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1.
We show that aperiodic and quasiperiodic variability of bright LMXBs – atoll and Z‐sources – on ∼ sec‐msec time scales is caused primarily by variations of the luminosity of the boundary layer. The emission of the accretion disk is less variable on these time scales and its power density spectrum follows P disk(f ) ∝ f –1 law, contributing to observed flux variation at low frequencies and low energies only. The kHz QPOs have the same origin as variability at lower frequencies, i.e. independent of the nature of the “clock”, the actual luminosity modulation takes place on the neutron star surface. The boundary layer spectrum remains nearly constant in the course of the luminosity variations and is represented to certain accuracy by the Fourier frequency resolved spectrum. In the investigated range of ∼ (0.1 – 1) Edd it depends weakly on the global mass accretion rate and in the limit ∼ Edd is close toWien spectrum with kT ∼ 2.4 keV. Its independence on the global value of lends support to the theoretical suggestion by Inogamov & Sunyaev (1999) that the boundary layer is radiation pressure supported. Based on the knowledge of the boundary layer spectrum we attempt to relate the motion along the Z‐track to changes of physically meaningful parameters. Our results suggest that the contribution of the boundary layer to the observed emission decreases along the Z‐track from conventional ∼50% on the horizontal branch to a rather small number on the normal branch. This decrease can be caused, for example, by obscuration of the boundary layer by the geometrically thickened accretion disk at ∼ Edd. Alternatively, this can indicate significant change of the structure of the accretion flow at ∼ Edd and disappearance of the boundary layer as a distinct region of the significant energy release associated with the neutron star surface. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
In this paper, we improve the previous work on the MHD Alfvén wave oscillation model for the neutron star (NS) kHz quasi‐periodic oscillations (QPOs), and compare the model with the updated twin kHz QPO data. For the 17 NS X‐ray sources with the simultaneously detected twin kHz QPO frequencies, the stellar mass M and radius R constraints are given by means of the derived parameter A in the model, which is associated with the averaged mass density of the star as 〈ρ 〉 = 3M /(4πR3) ≃ 2.4 × 1014 (A /0.7)2 g/cm3, and we also compare the M ‐R constraints with the stellar equations of state. Moreover, we also discuss the theoretical maximum kHz QPO frequency and maximum twin peak separation, and some expectations on SAX J1808.4–3658 are mentioned, such as its highest kHz QPO frequency ∼ 870 Hz, which is about 1.4–1.5 times less than those of the other known kHz QPO sources. The estimated magnetic fields for both Z sources (about Eddington accretion rate ) and Atoll sources (∼ 1% ) are approximately ∼109 G and ∼108 G, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
The polarization from a spot orbiting around Schwarzschild and extreme Kerr black holes is studied. We assume different models of local polarization. Firstly, as a toy model we set the local polarization vector either normal to the disc plane, or perpendicular to the toroidal magnetic field. Then we examine the more realistic situation with a spot arising due to the emission from the primary source above the disc. We employ either Rayleigh single scattering or Compton multiple scattering approximations. The time dependence of the degree and angle of polarization during the spot revolution is examined as a function of the observer's inclination angle and black hole angular momentum. The gravitational and Doppler shifts, lensing effect as well as time delays are taken into account. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
P. Kaaret 《Astronomische Nachrichten》2008,329(2):202-205
I discuss open questions regarding accreting black holes in binary systems, focusing on two questions: can we measure the spins of black holes and what is the nature of the ultraluminous X‐ray sources. XMM‐Newton could make significant strides in answering these questions and others over the next ten years. I suggest two observational programs designed to help increase our understanding of accreting black holes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
C.M. Zhang 《Astronomische Nachrichten》2009,330(4):398-403
The kHz quasi‐periodic oscillations (QPOs) have been detected by the RXTE satellite in about thirty neutron stars (NSs) in low mass X‐ray binaries (LMXBs), which are usually interpreted to be related to the Keplerian motions in the orbit close to NS surface where the accreted matter is sucked onto the star. Based on the MHD Alfvén wave oscillation model and the relativistic precession model for the neutron star (NS) kHz QPOs, estimations of mass M and radius R of some NSs are given, which can give clues to evaluate the models. Furthermore, comparisons with theoretical M ‐R relations by stellar equations of state (EOSs) are presented (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
