摘要:

On the average, one new publication on cosmic gamma-ray bursts enters the literature every day. The total number now exceeds 4100. I present here a complete bibliography which can be made available electronically to interested parties. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361496

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We have searched for gamma-ray bursts (GRBs) in the BATSE DISCLA data over a time period of 5.9 years. We employ a trigger requiring an excess of at least 5&sgr; over background for at least two modules in the 50–300 keV range. After excluding certain geographic locations of the satellite, we are left with 4485 triggers. Based on sky positions, we exclude triggers close to the sun, to Cyg X-1, to Nova Persei 1992 and the repeaterSGR&hthinsp;1806−20,while these sources were active. We accept 1013 triggers that correspond to GRBs in the BATSE catalog, and after visual inspection of the time profiles classify 378 triggers as cosmic GRBs. We denote the 1391 GRBs so selected as the “BD2 sample.” The BD2 sample effectively represents 2.003 years of full sky coverage for a rate of 694 GRBs per year. EuclideanV/Vmaxvalues have been derived through simulations in which each GRB is removed in distance until the detection algorithm does not produce a trigger. The BD2 sample produces a mean value⟨V/Vmax⟩=0.334±0.008.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361497

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present our current results of an off-line search for non-triggered gamma-ray bursts (GRBs) in the BATSE daily records (obtained with 1024 ms time resolution) covering about 8.6 years of observations. We found 1713 non-triggered and 1963 triggered GRBs. The scan was done with artificial test bursts added to the data which allowed us to measure the efficiency of the search. We extended thelog&hthinsp;N−log&hthinsp;Pdistribution down toP∼0.1&hthinsp;ph/s/cm2.Previous indications of a turnover of thelog&hthinsp;N−log&hthinsp;Pdistribution at smallPare not confirmed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361498

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Preliminary results on a systematic analysis of the data from the Gamma-Ray Burst Monitor on-board BeppoSAX are presented. The purpose of this analysis is the identification of true celestial gamma-ray bursts. The study considers events that are recognized or not by the on-board trigger system logic. As the on-board logic triggers also spurious events which mimic GRBs (e.g., events due to high energy particles, atmospheric events, etc), it becomes necessary to impose additional constraints in order to recognize true GRBs. These further conditions will be the subject of this contribution. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361499

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We present some statistical considerations on the BeppoSAX hunt for subsecond GRBs at the Scientific Operation Center. Archival analysis of a BATSE/SAX sub-sample of bursts indicates that the GRB Monitor is sensitive to short (⩽2 sec) events, that are in fact ≈22&percent; of the total. The non-detection of corresponding prompt X-ray counterparts to short bursts in the Wide Field Cameras, in about 3 years of operations, is discussed: with present data no implications on the X-to-&ggr;-ray spectra of short vs. long GRBs may be inferred. Finally, the status of searching procedures at the SOC is reviewed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361500

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The imaging COMPTEL telescope has accumulated 0.1–30 MeV spectra, time-histories, and positions of more than forty &ggr;-ray bursts within its ∼3 sr field of view in the eight years since its launch. CGRO-COMPTEL measures in both imaging “telescope” and single detector “burst spectroscopy” mode. In an ongoing collaboration with BACODINE/GCN, bursts are imaged automatically, with localizations relayed to a global network of multiwavelength observers in near real time (∼10 minutes). We have updated our burst search procedure in two ways: 1) using more sensitive search algorithms; and 2) using data from more detectors. The first are double change-point algorithms. With these we can find regions of significant excess flux with no assumptions on the wide range of burst time-scales (e.g., rise-times or decay-times) or intensities, and only one adjustable parameter (the time-averaged count-rate of the detectors). This makes it simpler to combine information on burst time-histories from the larger effective area (but cruder time bins) burst spectroscopy detectors, and hence better pinpoint the best times for imaging each burst. We report the eight bursts detected during 1998–1999. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361501

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The three gamma-ray burst (GRB) classes identified by statistical clustering analysis [7] are examined using the pattern recognition algorithm C4.5 [8]. 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. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361502

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We use ESX, a product of Information Acumen Corporation, to perform unsupervised learning on a data set containing 797 gamma-ray bursts taken from the BATSE 3B catalog [5]. Assuming all attributes to be distributed log-normally, Mukherjee &etal; [6] analyzed these same data using a statistical cluster analysis. Utilizing the logarithmic values for T90 duration, total fluence, and hardness ratio HR321 their results showed the instances formed three classes. Class I contained long/bright/intermediate bursts, class II consisted of short/faint/hard bursts and class III was represented by intermediate/intermediate/soft bursts. When ESX was presented with these data and restricted to forming a small number of classes, the two classes found by previous standard techniques [1] were determined. However, when ESX was allowed to form more than two classes, four classes were created. One of the four classes contained a majority of short bursts, a second class consisted of mostly intermediate bursts, and the final two classes were subsets of the Class I (long) bursts determined by Mukherjee &etal; We hypothesize that systematic biases may be responsible for this variation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361503

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Interpreting the BATSE burst intensity distribution requires an understanding of the biases introduced by the on-board trigger algorithm. We present a classification and description of these biases. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361504

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The fluence duration bias causes fluences and durations of faint gamma-ray bursts to be systematically underestimated relative to their peak fluxes. Using Monte Carlo analysis, we demonstrate how this effect explains characteristics of structure of the fluence vs. 1024 ms peak flux diagram. Evidence of this bias exists in the BATSE fluence duration database, and provides a partial explanation for the existence of burst class properties. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361505

出版商:AIP    

年代:1900

数据来源: AIP