摘要:

Gamma-ray burst detectors are aboard seven U.S. Air Force Defense Meteorological Satellite Program (DMSP) spacecraft, two of which are currently in use. Their 800 km altitude orbits give a field of view to 117 degrees from the zenith. A great many bursts have been detected, usually in coincidence with detections by GRO or other satellites such as PVO or Ulysses. The directions of the sources can be determined with considerable accuracy from such correlated observations, even when neither GRO nor BeppoSAX is involved. Results obtained from the most recently launched satellites (DMSP 13 and DMSP 14) are given in this paper. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55427

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Three pulse/time structure parameters that may be considered as invariants for cosmological sources of gamma-ray bursts are introduced. The values of these parameters are estimated for the bursts of the BATSE 3B catalog. The hypothesis of the independence of these parameters on burst brightness is tested. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55384

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Recent studies have found that the spectral evolution of pulses within gamma-ray bursts (GRBs) is consistent with simple radiative cooling. Perhaps more interesting was a report that some bursts may have a single cooling rate for the multiple pulses that occur within it. We determine the probability that the observed “cooling rate invariance” is purely coincidental by sampling values from the observed distribution of cooling rates. We find a 0.1–26&percent; probability that we would randomly observe a similar degree of invariance based on a variety of pulse selection methods and pulse comparison statistics. This probability is sufficiently high to warrant skepticism of any intrinsic invariance in the cooling rate. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55392

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The distributions of spectral characteristics and their correlations with fluence, peak flux, or duration, are essential in understanding the nature of GRBs. However, the selection effects involved in detecting GRBs can distort these distributions. Here, we discuss how to deal with selection effects involving the peak energyEpof the GRB&ngr;F&ngr;spectrum, which suffers from both an upper and lower threshold. We describe a new method to account for this double-sided truncation, and show that the true distribution ofEpis significantly different from the observed distribution. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55399

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The brightness (cumulativelog N−log P) distribution provides information on the intrinsic and spatial properties of the gamma-ray burst (GRB) population. The brightness distribution for the whole sample of GRBs shows a clear deviation from a three-dimensional Euclidean distribution. However, when spectral/duration classes are considered, GRBs show quite distinct properties from theirlog N−log Pdistributions. We find that among the whole sample of GRBs of the 3B catalogue,only the long/hard GRBs show a strong deviation from the Euclidean distribution. This property is at odds with simple extragalactic models of GRB formation, unless a strong spectral and luminosity cosmological evolution is invoked. The existence of multiple GRB populations with different origins cannot be excluded. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55298

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

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 gamma-ray bursts, along with some preliminary results. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55403

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A previous statistical analysis of the events of the BATSE 3B catalog has put in evidence the presence of two different classes of gamma-ray bursts in the plane duration-spectral hardness. The study of the two classes showed different physical characteristics and different space distributions. In both cases evidence for a galactic origin of the gamma-ray bursts is present: in one case a clear evidence of clustering of events along the galactic plane and in the other one, a gap and accumulation of events close to the galactic plane and the galactic bulge. At present a study of counterparts of the gamma-ray bursts in other energy ranges, which started with the BeppoSAX satellite observations [3], is in progress. This study represents another possible way to investigate the gamma-ray burst origin. Waiting for the results on counterparts, we present in this paper a further analysis of the BATSE 4B catalog data. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55410

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

On the average, one new publication on cosmic gamma-ray bursts enters the literature every day. The total number now exceeds 3200. I present here a complete bibliography which can be made available electronically to interested parties. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55299

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Studies using the GRB brightness as a distance indicator require a measure of brightness with a small intrinsic dispersion (close to a standard candle). There is unfortunately no general agreement on the definition of such a quantity. We show here that the comparison of the size-frequency curves obtained with various measures of brightness can be used to select the quantity which is closer to a standard candle. Our method relies on a few general assumptions on the burster spatial distribution, namely that nearby bursters are homogeneously distributed in a Euclidean space with no density or luminosity evolution. We apply it to 5 measures of GRB brightness in the Current BATSE Catalog and we find that the GRB size-frequency distribution depends significantly on the energy window used to measure the GRB brightness. The influence of the time window being, in comparison, negligible. Our method suggests that the best distance indicator in this Catalog is the fluence measured below 100 keV, indicating that GRB luminosities have a smallerintrinsicdispersion below 100 keV than above. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55422

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A review of the GRB Coordinates Network (GCN) will be given. The GCN has recently replaced the BATSE Coordinates Distribution Network (BACODINE), maintaining all of BACODINE’s original capabilities and services, but also providing new sources of GRB location information. These are: (1) source locations using the MSFC LOCBURST algorithm, (2) the Rossi-XTE detections (PCA and ASM), (3) the Interplanetary Network (IPN) locations, and (4) CGRO-COMPTEL locations. These new sources of locations are available for distribution in the minutes-to-hours-to-days time delay ranges, and they also have increasingly and significantly reduced error boxes, thus providing a broad range of time delays and error box sizes to fit within the observing capabilities of a broad range of follow-up instruments in the radio, optical, and TeV gamma-ray bands. Extreme-UV transients from ALEXIS are also now distributed. For all sources of location information, all the distribution methods are available (Internet Socket, E-mail, Alpha-numeric and Numeric Pagers, and Phone/modem) and several filters. Sites can choose which sources to receive and what filters to be applied. The GCN web site has been expanded to include a globally inclusive table of locations, light-curves, and fluence information which is automatically updated in real-time. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55426

出版商:AIP    

年代:1998

数据来源: AIP