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1.
Charles Meegan 《Astrophysics and Space Science》1998,261(1-4):215-224
There has been significant progress recently in our understanding of gamma-ray bursts. The long-sought counterparts at other
wavelengths have finally been found for a few bursts. This breakthrough is the result of coordinated observations involving
several satellites and ground-based optical and radio observatories. In one case, GRB970508, redshifted absorption lines have
been detected, finally settling the debate about the distance scale. The consensus is that the burst sources lie at cosmological
distances, requiring at least ∼ 1051ergs to be emitted in gamma rays in just a few seconds. The gamma radiation is thought to be produced by shocks in a highly
relativistic fireball. Many mysteries remain. There is no consensus on the nature of the sources, although coalescing neutron
stars are the leading candidate. There is evidence that the sources of the faintest bursts may be at redshifts above 2. If
so, gamma-ray bursts may ultimately tell us something about the early Universe.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Tanvir N. R. Le Floc’h E. Christensen L. Caruana J. Salvaterra R. Ghirlanda G. Ciardi B. Maio U. D’Odorico V. Piedipalumbo E. Campana S. Noterdaeme P. Graziani L. Amati L. Bagoly Z. Balázs L. G. Basa S. Behar E. De Cia A. Valle M. Della De Pasquale M. Frontera F. Gomboc A. Götz D. Horvath I. Hudec R. Mereghetti S. O’Brien P. T. Osborne J. P. Paltani S. Rosati P. Sergijenko O. Stanway E. R. Szécsi D. Tot́h L. V. Urata Y. Vergani S. Zane S. 《Experimental Astronomy》2021,52(3):219-244
Experimental Astronomy - At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer... 相似文献
3.
A possibility for gamma-ray bursts to arise due to thermonuclear flashes in the surface layers of accreting neutron stars is discussed. The principal difference of the sources of gamma-ray bursts from bursters is supposed to result from the existence of strong magnetic fields (1012–1013G) on the neutron star surface. It is shown that the thermonuclear energy released may be rapidly and effectively transported to the outer layers by MHD waves (in particular, by Alfvén waves). A very short growth time and rapid variations of some gamma-ray bursts may be easily explained in this case. 相似文献
4.
G. Chanmugam 《Astrophysics and Space Science》1976,42(1):83-87
A number of models have been proposed for the observed cosmic gamma-ray bursts. A class of such models involves the use of magnetic energy as the principal source of energy required for the bursts. In this case, arguments are presented to show that degenerate stars are favored. Mechanisms for magnetohydrodynamic instabilities in white dwarfs and neutron stars are discussed. Preliminary work indicates that magnetic white dwarfs can (but neutron stars probably cannot) account for many of the observed features of the bursts.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975. 相似文献
5.
Valentí Bosch-Ramon Gustavo E. Romero Josep M. Paredes 《Astrophysics and Space Science》2005,297(1-4):119-129
Population studies of EGRET gamma-ray sources indicate that there is a distinctive population of bright sources at low galactic
latitudes. The sources have a distribution consistent with that of young galactic objects, with a concentration toward the
inner spiral arms. There is a subgroup that displays strong variability with timescales from days to months. Following an
earlier suggestion by Kaufman Bernadó et al. (2002), we explore the possibility that these sources could be high-mass microquasars.
Detailed models for the gamma-ray emission that include inverse Compton interactions of electrons in the relativistic jets
and photons from all local fields (stellar UV photons, synchrotron photons, soft X-ray photons from the accretion disk, and
hard X-ray photons from a corona) are presented. We conclude that microquasars are excellent candidates for the parent population
of the subgroup of variable low-latitude EGRET sources. 相似文献
6.
The “strange star - NDAF” model (NDAF: Neutrino Dominated Accretion Flow) is proposed as an alternative central engine of gamma-ray bursts for unifying the interpretation of the prompt emission and postburst activities of gamma-ray bursts. The structure of NDAF around a strange star is calculated. Different from other central compact objects, the strange star will feed back the phase transition energy of strangization on the accretion flow, with neutrinos as energy carriers. The friction between NDAF and strange star is ignored in this paper. The results indicate: firstly, the structure of NDAF around a strange star is sensitive to accretion rate; secondly, if accretion rate is larger than 0.18 M? s-1, the “strange star - NDAF” model can unify the explanation on the prompt emission and postburst activities of gamma-ray bursts, and the range of allowable accretion rates is wider than that in frictionless “neutron star - NDAF” models; thirdly, the range of annihilation energy of “strange star - NDAF” model is very wide, when the accretion rate is higher than 0.3 M? s-1, the annihilation energy is greater than 1051 erg; finally, if the accretion rate is greater than 0.3 M? s-1, the annihilation energy of “strange star - NDAF” model is larger than what of “black hole - NDAF” model at the same accretion rate by more than one order of magnitude, it is favorable to explaining some extremely energetic gamma-ray bursts. 相似文献
7.
