Short gamma ray bursts are presumably results of binary neutron star mergers, which lead to the formation of a stellar mass black hole, surrounded by a remnant matter. The strong magnetic fields help collimate jets of plasma, launched along the axis of the black hole rotation. We study the structure and evolution of the accreting plasma in the short GRBs and we model the formation of the base of a relativistic, Poynting-dominated jets. Our numerical models are based on the general relativistic MHD, axisymmetric simulations. We discuss the origin of variability in the GRB jet emission, which timescales are related to the action of the magneto-rotational instability in the accreting plasma. We also estimate the value of a maximum achievable Lorentz factor in the jets produced by our simulations, and reached at the large distances, where the gamma ray emission is produced.
Optical re-brightenings in the afterglows of some gamma-ray bursts (GRBs) are unexpected within the framework of the simple external shock model. While it has been suggested that the central engines of some GRBs are newly born magnetars, we aim to relate the behaviors of magnetars to the optical re-brightenings. A newly born magnetar will lose its rotational energy in the form of Poynting-flux, which may be converted into a wind of electron-positron pairs through some magnetic dissipation processes. As proposed by Dai (2004), this wind will catch up with the GRB outflow and a long-lasting reve…
Short gamma-ray bursts result from mergers of two neutron stars or from collapsars, but probably at a smaller rate. In the first case, a kilonova occurs while in the second case a Type Ic supernova is expected. } {Even if future observations of kilonovae in association with gravitational wave events provide better data, detecting a kilonova during an afterglow follow-up would remain useful for exploring the diversity of the kilonova phenomenon. As supernovae produce a weaker gravitational signal, afterglow follow-up will be the only possible method to find one. In this work, we identify the co…
Jet-Structure Imprint on the Curvature Tail of Gamma-Ray Burst Prompt Emission
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（现代天文与天体物理教育部重点实验室（南京大学））；Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Center for Astronomical Mega-Science, Chinese Academy of Sciences（中国科学院天文大科学研究中心）；University of Bath（巴斯大学）；Institute for Astrophysics, School of Physics, Zhengzhou University（郑州大学物理学院天体物理研究所）；Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（高能物理研究所粒子天体物理教育部重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）
Under the assumption that a Gamma-ray Burst (GRB) is ultimately produced by a Blandford-Znajek (BZ) jet from a highly spinning black hole BH, we put limits on the magnetic field and BH mass needed to power observed long and short GRBs. For BHs in the range of $2-10 M_{\odot}$ (for long GRBs) and $0.5-4 M_{\odot}$ (for short GRBs), we find magnetic fields in the range of $5x10^{14} \lesssim B \lesssim 10^{17}$ G are needed to power the observed GRBs. Under the simple assumption of flux conservation, we estimate the magnetic fields of the progenitor systems for both long and short GRBs, finding …
Modeling the imprints of large-scale magnetized structures on $γ$-rays from extragalactic transients
Kyoto University（京都大学）；University of Florida（佛罗里达大学）；University of Johannesburg（约翰内斯堡大学）；The George Washington University（乔治华盛顿大学）；National Institute for Theoretical and Computational Sciences (NITheCS)（理论与计算科学国家研究所）；University of Maryland, Baltimore County（马里兰大学巴尔的摩县分校）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Stanford University（斯坦福大学）
The central engine in long gamma-ray bursts (GRBs) is thought to be a compact object produced by the core collapse of massive stars, but its exact nature (black hole or millisecond magnetar) is still debatable. Although the central engine of GRB collapsars is hidden to direct observation, its properties may be imprinted on the accompanying electromagnetic signals. We aim to decipher the generic properties of central engines that are consistent with prompt observations of long GRBs detected by the Burst Alert Telescope (BAT) on board the Neil Gehrels Swift Observatory. Adopting a generic model …
