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Systematic analysis of low/hard state RXTE spectra of GX 339–4 to constrain the geometry of the system

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Research in Astronomy and Astrophysics 2018年第5期18卷 37-46页

作者： Kalyani Bagri Ranjeev Misra Anjali Rao Jagdish Singh Yadav Shiv Kumar Pandey Pt. Ravishankar Shukla University Raipur Chhattisgard 492010 India Inter-University Centre for Astronomy and Astrophysics Ganeshkhind Pune 411007 India Tata Institute of Fundamental Research Colaba Mumbai 400005 India

One of the popular models for the low/hard state of black hole binaries is that the standard accretion disk is truncated and the hot inner region produces, via Comptonization, hard X-ray *** is supported by the value of the high energy photon index, which is often found to be small,～ 1.7（〈 2）, implying that the hot medium is starved of seed photons. On the other hand, the suggestive presence of a broad relativistic Fe line during the hard state would suggest that the accretion disk is not truncated but extends all the way to the innermost stable circular orbit. In such a case, it is a puzzle why the hot medium would remain photon starved. The broad Fe line should be accompanied by a broad smeared reflection hump at ～ 30 ke V and it may be that this additional component makes the spectrum hard and the intrinsic photon index is larger, i.e. 〉2. This would mean that the medium is not photon deficient, reconciling the presence of a broad Fe line in the observed hard state. To test this hypothesis,we have analyzed the RXTE observations of GX 339–4 from the four outbursts during 2002–2011 and identify observations when the system was in the hard state and showed a broad Fe line. We have then attempted to fit these observations with models, which include smeared reflection, to understand whether the intrinsic photon index can indeed be large. We find that, while for some observations the inclusion of reflection does increase the photon index, there are hard state observations with a broad Fe line that have photon indices less than 2.

关键词： accretion accretion disks - stars black holes - X-rays binaries - X-rays individual(GX 339-4)

Dynamics of coastline changes in Mexico

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Journal of Geographical Sciences 2019年第10期29卷 1637-1654页

作者： VALDERRAMA-LANDEROS Luis H. MARTELL-DUBOIS Raúl RESSL Rainer SILVA-CASARíN Rodolfo CRUZ-RAMíREZ Cesia J. MUNOZ-PEREZ Juan J. National Commission for the Knowledge and Use of Biodiversity Liga Periferico-Insurgentes Sur 4903 Col. Parques del Pedregal Del. Tlalpan Ciudad de Mexico. C.P. 14010 Mexico Instituto de Ingeniería UNAM Circuito Escolar s/n Ciudad UniversitariaDelegacion Coyoacan Ciudad de Mexico C.P. 04510 Mexico Physical Oceanography Cadiz University Dpto.de Física Aplicada CASEM11150 Puerto Real (Cadiz) Spain

The goal of our work was to locate and quantify changes that occurred in 66% of the Mexican coastline, based on four land cover maps generated by the Mexican Mangrove Monitoring System(SMMM) of the National Commission for the Knowledge and Use of Biodiversity(CONABIO) for the years 1970/81, 2005, 2010, and 2015. Our results showed overall dominance of erosion over accretion processes, beaches being the most affected coastal land cover. Emphasis was placed on identification and description of coastline sites in which land was either continuously lost(erosion) or gained(accretion) during the studied time periods. These sites were defined as continuous unidirectional dynamic sites and were compared with previous knowledge about the geodynamics of Mexican coasts. Continuous unidirectional dynamic sites were distributed throughout the study area and within all land cover types, but predominantly corresponded to areas covered by mangroves in the states of Campeche and Nayarit. Finally, we found an intensification of coastal erosion-accretion processes over time;coastline change rates having duplicated between the earliest(1970/81–2005) and the two more recent(2005–2010, and 2010–2015) analysed time periods, with erosion rates for each corresponding period of –3 m/yr,–7.5 m/yr, and –7.3 m/yr,and accretion rates of 2.8 m/yr, 7.3 m/yr, and 6.9 m/yr, respectively.

