GRB 110731 A是观测到的能量最高的伽马射线暴之一，能量范围从光学到GeV。先前对瞬发相的分析揭示了与费米观察到的大面积望远镜（LAT）爆发的相似之处：i）高能发射（$> 100$ MeV）的延迟开始，ii）稍后时间的短暂明亮峰值和iii）从这个阶段持续数百秒的时间延长组件。除了瞬发阶段，在不同时期的多波长观测表明，光谱能量分布更好地拟合风余辉模型。我们提出了一个轻子模型的基础上早期的余辉，在恒星风的祖先。我们应用这个模型来解释的时间延长LAT发射和最明亮的LAT峰所表现出的即时相的GRB 110731 A。此外，使用相同的一组参数，我们描述了多波长余辉观测。通过前向激波的同步辐射解释了时间上扩展的LAT、X射线和光通量的起源，并描述了引起反向激波的同步辐射自康普顿发射的最亮LAT峰。该模型中所需的体洛伦兹因子（$Γ\simeq520$）位于大多数LAT探测到的伽马射线暴所需的数值范围内。我们表明，在反向冲击区的磁场强度是$\sim$ 50倍强于在前向冲击区。这一结果表明，对于GRB 110731 A，中央发动机可能夹带着强磁场。
英文摘要：
One of the most energetic gamma-ray burst GRB 110731A was observed from optical to GeV energy range. Previous analysis on the prompt phase revealed similarities with the Large Area Telescope (LAT) bursts observed by Fermi: i) a delayed onset of the high-energy emission ($> 100$ MeV), ii) a short-lasting bright peak at later times and iii) a temporally extended component from this phase and lasting hundreds of seconds. Additionally to the prompt phase, multiwavelength observations over different epochs showed that the spectral energy distribution was better fitted by a wind afterglow model. We present a leptonic model based on an early afterglow that evolves in a stellar wind of its progenitor. We apply this model to interpret the temporally extended LAT emission and the brightest LAT peak exhibited by the prompt phase of GRB 110731A. Additionally, using the same set of parameters, we describe the multiwavelength afterglow observations. The origin of the temporally extended LAT, X-ray and optical flux is explained through synchrotron radiation from the forward shock and the brightest LAT peak is described evoking the synchrotron self-Compton emission from the reverse shock. The bulk Lorentz factor required in this model ($Γ\simeq520$) lies in the range of values demanded for most LAT-detected gamma-ray bursts. We show that the strength of the magnetic field in the reverse-shock region is $\sim$ 50 times stronger than in the forward-shock region. This result suggests that for GRB 110731A, the central engine is likely entrained with strong magnetic fields.
Afterglows of gamma-ray bursts often show flares, plateaus, and sudden intensity drops: these temporal features are difficult to explain as coming from the forward shock. We calculate radiative properties of early GRB afterglows with the dominant contribution from the reverse shock (RS) propagating in an ultra-relativistic (pulsar-like) wind produced by the long-lasting central engine. RS emission occurs in the fast cooling regime -- this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that: (i) mild wind power, of the order of $\sim 10^{46}$ erg s$^{-1}$…
We develop a model of early X-ray afterglows of gamma-ray bursts originating from the reverse shock (RS) propagating through ultra-relativistic, highly magnetized pulsar-like winds produced by long-lasting central engines. We first perform fluid and MHD numerical simulations of relativistic double explosions. We demonstrate that even for constant properties of the wind a variety of temporal behaviors can be produced, depending on the energy of the initial explosion and the wind power, the delay time for the switch-on of the wind, and magnetization of the wind. X-ray emission of the highly magn…
In the dynamical models of gamma-ray burst (GRB) afterglows, the uniform assumption of the shocked region is known as provoking total energy conservation problem. In this work we consider shocks originating from magnetized ejecta, extend the energy-conserving hydrodynamical model of Yan et al. (2007) to the MHD limit by applying the magnetized jump conditions from Zhang & Kobayashi (2005). Compared with the non-conservative models, our Lorentz factor of the whole shocked region is larger by a factor $\lesssim\sqrt{2}$. The total pressure of the forward shocked region is higher than the reverse…
Sub-relativistic materials launched during the merger of binary compact objects and the core-collapse of massive stars acquire velocity structures when expanding in a stratified environment. The remnant (either a spinning magnetized neutron star (NS) or a central black hole) from the compact-object or core-collapse could additionally inject energy into the afterglow via spin-down luminosity or/and by accreting fall-back material, producing a refreshed shock, modifying the dynamics, and leading to rich radiation signatures at distinct timescales and energy bands with contrasting intensities. We…
The well-sampled afterglows of gamma ray bursts (GRBs) not associated with a supernova (SN) explosion, can be scaled down to a simple dimensionless universal formula, which describes well their temporal behavior. Such SN-less GRBs include short hard bursts (SHBs) and long SN-less GRBs. The universal temporal behavior of their afterglows is that expected from a pulsar wind nebula powered by the rotational energy loss of the newly born pulsar.