Several planets have recently been discovered around stars that are old and metal-poor, implying that these planets are also old, formed in the early Universe together with their hosts. The canonical theory suggests that the conditions for their formation could not have existed at such early epochs. In this paper we argue that the required conditions, such as sufficiently high dust-to-gas ratio, could in fact have existed in the early Universe immediately following the first episode of metal production in Pop. III stars, both in metal-enhanced and metal-deficient environments. Metal-rich regions may have existed in multiple isolated pockets of enriched and weakly-mixed gas close to the massive Pop. III stars. Observations of quasars at redshifts z～5, and gamma-ray bursts at z～6, show a very wide spread of metals in absorption from [X/H]??3 to ??0.5. This suggests that physical conditions in the metal-abundant clumps could have been similar to where protoplanets form today. However, planets could have formed even in low-metallicity environments, where formation of stars is expected to proceed due to lower opacity at higher densities. In such cases, the circumstellar accretion disks are expected to rotate faster than their high-metallicity analogues. This in turn can result in the enhancement of dust particles at the disk periphery, where they can coagulate and start forming planetesimals. In conditions with the low initial specific angular momentum of the cloud, radiation from the central protostar can act as a trigger to drive small-scale instabilities with typical masses in the Earth to Jupiter mass range. Discoveries of planets around old metal-poor stars (e.g. HIP 11952, [Fe/H]～?1.95, ～13 Gyr) show that planets did indeed form in the early Universe and this may require modification of our understanding of the physical processes that produce them. This work is an attempt to provide one such heuristic scenario for the physical basis for their existence. 相似文献
8.
《New Astronomy》2020
GRB 170817A was confirmed to be associated with GW170817, which was produced by a neutron star - neutron star merger. It indicates that at least some short gamma-ray bursts come from binary neutron star mergers. Theoretically, it is widely accepted that short gamma-ray bursts can be produced by two distinctly different mechanisms, binary neutron star mergers and neutron star - black hole mergers. These two kinds of bursts should be different observationally due to their different trigger mechanisms. Motivated by this idea, we collect a universal data set constituted of 51 short gamma-ray bursts observed by Swift/BAT, among which 14 events have extended emission component. We study the observational features of these 51 events statistically. It is found that our samples consist of two distinct groups. They clearly show a bimodal distribution when their peak photon fluxes at 15–150 keV band are plotted against the corresponding fluences. Most interestingly, all the 14 short bursts with extended emission lie in a particular region of this plot. When the fluences are plotted against the burst durations, short bursts with extended emission again tend to concentrate in the long duration segment. These features strongly indicate that short gamma-ray bursts really may come from two distinct types of progenitors. We argue that those short gamma-ray bursts with extended emission come from the coalescence of neutron stars, while the short gamma-ray bursts without extended emission come from neutron star - black hole mergers. 相似文献
9.
A. N. Emelyanov V. A. Aref’ev E. M. Churazov M. R. Gilfanov R. A. Sunyaev 《Astronomy Letters》2001,27(12):781-789
We analyze 175 sessions of Galactic-center observations with the TTM/COMIS telescope onboard the Mir-Kvant observatory from 1987 until 1998. Because of its wide field of view (～ 15°×15°), much of the Galaxy and, hence, a large number of X-ray sources were simultaneously within the telescope aperture. During the observations, 47 X-ray bursts were detected, 33 of which are most likely type I bursts related to unstable helium burning on the surfaces of neutron stars. All the detected type I bursts were identified with known X-ray sources; the pre-and post-burst luminosities of these sources measured with the TTM telescope were high. No bursts were detected from voids, i.e., from sources whose luminosities in quiescence did not exceed the TTM detection threshold. This result allows us to constrain the combination of the number of binary sources with low accretion rates and the properties of X-ray bursts from such sources, in particular, the peak luminosity during bursts and the frequency of their occurrence. 相似文献
10.
Sandro Mereghetti 《Astronomy and Astrophysics Review》2008,15(4):225-287
Two classes of X-ray pulsars, the anomalous X-ray pulsars and the soft gamma-ray repeaters, have been recognized in the last
decade as the most promising candidates for being magnetars: isolated neutron stars powered by magnetic energy. I review the
observational properties of these objects, focussing on the most recent results, and their interpretation in the magnetar
model. Alternative explanations, in particular those based on accretion from residual disks, are also considered. The possible
relations between these sources and other classes of neutron stars and astrophysical objects are also discussed. 相似文献
11.
