We revisit the vertical structure of neutrino-dominated accretion flows in spherical coordinates. We stress that the flow should be geometrically thick when advection becomes dominant. In our calculation, the luminosity of neutrino annihilation is enhanced by one or two orders of magnitude. The empty funnel along the rotation axis can naturally explain the neutrino annihilable ejection.
In the classic picture of standard thin accretion disks, the viscous heating is balanced by the radiative cooling through the diffusion process, and the radiation-pressure-dominated inner disk suffers convective instability. However, recent simulations have shown that the vertical advection process owing to the magnetic buoyancy can make significant contribution to the energy transport. In addition, no convective instability has been found by comparing the simulation results with the local convective stability criterion. In this work, following the spirit of simulations, we revisit the vertica…
Recent simulations on super-Eddington accretion flows have shown that, apart from the diffusion process, the vertical advection based on magnetic buoyancy can be a more efficient process to release the trapped photons in the optically thick disk. As a consequence, the radiative luminosity from the accretion disk can be far beyond the Eddington value. Following this spirit, we revisit the structure and radiation of hyper-accretion disks with mass accretion rates in the range $10^{-3}\sim 10~M_{\sun}~{\rm s}^{-1}$. Our results show that, due to the strong cooling through the vertical advection, …
We investigate the vertical structure and elements distribution of neutrino-dominated accretion flows around black holes in spherical coordinates with the reasonable nuclear statistical equilibrium. According our calculations, heavy nuclei tend to be produced in a thin region near the disk surface, whose mass fractions are primarily determined by the accretion rate and the vertical distribution of temperature and density. In this thin region, we find that $^{56}\rm Ni$ is dominant for the flow with low accretion rate (e.g., $0.05 $$M_{\odot}$ $\rm s^{-1}$) but $^{56}\rm Fe$ is dominant for the…
We present the effects of the vertical convection on the structure and luminosity of the neutrino-dominated accretion flow (NDAF) around a stellar-mass black hole in spherical coordinates. We found that the convective energy transfer can suppress the radial advection in the NDAF, and that the density, temperature and opening angle are slightly changed. As a result, the neutrino luminosity and annihilation luminosity are increased, which is conducive to achieve the energy requirement of gamma-ray bursts.
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", an…
We consider gamma-ray burst models where the radiation is dominated by a photospheric region providing the MeV Band spectrum, and an external shock region responsible for the GeV radiation via inverse Compton scattering. We parametrize the initial dynamics through an acceleration law Gamma \propto r^μ, with μbetween 1/3 and 1 to represent the range between an extreme magnetically dominated and a baryonically dominated regime. We compare these models to several bright Fermi LAT bursts, and show that both the time integrated and the time resolved spectra, where available, can be well described b…
In the coalescence events of binary neutron star (NS) or a black hole (BH) and an NS, a BH hyperaccretion disk might be eventually formed. At very high mass accretion rates, MeV neutrinos will be emitted from this disk, which is called a neutrino-dominated accretion flow (NDAF). Neutrino annihilation in the space out of the disk is energetic enough to launch ultrarelativistic jets to power gamma-ray bursts. Moreover, vertical advection might exist in NDAFs, which can generate the magnetic buoyancy bubbles to release gamma-ray photons. In this paper, we visit the effects of the vertical advecti…
The composition of a jet is still an unsolved problem in gamma-ray bursts (GRBs). Several previous studies have suggested that the prompt emission spectrum of GRBs is likely to consist of a few components that may arise from different jet compositions. Here we present a systematic analysis to search for the GRBs that seem to show the transition from a fireball to the Poynting-flux-dominated outflow between well-separated pulses within a single burst, like the GRB 160626B, using the Gamma-ray Burst Monitor data of the \emph{Fermi} satellite. We obtain 43 GRBs with clear multiple pulses and find…
We study the narrowest spectra expected from gamma-ray bursts. We present an analytical function for the spectrum that is emitted from the photosphere of a radiation-dominated flow that is under acceleration. This is the narrowest possible spectrum and it differs from a Planck function. We also present numerical spectra from photospheres occurring during the transition into the coasting phase of the flow. Using these spectral models, we reanalyse Fermi observations of GRB100507 and GRB101219, which both have been reported to have very narrow spectra. The bursts can be fitted by the spectral mo…
Long-duration gamma-ray bursts (LGRBs) are generally considered to originate from the massive collapsars. It is believed that the central engine of gamma-ray bursts (GRBs) is a neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black hole (BH). The neutrino annihilation above the NDAF is a feasible mechanism to power GRB. In this work, we analyse the distributions of the isotropic gamma-ray radiated energy and jet kinetic energy of 48 LGRBs. According to the NDAF and fireball models, we estimate the mean accreted masses of LGRBs in our sample to investigate whether the NDA…
