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 a...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.展开更多
POLAR-2 is a gamma-ray burst(GRB)polarimeter that is designed to study the polarization in GRB radiation emissions,aiming to improve our knowledge of related mechanisms.POLAR-2 is expected to utilize an on-board polar...POLAR-2 is a gamma-ray burst(GRB)polarimeter that is designed to study the polarization in GRB radiation emissions,aiming to improve our knowledge of related mechanisms.POLAR-2 is expected to utilize an on-board polarimeter that is sensitive to soft X-rays(2-10 keV),called low-energy polarization detector.We have developed a new soft X-ray polari-zation detector prototype based on gas microchannel plates(GMCPs)and pixel chips(Topmetal).The GMCPs have bulk resistance,which prevents charging-up effects and ensures gain stability during operation.The detector is composed of low outgassing materials and is gas-sealed using a laser welding technique,ensuring long-term stability.A modulation factor of 41.28%±0.64% is obtained for a 4.5 keV polarized X-ray beam.A residual modulation of 1.96%±0.58% at 5.9 keV is observed for the entire sensitive area.展开更多
We present a verification of the short-term predictions of solar X-ray bursts for the maximum phase (2000–2001) of Solar Cycle 23, issued by two prediction centers. The results are that the rate of correct prediction...We present a verification of the short-term predictions of solar X-ray bursts for the maximum phase (2000–2001) of Solar Cycle 23, issued by two prediction centers. The results are that the rate of correct predictions is about equal for RWC-China and WWA; the rate of too high predictions is greater for RWC-China than for WWA, while the rate of too low predictions is smaller for RWC-China than for WWA.展开更多
^56Cu is close to the waiting-point nucleus ^56Ni and lies on the rapid proton capture (rp) process path in Type I X-ray bursts (XRBs). In this work, we obtained a revised thermonuclear reaction rate of ^55Niep;cT56Cu...^56Cu is close to the waiting-point nucleus ^56Ni and lies on the rapid proton capture (rp) process path in Type I X-ray bursts (XRBs). In this work, we obtained a revised thermonuclear reaction rate of ^55Niep;cT56Cu in the temperature region relevant to XRBs. This rate was recalculated based on the recent experimental level structure in ^56Cu, the recently measured proton separation energy of Sp = 579.8(7.1) keV, together with shell-model calculation, and the mirror nuclear structure in ^56Co. The associated uncertainties in the rates were estimated by a Monte Carlo method. Our revised rate is significantly different from the recent results, which were partially based on experimental results;in addition, we found that a result in a previous work was incorrect. We recommend our revised rate to be incorporated in the future astrophysical network calculations.展开更多
We study RXTE PCA data for the high mass X-ray binary source SMC X-1 between 2003–10 and 2003–12 when the source was in its high states.The source is found to be frequently bursting which can be seen as flares in li...We study RXTE PCA data for the high mass X-ray binary source SMC X-1 between 2003–10 and 2003–12 when the source was in its high states.The source is found to be frequently bursting which can be seen as flares in lightcurves that occur at a rate of one every 800 s, with an average of 4–5 Type Ⅱ X-ray bursts per hour.We note that typically a burst was short, lasting for a few tens of seconds in addition to a few long bursts spanning more than a hundred seconds that were also observed.The flares apparently occupied 2.5% of the total observing time of 225.5 ks.We note a total of 272 flares with mean FWHM of the flare ~21 s.The rms variability and aperiodic variability are independent of flares.As observed, the pulse profiles of the lightcurves do not change their shape, implying that there is no change in the geometry of an accretion disk due to a burst.The hardness ratio and rms variability of lightcurves exhibit no correlation with the flares.The flare fraction shows a positive correlation with the peak-to-peak ratio of the primary and secondary peaks of the pulse profile.The observed hardening or softening of the spectrum cannot be correlated with the flaring rate but may be due to the interstellar absorption of X-rays as evident from the change in hydrogen column density(n_H).It is found that the luminosity of the source increases with the flaring rate.Considering that the viscous timescale is equal to the mean recurrence time of flares, we fixed the viscosity parameter α ~ 0.16.展开更多
