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1.
The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 102∼104 s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar. 相似文献
2.
某些伽玛射线暴(简称伽玛暴)的中心致密天体可能是一颗具有强磁场的毫秒脉冲星,它通过磁偶极辐射可对伽玛暴外激波注入能量,从而导致早期余辉光变曲线的变平.近年来,从Swift卫星观测到的大量伽玛暴X射线余辉中发现,很多X射线余辉光变曲线在暴后10~2～10~4s期间的确存在明显的变平现象.利用周期为毫秒量级的磁星能量注入模型对11个加玛暴的X射线余辉光变曲线进行了拟合,显示该模型在解释余辉变平现象上的有效性和广泛性,通过对余辉光变曲线的拟合,同时也给出了相关中心磁星的磁场强度和旋转周期. 相似文献
3.
Yu Yu Yong-Feng Huang 《中国天文和天体物理学报》2007,7(5):669-674
With the successful launch of Swift satellite,more and more data of early X-ray afterglows from short gamma-ray bursts have been collected.Some interesting features such as unusual afterglow light curves and unexpected X-ray flares are revealed.Especially,in some cases,there is a fiat segment in the X-ray afterglow light curve.Here we present a simplified model in which we believe that the flattening part is due to energy injection from the central engine.We assume that this energy injection arises from the magnetic dipole radiation of a millisecond pulsar formed after the merger of two neutron stars.We check this model with the short GRB 060313.Our numerical results suggest that energy injection from a millisecond magnetar could make part of the X-ray afterglow light curve flat. 相似文献
4.
Comparison of the INTEGRAL upper limits on the hard X-ray flux before and after the low-energy GRB 031203 with the XMM measurements of the dust-scattered radiation at lower energies suggests that a significant fraction of the total burst energy could be released in the form of soft X-ray radiation at an early afterglow stage with a characteristic duration of ～100–1000 s. The overall time evolution of the afterglow from GRB 031203 may have not differed qualitatively from the behavior of standard (i.e., more intense) bursts studied by the SWIFT observatory. The available data also admit the possibility that the dust-scattered radiation was associated with an additional soft component in the spectrum of the gamma-ray burst itself. 相似文献
5.
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
6.
During the in-spiral stage of a compact binary, a wind bubble could be blown into the interstellar medium, if electromagnetic radiation due to the binary orbital motion is strong enough. Therefore, shortduration gamma-ray bursts(SGRBs) due to double neutron star mergers would in principle happen in a wind bubble environment, which can influence the propagation of the SGRB jet and consequent afterglow emission. By calculating the dynamics and synchrotron radiation of the jet-driven external shock, we reveal that an abrupt jump could appear in the afterglow light curves of SGRBs and the observational time of the jump is dependent on the viewing angle. This light curve jump provides an observational signature to constrain the radius of the wind bubble and thus the power of the electromagnetic radiation of the binary,by combining with gravitational wave detection. 相似文献
7.
The gamma-ray burst (GRB) 021211 had a simple light curve, containing only one peak and the expected Poisson fluctuations. Such a burst may be attributed to an external shock, offering the best chance for a unified understanding of the gamma-ray burst and afterglow emissions. We analyse the properties of the prompt (burst) and delayed (afterglow) emissions of GRB 021211 within the fireball model. Consistency between the optical emission during the first 11 min (which, presumably, comes from the reverse shock heating of the ejecta) and the later afterglow emission (arising from the forward shock) requires that, at the onset of deceleration (∼2 s), the energy density in the magnetic field in the ejecta, expressed as a fraction of the equipartition value (ɛ B ) , is larger than in the forward shock at 11 min by a factor of approximately 103 . We find that synchrotron radiation from the forward shock can account for the gamma-ray emission of GRB 021211; to explain the observed GRB peak flux requires that, at 2 s, ɛ B in the forward shock is larger by a factor 100 than at 11 min. These results suggest that the magnetic field in the reverse shock and early forward shock is a frozen-in field originating in the explosion and that most of the energy in the explosion was initially stored in the magnetic field. We can rule out the possibility that the ejecta from the burst for GRB 021211 contained more than 10 electron–positron pairs per proton. 相似文献
8.
