Could bright γ-ray burst optical transients have been recorded historically?

The brightest optical flash from a γ-ray burst （GRB） was, briefly, a naked- eye object. Several other GRBs have produced optical transients only slightly fainter. We argue that, based upon the recently accumulated data from hundreds of GRB transients, many such optical events should have been visible to the unaided eye in the course of human history. The most likely repositories of such observations are histor- ical records from the Orient, and we have located and discuss a number of candidates. We also consider the value of such observations, should any very likely ones be uncovered, to modern astrophysics.

The Relationship between the Rise Width and the Full Width of γ-ray Burst Pulses and Its Implications

We investigate the relationship between the rise width and the full width of gamma-ray burst pulses. Theoretical analysis shows that either width is proportional to Г^-2△τθ,FWHMRc/c（Г the Lorentz factor of the bulk motion, △τθ,FWHM a local pulse＇s width, Rc the radius of fireballs and c the velocity of light）. We study the relationship for four samples of observed pulses. We find： （1） merely the curvature effect could reproduce the relationship between the rise and full widths with the same slope as derived from the model of Qin et al.; （2） gamma-ray burst pulses, selected from both the short and long GRBs, follow the same sequence in the rise width vs. full width diagram, with the shorter pulses at one end; （3） all GRBs may intrinsically result from local Gaussian pulses. These features place constraints on the physical mechanism（s） for producing long and short GRBs.

GRB 200612A:An Ultralong Gamma-Ray Burst Powered by Magnetar Spinning Down

GRB 200612A could be classified as an ultralong gamma-ray burst due to its prompt emission lasting up to~1020 s and the true timescale of the central engine activity t_(burst)≥4×10^(4) s.The late X-ray light curve with a decay index ofα=7.53 is steeper than the steepest possible decay from an external shock model.We propose that this X-ray afterglow can be driven by dipolar radiation from the magnetar spindown during its early stage,while the magnetar collapsed into the black hole before its spindown,resulting in a very steep decay of the late X-ray light curve.The optical data show that the light curve is still rising after 1.1 ks,suggesting a late onset.We show that GRB 200612A’s optical afterglow light curve is fitted with the forward shock model by Gaussian structured off-axis jet.This is a special case among GRBs,as it may be an ultralong gamma-ray burst powered by a magnetar in an off-axis observation scenario.

Time-resolved Spectral Properties of Fermi-GBM Bright Long Gamma-Ray Bursts

The prompt emission mechanism of gamma-ray bursts(GRBs)is still unclear,and the time-resolved spectral analysis of GRBs is a powerful tool for studying their underlying physical processes.We performed a detailed time-resolved spectral analysis of 78 bright long GRB samples detected by Fermi/Gamma-ray Burst Monitor.A total of 1490 spectra were obtained and their properties were studied using a typical Band-shape model.First,the parameter distributions of the time-resolved spectrum are given as follows:the low-energy spectral indexα~-0.72,high-energy spectral indexβ~2.42,the peak energy E_(p)~221.69 keV,and the energy flux F~7.49×10^(-6)erg cm^(-2)s^(-1).More than 80%of the bursts exhibit the hardest low-energy spectral indexα_(max),exceeding the synchrotron limit(-2/3).Second,the evolution patterns of a and E_(p)were statistically analyzed.The results show that for multi-pulse GRBs the intensity-tracking pattern is more common than the hard-to-soft pattern in the evolution of both E_(p)andα.The hard-to-soft pattern is generally shown in single-pulse GRBs or in the initial pulse of multi-pulse GRBs.Finally,we found a significant positive correlation between F and E_(p),with half of the samples exhibiting a positive correlation between F andα.We discussed the spectral evolution of different radiation models.The diversity of spectral evolution patterns indicates that there may be more than one radiation mechanism occurring in the GRB radiation process,including photo spheric radiation and synchrotron radiation.However,it may also involve only one radiation mechanism,but more complicated physical details need to be considered.

