Spectral evolution of gamma-ray burst pulses assumed to arise from emission of fireballs is explored. It is found that, due to the curvature effect, the integrated flux and peak energy are well related by a power law in the decaying phase of pulses, where the index is about 3, being free of the intrinsic emission and the Lorentz factor. The spectrum of a pulse in its decaying phase differs slightly for different intrinsic spectral evolution patterns, indicating that it is dominated by the curvature effect. In the rising phase, the integrated flux keeps increasing whilst the peak energy remains unchanged when the intrinsic emission bears an unchanged spectrum. Within this phase, the flux decreases with the increasing of the peak energy for a hard-to-soft intrinsic spectrum, and for a soft-to-hard-to-soft intrinsic spectrum, the flux generally increases with the increasing of the peak energy. An intrinsic soft-to-hard-to-soft spectral evolution within a co-moving pulse would give rise to a pulse-like evolutionary curve for the peak energy.
We demonstrate how pulse structures in Short gamma-ray bursts (SGRBs), coupled with observations of GRB/GW 170817A, constrain the geometries of dying HMXRB systems composed of merging neutron stars.
We analyze pulse properties of Short gamma-ray bursts (GRBs) from a new catalog containing 434 pulses from 387 BATSE Time-Tagged Event (TTE) GRBs. Short GRB pulses exhibit correlated properties of duration, fluence, hardness, and amplitude, and they evolve hard-to-soft while undergoing similar triple-peaked light curves similar to those found in Long/Intermediate bursts. We classify pulse light curves using their temporal complexities, demonstrating that Short GRB pulses exhibit a range of complexities from smooth to highly variable. Most of the bright, hard, chaotic emission seen in complex p…
Multi-peaked features appear on the integrated pulse profiles of fast radio burst observed below 2.5 GHz and the instantaneous spectrum of many bursts observed between 4 and 8 GHz. The mechanism of pulse or spectrum shaping has attracted little attention. Here we show that these interference-like pulse profiles are mostly the instantaneous spectra near the source regions of fast radio bursts. The corresponding instantaneous spectra are coincident to the spectrum from a single electron passing through a tapered undulator. The multi-peaked spectrum observed between 4 and 8 GHz can also be explai…
We present compelling evidence that most gamma-ray burst (GRB) pulse light curves can be characterized by a smooth single-peaked component coupled with a more complex emission structure that is temporally-symmetric around the time of the pulse peak. The model successfully fits 86% of BATSE GRB pulses bright enough for structure properties to be measured. Surprisingly, a GRB pulse's light curve morphology can be accurately predicted by the pulse asymmetry and the stretching/compression needed to align the structural components preceding the temporal mirror with the time-reversed components foll…
New insight into the hard X-ray emission influenced by the type-\uppercase\expandafter{\romannumeral1} bursts observed by Insight-HXMT during outburst of 4U 1636--536
Pulse-resolved Classification and Characteristics of Long-duration GRBs with \emph{Swift}-BAT Data.I. Precursors versus Main Bursts
Institute of Fundamental Physics and Quantum Technology, Ningbo University（宁波大学基础物理与量子技术研究院）；School of Physical Science and Technology, Ningbo University（宁波大学物理科学与技术学院）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）
Sorted by the photon fluences of short Gamma-ray Bursts (SGRBs) detected by the Fermi- Gamma Ray Burst Monitor (GBM), nine brightest bursts are selected to perform a comprehensive analysis. All GRB lightcurves are fitted well by 1 to 3 pulses that are modelled by fast-rising exponential decay profile (FRED), within which the resultant rising time is strongly positive-correlated with the full time width at half maxima (FWHM). A photon spectral model involving a cutoff power-law function and a standard blackbody function (CPL + BB) could reproduce the spectral energy distributions of these SGRBs…
