Gamma-ray Transients Research Articles

DETECTION OF SPECTRAL EVOLUTION IN THE BURSTS EMITTED DURING THE 2008-2009 ACTIVE EPISODE OF SGR J1550–5418

In early October 2008, the Soft Gamma Repeater SGRJ1550 - 5418 (1E 1547.0 - 5408, AXJ155052 - 5418, PSR J1550 - 5418) became active, emitting a series of bursts which triggered the Fermi Gamma-ray Burst Monitor (GBM) after which a second especially intense activity period commenced in 2009 January and a third, less active period was detected in 2009 March-April. Here we analyze the GBM data all the bursts from the first and last active episodes. We performed temporal and spectral analysis for all events and found that their temporal characteristics are very similar to the ones of other SGR bursts, as well the ones reported for the bursts of the main episode (average burst durations \sim 170 ms). In addition, we used our sample of bursts to quantify the systematic uncertainties of the GBM location algorithm for soft gamma-ray transients to < 8 deg. Our spectral analysis indicates significant spectral evolution between the first and last set of events. Although the 2008 October events are best fit with a single blackbody function, for the 2009 bursts an Optically Thin Thermal Bremsstrahlung (OTTB) is clearly preferred. We attribute this evolution to changes in the magnetic field topology of the source, possibly due to effects following the very energetic main bursting episode.

LONG GAMMA-RAY TRANSIENTS FROM COLLAPSARS

In the collapsar model for common gamma-ray bursts, the formation of a centrifugally supported disk occurs during the first $\sim$10 seconds following the collapse of the iron core in a massive star. This only occurs in a small fraction of massive stellar deaths, however, and requires unusual conditions. A much more frequent occurrence could be the death of a star that makes a black hole and a weak or absent outgoing shock, but in a progenitor that only has enough angular momentum in its outermost layers to make a disk. We consider several cases where this is likely to occur - blue supergiants with low mass loss rates, tidally-interacting binaries involving either helium stars or giant stars, and the collapse to a black hole of very massive pair-instability supernovae. These events have in common the accretion of a solar mass or so of material through a disk over a period much longer than the duration of a common gamma-ray burst. A broad range of powers is possible, $10^{47}$ to $10^{50}\,$erg s$^{-1}$, and this brightness could be enhanced by beaming. Such events were probably more frequent in the early universe where mass loss rates were lower. Indeed this could be one of the most common forms of gamma-ray transients in the universe and could be used to study first generation stars. Several events could be active in the sky at any one time. A recent example of this sort of event may have been the SWIFT transient Sw-1644+57.

Searching for Space Debris Elements with the “Pi of the Sky” System

The main purpose of the “Pi of the Sky” system is to investigate short timescale astrophysical phenomena (particularly gamma-ray bursts, optical transients and variable stars). Wide field, short exposures and full automation of the system, together with effective algorithms, give good prospects for effective identification of space debris elements. These objects can be a great danger for current and future space missions, and should be continuously monitored and cataloged. Algorithms for identifying optical transients (OT), designed for the “Pi of the Sky” experiment enable moving objects like planes, satellites and space debris elements to be identified. The algorithm verifies each OT candidate against a database of known satellites and is also able to automatically self-identify moving objects not present in this database. The data collected by the prototype in the Las Campanas Observatory enabled us to obtain a large sample of observations of moving objects. Some of these objects were identified as high-orbit geostationary (GEO) satellites, which shows that it is possible to observe even distant satellites with small aperture photo lenses. The analysis of the sample is still going on. The preliminary results and algorithms for automatic identification of moving objects will be described here.

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

Since its early phases of operation, the AGILE mission is successfully observing Gamma Ray Bursts (GRBs) in the hard X-ray band with the SuperAGILE imager and in the MeV range with the Mini-Calorimeter. Up to now, three firm GRB detections were obtained above 25 MeV and some bursts were detected with lower statistical confidence in the same energy band. When a GRB is localized, either by SuperAGILE or Swift/BAT or INTEGRAL/IBIS or Fermi/GBM or IPN, inside the field of view of the Gamma Ray Imager of AGILE, a detection is searched for in the gamma ray band or an upper limit is provided. A promising result of AGILE is the detection of very short gamma ray transients, a few ms in duration and possibly identified with Terrestrial Gamma-ray Flashes. In this paper we show the current status of the observation of Gamma Ray Bursts and Terrestrial Gamma-ray Flashes with AGILE.

