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1.
In four years BATSE has observed more than 1000 gamma-ray bursts, making unprecedented measurements of their spatial and brightness distributions. These measurements and their implications for the origin of gamma-ray bursts are reviewed.  相似文献   

2.
使用currentBATSE catakog中的一部分数据，定义了2个分别反映γ射线暴的能谱形和光变曲线的物理量FR和TR，同时对它们的分布作了统计分析，发现对于两类不同的γ射线暴，它们的分布存在统计上的较为明显的差异。这意味着两类暴可能产生于不同的辐射区域，两类暴的暴源可能有本质的差异，这些结果支持了把γ射线暴分为长暴和短暴的分类方法。  相似文献   

3.
Of great importance in distinguishing between models for gamma-ray bursts (GRBs) is the experimental determination of the highest energy gamma rays associated with bursts. The EGRET detection of a 15 GeV gamma ray indicates that the spectra of at least some bursts extend well beyond the several MeV limit of the BATSE detectors (Hurleyet al., 1994). The low expected flux means that the collecting area of the present generation of satellite-based detectors is too small to detect gamma rays much above this energy efficiently, and such searches are currently undertaken with ground based detectors. In this paper searches made for very high energy GRBs with a southern hemisphere air shower particle array are described.  相似文献   

4.
We apply isotropy tests to our new uniform catalog of cosmic gamma-ray bursts (GRBs) (Stern and Tikhomirova 1999). The catalog contains trigger and nontrigger bursts found in 1024-ms BATSE records over seven years. Based on this catalog, we confirm isotropy of the GRB spatial distribution for a sample that surpasses previous samples in size (2934 bursts) and in achieved threshold (fluxes down to 0.1 phot. cm?2 s?1, which is a factor of ～2 lower than the BATSE trigger threshold). We also confirm that there is no excess of bursts toward the galaxy M 31.  相似文献   

5.
EGRET on the Compton Gamma Ray Observatory has detected 5 gammaray bursts above 30 MeV. The sub-MeV emission, as detected by BATSE, for these 5 bursts has the largest fluence,F, and peak intensity,I, of any of the BATSE detected bursts within the EGRET field of view. The BATSE data reported in the 2B catalog and the EGRET exposure,E, are combined to select additional bursts with largeF ×E andI ×E. The EGRET data for these bright BATSE bursts are searched for prompt, as well as delayed, emission above 30 MeV. The average properties of the >30 MeV emission are obtained by adding the EGRET data from the 5 bursts. On average the fluence is greater than 15% of the fluence detected by BATSE below an MeV, and the average spectrum is flatter than the spectrum from 1-30 MeV.  相似文献   

6.
We show that our original suggestion that gamma-ray bursts (GRB) may be flares on Magnetically Active Stellar Systems (MASS) namely flare stars, RS CVn binaries and Cataclysmic variables agrees well with the new observations of CGRO. We make a multi component fit to the log(N) - log(S) distribution and the high degree of isotropy as observed by the previous generation of satellites as well as BATSE/CGRO using the second BATSE catalogue. We then discuss individual source association and optical transient observations and show that they favor the present suggestion. We discuss the physical mechanisms and gamma-ray production processes that can occur on such systems giving the GRB their characteristics. We predict increase of anisotropy in the BATSE/CGRO observations for bright GRB.  相似文献   

7.
Gamma-ray burst spectroscopy has at times been thought of as the key to understanding these mysterious events, and at others as a source of disappointment and confusion. Early spectral measurements contained evidence for cyclotron-line-like absorption and emission features. These results were the main anchor for the galactic neutron star paradigm for the origin of gamma-ray bursts. Ginga provided striking confirmation with evidence in three bursts for cyclotron absorption with both first and second harmonics present. The absorption line energies were consistent with the teragauss magnetic fields expected for neutron stars. The BATSE experiment on CGRO has dealt a severe blow to this paradigm. BATSE has found no evidence for the expected galactic anisotropy and also no evidence for cyclotron lines. The exact degree of inconsistency between BATSE and earlier GRB line results remains a complicated and unresolved question. In general, burst spectra display a wide variety of both spectral and temporal behavior. In essentially all bursts where spectral measurements are possible, the spectrum evolves during the burst. This spectral complexity and variability has presented researchers with a challenging task. At the present time, only the broadest correlations and characterizations are in hand. This paper will; 1) give a brief historical overview of GRB spectroscopic measurements and 2) provide a summary of the current observational situation with emphasis on the BATSE/Ginga controversy.  相似文献   

