First detection of VHE gamma-ray emission from TXS 1515–273, study of its X-ray variability and spectral energy distribution
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V A Acciari↗
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Depleted Graphene-Insulator-Silicon Junctions for High Energy Detection of Ions and Gamma Rays.
Abstract not provided.
Ruiz, Isaac↗
Depleted Graphene-Insulator-Silicon Junctions for High Energy Detection of Ions and Gamma Rays.
Abstract not provided.
Ruiz, Isaac↗
Gamma-Ray Emission from Galaxies Hosting Molecular Outflows
Many star-forming galaxies and those hosting active galactic nuclei show evidence of massive outflows of material in a variety of phases including ionized, neutral atomic, and molecular. Molecular outflows in particular have been the focus of recent interest as they may be responsible for removing gas from the galaxy, thereby suppressing star formation. As material is ejected from the cores of galaxies, interactions of the outflowing material with the interstellar medium can accelerate cosmic rays and produce high-energy gamma rays. In this work, we search for gamma-ray emission from a sample of local galaxies known to host molecular outflows using data collected by the Fermi Large Area Telescope. We employ a stacking technique in order to search for and characterize the average gamma-ray emission properties of the sample. Gamma-ray emission is detected from the galaxies in our sample at the 4.4σ level with a power-law photon index of Γ ≈ 2 in the 1–800 GeV energy range. The emission is found to correlate with tracers of star formation activity, namely the 8–1000 μm infrared luminosity. We also find that the observed signal can be predominantly attributed to H II galaxies hosting energy-driven outflows. While we do not find evidence suggesting that the outflows are accelerating charged particles directly, galaxies with molecular outflows may produce more gamma rays than galaxies without outflows. In particular, the set consisting of gamma-ray-detected galaxies with molecular outflows are nearly perfect calorimeters and may be future targets for searches of high-energy neutrinos.
79 ASTRONOMY AND ASTROPHYSICS↗
Gamma-ray bursts from colliding neutron stars
Three distance scales to gamma-ray bursters are discussed: about 300 pc, about 2 - 50 kpc, and about 1 Gpc, corresponding to the Galactic disk, Galactic halo, and extragalactic origin. No compelling evidence is found in favor of any of them. The BATSE experiment on GRO should determine the distance scale by determining the angular distribution of very weak bursts. The rate of collisions between the neutron stars is about 0.0001/yr in our Galaxy, and about 10 exp 5/yr within the Hubble distance. The collisions are the final phases of binary orbit decay driven by gravitational radiation, and may produce gamma-ray bursts detectable at extra-galactic distances. If strange stars exist then their collisions must release about 10 exp 49 erg in gamma-rays over about 10 seconds. Such events should be detectable out to about 1 Gpc with the current instruments.
Paczynski, Bohdan↗
Gamma-ray astronomy: Nuclear transition region
This monograph reviews the major theoretical and experimental efforts made during the past 12 years in gamma-ray astronomy over the energy range from 10 keV to about 100 MeV, where nuclear-transition lines are expected. Early attempts to detect celestial gamma rays are recounted, mechanisms of gamma-ray line and continuum production are examined, and formulas giving the various possible differential gamma-ray spectral shapes are provided. Predicted fluxes are discussed for solar gamma rays as well as for gamma emission from supernova remnants, supernovae, neutron stars, flare stars, the galactic core and disk, black holes, and diffuse sources. Gamma-ray interactions with matter are analyzed, particularly the photoelectric effect, Compton scattering from free electrons, and pair production in nuclear fields. Significant results are summarized for observations of gamma rays from the sun as well as from point and extended sources within and beyond the Galaxy, including diffuse fluxes and transient gamma-ray bursts. Factors pertaining to the design of gamma-ray astronomy experiments are considered, especially detector background limitations, gamma-ray production within instruments, and present-day detection methods.
Chupp, E. L.↗
A catalog of gamma-ray bursts with earth crossing times
A catalog of 111 confirmed gamma-ray bursts detected between 1967 July and 1979 June is presented. Both localization information and earth crossing times for the gamma-ray wave fronts are given. Data which have appeared in some previous catalogs have been revised; many previously unpublished events detected by an international network of dedicated deep space and near-earth experiments since 1976 are also presented.
Klebesadel, R.↗
Gamma rays of energy or = 10(15) eV from Cyg X-3
The experimental data of extensive air showers observed at Akeno have been analyzed to detect the gamma ray signal from Cyg X-3. After muon poor air showers are selected, the correlation of data acquisition time with 4.8 hours X-ray period is studied, giving the data concentration near the phase 0.6, the time of X-ray maximum. The probability that uniform backgrounds create the distribution is 0.2%. The time averaged integral gamma ray flux is estimated as (1.1 + or - 0.4)x 10 to the -14th power cm(-2) sec(-1) for Eo 10 to the 15th power eV and (8.8 + or - 5.0)x 10 to the 14th power cm(-2) sec(-1) for Eo 6 x 10 to the 14th power eV.