Modeling and Simulation for Transient Pulse Gamma-ray Effects on Semiconductor Devices

The explosion of a nuclear weapon radiates a gamma-ray in the form of a transient pulse. If the gamma-ray introduces to semiconductor devices, much Electron-Hole Pairs(EHPs) are generated in depletion region of the devices[7]. as a consequence of that, high photocurrent is created and causes upset, latchup and burnout of semiconductor devices[8]. This phenomenon is known for Transient Radiation Effects on Electronics(TREE), also called dose-rate effects. In this paper 3D structure of inverter and NAND gate device was designed and transient pulse gamma-ray was modeled. So simulation for transient radiation effect on inverter and NAND gate was accomplished and mechanism for upset and latchup was analyzed.

GLAST large area telescope multiwavelength planning

Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch.

Gamma-Ray Spectral Characteristics of Thermal and Non-Thermal Emission from Three Black Holes

Cygnus X-1 and the gamma-ray transients GRO J0422+32 and GRO J1719-24 displayed similar spectral properties when they underwent transitions between the high and low gamma-ray (30 keV to few MeV) intensity states. When these sources were in the high γ-ray intensity state (γ2, for Cygnus X-1), their spectra featured two components: a Comptonized shape below 200-300keV with a soft power-law tail (photon index >3) that extended to ~1MeV or beyond.When the sources were in the low-intensity state (γ0, for Cygnus X-1), the Comptonized spectral shape below 200 keV typically vanished and the entire spectrum from 30 keV to ~1MeV can be characterized by a single power law with a relatively harder photon index ~2–2.7. Consequently the high- and low-intensity gamma-ray spectra intersect, generally in the ~400 keV – ~1MeV range, in contrast to the spectral pivoting seen previously at lower (~10 keV) energies. The presence of the power-law component in both the high- and low-intensity gamma-ray spectra strongly suggests that the non-thermal process is likely to be at work in both the high and the low-intensity situations. We have suggested a possible scenario (Ling & Wheaton, 2003), by combining the ADAF model of Esin et al. (1998) with a separate jet region that produces the non-thermal gamma-ray emission, and which explains the state transitions. Such a scenario will be discussed in the context of the observational evidence, summarized above, from the database produced by EBOP, JPL's BATSE earth occultation analysis system.

The Gamma-Ray Imaging Detector AGILE: Scientific Goals and Instrument Performance

AGILE is an ASI Small Scientific Mission dedicated to gamma-ray astrophysics, which will detect and image photons in the 30MeV - 50GeV and in the 10-40keV energy ranges. It is planned to be operational during the second half of 2005 and it will be the only mission entirely dedicated to high energy astrophysics above 30MeV during the period 2005-2007. We discuss the expected performance of the AGILE space detector, which scientific program emphasizes a quick response to gamma-ray transients and multiwavelength studies of gamma-ray sources.

THE AGILE MISSION AND GAMMA-RAY ASTROPHYSICS

Gamma-ray astrophysics in the energy range between 30 MeV and 30 GeV is in desperate need of arcminute angular resolution and source monitoring capability. The AGILE Mission planned to be operational in 2004-2006 will be the only space mission entirely dedicated to gamma-ray astrophysics above 30 MeV. The main characteristics of AGILE are the simultaneous X-ray and gamma-ray imaging capability (reaching arcminute resolution) and excellent gamma-ray timing (10-100 microseconds). AGILE scientific program will emphasize a quick response to gamma-ray transients and multiwavelength studies of gamma-ray sources.

Transient Gamma‐Ray Spectrometer Observations of Gamma‐Ray Lines from Novae. III. The 478 keV Line from7Be Decay

The Wind spacecraft, which carries the Transient Gamma Ray Spectrometer (TGRS), moves in an extremely elliptical orbit that largely avoids Earth's trapped radiation belts and albedo γ-radiation. The TGRS therefore enjoys a relatively low level of background, which is also extremely stable. We show how this stability enables modeling of the time variability of background lines, which in turn enables a novel technique of background subtraction for use in the detection of transient astrophysical lines. We apply a simple version of this method to the line at 478 keV that is expected to arise from nucleosynthesis of 7Be in nearby novae. This search covers the entire southern ecliptic hemisphere during 1995-1997, including five known individual events and possible undiscovered individual events. The TGRS design also uses Wind's 3 s rotation period to modulate signals from the Galactic center. We use this feature of the instrument to search for a quasi-constant level of 478 keV emission from the accumulation of 7Be from several novae that are expected to occur in the direction of the Galactic center during that isotope's 53 day half-life. We derive upper limits on the transient (single nova) emission that improve on previous limits by about an order of magnitude and limits on the steady (many nova) emission that represent a factor of 2 improvement. Only weak limits can be placed on the key parameters in the nucleosynthesis and ejection of 7Be, however.