Revise Thermal Winds of Remnant Neutron Stars in Gamma-Ray Bursts

It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star(NS)merger event,GW170817/GRB 170817A/kilonova AT2017gfo,places irreconcilable constraints to models of the prompt emission of this gamma-ray burst(GRB).The observed time delay between the merger of the two NSs and the trigger of the GRB and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously.We argue that the merger remnant should be an NS(last for,at least,a large fraction of 1 s),and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the NS and the delayed emergence of effective viscosity in the disk.Further,we extend the consideration of the effect of the energy deposition of neutrinos emitted from the NS.If the NS is the central object of a GRB with a distance and duration similar to that of GRB 170817A,thermal emission of the thermal bubble inflated by the NS after the termination of accretion may be detectable.If our scenario is verified,it would be of interest to investigate the cooling of nascent NSs.

Prospects for the detection rate of very-high-energyγ-ray emissions from shortγ-ray bursts with the HADAR experiment

The observation of short gamma ray bursts(SGRBs)in the TeV energy range plays an important role in understanding the radiation mechanism and probing potential new physics,such as Lorentz invariance violation(LIV).However,no SGRBs have been observed in this energy range owing to the short duration of SGRBs and the weakness of current experiments.New experiments with new technology are required to detect the very high energy(VHE)emission of SGRBs.In this study,we simulate the VHE γ-ray emissions from SGRBs and calculate the annu-al detection rate with the High Altitude Detection of Astronomical Radiation(HADAR)experiment.First,a set of pseudo-SGRB samples is generated and checked using the observations of the Fermi-GBM,Fermi-LAT,and Swift-BAT measurements.The annual detection rate is calculated from these SGRB samples based on the performance of the HADAR instrument.As a result,the HADAR experiment can detect 0.5 SGRBs per year if the spectral break-off of γ-rays caused by the internal absorption and Klein-Nishina(KN)effect is larger than 100 GeV.For a GRB090510-like GRB in HADAR's view,it should be possible to detect approximately 2000 photons considering the internal absorption and KN effect.With a time delay assumption due to LIV effects,a simulated light curve of GRB090510 has evident energy dependence.We hope that the HADAR experiment can perform SGRB observa-tions and test our calculations in the future.

Redshift Dependence of the Low-energy Spectral Index of Gamma-Ray Bursts Revisited

A negative correlation was found to exist between the low-energy spectral index and the redshift of gamma-ray bursts(GRBs)by Amati et al.It was later confirmed by Geng&Huang and Gruber et al.,but the correlation was also found to be quite dispersive when the sample size was significantly expanded.In this study,we have established two even larger samples of GRBs to further examine the correlation.One of our samples consists of316 GRBs detected by the Swift satellite,and the other one consists of 80 GRBs detected by the Fermi satellite.It is found that there is no correlation between the two parameters for the Swift sample,but there does exist a weak negative correlation for the Fermi sample.The correlation becomes even more significant when the spectral index at the peak flux is considered.It is argued that the absence of the correlation in the Swift sample may be due to the fact that Swift has a very narrow energy response so that it could not measure the low-energy spectral index accurately enough.Further studies based on even larger GRB samples are solicited.

AstroSat Observations of the Be/X-Ray Binary XTE J1946+274 During 2018 and 2021 Outbursts

We present the timing and spectral studies of the Be/X-ray binary XTE J1946+274 during its 2018 and 2021 giant outbursts using observations with the SXT and LAXPC instruments on the AstroSat satellite.Unlike the 1998 and 2010 outbursts,where a giant outburst was followed by several low intensity periodic outbursts,the 2018 and 2021 outbursts were single outbursts.The X-ray pulsations are detected over a broad energy band covering 0.5–80 keV from the compact object.We construct the spin evolution history of the pulsar over two decades and find that the pulsar spins-up during the outbursts but switches to spin-down state in the quiescent periods between the outbursts.Energy resolved pulse profiles generated in several bands in 0.5–80 keV show that the pulse shape varies with the energy.The energy spectrum of the pulsar is determined for the 2018 and 2021 outbursts.The best fit spectral models require presence of cyclotron resonant scattering feature at about 43 keV in the energy spectra of both the outbursts.We find indication of possible reversal in the correlation between the cyclotron line energy and luminosity which needs to be ascertained from future observations.Using the best fit spectra the X-ray luminosity of XTE J1946+274 is inferred to be 2.7×10^(37) erg s^(-1) for the 2018 observations and 2.3×10^(37) erg s^(-1) for the 2021 observations.We discuss possible mechanisms which can drive outbursts in this transient Be X-ray binary.