GRB 080503 late afterglow re-brightening: signature of a magnetar powered merger-nova
GRB 080503是一个由\emph{Swift}探测到的短伽马射线暴（GRB），被归类为致密恒星合并源GRB。在X射线和光学余辉光变曲线中的软扩展发射和同时的后期再增亮引起了关于其物理起源的有趣问题。我们发现，GRB 080503的宽带数据可以很好地解释在双中子星合并模型的框架内，提供的合并残余物是一个快速旋转的大质量中子星具有极高的磁场（即毫秒磁星）。我们表明，后期的光学再增亮是一致的发射从磁星供电的“合并新星”。这为与短伽玛暴相关的并合新星的不断增长的样本又增加了一个案例。软扩展发射和晚期X射线过量发射通过磁星偶极自旋下降光度演化函数很好地联系在一起，表明直接磁耗散是产生这些X射线的机制。X射线辐射最初是从被短伽玛射线暴喷流刺穿的合并喷出物中的一个洞泄漏出来的。在磁星向下旋转并且磁压力下降到冲压压力以下之后，孔随后关闭。然后X射线光子被捕获在合并新星喷出物的后面，直到喷出物在稍后的时间变得光学薄。这解释了光学和X射线光变曲线中基本上同时发生的再增亮。在这个模型中，未来的引力波源可能与一个明亮的X射线对应物以及合并新星相关联，即使短的伽马射线暴喷流远离地球。
We describe the afterglows of the long gamma-ray-burst (GRB) 130427A within the context of a binary-driven hypernova (BdHN). The afterglows originate from the interaction between a newly born neutron star ($ν$NS), created by an Ic supernova (SN), and a mildly relativistic ejecta of a hypernova (HN). Such a HN in turn results from the impact of the GRB on the original SN Ic. The mildly relativistic expansion velocity of the afterglow ($Γ\sim 3$) is determined, using our model independent approach, from the thermal emission between $196$~s and $461$~s. The power-law in the optical and X-ray band…
We performed calculations of the late radio and X-ray afterglow of GRB/GW170817 in the cocoon-jet paradigm, predicting the appearance of a second peak in the afterglow light curve ~ one-three years after the explosion. The model assumes that the prompt emission and early afterglows originate from a cocoon generated during break-out of the delayed magnetically powered jet. As the jet breaks out from the torus-generated wind, a nearly isotropic mildly relativistic outflow is generated; at the same time the primary jet accelerates to high Lorentz factors and avoids detection. As the fast jet slow…
We report multi-color optical imaging and polarimetry observations of the afterglow of the first TeV- detected gamma-ray burst, GRB 190114C, using RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until $\sim 7000\,$s post-burst. The light curves reveal a chromatic break at $\sim 400- 500\,$s, with initial temporal decay $α= 1.669 \pm 0.013$ flattening to $α\sim 1$ post-break, which we model as a combination of reverse and forward-shock components, with magnetization parameter $R_{\rm B} \sim 70$. The observed polarization degree decreases from …
SSC Emission as Explanation of The Gamma Ray Afterglow Observed in GRB 980923
GRB 980923是由爆发和瞬态源实验（BATSE）观测到的最明亮的爆发之一。以前的研究已经检测到两个不同的组件，除了主要的提示情节，这是很好地描述了乐队功能。其中第一个是持续时间为400秒的尾部，而第二个是持续时间为2秒的高能成分。在总结了观测结果后，我们提出了一个模型，并得出结论，尾巴可以被理解为早期的伽马射线余辉从正向冲击同步辐射，而高能量的组成部分描述的SSC从反向冲击发射。主要的假设是，一个厚壳的情况下，从高度磁化喷出物。计算得到的通量、破缺能、起始时间和谱指数与观测值一致。
In order to explain unusually high luminosity and spectral nature of ultra-luminous X-ray sources (ULXs), some of the underlying black holes are argued to be of intermediate mass, between several tens to million solar masses. Indeed, there is a long standing question of missing mass of intermediate range of black holes. However, as some ULXs are argued to be neutron stars too, often their unusual high luminosity is argued by super-Eddington accretions. Nevertheless, all the models are based on non-magnetized or weakly magnetized accretion. There are, however, evidences that magnetic fields in …
We present the results of our radio observational campaign on GRB 100418a, for which we used the Australia Telescope Compact Array (ATCA), Very Large Array (VLA) and the Very Long Baseline Array (VLBA). GRB 100418a was a peculiar GRB with unusual X-ray and optical afterglow profiles featuring a plateau phase with a very shallow rise. This observed plateau phase was believed to be due to a continued energy injection mechanism which powered the forward shock, giving rise to an unusual and long-lasting afterglow. The radio afterglow of GRB 100418a was detectable several weeks after the prompt emi…