A hyperaccretion disk formed around a stellar mass black hole is a plausible model for the central engine that powers gamma-ray bursts (GRBs). If the central black hole rotates and a poloidal magnetic field threads its horizon, a powerful relativistic jet may be driven by a process resembling the Blandford-Znajek mechanism. We estimate the luminosity of such a jet assuming that the poloidal magnetic field strength is comparable to the inner accretion disk pressure. We show that the jet efficiency attains its maximal value when the accretion flow is cooled via optically-thin neutrino emission. …
Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) are plausible candidates for the central engines of gamma-ray bursts (GRBs). NDAFs are hyperaccretion disks with accretion rates in the range of around 0.001-10 $M_\odot ~\rm s^{-1}$, which have high density and temperature and therefore are extremely optically thick and geometrically slim or even thick. We review the theoretical progresses in studying the properties of NDAFs as well as their applications to the GRB phenomenology. The topics include: the steady radial and vertical structure of NDAFs and t…
Recent observations and theoretical work on gamma-ray bursts (GRBs) favor the central engine model of a Kerr black hole (BH) surrounded by a magnetized neutrino-dominated accretion flow (NDAF). The magnetic coupling between the BH and disk through a large-scale closed magnetic field exerts a torque on the disk, and transports the rotational energy from the BH to the disk. We investigate the properties of the NDAF with this magnetic torque. For a rapid spinning BH, the magnetic torque transfers enormous rotational energy from BH into the inner disk. There are two consequences: (i) the luminosit…
A stellar mass black hole (BH) surrounded by a neutrino-dominated accretion flow (NDAF) has been discussed in a number of works as the central engine of gamma-ray bursts (GRBs). It is widely believed that NDAF cannot liberate enough energy for bright GRBs. However, these works have been based on the assumption of "no torque" boundary condition, which is invalid when the disk is magnetized. In this paper, we present both numerical and analytical solutions for NDAFs with non-zero boundary stresses, and reexamine their properties. We find that NDAF with such boundary torque can be powerful enough…
We present a model for gamma-ray bursts where a dissipative photosphere provides the usual spectral peak around MeV energies accompanied by a subdominant thermal component. We treat the initial acceleration of the jet in a general way, allowing for magnetic field- and baryon dominated outflows. In this model, the GeV emission associated with GRBs observed by Fermi LAT, arises as the interaction of photospheric radiation and the shocked electrons at the deceleration radius. Through recently discovered correlations between the thermal and non-thermal peaks within individual bursts, we are able t…
We present the results of a series of radiation-MHD simulations of a local patch of an accretion disk, with fixed vertical gravity profile but with different surface mass densities and a broad range of radiation to gas pressure ratios. Each simulation achieves a thermal equilibrium that lasts for many cooling times. After averaging over times long compared to a cooling time, we find that the vertically integrated stress is approximately proportional to the vertically-averaged total thermal (gas plus radiation) pressure. We map out--for the first time on the basis of explicit physics--the therm…
It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The advection and diffusion of the large-scale magnetic field of a NDAF is calculated, and the external magnetic field is found to be dragged inward efficiently by the accretion flow for a typical magnetic Prandtl number P_m=1. The maximal BZ jet power can be ~10^53-10^54 erg/sec for an extreme Kerr black hole, if an external magnetic field with 10^14 Gauss is advec…
The physical composition of the ejecta of gamma-ray bursts (GRBs) remains an open question. The radiation mechanism of the prompt gamma rays is also in debate. This problem can be solved for the bursts hosting distinct thermal radiation. However, the events with dominant thermal spectral components are still rare. In this work, we focus on GRB 220426A, a recent event detected by Fermi-GBM. The time-resolved and time-integrated data analyses yield very hard low-energy spectral indices and rather soft high-energy spectral indices. This means that the spectra of GRB 220426A are narrowly distribut…
We present the effects of the self-gravity on the vertical structure and neutrino luminosity of the neutrino-dominated accretion disks in cylindrical coordinates. It is found that significant changes of the structure appear in the outer region of the disk, especially for high accretion rates (e.g., $\ga 1 M_\odot~\rm s^{-1}$), and thus causes the slight increase of the neutrino luminosity. Furthermore, the gravitational instability of the disk is reviewed by the vertical distribution of the Toomre parameter \citep{Toomre1964}, which may account for the late-time flares in gamma-ray bursts and …