Fast radio bursts(FRBs)are short pulses observed in radio frequencies usually originating from cosmological distances.The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154sugg...Fast radio bursts(FRBs)are short pulses observed in radio frequencies usually originating from cosmological distances.The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154suggests that at least some FRBs can be generated by magnetars.However,the majority of X-ray bursts from magnetars are not associated with radio emission.The fact that only in rare cases can an FRB be generated raises the question regarding the special triggering mechanism of FRBs.Here we report long time spin evolution of SGR J1935+2154 until the end of 2022.According to v and v,the spin evolution of SGR J1935+2154 could be divided into two stages.The first stage evolves relatively steady evolution until 2020 April 27.After the burst activity in2020,the spin of SGR J1935+2154 shows strong variations,especially for v.After the burst activity in 2022October,a new spin-down glitch with△v/v=(-7.2±0.6)×10^(-6)is detected around MJD 59876,which is the second event in SGR J1935+2154.At the end,spin frequency and pulse profile do not show variations around the time of FRB 200428 and radio bursts 221014 and 221021,which supply strong clues to constrain the trigger mechanism of FRBs or radio bursts.展开更多
If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets, their early afterglows may differ from those of...If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets, their early afterglows may differ from those of GRBs, and when the ultra-relativistic outflow inter- acts with the surrounding medium, there are two shocks formed, a forward shock (FS), and a reverse shock (RS). We calculate numerically the early afterglow powered by uniform jets, Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differential equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets, the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect, but in the stellar wind environment, the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets (Gaussian and power-law jets), where there are emission materials on the line of sight, the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic (in stellar wind).展开更多
The fast blue optical transients(FBOTs)are a new population of extragalactic transients of unclear physical origin.A variety of mechanisms has been proposed including failed supernova explosion,shock interaction with ...The fast blue optical transients(FBOTs)are a new population of extragalactic transients of unclear physical origin.A variety of mechanisms has been proposed including failed supernova explosion,shock interaction with a dense medium,young magnetar,accretion onto a compact object and stellar tidal disruption event,but none is conclusive.Here we report the discovery of a possible X-ray quasi-periodicity signal with a period of~250 s(at a significance level of 99.76%)in the brightest FBOT AT2018cow through the analysis of XMM-Newton/PN data.The signal is independently detected at the same frequency in the average power density spectrum from data taken from the Swift telescope,with observations covering from 6 to 37 days after the optical discovery,though the significance level is lower(94.26%).This suggests that the quasi-periodic oscillation(QPO)frequency may be stable over at least 1.1×10^(4)cycles.Assuming the~250 s QPO to be a scaled-down analog of that typically seen in stellar mass black holes,a black hole mass of~103–10^(5)solar masses could be inferred.The overall X-ray luminosity evolution could be modeled with a stellar tidal disruption by a black hole of~10^(4)solar masses,providing a viable mechanism to produce AT2018cow.Our findings suggest that other bright FBOTs may also harbor intermediate-mass black holes.展开更多
Insight-HXIUT is China's hrst X-ray astronomy satellite.It was launched on 15 June 2017 and is currently in service smoothly.Insight-HXMT has been used to scan the Galactic plane repeatedly,making pointing observa...Insight-HXIUT is China's hrst X-ray astronomy satellite.It was launched on 15 June 2017 and is currently in service smoothly.Insight-HXMT has been used to scan the Galactic plane repeatedly,making pointing observations to neutron stars and black holes,and monitor the whole sky continuously in the MeV band.Insight-HXMT is also very flexible in making ToO observations,with the response time from about 3 hours to within a day.So far more than 50 refereed publications have been made with data from its observations;many more publications have used the data or results of Insight-HXMT one way or another.The scientific impacts of Insight-HXMT have been growing rapidly since launch.We expect Insight-HXMT to continue to operate for several more years.展开更多