GW170817/GRB170817A has offered unprecedented insight into binary neutron star post-merger systems. Its Prompt and afterglow emission imply the presence of a tightly collimated relativistic jet with a smooth transverse structure. However, it remains unclear whether and how the central engine can produce such structured jets. Here, we utilize 3D GRMHD simulations starting with a black hole surrounded by a magnetized torus with properties typically expected of a post-merger system. We follow the jet, as it is self-consistently launched, from the scale of the compact object out to more than 3 ord…
Jet precession is considered to universally exist in different-scale astronomical phenomena, including gamma-ray bursts (GRBs). For the long-lived GRB central engine, the relativistical precessing jets will periodically inject kinetic energy into the external shocks, then significantly modulate the shapes of the light curves (LCs) in GRB afterglows. In this paper, we adopt the standard external shock model to investigate the effects of jet precession on GRB X-ray afterglows in cases with different parameters, i.e., the steady or time-dependent jet powers, precession periods, precession angles,…
Many gamma-ray bursts are followed by periods of extended emission. At least in some cases, the burst afterglow may be powered by a rapidly rotating, highly-magnetised neutron star, which spins down due to electromagnetic and gravitational wave emission. Such a remnant is likely to strongly precess in the early stages of its life, which would lead to modulations in the X-ray luminosity as the triaxiality of the system evolves over time. Using a radiation profile appropriate for a precessing, oblique rotator, we find that Swift-XRT data of a long (080602) and a short (090510) burst matches the …
GRB~250704B/EP250704a a Short Gamma-Ray Burst Powered by a Magnetar
Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文学研究所）；Instituto de Fśica, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）；Division of Science, National Astronomical Observatory of Japan（日本国立天文台科学部）；The Graduate University for Advanced Studies (SOKENDAI)（高等研究院（SOKENDAI））；Cosmology, Gravity, and Astroparticle Physics Group, Center for Theoretical Physics of the Universe, Institute for Basic Science (IBS)（基础科学研究院宇宙理论物理中心宇宙学、引力与天体粒子物理学组）
We study the broadband radiation behavior of a kilonova ejecta-pulsar wind nebula (PWN) system. In this model, we jointly fit the observations of AT 2017gfo in UV-optical-IR bands and the late-time X-ray afterglow of GRB 170817A. Our work shows that a PWN powered by the remnant neutron star (NS) post GW170817 event could affect the optical transient AT 2017gfo and re-brighten the late-time X-ray afterglow of GRB 170817A. The PWN radiation will regulate the trend of future X-ray observations from a flattening to a steep decline until some other sources (e.g., a kilonova afterglow) become domina…
X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330: Further evidences for central engine afterglow from Gamma-ray Bursts
The fast radio burst FRB 121102 has repeated multiple times, enabling the identification of its host galaxy and of a spatially-coincident, compact, steady (`quiescent') radio synchrotron source. It was proposed that FRB 121102 is powered by a young flaring magnetar, embedded within a decades-old supernova remnant. Using a time-dependent one-zone model, we show that a single expanding magnetized electron-ion nebula (powered by the same outbursts likely responsible for the FRBs) can explain all the basic properties of the quiescent source (size, flux, self-absorption constraints) and the large b…
