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1.
The analysis of spectral lag between energy bands, which combines temporal and spectral analyses, can add strict constraints to gamma-ray burst (GRB) models. In previous studies, the lag analysis focused on the lags between channel 1 (25-57 keV) and channel 3 (115-320 keV) from the Burst and Transient Source Experiment (BATSE). In this Letter, we analyzed the cross-correlation average lags (including approximate uncertainties) between energy bands for two GRB samples: 19 events detected by Ginga and 109 events detected by BATSE. We paid special attention to the BATSE GRBs with known redshifts because there has been a reported connection between lag and luminosity. This extends our knowledge of spectral lags to lower energy ( approximately 2 keV). We found that lags between energy bands are small. The lag between the peak of approximately 50 keV photons and that of approximately 200 keV photons is approximately 0.08 s. The upper limit in the lag between approximately 9 and approximately 90 keV photons is approximately 0.5 s. Thus, there are not large shifts at low energy. We found that about 20% of GRBs have detectable lags between energy bands in the Ginga and BATSE samples. From the internal shock model, we found that there are three sources of time structure in GRB pulses: cooling, hydrodynamics, and angular effects. We argue that cooling is much too fast to account for our observed lags and that angular effects are independent of energy. Thus, only hydrodynamics can produce these lags. Perhaps the radiation process varies as the reverse shock moves through the shell.  相似文献   

2.
Cosmic gamma-ray burst spectroscopy   总被引：1，自引：0，他引：1  
A review is given of the gamma-ray burst energy spectrum measurements on Venera 11 and Venera 12 space probes. The gamma burst continuum approximates in shape thermal brems-strahlung emission of a hot plasma. The radiation temperature varies over a broad range, 50–1000 keV, for different events. Spectra of many bursts contain cyclotron absorption and/or redshifted annihilation lines. Strong variability is typically observed in both continuum and line spectra. These spectral data provide convincing evidence for the gamma-ray bursts being generated by neutron stars with superstrong magnetic fields 1012–1013 G.  相似文献   

3.
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   

4.
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   

5.
The gamma-ray burst (GRB) mission Swift has made a much deeper GRBsurvey than any previous one. I present a systematical comparison between GRB samples detected with pre-Swift missions and those from Swift, in order to investigate whether they show any statistical difference. Our Swift GRB sample includes the bursts detected by Swift/BAT before 2007 September. With both flux-limited surveys and redshift-known GRB samples, I show that, apparently, the observed distributions of the redshifts, T90, and log N-log P are significantly different, but not for the spectral hardness ratio, fluence and Eiso. The redshifts of the Swift GRB sample are statistically larger than those of pre-Swift GRBs, with a mean of 1.95±0.17 compared to ～ 1 for pre-Swift GRBs. The cosmological effect on the observables is thus considerable. This effect on the spectral hardness ratio, fluence and Eiso is cancelled out, and the distributions of these quantities indeed do not show significant differences between the Swift and pre-Swift GRBs. Taking this effect into account, I found that the corrected distributions of T90 for long GRBs and log N - log P observed with Swift/BAT are also consistent with those observed with CGRO/BATSE. These results indicate that the Swift and pre-Swift GRBs are from the same population.  相似文献   

6.
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   

7.
The traditional paradigm of a Galactic origin of gamma-ray bursts (GRBs) suffered a major reduction in popularity when BATSE revealed an isotropic but radially inhomogeneous distribution of GRBs. The lack of pronounced galactic anisotropies places severe constraints on models including significant source contributions from the usual disk, bulge, or halo components of the Milky Way. Although models can be designed to preserve the local disk origin, a perhaps more promising approach invokes a very extended Galactic halo. Populating such halos with neutron stars requires very high velocities. Injection of such neutron stars might be restricted to a phase of the early galaxy, or it may continue to the present. We discuss several observational constraints that address the question presented in the title.  相似文献   