Merging neutron stars (NSs) are hot candidates for the still enigmatic sources of short gamma-ray bursts (GRBs). If the central engines of the huge energy release are accreting relic black holes (BHs) of such mergers, it is important to understand how the properties of the BH–torus systems, in particular disc masses and mass and rotation rate of the compact remnant, are linked to the characterizing parameters of the NS binaries. For this purpose, we present relativistic smoothed particle hydrodynamic simulations with conformally flat approximation of the Einstein field equations and a physical, non-zero temperature equation of state. Thick disc formation is highlighted as a dynamical process caused by angular momentum transfer through tidal torques during the merging process of asymmetric systems or in the rapidly spinning triaxial post-merger object. Our simulations support the possibility that the first well-localized short and hard GRBs 050509b, 050709, 050724, 050813 have originated from NS merger events and are powered by neutrino-antineutrino annihilation around a relic BH–torus system. Using model parameters based on this assumption, we show that the measured GRB energies and durations lead to estimates for the accreted masses and BH mass accretion rates which are compatible with theoretical expectations. In particular, the low-energy output and short duration of GRB 050509b set a very strict upper limit of less than 100 ms for the time interval after the merging until the merger remnant has collapsed to a BH, leaving an accretion torus with a small mass of only ∼0.01 M⊙ . This favours a (nearly) symmetric NS+NS binary with a typical mass as progenitor system. 相似文献
12.
After initial claims and a long hiatus, it is now established that several binary stars emit high- (0.1–100 GeV) and very high-energy (>100 GeV) gamma rays. A new class has emerged called “gamma-ray binaries”, since most of their radiated power is emitted beyond 1 MeV. Accreting X-ray binaries, novae and a colliding wind binary (η Car) have also been detected—“related systems” that confirm the ubiquity of particle acceleration in astrophysical sources. Do these systems have anything in common? What drives their high-energy emission? How do the processes involved compare to those in other sources of gamma rays: pulsars, active galactic nuclei, supernova remnants? I review the wealth of observational and theoretical work that have followed these detections, with an emphasis on gamma-ray binaries. I present the current evidence that gamma-ray binaries are driven by rotation-powered pulsars. Binaries are laboratories giving access to different vantage points or physical conditions on a regular timescale as the components revolve on their orbit. I explain the basic ingredients that models of gamma-ray binaries use, the challenges that they currently face, and how they can bring insights into the physics of pulsars. I discuss how gamma-ray emission from microquasars provides a window into the connection between accretion–ejection and acceleration, while η Car and novae raise new questions on the physics of these objects—or on the theory of diffusive shock acceleration. Indeed, explaining the gamma-ray emission from binaries strains our theories of high-energy astrophysical processes, by testing them on scales and in environments that were generally not foreseen, and this is how these detections are most valuable. 相似文献
13.
The binary systems that have been detected in gamma rays have proven very useful to study high-energy processes, in particular particle acceleration, emission and radiation reprocessing, and the dynamics of the underlying magnetized flows. Binary systems, either detected or potential gamma-ray emitters, can be grouped in different subclasses depending on the nature of the binary components or the origin of the particle acceleration: the interaction of the winds of either a pulsar and a massive star or two massive stars; accretion onto a compact object and jet formation; and interaction of a relativistic outflow with the external medium. We evaluate the potentialities of an instrument like the Cherenkov telescope array (CTA) to study the non-thermal physics of gamma-ray binaries, which requires the observation of high-energy phenomena at different time and spatial scales. We analyze the capability of CTA, under different configurations, to probe the spectral, temporal and spatial behavior of gamma-ray binaries in the context of the known or expected physics of these sources. CTA will be able to probe with high spectral, temporal and spatial resolution the physical processes behind the gamma-ray emission in binaries, significantly increasing as well the number of known sources. This will allow the derivation of information on the particle acceleration and emission sites qualitatively better than what is currently available. 相似文献
14.
Coalescing binary neutron stars are the most promising candidates for detection by gravitational-wave detectors and are considered
to be most promising for explaining the phenomenon of short gamma-ray bursts. The magnetic fields of neutron stars during
their coalescence can produce a number of interesting observational manifestations and can affect significantly the shape
of the gravitationalwave signal. In this paper, we model the distribution of magnetic fields in coalescing neutron stars by
the population synthesis method using various assumptions about the initial parameters of the neutron stars and the evolution
laws of their magnetic fields. We discuss possible electromagnetic phenomena preceding the coalescence of magnetized neutron
stars and the effect of magnetic field energy on the shape of the gravitational-wave signal during the coalescence. For a
log-normal (Gaussian in logarithm) distribution of the initialmagnetic fields consistent with the observations of radio pulsars,
the distribution inmagnetic field energy during the coalescence is shown to describe adequately the observed luminosity function
of short gamma-ray bursts under various assumptions about the pattern of field evolution and initial parameters of neutron
stars. 相似文献
15.