We investigate how magnetically driven outflows are powered by a rotating, weakly magnetized accretion flow onto a supermassive black hole using axisymmetric magnetohydrodynamic simulations. Our proposed model focuses on the accretion dynamics on an intermediate scale between the Schwarzschild radius and the galactic scale, which is $\sim$1-100 pc. We demonstrate that a rotating disk formed on a parsec-scale acquires poloidal magnetic fields via accretion and this produces an asymmetric bipolar outflow at some point. The formation of the outflow was found to follow the growth of strongly magne…
Motivated by the detection of very high energy gamma-rays deep in the afterglow emission of a gamma-ray burst, we revisit predictions of the maximum energy to which electrons can be accelerated at a relativistic blast wave. Acceleration at the weakly-magnetized forward shock of a blast-wave can be limited either by the rapid damping of turbulence generated behind the shock, by the effect of a large-scale ambient magnetic field, or by radiation losses. Within the confines of a standard, single zone, synchrotron-self-Compton (SSC) model, we show that observations of GRB190829A rule out a rapid d…
Binary neutron star (BNS) mergers are one of the proposed origins for both repeating and non-repeating fast radio bursts (FRBs), which associates FRBs with gravitational waves and short gamma-ray bursts (GRBs). In this work, we explore detectability of radio afterglows from BNS mergers and compare it to the observed radio limits on FRB afterglows. We calculate the afterglow flux powered by the two components: a relativistic jet and a slower isotropic ejecta, and quantify the detection probability as a function of the source redshift, observing time, and flux sensitivity. The model parameter di…
SSC Emission as the Origin of the Gamma Ray Afterglow Observed in GRB 980923
GRB 980923是由爆发和瞬态源实验（BATSE）观测到的最明亮的爆发之一。以前的研究已经检测到两个不同的组件，除了主要的提示情节，这是很好地描述了乐队功能。其中第一个是一个尾巴的持续时间约。400秒，而第二个是一个高能量成分持续约。2先令我们总结的意见，并认为一个统一的模型，其中的尾巴可以被理解为早期的伽马射线余辉从正向冲击同步辐射，而高能量的组成部分来自同步自Comtpon（SSC）从反向冲击。厚壳发射的主要假设之间的一致性和协议的观测值和计算值之间的通量，破碎能量，开始时间和光谱指数导致的要求，喷出物高度磁化。
Magnetars are a kind of pulsars powered mainly by superhigh magnetic fields. They are popular sources with many unsolved issues in themselves, but also linked to various high energy phenomena, such as QPOs, giant flares, fast radio bursts and super-luminous supernovae. In this work, we first review our recent works on the dissipation of toroidal magnetic fields in magnetars and rotationally powered pulsars, then review the spin-down evolution of young and strongly magnetized pulsars, especially of magnetars. We present an interesting and important relation between the magnetization parameter, …
Gamma-ray bursts (GRBs) are believed to be powered by ultrarelativistic jets. If these jets encounter and accelerate excess electrons and positrons produced by particle dark matter (DM) annihilation, the observed electromagnetic radiation would be enhanced. In this paper, we study GRB afterglow emission with the presence of abundant DM under the weakly interacting massive particle annihilation conditions. We calculate the light curves and spectra of the GRB afterglows with different parameters, i.e., DM density, particle DM mass, annihilation channel, and electron density of the interstellar m…
A relativistic electron-positron ($e^{+}e^{-}$) pair wind from a rapidly rotating, strongly magnetized neutron star (NS) would interact with a gamma-ray burst (GRB) external shock and reshapes afterglow emission signatures. Assuming that the merger remnant of GW170817 is a long-lived NS, we show that a relativistic $e^{+}e^{-}$ pair wind model with a simple top-hat jet viewed off-axis can reproduce multi-wavelength afterglow lightcurves and superluminal motion of GRB 170817A. The Markov chain Monte Carlo (MCMC) method is adopted to obtain the best-fitting parameters, which give the jet half-op…
We perform three-dimensional (3D) general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of $θ_{\rm core}\approx4^{\circ}$, an opening angle of $θ_{\rm jet}\gtrsim10^{\circ}$, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also co…