8.
The Milagrito collaboration recently reported evidence for emission of very high energy gamma rays in the TeV range from one of the BATSE gamma-ray bursts, GRB 970417a. Here I discuss possible interpretations of this result. Taking into account the intergalactic absorption of TeV gamma rays by the cosmic infrared background, I found that the detection rate (one per 54 gamma-ray bursts [GRBs] observed by the Milagrito) and energy fluence can be consistently explained with the redshift of this GRB at z approximately 0.7 and the isotropic total energy in the TeV range, ETeV,iso greater, similar1054 ergs. This energy scale is not unreasonably large, but interestingly similar to the maximum total GRB energy in the sub-MeV range observed to date for GRB 990123. On the other hand, the energy emitted in the ordinary sub-MeV range becomes EMeV,iso approximately 1051 ergs for GRB 970417a, which is much smaller than the total energy in the TeV range by a factor of about 10(3). I show that the proton-synchrotron model of GRBs provides a possible explanation for these observational results. I also discuss some observational signatures expected in future experiments from this model.  相似文献   

9.
伽玛射线暴源的新分布“BATSE的观测结果   总被引：1，自引：0，他引：1  
介绍了康普顿γ射线天文台上ＢＡＴＳＥ有关暴源分布观测的新发展。这一发现对８０年代以前所普遍接受的γ射线暴起源于银盘内中子星的模型提出了严重挑战，并阐明了几种以ＢＡＳＥ结果基础的暴源分布模型。  相似文献   

10.
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   

11.
We are investigating the COBE DMR data at instances of known -ray bursts (GRBs) when any of the six DMR horn directions was coincident with the direction of a burst. The BATSE instrument on board GRO has detected 207 bursts during the eight-month period of overlap corresponding to the current release of COBE data. The odds of a GRB occurring within the DMR field of view are near one coincidence per year. Here we report on one such serendipitous observation in 1991, GRB 911226, for which a detailed analysis is currently in progress.  相似文献   

12.
A 6.4 keV emission line was discovered in an unusual burst from the soft gamma repeater SGR 1900+14 with the Rossi X-ray Timing Explorer (RXTE). The line was detected in part of a complex multipeak precursor that preceded the unusual burst of 1998 August 29, i.e. two days after the giant flare of August 27 from the source. The origin of the line was not firmly identified and two possible interpretations were equally plausible including (a) Kα fluorescence from a small iron rich material that was ejected to the magnetosphere during the August 27 flare, and (b) proton or α-particle cyclotron resonance. If the iron scenario was correct, we expect to find evidence for the line during the intervening interval between the flare and the August 29 burst, i.e. on August 28. Here we present the results of the August 28 burst observation, taken with RXTE. We detect a total of seven bursts whose individual and joint spectra do not show evidence for spectral lines. We also investigated a sample of nine bursts before and after the August 29 burst (from 1998 June to December) that do not reveal evidence for a spectral line near 6.4 keV or elsewhere. These results disfavor the iron scenario and make the proton/α-particle cyclotron resonance interpretation more plausible. The appearance of the emission line in part of a complex burst and its absence from the studied sample indicate that the line is likely due to a transient phenomenon that may depend on the burst morphology, energetics and the properties of the emission region.   相似文献   

13.
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   

14.
Based on nine BATSE GRBs with known redshifts, we found that the maximum spectral lag of all the pulses in a gamma-ray burst (GRB) appears to be anti-correlated with the redshift of the burst. In order to confirm this finding, we analyzed 10 GRBs detected by HETE-2 with known redshifts and found a similar relation. Using the relation, we estimated the redshifts of 878 long GRBs in the BATSE catalog, then we investigated the distributions of the redshifts and 869 Eiso of these GRBs. The distribution of the estimated redshifts is concentrated at z = 1.4 and the distribution of Eiso peaks at 1052.5 erg. The underlying physics of the correlation is unclear at present.  相似文献   

15.
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   

16.
We present evidence for burst emission from SGR 1900+14 with a power-law high-energy spectrum extending beyond 500 keV. Unlike previous detections of high-energy photons during bursts from soft gamma repeaters (SGRs), these emissions are not associated with extraordinarily bright flares. Not only is the emission hard, but the spectra are better fitted by D. Band's gamma-ray burst (GRB) function rather than by the traditional optically thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anticorrelation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer ( approximately 1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of greater, similar1011 between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.  相似文献   

