Bing Zhang
Fast radio bursts are mysterious millisecond-duration transients prevalent in the radio sky. Rapid accumulation of data in recent years has facilitated an understanding of the underlying physical mechanisms of these events. Knowledge gained from the neighboring fields of gamma-ray bursts and radio pulsars also offered insight. Here I review developments in this fast-moving field.Two generic categories of radiation model invoking either magnetospheres of compact objects (neutron stars or black holes) or relativistic shocks launched from such objects have been much debated. The recent detection of a Galactic fast radio burst in association with a soft gamma-ray repeater suggests that magnetar engines can produce at least some, and probably all, fast radio bursts. Other engines that could produce fast radio bursts are not required, but are also not impossible.
Bing Zhang
Feb 22, 2020·astro-ph.HE·PDF Growing evidence suggests that synchrotron radiation plays a significant role in shaping the spectra of most $γ$-ray bursts. The relativistic jets producing them likely carry a significant fraction of energy in the form of a Poynting flux.
Bing Zhang
The first gravitational wave (GW) - gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by $\sim$1.7 s with respect to the merger time of the GW signal. We generally discuss the astrophysical origin of the delay time, $Δt$, of GW-GRB associations within the context of compact binary coalescence (CBC) -- short GRB (sGRB) associations and GW burst -- long GRB (lGRB) associations. In general, the delay time should include three terms, the time to launch a clean (relativistic) jet, $Δt_{\rm jet}$; the time for the jet to break out from the surrounding medium, $Δt_{\rm bo}$; and the time for the jet to reach the energy dissipation and GRB emission site, $Δt_{\rm GRB}$. For CBC-sGRB associations, $Δt_{\rm jet}$ and $Δt_{\rm bo}$ are correlated, and the final delay can be from 10 ms to a few seconds. For GWB-lGRB associations, $Δt_{\rm jet}$ and $Δt_{\rm bo}$ are independent. The latter is at least $\sim$10 s, so that $Δt$ of these associations is at least this long. For certain jet launching mechanisms of lGRBs, $Δt$ can be minutes or even hours long due to the extended engine waiting time $Δt_{\rm wait}$ to launch a jet. We discuss the cases of GW170817/GRB 170817A and GW150914/GW150914-GBM within this theoretical framework and suggest that the delay times of future GW/GRB associations will shed light into the jet launching mechanisms of GRBs.
Bing Zhang
Jan 15, 2017·astro-ph.HE·PDF Recent observations of fast radio bursts (FRBs) indicate a perplexing, inconsistent picture. We propose a unified scenario to interpret diverse FRBs observed. A regular pulsar, otherwise unnoticeable at a cosmological distance, may produce a bright FRB if its magnetosphere is suddenly "combed" by a nearby, strong plasma stream towards the anti-stream direction. If the Earth is to the night side of the stream, the combed magnetic sheath would sweep across the direction of Earth and make a detectable FRB. The stream could be an AGN flare, a GRB or supernova blastwave, a tidal disruption event, or even a stellar flare. Since it is the energy {\em flux} received by the pulsar rather than the luminosity of the stream origin that defines the properties of the FRB, this model predicts a variety of counterparts of FRBs, including a possible connection between FRB 150418 and an AGN flare, a possible connection between FRB 131104 and a weak GRB, a steady radio nebula associated with the repeating FRB 121102, and probably no bright counterparts for some FRBs.
Bing Zhang
Open questions in GRB physics are summarized as of 2011, including classification, progenitor, central engine, ejecta composition, energy dissipation and particle acceleration mechanism, radiation mechanism, long term engine activity, external shock afterglow physics, origin of high energy emission, and cosmological setting. Prospects of addressing some of these problems with the upcoming Chinese-French GRB mission, SVOM, are outlined.
Bing Zhang, Peter Meszaros, Junfeng Wang
Extensive observational campaigns of afterglow hunting have greatly enriched our understanding of the gamma-ray burst (GRB) phenomenon. Efforts have been made recently to explore some afterglow properties or signatures that will be tested by the on-going or the future observational campaigns yet come. These include the properties of GRB early afterglows in the temporal domain; the GeV-TeV afterglow signatures in the spectral domain; as well as a global view about the GRB universal structured jet configuration. These recent efforts are reviewed. Within the standard cosmological fireball model, the very model(s) responsible for the GRB prompt emission is (are) not identified. These models are critically reviewed and confronted with the current data.