We perform 3D vertically-stratified local shearing-box ideal MHD simulations of the magnetorotational instability (MRI) that include a net vertical magnetic flux, which is characterized by beta_0 (ratio of gas pressure to magnetic pressure of the net vertical field at midplane). We have considered beta_0=10^2, 10^3 and 10^4 and in the first two cases the most unstable linear MRI modes are well resolved in the simulations. We find that the behavior of the MRI turbulence strongly depends on beta_0: The radial transport of angular momentum increases with net vertical flux, achieving alpha=0.08 fo…
We present the first vertically resolved hydrodynamic simulations of a laterally propagating, deflagrating flame in the thin helium ocean of a rotating accreting neutron star. We use a new hydrodynamics solver tailored to deal with the large discrepancy in horizontal and vertical length scales typical of neutron star oceans, and which filters out sound waves that would otherwise limit our timesteps. We find that the flame moves horizontally with velocities of order $10^5$ cm s$^{-1}$, crossing the ocean in few seconds, broadly consistent with the rise times of Type I X-ray bursts. We address t…
The system of accretion disk and black hole is usually considered as the central engine of Gamma-ray Bursts (GRBs). It is usually thought that the disk in the central engine of GRBs is the advection-dominated accretion disk, which is developed from a massive (mass M_disk) torus at radius r_disk. We find a positive correlation between the isotropic gamma-ray energy E_iso and duration (so-called T_90) for GRBs. We interpret this correlation within the advection-dominated accretion disk model, associating E_iso and T_90 with M_ disk and viscous timescale respectively.
Recent observations by the Fermi-LAT showed that there are delayed arrivals of GeV photons relative to the onset of MeV photons in some GRBs. In order to avoid a large optical depth, the minimal value of the Lorentz factor has been estimated to be higher than 1000 in some brightest bursts. In this paper, we present a detailed calculation of the time delay between the MeV and GeV photons in the framework of the magnetic-dominated jet model. We find that the time delay strongly depends on the saturated bulk Lorentz factor of the jet. Inspired by this fact, we use this model to calculate the Lore…
We investigate the vertical structure of neutrino dominated accretion disks by self-consistently considering the detailed microphysics, such as the neutrino transport, vertical hydrostatic equilibrium, the conservation of lepton number, as well as the balance between neutrino cooling, advection cooling and viscosity heating. After obtaining the emitting spectra of neutrinos and antineutrinos by solving the one dimensional Boltzmann equation of neutrino and antineutrino transport in the disk, we calculate the neutrino/antineutrino luminosity and their annihilation luminosity. We find that the t…
We solve the set of hydrodynamic (HD) equations for optically thin Advection Dominated Accretion Flows (ADAFs) by assuming radially self-similar in spherical coordinate system $ (r, θ, ϕ) $. The disk is considered to be steady state and axi-symmetric. We define the boundary conditions at the pole and the equator of the disk and to avoid singularity at the rotation axis, the disk is taken to be symmetric with respect to this axis. Moreover, only the $ τ_{r ϕ} $ component of viscous stress tensor is assumed and we have set $ v_θ = 0 $. The main purpose of this study is to investigate the variati…
GRB 101225A is a prototype of the class of blackbody-dominated (BBD) gamma-ray bursts (GRBs). It has been suggested that BBD-GRBs result from the merger of a binary system formed by a neutron star and the helium core of an evolved star. We have modelled the propagation of ultrarelativistic jets through the environment left behind the merger by means of relativistic hydrodynamic simulations. In this paper, the output of our numerical models is post-processed to obtain the (thermal) radiative signature of the resulting outflow. We outline the most relevant dynamical details of the jet propagatio…
Neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black hole (BH) is one of the plausible candidates for the central engines of gamma-ray bursts (GRBs). Because the time-variant and anisotropic emission of neutrinos from NDAFs leads to GRB variability, NDAFs can be regarded as the sources of the strong gravitational waves (GWs). We calculate the dependences of the GW strains on both the BH spin and the accretion rate. We demonstrate that for typical GRBs with either single pulse or multiple pulses, the GWs from NDAFs might be detected at a distance of $\sim 100$ kpc/$\sim…
The composition of relativistic outflows producing gamma-ray bursts is a long standing open question. One of the main arguments in favor of magnetically dominated outflows is the absence of photospheric component in their broadband time resolved spectra, with such notable example as GRB 080916C. Here, we perform a time-resolved analysis of this burst and confirm the previous detection of an additional spectral component. We show that this subdominant component is consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. We argue that, contrary to previ…
We revisit the vertical structure of black hole accretion disks in spherical coordinates. By comparing the advective cooling with the viscous heating, we show that advection-dominated disks are geometrically thick, i.e., with the half-opening angle > 2π/5, rather than slim as supposed previously in the literature.
