Astrophysical Explosions: From Solar Flares to Cosmic Gamma-ray Bursts
J. Craig Wheeler
备注：
26 pages, 11 Figures. To be published in the Special Issue on Physics, Chemistry and Dynamics of Explosions of the Philosophical Transactions of the Royal Society
Astrophysical explosions result from the release of magnetic, gravitational, or thermonuclear energy on dynamical timescales, typically the sound-crossing time for the system. These explosions include solar and stellar flares, eruptive phenomena in accretion disks, thermonuclear combustion on the surfaces of white dwarfs and neutron stars, violent magnetic reconnection in neutron stars, thermonuclear and gravitational collapse supernovae and cosmic gamma-ray bursts, each representing a different type and amount of energy release. This paper summarizes the properties of these explosions and describes new research on thermonuclear explosions and explosions in extended circumstellar media. Parallels are drawn between studies of terrestrial and astrophysical explosions, especially the physics of the transition from deflagration to detonation.
Keywords: neutron stars, black holes, supernovae, gamma-ray bursts, deflagration, detonation.
Bright X-ray flares are routinely detected by the Swift satellite during the early afterglow of gamma-ray bursts, when the explosion ejecta drives a blast wave into the external medium. We suggest that the flares are produced as the reverse shock propagates into the tail of the ejecta. The ejecta is expected to contain a few dense shells formed at an earlier stage of the explosion. We show an example of how such dense shells form and describe how the reverse shock interacts with them. A new reflected shock is generated in this interaction, which produces a short-lived X-ray flare. The model pr…
Magnetars, the likely sources of Fast Radio Bursts (FRBs), produce both steady highly relativistic magnetized winds, and occasional ejection events. We demonstrate that the requirement of conservation of the magnetic flux dominates the overall dynamics of magnetic explosions. This is missed in conventional hydrodynamic models of the ejections as expanding shell with parametrically added magnetic field, as well as one-dimensional models of magnetic disturbances. Most of the initial free energy of an explosion is actually spent on stretching its own internal magnetic field, while doing minimal $…
Recent results from IceCube regarding TXS 0506+056 suggest the presence of neutrino flares that are not temporally coincident with a significant corresponding gamma ray flare. Such flares are particularly difficult to identify, as their presence must be inferred from the temporal distribution of neutrino data alone. Here we present the results of using a novel method to search for all such flares across the entire neutrino sky in 10 years of IceCube data, using both Gaussian and box-shaped flare hypotheses. Unlike for past searches, that looked for only the most significant neutrino flare in t…
Many explosive astrophysical events, like magnetars' bursts and flares, are magnetically driven. We consider dynamics of such magnetic explosions - relativistic expansion of highly magnetized and highly magnetically over-pressurized clouds. The corresponding dynamics is qualitatively different from fluid explosions due to the topological constraint of the conservation of the magnetic flux. Using analytical, relativistic MHD as well as force-free calculations, we find that the creation of a relativistically expanding, causally disconnected flow obeys a threshold condition: it requires sufficien…
A large variety of explosions result in mildly or ultra relativistic shock breakouts. Here we calculate the luminosity and spectrum that these breakouts produce. In order to do so we improve an analytic description of relativistic radiation mediated shocks and follow the system from the breakout itself, through the planar phase and into the spherical phase. We limit our calculation to cases where the post breakout acceleration of the gas ends during the planar phase. (i.e., the final gas Lorentz factor <~30). We find that spherical relativistic breakouts produce a flash of gamma-rays with ener…
Strong magnetic fields in magnetospheres of neutron stars (especially magnetars) and other astrophysical objects may release their energy in violent, intense episodes of magnetic reconnection. While reconnection has been studied extensively, the extreme field strength near neutron stars introduces new effects: synchrotron cooling and electron-positron pair production. Using massively parallel particle-in-cell simulations that self-consistently incorporate these new quantum-electrodynamic effects, we investigate relativistic magnetic reconnection in the strong-field regime. We show that reconne…
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…
New Signs Pointing Toward a Correlation Between Astrophysical Neutrinos and Radio Flares
University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；University of Washington（华盛顿大学）；University of Wisconsin-Whitewater（威斯康星大学惠特沃分校）；University of California, Merced（加州大学默塞德分校）