High‐Resolution Spectroscopy of Gamma‐Ray Bursts with the Transient Gamma‐Ray Spectrometer

A search for spectral lines in gamma-ray bursts detected with the Transient Gamma-Ray Spectrometer has been unable to confirm their existence. The spectrometer, aboard the Wind spacecraft, has detected gamma-ray bursts and other transients since 1995. We have performed a systematic search for narrow spectral lines in gamma-ray bursts detected with this instrument that augments and extends the results of a similar search of bursts detected with BATSE. This search procedure tests for statistically significant lines at all possible times and durations during a burst using the method of maximum likelihood and C-statistic. Simulations demonstrated the effectiveness of this procedure, particularly on Poisson distributed data, for distinguishing real features from statistical fluctuations. The most promising line candidates were consistent with chance fluctuations, given the large number of spectra searched.

The BeppoSAX sub-second bursts project

Sub-second GRBs have been identified as a separate class of gamma ray transients. However, despite recent advances in the field, sub-second GRB counterparts have yet to be found successfully. In order to explore the nature of these fast transients an on-line procedure is to be implemented at the BeppoSAX Scientific Operation Centre. The main objectives are the identification of true events and rapid position determination of their X-ray counterparts.

Transient Gamma Ray Spectrometer Observations of Gamma‐Ray Lines from Novae. I. Limits on the Positron Annihilation Line in Five Individual Novae

The Transient Gamma Ray Spectrometer (TGRS) on board the Wind spacecraft has spent most of the interval 1995-1997 in a high-altitude orbit where γ-ray backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect weak lines that are slightly offset from stronger background features. One such line is predicted from nucleosynthesis in classical novae, where β decays on a timescale of a few hours in an expanding envelope produce positrons that annihilate to generate a line that is blueshifted by a few keV away from the background annihilation line at 511 keV. The broad TGRS field of view contained five known Galactic novae during 1995 January-1997 June, and we have searched the spectra taken around the times of these events for the blueshifted nova annihilation line. Although no definite detections were made, the method is shown to be sensitive enough to detect novae occurring on ONeMg-rich white dwarfs out to about 2.5 kpc.

Non-Blazar Gamma-Ray Variables in the Galactic Plane: A New Class of Gamma-Ray Sources

AbstractWe discuss recent detections of time-variable gamma-ray sources near the Galactic plane. A new bright gamma-ray transient was detected by EGRET in June 1995 near the Galactic center (GRO J1838-04). Also one of the most interesting unidentified gamma-ray sources in the plane, 2CG 135+1, was recently shown to be variable. Both GRO J1838-04 and 2CG 135+1 share many characteristics: variability of the gamma-ray flux within days/weeks, occasional peak gamma-ray emission of comparable flux (˜ 4 x 10-6ph cm-2s-1), absence of radio-loud spectrally-flat AGNs or prominent radio pulsars within their error boxes, lack of strong X-ray and/or hard X-ray counterparts. These characteristics do not match those of either gamma-ray blazars or isolated pulsars. Therefore, GRO J1838-04 and 2CG 135+1 provide strong evidence for the existence of a new class of variable gamma-ray sources.

Characterization of vacancy-related defects introduced into silicon during heat treatment by deep-level transient spectroscopy and gamma-ray diffraction techniques

Vacancy-related defects introduced into n-Si during annealing or aluminium diffusion at high temperature (1000–1250°C) have been studied. Different ambients (argon, nitrogen, vacuum and chlorine-containing atmosphere) were used to create a vacancy supersaturation during heat treatments. Three deep-level centers whose formation is governed by the presence of vacancies have been identified. They were characterized by the following temperature dependences of the thermal emission rate:e3 = 7.92 × 107T2 × exp(− 0.455/kT),e5 = 2.64 × 106T2 × exp( − 0.266/kT),e7 = 7.26 × 106T2 × exp (− 0.192/kT). The influence of different factors, such as heat-treatment conditions, concentration of oxygen and doping level in initial crystals, on center formation was studied. An asymmetric diffuseγ-ray scattering was observed near the surface of a crystal irradiated by thermal neutrons and annealed in a chlorine-containing atmosphere. This scattering is related to the formation of structural defects of the vacancy type. In the same region of the crystal, the concentration of the E7 center was one order of magnitude higher than that of other deep-level centers. Comparison of theγ-ray diffraction and deeplevel transient spectroscopy (DLTS) data suggests that the formation of the center occurs under the conditions of Si supersaturation with vacancies.

Characterization of vacancy-related defects introduced into silicon during heat treatment by deep-level transient spectroscopy and gamma-ray diffraction techniques

Characterization of vacancy-related defects introduced into silicon during heat treatment by deep-level transient spectroscopy and gamma-ray diffraction techniques

First results from the TGRS high-resolution GRB Spectrometer

The Transient Gamma Ray Spectrometer (TGRS) is a 215 cm3 passivelycooled germanium detector designed primarily to study spectral features of gamma ray bursts. Since shortly after its launch on 1994 Nov. 1 it has been producing high-resolution spectra of GRBs and solar flares. Some of these spectra are presented here.