8.
Based on Link & Epstein's study of temporal asymmetry of 631 gamma-ray bursts from the BATSE 3B catalogue, we identify the population of bursts with rising times that are longer than their decays, thus showing atypical profiles. We analyse their sky distribution, morphology, time–space clustering and other average properties and compare them with those associated with the bulk of the bursts. We show how most of the peculiar bursts analysed are consistent with recent fireball models, but a fraction of bursts (∼4 per cent of the total sample) appear to be inconsistent.  相似文献   

9.
A statistical analysis of the spectral and temporal parameters for 546 triggering events on the APEX gamma-ray detector onboard the Phobos-2 spacecraft has revealed a group of 28 events that are probably short cosmic gamma-ray bursts (GRBs). The distribution of the full group of 74 events of the APEX experiment in duration parameter is bimodal in shape, which is in good agreement with the bimodal shape of the BATSE GRB distribution. A search for the detected group of short events using data from the LILAS X-ray and soft gamma-ray detector onboard the same spacecraft has yielded no positive result. A comparison of the APEX and LILAS data has led us to conclude that the short GRBs have a significantly reduced soft gamma-ray flux at energies <100 keV relative to the power law dN/dE=CE?α with the average index α=2.62.  相似文献   

10.
韦大明 《天文学进展》1995,13(3):234-248
介绍了ＣｏｍｐｔｏｎＧＲＯ卫星对Ⅱ暴的最新观测结果。观测表明，γ暴源的空间分布是各向同性但不均匀的。这种分布基本上排除了γ暴起源于银盘内中子星的模型，表明γ暴要么位于展延的银晕里，要么位于宇宙学距离上。  相似文献   

11.
We developmatch probability statistics to test the recurrences of gamma-ray bursts in the BATSE catalog 1B and 2B. We do not find a signal of repetitions at the match level of 10–3.  相似文献   

12.
We assume that gamma-ray bursts come from relativistic beaming in random directions, with the bursts being standard candles in their own rest frames and following a power-law distribution, and that the rate of occurrence is a constant in the comoving frame of the Ω = 1, Λ = 0 Friedmann universe. This model is very sensitive to the beaming velocity. For a Lorentz factor Γ < 10 and a power-law index n < 1.0 our calculated statistics agree with the BATSE data of weak bursts and the PVO data of strong bursts.  相似文献   

13.
We searched for anomalously long gamma-ray bursts (GRBs) in the archival records of the Burst and Transient Sources Experiment (BATSE). Ten obvious superlong (>500 s) GRBs with almost continuous emission episodes were found. Nine of these events were known from the BATSE catalog, but five had no duration estimates; we found one burst for the first time. We also detected events with emission episodes separated by a long period of quiescence (up to ～1000 s) with a total duration of 1000–2000 s. In the latter case, we cannot reach an unequivocal conclusion about a common origin of the episodes due to the BATSE poor angular resolution. However, for most of these pairs, the probability of independent GRBs coinciding is much lower than unity, and the probability that all of these are coincidences is ～10?8. All of the events have a hardness ratio (the ratio of the count rates in different energy channels) typical of GRBs, and their unique duration is unlikely to be related to their high redshifts. Superlong bursts do not differ in their properties from typical long (>2 s) GRBs. We estimated the fraction of superlong GRBs (>500 s) among the long (>2 s)GRBs in the BATSE sample with fluxes up to 0.1 ph cm?2 s?1 to be between 0.3 and 0.5%, which is higher than the estimate based on the BATSE catalog.  相似文献   

14.
No absorption lines between 15 and 100 keV have been detected in burst spectra accumulated by BATSE. Almost 250 bursts have been inspected visually, and a computerized search has begun. Our simulations show that BATSE could indeed detect lines similar to those observed byGinga in strong bursts, and our tests of the detectors' actual capabilities demonstrate they function as understood. The apparent discrepancy between BATSE andGinga is not yet compelling, and therefore the BATSE nondetections do not invalidate theGinga detections. Nonetheless, the absence of BATSE line detections indicates a low line-occurrence frequency.  相似文献   