17.
The gamma-ray burst GR170817 A associated with GW170817 is subluminous and subenergetic compared with other typical short gamma-ray bursts. It may be due to a relativistic jet viewed off-axis, or a structured jet or cocoon emission. Giant flares from magnetars may possibly be ruled out.However, the luminosity and energetics of GRB 170817 A are coincident with those of magnetar giant flares. After the coalescence of a binary neutron star, a hypermassive neutron star may be formed. The hypermassive neutron star may have a magnetar-strength magnetic field. During the collapse of this hypermassive neutron star, magnetic field energy will also be released. This giant-flare-like event may explain the luminosity and energetics of GRB 170817 A. Bursts with similar luminosity and energetics are expected in future neutron star-neutron star or neutron star-black hole mergers.  相似文献   

18.
伴随着引力波事件GW170817的短暴GRB (Gamma-Ray Burst) 170817A首次提供了双中子星并合与短暴相联系的直接证据.但是短暴GRB 170817A具有非常弱的光度,意味着观测的视线方向可能偏离喷流轴方向.根据短暴静止系的峰值能量E_(p,i)和各向同性光度L_(iso)。之间的关系以及洛伦兹因子Γ和L_(iso)。之间的关系估算了短暴GRB 170817A以及长短暴GRB 060614观测角与喷流边缘的夹角θ'_(obs)和洛伦兹因子Γ,结果表明GRB 170817A的Γ=45±27,θ'_(obs)=2.2±0.5°,而GRB 060614的Γ=214±93,θ'_(obs)=0.5±0.1°.这个结果相当于GRB 170817A的正轴各向同性光度L_(iso,on)=(2.1±0.7)×10~(49) erg·s~(-1),比典型的短暴少2-3个数量级.GRB 060614的L_(iso,on)=(5.12±1.91)×10~(51) erg·s~(-1)与典型短暴相当.这意味着GRB 060614可能属于短暴类型,而GRB 170817A可能本质上就是一个弱暴.  相似文献   

19.
GRB 170817A, associated with the LIGO-Virgo GW170817 neutron-star merger event, lacks the short duration and hard spectrum of a Short gamma-ray burst (GRB) expected from long-standing classification models. Correctly identifying the class to which this burst belongs requires comparison with other GRBs detected by the Fermi GBM. The aim of our analysis is to classify Fermi GRBs and to test whether or not GRB 170817A belongs—as suggested—to the Short GRB class. The Fermi GBM catalog provides a large database with many measured variables that can be used to explore gamma-ray burst classification. We use statistical techniques to look for clustering in a sample of 1298 gamma-ray bursts described by duration and spectral hardness. Classification of the detected bursts shows that GRB 170817A most likely belongs to the Intermediate, rather than the Short GRB class. We discuss this result in light of theoretical neutron-star merger models and existing GRB classification schemes. It appears that GRB classification schemes may not yet be linked to appropriate theoretical models, and that theoretical models may not yet adequately account for known GRB class properties. We conclude that GRB 170817A may not fit into a simple phenomenological classification scheme.  相似文献   

20.
We interpret the puzzling-ray bursts as emitted by cooling sparks from the surface of spasmodically accreting, old neutron stars. Their spiky, anisotropic radiation is oriented w.r.t. the galactic disk via interstellar accretion, whose orbital angular momentum tends to counteralign with the galactic spin; in this way, larger source numbers in directions of the galactic disk are compensated by smaller beaming probabilities, resulting in a near-isotropic arrival distribution, as observed by BATSE. The source distances range between 10 pc and 500 pc. Their radiated energies are of order 1035 erg, corresponding to accreted clumps (blades) of typical mass 1015 g per burst. Magnetic surface field strengths range between 1010 and 1012 G, somewhat weaker than those of newborn neutron stars.  相似文献   

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