Agile Solar Radiotelescope (FASR) with the emphasis on their ability to measure the coronal magnetic fields in active regions and flares. In particular, we emphasize the new tools for 3D modeling of the radio emission and forward fitting tools in development needed to derive the magnetic field data from the radio measurements.

Infrared images of distant 3C radio galaxies

NASA Technical Reports Server (NTRS)

Eisenhardt, Peter; Chokshi, Arati

1990-01-01

J (1.2-micron) and K (2.2 micron) images have been obtained for eight 3CR radio galaxies with redshifts from 0.7 to 1.8. Most of the objects were known to have extended asymmetric optical continuum or line emission aligned with the radio lobe axis. In general, the IR morphologies of these galaxies are just as peculiar as their optical morphologies. For all the galaxies, when asymmetric structure is present in the optical, structure with the same orientation is seen in the IR and must be accounted for in any model to explain the alignment of optical and radio emission.

On the Nature of Part-Time Radio Pulsars

NASA Astrophysics Data System (ADS)

Li, Xiang-Dong

2006-08-01

The recent discovery of rotating radio transients and the quasi-periodicity of pulsar activity in the radio pulsar PSR B1931+24 has challenged the conventional theory of radio pulsar emission. Here we suggest that these phenomena could be due to the interaction between the neutron star magnetosphere and the surrounding debris disk. The pattern of pulsar emission depends on whether the disk can penetrate the light cylinder and efficiently quench the processes of particle production and acceleration inside the magnetospheric gap. A precessing disk may naturally account for the switch-on/off behavior in PSR B1931+24.

eGSM: A extended Sky Model of Diffuse Radio Emission

NASA Astrophysics Data System (ADS)

Kim, Doyeon; Liu, Adrian; Switzer, Eric

2018-01-01

Both cosmic microwave background and 21cm cosmology observations must contend with astrophysical foreground contaminants in the form of diffuse radio emission. For precise cosmological measurements, these foregrounds must be accurately modeled over the entire sky Ideally, such full-sky models ought to be primarily motivated by observations. Yet in practice, these observations are limited, with data sets that are observed not only in a heterogenous fashion, but also over limited frequency ranges. Previously, the Global Sky Model (GSM) took some steps towards solving the problem of incomplete observational data by interpolating over multi-frequency maps using principal component analysis (PCA).In this poster, we present an extended version of GSM (called eGSM) that includes the following improvements: 1) better zero-level calibration 2) incorporation of non-uniform survey resolutions and sky coverage 3) the ability to quantify uncertainties in sky models 4) the ability to optimally select spectral models using Bayesian Evidence techniques.

Web-dendritic ribbon growth

NASA Technical Reports Server (NTRS)

Hilborn, R. B., Jr.; Faust, J. W., Jr.

1976-01-01

A web furnace was constructed for pulling dendritic-web samples. The effect of changes in the furnace thermal geometry on the growth of dendritic-web was studied. Several attempts were made to grow primitive dendrites for use as the dendritic seed crystals for web growth and to determine the optimum twin spacing in the dendritic seed crystal for web growth. Mathematical models and computer programs were used to determine the thermal geometries in the susceptor, crucible melt, meniscus, and web. Several geometries were determined for particular furnace geometries and growth conditions. The information obtained was used in conjunction with results from the experimental growth investigations in order to achieve proper conditions for sustained pulling of two dendrite web ribbons. In addition, the facilities for obtaining the following data were constructed: twin spacing, dislocation density, web geometry, resistivity, majority charge carrier type, and minority carrier lifetime.

Radio detection of extensive air showers at the Pierre Auger Observatory

NASA Astrophysics Data System (ADS)

Berat, C.

2013-08-01

The Pierre Auger Observatory explores the potential of radio-detection techniques to measure extensive air showers (EAS) induced by ultra-high energy cosmic rays. To study in detail the mechanisms responsible for radio emission in the MHz range, the Auger Engineering Radio Array has been installed at the Observatory. Presently consisting of 24 radio-detection stations, this number will grow to 150 units covering an area of almost 20 km2. Novel detection techniques based on the GHz emission from the EAS are currently being studied. AMBER (Air-shower Microwave Bremsstrahlung Experimental Radiometer) and MIDAS (Microwave Detection of Air Showers) are prototypes for a large imaging dish antenna. In EASIER (Extensive Air Shower Identification using Electron Radiometer), the microwave emission is detected by antenna horns located on each surface detector. MIDAS is a self-triggering system while AMBER and EASIER use the trigger from the Auger detectors to record the emission. The status of these radio-detection R&D efforts at the Pierre Auger Observatory will be reported.

Radio Detection of Cosmic Rays-Achievements and Future Potential

NASA Astrophysics Data System (ADS)

Huege, Tim

When modern efforts for radio detection of cosmic rays started about a decade ago, hopes were high but the true potential was unknown. Since then, we have achieved a detailed understanding of the radio emission physics and have consequently succeeded in developing sophisticated detection schemes and analysis approaches. In particular, we have demonstrated that the important air-shower parameters arrival direction, particle energy and depth of shower maximum can be reconstructed reliably from radio measurements, with a precision that is comparable with that of other detection techniques. At the same time, limitations inherent to the radio-emission mechanisms have become apparent. In this article, I shortly review the capabilities of radio detection in the very high-frequency band, and discuss the potential for future application in existing and new experiments for cosmic-ray detection.

The Outer Heliosphere: Solar Wind, Cosmic Ray and VLF Radio Emission Variations

NASA Technical Reports Server (NTRS)

McNutt, Ralph L., Jr.

1995-01-01

The Voyager 1 and 2 spacecraft now 45 astronomical units (AU) from Earth continue to monitor the outer heliosphere field and particles environment on a daily basis during their journey to the termination shock of the solar wind. Strong transient shocks continue to be detected in the solar wind plasma. The largest of these are associated with Global Merged Interaction Regions (GMIR's) which, in turn, block cosmic ray entry into the inner heliosphere and are apparently responsible for triggering the two major episodes of VLF radio emissions now thought to come from the heliopause. Distance estimates to the termination shock are consistent with those determined from observations of anomalous cosmic rays. Current observations and implications for heliospheric structure are discussed.