15.
Of the over one thousand detected cosmic transient gamma-ray sources, only three are known to have exhibited recurrent activity. Apart from their recurrent nature, these events differ from the majority of bursts in that they are of much shorter duration and have relatively soft spectra. They can thus be considered as a distinct class of objects- the Soft Gamma Repeaters (SGRs). Their embryonic sky distribution suggests that they are galactic objects. The absence of detection of new sources in the 4.0 years of BATSE operation, together with the BATSE detection of the reactivation of two of the three already known SGRs, indicates that these objects are rare. We present here a short review of the overall SGR activity and their global characteristics.  相似文献   

16.
There is increasing evidence of a local population of short duration gamma-ray bursts (sGRB), but it remains to be seen whether this is a separate population to higher redshift bursts. Here we choose plausible luminosity functions (LFs) for both neutron star binary mergers and giant flares from soft gamma repeaters (SGR), and combined with theoretical and observed Galactic intrinsic rates we examine whether a single progenitor model can reproduce both the overall Burst and Transient Source Experiment (BATSE) sGRB number counts and a local population, or whether a dual progenitor population is required. Though there are large uncertainties in the intrinsic rates, we find that at least a bimodal LF consisting of lower and higher luminosity populations is required to reproduce both the overall BATSE sGRB number counts and a local burst distribution. Furthermore, the best-fitting parameters of the lower luminosity population agree well with the known properties of SGR giant flares, and the predicted numbers are sufficient to account for previous estimates of the local sGRB population.  相似文献   

17.
The BATSE and OSSE instrument teams have modified flight software to promptly (within 2 min of trigger) slew the OSSE detectors to burst locations determined on-board by BATSE. This enables OSSE to make sensitive searches for prompt and delayed post-burst line and continuum emission above 50 keV. In the best cases our sensitivity will be more than an order of magnitude better than any other search in this energy range. We expect to slew to 1–2 bursts per month, based on the OSSE FOV and BATSE event rate. Detections or limits from continued operation of this system may provide significant constraints on burst models. As an example of the observations made using this system, we present preliminary limits for post-burst emission from GRB 950223 on several time scales.  相似文献   

18.
Assuming that gamma-ray bursts (GRB) originate from binary neutron star (NS) or black holes (BH) merging in distant galaxies, theoretical logN-logS distributions for gamma-ray bursts (GRB) are calculated using the compact binaries coalescence rates computed for model galaxies with different star formation histories. A flat cosmological model ( = 1) with different values of the cosmological constant is used. The calculated source evolution predicts a 5–10 times increase of the source statistics at count rates 3–10 times lower than the existing BATSE sensitivity limit. The most important parameter in fitting the 2nd BATSE catalogue is the initial redshift of star formation, which is found to bez * = 2 — 5 depending on a poorly determined average spectral index of GRB.  相似文献   

19.
The proposed correlations between the energetics of gamma-ray bursts (GRBs) and their spectral properties, namely the peak energy of their prompt emission, can broadly account for the observed fluence distribution of all 'bright' BATSE GRBs, under the hypothesis that the GRB rate is proportional to the star formation rate and that the observed distribution in peak energy is independent of redshift. The correlations can also be broadly consistent with the properties of the whole BATSE long GRB population for a peak energy distribution smoothly extending towards lower energies, and in agreement with the properties of a sample at 'intermediate' fluences and with the luminosity functions inferred from the GRB number counts. We discuss the constraints that this analysis imposes on the shape of such peak energy distribution, the opening angle distribution and the tightness of the proposed correlations.  相似文献   

20.
Hakkila  J.  Meegan  C.  Horack  J.  Pendleton  G.  Briggs  M.  Paciesas  W.  Emslie  G.  Mallozzi  R. 《Astrophysics and Space Science》1995,231(1-2):369-372
Constraints are found on the gamma-ray burst luminosity function from an analysis of the combined BATSE/PVO intensity distribution. If bursts originate in an extended Galactic halo, then the intrinsic luminosity range is narrow, with bursts spanning only a factor of five or less in luminosity. If bursts originate in a simple Friedmann cosmology with = 1 and = 0, then very few luminosity constraints exist.National Research Council Fellow at NASA/MSFC  相似文献   

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