Yi Xie Zhao-Yan Huang Xiang-Fu Jia Shao-Juan Fan Fang-Fang Liu 《Monthly notices of the Royal Astronomical Society》2009,398(2):583-590
We consider the influence of magnetic fields on the model of neutrino-dominated accretion flows (NDAFs) for gamma-ray bursts (GRBs) via the assumption that the accretion rate of the disc is totally caused by the torque of the Lorentz force, i.e. the magnetic braking of large-scale magnetic fields and magnetic viscosity of small-scale magnetic fields. We calculate the structure, composition, luminosity of neutrino emission and the Poynting flux, and the rate of mass loss driven by neutrino heating or launched centrifugally by large-scale magnetic fields, based on the physical condition of the magnetized NDAFs. It is shown that the magnetized disc is favourable to interpret the diverse prompt emissions as well as the X-ray flares observed in the early afterglow of GRBs. 相似文献
9.
Swift卫星的X射线望远镜观测揭示部分伽玛暴的早期余辉光变曲线有一个缓慢衰减的成分,而相当一部分却没有这样的成分.研究比较这两种暴的观测性质发现两类暴的持续时间、伽玛辐射总流量、谱指数、谱硬度比峰值能量等物理量均没有显著差异.然而有该成分的那些伽玛暴谱比较软、早期X射线余辉比较弱、伽玛射线辐射效率显著高于没有这个成分的那些暴.结果表明两类暴的前身星和中心机制一致,是否呈现这个缓慢衰减成分可能取决于外部介质. 相似文献
10.
Observational parameters of the optical and gamma-ray emissions from 58 gamma-ray bursts (GRBs) with discovered afterglows and known redshifts are analyzed. The distributions of these parameters and pair correlations between them are studied. Approximately half of the objects exhibit a relatively slow decrease in the optical flux at initial afterglow phases (with a power-law index in the decay law α < 1). Correlations have been found between the luminosities, energies, and durations of the optical and gamma-ray emissions, which can be explained by the presence of universal features in the light curves. A correlation of the peak luminosity for afterglows with the redshift and an anticorrelation of their durations with the redshift have been found for the first time. Against the background of a weak z dependence of the total afterglow energy, this effect can be explained by cosmological evolution of the GRB environment, which determines the rate of optical energy release. 相似文献
11.
本文认为强磁场中的逆Compton散射可能是γ射线爆的主要辐射机制.其能谱是由源区质子产生的低频光子经强磁场中非热电子的Compton散射形成的.我们利用非相对论情形(B/B_(cr)≤1,hv_i/m_ec~2≤1)下强磁场中的Compton散射微分截面,导出了上述Compton散射的辐射谱公式,由此很好地拟合了典型γ射线爆GB811016的观测能谱. 相似文献
12.
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
13.
K.-I. Nishikawa C. B. Hededal P. E. Hardee G. J. Fishman C. Kouveliotou Y. Mizuno 《Astrophysics and Space Science》2007,307(1-3):319-323
We have applied numerical simulations and modeling to the particle acceleration, magnetic field generation, and emission from
relativistic shocks. We investigate the nonlinear stage of theWeibel instability and compare our simulations with the observed
gamma-ray burst emission. In collisionless shocks, plasma waves and their associated instabilities (e.g., the Weibel, Buneman
and other two-stream instabilities) are responsible for particle (electron, positron, and ion) acceleration and magnetic field
generation. 3-D relativistic electromagnetic particle (REMP) simulations with three different electron-positron jet velocity
distributions and also with an electron-ion plasma have been performed and show shock processes including spatial and temporal
evolution of shocks in unmagnetized ambient plasmas. The growth time and nonlinear saturation levels depend on the initial
jet parallel velocity distributions. Simulations show that the Weibel instability created in the collisionless shocks accelerates
jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude
of densities, currents, electric, and magnetic fields in the electron-positron shocks are larger for smaller jet Lorentz factor.
This comes from the fact that the growth time of the Weibel instability is proportional to the square of the jet Lorentz factor.
We have performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which is assumed to be
created by photon annihilation. Simulation results with this broad distribution show that the Weibel instability is excited
continuously by the wide-range of jet Lorentz factor from lower to higher values. In all simulations the Weibel instability
is responsible for generating and amplifying magnetic fields perpendicular to the jet propagation direction, and contributes
to the electron’s (positron’s) transverse deflection behind the jet head. This small scale magnetic field structure contributes
to the generation of “jitter” radiation from deflected electrons (positrons), which is different from synchrotron radiation
in uniform magnetic fields. The jitter radiation resulting from small scale magnetic field structures may be important for
understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources
containing relativistic jets and relativistic collisionless shocks. The detailed studies of shock microscopic process evolution
may provide some insights into early and later GRB afterglows. 相似文献
14.