The X-ray pulsar GRO J1744-28 is a unique source which shows both pulsations and type-II X-ray bursts, allowing studies of the interaction of the accretion disk with the magnetosphere at huge mass accretion rates exceeding $10^{19}$ g s$^{-1}$ during its super-Eddington outbursts. The magnetic field strength in the source, $B\approx 5\times 10^{11}$ G, is known from the cyclotron absorption feature discovered in the energy spectrum around 4.5 keV. Here, we explore the flux variability of the source in context of interaction of its magnetosphere with the radiation-pressure dominated accretion d…
Most Gamma-ray bursts (GRBs) have erratic light curves, which demand that the GRB central engine launches an episodic outflow. Recent Fermi observations of some GRBs indicate a lack of the thermal photosphere component as predicted by the baryonic fireball model, which suggests a magnetic origin of GRBs. In view that powerful episodic jets have been observed along with continuous jets in other astrophysical black hole systems, here we propose an intrinsically episodic, magnetically-dominated jet model for GRB central engine. Accumulation and eruption of free magnetic energy in the corona of a …
Thermal Stability of Radiation-Pressure-Dominated Accretion Disks Threaded by Net Vertical Magnetic Flux
Western University（韦仕敦大学）；Ferdowsi University of Mashhad（马什哈德费尔多西大学）；International Centre for Theoretical Sciences, Tata Institute of Fundamental Research（塔塔基础研究院国际理论科学中心）
We show that, contrary to common belief, internal shocks can arise in an accelerating radiation-dominated jet if it is confined even weakly to a converging opening angle because the acceleration declines. The radiation-dominated internal shock (RDIS) enables a very efficient yet highly nonthermal emission by Fermi-like photon acceleration, keeping the electron-positron ($e^{\pm}$) pair photosphere and inertia up to a high Lorentz factor >1000. In gamma-ray bursts (GRBs), a weak confinement would persist beyond the progenitor star or surrounding matter because of the fast cocoon accompanying th…
We propose a backscattering dominated prompt emission model for gamma-ray bursts (GRB) prompt phase in which the photons generated through pair annihilation at the centre of the burst are backscattered through Compton scattering by an outflowing stellar cork. We show that the obtained spectra are capable of explaining the low and high energy slopes as well as the distribution of spectral peak energies in their observed prompt spectra.
Force due to the self-gravity of the disc in the vertical direction is considered to study its possible effects on the structure of a magnetized advection-dominated accretion disc. We present steady-sate self similar solutions for the dynamical structure of such a type of the accretion flows. Our solutions imply reduced thickness of the disc because of the self-gravity. It also imply that the thickness of the disc will increase by adding the magnetic field strength.
