A Simple BATSE Measure of GRB Duty Cycle

We introduce a definition of gamma-ray burst (GRB) duty cycle that describes the GRB's efficiency as an emitter; it is the GRB's average flux relative to the peak flux. This GRB duty cycle is easily described in terms of measured BATSE parameters; it is essentially fluence divided by the quantity peak flux times duration. Since fluence and duration are two of the three defining characteristics of the GRB classes identified by statistical clustering techniques (the other is spectral hardness), duty cycle is a potentially valuable probe for studying properties of these classes.Comment: 4 pages, 1 figure, presented at the 5th Huntsville Gamma-Ray Burst Symposiu

BATSE Data Analysis

The four primary tasks of the Burst and Transient Source Experiment (BATSE) were completed. The Detector Response Matrices were maintained and some improvements implemented. The spectral analysis tasks based on the 4 channel lad data were accomplished. The BLOT team effort was completed and the SN1987A balloon flight data analysis paper was submitted

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

Average Emissivity Curve of BATSE Gamma-Ray Bursts with Different Intensities

Six intensity groups with ~150 BATSE gamma-ray bursts each are compared using average emissivity curves. Time-stretch factors for each of the dimmer groups are estimated with respect to the brightest group, which serves as the reference, taking into account the systematics of counts-produced noise effects and choice statistics. A stretching/intensity anti-correlation is found with good statistical significance during the average back slopes of bursts. A stretch factor ~2 is found between the 150 dimmest bursts, with peak flux 4.1 ph cm^{-2} s^{-1}. On the other hand, while a trend of increasing stretching factor may exist for rise fronts for burst with decreasing peak flux from >4.1 ph cm^{-2} s^{-1} down to 0.7 ph cm^{-2} s^{-1}, the magnitude of the stretching factor is less than ~ 1.4 and is therefore inconsistent with stretching factor of back slope.Comment: 21 pages, 3 figures. Accepted to Ap

Do Gamma-Ray Burst Sources Repeat?

The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports (Quashnock and Lamb 1993; Wang and Lingenfelter 1993) of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analyze the angular distribution of 585 bursts of the second BATSE catalog (Meegan et al. 1994). We search for evidence of burst recurrence using the nearest and farthest neighbor statistic and the two-point angular correlation function. We find the data to be consistent with the hypothesis that burst sources do not repeat; however, a repeater fraction of up to about 20% of the observed bursts cannot be excluded.Comment: ApJ Letters, in press, 13 pages, including three embedded figures. uuencoded Unix-compressed PostScrip