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.

Atlas of dynamic spectra of fast radio burst FRB 20201124A

Fast radio bursts(FRBs) are highly dispersed millisecond-duration radio bursts,[1,2]of which the physical origin is still not fully understood. FRB 20201124A is one of the most actively repeating FRBs. In this paper, we present the collection of 1863 burst dynamic spectra of FRB 20201124A measured with the Five-hundred-meter Aperture Spherical radio Telescope(FAST). The current collection, taken from the observation during the FRB active phase from April to June 2021, is the largest burst sample detected for any FRB so far. The standard PSRFITs format is adopted, including dynamic spectra of the burst, and the time information of the dynamic spectra, in addition, mask files help readers to identify the pulse positions are also provided. The dataset is available in Science Data Bank, with the link https://www.doi.org/10.57760/sciencedb.j00113.00076.

多翼离心风机叶轮的多目标优化试验研究

通过叶轮参数的优化来提升多翼离心风机的各种性能指标具有重要意义。研究运用正交试验分析的方法,通过单指标和多指标综合极差分析研究了叶轮进口角α、叶轮出口角β、叶轮内外径比D1/D2、进口段斜切深度比h/B对风机的最大风量、噪声、最大静压和全压效率的影响程度。研究表明:四个因素及其交互作用对不同指标的影响程度是不同的,不同因素的同一水平对不同指标并不一定都是最优的,其中出口角角度值影响程度最大;多指标综合评分分析法针对不同指标进行加权计算,得出最优方案为β(170),h/B (0.1),α(75),D1/D2(0.86);优化后方案的综合性能相比正交设计中方案最优值提升45.6%。

Constraints on generalized Chaplygin gas model including gamma-ray bursts

Generalized Chaplygin gas (whose equation of state is pGCG = -A/ραGCG) was proposed as a candidate for unification of dark energy and dark matter. We investigate constraints on this model with the latest observed data. We test the model with type-Ia supernovae (SNe Ia), cosmic microwave background (CMB) anisotropy, X-ray gas mass fractions in clusters, and gamma-ray bursts (GRBs). We calibrate the GRB luminosity relations without assuming any cosmological models using SNe Ia. We show that GRBs can extend the Hubble diagram to higher redshifts (z > 6). The GRB Hubble diagram is well behaved and delineates the shape of the Hubble diagram well. We measure As ≡ A/ρα+1GCG,0 = 0.68+0.04/-0.08 (where ρGCG,0 is the energy density today) and α = -0.22+0.15-0.13 at the 1σ confidence level using all the datasets. Our results rule out the standard Chaplygin gas model (α = 1) at the 3σ confidence level. The ΛCDM is allowed at the 2σ confidence level. We find that acceleration could have started at a redshift of z ～ 0.70. The concordance of the generalized Chaplygin gas model with the age estimate of an old high redshift quasar is found. In addition, we show that GRBs can break the degeneracy between the generalized Chaplygin gas model and the XCDM model.

Modeling the quasi-periodic oscillation of Swift J1644+57

A 200-second X-ray quasi-periodicity in the 2-8 ke V band from Swift J1644+57 was found by Reis et al.From the onset time of quasi-periodic oscillation(QPO),we show that Swift J1644+57 is a plunging event.This QPO may be related to discrete clumps from the accretion disk falling into a supermassive black hole,then the outflow in the jet may be also discontinuous.We estimate the lifetime of clumps to be about several hundreds seconds and the fraction of clumpy ejecta to be about 30% from the QPO.The other possible model involves the interface between the inflow and jet magnetosphere in the magnetically choked accretion flow.Theory and numerical simulations indicate that a magnetic Rayleigh-Taylor and Kelvin-Helmholtz unstable magnetospheric interface can produce a jet-disk QPO mechanism.This event may be the first evidence of jet-disk QPO.From observations,the two models are comparable.