Four suspected optical flashes on archival plates with coordinates within or near to the error boxes of gamma-ray bursts, respectively, are investigated by surface photometry, Their density profiles are shown to be consistent with that of stars of similar magnitude. Hence, the suspected flashes are not likely to be plate defects but real objects on the sky. 相似文献
16.
Possible phase transitions in neutron star matter, particularly the melting of neutron stars' crystalline cores, are discussed. Such processes may explain the observed luminosity of pulsars. They are used also as a basis for an explanation of the origin of low energy gamma-ray bursts which have been intensively studied for the last few years. The authors discuss the structure of gamma-ray bursts and the possibility of obtaining from observational data some information on thermal evolution of neutron stars and dynamic processes in the pulsar crust. 相似文献
17.
Gamma-ray bursts from internal shocks in a relativistic wind: temporal and spectral properties 总被引：1，自引：0，他引：1
We construct models for gamma-ray bursts in which the emission comes from internal shocks in a relativistic wind with a highly non-uniform distribution of the Lorentz factor. We follow the evolution of the wind using a very simplified approach in which a large number of layers interact by direct collisions but all pressure waves have been suppressed. We suppose that the magnetic field and the electron Lorentz factor reach large equipartition values in the shocks. Synchrotron photons emitted by the relativistic electrons have a typical energy in the gamma-ray range in the observer frame. Synthetic bursts are constructed as the sum of the contributions from all the internal elementary shocks, and their temporal and spectral properties are compared with the observations. We reproduce the diversity of burst profiles, the 'FRED' shape of individual pulses and the short time-scale variability. Synthetic bursts also satisfy the duration–hardness relation and individual pulses are found to be narrower at high energy, in agreement with the observations. These results suggest that internal shocks in a relativistic wind may indeed be at the origin of gamma-ray bursts. A potential problem, however, is the relatively low efficiency of the dissipation process. If the relativistic wind is powered by accretion from a disc to a stellar mass black hole, it implies that a substantial fraction of the available energy is injected into the wind. 相似文献
18.
We revisit the vertical structure of neutrino-dominated accretion flows (NDAFs) in spherical coordinates with a new boundary
condition based on the mechanical equilibrium. The solutions show that NDAF is significantly thick. The Bernoulli parameter
and neutrino trapping are determined by the mass accretion rate and the viscosity parameter. According to the distribution
of the Bernoulli parameter, the possible outflow may appear in the outer region of the disk. The neutrino trapping can essentially
affect the neutrino radiation luminosity. The vertical structure of NDAF is like a “sandwich”, and the multilayer accretion
may account for the flares in gamma-ray bursts. 相似文献
19.
Observations of 85 gamma bursts by the KONUS instruments on the Venera 11 and Venera 12 spacecraft in the period September 1978 to May 1979 inclusive have provided proof of a galactic localization of the gamma-burst sources based on an analysis of the logN-logS plot and the revealed anisotropy in the angular distribution of sources over the celestial sphere. Evaluation of the energy released in the sources yields 1040–1041 erg. There apparently exist several types of gamma bursts differing in time profile, duration and shape of their energy spectrum. In some cases, extensive evolution of the energy spectrum is observed during a burst. The discovery of a flaring X-ray pulsar in Dorado has provided the first observational evidence for a connection of gamma bursts with neutron stars. Repeated short bursts from this source have revealed for the first time the recurrent features of this phenomenon. Repeated bursts have been detected from one more source in the short burst class. The data obtained thus far impose a number of restrictions on the applicability of many theoretical suggestions concerning the nature of the gamma bursts. The most plausible model for the gamma-burst source appears to be a binary with a neutron star with strongly non-stationary accretion involving, possibly, non-stationary thermonuclear fusion of matter falling onto the surface of a degenerate star.Paper presented at the Symposium on Cosmic Gamma-Ray Bursts, held at Toulouse, France, 26–29 November, 1979. 相似文献
20.
伽玛射线暴的产生机制比较公认的是:长暴产生于大质量恒星死亡;短暴产生于密近双星合并.因此人们很自然地推测长暴和恒星形成率直接成比例,但是最近数据分析表明这并不能很好地拟合观测.考虑到只有质量大于某一临界质量的大质量恒星才可能产生长暴,因此恒星初始质量分布函数对长暴的产生率会有较大影响.考虑用恒星初始质量分布函数来解释长暴观测个数随红移的分布,得到了比较好的结果. 相似文献