共查询到20条相似文献,搜索用时 15 毫秒
1.
G. S. Bisnovatyi-Kogan 《Astrophysics and Space Science》1994,215(1):47-51
When measurements are performed with a detector under the conditions of a variable threshold, systematic errors in the threshold determination strongly influence thelogN-log(C/C
min) distribution. Applications to gamma ray burst samples are discussed. 相似文献
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A.J. Castro-Tirado 《Astrophysics and Space Science》1998,263(1-4):15-26
Since their discovery in 1973, Gamma-Ray Bursts (GRBs) have remained for many years one of the most elusive mysteries in High
Energy-Astrophysics. Despite the fact that ∼800 GRBs are detected every year in the full sky, only a few of them can be localized
accurately to less than half a degree. Thus the main problem regarding the nature of GRBs has usually been the lack of knowledge
of their distance scale. For many years, follow-up observations by other satellites and ground-based telescopes were conducted,
but no counterparts at other wavelengths were found. The breakthrough took place in 1997, thanks to the observation by BSAX
and RXTE of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. This
emission (the afterglow) extends at longer wavelengths, and the good accuracy in the position determination has led to the
discovery of the first counterparts at other wavelengths, greatly improving our understanding of these puzzling sources. Now
it is widely accepted that GRBs originate at cosmological distances but the central engines that power these extraordinary
events remain still unknown.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Ken’ichi Nomoto Keiichi Maeda Nozomu Tominaga Takuya Ohkubo Jinsong Deng Paolo A. Mazzali 《Astrophysics and Space Science》2005,298(1-2):81-86
The nature of very energetic supernovae (hypernovae) is discussed. They are the explosive death of stars more massive than
~20–25M
⊙, probably linked to the enigmatic Gamma-Ray Bursts. The optical properties of hypernovae indicate that they are significantly
aspherical. Synthetic light curves and late-phase spectra of aspherical supernova/hypernova models are presented. These models
can account for the optical observations of SNe 1998bw and 2002ap. The abundance patterns of hypernovae are characterized
by large ratios (Zn, Co)/Fe and small ratios (Mn, Cr)/Fe, indicating a significant contribution of hypernovae to the early
Galactic chemical evolution. 相似文献
5.
When the axis of a gamma-ray burst (GRB) does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction ξe, the magnetic energy fraction ξ2B, the width of ring A0 and the medium number density n. The overall light curve can be divided into three power-law stages, I.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet. 相似文献
6.
O. Bertolami 《Astrophysics and Space Science》1998,261(1-4):225-228
Axions emitted in supernovae are interesting candidates to account for Gamma-Ray Bursts provided their energy can be effectively
converted into electromagnetic energy elsewhere. We point out that this convertion may occur more efficiently if one considers
the coupling between intermediate scale axions and the string theory dilaton along with the inclusion of string loops.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Ken’ichi Nomoto Keiichi Maeda Masaomi Tanaka Tomoharu Suzuki 《Astrophysics and Space Science》2011,336(1):129-137
The connection between long Gamma Ray Bursts (GRBs) and Supernovae (SNe) have been established through the well observed cases.
These events can be explained as the prompt collapse to a black hole (BH) of the core of a massive star (M≳40M
⊙). The energies of these GRB-SNe were much larger than those of typical SNe, thus these SNe are called Hypernovae (HNe). The
case of SN 2006aj/GRB060218 appears different: the GRB was weak and soft, being called an X-Ray Flash (XRF); the SN is dimmer
and has very weak oxygen lines. The explosion energy of SN 2006aj was smaller, as was the ejected mass. In our model, the
progenitor star had a smaller mass than other GRB-SNe (M∼20M
⊙), suggesting that a neutron star (NS) rather than a BH was formed. If the nascent NS was strongly magnetized as a magnetar
and rapidly spinning, it may launch a weak GRB or an XRF. The peculiar light curve of Type Ib SN 2005bf may also be powered
by a magnetar. The blue-shifted nebular emission lines of 2005bf indicate the unipolar explosion possibly related to standing
accretion shock instability (SASI) associated with a newly born NS. 相似文献
8.
Gamma—Ray Bursts:Afterglows and Central Engines 总被引:5,自引:0,他引:5
K.S.Cheng T.Lu 《中国天文和天体物理学报》2001,1(1):1-20
Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmoligical distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands. 相似文献
9.
We propose that gamma-ray bursts (GRBs) are produced by a shower of heavy blobs running into circumstellar material at highly relativistic speeds. The gamma-ray emission is produced in the shocks these bullets drive into the surrounding medium. The short-term variability seen in GRBs is set by the slowing-down time of the bullets, while the overall duration of the burst is set by the lifetime of the central engine. A requirement of this model is that the ambient medium be dense, consistent with a strong stellar wind. The efficiency of the burst can be relatively high. 相似文献
10.
By now there is no doubt that the gamma-ray bursts (GRB) have a cosmological origin. This allows to regard GRB as the most
powerful known energy sources, ε∼ 1054 erg (with a total number of gamma quanta N_γ∼ 1060). A plausible mechanism of coherent synchrotron radiation (CSR) of relativistic electrons driven by a local magnetic field
is studied in this paper. We consider relativistic electrons arising in the Compton scattering of a GRB in directions close
to that of the ray from the source to a ground-based observer. The synchrotron pulses from Compton electrons located at different
points on the line between the GRB source and the observer arrive at the observation point simultaneously. This simultaneity
ensures the coherence of the detected radiation. Both molecular clouds in the host galaxy of the GRB and our own Galaxy, as
well as the Earth atmosphere are assumed to be scatterers of the GRB radiation. Signals of each scatterer reach the Earth
surface, and can be detected at radio wavelengths. We estimate the characteristics of this radiation. The comparison of GRB
data with the corresponding information on CSR pulses offers a way to determine some global characteristics of the medium
between the Earth and the GRB source. 相似文献
11.