Radio and X-ray structure of Centaurus A

NASA Technical Reports Server (NTRS)

Feigelson, E. D.

1982-01-01

Recent studies of the nearby radio galaxy Centaurus A with the Very Large Array and the Einstein X-Ray Observatory reveal complex radio and X-ray structures. A prominent one-sided jet comprised of resolved knots located 0.2-6 kpc from the nucleus is seen in both radio and X-rays. The X-ray emission is probably synchrotron, requiring in situ reacceleration up to about ten million. Inverse Compton emission is not a likely explanation though a thermal model in which the nucleus ejects dense 100,000 solar mass clouds cannot be excluded. An elongated X-ray region is also found near the 'middle' radio lobe and optical HII regions about 30 kpc NE of the nucleus. Conditions around the active nucleus, the absence of X-rays from the inner radio lobes, and X-ray evidence for a hot interstellar medium are briefly discussed

MASER: A Tool Box for Solar System Low Frequency Radio Astronomy

NASA Astrophysics Data System (ADS)

Cecconi, B.; Le Sidaner, P.; Savalle, R.; Bonnin, X.; Zarka, P.; Louis, C.; Coffre, A.; Lamy, L.; Denis, L.; Griessmeier, J.-M.; Faden, J.; Piker, C.; André, N.; Génot, V.; Erard, S.; King, T. A.; Mafi, J. N.; Sharlow, M.; Sky, J.; Demleitner, M.

2018-04-01

MASER (Measuring, Analysing, and Simulating Radio Emissions) is a toolbox for solar system radio astronomy. It provides tools for reading, displaying, finding, and modeling low frequency radio datasets.

Coherent emission mechanisms in astrophysical plasmas

NASA Astrophysics Data System (ADS)

Melrose, D. B.

2017-12-01

Three known examples of coherent emission in radio astronomical sources are reviewed: plasma emission, electron cyclotron maser emission (ECME) and pulsar radio emission. Plasma emission is a multi-stage mechanism with the first stage being generation of Langmuir waves through a streaming instability, and subsequent stages involving partial conversion of the Langmuir turbulence into escaping radiation at the fundamental (F) and second harmonic (H) of the plasma frequency. The early development and subsequent refinements of the theory, motivated by application to solar radio bursts, are reviewed. The driver of the instability is faster electrons outpacing slower electrons, resulting in a positive gradient ({d}f(v_allel )/{d}v_allel >0) at the front of the beam. Despite many successes of the theory, there is no widely accepted explanation for type I bursts and various radio continua. The earliest models for ECME were purely theoretical, and the theory was later adapted and applied to Jupiter (DAM), the Earth (AKR), solar spike bursts and flare stars. ECME strongly favors the x mode, whereas plasma emission favors the o mode. Two drivers for ECME are a ring feature (implying {d}f(v)/{d}v>0) and a loss-cone feature. Loss-cone-driven ECME was initially favored for all applications. The now favored driver for AKR is the ring-feature in a horseshoe distribution, which results from acceleration by a parallel electric on converging magnetic field lines. The driver in DAM and solar and stellar applications is uncertain. The pulsar radio emission mechanism remains an enigma. Ingredients needed in discussing possible mechanisms are reviewed: general properties of pulsars, pulsar electrodynamics, the properties of pulsar plasma and wave dispersion in such plasma. Four specific emission mechanisms (curvature emission, linear acceleration emission, relativistic plasma emission and anomalous Doppler emission) are discussed and it is argued that all encounter difficulties. Coherent

Radio Observations of the Tidal Disruption Event XMMSL1 J0740-85

NASA Astrophysics Data System (ADS)

Alexander, K. D.; Wieringa, M. H.; Berger, E.; Saxton, R. D.; Komossa, S.

2017-03-01

We present radio observations of the tidal disruption event candidate (TDE) XMMSL1 J0740-85 spanning 592 to 875 days post X-ray discovery. We detect radio emission that fades from an initial peak flux density at 1.6 GHz of 1.19 ± 0.06 mJy to 0.65 ± 0.06 mJy, suggesting an association with the TDE. This makes XMMSL1 J0740-85 at d = 75 Mpc the nearest TDE with detected radio emission to date and only the fifth TDE with radio emission overall. The observed radio luminosity rules out a powerful relativistic jet like that seen in the relativistic TDE Swift J1644+57. Instead, we infer from an equipartition analysis that the radio emission most likely arises from a non-relativistic outflow similar to that seen in the nearby TDE ASASSN-14li, with a velocity of about 104 km s-1 and a kinetic energy of about 1048 erg, expanding into a medium with a density of about 102 cm-3. Alternatively, the radio emission could arise from a weak initially relativistic but decelerated jet with an energy of ˜ 2× {10}50 erg, or (for an extreme disruption geometry) from the unbound debris. The radio data for XMMSL1 J0740-85 continues to support the previous suggestion of a bimodal distribution of common non-relativistic isotropic outflows and rare relativistic jets in TDEs (in analogy with the relation between Type Ib/c supernovae and long-duration gamma-ray bursts). The radio data also provide a new measurement of the circumnuclear density on a sub-parsec scale around an extragalactic supermassive black hole.