A pulsating ultraluminous X-ray source(PULX)is a new kind of pulsar(PSR)whose characteristics are different from all known neutron stars.The magnetic field of PULX is suspected to be the main reason to support its sup...A pulsating ultraluminous X-ray source(PULX)is a new kind of pulsar(PSR)whose characteristics are different from all known neutron stars.The magnetic field of PULX is suspected to be the main reason to support its supper Eddington luminosity of PULX.NGC 7793 P13,which is the second confirmed PULX,can be easily studied due to its nearby position and isolation from other sources in its host galaxy.In this paper,we calculate its magnetic field to be∼1.0×10^(12) G based on the continued observations from 2016 to 2020.The magnetic field evolution of NGC 7793 P13 is analyzed,which shows that the source has spent about 10^(4) yr for the field decaying from the simulated initial strength 4.0×10^(14) G to the present value.In case of an assumed constant accretion and the limitation of the companion mass,it will be a recycled PSR whose magnetic field is ∼10^(9) G and spin period is a few hundred milliseconds.We estimate the field strength of the other confirmed PULXs and find main range is 10^(13)-10^(14) G.Their positions of the magnetic field and spin period are around or below the magnetars.This is because these PULXs are in the binary systems and are with the spin-up rate that are 2-3 orders higher than the normal binary pulsars.We suggest that PULXs are the accreting magnetars whose multi-pole strong magnetic field can support the supper Eddington luminosity.They would be helpful for studying the evolution of the magnetars,the formation of the binary PSRs above the Eddington spin-up line,and the millisecond PSRs with the magnetic field stronger than ∼10^(9) G.展开更多
With the successful launch of Swift satellite, more and more data of early X-ray afterglows from short gamma-ray bursts have been collected. Some interesting features such as unusual afterglow light curves and unexpec...With the successful launch of Swift satellite, more and more data of early X-ray afterglows from short gamma-ray bursts have been collected. Some interesting features such as unusual afterglow light curves and unexpected X-ray flares are revealed. Especially, in some cases, there is a flat segment in the X-ray afterglow light curve. Here we present a simplified model in which we believe that the flattening part is due to energy injection from the central engine. We assume that this energy injection arises from the magnetic dipole radiation of a millisecond pulsar formed after the merger of two neutron stars. We check this model with the short GRB 060313. Our numerical results suggest that energy injection from a millisecond magnetar could make part of the X-ray afterglow light curve flat.展开更多
A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral...A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and γ-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.展开更多
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...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.展开更多
Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated fight curves and an X-ray burst from the X-ray burster 4...Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated fight curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which axe typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately.展开更多
By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of ^21Na(p,γ)^22Mg. The derived result shows that the effect of electron screening o...By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of ^21Na(p,γ)^22Mg. The derived result shows that the effect of electron screening on resonant reaction is prominent in astrophysical interesting temperature range. In conjunction with the experimental results, the recommended rates of^21Na(p,γ)^22 Mg would increase at least 10%, which undoubtedly affect the nucleosynthesis of some heavier nuclei in a variety of astrophysical sites.展开更多
Similar to the case of pulsars the magnetic axis and the spin axis of gamma-ray burst sources may not lie on the same line. This may cause the formation of a ring-like jet due to collimation of the precessing magnetic...Similar to the case of pulsars the magnetic axis and the spin axis of gamma-ray burst sources may not lie on the same line. This may cause the formation of a ring-like jet due to collimation of the precessing magnetic axis. We analyze the tail emission from such a jet, and find that it has a shallow decay phase with a temporal index of - 1/2 if the Lorentz factor of the ejecta is not very high, which is consistent with the shallow decay phase of some early X-ray afterglow detected by Swift. The ring-like jet has a tail cusp with sharp rising and very sharp decay. This effect can provide an explanation for the re-brightening and sharp decay of the X-ray afterglow'of GRB 050709.展开更多
Strange stars(SSs)are compact objects made of deconfined quarks.It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS.Her...Strange stars(SSs)are compact objects made of deconfined quarks.It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS.Here we suggest that the intriguing repeating fast radio bursts(FRBs)are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of materials accreted from its low-mass companion.The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario.Especially,the periodicity is attributed to the modulation of accretion rate through the disk instabilities.To account for a~16-day periodicity of the repeating FRB source of 180916.J0158+65,a Shakura-Sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3×10^(16)gs^(-1) is invoked.Our scenario,if favored by future observations,will serve as indirect evidence for the strange quark matter hypothesis.展开更多