Bing Zhang
Oct 10, 2001·astro-ph·PDF In the hot environments of the anomalous X-ray pulsars and the soft gamma-ray repeaters, as indicated by their luminous, pulsed, quiescent X-ray emission, $γ$-rays generated from the inner gaps may have shorter attenuation lengths via two photon pair production than via magnetic photon splitting. The AXP/SGR environments may not be pairless, even if photon splitting could completely suppress one photon pair production in super-strong magnetic fields, as conjectured by Baring & Harding. Two-photon pair production more likely occurs near the threshold, which tends to generate low energy pairs that are not energetic enough to power radio emission in the observed bands. However, emission in longer wavelengths may not be prohibited in principle if these objects are indeed magnetars. The so-called ``photon splitting deathlines'' are still valid for high magnetic field pulsars which are much dimmer in X-rays, if $γ$-rays with both polarization modes split.
Bing Zhang, Peter Meszaros
Jun 11, 2002·astro-ph·PDF Typical gamma-ray burst spectra are characterized by a spectral break, Ep, which for bright BATSE bursts is found to be narrowly clustered around 300 keV. Recently identified X-ray flashes, which may account for a significant portion of the whole GRB population, seem to extend the Ep distribution to a broader range below 40 keV. Positive correlations among Ep and some other observed parameters have been noticed. On the other hand, within the cosmological fireball model, the issues concerning the dominant energy ingredient of the fireball as well as the location of the GRB emission site are still unsettled, leading to several variants of the fireball model. Here we analyze these models within a unified framework, and critically reexamine the Ep predictions in the various model variants. Attention is focused on the predictions of the narrowness of the Ep distribution in different models, and the correlations among Ep and some other measurable observables. These model properties may be tested against the current and upcoming GRB data, through which the nature of the fireball as well as the mechanism and site of the GRB emission will be identified. In view of the current data, various models are appraised through a simple Monte-Carlo simulation, and a tentative discussion about the possible nature of X-ray flashes is presented.
Bing Zhang
Sep 19, 2005·astro-ph·PDF The successful launch and operation of NASA's Swift Gamma-Ray Burst Explorer open a new era for the multi-wavelength study of the very early afterglow phase of gamma-ray bursts (GRBs). GRB early afterglow information is essential to explore the unknown physical composition of GRB jets, the link between the prompt gamma-ray emission and the afterglow emission, the GRB central engine activity, as well as the immediate GRB environment. Here I review some of the recent theoretical efforts to address these problems and describe how the latest Swift data give answers to these outstanding questions.
Bing Zhang, Abraham Loeb
Jun 27, 2004·astro-ph·PDF The binary J0737-3039 A & B includes two pulsars in a highly relativistic orbit. The pulsed radio flux from pulsar B brightens considerably during two portions of each orbit. This phenomenon cannot be naturally triggered by the illumination of $γ$-rays or X-rays from pulsar A or the bow shock around pulsar B. Instead, we explain these periodic flares quantitatively as episodes during which pairs from pulsar A's wind flow into the open field line region of pulsar B and emit curvature radiation at radio frequencies within an altitude of $\sim 10^8$ cm. The radio photons then travel through B's magnetosphere and eventually reach the observer on the other side of the pulsar. Our model requires that A's wind be anisotropic and that B's spin axis be somewhat misaligned relative to the orbital angular momentum. We estimate the expected $γ$-ray and X-ray emission from the system.
Bing Zhang, Shiho Kobayashi
Apr 19, 2005·astro-ph·PDF Lyutikov (astro-ph/0503505) raised a valid point that for shock deceleration of a highly magnetized outflow, the fate of the magnetic fields after shock crossing should be considered. However, his comment that the deceleration radius should be defined by the total energy rather than by the baryonic kinetic energy is incorrect. As strictly derived from the shock jump conditions in Zhang & Kobayashi (2005), during the reverse shock crossing process the magnetic energy is not tapped. As a result, the fireball deceleration radius is defined by the baryonic energy only. The magnetic energy is expected to be transferred to the circumburst medium after the reverse shock disappears. The evolution of the system then mimicks a continuously-fed fireball. As a result, Lyutikov's naive conclusion that the forward shock dynamics is independent on the ejecta content is also incorrect. The shock deceleration dynamics and the reverse shock calculation presented in Zhang & Kobayashi (2005) are robust and correct.