Weak and Compact Radio Emission in Early High-Mass Star Forming Regions

NASA Astrophysics Data System (ADS)

Rosero, Viviana; P. Hofner, M. Claussen, S. Kurtz, R. Cesaroni, E. D. Araya, C. Carrasco-González, L. F. Rodríguez, K. M. Menten, F. Wyrowski, L. Loinard, S. P. Ellingsen

2018-01-01

High-mass protostars are difficult to detect: they have short evolutionary timescales, they tend to be located at large distances, and they are usually embedded within complicated cluster environments. In this work, we aimed to identify and analyze candidates at the earliest stages of high-mass star formation, where only low-level (< 1 mJy) radio emission is expected. We used the Karl G. Jansky Very Large Array to achieve one of the most sensitive (image RMS < 3 -- 10 μJy/beam) centimeter continuum surveys towards high-mass star forming regions to date, with observations at 1.3 and 6 cm and an angular resolution < 0.5". The sample is composed of cold molecular clumps with and without infrared sources (CMC--IRs and CMCs, respectively) and hot molecular cores (HMCs), covering a wide range of parameters such as bolometric luminosity and distance. We detected 70 radio continuum sources that are associated with dust clumps, most of which are weak and compact. We detected centimeter wavelength sources in 100% of our HMCs, which is a higher fraction than previously expected and suggests that radio continuum may be detectable at weak levels in all HMCs. The lack of radio detections for some objects in the sample (including most CMCs) contributes strong evidence that these are prestellar clumps, providing interesting constraints and ideal follow up candidates for studies of the earliest stages of high-mass stars. Our results show further evidence for an evolutionary sequence in the formation of high-mass stars, from starless cores (i.e., CMCs) to relatively more evolved ones (i.e., HMCs). Many of our detections have morphologies and other observational parameters that resemble collimated ionized jets, which is highly relevant for recent theoretical models based on core accretion that predict that the first stages of ionization from high-mass stars are in the form of jets. Additionally, we found that properties of ionized jets from low and high-mass stars are extremely well

47 CFR 74.133 - Emission authorized.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 4 2012-10-01 2012-10-01 false Emission authorized. 74.133 Section 74.133 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES EXPERIMENTAL RADIO....133 Emission authorized. In case emission of a different type than that specified in the license is...

47 CFR 74.133 - Emission authorized.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 4 2011-10-01 2011-10-01 false Emission authorized. 74.133 Section 74.133 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES EXPERIMENTAL RADIO....133 Emission authorized. In case emission of a different type than that specified in the license is...

47 CFR 74.133 - Emission authorized.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 4 2010-10-01 2010-10-01 false Emission authorized. 74.133 Section 74.133 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) BROADCAST RADIO SERVICES EXPERIMENTAL RADIO....133 Emission authorized. In case emission of a different type than that specified in the license is...

Stress-driven lithium dendrite growth mechanism and dendrite mitigation by electroplating on soft substrates

NASA Astrophysics Data System (ADS)

Wang, Xu; Zeng, Wei; Hong, Liang; Xu, Wenwen; Yang, Haokai; Wang, Fan; Duan, Huigao; Tang, Ming; Jiang, Hanqing

2018-03-01

Problems related to dendrite growth on lithium-metal anodes such as capacity loss and short circuit present major barriers to next-generation high-energy-density batteries. The development of successful lithium dendrite mitigation strategies is impeded by an incomplete understanding of the Li dendrite growth mechanisms, and in particular, Li-plating-induced internal stress in Li metal and its effect on Li growth morphology are not well addressed. Here, we reveal the enabling role of plating residual stress in dendrite formation through depositing Li on soft substrates and a stress-driven dendrite growth model. We show that dendrite growth is mitigated on such soft substrates through surface-wrinkling-induced stress relaxation in the deposited Li film. We demonstrate that this dendrite mitigation mechanism can be utilized synergistically with other existing approaches in the form of three-dimensional soft scaffolds for Li plating, which achieves higher coulombic efficiency and better capacity retention than that for conventional copper substrates.

Abell 1033: birth of a radio phoenix

DOE PAGES

de Gasperin, F.; Ogrean, G. A.; van Weeren, R. J.; ...

2015-02-26

We report that extended steep-spectrum radio emission in a galaxy cluster is usually associated with a recent merger. However, given the complex scenario of galaxy cluster mergers, many of the discovered sources hardly fit into the strict boundaries of a precise taxonomy. This is especially true for radio phoenixes that do not have very well defined observational criteria. Radio phoenixes are aged radio galaxy lobes whose emission is reactivated by compression or other mechanisms. Here in this paper, we present the detection of a radio phoenix close to the moment of its formation. The source is located in Abell 1033,more » a peculiar galaxy cluster which underwent a recent merger. To support our claim, we present unpublished Westerbork Synthesis Radio Telescope and Chandra observations together with archival data from the Very Large Array and the Sloan Digital Sky Survey. We discover the presence of two subclusters displaced along the N–S direction. The two subclusters probably underwent a recent merger which is the cause of a moderately perturbed X-ray brightness distribution. A steep-spectrum extended radio source very close to an active galactic nucleus (AGN) is proposed to be a newly born radio phoenix: the AGN lobes have been displaced/compressed by shocks formed during the merger event. This scenario explains the source location, morphology, spectral index, and brightness. Finally, we show evidence of a density discontinuity close to the radio phoenix and discuss the consequences of its presence.« less

Are the infrared-faint radio sources pulsars?

NASA Astrophysics Data System (ADS)

Cameron, A. D.; Keith, M.; Hobbs, G.; Norris, R. P.; Mao, M. Y.; Middelberg, E.

2011-07-01

Infrared-faint radio sources (IFRS) are objects which are strong at radio wavelengths but undetected in sensitive Spitzer observations at infrared wavelengths. Their nature is uncertain and most have not yet been associated with any known astrophysical object. One possibility is that they are radio pulsars. To test this hypothesis we undertook observations of 16 of these sources with the Parkes Radio Telescope. Our results limit the radio emission to a pulsed flux density of less than 0.21 mJy (assuming a 50 per cent duty cycle). This is well below the flux density of the IFRS. We therefore conclude that these IFRS are not radio pulsars.

The Extragalactic Radio Background

NASA Technical Reports Server (NTRS)

Kogut, A.; Fixsen, D. J.; Levin, S. M.; Limon, M.; Lubin, P. M.; Seiffert, M.; Singal, J.; Villela, T.; Wollack, E.; Wuensche, C. A.

2011-01-01

The existence of an isotropic component of the high-latitude radio sky has been recognized for nearly fifty years, but has typically been assumed to be Galactic in origin. We use recent radio observations to test whether the observed high-latitude component could originate within either an extended Galactic halo or a more local "bubble" structure. The lack of significant polarization from the isotropic component, combined with the lack of significant correlation with the Galactic far-infrared emission, rule out an origin within the Galaxy. We conclude that an extragalactic origin is the only viable alternative for the bulk of the isotropic high-latitude emission. The extragalactic component is 2-3 times brighter than local (Galactic) emission towards the Galactic poles and is consistent with a power law in frequency with amplitude T(sub r) = 24.1 plus or minus 2.1 K and spectral index beta = -2.599 plus or minus 0.036 evaluated at reference frequency 310 MHz.