As China’s first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15, 2017, is a wide-band(1-250 ke V) slat-collimator-based X-ray as...As China’s first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15, 2017, is a wide-band(1-250 ke V) slat-collimator-based X-ray astronomy satellite with the capability of all-sky monitoring in 0.2-3 Me V. It was designed to perform pointing, scanning and gamma-ray burst(GRB)observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed.Here we give an overview of the mission and its progresses, including payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and some preliminary results.展开更多
Through the use of the independently developed Thunderstorm Energetic Radiation Observation System(TEROS),observation experiments of rocket-triggered lightning energetic radiation(RLER)were conducted for the first tim...Through the use of the independently developed Thunderstorm Energetic Radiation Observation System(TEROS),observation experiments of rocket-triggered lightning energetic radiation(RLER)were conducted for the first time at the Field Experiment Base on Lightning Sciences,China Meteorological Administration from May 2021 to July 2021.A total of 17 X-ray bursts were detected during all of the 22 leader/return strokes.In this study,the energy,time,and direction characteristics of Xray burst and its relationships with the corresponding discharge parameters,such as the return stroke peak current,half-peak width,rise time,and interstroke time interval,as well as the associated physical processes,are analyzed and discussed.Results showed that energetic radiation is ubiquitous in triggered lightning and is closely related to the last downward leader phase before the return stroke.The photon energies were concentrated in tens to hundreds of ke V,and the average duration of RLER was approximately 27μs.Moreover,RLER exhibited directional property inconsistent with a vertical downward beam,which may be related to the development orientation of the lightning leader.The intensity of RLER was positively correlated with the return stroke peak current,indicating that it directly depends on the lightning intensity,but it would be modulated by the lightning channel conditions.The 17 RLER events showed 3 different time distribution patterns,namely,discrete,continuous,and discrete/continuous pulses,of which the discharge parameters were also different.The discrete pulse event had the longest duration,a small half-peak width,and a long interstroke time interval.Furthermore,all of these events occurred during the last several leader/return strokes.The continuous pulse event had a short duration and a small peak current.The discrete/continuous pulse event had a moderate duration and a large half-peak width and peak current.These three distinct time distribution patterns may be determined by different development types of lightning leaders.Our observations support the leader high-field runaway mechanism.展开更多
The future experimental campaign with the SAMURAI setup at RIKEN will explore a wide range of neutron-deficient nuclei with a particular focus on the most critical(p, γ) reaction rates relevant to the astrophysical r...The future experimental campaign with the SAMURAI setup at RIKEN will explore a wide range of neutron-deficient nuclei with a particular focus on the most critical(p, γ) reaction rates relevant to the astrophysical rp-process in type-I X-ray bursts(XRB). Intense radioactive-ion(RI) beams at an energy of a few hundred Me V/nucleon will be deployed to populate proton-unbound states in the nuclei of interest through the Coulomb excitation or nucleon-removal processes. The decay of these states into a proton and a heavy residue will be measured using complete kinematics and the information about time reversal proton-capture process will be obtained. This method will provide the vital experimental data on the resonances, which dominate the stellar(p, γ) reaction rates, as well as on the direct proton-capture process for some other cases. The experimental setup will utilize for the first time the High-Resolution90?-mode of the SAMURAI spectrometer in combination with the existing detection systems, including custom-designed Si-strip detectors for simultaneous detection and tracking of heavy ions and protons emitted from the target. The details of the experimental method and the utilized apparatus are discussed in this paper.展开更多
基金supported by the National Key R&D Program of China(2021YFA0718500)the National Natural Science Foundation of China under grants U2038106 and 12065017partially by the Jiangxi Provincial Natural Science Foundation under grant 20224ACB211001。
文摘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.