Based on the magnetar model, we have studied in detail the processes of neutrino cooling of an electron-positron plasma generating
an SGR giant flare and the influence of the magnetar magnetic field on these processes. Electron-positron pair annihilation
and synchrotron neutrino emission are shown to make a dominant contribution to the neutrino emissivity of such a plasma. We
have calculated the neutrino energy losses from a plasma-filled region at the long tail stage of the SGR 0526-66, SGR 1806–20,
and SGR 1900+14 giant flares. This plasma can emit the energy observed in an SGR giant flare only in the presence of a strongmagnetic
field suppressing its neutrino energy losses. We have obtained a lower bound on the magnetic field strength and showed this
value to be higher than the upper limit following from an estimate of the magnetic dipole losses for the magnetars being analyzed
in a wide range of magnetar model parameters. Thus, it is problematic to explain the observed energy release at the long tail
stage of an SGR giant flare in terms of the magnetarmodel. 相似文献
15.
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
16.
Woods PM Kouveliotou C van Paradijs J Briggs MS Hurley K Göğüş E Preece RD Giblin TW Thompson C Duncan RC 《The Astrophysical journal》1999,527(1):L47-L50
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.
It is believed that orphan afterglow searches can help to measure the beaming angle in gamma-ray bursts (GRBs). Great expectations have been put on this method. We point out that the method is in fact not as simple as we originally expected. As a result of the baryon-rich environment that is common to almost all popular progenitor models, there should be many failed gamma-ray bursts, i.e. fireballs with Lorentz factor much less than 100–1000 , but still much larger than unity. In fact, the number of failed gamma-ray bursts may even be much larger than that of successful bursts. Owing to the existence of these failed gamma-ray bursts, there should be many orphan afterglows even if GRBs are due to isotropic fireballs, then the simple discovery of orphan afterglows never means that GRBs are collimated. Unfortunately, to distinguish between a failed-GRB orphan and a jetted but off-axis GRB orphan is not an easy task. The major problem is that the trigger time is unknown. Some possible solutions to the problem are suggested. 相似文献
18.
R. A. Burenin 《Astronomy Letters》2000,26(5):269-276
In the relativistic fireball model, the afterglow of a gamma-ray burst (GRB) is produced by synchrotron radiation of the electrons accelerated in the external shock that emerges as the relativistic flow moves. According to this model, the afterglow peaks on a time scale of ～10 s when observed in the soft gamma-ray band. The peak flux can be high enough to be detected by modern all-sky monitors. We investigate the emission from short (ΔT<1 s) GRBs on a time scale t≈10 s using BATSE/CGRO data. A significant flux is recorded for ～20% of the events. In most cases, the observed persistent emission can be explained in terms of the model as an early burst afterglow. No early afterglows of most short GRBs are observed. The model parameters for these bursts are constrained. 相似文献
19.
Elena Rossi Davide Lazzati Martin J. Rees 《Monthly notices of the Royal Astronomical Society》2002,332(4):945-950
Gamma-ray bursts are often modelled as jet-like outflows directed towards the observer; the cone angle of the jet is then commonly inferred from the time at which there is a steepening in the power-law decay of the afterglow. We consider an alternative model in which the jet has a beam pattern where the luminosity per unit solid angle (and perhaps also the initial Lorentz factor) decreases smoothly away from the axis, rather than having a well-defined cone angle within which the flow is uniform. We show that the break in the afterglow light curve then occurs at a time that depends on the viewing angle. Instead of implying a range of intrinsically different jets – some very narrow, and others with a similar power spread over a wider cone – the data on afterglow breaks could be consistent with a standardized jet, viewed from different angles. We discuss the implication of this model for the luminosity function. 相似文献
20.
We consider a formation scenario for supramassive neutron stars (SMNSs) that takes place through mass and angular momentum transfer from a close companion during a low-mass X-ray binary phase, with the ensuing suppression of the magnetic field. After the end of the mass transfer phase, SMNSs will lose, through magnetic dipole radiation, most of their angular momentum, triggering the star's collapse to a black hole. We discuss the rate of occurrence of these collapses and propose that these stars, because of the baryon-clear environment in which the implosion/explosion takes place, are the originators of gamma-ray bursts. 相似文献