Kifune, T.↗
Analysis of Gamma-Ray Data from Solar Flares in Cycles 21 and 22
One of our primary accomplishments under grant NAGW-35381 was the systematic derivation and compilation, for the first time, of physical parameters for all gamma-ray flares detected by the SMM GRS during its ten year lifetime. The flare parameters derived from the gamma-ray spectra include: bremsstrahlung fluence and best-fit power-law parameters, narrow nuclear line fluence, positron annihilation line fluence, neutron capture line fluence, and an indication of whether or not greater than 10 MeV emissions were present. We combined this compilation of flare parameters with our plots of counting rate time histories and flare spectra to construct an atlas of gamma-ray flare characteristics. The atlas time histories display four energy bands: 56-199 kev, 298526 keV, 4-8 MeV, and 10-25 MeV. These energy bands respectively measure nonrelativistic bremsstrahlung, trans-relativistic bremsstrahlung, nuclear de-excitation, and ultra-relativistic bremsstrahlung. The atlas spectra show the integrated high-energy spectra measured for all GRS flares and dissects them into electron bremsstrahlung, positron annihilation and nuclear emission components. The atlas has been accepted for publication in the Astrophysical Journal Supplements and is currently in press. The atlas materials were also supplied to the Solar Data Analysis Center at Goddard Space Flight Center and were made available through a web site at the University of New Hampshire. Since a uniform methodology was adopted for deriving the flare parameters, this atlas will be very useful for future statistical and correlative studies of solar flares-three independent groups are presently using it to correlate interplanetary energetic particle measurements with our gamma-ray measurements. A better model for the response of the GRS instrument to high energy radiation was also developed. A refined response model was needed because the old model was not adequate for predicting the first and second escape peaks associated with strong nuclear lines nor could it accurately describe the Compton continuum shape. The new response was developed using a GEANT based simulation code and tested against preflight calibration data. The refinement of the response model and the removal of systematic errors now allow more detailed spectral studies of the GRS gamma-ray measurements. This refined response function was supplied to the Solar DAC at Goddard and was also made available via a web site at the University of New Hampshire.
Vestrand, W. Thomas↗
X-ray Properties of an Unbiased Hard X-ray Detected Sample of AGN
The SWIFT gamma ray observatory's Burst Alert Telescope (BAT) has detected a sample of active galactic nuclei (AGN) based solely on their hard X-ray flux (14-195keV). In this paper, we present for the first time XMM-Newton X-ray spectra for 22 BAT AGXs with no previously analyzed X-ray spectra. If our sources are a representative sample of the BAT AGN, as we claim, our results present for the first time global X-ray properties of an unbiased towards absorption (n(sub H) < 3 x 10(exp 25)/sq cm), local (< z >= 0.03), AGN sample. We find 9/22 low absorption (n(sub H) < 10(exp 23)/sq cm), simple power law model sources, where 4 of these sources have a statistically significant soft component. Among these sources, we find the presence of a warm absorber statistically significant for only one Seyfert 1 source, contrasting with the ASCA results of Reynolds (1997) and George et al. (1998), who find signatures of warm absorption in half or more of their Seyfert 1 samples at similar redshifts. Additionally, the remaining sources (13122) have more complex spectra, well-fit by an absorbed power law at E > 2.0 keV. Five of the complex sources (NGC 612, ESO 362-G018, MRK 417, ESO 506-G027, and NGC 6860) are classified as Compton-thick candidates. Further, we find four more sources (SWIFT J0641.3+3257, SWIFT J0911.2+4533, SWIFT J1200.8+0650, and NGC 4992) with properties consistent with the hidden/buried AGN reported by Ueda et al. (2007). Finally, we include a comparison of the XMM EPIC spectra with available SWIFT X-ray Telescope (XRT) observations. From these comparisons, we find 6/16 sources with varying column densities, 6/16 sources with varying power law indices, and 13/16 sources with varying fluxes, over periods of hours to months. Flux and power law index are correlated for objects where both parameters vary.