The work reported in this dissertation will concern the study of kinetics, cycles and quantum mechanic processes of nuclear reactions involved in massive stars together with explosive nucleosynthesis phenomena having a key role in supernovae explosion. Four main fields will be explored: physics of nuclear reaction, hydrogen burning, CNO cycles and explosive supernovae phenomena. The first chapter will provide an overview of the background of the nuclear physics and of the potential approaches to the field as quantum mechanic aspects, cross section and Maxwell-Boltzmann distribution. The next c…
Analyses of quasi-periodic oscillations (QPOs) are important to understanding the dynamic behaviour in many astrophysical objects during transient events like gamma-ray bursts, solar flares, magnetar flares and fast radio bursts. Astrophysicists often search for QPOs with frequency-domain methods such as (Lomb-Scargle) periodograms, which generally assume power-law models plus some excess around the QPO frequency. Time-series data can alternatively be investigated directly in the time domain using Gaussian Process (GP) regression. While GP regression is computationally expensive in the general…
We give an overview of recent efforts to model Type Ia supernovae and related astrophysical transients resulting from thermonuclear explosions in white dwarfs. In particular we point out the challenges resulting from the multi-physics multi-scale nature of the problem and discuss possible numerical approaches to meet them in hydrodynamical explosion simulations and radiative transfer modeling. We give examples of how these methods are applied to several explosion scenarios that have been proposed to explain distinct subsets or, in some cases, the majority of the observed events. In case we com…
Magnetars are young, highly magnetized neutron stars that produce extremely rare giant flares of gamma-rays, the most luminous astrophysical phenomena in our Galaxy. The detection of these flares from outside the Local Group of galaxies has been predicted, with just two candidates so far. Here we report on the extremely bright gamma-ray flare GRB 200415A of April 15, 2020, which we localize, using the Interplanetary Network, to a tiny (20 sq. arcmin) area on the celestial sphere, that overlaps the central region of the Sculptor galaxy at 3.5 Mpc from the Milky Way. From the Konus-Wind detectio…
X-ray flares detected in nearly half of gamma-ray burst (GRB) afterglows are one of the most intriguing phenomena in high-energy astrophysics. All the observations indicate that the central engines of bursts, after the gamma-ray emission has ended, still have long periods of activity, during which energetic explosions eject relativistic materials, leading to late-time X-ray emission. It is thus expected that X-ray flares provide important clues to the nature of the central engines of GRBs, and more importantly, unveil the physical mechanism of the flares themselves, which has so far remained m…
We investigate the relativistic breakout of a shock wave from the surface of a star. In this process, each fluid shell is endowed with some kinetic and thermal energy by the shock, and then continues to accelerate adiabatically by converting thermal energy into kinetic energy. This problem has been previously studied for a mildly relativistic breakout, where the acceleration ends close to the surface of the star. The current work focuses on the case where the acceleration ends at distances much greater than the radius of the star. We derive an analytic description for the hydrodynamic evolutio…
We can probe observationally and reproduce theoretically intricate properties of the Crab Nebula nearest to the pulsar - The Inner Knot. The tiny knot is indeed a bright spot on the surface of a quasi-stationary magnetic relativistic shock that accelerates particles. It is required that the part of the wind that produces the Inner Knot has low magnetization; thus, it is not a site of gamma-ray flares. We develop a model of particle acceleration during explosive reconnection events in relativistic highly magnetized plasma and apply the model to explain the Crab gamma-ray flares. Particles are e…
The occurrence rates of bright X-ray flares in z<1 gamma-ray bursts (GRBs) with or without observed supernovae (SNe) association were compared. Our Sample I: the z<1 long GRBs (LGRBs) with SNe association (SN-GRBs) and with early Swift/X-Ray Telescope (XRT) observations, consists of 18 GRBs, among which only two GRBs have bright X-ray flares. Our Sample II: for comparison, all the z<1 LGRBs without observed SNe association and with early Swift/XRT observations, consists of 45 GRBs, among which 16 GRBs present bright X-ray flares. Thus, the study indicates a lower occurrence rate of bright X-ra…
Particle acceleration by cascading Alfven wave turbulence was suggested (Eichler, 1979b) as being responsible for energetic particle populations in $^3$He-rich solar flares. In particular, it was noted that the damping of the turbulence by the tail of the particle distribution in rigidity naturally leads to dramatic enhancement of pre-accelerated species - as $^3$He is posited to be - and superheavy elements. The subsequent detection of large enrichment of ultraheavies, relative to iron, has apparently confirmed this prediction, lending support to the original idea. It is shown here that this …