关键词： changes in Mexican coastline Mexico coast erosion coast accretion

Reanalysis of the RXTE observations of the black-hole candidate XTE J1650-500 in the 2001/2002 outburst

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Research in Astronomy and Astrophysics 2012年第3期12卷 269-286页

作者： Li-Hong Yan Jian-Cheng Wang National Astronomical Observatories/Yunnan Observatory Chinese Academy of SciencesKunming 650011China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650011China Graduate University of Chinese Academy of Sciences Beijing 100049China

We present the results of the spectral fits made to 59 Rossi X-ray Timing Explorer （RXTE） observations of the Galactic X-Ray Black-Hole Candidate XTE J1650–500 covering the first 30d of its 2001/2002 outburst when the source was in a transition from the hard state to the soft state. The photon spectra can be well fit- ted with a phenomenological model of a power-law/cutoff power-law and a physical model of bulk-motion Comptonization. The spectral properties smoothly evolve away from the hard state and then stay in the soft state. The fitting results of the physical model reveal the peak of the burst had a flux of 2.90 × 10-8 erg cm-2 s-1 in the 2–100 keV energy range and was observed on 2001 Sep. 9; it transitioned to the hard state. The total flux decays by a factor of ～3 as it evolves into the soft state. The photon index Γ increases from ～1.5 in the hard state and stays at ～2.5 in the soft state. We found that the effective area of the high-energy X-ray emission region （the Compton cloud） decreases, i.e. the area of the Compton cloud decreases by a factor of ～23 during the transition from the hard state to the soft state. Combining the new radio and quasi-periodic oscillation studies, the model of total flux in the 2–100 keV energy range, the jet emission and the timing analysis during the state transition, we suggest a possible geometry and evolution for the （jet＋corona＋disk） system, like that proposed by Kalemci et al. based on enhanced lags and peak frequency shift during the transition.

关键词： accretion accretion disks—black hole physics—X-rays binaries: in- dividual (XTE J1650–500)—X-rays: stars

Gravitational wave radiation from a double white dwarf system inside our galaxy: a potential method for seeking strange dwarfs

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Research in Astronomy and Astrophysics 2009年第7期9卷 745-750页

作者： Zhan-Kui Lu Shi-Wei Wu Zhi-Cheng Zeng Department of Astronomy Nanjing University Nanjing 210008 China

Like the investigation of double white dwarf （DWD） systems, strange dwarf （SD） - white dwarf （WD） system evolution in Laser Interferometer Space Antenna （LISA）＇s absolute amplitude-frequency diagram is investigated. Since there is a strange quark core inside an SD, SDs＇ radii are significantly smaller than the value predicted by the standard WD model, which may strongly affect the gravitational wave （GW） signal in the mass-transferring phases of binary systems. We study how an SD-WD binary evolves across LISA＇s absolute amplitude-frequency diagram. In principle, we provide an executable way to detect SDs in the Galaxy＇s DWD systems by radically new windows offered by GW detectors.

关键词： accretion accretion disks - binaries close - dense matter - gravitational waves

Variability of Young Stellar Objects in the Perseus Molecular Cloud

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Research in Astronomy and Astrophysics 2023年第7期23卷 174-196页

作者： Xiao-Long Wang Min Fang Gregory J.Herczeg Yu Gao Hai-Jun Tian Xing-Yu Zhou Hong-Xin Zhang Xue-Peng Chen Purple Mountain Observatory Chinese Academy of SciencesNanjing 210023China University of Chinese Academy of Sciences Beijing 100049China School of Astronomy and Space Science University of Science and Technology of ChinaHefei 230026China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy Peking UniversityBeijing 100871China Department of Astronomy Xiamen UniversityXiamen 361005China School of Science Hangzhou Dianzi UniversityHangzhou 310018China Key Laboratory for Research in Galaxies and Cosmology Department of AstronomyUniversity of Science and Technology of ChinaHefei 230026China

We present an analysis of 288 young stellar objects(YSOs)in the Perseus molecular cloud that have well defined g and r-band lightcurves from the Zwicky Transient *** the 288 YSOs,238 sources(83%of our working sample)are identified as variables based on the normalized peak-to-peak variability metric,with variability fraction of 92%for stars with disks and 77%for the diskless *** variables are classified into different categories using the quasiperiodicity(Q)and flux asymmetry(M)***-three variables are classified as strictly periodic objects that are well phased and can be attributed to spot modulated stellar *** also identify 22 bursters and 25 dippers,which can be attributed to accretion burst and variable extinction,*** with disks tend to have asymmetric and non-repeatable lightcurves,while the YSOs without disks tend to have(quasi)periodic *** periodic variables have the steepest change in g versus g-r,while bursters have much flatter changes than dippers in g versus *** and quasiperiodic variables display the lowest variability *** models suggest that the variability amplitudes of periodic variables correspond to changes of the spot coverage of 30%-40%,burster variables are attributed to accretion luminosity changes in the range of L_(acc)/L_(*)=0.1-0.3,and dippers are due to variable extinction with A_(V)changes in the range of 0.5-1.3 mag.