Winter, Lisa M.↗
Gamma-Ray Pulsar Candidates for GLAST
The Gamma-ray Large Area Space Telescope (GLAST) will be launched this year, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio frequencies, are likely to emit greater than 100 MeV gamma rays with intensities detectable by the LAT. The main figure of merit used to select gamma-ray pulsar candidates is sqrt(E-dot)/d2, where E-dot is the energy loss due to rotational spin-down, and d is the distance to the pulsar. The figure of merit incorporates spin-down flux at earth (proportional to E-dot/d2) times efficiency, assumed proportional to l/sqrt(E-dot). A few individual objects are cited to illustrate the issues. Since large E-dot pulsars also tend to have large timing noise and occasional glitches, their ephemerides can become inaccurate in weeks to months. To detect and study the gamma-ray emission the photons must be accurately tagged with the pulse phase. With hours to days between gamma-ray photon arrival times from a pulsar and months to years of LAT exposure needed for good detections, GLAST will rely on radio and X-ray timing measurements throughout the continuous gamma-ray observations. The poster will describe efforts to coordinate pulsar timing of the candidate gamma-ray pulsars.
Thompson, D. J.↗
Optimization and characterization of a silicon photomultiplier-based ZnS(Ag) proton recoil fast neutron detector for nuclear fuel performance monitoring at TREAT
The restart of the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory and consequent refurbishment of the Fuel Motion Monitoring System (FMMS), or Hodoscope, offers the opportunity to upgrade the detector system used for neutron imaging. Silicon photomultipliers (SiPMs) are a viable option for updating the Hodoscope to yield improved fuel monitoring capability. The Hodoscope uses ZnS(Ag) proton recoil scintillators (PRS) that provide good gamma-ray suppression and discrimination. Previous work showed that the Hamamatsu S13360-6075CS SiPM offers the best neutron detection and gamma-ray discrimination capability with the ZnS PRS. This work optimizes a SiPM-based detector and develops a PRS prototype for testing. Specifically, possible overvoltages for use are determined by confirming steady operation over extended measurement times. In addition, various SiPM-circuit implementations are tested to optimize the detector according to desired properties, and ultimately a PRS prototype is developed with modifiable components for versatile testing. Measurements of the neutron detection efficiency and gamma-ray rejection efficiency of SiPM-based PRS detectors and a reference PMT-based detector are also carried out. Neutron detection efficiency ranges between 1-2%, and detected gamma-ray rejection efficiency is on the order of 10 -7 . In conclusion, use of a low-pass filter only or a low-pass filter and 50-ω shunt resistor is recommended for the SiPM-based detector, and both configurations demonstrate improved performance over the PMT-based detector.
46 - INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AN↗
Analysis of New Orion Gamma Ray Data and Monte Carlo Simulations of BATSE Gamma Ray Bursts
These studies were stimulated by the reported COMPTEL detection of nuclear gamma ray line emission from the Orion star formation region. Although the observation have very recently been retracted, the detailed analyses that we carried out clearly showed that the low energy cosmic rays that would have been required to explain the reported fluxes were exceedingly restrictive and thus highly improbable. Moreover, these studies proved to be the trigger for very productive new work. In particular, they led us into carefully re-examining the problem of the origin of the light elements, Li, Be and B, where we showed that the light elements could, in fact, be produced primarily by Galactic cosmic rays and did not require an unobserved low energy cosmic ray source , as had been suggested. We further showed that the observed abundances of Be and B in old halo stars contradicted the common belief that the Galactic cosmic rays were accelerated out of the well mixed interstellar medium, and required instead that they be accelerated out of freshly synthesized matter from supernovae. This work, in turn, led us to propose a new origin of Galactic cosmic rays from the refractory grains in supernova enriched cores of superbubbles.
Lingenfelter, Richard E.↗
Theoretical Studies in Gamma-Ray Astrophysics
These studies were stimulated by the reported COMPTEL detection of nuclear gamma ray line emission from the Orion star formation region. Although the observation have very recently been retracted, the detailed analyses that we carried out clearly showed that the low energy cosmic rays that would have been required to explain the reported fluxes were exceedingly restrictive and thus highly improbable. More importantly, these studies proved to be the trigger for very productive new work. In particular, they led us into carefully re-examining the problem of the origin of the light elements, Li, Be and B, where we showed that the light elements could, in fact, be produced primarily by Galactic cosmic rays and did not require an unobserved low energy cosmic ray source , as had been suggested. We further showed that the observed abundances of Be and B in old halo stars contradicted the common belief that the Galactic cosmic rays were accelerated out of the well mixed interstellar medium, and required instead that they be accelerated out of freshly synthesized matter from supernovae. This work, in turn, led us to propose a new origin of Galactic cosmic rays from the refractory grains in supernova enriched core of superbubbles, which is now the subject of our on-going research under a new grant from the Astrophysics Theory Program.
