查看更多>>摘要：The study of a disturbed accretion disk holds great significance in the realm of astrophysics,as such events play a crucial role in revealing the nature of disk structure,the release of energy,and the generation of shock waves.Consequently,they can help explain the causes of X-ray emissions observed in black hole accretion disk systems.In this paper,we perturb the stable disk formed by spherical accretion around Kerr and Einstein-Gauss-Bonnet(EGB)black holes.This perturbation reveals one-and two-armed spiral shock waves around the black hole.We find a strong connection between these waves and the black hole spin parameter(a/M)and the EGB coupling constant(α).Specifically,we find that as α increases in the negative direction,the dynamics of the disk and the waves become more chaotic.Additionally,we observe that the angular momentum of the perturbing matter significantly affects mass accretion and the oscillation of the arising shock waves.This allows us to observe changes in QPO frequencies,particularly,perturbations with angular momentum matching the observed C-type low-frequency QPOs of the GRS 1915+105 source.Thus,we conclude that the possibility of the occurrence of shock waves within the vicinity of GRS 1915+105 is substantial.
查看更多>>摘要：In this study,we present an investigation of the newly discovered dwarf nova ASASSN-19oc during its superoutburst on 2019 June 2.We carried out detailed UBVRcIc-photometric observations and also obtained a spectrum on day 7 of the outburst,which shows the presence of hydrogen absorption lines commonly found in dwarf nova outbursts.Analysis of photometric data reveals the occurrence of early superhumps in the initial days of observations,followed by ordinary and late superhumps.We have accurately calculated the period of the ordinary superhumps as Pord=0.05681(10)days and determined the periods at different stages,as well as the rate of change of the superhump period(Pdot=(P)/P=8.1×10-5).Additionally,we have derived the mass ratio of the components(q=0.09),and estimated the color temperature during the outburst as～11,000 K,the distance to the system(d=560 pc)and absolute magnitude of the system in outburst(Mv=5.3).We have shown that outbursts of this star are very rare:based on brightness measurements on 600 archival photographic plates,we found only one outburst that occurred in 1984.This fact,as well as the properties listed above,convincingly shows that the variable ASASSN-19oc is a dwarf nova of WZ Sge type.
查看更多>>摘要：Theoretically,a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars.GRB 210323A is a short-duration gamma-ray burst(GRB)with a duration of lasting～1 s.The light curve of the prompt emission of GRB 210323A shows a signal-peaked structure and a cutoff power-law model can adequately fit the spectra with Ep=1826±747.More interestingly,it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of～104s,and then follows a rapid decay with a decay slope～3.2.This temporal feature is challenging by invoking the external shock mode.In this paper,we suggest that the observed long-lasting X-ray plateau emission is caused by the energy injection of dipole radiation from supra-massive magnetar,and the abrupt decay following the long-lasting X-ray plateau emission is explained by supra-massive magnetar collapsing into a black hole.It is the short GRB(SGRB)with the longest X-ray intemal plateau emission powered by a supra-massive neutron star.If this is the case,one can estimate the physical parameters of a supra-massive magnetar,and compare with other SGRBs.We also discuss the possible gravitational-wave emission,which is powered by a supra-massive magnetar and its detectability,and the possible kilonova emission,which is powered by r-process and magnetar spin-down to compare with the observed data.
查看更多>>摘要：Theories of modified gravity suggest that the propagation speed of gravitational waves(GW)vg may deviate from the speed of light c.A constraint can be placed on the difference between c and vg with a simple method that uses the arrival time delay between GW and electromagnetic wave simultaneously emitted from a burst event.We simulated the joint observation of GW and short gamma-ray burst signals from binary neutron star merger events in different observation campaigns,involving advanced LIGO(aLIGO)in design sensitivity and Einstein Telescope(ET)joint-detected with Fermi/GBM.As a result,the relative precision of constraint on vg can reach～10-17(aLIGO)and～10-18(ET),which are one and two orders of magnitude better than that from GW170817,respectively.We continue to obtain the bound of graviton mass mg ≤ 7.1(3.2)×10-20eV with aLIGO(ET).Applying the Standard-Model Extension test framework,the constraint on vg allows us to study the Lorentz violation in the nondispersive,nonbirefringent limit of the gravitational sector.We obtain the constraints of the dimensionless isotropic coefficients(s)(4)00at mass dimension d=4,which are-1×10-15＜(s)(4)00＜9×10-17 for aLIGO and-4×10-16＜(s)(4)00＜8×10-18 for ET.
