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The Burst and Transient Source Experiment (BATSE) has observed over 600 gamma-ray bursts since its activation on 1991 April 21. We present here results on the global properties of the first 542 events. Their angular distribution is consistent with isotropy; their peak intensity distribution shows a depletion at low intensities, consistent with inhomogeneity in Euclidean space.
An optical photometric and proper motion survey of a approximately = 160 sq arcmin region centered on an interplanetary network 41 sq arcmin GRB 790329 error box is presented. No obvious counterparts to the gamma-ray burst were identified. The distribution of stellar colors in the survey region was that expected for the galactic latitude of the burst field. Six stars with significant proper motions were identified. One of these, Gl 397, was found to be a double star. The companion has the color and luminosity of an M4/5 dwarf. We note that associating the gamma-ray burst with the Gl 397 system seems to require energies beyond that seen in the flares of other late-type dwarfs. A small number of galaxies were identified, one of which (object #4), was the bluest object found in the survey (V - I = 0.49).
The first results from the ISSEE-3 radiatively colled germanium gamma ray burst spectrometer are presented. Spectra and time histories from two events on the 1978 November 4 and 1978 November 19 are given. A significant difference in the continuum spectra for the two events was observed. Evidence is presented for two spectral features in the features in the November 19 events, a broad one at approximately 420 key KeV and a narrower one at 740 KeV with a suggestion of an accompanying high energy tail.
Statistical considerations support the positional identification of the giant March 5, 1979, gamma-ray burst ('M5') with the supernova remnant ('SNR') N49 in the Large Magellanic Cloud ('LMC'). Several theoretical objections to the identification are examined and found to be invalid. Constraints on models are discussed briefly.
Ramatry, et al. proposed a model to account for the 5 March 1979 gamma ray burst in terms of a neutron star corequake and subsequent shock heating of the neutron star atmosphere. This model is extended by examining the overall energetics and characteristics of these shocks, taking into account the e(+)-e(-) pair production behind the shock. The effects of a dipole magnetic field in the shock jump conditions are also examined and it is concluded that the uneven heating produced by such a field can account for the temperature difference between pole and equator implied by the pulsating phase of the burst. The overall energetics and distribution of energy between e(+)-(-) pairs and photons appears to be in agreement with observations if this event is at a distance of 55 kpc as implied by its association with the Large Magellanic Cloud.
Ramatry, et al. proposed a model to account for the 5 March 1979 gamma ray burst in terms of a neutron star corequake and subsequent shock heating of the neutron star atmosphere. This model is extended by examining the overall energetics and characteristics of these shocks, taking into account the e(+)-e(-) pair production behind the shock. The effects of a dipole magnetic field in the shock jump conditions are also examined and it is concluded that the uneven heating produced by such a field can account for the temperature difference between pole and equator implied by the pulsating phase of the burst. The overall energetics and distribution of energy between e(+)-e(-) pairs and photons appear to be in agreement with observations if this event is at a distance of 55 kpc as implied by its association with the Large Magellanic Cloud. Previously announced in STAR as N83-31568
Attention is given to a synchrotron self-Compton emission model for gamma-ray bursts which produces narrow annihilation features for a variety of field strengths, primary electron injection energies, and injection rates. In this model, primary electrons are injected and cooled by synchrotron emission in a strong, homogeneous magnetic field, resulting in a pair cascade. Multiple resonant scattering with cyclotron photons efficiently traps and cools pairs in the ground state to an average energy where the Compton energy loss rate is zero, which is in agreement with previous estimates of a Compton temperature. The particle distributions in the ground state are determined by numerically solving the Fokker-Planck equation in the steady state. In the case of isotropic injection of primary electrons, a significant narrow-line feature appears in the overall emission. In the case of beamed injection, the annihilation line is broadened to the extent that it would not be observable.