Dendritic excitability modulates dendritic information processing in a purkinje cell model.

PubMed

Coop, Allan D; Cornelis, Hugo; Santamaria, Fidel

2010-01-01

Using an electrophysiological compartmental model of a Purkinje cell we quantified the contribution of individual active dendritic currents to processing of synaptic activity from granule cells. We used mutual information as a measure to quantify the information from the total excitatory input current (I(Glu)) encoded in each dendritic current. In this context, each active current was considered an information channel. Our analyses showed that most of the information was encoded by the calcium (I(CaP)) and calcium activated potassium (I(Kc)) currents. Mutual information between I(Glu) and I(CaP) and I(Kc) was sensitive to different levels of excitatory and inhibitory synaptic activity that, at the same time, resulted in the same firing rate at the soma. Since dendritic excitability could be a mechanism to regulate information processing in neurons we quantified the changes in mutual information between I(Glu) and all Purkinje cell currents as a function of the density of dendritic Ca (g(CaP)) and Kca (g(Kc)) conductances. We extended our analysis to determine the window of temporal integration of I(Glu) by I(CaP) and I(Kc) as a function of channel density and synaptic activity. The window of information integration has a stronger dependence on increasing values of g(Kc) than on g(CaP), but at high levels of synaptic stimulation information integration is reduced to a few milliseconds. Overall, our results show that different dendritic conductances differentially encode synaptic activity and that dendritic excitability and the level of synaptic activity regulate the flow of information in dendrites.

A transient, flat spectrum radio pulsar near the Galactic Centre

NASA Astrophysics Data System (ADS)

Dexter, J.; Degenaar, N.; Kerr, M.; Deller, A.; Deneva, J.; Lazarus, P.; Kramer, M.; Champion, D.; Karuppusamy, R.

2017-06-01

Recent studies have shown possible connections between highly magnetized neutron stars ('magnetars'), whose X-ray emission is too bright to be powered by rotational energy, and ordinary radio pulsars. In addition to the magnetar SGR J1745-2900, one of the radio pulsars in the Galactic Centre (GC) region, PSR J1746-2850, had timing properties implying a large magnetic field strength and young age, as well as a flat spectrum. All characteristics are similar to those of rare, transient, radio-loud magnetars. Using several deep non-detections from the literature and two new detections, we show that this pulsar is also transient in the radio. Both the flat spectrum and large amplitude variability are inconsistent with the light curves and spectral indices of three radio pulsars with high magnetic field strengths. We further use frequent, deep archival imaging observations of the GC in the past 15 yr to rule out a possible X-ray outburst with a luminosity exceeding the rotational spin-down rate. This source, either a transient magnetar without any detected X-ray counterpart or a young, strongly magnetized radio pulsar producing magnetar-like radio emission, further blurs the line between the two categories. We discuss the implications of this object for the radio emission mechanism in magnetars and for star and compact object formation in the GC.

X-rays from the radio halo of Virgo A = M87

NASA Technical Reports Server (NTRS)

1985-01-01

The purpose of this study is to investigate in more detail the associated X-ray and radio emission in the Virgo A halo discovered by SGF. Improved Einstein HRI data and new radio maps obtained with the Very Large Array are described and the relation between the X-ray and radio structures is carefully examined. Several possible explanations are presented for the X-ray emission. The inverse compton model is found to be viable only if the magnetic field is variable and substantially weaker than the equipartition value. The principal alternative is excess thermal X-rays due to compression of the intracluster medium by the radio lobe. In either case, the association of such prominent radio and X-ray structures is unique among known radio galaxies.

Radio and X-Ray Observations of the 1998 Outburst of the Recurrent X-Ray Transient 4U 1630-47

NASA Technical Reports Server (NTRS)

Hjellming, R. M.; Rupen, M.; Mioduszewski, A. J.; Kuulkers, E.; McCollough, M. L.; Harmon, B. Alan; Buxton, M.; Sood, R.; Tzioumis, A.

1998-01-01

We report radio (VLA and ATCA), soft X-ray (RXTE ASM), and hard X-ray (CGRO BATSE) observations of a 1998 outburst in the recurring X-ray transient 4U 1630-47 where radio emission was detected for the first time. The radio observations identify the position of 4U 1630-47 to within 1". Because the radio emission is optically thin with a spectral index of approximately -0.6 during the rise and approximately -1 during the peak and decay of the initial radio event, the emission is probably coming from an optically thin radio jet ejected over a period of time. The 20-100 keV emission first appeared 1998 January 28 (MJD 50841), the 2-12 keV emission first appeared February 3 (MJD 50847), and the first radio emission was detected February 12.6 (MJD 50856.6). The rise of the radio emission probably began about February 7 (MJD 50851) when the X-rays were in a very hard, fluctuating hardness state, just before changing to a softer, more stable hardness state.

Discovery of a radio nebula around PSR J0855-4644

NASA Astrophysics Data System (ADS)

Maitra, C.; Roy, S.; Acero, F.; Gupta, Y.

2018-06-01

We report the discovery of a diffuse radio emission around PSR J0855-4644 using an upgraded GMRT (uGMRT) observation at 1.35 GHz. The radio emission is spatially coincident with the diffuse X-ray pulsar wind nebula (PWN) seen with XMM-Newton but is much larger in extent compared to the compact axisymmetric PWN seen with Chandra. The morphology of the emission, with a bright partial ring-like structure and two faint tail-like features strongly resembles a bow shock nebula, and indicates a velocity of 100 km s-1 through the ambient medium. We conclude that the emission is most likely to be associated with the radio PWN of PSR J0855-4644. From the integrated flux density, we estimate the energetics of the PWN.

