摘要:

The 4B catalog of gamma-ray bursts includes all BATSE triggered bursts from launch until 29 August 1996. The total number of bursts is 1637, including 515 bursts since the end of the 3B catalog. The post-3B time interval includes periods when the trigger criteria were not at the nominal energy interval or intensity. Therefore, care must be exercised in deriving global properties from this catalog. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55355

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The Konus-Wind gamma-ray burst instrument on board the GGS-Wind spacecraft has operated flawlessly since launch in November 1994. The orbit of Wind, well beyond the magnetosphere and with no Earth occultation, provides a stable background for the continuous monitoring of gamma-ray bursts, as well as for X-ray transients such as the recent Bursting Pulsar. The two detectors viewing the ecliptic hemispheres have moderate energy resolution in the range from 10 keV to 10 MeV and time resolution down to 2 ms, permitting their use in the interplanetary network, such as for the event of 970228. A comprehensive data base has been obtained in which more than 750 gamma-ray bursts have been observed in the last three years. A brief review of the observations and a summary of the results are presented. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55304

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate the presence of a hardness-intensity correlation (HIC) in a sample of 77 bright GRBs detected by Phebus/GRANAT and the Ulysses GRB detector. Using simulations, we find that the peak spectral hardness and the peak intensity in Phebus are correlated at a 5 &sgr; confidence level. This significant correlation is associated with a⟨V/Vmax⟩=0.5in Ulysses. These two results together imply several constraints on the spatial distribution of bursters. In a cosmological scenario, the apparent contradiction between the presence of a HIC, requiring high redshifts, and⟨V/Vmax⟩=0.5,characteristic of nearby bursters, can be resolved by assuming a density evolution of sources. In this case our calculations show that the typical bright sources observed by Phebus and Ulysses should be atzmax≈2−3to explain the strength of the hardness-intensity correlation. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55301

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We describe a set of cosmologically invariant parameters of gamma-ray bursts, which may be used to compare emitters of different intensity groups in co-moving reference frames. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55323

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have identified two types of bursts with luminosities that differ by about an order of magnitude. The more luminous HE bursts are identified by strong high-energy flux(E>300 keV).The dimmer NHE bursts are identified by a marked lack of high-energy flux. The spectral properties that are used to identify these two burst populations are also influenced by redshifting in the cosmological scenario. The observed burst spectral and intensity data are compared to both a cosmological model with a monoluminous burst population and a cosmological model containing two burst populations with distinctly different luminosities. These comparisons are used to characterize the luminosity difference between HE and NHE bursts more accurately as well as to evaluate the consistency between the redshifting effects and the shape of the intensity distribution for the two models. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55332

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using the peak aligned averaging method we analyze a subset of BATSE gamma-ray bursts (GRBs) with positions within the fields of view of the COMPTEL and EGRET instruments. We consider GRBs detected by the two telescopes as well as those individually undetected. With this averaging method we make a collective detection of GRBs that were undetected individually at high energies. The average temporal and spectral properties of bursts above 1 MeV are determined. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55341

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We argue that recent observations of afterglows and some theoretical considerations indicate that the gamma-ray fluence may be a better measure of strength of a burst than its peak flux. We discuss how the distribution of the fluence, or any physical quantity related to the peak counts (or flux), can be obtained with proper correction for threshhold effects. Using this method, we compare the cumulative and differential distributions of flux and fluence. We find some differences between these distributions, but more remarkable are the similarities between these distributions. The other striking feature is how different these distributions are from those of other extragalactic objects. Using the fluence distributions, we derive the expected comoving density rate evolution for different assumed total luminosity; we compare this with the GRB rate expected from the recently determined star formation rate. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55349

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Gamma-ray bursts have been observed to have a very broad range of spectral and temporal shapes, with characteristic energies ranging from roughly 10 keV to at least a few MeV and characteristic durations ranging from about 0.01 s to a few 100 s. These wide ranges result in very strong selection biases that greatly distort the observed distributions compared to the unbiased, intrinsic distributions. We show, as an example, how to correct for the effects of BATSE spectral selection bias to determine the intrinsic spectral distribution from the observed burst sample. Such corrections are essential for a better understanding of the intrinsic properties of gamma-ray bursts and the implications for their origins. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55357

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The archival data from BATSE permit a search for transients that did not activate the onboard burst trigger. Examples of such non-triggered events include faint gamma-ray bursts (GRBs), emission from soft gamma-ray repeaters (SGRs), and bursts and flares from X-ray binaries. A GRB may fail to trigger onboard because it is too faint, because it occurs while the onboard trigger is disabled, or because it biases the onboard background estimation. We describe a search of the BATSE archival data that is sensitive to GRBs with peak fluxes fainter by a factor of ∼2 than those detected with the onboard burst trigger (on the 1.024 s time scale). ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55364

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Ulysses has detected 443 bursts out of the 1637 in the BATSE 4B catalog. The average width of the triangulation annuli for these events is5′.This reduces the area of the BATSE error circles by a factor of ≳50. The resulting positions may be used for counterpart searches and statistical studies. This catalog, now undergoing final revision, can be made available to interested parties. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55373

出版商:AIP    

年代:1998

数据来源: AIP