We present the first systematic study of X-ray flare candidates in short gamma-ray bursts (SGRBs) exploiting the large 6-year Swift database with the aim to constrain the physical nature of such fluctuations. We find that flare candidates appear in different types of SGRB host galaxy environments and show no clear correlation with the X-ray afterglow lifetime; flare candidates are detected both in SGRBs with a bright extended emission in the soft gamma-rays and in SGRBs which do not show such component. We furthermore show that SGRB X-ray flare candidates only partially share the set of observ…
X-ray afterglow light curves have been collected for over 400 Swift gamma-ray bursts with nearly half of them having X-ray flares superimposed on the regular afterglow decay. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and fol…
Nearby core-collapse supernovae (CCSNe) are powerful multi-messenger sources for gravitational-wave, neutrino and electromagnetic telescopes as they emit gravitational waves in the ideal frequency band for ground based detectors. Once a CCSN gravitational-wave signal is detected, we will need to determine the parameters of the signal, and understand how those parameters relate to the source's explosion, progenitor and remnant properties. This is a challenge due to the stochastic nature of CCSN explosions, which is imprinted on their time series gravitational waveforms. In this paper, we perfor…
A detection of a core-collapse supernova signal with an Advanced LIGO and Virgo gravitational-wave detector network will allow us to measure astrophysical parameters of the source. In real advanced gravitational-wave detector data there are transient noise artifacts that may mimic a true gravitational-wave signal. In this paper, we outline a procedure implemented in the Supernova Model Evidence Extractor (SMEE) that determines if a core-collapse supernova signal candidate is a noise artefact, a rapidly-rotating core-collapse supernova signal, or a neutrino explosion mechanism core-collapse sup…
Relativistic magnetic reconnection events can widely exist in magnetized plasmas in astrophysical systems. During this process, oppositely directed magnetic field lines reconnect and release magnetic energy, efficiently accelerating nonthermal particles. However, so far there is little clear observational signatures of relativistic magnetic reconnection events in astrophysical systems. Blazars are relativistic magnetized plasma outflows from supermassive black holes. Their multi-wavelength flares may be powered by relativistic magnetic reconnection. The highly variable radiation and polarizati…
From Rare Events to a Population: Discovering Overlooked Extragalactic Magnetar Giant Flare Candidates in Archival Fermi Gamma-ray Burst Monitor Data
NASA Marshall Space Flight Center（美国国家航空航天局马歇尔太空飞行中心）；Louisiana State University（路易斯安那州立大学）；Universities Space Research Association（大学空间研究协会）；University of Alabama in Huntsville（阿拉巴马大学亨茨维尔分校）；Ioffe Institute（约费研究所）
During their violent merger, two neutron stars can shed a few percent of their mass. As this ejecta expands, it collides with the surrounding interstellar gas, producing a slowly-fading radio flare that lasts for years. Radio flares uniquely probe the neutron star merger populations as many events from past decades could still be detectable. Nonetheless, no radio flare observation has been reported to date. Here we show that the radio transient FIRST J1419+3940, first observed in 1993 and still detectable, could have originated from a neutron star merger. We carry out numerical simulations of …
In 2007 September, the Crab Nebula exhibited a bright gamma-ray flare in the GeV energy range that was detected by AGILE. The observed emission at >160 MeV indicates that the radiating electrons had energies above the classical synchrotron radiation-reaction limit, thus presenting a serious challenge to classical models for electron acceleration in astrophysical environments. In this paper, we apply our recently developed time-dependent self-similar analytical model describing electrostatic acceleration in the explosive reconnection region around the pulsar wind termination shock to the 2007 S…
Three-dimensional hydrodynamic simulations exploring the first 18 hours of the 2010 January 28 outburst of the recurrent nova U Scorpii have been performed. Special emphasis was placed on capturing the enormous range in spatial scales in the blast. The pre-explosion system conditions included the secondary star and a flared accretion disk. These conditions can have a profound influence on the evolving blast wave. The blast itself is shadowed by the secondary star, which itself gives rise to a low-temperature bow-shock. The accretion disk is completely destroyed in the explosion. A model with a…
A detection of a core-collapse supernova (CCSN) gravitational-wave (GW) signal with an Advanced LIGO and Virgo detector network may allow us to measure astrophysical parameters of the dying massive star. GWs are emitted from deep inside the core and, as such, they are direct probes of the CCSN explosion mechanism. In this study we show how we can determine the CCSN explosion mechanism from a GW supernova detection using a combination of principal component analysis and Bayesian model selection. We use simulations of GW signals from CCSN exploding via neutrino-driven convection and rapidly-rota…