A Measurement of the Millimeter Emission and the Sunyaev-Zel'dovich Effect Associated with Low-Frequency Radio Sources

NASA Technical Reports Server (NTRS)

Gralla, Megan B.; Crichton, Devin; Marriage, Tobias; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard;

Global Sky Model (GSM): A Model of Diffuse Galactic Radio Emission from 10 MHz to 100 GHz

NASA Astrophysics Data System (ADS)

de Oliveira-Costa, Angelica; Tegmark, Max; Gaensler, B. M.; Jonas, Justin; Landecker, T. L.; Reich, Patricia

2010-11-01

Understanding diffuse Galactic radio emission is interesting both in its own right and for minimizing foreground contamination of cosmological measurements. Cosmic Microwave Background experiments have focused on frequencies > 10 GHz, whereas 21 cm tomography of the high redshift universe will mainly focus on < 0.2 GHz, for which less is currently known about Galactic emission. Motivated by this, we present a global sky model derived from all publicly available total power large-area radio surveys, digitized with optical character recognition when necessary and compiled into a uniform format, as well as the new Villa Elisa data extending the 1.4 GHz map to the entire sky. We quantify statistical and systematic uncertainties in these surveys by comparing them with various global multi-frequency model fits. We find that a principal component based model with only three components can fit the 11 most accurate data sets (at 10, 22, 45 & 408 MHz and 1.4, 2.3, 23, 33, 41, 61, 94 GHz) to an accuracy around 1%-10% depending on frequency and sky region. The data compilation and software returning a predicted all-sky map at any frequency from 10 MHz to 100 GHz are publicly available at the link below.

Remote sensing of the Io torus plasma ribbon using natural radio occultation of the Jovian radio emissions

NASA Astrophysics Data System (ADS)

Boudjada, M. Y.; Galopeau, P. H. M.; Sawas, S.; Lammer, H.

2014-09-01

We study the Jovian hectometric (HOM) emissions recorded by the RPWS (Radio and Plasma Wave Science) experiment onboard the Cassini spacecraft during its Jupiter flyby. We analyze the attenuation band associated with the intensity extinction of HOM radiation. This phenomenon is interpreted as a refraction effect of the Jovian hectometric emission inside the Io plasma torus. This attenuation band was regularly observed during periods of more than 5 months, from the beginning of October 2000 to the end of March 2001. We estimate for this period the variation of the electron density versus the central meridian longitude (CML). We find a clear local time dependence. Hence the electron density was not higher than 5.0 × 104 cm-3 during 2 months, when the spacecraft approached the planet on the dayside. In the late afternoon and evening sectors, the electron density increases to 1.5 × 105 cm-3 and reach a higher value at some specific occasions. Additionally, we show that ultraviolet and hectometric wavelength observations have common features related to the morphology of the Io plasma torus. The maxima of enhancements/attenuations of UV/HOM observations occur close to the longitudes of the tip of the magnetic dipole in the southern hemisphere (20° CML) and in the northern hemisphere (200° CML), respectively. This is a significant indication about the importance of the Jovian magnetic field as a physical parameter in the coupling process between Jupiter and the Io satellite.

Measurement of RF lightning emissions

NASA Technical Reports Server (NTRS)

Lott, G. K., Jr.; Honnell, M. A.; Shumpert, T. H.

1981-01-01

A lightning radio emission observation laboratory is described. The signals observed and recorded include HF, VHF and UHF radio emissions, optical signature, electric field measurements, and thunder. The objectives of the station, the equipment used, and the recording methods are discussed.

Radio detection of extensive air showers

NASA Astrophysics Data System (ADS)

Huege, Tim

2017-12-01

Radio detection of extensive air showers initiated in the Earth's atmosphere has made tremendous progress in the last decade. Today, radio detection is routinely used in several cosmic-ray observatories. The physics of the radio emission in air showers is well-understood, and analysis techniques have been developed to determine the arrival direction, the energy and an estimate for the mass of the primary particle from the radio measurements. The achieved resolutions are competitive with those of more traditional techniques. In this article, I shortly review the most important achievements and discuss the potential for future applications.

Remote radio observations of solar wind parameters upstream of planetary bow shocks

NASA Technical Reports Server (NTRS)

Macdowall, R. J.; Stone, R. G.; Gaffey, J. D., Jr.

1992-01-01

Radio emission is frequently produced at twice the electron plasma frequency 2fp in the foreshock region upstream of the terrestrial bow shock. Observations of this emission provide a remote diagnostic of solar wind parameters in the foreshock. Using ISEE-3 radio data, we present the first evidence that the radio intensity is proportional to the kinetic energy flux and to other parameters correlated with solar wind density. We provide a qualitative explanation of this intensity behavior and predict the detection of similar emission at Jupiter by the Ulysses spacecraft.

Nanosecond radio bursts from strong plasma turbulence in the Crab pulsar.

PubMed

Hankins, T H; Kern, J S; Weatherall, J C; Eilek, J A

2003-03-13

The Crab pulsar was discovered by the occasional exceptionally bright radio pulses it emits, subsequently dubbed 'giant' pulses. Only two other pulsars are known to emit giant pulses. There is no satisfactory explanation for the occurrence of giant pulses, nor is there a complete theory of the pulsar emission mechanism in general. Competing models for the radio emission mechanism can be distinguished by the temporal structure of their coherent emission. Here we report the discovery of isolated, highly polarized, two-nanosecond subpulses within the giant radio pulses from the Crab pulsar. The plasma structures responsible for these emissions must be smaller than one metre in size, making them by far the smallest objects ever detected and resolved outside the Solar System, and the brightest transient radio sources in the sky. Only one of the current models--the collapse of plasma-turbulent wave packets in the pulsar magnetosphere--can account for the nanopulses we observe.

