Search

We present a possible Cepheid-like luminosity estimator for the long gamma-ray bursts based on the variability of their light curves. To construct the luminosity estimator, we use CGRO/BATSE data for 13 bursts, Wind/KONUS data for 5 bursts, Ulysses/GRB data for 1 burst, and NEAR/XGRS data for 1 burst. Spectroscopic redshifts, peak fluxes, and high resolution light curves are available for 11 of these bursts; partial information is available for the remaining 9 bursts. We find that the isotropic-equivalent luminosities L of these bursts positively correlate with a rigorously-constructed measure V of the variability of their light curves. We fit a model to these data that accommodates both intrinsic scatter (statistical variance) and extrinsic scatter (sample variance). If one excludes GRB 980425 from the fit on the grounds that its association with SN 1998bw at a redshift of z = 0.0085 is not secure, the luminosity estimator spans approx. 2.5 orders of magnitude in L, and the slope of the correlation between L and V is positive with a probability of 1 - 1.4 x 10^-4 (3.8 sigma). Although GRB 980425 is excluded from this fit, its L and V values are consistent with the fitted model, which suggests that GRB 980425 may well be associated with SN 1998bw, and that GRB 980425 and the cosmological bursts may share a common physical origin. If one includes GRB 980425 in the fit, the luminosity estimator spans approx. 6.3 orders of magnitude in L, and the slope of the correlation is positive with a probability of 1 - 9.3 x 10^-7 (4.9 sigma). Independently of whether or not GRB 980425 should be included in the fit, its light curve is unique in that it is much less variable than the other approx. 17 light curves in our sample for which the signal-to-noise is reasonably good., Comment: Accepted to The Astrophysical Journal, 31 pages, 13 figures, LaTeX

We have performed a blind search for a gamma-ray transient of arbitrary duration and energy spectrum around the time of the LIGO gravitational-wave event GW150914 with the six-spacecraft interplanetary network (IPN). Four gamma-ray bursts were detected between 30 hr prior to the event and 6.1 hr after it, but none could convincingly be associated with GW150914. No other transients were detected down to limiting 15-150 keV fluences of roughly 5 x 10(exp -8) -5 x 10(exp -7) erg cm(exp -2). We discuss the search strategies and temporal coverage of the IPN on the day of the event and compare the spatial coverage to the region where GW150914 originated. We also report the negative result of a targeted search for the Fermi-GBM event reported in conjunction with GW150914.

Analysis of data from the Spectroscopy Detectors (SDs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO) has found no convincing line features in the spectra of gamma-ray bursts (GRBs) in almost 3 years of operation, in contrast to expectations based on results from other experiments. In this Letter we discuss the visual search for narrow lines in the SD data. The search has examined 192 bursts, of which approximately 18 were intense enough that lines similar to those seen by instruments on the Ginga satellite would have been visible between approximately 20 and approximately 100 keV. A simplified calculation shows that the BATSE and Ginga results are consistent at the 13% level.

This paper presents comprehensive results on the spectra of 30 bright gamma ray bursts (GRBs) as observed by the Spectroscopy Detectors (SDs) of the Burst And Transient Source Experiment (BATSE). The data selection was strict in including only spectra that are of high reliability for continuum shape studies. This BATSE Spectroscopy Catalog presents fluences, model fits (for five spectral models for three energy ranges), and photon spectra in a standard manner for each burst. Complete information is provided to describe the data selection and analysis procedures. The catalog results are also presented in electronic format (from the Compton Observatory Science Support Center) and CD-ROM format (AAS CD-ROM series, Vol. 2). These electronic formats also present the count spectra and detector response matrices so as to allow for independent study and fitting by researchers outside the BATSE Team. This BATSE Spectroscopy Catalog complements the catalog from BATSE Large Area Detector (LAD) data by Fishman et al. (1994).

A fading counterpart to a gamma-ray burst (GRB) would appear as a point source inside a GRB error region soon after the burst which dims on a timescale from minutes to days. The favorable circumstances of the burst GRB 930131 allowed for an international campaign to search for fading counterparts starting 6.8 hr after the burst. We report observations from many optical sites, two radio telescopes, and archival ROSAT data, including deep Schmidt exposures 35, 44, and 64 hr after the burst. No fading counterparts were detected with our observations.

It has been suggested that gamma-ray burst light curves may consist of many superposed flares with a duration shorter than 30/microsec. If true, the implications for the interpretation of burst data are enormous. With the launch of the Compton Gamma-Ray Observatory, four predictions of Mitrofanov's (1989) suggestion can be tested. Our results which contradict this suggestion are (1) the photon arrival times are not correlated between independent detectors, (2) the spectral hardness and intensity does not depend on the detector area, (3) the bursts seen by detectors which measure photon positions do not see microsecond flares, and (4) burst positions deduced from detectors with different projected areas are close to the positions deduced from time-of-flight differences between separated spacecraft. We conclude, therefore, that gamma-ray bursts are not composed of microsecond flares.

Model fits are presented for 18 gamma-ray burst spectra from 100 keV to 27 MeV made with the BATSE spectroscopy detectors on the Compton Gamma Ray Observatory. Most of the bursts are well fitted as power laws with spectral indices between -1.36 and -2.29; however, five bursts show definite departures from a simple power-law fit at high energies. Three of these bursts are well fitted with broken power-law spectra and break energies of from 400 to 690 keV, such as might arise from photon-photon interactions. If so, then the source compactness and hence distance will be sharply constrained. Two of the bursts have spectra with sharply confined slope changes and are well fitted with broken power-law spectra with break energies of 1.2 and 1.6 MeV at peak, such as might arise from photon-magnetic field interactions. If so, then these spectral breaks provide strong evidence for the existence of high magnetic fields in the burst emission region.

The Burst and Transient Source Experiment (BATSE) Spectroscopy Analysis System (BSAS) is the software system which is the primary tool for the analysis of spectral data from BATSE. As such, Guest Investigators and the community as a whole need to know its basic properties and characteristics. Described here are the characteristics of the BATSE spectroscopy detectors and the BSAS.

We present preliminary analyses of gamma-ray burst spectra from the BATSE Spectroscopy Detectors. Our conclusions are: (1) No spectral lines have yet been detected in BATSE data from any cosmic gamma-ray burst. This is not surprising as the data for few bright bursts is available, and previous experiments saw lines in only a small fraction of the bursts. (2) Burst spectra show emission up to 20 MeV, with four of eight examined bursts having significant spectral breaks from 1 to 2 MeV. These breaks are consistent with opacity effects due to the interaction of photons with a high magnetic field. (3) Various distance independent parameters from burst spectra and time histories have no correlation with parameters related to distance. In other words, bright bursts look the same as faint bursts. This places a strong constraint on two population models of bursts. (4) The detection time of individual photons is not correlated from detector to detector, as predicted by Mitrofanov's pulsed emission model.

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.

The discovery of cosmic gamma ray bursts was made with systems designed at Los Alamos Laboratory for the detection of nuclear explosions beyond the atmosphere. HELIOS-2 was the first gamma ray burst instrument launched; its initial results in 1976, seemed to deepen the mystery around gamma ray transients. Interplanetary spacecraft data were reviewed in terms of explaining the behavior and source of the transients.

The papers presented cover a broad segment of space research and are an acknowledgement of the personal involvement of Frank McDonald in many of these efforts. The totality of the papers were chosen so as to sample the scientific areas influenced by him in a significant manner. Three broad areas are covered: particles and fields of the solar system; cosmic ray astrophysics; and gamma ray, X-ray, and infrared astronomics.