基金supported by Department of Physics and GXUNAOC Center for Astrophysics and Space Sciences,Guangxi UniversityThe National Natural Science Foundation of China(Nos.12027803,U1731239,12133003,12175241,U1938201,U1732266)the Guangxi Science Foundation(Nos.2018GXNSFGA281007,2018JJA110048).
文摘POLAR-2 is a gamma-ray burst(GRB)polarimeter that is designed to study the polarization in GRB radiation emissions,aiming to improve our knowledge of related mechanisms.POLAR-2 is expected to utilize an on-board polarimeter that is sensitive to soft X-rays(2-10 keV),called low-energy polarization detector.We have developed a new soft X-ray polari-zation detector prototype based on gas microchannel plates(GMCPs)and pixel chips(Topmetal).The GMCPs have bulk resistance,which prevents charging-up effects and ensures gain stability during operation.The detector is composed of low outgassing materials and is gas-sealed using a laser welding technique,ensuring long-term stability.A modulation factor of 41.28%±0.64% is obtained for a 4.5 keV polarized X-ray beam.A residual modulation of 1.96%±0.58% at 5.9 keV is observed for the entire sensitive area.
基金Supported by the National Natural Science Foundation of China
文摘We present a verification of the short-term predictions of solar X-ray bursts for the maximum phase (2000–2001) of Solar Cycle 23, issued by two prediction centers. The results are that the rate of correct predictions is about equal for RWC-China and WWA; the rate of too high predictions is greater for RWC-China than for WWA, while the rate of too low predictions is smaller for RWC-China than for WWA.
基金supported by the National Natural Science Foundation of China(Nos.11825504,11490562,and 11675229)the Major State Basic Research Development Program of China(No.2016YFA0400503)
文摘^56Cu is close to the waiting-point nucleus ^56Ni and lies on the rapid proton capture (rp) process path in Type I X-ray bursts (XRBs). In this work, we obtained a revised thermonuclear reaction rate of ^55Niep;cT56Cu in the temperature region relevant to XRBs. This rate was recalculated based on the recent experimental level structure in ^56Cu, the recently measured proton separation energy of Sp = 579.8(7.1) keV, together with shell-model calculation, and the mirror nuclear structure in ^56Co. The associated uncertainties in the rates were estimated by a Monte Carlo method. Our revised rate is significantly different from the recent results, which were partially based on experimental results;in addition, we found that a result in a previous work was incorrect. We recommend our revised rate to be incorporated in the future astrophysical network calculations.
文摘We study RXTE PCA data for the high mass X-ray binary source SMC X-1 between 2003–10 and 2003–12 when the source was in its high states.The source is found to be frequently bursting which can be seen as flares in lightcurves that occur at a rate of one every 800 s, with an average of 4–5 Type Ⅱ X-ray bursts per hour.We note that typically a burst was short, lasting for a few tens of seconds in addition to a few long bursts spanning more than a hundred seconds that were also observed.The flares apparently occupied 2.5% of the total observing time of 225.5 ks.We note a total of 272 flares with mean FWHM of the flare ~21 s.The rms variability and aperiodic variability are independent of flares.As observed, the pulse profiles of the lightcurves do not change their shape, implying that there is no change in the geometry of an accretion disk due to a burst.The hardness ratio and rms variability of lightcurves exhibit no correlation with the flares.The flare fraction shows a positive correlation with the peak-to-peak ratio of the primary and secondary peaks of the pulse profile.The observed hardening or softening of the spectrum cannot be correlated with the flaring rate but may be due to the interstellar absorption of X-rays as evident from the change in hydrogen column density(n_H).It is found that the luminosity of the source increases with the flaring rate.Considering that the viscous timescale is equal to the mean recurrence time of flares, we fixed the viscosity parameter α ~ 0.16.