We consider radio bursts that originate from extragalactic neutron stars (NSs) by addressing three questions about source distances. What are the physical limitations on coherent radiation at GHz frequencies? Do they permit detection at cosmological distances? How many bursts per NS are needed to produce the inferred burst rate $\sim 10^3$-$10^4 $sky$^{-1}$ day$^{-1}$? The burst rate is comparable to the NS formation rate in a Hubble volume, requiring only one per NS if they are bright enough. However, radiation physics causes us to favor a closer population. More bursts per NS are then requir…
If gamma-ray burst prompt emission originates at a typical radius, and if material producing the emission moves at relativistic speed, then the variability of the resulting light curve depends on the viewing angle. This is due to the fact that the pulse evolution time scale is Doppler contracted, while the pulse separation is not. For off-axis viewing angles $θ_{\rm view} \gtrsim θ_{\rm jet} + Γ^{-1}$, the pulse broadening significantly smears out the light curve variability. This is largely independent of geometry and emission processes. To explore a specific case, we set up a simple model of…
We discuss identification of possible counterparts and persistent sources related to Fast Radio Bursts (FRBs) in the framework of the model of supergiant pulses from young neutron stars with large spin-down luminosities. In particular, we demonstrate that at least some of sources of FRBs can be observed as ultraluminous X-ray sources (ULXs). At the moment no ULXs are known to be coincident with localization areas of FRBs. We searched for a correlation of FRB positions with galaxies in the 2MASS Redshift survey catalogue. Our analysis produced statistically insignificant overabundance ($p$-valu…
Isolated Swift gamma-ray burst (GRB) pulses, like their higher-energy BATSE counterparts, emit the bulk of their pulsed emission as a hard-to-soft component that can be fitted by the Norris et al. (2005) empirical pulse model. This signal is overlaid by a fainter, three-peaked signal that can be modeled by an empirical wave-like function (Hakkila and Preece, 2014): the two fits combine to reproduce GRB pulses with distinctive three-peaked shapes. The precursor peak appears on or before the pulse rise and is often the hardest component, the central peak is the brightest, and the decay peak conv…
GRB 090618: different pulse temporal and spectral characteristics within a burst
GRB 090618同时被Swift-BAT和Fermi-GBM探测到。它的光变曲线显示了两个发射事件，由四个突出的脉冲组成。第一次发作（发作A）中的脉冲比第二次发作（发作B）中的三个脉冲具有更平滑的形态。利用脉冲峰值拟合方法，我们对这四个脉冲的时间和频谱特性进行了详细的分析，发现第一个脉冲（脉冲A）在以下方面表现出明显不同于事件B中的其他脉冲（脉冲B1，B2和B3）的特性。(i)发现GRB 090618的脉冲宽度（$w$）和脉冲的上升衰减比（$r/d$，脉冲不对称性）都与能量有关。B期脉冲的$w$和$E$之间的幂律相关指数大于A期。此外，脉冲B1、B2和B3在较高的能带处趋于更对称，而脉冲A显示相反的趋势。(ii)脉冲A表现出从硬到软的光谱演化模式，而B事件中的三个脉冲遵循光变曲线趋势。(iii)脉冲A具有比脉冲B1、B2和B3更长的滞后。引起单个伽玛暴不同脉冲特性的机制尚不清楚。
Gamma-ray bursts (GRBs) are highly variable and exhibit strong spectral evolution. In particular, the emission properties vary from pulse to pulse in multipulse bursts. Here we present a time-resolved Bayesian spectral analysis of a compilation of GRB pulses observed by the {\it Fermi}/Gamma-ray Burst Monitor. The pulses are selected to have at least four timebins with a high statistical significance, which ensures that the spectral fits are well determined and that spectral correlations can be established. The sample consists of 39 bursts, 117 pulses, and 1228 spectra. We confirm the general …
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…
There are some similarities between bursts of repeating fast radio bursts (FRBs) and giant pulses (GPs) of pulsars. To explore possible relations between them, we study the cumulative energy distributions of these two phenomena using the observations of repeating FRB 121102 and the GPs of Crab pulsar. We find that the power-law slope of GPs (with fluence $\geq$130 Jy ms) is $2.85\pm0.10$. The energy distribution of FRB 121102 can be well fitted by a smooth broken power-law function. For the bursts of FRB 121102 above the break energy (1.22 $\times 10^{37}$ erg), the best-fitting slope is $2.90…