We analyze GRB 151027A within the binary-driven hypernova (BdHN) approach, with progenitor a carbon-oxygen core on the verge of a supernova (SN) explosion and a binary companion neutron star (NS). The hypercritical accretion of the SN ejecta onto the NS leads to its gravitational collapse into a black hole (BH), to the emission of the GRB and to a copious $e^+e^-$ plasma. The impact of this $e^+e^-$ plasma on the SN ejecta explains {the} early soft X-ray flare observed in long GRBs. We here apply this approach to the UPE and to the hard X-ray flares. We use GRB 151027A as a prototype. From the…
Astrophysical plasmas can have parameters vastly different from the more studied laboratory and space plasmas. In particular, the magnetic fields can be the dominant component of the plasma, with energy-density exceeding the particle rest-mass energy density. Magnetic fields then determine the plasma dynamical evolution, energy dissipation and acceleration of non-thermal particles. Recent data coming from astrophysical high energy missions, like magnetar bursts and Crab nebula flares, point to the importance of magnetic reconnection in these objects. In this review we outline a broad spectrum …
Solar flares - the most powerful explosions in the solar system - are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energe…
Magnetars younger than one century are expected to be hyper active. Besides winds powered by rotation they generate frequent magnetic flares, which launch powerful blast waves into the wind. These internal shocks act as masers producing fast (millisecond) radio bursts (FRBs) with the following properties. (1) GHz radio emission occurs at radii $r\sim 10^{14}$ cm and lasts $\lesssim 1$ ms in observer's time. (2) Induced scattering in the surrounding wind does not suppress the radio burst. (3) The emission has linear polarization set by the magnetar rotation axis. (4) The emission drifts to lowe…
Using blazar light curves from the optical All-Sky Automated Survey for Supernovae (ASAS-SN) and the $γ$-ray \textit{Fermi}-LAT telescope, we performed the most extensive statistical correlation study between both bands, using a sample of 1,180 blazars. This is almost an order of magnitude larger than other recent studies. Blazars represent more than 98\% of the AGNs detected by \textit{Fermi}-LAT and are the brightest $γ$-ray sources in the extragalactic sky. They are essential for studying the physical properties of astrophysical jets from central black holes. However, their $γ$-ray flare me…
Recent multiwavelength observations of PKS 0208-512 by SMARTS, Fermi, and Swift revealed that gamma-ray and optical light curves of this flat spectrum radio quasars are highly correlated, but with an exception of one large optical flare having no corresponding gamma-ray activity or even detection. On the other hand, recent advances in SNRs observations and plasma simulations both reveal that magnetic field downstream of astrophysical shocks can be largely amplified beyond simple shock compression. These amplifications, along with their associated particle acceleration, might contribute to blaz…
BL Lacertae (BL Lac) is categorized as TeV blazar and considered as a possible source of astrophysical neutrinos. In 2020, the brightest X-ray flare ever detected from it. A detailed study can answer many puzzling questions related to multiband emissions and fast-flux variability often seen in this kind of source. We have performed the temporal and spectral analysis of the brightest flare. The variability is characterized by the fractional variability amplitude and the variability time. We found that the source has crossed all its previous limits of flux and reached the maximum ever seen from …
The gamma-ray space telescopes AGILE and Fermi detected short and bright synchrotron gamma-ray flares at photon energies above 100 MeV in the Crab Nebula. This discovery suggests that electron-positron pairs in the nebula are accelerated to PeV energies in a milliGauss magnetic field, which is difficult to explain with classical models of particle acceleration and pulsar wind nebulae. We investigate whether particle acceleration in a magnetic reconnection layer can account for the puzzling properties of the flares. We numerically integrate relativistic test-particle orbits in the vicinity of t…
A knowledge of the particle escape time from the acceleration regions of many space and astrophysical sources is of critical importance in the analysis of emission signatures produced by these particles and in the determination of the acceleration and transport mechanisms at work. This paper addresses this general problem, in particular in solar flares, where in addition to scattering by turbulence, the magnetic field convergence from the acceleration region towards its boundaries also influences the particle escape. We test an (approximate) analytic relation between escape and scattering time…