Lingenfelter, Richard E.↗
The Compton Gamma Ray Observatory
The Arthur Holly Compton Gamma Ray Observatory (Compton) was launched by the Space Shuttle Atlantis on 5 April 1991. The spacecraft and instruments are in good health and returning exciting results. The mission provides nearly six orders of magnitude in spectral coverage, from 30 keV to 30 GeV, with sensitivity over the entire range an order of magnitude better than that of previous observations. The 16,000 kilogram observatory contains four instruments on a stabilized platform. The mission began normal operations on 16 May 1991 and is now over half-way through a full-sky survey. The mission duration is expected to be from six to ten years. A Science Support Center has been established at Goddard Space Flight Center for the purpose of supporting a vigorous Guest Investigator Program. New scientific results to date include: (1) the establishment of the isotropy, combined with spatial inhomogeneity, of the distribution of gamma-ray bursts in the sky; (2) the discovery of intense high energy (100 MeV) gamma-ray emission from 3C 279 and other quasars and BL Lac objects, making these the most distant and luminous gamma-ray sources ever detected; (3) one of the first images of a gamma-ray burst; (4) the observation of intense nuclear and position-annihilation gamma-ray lines and neutrons from several large solar flares; and (5) the detection of a third gamma-ray pulsar, plus several other transient and pulsing hard X-ray sources.
Gehrels, N.↗
Instrumental and atmospheric background lines observed by the SMM gamma-ray spectrometer
Preliminary identifications of instrumental and atmospheric background lines detected by the gamma-ray spectrometer on NASA's Solar Maximum Mission satellite (SMM) are presented. The long-term and stable operation of this experiment has provided data of high quality for use in this analysis. Methods are described for identifying radioactive isotopes which use their different decay times. Temporal evolution of the features are revealed by spectral comparisons, subtractions, and fits. An understanding of these temporal variations has enabled the data to be used for detecting celestial gamma-ray sources.
Share, G. H.↗
Characterization Techniques Investigated for Characterization of Anomalous Materials in Plutonium Oxide – 25666
The DOE has adopted a Dilute and Dispose approach for processing surplus plutonium which consists of blending plutonium oxide with adulterants and packaging it in a form which is acceptable for disposal at the Waste Isolation Pilot Plant. The feed material for the downblend process is intended to be pure plutonium oxide powder, however other objects are occasionally encountered within the oxide, particularly with legacy material. Potential technologies which could assist in the resolution of incidents where such anomalies are encountered have been investigated. Resolution of these incidents requires characterization of the anomalous object so that plutonium oxide processing can resume and so that a disposition pathway can be determined for the anomalous material. Technologies including gamma ray spectroscopy, alpha-gamma coincidence, LiDAR volumetric measurements, and surface conductivity measurements were investigated for this purpose, with a focus on systems which can be easily introduced into the processing environment when an anomaly is encountered, then removed from the environment after resolution to avoid impeding normal processing activities. This places an emphasis on small and portable measurement systems and systems that can operate in a high-background, oxide-processing environment. Gamma ray systems investigated include the GR1™a CZT detector and the MicroGe™a germanium detector, with a focus on detecting characteristic gamma rays from Pu-239 and other actinides. A gamma ray and alpha particle coincidence method was investigated with the goal of identifying actinides in the presence of a gamma ray background produced by adjacent plutonium oxide material. Leica™b BLK360 G1 and Keyence™c LJ-X8300 LiDAR systems were investigated for use in conjunction with mass measurements to gain accurate material density values, and a Foerster Sigmatest™d 2.070 was tested to determine surface conductivity. The combination of these properties would allow improved identification and characterization of a wide variety of potential anomalous material.
Munson, Justin M.↗
The Ever Changing X-ray Sky: X-ray Transients Observed With BATSE
X-ray transients are typically sources in our own galaxy. They are called "transient" because they usually spend more time in quiescence than in outburst. These transients consist of a compact object and a "normal" star in a binary system. The compact objects in some of these systems are known to be neutron stars because they exhibit X-ray bursts or periodic pulsations, Other systems are believed to contain black holes based upon their outburst behavior and in some cases, optical measurements of their masses. The Burst and Transient Source Experiment (BATSE), one of 4 instruments on the Compton Gamma Ray Observatory, was an all-sky instrument sensitive to photons from about 20 keV to 2 MeV, designed primarily to detect gamma-ray bursts. Transient and persistent hard X-ray point sources were extracted from the data using the Earth occultation method to measure source intensities. In this method, the change in count rate in a BATSE detector was measured just before and just after a source location was occulted by the Earth. For long period pulsars (>1 second) Fourier transforms and epoch-folded searches were used to measure pulse frequency and pulsed flux. Using these methods, 3 black hole candidates and 6 X-ray pulsars were discovered with BATSE during its 9 years in orbit. BATSE provided unprecedented temporal coverage in the 20 keV - 2 MeV band, allowing detection of numerous new outbursts of X-ray transients. In this talk, I will describe the BATSE instrument, discuss methods we use to detect hard X-ray sources, and describe observations of X-ray transients.
Wilson-Hodge, Colleen A.↗