Dense gas linked to star-forming regions photoionised by embedded gamma-ray bursts
Istituto di Astrofisica e Planetologia Spaziali, INAF（太空天体物理学与行星学研究所，意大利国家天体物理研究所）；Osservatorio Astronomico di Roma, INAF（罗马天文台，意大利国家天体物理研究所）；Physics Department, University of Calabria（卡拉布里亚大学物理系）；Osservatorio di Astrofisica e Scienza dello Spazio, INAF（空间天体物理学与科学观测站，意大利国家天体物理研究所）；Laboratori Nazionali di Frascati, INFN（弗拉斯卡蒂国家实验室，意大利国家核物理研究所）；Instituto de Astronomía, Universidad Nacional Autónoma de México（墨西哥国立自治大学天文学研究所）；Department of Physics, University of Western Australia（西澳大利亚大学物理系）；College of Science and Mathematics, University of the Virgin Islands（维尔京群岛大学科学与数学学院）
Gamma-ray Bursts (GRBs) are the most powerful explosions known, capable of outshining the rest of gamma-ray sky during their short-lived prompt emission. Their cosmological nature makes them the best tool to explore the final stages in the lives of very massive stars up to the highest redshifts. Furthermore, studying the emission from their low-energy counterparts (optical and infrared) via rapid spectroscopy, we have been able to pin down the exact location of the most distant galaxies as well as placing stringent constraints on their host galaxies and intervening systems at low and high-reds…
Due to relativistic bulk motion, the structure and orientation of gamma-ray burst jets have a fundamental role in determining how they appear. The recent discovery of the GW170817 binary neutron star merger and the associated GRB boosted the interest in the modelling and search of signatures of the presence of a (possibly quasi-universal) jet structure in long and short GRBs. In this review, following a pedagogical approach, we summarize the history of GRB jet structure research over the last two decades, from the inception of the idea of a universal jet structure to the current understanding …
The role of relativistic jets in unbinding the stellar envelope during a supernova (SN) associated with a gamma-ray burst (GRB) is unclear. To study that, we explore observational signatures of stellar explosions that are driven by jets. We focus on the final velocity distribution of the outflow in such explosions and compare its observational imprints to SN/GRB data. We find that jet driven explosions produce an outflow with a flat distribution of energy per logarithmic scale of proper velocity. The flat distribution seems to be universal as it is independent of the jet and the progenitor pro…
Gamma-ray bursts (GRBs) are ideal probes of the epoch of the first stars and galaxies. We review the recent theoretical understanding of the formation and evolution of the first (so-called Population III) stars, in light of their viability of providing GRB progenitors. We proceed to discuss possible unique observational signatures of such bursts, based on the current formation scenario of long GRBs. These include signatures related to the prompt emission mechanism, as well as to the afterglow radiation, where the surrounding intergalactic medium might imprint a telltale absorption spectrum. We…
We investigate the stability of a neutrino-dominated accretion flow (NDAF), which is expected to be formed in the gravitational collapse of a massive star or the merger of a neutron star binary, based on the variable-$α$ prescription. Recent magnetohydrodynamic (MHD) simulations shows that the viscosity parameter $α$ is proportional to the power of the magnetic Prandtl number ${\rm Pm}=ν/η$, where $ν$ and $η$ are the kinematic viscosity and electric resistivity of the fluid, respectively. In the inner region of a hyperaccretion flow, the viscosity and resistivity are carried by mildly, relativ…