Statistical Properties of X-Ray Bursts from SGR J1935+2154 Detected by Insight-HXMT

As one class of the most important objects in the universe,magnetars can produce a lot of different frequency bursts including X-ray bursts.In Cai et al.,75 X-ray bursts produced by magnetar SGR J1935+2154 during an active period in 2020 are published,including the duration and net photon counts of each burst,and waiting time based on the trigger time difference.In this paper,we utilize the power-law model,dN(x)/dx∝(x+x_0)~((-α)_x),to fit the cumulative distributions of these parameters.It can be found that all the cumulative distributions can be well fitted,which can be interpreted by a self-organizing criticality theory.Furthermore,we check whether this phenomenon still exists in different energy bands and find that there is no obvious evolution.These findings further confirm that the X-ray bursts from magnetars are likely to be generated by some self-organizing critical process,which can be explained by a possible magnetic reconnection scenario in magnetars.

Constraining Lorentz Invariance Violation Using Short Gamma-Ray Bursts

Lorentz Invariance is a foundational principle in modern physics, but some recent quantum gravity theories have hinted that it may be violated at extremely high energies. Gamma-ray bursts (GRBs) provide a promising tool for checking and constraining any deviations from Lorentz Invariance due to their huge energies and cosmological distances. Gamma-ray bursts, which are the most intense and powerful explosions in the universe, are traditionally divided into long bursts whose observed duration exceeds 2 s, and short bursts whose observed duration is less than 2 s. In this study, we employ a recent sample of 46 short GRBs to check for any deviation from Lorentz Invariance. We analyze the spectral lag of the bursts in our data sample and check for any redshift dependence in the GRB rest frame, which would indicate a violation of Lorentz Invariance. Our results are consistent, to within 1σ, with no deviation from Lorentz Invariance.

Gamma-Ray Bursts and Fermi Bubbles

According to a recent calculation, 1058 erg of radiant energy was released by Sgr A*, when it formed the Fermi bubbles. Here, it is argued that this explosion constituted a long gamma-ray burst. .

Measurement of the high energyγ-rays from heavy ion reactions usingČerenkov detector

The energetic bremsstrahlung photons up to 100 MeV produced in heavy ion collisions can be used as a sensitive probe for short-range correlation in atomic nuclei. The energy of the γ-rays can be measured by collecting the Čerenkov light in the medium induced by the fast electrons generated in the Compton scattering or electromagnetic shower of the incident γray. Two types of detectors based on pure water and lead glass as sensitive materials were designed for this purpose. The γresponse and optical photon propagation in the detectors were simulated based on electromagnetic and optical processes in Geant4. The inherent energy resolutions of 0.022(4) + 0.51(2)∕E^(1/2)_(γ) for water and 0.0026(3) + 0.446(3)∕E^(1/2)_(γ) for lead glass were obtained. The geometry sizes of the lead glass and water were optimized to 30 cm × 30 cm × 30 cm and 60 cm × 60 cm ×120 cm, respectively, to detect high-energy γ-rays at 160 MeV. The Hough transform method was applied to reconstruct the direction of the incident γ-rays, providing the ability to experimentally distinguish the high-energy γ-rays produced in the reactions on the target from random background cosmic-ray muons.