The complete Swift Burst Alert Telescope and X-Ray Telescope light curves of 118 gamma-ray bursts (GRBs) with known redshifts were fitted using the physical model of GRB pulses by Willingale et al. to produce a total of 607 pulses. We compute the pulse luminosity function utilizing three GRB formation rate models: a progenitor that traces the cosmic star formation rate density (CSFRD) with either a single population of GRBs, coupled to various evolutionary parameters, or a bimodal population of high- and low-luminosity GRBs, and a direct fit to the GRB formation rate excluding any a priori ass…
The widths, dispersion measures, dispersion indices and fluences of Fast Radio Bursts (FRB) impose coupled constraints that all models must satisfy. Observation of dispersion indices close to their low density limit of $-2$ sets a model-independent upper bound on the electron density and a lower bound on the size of any dispersive plasma cloud. The non-monotonic dependence of burst widths (after deconvolution of instrumental effects) on dispersion measure excludes the intergalactic medium as the location of scattering that broadens the FRB in time. Temporal broadening far greater than that of …
The observed lightcurves and estimated sky rate of fast extragalactic x-ray transients (XRTs) discovered in archival Chandra data indicate that they belong to two distinct XRT populations. The first population of relatively short duration pulses, which typically last less than few minutes seems to be pulses of x-ray flashes (XRFs), which are nearby long duration gamma ray bursts viewed from far off axis. The second population of much longer pulses, which typically last hours, seems to be the early time afterglows of short gamma ray bursts (SGRBs) which are beamed away from Earth, as was shown …
Fast radio bursts are radio transients observed mainly around 1.5 GHz. Their peak frequency decreases at a rate of 100 ~ 500 MHz/s and some of them have a broader pulse with an exponentially decaying tail. Common assumptions for fast radio bursts include a dispersion effect resulting in the peak frequency drifting and a scattering effect resulting in pulse broadening. These assumptions attribute the abnormally large dispersion measure and scattering measure to the environmental medium of the host galaxy. Here we show that the radiation of fast radio bursts can be explained as an undulator radi…
We carry out a systematical study of the spectral lag properties of 50 single-pulsed Gamma-Ray Bursts (GRBs) detected by Fermi/GBM. By dividing the light curves into multiple consecutive energy channels we provide a new measurement of the spectral lag which is independent on energy channel selections. We perform a detailed statistical study of our new measurements. We find two similar power-law energy dependencies of both the pulse arrival time and pulse width. Our new results on the power-law indices would favor the relativistic geometric effects for the origin of spectral lag. However, a com…
We discuss possible association of fast radio bursts (FRBs) with supergiant pulses emitted by young pulsars (ages $\sim$ tens to hundreds of years) born with regular magnetic field but very short -- few milliseconds -- spin periods. FRBs are extra-Galactic events coming from distances $d \lesssim 100$ Mpc. Most of the dispersion measure (DM) comes from the material in the freshly ejected SNR shell; for a given burst the DM should decrease with time. FRBs are not expected to be seen below $\sim 300 $ MHz due to free-free absorption in the expanding ejecta. A supernova might have been detected y…
Aims. To make a detailed study of the nulling and subpulse drifting in PSR J1727$-$2739 for investigation of its radiation properties. Methods. The observations were carried out on 20 March, 2004 using the Parkes 64-m radio telescope, with a central frequency of 1518 MHz. A total of 5568 single pulses were analysed. Results. This pulsar shows well defined nulls with lengths lasting from 6 to 281 pulses and separated by burst phases ranging from 2 to 133 pulses. We estimate a nulling fraction of around 68\%. No emission in the average pulse profile integrated over all null pulses is detected wi…