A hyperaccreting stellar-mass black hole has been proposed as the candidate central engine of gamma-ray bursts (GRBs). The rich observations of GRBs by \textit{Fermi} and \textit{Swift} make it possible to constrain the central engine model by comparing the model predications against data. This paper is dedicated to studying the temporal evolution of central engine parameters for both prompt emission and afterglow phases. We consider two jet launching mechanisms, i.e., $ν\barν$ annihilations and the Blandford-Znajek (BZ) processe, and obtain analytical solutions to these two models. We then in…
Both long and short gamma-ray bursts (GRBs) are expected to occur in the dense environments of active galactic nuclei (AGN) accretion disks. As these bursts propagate through the disks they live in, they photoionize the medium causing time-dependent opacity that results in transients with unique spectral evolution. In this paper we use a line-of-sight radiation transfer code coupling metal and dust evolution to simulate the time-dependent absorption that occurs in the case of both long and short GRBs. Through these simulations, we investigate the parameter space in which dense environments lea…
The hypothesis that one or more biodiversity drops in the Phanerozoic eon, evident in the geological record, might have been caused by the most powerful kind of stellar explosion so far known Gamma Ray Bursts (GRB) has been discussed in several works. These stellar explosions could have left an imprint in the biological evolution on Earth and in other habitable planets. In this work we calculate the short-term lethality that a GRB would produce in the aquatic primary producers on Earth. This effect on life appears because of ultraviolet (UV) retransmission in the atmosphere of a fraction of th…
Redshift Identifiability from Gamma-Ray Burst Prompt Emission
State Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理国家重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）
Probing Pre-galactic Metal Enrichment with High-Redshift Gamma-Ray Bursts
我们探讨高红移伽马射线暴（GRB）作为有前途的工具，探测前银河系金属富集。利用原始矮星系中爆发的Pop III GRB的明亮余辉作为发光背景源，计算了星系际介质（IGM）中第一重元素留下的金属吸收线的强度。为了得到伽玛射线暴吸收线的诊断，我们使用了一个现有的高分辨率模拟的第一个星系的形成，其特征是在一个维里温度>10^4 K的晕中氢原子冷却的开始。我们探索不寻常的环爆环境内的系统，举办流行III星，模拟密度演化与自相似的解决方案的香槟流。对于接近冷却阈值的微晕，环爆流密度大致与（1+z）成正比，其值约为几cm^{-3}。在质量更大的晕中，对应于第一个星系，密度可能更大，n>100 cm^{-3}。由此产生的余辉通量可以分别在近红外和无线电波段用JWST和VLA检测到，直到红移z>20。我们预测，余辉发射的最大值从近红外到毫米波段移动，峰值通量从mJy到Jy在不同的观测时间。伽玛暴具有高亮度和无特征的幂律谱，是探测IGM早期金属富集的理想工具。由第一颗超新星（SN）爆炸产生的第一个星系中的金属可能处于低电离阶段。我们表明，如果余辉可以观察到足够早，分析的金属线可以区分是否产生的第一个重元素的PISN，或核心塌陷（II型）SN，从而约束的初始质量函数的第一个恒星。
We present the first global model of prompt emission from a short gamma-ray burst that consistently describes the evolution of the central black-hole (BH) torus system, the propagation of the jet through multi-component merger ejecta, the transition into free expansion, and the photospheric emission from the relativistic jet. To this end, we perform a special relativistic neutrino-hydrodynamics simulation of a viscous BH-torus system, which is formed about 500ms after the merger and is surrounded by dynamical ejecta as well as neutron star winds, along with a jet that is injected in the vicini…
Evolution and afterglow emission of gamma-ray burst jets from binary neutron star mergers
SISSA（的里雅斯特国际高等研究院）；INAF, Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；INFN, Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；INAF, Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；INFN, Sezione di Milano-Bicocca（意大利国家核物理研究所米兰比可卡分部）；INFN, Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；IFPU（的里雅斯特基础物理学研究所）
At low redshifts, the observed baryonic density falls far short of the total number of baryons predicted. Cosmological simulations suggest that these baryons reside in filamentary gas structures, known as the warm-hot intergalactic medium (WHIM). As a result of the high temperatures of these filaments, the matter is highly ionised such that it absorbs and emits far-UV and soft X-ray photons. Athena, the proposed European Space Agency X-ray observatory, aims to detect the `missing' baryons in the WHIM up to redshifts of $z=1$ through absorption in active galactic nuclei and gamma-ray burst afte…