FAST Observations of an Extremely Active Episode of FRB 20201124A.Ⅲ.Polarimetry

As the third paper in the multiple-part series,we report the statistical properties of radio bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode between the 25th and 28th of September 2021(UT).We focus on the polarization properties of536 bright bursts with S/N>50.We found that the Faraday rotation measures(RMs)monotonically dropped from-579to-605 rad m^(-2)in the 4 day window.The RM values were compatible with the values(-300 to-900 rad m^(-2))reported 4 months ago.However,the RM evolution rate in the current observation window was at least an order of magnitude smaller than the one(~500 rad m^(-2)day^(-1))previously reported during the rapid RM-variation phase,but is still higher than the one(≤1 rad m^(-2)day^(-1))during the later RM no-evolution phase.The bursts of FRB 20201124A were highly polarized with the total degree of polarization(circular plus linear)greater than 90%for more than 90%of all bursts.The distribution of linear polarization position angles(PAs),degree of linear polarization(L/I)and degree of circular polarization(V/I)can be characterized with unimodal distribution functions.During the observation window,the distributions became wider with time,i.e.,with larger scatter,but the centroids of the distribution functions remained nearly constant.For individual bursts,significant PA variations(confidence level 5σ)were observed in 33%of all bursts.The polarization of single pulses seems to follow certain complex trajectories on the Poincarésphere,which may shed light on the radiation mechanism at the source or the plasma properties along the path of FRB propagation.

FAST Observations of an Extremely Active Episode of FRB 20201124A.Ⅳ.Spin Period Search

We report the properties of more than 800 bursts detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25th-28th in a series of four papers.In this fourth paper of the series,we present a systematic search of the spin period and linear acceleration of the source object from both 996 individual pulse peaks and the dedispersed time series.No credible spin period was found from this data set.We rule out the presence of significant periodicity in the range between 1 ms and 100 s with a pulse duty cycle<0.49±0.08(when the profile is defined by a von-Mises function,not a boxcar function)and linear acceleration up to 300 m s^(-2)in each of the four one-hour observing sessions,and up to 0.6 m s^(-2)in all 4 days.These searches contest theoretical scenarios involving a 1 ms–100 s isolated magnetar/pulsar with surface magnetic field<10^(15)G and a small duty cycle(such as in a polar-cap emission mode)or a pulsar with a companion star or black hole up to 100 M_(⊙)and P_(b)>10 hr.We also perform a periodicity search of the fine structures and identify 53 unrelated millisecond-timescale“periods”in multicomponents with the highest significance of 3.9σ.The“periods”recovered from the fine structures are neither consistent nor harmonically related.Thus they are not likely to come from a spin period.We caution against claiming spin periodicity with significance below~4σwith multi-components from one-off FRBs.We discuss the implications of our results and the possible connections between FRB multi-components and pulsar microstructures.

The updated Bulk Lorentz Factors of Gamma-Ray Burst X-Ray Flares

X-ray flares are the most common phenomena in the afterglow phase of gamma-ray bursts(GRBs) in the Swift era,and are known as a canonical component in X-ray afterglows.In this work,we constrain the Lorentz factor of X-ray flares with an updated sample.We extensively search for X-ray light curves showing flare and jet break simultaneously.A smooth broken power law function is used to fit the jet breaks in 11 GRBs.We also use a smooth broken power law function to fit the profile of X-ray flares,and the total number of the flares is 20.We obtain the lower and upper limits of Lorentz factor(Γ_X) with the timescale,half-opening angle and mean luminosity of the X-ray flares for interstellar medium(ISM) and wind cases.The lower limits on Γ_X range from tens to a few hundred,and the upper limits are mainly about a few hundred.We also apply the limited Lorentz factor to test correlations of Γ_0-E_(γ,iso) and Γ_0-L_(γ,iso) for GRBs,and find X-ray flares in the ISM case are much more consistent with those of prompt emission than the wind case in a statistical sense for both correlations.X-ray flares are almost consistent with the trend in the correlations of Γ_0-E__(γ,iso)(L_(γ,iso)) for prompt GRBs,indicating X-ray flares and prompt bursts may have the same physical origin.

Scintillation Arc from FRB 20220912A

We present the interstellar scintillation analysis of fast radio burst(FRB)20220912A during its extremely active episode in 2022using data from the Five-hundred-meter Aperture Spherical Radio Telescope(FAST).We detect a scintillation arc in the FRB’s secondary spectrum,which describes the power in terms of the scattered FRB signals’time delay and Doppler shift.The arc indicates that the scintillation is caused by a highly localized region.Our analysis favors a Milky Way origin of the ionized interstellar medium(IISM)for the localized scattering medium but cannot rule out a host galaxy origin.We present our method for detecting the scintillation arc,which can be applied generally to sources with irregularly spaced bursts or pulses.These methods could help shed light on the complex interstellar environment surrounding the FRBs and in our Galaxy.