Gamma-Ray Bursts in the Swift Era 总被引:1,自引:0,他引:1
Bing Zhang 《中国天文和天体物理学报》2007,7(1):1-50
1 INTRODUCTION Gamma-ray bursts (GRBs) are fascinating celestial objects. These short, energetic bursts of gamma-rays mark the most violent, cataclysmic explosions in the universe, likely associated with the births of stellar- size black holes or rapidly spinning, highly magnetized neutron stars. Since the detections of their long- wavelength afterglows (Costa et al. 1997; van Paradijs et al. 1997; Frail et al. 1997), GRBs are observa- tionally accessible in essentially all electromagn… 相似文献
12.
We recalculate the diffuse flux of high-energy neutrinos produced by gamma-ray bursts in the relativistic fireball model. Although we confirm that the average single burst produces only approximately 10-2 high-energy neutrino events in a detector with a 1 km2 effective area, i.e., about 10 events yr-1, we show that the observed rate is dominated by burst-to-burst fluctuations that are very large. We find event rates that are expected to be larger by 1 order of magnitude, likely more, which are dominated by a few very bright bursts. This greatly simplifies their detection. 相似文献
13.
J -P. Dezalay C. Barat R. Talon O. Terekhov R. Sunyaev A. Kuznetsov 《Astrophysics and Space Science》1995,231(1-2):115-118
Statistical studies of Gamma-Ray Burst (GRB) properties have recently led to the discovery of a subclass within the population of classical events (Dezalayet al. 1992, Kouveliotouet al. 1993). Bursts belonging to this subclass are characterized by short durations, typically less than 2 seconds, and harder spectra on average. Using the PHEBUS GRB data set, we analyse the distributions of peak intensity, hardness ratio, and duration of the two subclasses. We also compare the sum spectra obtained with the brightest events to determine the ratio of total energies observed for each population. 相似文献
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本文假定γ暴来自相对论性Beaming,其方向满足随机分布,γ暴在自己的静止参考系中满足标准烛光和幂律谱假设.假设暴的发生率密度在Ω=1,A=0的Friedmann宇宙模型下,共动坐标系中是常数,模型对于Beaming的速度非常敏感,当络仑兹因子г值小于10幂律谱指数小于1时,计算的统计分布与弱暴的BATSE数据及强暴的PVO数据分布一致. 相似文献
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17.
Mei Wu Li Chen Ti-Pei LiKey Lab. of Particle Astrophys. Inst. of High Energy Phys. Chinese Academy of Sciences Beijing Department of Astronomy Beijing Normal University Beijing Center for Astrophysics Tsinghua University Beijing 《中国天文和天体物理学报》2005,5(1):57-64
Large-voltage, high-temperature plasma columns produced by pinch discharge can generate γ-ray flashes with energy spectra and spectral evolution consistent with what are observed in γ-ray bursts (GRBs), and the inverse Compton scattering (ICS) during the discharge process can produce high linear polarization. Our calculation indicates that the observed polarization depends on the angle between the line-of-sight todischarge, but only weakly depends onthe GRB and the direction of the pinch discharge, but only weakly depends on observed γray energy. 相似文献
18.
S. B. Pandey 《Journal of Astrophysics and Astronomy》2013,34(2):157-173
Study of energetic cosmic explosions as a part of time domain astronomy is one of the key areas that could be pursued with upcoming Giant segmented optical-IR telescopes with a very large photon collecting area applying cutting edge technology. Existing 8–10 m class telescopes have been helpful to improve our knowledge about core-collapse supernovae, gamma-ray bursts and nature of their progenitors and explosion mechanisms. However, many aspects about these energetic cosmic explosions are still not well-understood and require much bigger telescopes and back-end instruments with high precision to address the evolution of massive stars and high-redshift Universe in more detail. In this presentation, possible thrust research areas towards core-collapse supernovae and gamma-ray bursts with the Thirty-Meter Telescope and back-end instruments are presented. 相似文献
19.
The observation of the time delay between the soft emission and the high-energy radiation from cosmological gamma ray bursts
can be used as an important observational test of multi-dimensional physical theories. The main source of the time delay is
the variation of the electromagnetic coupling, due to dimensional reduction, which induces an energy dependence of the speed
of light. For photons with energies around 1 TeV, the time delay could range from a few seconds in the case of Kaluza–Klein
models to a few days for models with large extra-dimensions. Based on these results we suggest that the detection of the 18-GeV
photon ∼4500 s after the keV/MeV burst in GRB 940217 provides a strong evidence for the existence of extra-dimensions. The
time delay of photons, if observed by the next generation of high energy detectors, like, for example, the SWIFT and GLAST
satellite based detectors, or the VERITAS ground-based TeV gamma-ray instrument, could differentiate between the different
models with extra-dimensions. 相似文献
20.
B. Haskell 《Astrophysics and Space Science》2007,308(1-4):541-543
The aim of this work is to compare a neutron star with an accreted crust and one with a non-accreted crust, and estimate which
one is potentially a better source of gravitational waves (i.e. can sustain a larger “mountain”). To do this we present a
new formalism, and find that a non-accreted crust can sustain a slightly larger “mountain”. We also discuss the importance
of relativistic effects.
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