Dendritic Alloy Solidification Experiment (DASE)

NASA Technical Reports Server (NTRS)

Beckermann, C.; Karma, A.; Steinbach, I.; deGroh, H. C., III

2001-01-01

A space experiment, and supporting ground-based research, is proposed to study the microstructural evolution in free dendritic growth from a supercooled melt of the transparent model alloy succinonitrile-acetone (SCN-ACE). The research is relevant to equiaxed solidification of metal alloy castings. The microgravity experiment will establish a benchmark for testing of equiaxed dendritic growth theories, scaling laws, and models in the presence of purely diffusive, coupled heat and solute transport, without the complicating influences of melt convection. The specific objectives are to: determine the selection of the dendrite tip operating state, i.e. the growth velocity and tip radius, for free dendritic growth of succinonitrile-acetone alloys; determine the growth morphology and sidebranching behavior for freely grown alloy dendrites; determine the effects of the thermal/solutal interactions in the growth of an assemblage of equiaxed alloy crystals; determine the effects of melt convection on the free growth of alloy dendrites; measure the surface tension anisotropy strength of succinon itrile -acetone alloys establish a theoretical and modeling framework for the experiments. Microgravity experiments on equiaxed dendritic growth of alloy dendrites have not been performed in the past. The proposed experiment builds on the Isothermal Dendritic Growth Experiment (IDGE) of Glicksman and coworkers, which focused on the steady growth of a single crystal from pure supercooled melts (succinonitrile and pivalic acid). It also extends the Equiaxed Dendritic Solidification Experiment (EDSE) of the present investigators, which is concerned with the interactions and transients arising in the growth of an assemblage of equiaxed crystals (succinonitrile). However, these experiments with pure substances are not able to address the issues related to coupled heat and solute transport in growth of alloy dendrites.

Deep Limits on the X-ray and Radio Emission From the Nearby Type Iax SN2014dt

NASA Astrophysics Data System (ADS)

Stauffer, Candice; Margutti, Raffaella; Coppejans, Deannne

2018-01-01

Type Iax Supernovae (SN Iax) have been recently recognized as a new class of stellar explosions in 2012. SN Iax constitute the largest class of ``peculiar thermonuclear explosions'' from white dwarf (WD) stellar progenitors in binary systems. They are characterized by lower ejecta velocity, lower luminsity and non-standard late-time spectral evolution, when compared to the more common Type Ia SNe. Here I present deep radio and X-ray observations of the closest type Iax SN yet discovered, SN2014dt. The SN shock interaction with the medium is a very well known source of radio and X-ray emission. My observations of SN2014dt uniquely constrain the density in the SN sub-pc environment (which cannot be investigated otherwise), and allow me to put constraints on the mysterious nature of the stellar companion.

Radio emission from RS CVn binaries. II - Polarization and spectral properties

NASA Technical Reports Server (NTRS)

Mutel, R. L.; Morris, D. H.; Doiron, D. J.; Lestrade, J. F.

1987-01-01

Multiepoch radio observations of circular polarization and spectral characteristics of several close, late-type stellar binaries are reported. The median luminosity of four well-studied systems ranged from 16.2 to 17.1 ergs/s/Hz. For individual systems, the fractional circular polarization decreases with increasing luminosity, particularly at frequencies above 5 GHz. Eclipsing binaries have significantly lower average circular polarization compared with noneclipsing systems. Helicity reversal is almost always observed between 1.4 and 4.9 GHz for systems with high orbital inclination. Comparison with ten years of previously published polarization observations for two RS CVn stellar systems show that the same helicity occurs at a given frequency for a given source, indicating a very stable, large-scale magnetic field geometry. These spectral and polarization characteristics strongly support a model of inhomogeneous gyrosynchrotron emission arising from electrons with power law energy spectra interacting with inhomogeneous magnetic fields.

POST-OUTBURST RADIO OBSERVATIONS OF THE HIGH MAGNETIC FIELD PULSAR PSR J1119-6127

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

Majid, Walid A.; Pearlman, Aaron B.; Dobreva, Tatyana

We have carried out high-frequency radio observations of the high magnetic field pulsar PSR J1119-6127 following its recent X-ray outburst. While initial observations showed no evidence of significant radio emission, subsequent observations detected pulsed emission across a large frequency band. In this Letter, we report on the initial disappearance of the pulsed emission and its prompt reactivation and dramatic evolution over several months of observation. The periodic pulse profile at S -band (2.3 GHz) after reactivation exhibits a multi-component emission structure, while the simultaneous X -band (8.4 GHz) profile shows a single emission peak. Single pulses were also detected atmore » S -band near the main emission peaks. We present measurements of the spectral index across a wide frequency bandwidth, which captures the underlying changes in the radio emission profile of the neutron star. The high-frequency radio detection, unusual emission profile, and observed variability suggest similarities with magnetars, which may independently link the high-energy outbursts to magnetar-like behavior.« less

Origin of superluminal radio jets in microquasars

NASA Astrophysics Data System (ADS)

Yadav, J. S.; Bhandare, R. S.

In Microquasars, superluminal radio jets are seen at large distances from few hundred AU to 5000 AU with very high radio luminosity. We suggest that these superluminal jets are due to internal shocks which form in the previously generated slowly moving wind (from the accretion disk or the companion star) with beta < 0.01 as the fast moving discrete jet with beta sim 1 catches up and interacts with it. The black hole X-ray binaries with transient radio emission (mostly LMXBs) produce superluminal jets with beta_app > 1 when the accretion rate is high and the bolometric luminosity, L_bol approaches the Eddington Luminosity, L_Edd. On the other hand, the black hole X-ray binaries with persistent radio emission (mostly HMXBs) produce superluminal jets with beta_app < 1 at relatively low accretion rate. Our work here brings Galactic microquasars closer to extragalactic AGNs and quasars as the environment plays an important role in the formation of superluminal jets.

Observations of (S III) emission from Galactic radio sources - The detection of distant planetary nebulae and a search for supernova remnant emission

NASA Technical Reports Server (NTRS)

Kistiakowsky, V.; Helfand, D. J.

1993-01-01

Narrow-band near-infrared imaging observations at wavelengths corresponding to forbidden S III 9069,9532 A have been carried out at the MDM 1.3 m telescope for 23 radio sources near the Galactic plane in an attempt to detect emission associated with nebulae marking the endpoints of stellar evolution. While none of the known remnants or remnant candidates were detected, 10 of the 11 PN candidates from a new radio imaging survey of the Galactic plane were clearly seen in the forbidden S III 9532 A line. We present a calculation of the relative efficacy of searching for PNe in the forbidden O III and forbidden S III lines; for the majority of all PNe, the observed forbidden S III 9532 A line is predicted to be stronger than forbiden O III 5007 A whenever the visual extinction exceeds 3 magnitudes. This makes forbidden S III the superior tracer of PNe at distances exceeding a few kpc. We briefly comment on the significance of this approach to defining the spatial distribution of the PN population of the Galaxy.