Prediction models of burst strength degradation for casing with considerations of both wear and corrosion

Casing wear and casing corrosion are serious problems affecting casing integrity failure in deep and ultra-deep wells.This paper aims to predict the casing burst strength with considerations of both wear and corrosion.Firstly,the crescent wear shape is simplified into three categories according to common mathematical models.Then,based on the mechano-electrochemical(M-E)interaction,the prediction model of corrosion depth is built with worn depth as the initial condition,and the prediction models of burst strength of the worn casing and corroded casing are obtained.Secondly,the accuracy of different prediction models is validated by numerical simulation,and the main influence factors on casing strength are obtained.At last,the theoretical models are applied to an ultra-deep well in Northwest China,and the dangerous well sections caused by wear and corrosion are predicted,and the corrosion rate threshold to ensure the safety of casing is obtained.The results show that the existence of wear defects results in a stress concentration and enhanced M-E interaction on corrosion depth growth.The accuracy of different mathematical models is different:the slot ring model is most accurate for predicting corrosion depth,and the eccentric model is most accurate for predicting the burst strength of corroded casing.The burst strength of the casing will be overestimated by more than one-third if the M-E interaction is neglected,so the coupling effect of wear and corrosion should be sufficiently considered in casing integrity evaluation.

A Comparative Study of the Power-law Relationship between the Pulse width and Energy of Precursor and Main Burst

In gamma-ray burst prompt emission,there is still no consistent conclusion if the precursor and main burst share the same origin.In this paper,we try to study this issue based on the relationship between pulse width and energy of the precursor and main burst.We systematically search the light curve data observed by Swift/BAT and Fermi/GBM,and find 13 long bursts with well-structured precursors and main bursts.After fitting the precursor light curve of each different energy channel with the Norris function,we find that there is not only a power-law relationship between precursor width and energy,but also a power-law relationship between the ratio of the rising width to the decaying width and energy.By comparing the relationship between the precursors and the main burst pulses,we find that the distribution of the precursors and the relationship between the power-law indices are roughly the same as those of the main burst.In addition,it is found that the precursor width distribution as well as the upper limit of the pulse width ratio does not exceed 1 and both are asymmetric,which are also consistent with the main burst.These indicate that the precursor and the main burst are indistinguishable,and the precursor and the main burst may have the same physical origin.

Artificial neural network-based method for discriminating Compton scattering events in high-purity germaniumγ-ray spectrometer

To detect radioactive substances with low activity levels,an anticoincidence detector and a high-purity germanium(HPGe)detector are typically used simultaneously to suppress Compton scattering background,thereby resulting in an extremely low detection limit and improving the measurement accuracy.However,the complex and expensive hardware required does not facilitate the application or promotion of this method.Thus,a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector,whereby Compton scattering background is suppressed and a low minimum detectable activity(MDA)is achieved without using an expensive and complex anticoincidence detector and device.The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location,as well as the characteristics of energy-deposition distributions for fulland partial-energy deposition events.This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification.To accurately determine the relationship between the deposited energy of gamma(γ)rays in the detector and the deposition location,we extract four shape parameters from the pulse signals output by the detector.Machine learning is used to input the four shape parameters into the detector.Subsequently,the pulse signals are identified and classified to discriminate between partial-and full-energy deposition events.Some partial-energy deposition events are removed to suppress Compton scattering.The proposed method effectively decreases the MDA of an HPGeγ-energy dispersive spectrometer.Test results show that the Compton suppression factors for energy spectra obtained from measurements on ^(152)Eu,^(137)Cs,and ^(60)Co radioactive sources are 1.13(344 keV),1.11(662 keV),and 1.08(1332 keV),respectively,and that the corresponding MDAs are 1.4%,5.3%,and 21.6%lower,respectively.

Rotating Massive Strangeon Stars and X-Ray Plateau of Short GRBs

Strangeon stars,which are proposed to describe the nature of pulsar-like compact stars,have passed various observational tests.The maximum mass of a non-rotating strangeon star could be high,which implies that the remnants of binary strangeon star mergers could even be long-lived massive strangeon stars.We study rigidly rotating strangeon stars in the slowly rotating approximation,using the Lennard-Jones model for the equation of state.Rotation can significantly increase the maximum mass of strangeon stars with unchanged baryon numbers,enlarging the mass-range of long-lived strangeon stars.During spin-down after merger,the decrease of radius of the remnant will lead to the release of gravitational energy.Taking into account the efficiency of converting the gravitational energy luminosity to the observed X-ray luminosity,we find that the gravitational energy could provide an alternative energy source for the plateau emission of X-ray afterglow.The fitting results of X-ray plateau emission of some short gamma-ray bursts suggest that the magnetic dipole field strength of the remnants can be much smaller than that of expected when the plateau emission is powered only by spin-down luminosity of magnetars.