Bing Zhang, Xuyang Zhao, Jiangtian Nie, Jianhang Tang, Yuling Chen, Yang Zhang, Dusit Niyato
Most recent surveys and reviews on Influential Node Ranking Methods (INRMs) hightlight discussions on the methods' technical details, but there still lacks in-depth research on the fundamental issue of how to verify the considerable influence of these nodes in a network. Compared to conventional verification models such as cascade failure and linear threshold, the epidemic model is more widely used. Accordingly, we conducted a survey of INRM based on epidemic model on 81 primary studies and analyzed their Capability and Correctness which we defined in our work. Our study categorized 4 types of networks used by INRM, classified 7 categories of INRMs for analyzing the networks and defined 2 evaluation metrics set of Capability and Correctness for evaluating INRM from Ranking Rationality Perspective. We also discussed particular real-world networks that were used to evaluate INRM and the Capability and Correctness of different INRMs on ranking nodes in specific networks. This is, as far as we know, the first survey aimed at systematically summarizing the Capability and Correctness of INRM. Our findings can assist practitioners and researchers in choosing and comparing INRMs and identifying research gaps.
Bing Zhang, Asaf Pe'er
Apr 20, 2009·astro-ph.HE·PDF 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 significant fraction of the outflow energy is initially not in the ``fireball'' form, but is likely in a Poynting flux entrained with the baryonic matter. The ratio between the Poynting and baryonic fluxes is at least ~(15-20) at the photosphere radius, if the Poynting flux is not directly converted to kinetic energy below the photosphere.
Bing Zhang
Fast radio bursts (FRBs), millisecond-duration bursts prevailing in the radio sky, are the latest big puzzle in the universe and have been a subject of intense observational and theoretical investigations in recent years. The rapid accumulation of the observational data has painted the following sketch about the physical origin of FRBs: They predominantly originate from cosmological distances so that their sources produce the most extreme coherent radio emission in the universe; at least some, probably most, FRBs are repeating sources that do not invoke cataclysmic events; and at least some FRBs are produced by magnetars, neutron stars with the strongest magnetic fields in the universe. Many open questions regarding the physical origin(s) and mechanism(s) of FRBs remain. This article reviews the phenomenology and possible underlying physics of FRBs. Topics include: a summary of the observational data, basic plasma physics, general constraints on FRB models from the data, radiation mechanisms, source and environment models, propagation effects, as well as FRBs as cosmological probes. Current pressing problems and future prospects are also discussed.
Houjun Lv, Enwei Liang, Binbin Zhang, Bing Zhang
Recent Swift observations suggest that the traditional long vs. short GRB classification scheme does not always associate GRBs to the two physically motivated model types, i.e. Type II (massive star origin) vs. Type I (compact star origin). We propose a new phenomenological classification method of GRBs by introducing a new parameter epsilon=E_{gamma, iso,52}/E^{5/3}_{p,z,2}, where E_{γ,iso} is the isotropic gamma-ray energy (in units of 10^{52} erg), and E_{p,z} is the cosmic rest frame spectral peak energy (in units of 100 keV). For those short GRBs with "extended emission", both quantities are defined for the short/hard spike only. With the current complete sample of GRBs with redshift and E_p measurements, the epsilon parameter shows a clear bimodal distribution with a separation at epsilon ~ 0.03. The high-epsilon region encloses the typical long GRBs with high-luminosity, some high-z "rest-frame-short" GRBs (such as GRB 090423 and GRB 080913), as well as some high-z short GRBs (such as GRB 090426). All these GRBs have been claimed to be of the Type II origin based on other observational properties in the literature. All the GRBs that are argued to be of the Type I origin are found to be clustered in the low-epsilon region. They can be separated from some nearby low-luminosity long GRBs (in 3sigma) by an additional T_{90} criterion, i.e. T_{90,z}<~ 5 s in the Swift/BAT band. We suggest that this new classification scheme can better match the physically-motivated Type II/I classification scheme.