LOFAR/H-ATLAS: the low-frequency radio luminosity-star formation rate relation

NASA Astrophysics Data System (ADS)

Gürkan, G.; Hardcastle, M. J.; Smith, D. J. B.; Best, P. N.; Bourne, N.; Calistro-Rivera, G.; Heald, G.; Jarvis, M. J.; Prandoni, I.; Röttgering, H. J. A.; Sabater, J.; Shimwell, T.; Tasse, C.; Williams, W. L.

2018-04-01

Radio emission is a key indicator of star formation activity in galaxies, but the radio luminosity-star formation relation has to date been studied almost exclusively at frequencies of 1.4 GHz or above. At lower radio frequencies, the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays. As part of the LOFAR Surveys Key Science project, the Herschel-ATLAS NGP field has been surveyed with LOFAR at an effective frequency of 150 MHz. We select a sample from the MPA-JHU catalogue of Sloan Digital Sky Survey galaxies in this area: the combination of Herschel, optical and mid-infrared data enable us to derive star formation rates (SFRs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity-star formation relation in the nearby Universe. For those objects selected as star-forming galaxies (SFGs) using optical emission line diagnostics, we find a tight relationship between the 150 MHz radio luminosity (L150) and SFR. Interestingly, we find that a single power-law relationship between L150 and SFR is not a good description of all SFGs: a broken power-law model provides a better fit. This may indicate an additional mechanism for the generation of radio-emitting cosmic rays. Also, at given SFR, the radio luminosity depends on the stellar mass of the galaxy. Objects that were not classified as SFGs have higher 150-MHz radio luminosity than would be expected given their SFR, implying an important role for low-level active galactic nucleus activity.

Radio and X-Ray Observations of the 1998 Outburst of the Recurrent X-Ray Transient 4U 1630-47

NASA Astrophysics Data System (ADS)

Hjellming, R. M.; Rupen, M. P.; Mioduszewski, A. J.; Kuulkers, E.; McCollough, M.; Harmon, B. A.; Buxton, M.; Sood, R.; Tzioumis, A.; Rayner, D.; Dieters, S.; Durouchoux, P.

1999-03-01

We report radio (NRAO VLA and Australia Telescope Compact Array), soft X-ray (Rossi X-Ray Timing Explorer ASM), and hard X-ray (Compton Gamma Ray Observatory BATSE) observations of a 1998 outburst in the recurring X-ray transient 4U 1630-47, where radio emission was detected for the first time. The radio observations identify the position of 4U 1630-47 to within 1". Because the radio emission is optically thin with a spectral index of ~-0.8 during the rise, peak, and decay of the initial radio event, the emission is probably coming from an optically thin radio jet ejected over a period of time. The 20-100 keV emission first appeared 1998 January 28 (MJD 50841), the 2-12 keV emission first appeared 1998 February 3 (MJD 50847), and the first radio emission was detected 1998 February 12.6 (MJD 50856.6). The rise of the radio emission probably began about 1998 February 7 (MJD 50851) when the X-rays were in a very hard fluctuating-hardness state, just before changing to a softer, more stable hardness state.

The Mobile Laboratory for Radio-Frequency Interference Monitoring at the Sardinia Radio Telescope

NASA Astrophysics Data System (ADS)

Bolli, Pietro; Gaudiomonte, Francesco; Ambrosini, Roberto; Bortolotti, Claudio; Roma, Mauro; Barberi, Carlo; Piccoli, Fabrizio

2013-10-01

In this paper, a quite unique mobile laboratory for monitoring radio-frequency interference with a radio-astronomical observatory is described. The unit is fully operational at the new Sardinia Radio Telescope, a 64-m antenna now in the commissioning phase in Italy. The mobile laboratory is mainly used to identify the source of interference with the radio astronomy service using iterative triangulations in the azimuth directions. Both the design and realization of this prototype were handled with outstanding care to limit the emission of self-interference as much as possible. The laboratory was equipped with excellent microwave instruments in terms of sensitivity, frequency coverage, dynamic range, and various demodulation and signal-analysis facilities. The unit can be quickly switched to different RF and power-supply configurations, while offering operators a safe and efficient workplace, even in adverse meteorological and driving conditions. In the past months, the mobile laboratory has proven to be successful in detecting and identifying many radio interferers. Two examples of measurement campaigns are described.

Onion-shell model for cosmic ray electrons and radio synchrotron emission in supernova remnants

NASA Technical Reports Server (NTRS)

Beck, R.; Drury, L. O.; Voelk, H. J.; Bogdan, T. J.

1985-01-01

The spectrum of cosmic ray electrons, accelerated in the shock front of a supernova remnant (SNR), is calculated in the test-particle approximation using an onion-shell model. Particle diffusion within the evolving remnant is explicity taken into account. The particle spectrum becomes steeper with increasing radius as well as SNR age. Simple models of the magnetic field distribution allow a prediction of the intensity and spectrum of radio synchrotron emission and their radial variation. The agreement with existing observations is satisfactory in several SNR's but fails in other cases. Radiative cooling may be an important effect, especially in SNR's exploding in a dense interstellar medium.

Microtubule nucleation and organization in dendrites

PubMed Central

Delandre, Caroline; Amikura, Reiko; Moore, Adrian W.