Solar breeze

With the assistance of the Moon's gravitational field, NASA will launch the Wind spacecraft November 1 to the forward libration point to study the physics of the solar‐terrestrial system. Eight instruments aboard the 1250‐kg satellite will measure various quantities in the solar wind about 1 hour before it reaches the Earth. The highly quantitative measurements will help scientists predict how changes in solar wind affect the Earth's atmosphere. “Extensive use has been made of ‘intelligent’ instruments, and they are able to operate in a wide variety of modes and productivity will be high,” says Keith Ogilvie, deputy project scientist. “It's pretty modern stuff,” Ogilvie says. Wind is the first of two missions of the Global Geospace Science (GGS) initiative, the U.S. component of the International Solar‐Terrestrial Physics program. The launch of Polar, the second GGS satellite, is slated for late 1995. Polar is designed to measure the flow of plasma within Earth's magnetosphere. Both craft, which together cost about $458 million to develop, are part of a larger project to provide simultaneous, interactive data on key regions of Earth's space environment, from beyond the Earth foreshock region to the magnetosphere to transient gamma ray events.

SMM observations of gamma-ray transients. 3: A search for a broadened, redshifted positron annihilation line from the direction of the Galactic center

view Abstract Citations (17) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SMM Observations of Gamma-Ray Transients. III. A Search for a Broadened, Redshifted Positron Annihilation Line from the Direction of the Galactic Center Harris, Michael J. ; Share, Gerald H. ; Leising, Mark D. Abstract We have searched for 1980-1988 Solar Maximum Mission gamma-ray spectrometer data for transient emission on timescales from hours to approximately 12 days of broad gamma-ray lines at energies approximately 400 keV, which were reported by the High Energy Astronomy Observatory (HEAO) 1 and SIGMA experiments from two sources lying toward the Galactic center. The lines have been interpreted as the product of the annihilation of positrons in pair plasmas surrounding the black hole candidate 1E 1740.7-2942 and the X-ray binary 1H 1822-371. Our results from a combined exposure of approximately 1.5 x 107s provide no convincing evidence for transient emission of this line on any timescale between approximately 9 hr and approximately 1 yr. Our 3 sigma upper limits on the line flux during approximately 12 day intervals are characteristically 4.8 x 10-3 photon/sq cm/s, while for approximately 1 day intervals our 3 sigma upper limits are characteristically 4.9 x 10-3 photon/sq cm/s. These results imply a duty cycle of less than 1.3% for the transient line measured from 1H 1822-371 during a approximately 3 week interval in 1977 by HEAO 1, and a duty cycle of less than or = 0.8% for the transient line detected in 1990 and 1992 from 1E 1740.7-2942 on approximately 1 day timescales by SIGMA. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174627 Bibcode: 1994ApJ...433...87H Keywords: Emission Spectra; Gamma Ray Astronomy; Gamma Ray Spectra; Line Spectra; Positron Annihilation; Space Plasmas; Spaceborne Astronomy; X Ray Binaries; Astronomical Spectroscopy; Black Holes (Astronomy); Gamma Ray Spectrometers; Solar Maximum Mission; Astronomy; GALAXY: CENTER; GAMMA RAYS: OBSERVATIONS full text sources ADS | data products SIMBAD (3) Related Materials (2) Part 1: 1993ApJ...416..601H Part 2: 1994ApJ...420..649H

SMM observations of gamma-ray transients. 2: A search for gamma-ray lines between 400 and 600 keV from the Crab Nebula

We have search spectra obtained by the Solar Maximum Mission Gamma-Ray Spectrometer during 1981-1988 for evidence of transient gamma-ray lines from the Crab Nebula which have been reported by previous experiments at energies 400-460 keV and 539 keV. We find no evidence for significant emission in any of these lines on time scales between aproximately 1 day and approximately 1 yr. Our 3 sigma upper limits on the transient flux during 1 d intervals are approximately equal to 2.2 x 10(exp -3) photons/sq cm/s for narrow lines at any energy, and approximately equal to 2.9 x 10(exp -3) photons/sq cm/s for the 539 keV line if it is as broad as 42 keV Full Width at Half Maximum (FWHM). We also searched our data during the approximately 5 hr period on 1981 June 6 during which Owens, Myers, & Thompson (1985) reported a strong line at 405 keV. We detected no line down to a 3 upper sigma limit of 3.3 x 10(exp -3) photons/sq cm/s in disagreement with the flux 7.2 +/- 2.1 x 10(exp -3) photos/sq cm/s measured by Owens et al.