Predicting Rock Burst in Underground Engineering Leveraging a Novel Metaheuristic-Based LightGBM Model

Rock bursts represent a formidable challenge in underground engineering,posing substantial risks to both infrastructure and human safety.These sudden and violent failures of rock masses are characterized by the rapid release of accumulated stress within the rock,leading to severe seismic events and structural damage.Therefore,the development of reliable prediction models for rock bursts is paramount to mitigating these hazards.This study aims to propose a tree-based model—a Light Gradient Boosting Machine(LightGBM)—to predict the intensity of rock bursts in underground engineering.322 actual rock burst cases are collected to constitute an exhaustive rock burst dataset,which serves to train the LightGBMmodel.Two population-basedmetaheuristic algorithms are used to optimize the hyperparameters of the LightGBM model.Finally,the sensitivity analysis is used to identify the predominant factors that may incur the occurrence of rock bursts.The results show that the population-based metaheuristic algorithms have a good ability to search out the optimal hyperparameters of the LightGBM model.The developed LightGBM model yields promising performance in predicting the intensity of rock bursts,with which accuracy on training and testing sets are 0.972 and 0.944,respectively.The sensitivity analysis discloses that the risk of occurring rock burst is significantly sensitive to three factors:uniaxial compressive strength(σc),stress concentration factor(SCF),and elastic strain energy index(Wet).Moreover,this study clarifies the particular impact of these three factors on the intensity of rock bursts through the partial dependence plot.

Turbo Message Passing Based Burst Interference Cancellation for Data Detection in Massive MIMO-OFDM Systems

This paper investigates the fundamental data detection problem with burst interference in massive multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM) systems. In particular, burst interference may occur only on data symbols but not on pilot symbols, which means that interference information cannot be premeasured. To cancel the burst interference, we first revisit the uplink multi-user system and develop a matrixform system model, where the covariance pattern and the low-rank property of the interference matrix is discussed. Then, we propose a turbo message passing based burst interference cancellation(TMP-BIC) algorithm to solve the data detection problem, where the constellation information of target data is fully exploited to refine its estimate. Furthermore, in the TMP-BIC algorithm, we design one module to cope with the interference matrix by exploiting its lowrank property. Numerical results demonstrate that the proposed algorithm can effectively mitigate the adverse effects of burst interference and approach the interference-free bound.

基于Altmetrics指标和Burst强度的前沿探测方法研究——以光伏发电技术为例

[目的/意义]将研究成果的社会影响力指标与学术影响力指标相结合来开展前沿探测研究,可以更充分地发掘科技前沿。[方法/过程]基于Altmetrics指标与Burst强度,将社会影响力与学术影响力相结合,构建了知识基础影响力加权评分指数,并在此基础上对研究前沿文献进行关键词共现分析,绘制了研究前沿关键词共现图谱,最后以光伏发电技术为例对其前沿研究主题进行了总结分析。[结果/结论]基于Altmetrics指标的研究前沿主题与基于Burst强度的研究前沿主题既有联系也有区别,基于两种指标开展的前沿探测研究可以为前沿探测方法的拓展提供新的思路。

X-ray flares of γ-ray bursts: Quakes of solid quark stars?

A star-quake model is proposed to understand X-ray flares of both long and short γ-ray bursts (GRBs) in a solid quark star regime. Two kinds of central engines for GRBs are available if pulsar-like stars are actually (solid) quark stars, i.e., the SNE-type GRBs and the SGR-type GRBs. It is found that a quark star could be solidified about 103 to 106 s later after its birth if the critical temperature of phase transi- tion is a few Metga-electron-volts, and then a new source of free energy (i.e., elastic and gravitational ones, rather than rotational or magnetic energy) could be possible to power GRB X-ray flares.