基金supported by the National Key R&D Program of China(2021YFA0718500)from the Minister of Science and Technology of China(MOST)supports from the National Natural Science Foundation of China under grants 12173103,12003028,U2038101,U2038102 and 11733009+2 种基金supported by International Partnership Program of Chinese Academy of Sciences(grant No.113111KYSB20190020)the National SKA Program of China(2022SKA0130100)the China Manned Spaced Project(CMS-CSST-2021-B11)。
文摘Fast radio bursts(FRBs)are short pulses observed in radio frequencies usually originating from cosmological distances.The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154suggests that at least some FRBs can be generated by magnetars.However,the majority of X-ray bursts from magnetars are not associated with radio emission.The fact that only in rare cases can an FRB be generated raises the question regarding the special triggering mechanism of FRBs.Here we report long time spin evolution of SGR J1935+2154 until the end of 2022.According to v and v,the spin evolution of SGR J1935+2154 could be divided into two stages.The first stage evolves relatively steady evolution until 2020 April 27.After the burst activity in2020,the spin of SGR J1935+2154 shows strong variations,especially for v.After the burst activity in 2022October,a new spin-down glitch with△v/v=(-7.2±0.6)×10^(-6)is detected around MJD 59876,which is the second event in SGR J1935+2154.At the end,spin frequency and pulse profile do not show variations around the time of FRB 200428 and radio bursts 221014 and 221021,which supply strong clues to constrain the trigger mechanism of FRBs or radio bursts.
基金Supported by the National Natural Science Foundation of China.
文摘If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets, their early afterglows may differ from those of GRBs, and when the ultra-relativistic outflow inter- acts with the surrounding medium, there are two shocks formed, a forward shock (FS), and a reverse shock (RS). We calculate numerically the early afterglow powered by uniform jets, Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differential equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets, the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect, but in the stellar wind environment, the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets (Gaussian and power-law jets), where there are emission materials on the line of sight, the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic (in stellar wind).
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11822301,12192220,12192221 and 11833007)support from the NSFC(Grant No.12122306)+1 种基金support from the NSFC(Grant Nos.11733009 and U2031205)support by the science research grants from the China Manned Space Project through No.CMS-CSST-2021-A06。
文摘The fast blue optical transients(FBOTs)are a new population of extragalactic transients of unclear physical origin.A variety of mechanisms has been proposed including failed supernova explosion,shock interaction with a dense medium,young magnetar,accretion onto a compact object and stellar tidal disruption event,but none is conclusive.Here we report the discovery of a possible X-ray quasi-periodicity signal with a period of~250 s(at a significance level of 99.76%)in the brightest FBOT AT2018cow through the analysis of XMM-Newton/PN data.The signal is independently detected at the same frequency in the average power density spectrum from data taken from the Swift telescope,with observations covering from 6 to 37 days after the optical discovery,though the significance level is lower(94.26%).This suggests that the quasi-periodic oscillation(QPO)frequency may be stable over at least 1.1×10^(4)cycles.Assuming the~250 s QPO to be a scaled-down analog of that typically seen in stellar mass black holes,a black hole mass of~103–10^(5)solar masses could be inferred.The overall X-ray luminosity evolution could be modeled with a stellar tidal disruption by a black hole of~10^(4)solar masses,providing a viable mechanism to produce AT2018cow.Our findings suggest that other bright FBOTs may also harbor intermediate-mass black holes.
文摘Insight-HXIUT is China's hrst X-ray astronomy satellite.It was launched on 15 June 2017 and is currently in service smoothly.Insight-HXMT has been used to scan the Galactic plane repeatedly,making pointing observations to neutron stars and black holes,and monitor the whole sky continuously in the MeV band.Insight-HXMT is also very flexible in making ToO observations,with the response time from about 3 hours to within a day.So far more than 50 refereed publications have been made with data from its observations;many more publications have used the data or results of Insight-HXMT one way or another.The scientific impacts of Insight-HXMT have been growing rapidly since launch.We expect Insight-HXMT to continue to operate for several more years.