A hyperaccretion flow around a stellar mass black hole is thought to be the most plausible engine that powers gamma-ray bursts (GRBs). The flow efficiently cools via neutrino emission at >~ 0.003-0.01 M_sun s^{-1} (corresponding to a luminosity of ~10^50 erg s^{-1}), while neither neutrino nor photon emission is efficient below this rate, so the flow should be advection dominated. We carefully solve how a transition occurs from the advection-dominated to the neutrino-dominated branches, and find that the slope of the thermal equilibrium curve is negative in the surface density - accretion rate…
Blackbody-dominated (BBD) gamma-ray bursts (GRBs) are events characterized by the absence of a typical afterglow, long durations and the presence of a significant thermal component following the prompt gamma-ray emission. GRB 101225A (the `Christmas burst') is a prototype of this class. A plausible progenitor system for it, and for the BBD-GRBs, is the merger of a neutron star (NS) and a helium core of an evolved, massive star. Using relativistic hydrodynamic simulations we model the propagation of an ultrarelativistic jet through the enviroment created by such a merger and we compute the whol…
As gamma-ray burst (GRB) jet drills its way through the collapsing star, it traps a baryonic cork ahead of it. Here we explore a prompt emission model for GRBs in which the jet does not cross the cork, but rather photons that are emitted deep in the flow largely by pair annihilation are scattered inside the expanding cork and escape largely from the back end of it as they push it from behind. Due to the relativistic motion of the cork, these photons are easily seen by an observer close to the jet axis peaking at $\varepsilon_{peak}\sim~few \times 100 keV$. We show that this model naturally exp…
The ejecta composition is an open question in gamma-ray bursts (GRB) physics. Some GRBs possess a quasi-thermal spectral component in the time-resolved spectral analysis, suggesting a hot fireball origin. Others show a featureless non-thermal spectrum known as the "Band" function, consistent with a synchrotron radiation origin and suggesting that the jet is Poynting-flux-dominated at the central engine and likely in the emission region as well. There are also bursts showing a sub-dominant thermal component and a dominant synchrotron component suggesting a likely hybrid jet composition. Here we…
Blackbody-dominated (BBD) gamma-ray bursts (GRBs) are events characterized by long durations and the presence of a significant thermal component following the prompt emission, as well as by the absence of a typical afterglow. GRB 101225A is the most prominent member of this class. A plausible progenitor system for it and for BBD-GRBs is the merger a neutron star and a helium core of an evolved, massive star. Using relativistic hydrodynamic simulations we model the propagation of ultrarelativistic jets through the environments created by such mergers. In a previous paper we showed that the ther…
Within the framework of the external shock model of gamma-ray bursts (GRBs) afterglows, we perform a morphological analysis of the early optical lightcurves to directly constrain model parameters. We define four morphological types, i.e. the reverse shock dominated cases with/without the emergence of the forward shock peak (Type I/ Type II), and the forward shock dominated cases without/with $ν_m$ crossing the band (Type III/IV). We systematically investigate all the Swift GRBs that have optical detection earlier than 500 s and find 3/63 Type I bursts (4.8%), 12/63 Type II bursts (19.0%), 30/6…
We present the first realistic 3D simulations of flame front instabilities during type I X-ray bursts. The unperturbed front is characterised by the balance between the pressure gradient and the Coriolis force of a spinning neutron star (ν = 450 Hz in our case). This balance leads to a fast horizontal velocity field parallel to the flame front. This flow is strongly sheared in the vertical direction. When we perturb the front an instability quickly corrugates the front. We identify this instability as the baroclinic instability. Most importantly, the flame is not disrupted by the instability a…
Standard models of radiation supported accretion disks generally assume that diffusive radiation flux is solely responsible for vertical heat transport. This requires that heat must be generated at a critical rate per unit volume if the disk is to be in hydrostatic and thermal equilibrium. This raises the question of how heat is generated and how energy is transported in MHD turbulence. By analysis of a number of radiation/MHD stratified shearing-box simulations, we show that the divergence of the diffusive radiation flux is indeed capped at the critical rate, but deep inside the disk, substan…
The saturation level of the magneto-rotational instability (MRI) in a strongly radiation dominated accretion disk is studied using a new Godunov radiation MHD code in the unstratified shearing box approximation. Since vertical gravity is neglected in this work, our focus is on how the MRI saturates in the optically thick mid-plane of the disk. We confirm that turbulence generated by the MRI is very compressible in the radiation dominated regime, as found by previous calculations using the flux-limited diffusion approximation. We also find little difference in the saturation properties in calcu…
The binary neutron star (BNS) merger event GW170817 clearly shows that a BNS merger launches a short Gamma-Ray Burst (sGRB) jet. Unlike collapsars, where the ambient medium is static, in BNS mergers the jet propagates through the merger ejecta that is expanding outward at substantial velocities ($\sim 0.2c$). Here, we present semi-analytic and analytic models to solve the propagation of GRB jets through their surrounding media. These models improve our previous model by including the jet collimation by the cocoon self-consistently. We also perform a series of 2D numerical simulations of jet pr…