The Crab Nebula was formed after the collapse of a massive star about a thousand years ago, leaving behind a pulsar that inflates a bubble of ultra-relativistic electron-positron pairs permeated with magnetic field. The observation of brief but bright flares of energetic gamma rays suggests that pairs are accelerated to PeV energies within a few days; such rapid acceleration cannot be driven by shocks. Here, it is argued that the flares may be the smoking gun of magnetic dissipation in the Nebula. Using 2D and 3D particle-in-cell simulations, it is shown that the observations are consistent wi…
Reflection of X-ray emission on molecular clouds in the inner $\sim$ 100 pc of our Galaxy reveals that, despite being extremely quiet at the moment, our supermassive black hole Sgr A* should have experienced bright flares of X-ray emission in the recent past. Thanks to the improving characterisation of the reflection signal, we are able to infer parameters of the most recent flare(s) (age, duration and luminosity) and relative line-of-sight disposition of the brightest individual molecular complexes. We show that combining these data with measurements of polarisation in the reflected X-ray con…
In the current work an equation of state model with a first-order phase transition for astrophysical applications is presented. The model is based on a two-phase approach for quark-hadron phase transitions, which leads by construction to a first-order phase transition. The resulting model has already been successfully used in several astrophysical applications, such as cold neutron stars, core-collapse supernova explosions and binary neutron star mergers. Main goal of this work is to present the details of the model, discuss certain features and eventually publish it in a tabulated form for fu…
The astrophysical S-factor of the 4He-12C radiative capture is calculated in the potential model at the energy range 0.1-2.0 MeV. Radiative capture 12C(α,γ)16O is extremely relevant for the fate of massive stars and determines if the remnant of a supernova explosion becomes a black hole or a neutron star. Because this reaction occurs at low-energies the experimental measurements is very difficult and perhaps impossible. In this paper, radiative capture of the 12C(α,γ)16O reaction at very low-energies is taken as a case study. In comparison with other theoretical methods and available experimen…
Relativistic antiparticles can be created in high-energy nuclear interactions; thus, detection of antiparticles in an astrophysical source can tell us something remarkable about the underlying high-energy processes and nuclear interactions. However, once created, the antiparticles remain a minor fraction of their conjugant normal particles, so the detection of the antiparticles represents a big science challenge. To address this challenge we employ imaging and polarimetry of microwave radiation produced as the positrons gyrate in the ambient magnetic field. The key property of the radiation us…
We develop a first-principles model for the relativistic magnetic reconnection rate in strongly magnetized pair plasmas. By considering the energy budget and required current density near the x-line, we analytically show that in the magnetically-dominated relativistic regime, the x-line thermal pressure is significantly lower than the upstream magnetic pressure due to the extreme energy needed to sustain the current density, consistent with kinetic simulations. This causes the upstream magnetic field lines to collapse in, producing the open outflow geometry which enables fast reconnection. The…
Solar-type stars exhibit their highest levels of magnetic activity during their early convective pre-main sequence (PMS) phase of evolution. The most powerful PMS flares, super-flares and mega-flares, have peak X-ray luminosities of $\log(L_X)=30.5-34.0$~erg~s$^{-1}$ and total energies $\log(E_X)=34-38$~erg. Among $>24,000$ X-ray selected young ($t<5$~Myr) members of 40 nearby star-forming regions from our earlier $Chandra$ MYStIX and SFiNCs surveys, we identify and analyze a well-defined sample of 1,086 X-ray super-flares and mega-flares, the largest sample ever studied. Most are considerably…
Astrophysical explosions such as supernovae are fascinating events that require sophisticated algorithms and substantial computational power to model. Castro and MAESTROeX are nuclear astrophysics codes that simulate thermonuclear fusion in the context of supernovae and X-ray bursts. Examining these nuclear burning processes using high resolution simulations is critical for understanding how these astrophysical explosions occur. In this paper we describe the changes that have been made to these codes to transform them from standard MPI + OpenMP codes targeted at petascale CPU-based systems int…
Magnetic reconnection is a fundamental process of magnetic field topology change. We analyze the connection of this process with turbulence which is ubiquitous in astrophysical environments. We show how Lazarian & Vishniac (1999) model of turbulent reconnection is connected to the experimentally proven concept of Richardson diffusion and discuss how turbulence violates the generally accepted notion of magnetic flux freezing. We note that in environments that are laminar initially turbulence can develop as a result of magnetic reconnection and this can result in flares of magnetic reconnection …
