摘要:

Sixteen short bursts of photons in the energy range 0.2–1.5 MeV have been observed between 1969 July and 1972 July using widely separated spacecraft. Burst durations ranged from less than 0.1 s to ∼30 s, and time‐integrated flux densities from ∼10−5ergs cm−2to ∼2 × 10−4ergs cm−2in the energy range given. Significant time structure within bursts was observed. Directional information eliminates the Earth and Sun as sources. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810791

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Gamma ray bursts remained essentially non‐understood or misunderstood from their 1973 discovery (not, I will claim, “serendipitous”) to the first, 1997, redshift. This is by no means a record. The poster explored some of the examples of longer‐standing puzzles and the after‐dinner talk some of the details of the GRB case. The most striking feature of the GRB history is probably the unanimity with which “all we, like sheep, went astray,” which followed the epoch of “we have turned everyone to his own way.” Some of the reasons for this, the range of hypotheses, and how GRBs were presented to the astronomical and larger communities are discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810792

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

HETE‐2 has provided strong evidence that the properties of X‐Ray Flashes (XRFs) and GRBs form a continuum, and therefore that these two types of bursts are the same phenomenon. We show that both the structured jet and the uniform jet models can explain the observed properties of GRBs reasonably well. However, if one tries to account for the properties of both XRFs and GRBs in a unified picture, the uniform jet model works reasonably well while the structured jet model fails utterly. The uniform jet model of XRFs and GRBs implies that most GRBs have very small jet opening angles (∼ half a degree). This suggests that magnetic fields play a crucial role in GRB jets. The model also implies that the energy radiated in gamma rays is ∼ 100 times smaller than has been thought. Most importantly, the model implies that there are ∼ 104– 105more bursts with very small jet opening angles for every such burst we see. Thus the rate of GRBs could be comparable to the rate of Type Ic core collapse supernovae. Accurate, rapid localizations of many XRFs, leading to identification of their X‐ray and optical afterglows and the determination of their redshifts, will be required in order to confirm or rule out these profound implications. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810793

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A substantial fraction of prompt GRB spectra have soft spectral indexes exceeding the maximum allowed by the synchrotron model &agr;max= −2/3. Some spectra also exhibit a very sharp break atEp, inconsistent with the smooth synchrotron spectra. These facts pose a serious problem for the “optically thin synchrotron” interpretation of the prompt emission. We review various models suggested in order to resolve this puzzle. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810794

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this paper I review some significant results obtained with the wide field instruments (2 Wide Field Cameras and a Gamma Ray Burst Monitor) aboard theBeppoSAXsatellite, and their implications for the current models concerning GRB progentors and their environments. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810795

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The availability of a few dozen GRB redshifts now allows studies of the intrinsic properties of these high energy transients. Amati et al. recently discovered a correlation between Epeak, the intrinsic peak energy of thevfvspectrum, and Eiso, the isotropic equivalent energy radiated by the source. Lamb et al. have shown that HETE‐2 data confirm and extend this correlation. We discuss here one of the consequences of this correlation: the existence of a ‘spectral standard candle’, which can be used to construct a simple redshift indicator for GRBs. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810796

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

After taking into account threshold effects, we find that the isotropic‐equivalent energiesEisoand luminositiesLisoof gamma‐ray bursts (GRBs) are correlated with redshift at the 5&percent; and 0.9&percent; signficance levels, respectively. Our results are based on 10BeppoSAX GRBs and 11 HETE‐2 GRBs with known redshifts. Our results suggest that the isotropic‐equivalent energies and luminosities of GRBs increase with redshift. They strengthen earlier clues to this effect from analyses of the BATSE catalog of GRBs, using the variability of burst time histories as an estimator of burst luminosities (and therefore redshifts), and from an analysis ofBeppoSAX bursts only. If the isotropic‐equivalent energies and luminosities of GRBs really do increase with redshift, it suggests that GRB jets at high redshifts may be narrower and thus the cores of GRB progenitor stars at high redshifts may be rotating more rapidly. It also suggests that GRBs at very high redshifts may be more luminous — and therefore easier to detect — than has been thought, which would make GRBs a more powerful probe of cosmology and the early universe than has been thought. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810797

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

HETE‐2 has provided new evidence that gamma‐ray bursts may evolve with redshift. We investigate the consequences of this possibility for the unified jet model of XRFs and GRBs. We find that burst evolution with redshift can be naturally explained within the unified jet model, and the resulting model provides excellent agreement with existing HETE‐2 andBeppoSAX data sets. In addition, this evolution model produces reasonable fits to the BATSE peak photon number flux distribution — something that cannot be easily done without redshift evolution. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810798

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We have identified two GRBs in which early emission is very different than late emission. Post‐quiescent pulses of BATSE GRBs 960530 and 980125 have long lags, smooth morphologies, and soft spectral evolution. The early emission satisfies the standard internal shock paradigm, while the late emission is consistent with external shocks. The peak luminosity ratio between early and late episodes is not in agreement with that predicated by the lag vs. peak luminosity relationship. We briefly discuss these observations in terms of a current hypernova jet model. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810799

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

During its >2.5 years of operation, the High Energy Transient Explorer (HETE‐2) has detected nearly 300 GRBs, over 800 XRBs, and ∼50 bursts from SGRs in on‐orbit operations and sophisticated ground searches of archived data. In addition to these bursts, there have been over 1500 other triggers detected using on‐board or ground algorithms, hundreds of which are as yet unidentified and may come from cosmic sources. We have developed the HETE Burst Catalog as a means of organizing and analyzing the data from these nearly 3000 triggers in a systematic way. We present preliminary results from the HETE burst catalog. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1810800

出版商:AIP    

年代:1904

数据来源: AIP