Although the physical origin of prompt emission in gamma-ray bursts (GRBs) remains inconclusive, previous studies have considered the synchrotron radiation of relativistic electrons as a promising mechanism. These works usually adopted a invariable injection rate of electrons ($Q$) which may be discordant with that in a Poynting-flux dominated jet. In a Poynting-flux dominated jet (e.g., ICMART model, Zhang & Yan 2011), the number of magnetic reconnections occurred simultaneously may grow rapidly with time and results in an increase of $Q$ with time. This paper is dedicated to study the synchr…
Context: Swift observations suggest that the X-ray afterglow emission of some gamma-ray bursts (GRB) may have internal origins, and the conventional external shock (ES) cannot be the exclusive source of the afterglow emission. Aims: If the central compact objects of some GRBs are millisecond magentars, the magnetar winds could play an important role in the (internal) X-ray afterglow emission, which is our focus here. Methods: The dynamics and the synchrotron radiation of the termination shock (TS) of the magmnetar winds, as well as the simultaneous GRB ES, are investigated by considering the m…
We study the long-term thermal stability of radiation dominated disks in which the vertical structure is determined self-consistently by the balance of heating due to dissipation of MHD turbulence driven by the magneto-rotational instability (MRI), and cooling due to radiation emitted at the photosphere. The calculations adopt the local shearing box approximation, and utilize the recently developed radiation transfer module in the Athena MHD code based on a variable Eddington tensor rather than an assumed local closure. After saturation of the MRI, in many cases the disk maintains a steady ver…
Time-resolved spectro-polarimetric analysis of extremely bright GRB 230307A: Possible Evidence of evolution from photospheric to synchrotron dominated emission
GRB 230307A的光谱偏振分析揭示了从光球主导到同步辐射主导的转变，可能表明磁场在喷流动力学中的演变作用。
The composition of gamma-ray burst (GRB) ejecta is still a mystery. The standard model invokes an initially hot ``fireball'' composed of baryonic matter. Here we analyze the broad band spectra of GRB 080916C detected by the Fermi satellite. The featureless Band-spectrum of all five epochs as well as the detections of >~10 GeV photons in this burst place a strong constraint on the prompt emission radius, which is typically >~ 10^{15} cm, independent on the details of the emission process. The lack of detection of a thermal component as predicted by the baryonic models strongly suggests that a s…
We investigate the effects of the convection in the hyperaccretion disk around a stellar-mass black hole, which is considered to be the central engine of gamma-ray bursts (GRBs), with simple analytical calculations. If the convective energy transfer in the vertical direction becomes efficient compared with the inward advective energy transport, the hyperaccretion disk is expected to be hotter and the neutrino emission due to the electron-positron annihilation becomes the most efficient cooling process. We find that the sequence of the thermal equilibrium solutions for the convective hyperaccre…
Type I X-ray bursts are produced by thermonuclear runaways that develop on accreting neutron stars. Once one location ignites, the flame propagates across the surface of the star. Flame propagation is fundamental in order to understand burst properties like rise time and burst oscillations. Previous work quantified the effects of rotation on the front, showing that the flame propagates as a deflagration and that the front strongly resembles a hurricane. However the effect of magnetic fields was not investigated, despite the fact that magnetic fields strong enough to have an effect on the propa…
One of the most important unresolved issues in gamma-ray burst physics is the origin of the prompt gamma-ray spectrum. Its general non-thermal character and the softness in the X-ray band remain unexplained. We tackle these issues by performing Monte Carlo simulations of radiation-matter interactions in a scattering dominated photon-lepton plasma. The plasma -- initially in equilibrium -- is driven to non-equilibrium conditions by a sudden energy injection in the lepton population, mimicking the effect of a shock wave or the dissipation of magnetic energy. Equilibrium restoration occurs due to…
The prompt emission in long gamma-ray bursts arises from within relativistic outflows created during the collapse of massive stars, and the mechanism by which radiation is produced may be either magnetically- or matter-dominated. In this work we suggest an observational test of a magnetically-dominated Poynting flux model that predicts both gamma-ray and low-frequency radio pulses. A common feature among early light curves of long gamma-ray bursts are X-ray flares, which have been shown to arise from sites internal to the jet. Ascribing these events to the prompt emission, we take an establish…
The recent Fermi observation of GRB 080916C shows that the bright photosphere emission associated with a putative fireball is missing, which suggests a Poynting-flux-dominated outflow. We propose a model of gamma-ray burst (GRB) prompt emission in the Poynting-flux-dominated regime, namely, the Internal-Collision-induced MAgnetic Reconnection and Turbulence (ICMART) model. It is envisaged that the GRB central engine launches an intermittent, magnetically-dominated wind, and that in the GRB emission region, the ejecta is still moderately magnetized. Similar to the internal shock (IS) model, the…