Yosuke Mizuno, Bing Zhang, Bruno Giacomazzo, Ken-Ichi Nishikawa, Philip E. Hardee, Shigehiro Nagataki, Dieter H. Hartmann
Oct 15, 2008·astro-ph·PDF We solve the Riemann problem for the deceleration of an arbitrarily magnetized relativistic flow injected into a static unmagnetized medium in one dimension. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization σ(the Poynting-to kinetic energy flux ratio), and the shock becomes a rarefaction wave when σexceeds a critical value, σ_c, defined by the balance between the magnetic pressure in the flow and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly larger than the initial value. This acceleration mechanism is due to the strong magnetic pressure in the flow. We discuss the implications of these results for models of gamma-ray bursts and active galactic nuclei.
Bing Zhang, Xiang-Yu Wang, Jian-He Zheng
Nov 23, 2023·astro-ph.HE·PDF We argue that the broad-band observations of the brightest-of-all-time (BOAT) GRB 221009A reveal a physical picture involving two jet components: a narrow ($\sim 0.6$ degree half opening angle) pencil-beam jet that has a Poynting-flux-dominated jet composition, and a broader matter-dominated jet with an angular structure. We discuss various observational evidence that supports such a picture. To treat the problem, we develop an analytical structured jet model for both forward and reverse shock emission from the matter dominated structured jet wing during the deceleration phase. We discuss the physical implications of such a two-component jet configuration for this particular burst and for GRBs in general. We argue that some bright X-ray flares could be similar narrow jets viewed slightly outside the narrow jet cone and that narrow jets may exist in many more GRBs without being detected.
Bing Zhang, Peter Meszaros
Nov 13, 2003·astro-ph·PDF The cosmological gamma-ray burst (GRB) phenomenon is reviewed. The broad observational facts and empirical phenomenological relations of the GRB prompt emission and afterglow are outlined. A well-tested, successful fireball shock model is introduced in a pedagogical manner. Several important uncertainties in the current understanding of the phenomenon are reviewed, and prospects of how future experiments and extensive observational and theoretical efforts may address these problems are discussed.
Bing Zhang
Fast radio bursts are brief, highly dispersed bursts detected in the radio band, originating from cosmological distances. The only such event detected in the Milky Way galaxy, FRB 20200428DD, was associated with an X-ray burst emitted by a magnetar named SGR J1935+2154, revealing the first case of a multi-wavelength counterpart of an FRB. Counterparts in other wavelengths accompanying or following FRBs, as well as the bright emission associated with the progenitor of the FRB engine, have been proposed in various FRB models, but no robust detection has been made so far. In general, FRBs as we know them are not favorite multi-messenger emitters. Nonetheless, possible neutrino and gravitational wave emission signals associated with FRBs or FRB-like events have been discussed in the literature. Here I review these suggested multi-wavelength and multi-messenger counterparts of FRBs or FRB-like events and the observational progress in searching for these signals. The topics include multi-wavelength (X-rays, $γ$-rays, optical) emission and neutrino emission from FRBs within the framework of the magnetar source models and possible FRB-like events associated with gravitational waves.
Bing Zhang
Apr 22, 2012·astro-ph.HE·PDF Phenomenologically, two classes of GRBs (long/soft vs. short/hard) are identified based on their gamma-ray properties. The boundary between the two classes is vague. Multi-wavelength observations lead to identification of two types of GRB progenitor: one related to massive stars (Type II), and another related to compact stars (Type I). Evidence suggests that the majority of long GRBs belong to Type II, while at least the majority of nearby short GRBs belong to Type I. Nonetheless, counter examples do exist. Both long-duration Type I and short-duration Type II GRBs have been observed. In this talk, I review the complications in GRB classification and efforts in diagnosing GRB progenitor based on multiple observational criteria. In particular, I raise the caution to readily accept that all short/hard GRBs detected by BATSE are due to compact star mergers. Finally, I propose to introduce "amplitude" as the third dimension (besides "duration" and "hardness") to quantify burst properties, and point out that the "tip-of-iceberg" effect may introduce confusion in defining the physical category of GRBs, especially for low-amplitude, high-redshift GRBs.