查看更多>>摘要：With the exceptional sensitivity of the Five-hundred-meter Aperture Spherical radio Telescope,we conducted observations of the neutral hydrogen(H I)in the circumgalactic medium of Andromeda's(M31)satellite galaxies,specifically Andromeda Ⅱ,NGC 205,and NGC 185.Initially,three drift scans were executed for these satellites,with a detection limit of 4×1018cm-2(approximately 1.88×103M☉ of HI mass),followed by a more in-depth scan of a specific region.We discovered a C-shaped HI arc structure sharing a position and line-of-sight velocity similar to a stellar ring structure around Andromeda Ⅱ,hinting at a potential connection with Andromeda Ⅱ.In the context of NGC 205,we identified two mass concentrations in the northeast direction,which could be indicative of tidal streams resulting from the interaction between this galaxy and M31.These new lumps discovered could be very helpful in solving the missing interstellar medium problem for NGC 205.Observations regarding NGC 185 are consistent with previous studies,and we did not detect any additional HI material around this galaxy.These observational results enhance our understanding of the evolution of these satellite galaxies and provide insight into their historical interactions with the galaxy M31.
查看更多>>摘要：The image quality of a large field survey telescope with a fast focal ratio of the primary mirror is high sensitivity to the optical elements'misalignments and the primary mirror's deformations.To maintain good optical performance,the perturbations need to be aligned,and the tomographic reconstruction of these perturbations can be derived from wavefront sensing with multi-field points for alignment.This work undertakes a comprehensive examination related to the implementation and optimization of a multi-field split curvature wavefront sensing system,including defocus distance,signal pre-processing,deblending of overlapped doughnuts,field-dependent correction,and distorted coordinate correction.We also conduct experiments to demonstrate the application and performance of a multi-field split curvature wavefront sensing system in Mephisto.In the context of the decentering of the secondary mirror,the coefficient of determination(R)attains a high value of 0.993,indicating a robust linearity between the coma coefficients and the decentering of the secondary mirror.A comparative analysis of the simulated and experimental results shows that the difference between them is less than 0.1 λ.
Raja Adibah Raja Halim ShahNurul Shazana Abdul HamidMardina AbdullahAdlyka Annuar...
75-84页
查看更多>>摘要：A geomagnetic storm is a global disturbance of Earth's magnetosphere,occurring as a result of the interaction with magnetic plasma ejected from the Sun.Despite considerable research,a comprehensive classification of storms for a complete solar cycle has not yet been fully developed,as most previous studies have been limited to specific storm types.This study,therefore,attempted to present complete statistics for solar cycle 24,detailing the occurrence of geomagnetic storm events and classifying them by type of intensity(moderate,intense,and severe),type of complete interval(normal or complex),duration of the recovery phase(rapid or long),and the number of steps in the storm's development.The analysis was applied to data from ground-based magnetometers,which measured the Dst index as provided by the World Data Center for Geomagnetism,Kyoto,Japan.This study identified 211 storm events,comprising moderate(177 events),intense(33 events),and severe(1 event)types.About 36％of ICMEs and 23％of CIRs are found to be geoeffective,which caused geomagnetic storms.Up to four-step development of geomagnetic storms was exhibited during the main phase for this solar cycle.Analysis showed the geomagnetic storms developed one or more steps in the main phase,which were probably related to the driver that triggered the geomagnetic storms.A case study was additionally conducted to observe the variations of the ionospheric disturbance dynamo(Ddyn)phenomenon that resulted from the geomagnetic storm event of 2015 July 13.The attenuation of the Ddyn in the equatorial region was analyzed using the H component of geomagnetic field data from stations in the Asian sector(Malaysia and India).The variations in the Ddyn signatures were observed at both stations,with the TIR station(India)showing higher intensity than the LKW station(Malaysia).