基金supported by the National Natural Science Foundation of China(12130342,12273030 and U1938107)。
文摘A pulsating ultraluminous X-ray source(PULX)is a new kind of pulsar(PSR)whose characteristics are different from all known neutron stars.The magnetic field of PULX is suspected to be the main reason to support its supper Eddington luminosity of PULX.NGC 7793 P13,which is the second confirmed PULX,can be easily studied due to its nearby position and isolation from other sources in its host galaxy.In this paper,we calculate its magnetic field to be∼1.0×10^(12) G based on the continued observations from 2016 to 2020.The magnetic field evolution of NGC 7793 P13 is analyzed,which shows that the source has spent about 10^(4) yr for the field decaying from the simulated initial strength 4.0×10^(14) G to the present value.In case of an assumed constant accretion and the limitation of the companion mass,it will be a recycled PSR whose magnetic field is ∼10^(9) G and spin period is a few hundred milliseconds.We estimate the field strength of the other confirmed PULXs and find main range is 10^(13)-10^(14) G.Their positions of the magnetic field and spin period are around or below the magnetars.This is because these PULXs are in the binary systems and are with the spin-up rate that are 2-3 orders higher than the normal binary pulsars.We suggest that PULXs are the accreting magnetars whose multi-pole strong magnetic field can support the supper Eddington luminosity.They would be helpful for studying the evolution of the magnetars,the formation of the binary PSRs above the Eddington spin-up line,and the millisecond PSRs with the magnetic field stronger than ∼10^(9) G.
基金Supported by the National Natural Science Foundation of China.
文摘With the successful launch of Swift satellite, more and more data of early X-ray afterglows from short gamma-ray bursts have been collected. Some interesting features such as unusual afterglow light curves and unexpected X-ray flares are revealed. Especially, in some cases, there is a flat segment in the X-ray afterglow light curve. Here we present a simplified model in which we believe that the flattening part is due to energy injection from the central engine. We assume that this energy injection arises from the magnetic dipole radiation of a millisecond pulsar formed after the merger of two neutron stars. We check this model with the short GRB 060313. Our numerical results suggest that energy injection from a millisecond magnetar could make part of the X-ray afterglow light curve flat.
基金the National Natural Science Foundation of China.
文摘A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and γ-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 10573002, 10778611, and 10873002) the National Basic Research Program of China (Grant No. 2009CB824800)+1 种基金the Research Foundation of Guangxi University (Grant No. M30520)the LCWR (Grant No. LHXZ200602)
文摘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.
基金Supported by the National Natural Science Foundation of China.
文摘Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated fight curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which axe typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately.
基金Project supported by the National Natural Science Foundation of China (Grant No 10347008), the Scientific Research and Fund of Sichuan Provincial Education Department of China (Grant No 2006A079) and the Science and Technological Foundation of China West Normal University.
文摘By using the new Coulomb screening model and most recent experimental results, this paper calculates the resonance reaction rates of ^21Na(p,γ)^22Mg. The derived result shows that the effect of electron screening on resonant reaction is prominent in astrophysical interesting temperature range. In conjunction with the experimental results, the recommended rates of^21Na(p,γ)^22 Mg would increase at least 10%, which undoubtedly affect the nucleosynthesis of some heavier nuclei in a variety of astrophysical sites.
基金Supported by the National Natural Science Foundation of China.
文摘Similar to the case of pulsars the magnetic axis and the spin axis of gamma-ray burst sources may not lie on the same line. This may cause the formation of a ring-like jet due to collimation of the precessing magnetic axis. We analyze the tail emission from such a jet, and find that it has a shallow decay phase with a temporal index of - 1/2 if the Lorentz factor of the ejecta is not very high, which is consistent with the shallow decay phase of some early X-ray afterglow detected by Swift. The ring-like jet has a tail cusp with sharp rising and very sharp decay. This effect can provide an explanation for the re-brightening and sharp decay of the X-ray afterglow'of GRB 050709.
基金partially supported by National SKA Program of China no.2020SKA0120300by the National Natural Science Foundation of China(grant nos.11903019,11873030,11833003,12041306,U1938201,U1838113)+1 种基金by the Strategic Priority Research Program of the Chinese Academy of Sciences(multi-waveband Gravitational Wave Universe,grant no.XDB23040000)by the science research grants from the China Manned Space Project with no.CMS-CSST-2021-B11.