The hardness and intensity are easily measured quantities for all gamma-ray bursts (GRBs), and so, many past and current studies have sought correlations between them. This Letter presents many serious methodological problems with the practical definitions for both hardness and intensity. These difficulties are such that significant correlations can be easily introduced as artifacts of the reduction procedure. In particular, cosmological models of GRBs cannot be tested with hardness/intensity correlations with current instrumentation and the time evolution of the hardness in a given burst may be correlated with intensity for reasons that are unrelated to intrinsic change in the spectral shape.
A cosmological model for gamma-ray bursts is explored in which the radiation is produced as a broadly beamed pair fireball along the rotation axis of an accreting black hole. The black hole may be a consequence of neutron star merger or neutron star-black hole merger, but for long complex bursts, it is more likely to come from the collapse of a single Wolf-Rayet star endowed with rotation ('failed' Type Ib supernova). The disk is geometrically thick and typically has a mass inside 100 km of several tenths of a solar mass. In the failed supernova case, the disk is fed for a longer period of time by the collapsing star. At its inner edge the disk is thick to its own neutrino emission and evolves on a viscous time scale of several seconds. In a region roughly 30 km across, interior to the accretion disk and along its axis of rotation, a pair fireball is generated by neutrino annihilation and electron-neutrino scattering which deposit approximately 10 exp 50 ergs/s.
We describe Bayesian methods for analyzing the distribution of gamma-ray burst peak photon fluxes and directions. These methods fit the differential distribution, and have the following advantages over rival methods: (1) they do not destroy information by binning or averaging the data (as do, say, chi squared, the averaged value of V/V(sub max), and angular moment analyses); (2) they straightforwardly handle uncertainties in the measured quantities; (3) they analyze the strength and direction information jointly; (4) they use information available about nondetections; and (5) they automatically identify and account for biases and selection effects given a precise description of the experiment. In these methods, the most important information needed about the instrument threshold is not its value at the times of burst triggers, as is used in the average value of V/V(sub max) analyses, but rather the value of the threshold at times when no trigger occurred. We show that this information can be summarized as an average detection efficiency that is similar to the product of the exposure and efficiency reported in the First Burst and Transient Source Experiment (BATSE) Burst (1B) Catalog, but significantly different from it at low fluxes. We also quantify an important bias that results from estimating the peak flux by scanning the burst to find the peak number of counts in a window of specified duration, as was done for the 1B Catalog. When the duration of the peak of the light curve is longer than the window duration, a simple flux estimate based on the peak counts significantly overestimates the peak flux in a nonlinear fashion that distorts the shape of the log(N)-log(P) distribution. This distortion also corrupts analyses of the V/V(sub max) distribution that use ratios of counts above background to estimate V/V(sub max). The Bayesian calculation specifies how to account for this bias. Implementation of the Bayesian approach requires some changes in the way burst data are reported that we describe in detail. Subsequent papers will report analyses of the 1B Catalog data using the methods described here.
A comprehensive search of BATSE Spectroscopy Detector data from 117 Gamma Ray Bursts (GRBs) has uncovered 13 statistically significant line candidates. The case of a candidate in GRB-930916 is discussed. In the data of SD-2 there appears to be a emission line at 46 keV, however the line is not seen in the data of SD-7. Simulations indicate that the lack of agreement between the results from SD-2 and SD-7 is implausible but not impossible.
The current scenario for gamma-ray bursts (GRBs) involves internal shocks for the prompt GRB emission phase and external shocks for the afterglow phase. Assuming synchrotron emission from energetic shocked electrons. GRB spectra observed with a low-energy power-law spectral index greater than -2/3 (for positive photon number indices E(sup alpha) indicate a problem with this model. The remaining spectra can test the synchrotron shock model prediction that the emission from a single distribution of electrons, cooling rapidly, is responsible for both the low-energy and high-energy power-low portions of the spectra. We find that the inferred relationship between the two spectral indices of observed GRB spectra is inconsistent with the constraints from the model, posing another problem for the synchrotron shock emission model. To overcome this problem, we describe a model where the average of -1, rather than the value of -3/2 predicted for cooling electrons. Situations where this might arise have been discussed in other contexts, and involve deceleration of the internal shocks during the GRB phase.
