Gamma ray bursts: Current status of observations and theory

Gamma-ray bursts display a wide range of temporal and spectral characteristics, but typically last several seconds and emit most of their energy in the low-energy gamma-ray region. The burst sources appear to be isotropically distributed on the sky. Several lines of evidence suggest magnetic neutron stars as sources for bursts. A variety of energy sources and emission mechanisms were proposed

GRB Studies with Fermi

This slide presentation reviews the studies of Gamma Ray Bursts (GRB) with the Fermi Gamma Ray Space Telescope. Included are pictures of the observatory, with illustrations of the Large Area Telescope (LAT), and the Gamma-ray Burst Monitor (GBM) including information about both their capabilities. Graphs showing the GBM count rate over time after the GBM trigger for three GRBs, preliminary charts showing the multiple detector light curves the spectroscopy of the main LAT peak and the spectral evolution of GRB 080916C Burst Temporally-extended LAT emission

Anisotropy in the sky distributions of the short and intermediate gamma-ray bursts: Breakdown of the cosmological principle?

After the discovery of the anisotropy in the sky-distribution of intermediate gamma-ray bursts recently also the distribution of the short gamma-ray bursts is proven to be anisotropic. The impact of these behaviors on the validity of the cosmological principle is shortly discussed.Comment: 3 pages, 1 figure, to appear in the proceedings of the Sixth Huntsville Gamma-Ray Burst Symposium, edited by C.A. Meegan, N. Gehrels, and C. Kouvelioto

From blast wave to observation

Gamma-ray burst (GRB) afterglows are well described by synchrotron emission originating from the interaction between a relativistic blast wave and the external medium surrounding the GRB progenitor. We introduce a code to reconstruct spectra and light curves from arbitrary fluid configurations, making it especially suited to study the effects of fluid flows beyond those that can be described using analytical approximations. As a check and first application of our code we use it to fit the scaling coefficients of theoretical models of afterglow spectra. We extend earlier results of other authors to general circumburst density profiles. We rederive the physical parameters of GRB 970508 and compare with other authors. We also show the light curves resulting from a relativistic blast wave encountering a wind termination shock. From high resolution calculations we find that the observed transition from a stellar wind type light curve to an interstellar medium type light curve is smooth and without short-time transitory features.Comment: conference proceedings 6th Huntsville symposium, 20-23 October 2008. Editors: C.A. Meegan, N. Gehrels, and C. Kouvelioto

Description of a subset of single events from the BATSE gamma ray burst data

About 15 percent of the gamma ray bursts in the Burst and Transient Source Experiment (BATSE) data exhibit a simple light curve consisting mainly of a single pulse without fine substructures. In 12 of the burst profiles, the pulse shapes show a linear rise and decay. Three events have a distinct sharp rise followed by a long, almost exponential decay. Searches based on only a sharp rise selection criterion resulted in five more grbs with different profile complexities. In one case, we identify an envelope of fast oscillations with a long, softer tail lasting about 100 seconds. The majority of events were detectable at energies above 300 keV, with tentative estimates for fluences that vary between 4.0 x 10(exp -8) and 5.4 x 10(exp -6) ergs/sq cm. We describe here their general characteristics (durations, rise-decay times) and their hardness ratios

Properties of Gamma-Ray Burst Classes

The three gamma-ray burst (GRB) classes identified by statistical clustering analysis (Mukherjee et al. 1998) are examined using the pattern recognition algorithm C4.5 (Quinlan 1986). Although the statistical existence of Class 3 (intermediate duration, intermediate fluence, soft) is supported, the properties of this class do not need to arise from a distinct source population. Class 3 properties can easily be produced from Class 1 (long, high fluence, intermediate hardness) by a combination of measurement error, hardness/intensity correlation, and a newly-identified BATSE bias (the fluence duration bias). Class 2 (short, low fluence, hard) does not appear to be related to Class 1.Comment: 5 pages, 4 imbedded figures, presented at the 5th Huntsville Gamma-Ray Burst Symposiu

AI Gamma-Ray Burst Classification: Methodology/Preliminary Results

Artificial intelligence (AI) classifiers can be used to classify unknowns, refine existing classification parameters, and identify/screen out ineffectual parameters. We present an AI methodology for classifying new gamma-ray bursts, along with some preliminary results.Comment: 5 pages, 2 postscript figures. To appear in the Fourth Huntsville Gamma-Ray Burst Symposiu

Monitoring Cen X-3 with BATSE

The eight uncollimated BATSE Large Area Detectors (LAD's) provide the ability to monitor pulsed hard x ray sources on a nearly continuous basis. Using data from the LAD's, the pulse timing and pulsed flux of the 4.8 second period binary x ray pulsar Centaurus X-3 was analyzed over a two month period. The methods and initial results of this analysis, which includes both data folded onboard GRO and 1.024 second resolution discriminator rates folded on the ground, are presented