We demonstrate that the `smoke' of limited instrumental sensitivity smears out structure in gamma-ray burst (GRB) pulse light curves, giving each a triple-peaked appearance at moderate signal-to-noise and a simple monotonic appearance at low signal-to-noise. We minimize this effect by studying six very bright GRB pulses (signal-to-noise generally $> 100$), discovering surprisingly that each exhibits $\textit{complex time-reversible}$ wavelike residual structures. These `mirrored' wavelike structures can have large amplitudes, occur on short timescales, begin/end long before/after the onset of …
The variability in multi-pulse gamma-ray bursts (GRBs) may help to reveal the mechanism of underlying processes from the central engine. To investigate whether the self-organized criticality (SOC) phenomena exist in the prompt phase of GRBs, we statistically study the properties of GRBs with more than 3 pulses in each burst by fitting the distributions of several observed physical variables with a Markov Chain Monte Carlo approach, including the isotropic energy $E_{\rm iso}$, the duration time $T$ and the peak count rate $P$ of each pulse. Our sample consists of 454 pulses in 93 GRBs observed…
A new method of pulse-wise spectral analysis of Gamma-ray Bursts
时间分辨谱分析是理解伽马射线暴（GRB）发射机制的一种很有前途的方法，但由于统计性差，在实际应用中很难实现。我们提出了一种新的方法，脉冲方式的时间分辨光谱研究的单个脉冲的伽玛暴，利用这一事实，许多光谱参数是常数或时间的光滑函数。我们使用这种方法的两个脉冲的伽玛暴081221，最明亮的伽玛暴与可分离的脉冲。我们选择，从文献中，一组可能的模型，其中包括带模型，黑体与幂律（BBPL），一个集合的黑体与一个平滑变化的温度分布，随着幂律（mBBPL），和两个黑体与幂律（2BBPL）。首先，我们进行时间分辨的研究，以确认光谱参数的变化，然后构建新的模型进行联合光谱拟合。我们发现，任何光球发射的黑体主要是在上升部分的脉冲和下降部分可以充分解释的能带模型，与同步辐射模型的范围内的低能光子指数。有趣的是，我们发现2BBPL在所有剧集中都与Band模型相当，有时甚至更好，尽管幅度很小。对费米时代最亮的伽玛暴-- GRB 090618也得到了一致的结果。我们指出，该方法是通用的，足以测试任何光谱模型定义良好的参数变化。
Magnetars are a special subset of the isolated neutron star family, with X-ray and radio emission mainly powered by the decay of their immense magnetic fields. Many attributes of magnetars remain poorly understood: spin-down glitches or the sudden reductions in the star's angular momentum, radio bursts reminiscent of extra-galactic Fast Radio Bursts (FRBs), and transient pulsed radio emission lasting months to years. Here we unveil the detection of a large spin-down glitch event ($|Δν/ν| = 5.8_{-1.6}^{+2.6}\times10^{-6}$) from the magnetar SGR~1935+2154 on 2020 October 5 (+/- 1 day). We find n…
A Comprehensive Analysis of Fermi Gamma-ray Burst Data: II. $E_{\rm p}$-Evolution Patterns and Implications for the Observed Spectrum-Luminosity Relations
Fast radio bursts (FRBs) are cosmological radio transients with unclear generation mechanism. Known characteristics such as their luminosity, duration, spectrum and repetition rate, etc. suggest that FRBs are powerful coherent radio signals at GHz frequencies, but the status of FRBs near source remain unknown. As an extreme astronomical event, FRBs should be accompanied by energy -- comparable or even more powerful x/γ-ray counterparts. Here, particle-in-cell simulations of ultra-strong GHz radio pulse interaction with GeV photons show that at 3*10^12V/cm field-strengths, quantum cascade can g…
The nearly 100% linear polarization has been reported for a few fast radio bursts. This finding places severe limits on the emission mechanism. I argue that the totally polarized radiation could be generated in the course of relativistic magnetic reconnection in the outer magnetosphere of the magnetar. At the onset of the magnetar flare, a large scale magnetic perturbation forms a magnetic pulse, which propagates from the flare cite outwards. The pulse strongly compresses magnetospheric plasma and pushes it away. The high-frequency MHD waves are generated when the magnetic pulse reaches the cu…
We have developed a new coherent dedispersion mode to study the emission of Fast Radio Bursts that trigger the voltage capture capability of the Australian SKA Pathfinder (ASKAP) interferometer. In principle the mode can probe emission timescales down to 3 ns with full polarimetric information preserved. Enabled by the new capability, here we present a spectropolarimetric analysis of FRB 181112 detected by ASKAP, localized to a galaxy at redshift 0.47. At microsecond time resolution the burst is resolved into four narrow pulses with a rise time of just $15 μ$s for the brightest. The pulses hav…