关键词： stars:variables:general stars:late-type stars:emission-line Be (stars:)starspots accretion accretion disks

The Spin Measurement of MAXI J0637-430:a Black Hole Candidate with High Disk Density

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Research in Astronomy and Astrophysics 2023年第7期23卷 277-287页

作者： Nan Jia Ye Feng Yu-Jia Song Jun Yang Jieun Yuh Pei-Jun Huang Li-Jun Gou Key Laboratory for Computational Astrophysics National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China Shanghai American School Puxi Campus Shanghai 201107China Shenzhen Yaohua Experimental School Shenzhen 518034China

The Galactic black hole candidate MAXI J0637-430 was first discovered by MAXI/GSC on 2019 November *** study the spectral properties of MAXI J0637-430 by using the archived NuSTAR data and Swift/XRT *** fitting the eight spectra by using a disk component and a powerlaw component model with absorption,we select the spectra with relatively strong reflection components for detailed X-ray reflection *** the most state-of-art reflection model,relxillCp,the spectral fitting measures a black hole spin a_(*)>0.72 and the inclination angle of the accretion disk i=46.1_(-5.3)^(+4.0)degrees,at a 90%confidence *** addition,the fitting results show an extreme supersolar iron *** with the fitting results of reflection model reflionx_hd,we consider that this unphysical iron abundance may be caused by a very high-density accretion disk(n_(e)>2.34×10^(21)cm^(-3))or a strong Fe K_(α) emission *** soft excess is found in the soft state spectral fitting results,which may be an extra free-free heating effect caused by high density of the accretion ***,we discuss the robustness of black hole spin obtained by X-ray reflection *** result of relatively high spin is self-consistent with broadened Fe K_(α) *** abundance and disk density have no effect on the spin results.

关键词： black hole physics X-rays:binaries accretion accretion disks

Study on the X-Ray Re-brightening Signature of GRB 220117A

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Research in Astronomy and Astrophysics 2023年第11期23卷 118-124页

作者： Li-Tao Zhao School of Mathematics and Science Hebei GEO UniversityShijiazhuang 050016China

The Swift/XRT detected the X-ray afterglow of long burst GRB 220117A,which began to rebrighten 300 s after triggering and followed a single power-law decay segment after thousands of seconds of the orbital observation *** segment is different from the shallow decay segment(plateau)and flare,and may belong to a giant X-ray *** investigated this segment by the fall-back accretion model and found that the model can interpret this segment with reasonable parameter *** this physical model scenario,the fall-back accretion rate reaches a peak value~1.70×10~(-5)M_⊙s~(-1)around 300 s in the central engine frame,which is compatible with the late mass supply rate of some low-metallicity massive progenitor *** initial black hole(BH)spin is a_0=0.64_(-0.26)~(+0.24)and implies that this re-brightening signature requires a larger BH *** total accretion mass during the fall-back process is M_(acc)=(3.09±0.02)×10~(-2)M_⊙.The jet energy from the fall-back accretion is(9.77±0.65)×10~(52)erg,with a ratio of 0.066 to the isotropic-equivalent radiation energies of the GRB prompt phase in the 1-10~4 keV *** fall-back radius r_p corresponding to the peak time of fall-back t_p is(3.16±0.05)×10~(10)cm,which is consistent with the typical radius of Wolf-Rayet *** summary,our results provide additional support for the origin of the long burst from the core collapse of Wolf-Rayet stars,and its late central engine activity is likely due to the fall-back accretion process.

关键词： accretion accretion disks black hole physics (stars:)gamma-ray burst:general

Bare Strange Stars Might Not Be Bare

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Chinese Physics Letters 1998年第12期15卷 934-936页

作者： XU Ren-xin QIAO Guo-jun Department of Geophysics Peking UniversityBeijing 100871 Chinese Academy of Sciences-Peking University Joint Beijing Astrophysical Center Beijing 100871

It is proposed that the bare strange matter stars might not be bare,and the observed pulsars might be in fact the bare strange *** intensely magnetized strange matter stars rotate,the induced unipolar electric fields would be large enough to construct *** situation is very similar to that discussed by many authors for rotating neutron ***,the strange stars with accretion crusts in binaries could act as x-ray pulsars or x-ray *** are some advantages if pulsars are bare strange stars.

关键词： stars crust accretion

Modeling the quasi-periodic oscillation of Swift J1644+57

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Research in Astronomy and Astrophysics 2020年第2期20卷 31-36页

作者： Meng-Meng Zheng Shuang-Xi Yi Fa-Yin Wang Yuan-Chuan Zou School of Physics and Physical Engineering Qufu Normal UniversityQufu 273165China School of Astronomy and Space Science Nanjing UniversityNanjing 210093China School of Physics Huazhong University of Science and TechnologyWuhan 430074China

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

关键词： accretion accretion discs gamma-ray burst:general radiation mechanism:non-thermal