查看更多>>摘要：Pulsar timing offers a comprehensive avenue for exploring diverse topics in physics and astrophysics.High-precision solar system planetary ephemeris is crucial for pulsar timing as it provides the positions and velocities of solar system planets including the Earth.However,it is inevitable that inherent inconsistencies exist in these ephemerides.Differences between various ephemerides can significantly impact pulsar timing and parameter estimations.Currently,pulsar timing highly depends on the JPL DE ephemeris,for instance,the Pulsar Timing Array data analysis predominantly utilizes DE436.In this study,we examine inconsistencies across various ephemeris series,including JPL DE,EPM,and INPOP.Notably,discrepancies emerge particularly between the current ephemeris DE436 and the earliest released ephemeris DE200,as well as the most recent ephemerides,e.g.,DE440,INPOP21A,and EPM2021.Further detailed analysis of the effects of ephemeris on geometric correction procedures for the conversion of measured topocentric times of arrival is presented in this study.Our researches reveal that variations in the Roemer delays across different ephemerides lead to distinct differences.The timing residuals and the fact that these discrepancies can be readily incorporated into the subsequent pulsar parameters,leading to inconsistent fitting estimates,suggest that the influence of errors in the ephemeris on the timing process might currently be underappreciated.
查看更多>>摘要：Accurate flux density calibration is essential for precise analysis and interpretation of observations across different observation modes and instruments.In this research,we first introduce the flux calibration model that incorporated in HiFAST pipeline,and designed for processing Hl 21cm spectra.Furthermore,we investigate different calibration techniques and assess the dependence of the gain parameter on the time and environmental factors.A comparison is carried out in various observation modes(e.g.,tracking and scanning modes)to determine the flux density gain(G),revealing insignificant discrepancies in G among different methods.Long-term monitoring data shows a linear correlation between G and atmospheric temperature.After subtracting the G-Temperature dependence,the dispersion of G is reduced to＜3％over a one-year timescale.The stability of the receiver response of Five-hundred-meter Aperture Spherical radio Telescope(FAST)is considered sufficient to facilitate HI observations that can accommodate a moderate error in flux calibration(e.g.,＞～5％)when utilizing a constant G for calibration purposes.Our study will serve as a useful addition to the results provided by Jiang et al.Detailed measurement of G for the 19 beams of FAST,covering the frequency range 1000-1500 MHz,can be found on the HiFAST homepage:https://hifast.readthedocs.io/fluxgain.
查看更多>>摘要：This paper presents the design,calibration,and survey strategy of the Fast Radio Burst(FRB)digital backend and its real-time data processing pipeline employed in the Tianlai Cylinder Pathfinder Array.The array,consisting of three parallel cylindrical reflectors and equipped with 96 dual-polarization feeds,is a radio interferometer array designed for conducting drift scans of the northern celestial semi-sphere.The FRB digital backend enables the formation of 96 digital beams,effectively covering an area of approximately 40 square degrees with the 3 dB beam.Our pipeline demonstrates the capability to conduct an automatic search of FRBs,detecting at quasi-real-time and classifying FRB candidates automatically.The current FRB searching pipeline has an overall recall rate of 88％.During the commissioning phase,we successfully detected signals emitted by four well-known pulsars:PSR B0329+54,B2021+51,B0823+26,and B2020+28.We report the first discovery of an FRB by our array,designated as FRB 20220414A.We also investigate the optimal arrangement for the digitally formed beams to achieve maximum detection rate by numerical simulation.
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