We discuss dissipative processes occurring during production and escape of Fast Radio Bursts (FRBs) from magnetars' magnetospheres, the presumed loci of FRBs. High magnetic fields are required in the emission region, both to account for the overall energetics of FRBs, and in order to suppress ``normal'' (non-coherent) radiative losses of radio emitting particles; this limits the emission radii to $\leq {\rm few} \times 10 R_{NS}$. Radiative losses by particles in the strong FRB pulse may occur in the outer regions of the magnetosphere for longer rotation periods, $P\geq 1$ second. These losses…
The spectral evolution and spectral lag behavior of 92 bright pulses from 84 gamma-ray bursts (GRBs) observed by the Fermi GBM telescope are studied. These pulses can be classified into hard-to-soft pulses (H2S, 64/92), H2S-dominated-tracking pulses (21/92), and other tracking pulses (7/92). We focus on the relationship between spectral evolution and spectral lags of H2S and H2S-dominated-tracking pulses. %in hard-to-soft pulses (H2S, 64/92) and H2S-dominating-tracking (21/92) pulses. The main trend of spectral evolution (lag behavior) is estimated with $\log E_p\propto k_E\log(t+t_0)$ (${\hat…
The pulse morphology of fast radio bursts (FRBs) provides key information in both understanding progenitor physics and the plasma medium through which the burst propagates. We present a study of the profiles of 33 bright FRBs detected by the Australian Square Kilometre Array Pathfinder. We identify seven FRBs with measureable intrinsic pulse widths, including two FRBs that have been seen to repeat. In our modest sample we see no evidence for bimodality in the pulse width distribution. We also identify five FRBs with evidence of millisecond timescale pulse broadening caused by scattering in inh…
We report the detection of 72 new pulses from the repeating fast radio burst FRB 121102 in Breakthrough Listen C-band (4-8 GHz) observations at the Green Bank Telescope. The new pulses were found with a convolutional neural network in data taken on August 26, 2017, where 21 bursts have been previously detected. Our technique combines neural network detection with dedispersion verification. For the current application we demonstrate its advantage over a traditional brute-force dedis- persion algorithm in terms of higher sensitivity, lower false positive rates, and faster computational speed. To…
We report on NICER X-ray monitoring of the magnetar SGR 1830-0645 covering 223 days following its October 2020 outburst, as well as Chandra and radio observations. We present the most accurate spin ephemerides of the source so far: $ν=0.096008680(2)$~Hz, $\dotν=-6.2(1)\times10^{-14}$~Hz~s$^{-1}$, and a significant second and third frequency derivative terms indicative of non-negligible timing noise. The phase-averaged 0.8--7~keV spectrum is well fit with a double-blackbody (BB) model throughout the campaign. The BB temperatures remain constant at 0.46 and 1.2 keV. The areas and flux of each co…
This work extends a contemporaneous effort (Panaitescu & Vestrand 2022) to study the properties of the lower-energy counterpart synchrotron emission produced by the cooling of relativistic Gamma-Ray Burst (GRB) electrons through radiation (synchrotron and self-Compton) emission and adiabatic losses. We derive the major characteristics (pulse duration, lag-time after burst, brightness relative to the burst) of the Prompt Optical Counterpart (POC) accompanying GRBs. Depending on the magnetic field life-time, duration of electron injection, and electron transit-time Dto from hard X-ray (GRB) to o…
Knowledge about the Lorentz factor and its evolution of relativistic jets in gamma-ray bursts (GRBs) is crucial to understand their physics. An exact value of bulk Lorentz factor can be estimated based on a high-energy spectral cutoff, which may appear in GRBs' prompt emission owing to the absorption of photon-photon pair production. In this work, we focus on the investigation of the bulk Lorentz factor evolution of jets in an individual burst. Based on \textsl{Fermi} observations, we search for the bursts with multiple $γ$-ray pulses characterized by a high-energy spectral cutoff, and nine GR…