2016-01-01

ABSTRACT Dendrite branching is an essential process for building complex nervous systems. It determines the number, distribution and integration of inputs into a neuron, and is regulated to create the diverse dendrite arbor branching patterns characteristic of different neuron types. The microtubule cytoskeleton is critical to provide structure and exert force during dendrite branching. It also supports the functional requirements of dendrites, reflected by differential microtubule architectural organization between neuron types, illustrated here for sensory neurons. Both anterograde and retrograde microtubule polymerization occur within growing dendrites, and recent studies indicate that branching is enhanced by anterograde microtubule polymerization events in nascent branches. The polarities of microtubule polymerization events are regulated by the position and orientation of microtubule nucleation events in the dendrite arbor. Golgi outposts are a primary microtubule nucleation center in dendrites and share common nucleation machinery with the centrosome. In addition, pre-existing dendrite microtubules may act as nucleation sites. We discuss how balancing the activities of distinct nucleation machineries within the growing dendrite can alter microtubule polymerization polarity and dendrite branching, and how regulating this balance can generate neuron type-specific morphologies. PMID:27097122

Non-dipolar magnetic field models and patterns of radio emission: Uranus and Neptune compared

NASA Technical Reports Server (NTRS)

Evans, D. R.

1994-01-01

The magnetic field geometries of Uranus and Neptune are superficially similar, and are similarly unlike those of other planets: the field strengths are similar, and they contain extraordinarily large non-dipolar components. As a corollary, the best dipolar field models of each of the two planets comprises a dipole that is considerably offset from the planetary center and tilted away from the rotational axis. However, in other respects the best field models of the two planets are quite different. Uranus has a quadrupole model in which all the terms are well determined and in which none of the higher order terms is determined. To represent the magnetometer data acquired during Voyager's Neptune encounter requires a model of order 8 (instead of Uranus' order 2), yet many of the coefficients are poorly determined. A second model, an octupole model comprising the terms up to order three of the order 8 model, has been suggested by the magnetometer team as being useful; its use, however, is limited only to the region outside of about 2R(exp N), whereas planetary radio emissions have their sources well inside this surface. Computer code has been written that permits an analysis of the detailed motion of low energy charged particles moving in general planetary magnetic fields. At Uranus, this code reveals the existence of an isolated region of the inner magnetosphere above the day side in which particles may be trapped, separate from the more general magnetospheric trapping. An examination of the so-call ordinary mode uranian radio emissions leads us to believe that these emissions are in fact extraordinary mode emissions coming from particles trapped in this isolated region. A similar attempt to discover trapping regions at Neptune has proved, unfortunately, to be impossible. This arises from three factors: (1) the computation needed to track particles in an eighth order field is more than an order of magnitude greater than that needed to perform a similar calculation in a

THE COMPLEX NORTH TRANSITION REGION OF CENTAURUS A: RADIO STRUCTURE

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

Neff, Susan G.; Eilek, Jean A.; Owen, Frazer N., E-mail: susan.g.neff@nasa.gov

2015-04-01

We present deep radio images of the inner ∼50 kpc of Centaurus A, taken with the Karl G. Jansky Very Large Array at 90 cm. We focus on the Transition Regions between the inner galaxy—including the active nucleus, inner radio lobes, and star-forming disk—and the outer radio lobes. We detect previously unknown extended emission around the Inner Lobes, including radio emission from the star-forming disk. We find that the radio-loud part of the North Transition Region (NTR), known as the North Middle Lobe, is significantly overpressured relative to the surrounding interstellar medium. We see no evidence for a collimated flow from themore » active galactic nucleus through this region. Our images show that the structure identified by Morganti et al. as a possible large-scale jet appears to be part of a narrow ridge of emission within the broader, diffuse, radio-loud region. This knotty radio ridge is coincident with other striking phenomena: compact X-ray knots, ionized gas filaments, and streams of young stars. Several short-lived phenomena in the NTR, as well as the frequent re-energization required by the Outer Lobes, suggest that energy must be flowing through both Transition Regions at the present epoch. We suggest that the energy flow is in the form of a galactic wind.« less

Search for X-ray jets from high redshift radio sources.

NASA Astrophysics Data System (ADS)

Schwartz, Daniel A.; Cheung, Teddy; Gobeille, Doug; Marshall, Herman L.; Migliori, Giulia; Siemiginowska, Aneta; Wardle, John F. C.; Worrall, Diana M.; Birkinshaw, Mark

2018-06-01

We are conducting a Chandra "snapshot" survey of 14 radio quasars at redshifts z>3. These are selected to have one sided, arc-sec scale structure, either a jet or lobe, and come from a complete, objectively-defined sample of sources with radio flux density > 70 mJy, and with a spectroscopic redshift from the SDSS. Our objectives are to find X-ray emitting jets, compare the X-ray and radio morphology, and detect X-ray emission arising from inverse Compton scattering of the cosmic microwave background even for those cases where the radio emission is no longer detectable. For this meeting, we expect 5 of the 14 sources to have been observed.

Testing the Triggering Mechanism for Luminous, Radio-Quiet Red Quasars in the Clearing Phase: A Comparison to Radio-Loud Red Quasars

NASA Astrophysics Data System (ADS)

Glikman, Eliat

2016-10-01

We propose to conduct a controlled study of the relationship between radio emission and host galaxy morphology for a new sample of radio-quiet dust-reddened quasars selected by their infrared colors in WISE and 2MASS (W2M). These sources are the radio-quiet analogs to the FIRST-2MASS (F2M) red quasars, which we found to be predominantly driven by major mergers. F2M red quasars are accreting at very high rates and exhibit broad absorption lines associated with outflows and feedback. Their properties are consistent with buried quasars expelling their dusty shrouds in an an evolutionary phase predicted by merger-driven co-evolution models. The quasars in both samples are the most intrinsically luminous objects in the Universe - the regime where we expect mergers to dominate. However, recent lines of evidence suggest that radio emission may be linked to AGN reddening and merging hosts. We will use WFC3/IR and ACS to image the host galaxies of W2M quasars in the two redshift regimes that our previous studies probed, z 0.7 and z 2, testing the merger-driven quasar paradigm across the full radio range with a minimum of selection effects or other biases that plague many studies comparing different samples. The images proposed here will sample the host galaxies in rest-frame visible and UV light to look for merger signatures. Evidence for mergers in these quasar hosts would support a picture in which luminous quasars and galaxies co-evolve through major-mergers, independent of their radio properties. The absence of mergers in our data would link radio emission to mergers and require an alternate explanation for the extreme properties of these radio-quiet sources.