文摘Strange stars(SSs)are compact objects made of deconfined quarks.It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS.Here we suggest that the intriguing repeating fast radio bursts(FRBs)are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of materials accreted from its low-mass companion.The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario.Especially,the periodicity is attributed to the modulation of accretion rate through the disk instabilities.To account for a~16-day periodicity of the repeating FRB source of 180916.J0158+65,a Shakura-Sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3×10^(16)gs^(-1) is invoked.Our scenario,if favored by future observations,will serve as indirect evidence for the strange quark matter hypothesis.
基金project funded by China National Space Administration(CNSA)and the Chinese Academy of Sciences(CAS)support from the National Key Research and Development Program of China(Grant No.2016YFA0400800)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA04010202,XDA04010300,and XDB23040400)the National Natural Science Foundation of China(Grant Nos.U1838201,and U1838102).
文摘As China’s first X-ray astronomical satellite, the Hard X-ray Modulation Telescope (HXMT), which was dubbed as Insight-HXMT after the launch on June 15, 2017, is a wide-band(1-250 ke V) slat-collimator-based X-ray astronomy satellite with the capability of all-sky monitoring in 0.2-3 Me V. It was designed to perform pointing, scanning and gamma-ray burst(GRB)observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed.Here we give an overview of the mission and its progresses, including payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and some preliminary results.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA17040503)the Basic Research Fund of the Chinese Academy of Meteorological Sciences(Grant No.2021Z011)。
文摘Through the use of the independently developed Thunderstorm Energetic Radiation Observation System(TEROS),observation experiments of rocket-triggered lightning energetic radiation(RLER)were conducted for the first time at the Field Experiment Base on Lightning Sciences,China Meteorological Administration from May 2021 to July 2021.A total of 17 X-ray bursts were detected during all of the 22 leader/return strokes.In this study,the energy,time,and direction characteristics of Xray burst and its relationships with the corresponding discharge parameters,such as the return stroke peak current,half-peak width,rise time,and interstroke time interval,as well as the associated physical processes,are analyzed and discussed.Results showed that energetic radiation is ubiquitous in triggered lightning and is closely related to the last downward leader phase before the return stroke.The photon energies were concentrated in tens to hundreds of ke V,and the average duration of RLER was approximately 27μs.Moreover,RLER exhibited directional property inconsistent with a vertical downward beam,which may be related to the development orientation of the lightning leader.The intensity of RLER was positively correlated with the return stroke peak current,indicating that it directly depends on the lightning intensity,but it would be modulated by the lightning channel conditions.The 17 RLER events showed 3 different time distribution patterns,namely,discrete,continuous,and discrete/continuous pulses,of which the discharge parameters were also different.The discrete pulse event had the longest duration,a small half-peak width,and a long interstroke time interval.Furthermore,all of these events occurred during the last several leader/return strokes.The continuous pulse event had a short duration and a small peak current.The discrete/continuous pulse event had a moderate duration and a large half-peak width and peak current.These three distinct time distribution patterns may be determined by different development types of lightning leaders.Our observations support the leader high-field runaway mechanism.
文摘The future experimental campaign with the SAMURAI setup at RIKEN will explore a wide range of neutron-deficient nuclei with a particular focus on the most critical(p, γ) reaction rates relevant to the astrophysical rp-process in type-I X-ray bursts(XRB). Intense radioactive-ion(RI) beams at an energy of a few hundred Me V/nucleon will be deployed to populate proton-unbound states in the nuclei of interest through the Coulomb excitation or nucleon-removal processes. The decay of these states into a proton and a heavy residue will be measured using complete kinematics and the information about time reversal proton-capture process will be obtained. This method will provide the vital experimental data on the resonances, which dominate the stellar(p, γ) reaction rates, as well as on the direct proton-capture process for some other cases. The experimental setup will utilize for the first time the High-Resolution90?-mode of the SAMURAI spectrometer in combination with the existing detection systems, including custom-designed Si-strip detectors for simultaneous detection and tracking of heavy ions and protons emitted from the target. The details of the experimental method and the utilized apparatus are discussed in this paper.