Simultaneous observations by the large number of gamma-ray burst detectors that will operate in the GLAST era will provide the spectra, lightcurves and locations necessary for studying burst physics and testing the putative relations between intrinsic burst properties. I review the burst detection sensitivities, spectral bands, and localization capabilities of the GLAST (GBM and LAT), Swift (BAT), INTEGRAL (ISGRI), Suzaku (wAM), AGILE (Super-AGILE) and wind (Konus) detectors; the detectors' energy band and the accumulation timescale of their trigger system affect their sensitivity to hard vs. soft and long vs. short bursts. In addition, I estimate the rate of simultaneous burst observations. In particular, coordination of the Swift observing plan consistent with Swift's other science objectives could increase the rate of GLAST bursts with redshifts
Simultaneous observations by the large number of gamma-ray burst detectors operating in the GLAST era will provide the spectra, lightcurves and locations necessary for studying burst physics and testing the putative relations between intrinsic burst properties. The detectors' energy band and the accumulation timescale of their trigger system affect their sensitivity to hard vs. soft and long vs. short bursts. Coordination of the Swift and GLAST observing plans consistent with Swift's other science objectives could increase the rate of GLAST bursts with redshifts.
Simultaneous observations by the large number of gamma-ray burst detectors operating in the GLAST era will provide the spectra, lightcurves and locations necessary for studying burst physics and testing the putative relations between intrinsic burst properties. 1 will review the burst detection sensitivities, spectral bands, and localization capabilities of the GLAST (GBM and LAT), Swift (BAT), INTEGRAL (ISGRI), Suzaku (WAM), AGILE (Super-AGILE) and Wind (Konus) detectors; the detectors' energy band and the accumulation timescale of their trigger system affect their sensitivity to hard vs. soft and long vs. short bursts. In addition, I estimate the rate of simultaneous burst observations. In particular, coordination of the Swift observing plan consistent with Swift's other science objectives could increase the rate of GLAST bursts with redshifts.
This viewgraph presentation reviews the current understanding of Gamma Ray Bursts. It covers the Long GRBs, our current understanding of Collapsar, Short GRBs, afterglows, and reduced trigger threshold. It also discusses the Hard X-ray Sky Survey.
This viewgraph presentation reviews the current understanding of Gamma Ray Bursts. It covers the Long GRBs, our current understanding of Collapsar, Short GRBs, afterglows, and reduced trigger threshold. It also discusses the Hard X-ray Sky Survey.
GRB 120422A is a low-luminosity gamma-ray burst (GRB) associated with a bright supernova, which distinguishesitself by its relatively short T(sub 90) (approximately 5 s) and an energetic and steep-decaying X-ray tail. We analyze the Swift BurstAlert Telescope and X-ray Telescope data and discuss the physical implications. We show that the steep declineearly in the X-ray light curve can be interpreted as the curvature tail of a late emission episode around 58-86 s,with a curved instantaneous spectrum at the end of the emission episode. Together with the main activity in thefirst 20 s and the weak emission from 40 s to 60 s, the prompt emission is variable, which points to a centralengine origin in contrast to a shock-breakout origin, which is used to interpret some other nearby low-luminosity supernova GRBs. Both the curvature effect model and interpreting the early shallow decay as the coasting externalforward shock emission in a wind medium provide a constraint on the bulk Lorentz factor to be around several.Comparing the properties ofGRB 120422A and other supernova GRBs,we find that themain criterion to distinguish engine-driven GRBs from shock-breakout GRBs is the time-averaged -ray luminosity. Engine-driven GRBs likelyhave a luminosity above approximately 10(sup 48) erg s(sup -1).