We collect the data of twin kilohertz quasi‐periodic oscillations (kHz QPOs) published before 2012 from 26 neutron star (NS) low‐mass X‐ray binary (LMXB) sources, then we analyze the centroid frequency (ν) distribution of twin kHz QPOs (lower frequency ν1 and upper frequency ν2) both for Atoll and Z sources. For the data without shift‐and‐add, we find that Atoll and Z sources show different distributions of ν1, ν2 and ν2/ν1, but the same distribution of Δν (difference of twin kHz QPOs), which indicates that twin kHz QPOs may share the common properties of LXMBs and have the same physical origins. The distribution of Δν is quite different from a constant value, so is ν 2/ν1 from a constant ratio. The weighted mean values and maxima of ν1 and ν2 in Atoll sources are slightly higher than those in Z sources. We also find that shift‐and‐add technique can reconstruct the distributions of ν1 and Δν. The K‐S test results of ν1 and Δν between Atoll and Z sources from data with shift‐and‐add are quite different from those without it, and we think that this may be caused by the selection biases of the sample. We also study the properties of the quality factor (Q) and the root‐meansquared (rms) amplitude of 4U 0614+09 with data from the two observational methods, but the errors are too big to make a robust conclusion. The NS spin frequency (νs) distribution of 28 NS‐LMXBs show a bigger mean value (∼408 Hz) than that (∼281 Hz) of the radio binary millisecond pulsars (MSPs), which may be due to the lack of the spin detections from Z sources (systematically lower than 281 Hz). Furthermore, on the relations between the kHz QPOs and NS spin frequency νs, we find the approximate correlations of the mean values of Δν with NS spin and its half, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
7.
《Astronomische Nachrichten》2017,338(2-3):227-233
For the past 17 years, both XMM ‐Newton and Chandra have brought the powerful combination of high spatial and spectral resolution to the study of black hole systems. Each of these attributes requires special consideration—in comparison to lower spatial resolution charge‐coupled device (CCD)‐ quality spectra—when modeling observations obtained by these spacecraft. A good understanding of the high‐resolution spectra is in fact required to model properly lower resolution CCD spectra, with the reflection grating spectrometer (RGS ) instrument on XMM ‐Newton maintaining the highest “figure of merit” at soft X‐ray energies for all missions flying or currently planned for the next decade. Thanks to its even higher spectral resolution, the use of Chandra high‐energy transmission gratings (HETGs ), albeit with longer integration times, allows for one to bring further clarity to RGS studies. A further promising route for continued studies is the combination of high spectral resolution at soft X‐rays, via RGS and/or HETG , with contemporaneous broadband coverage extending to hard X‐rays (e.g., NuSTAR or INTEGRAL spectra). Such studies offer special promise for answering fundamental questions about accretion in black hole systems; however, they have received only moderate consideration to date. This may be due in part to the difficulty of analyzing high‐resolution spectra. In response, we must continue to develop software tools that make the analysis of high‐resolution X‐ray spectra more accessible to the wider astrophysics community. 相似文献
8.
Almost all low‐mass black hole X‐ray binaries are transient sources. Most of these sources show a hysteresis: they evolve from the low‐hard state through intermediate state(s) into the high‐soft state and then return to the hard state at lower luminosity, again passing through the intermediate states. However, there are outbursts that remain in the hard state (so called “failed” outbursts). While mean X‐ray spectra allow us to study the time‐averaged spectral shape, we need to make use of “variability spectra,” like, for example, covariance spectra, to investigate the variability of individual spectral components on different time scales. Comprehensive studies of covariance spectra of a sample of black hole X‐ray binaries observed in the low‐hard state of “normal” outbursts revealed an increase of the covariance ratios toward lower energies that has been interpreted as the sign of additional disk variability on long time scales. In the case of GX 339‐4, we found that the covariance ratio increases and steeps during outburst decay, consistent with increased disk instabilities. There are two sources (H 1743‐322 and GS 1354‐64) that do not show an increase toward lower energies in their covariance ratio. We show that there is no correlation between the shape of the covariance ratio and the amount of fractional rms variability. Both these sources have been observed during “failed” outbursts and their photon indices are at the hard end of the photon index range usually observed in black hole X‐ray binaries. 相似文献
9.
J. Greiner R. Schwarz C. Tappert R.E. Mennickent K. Reinsch G. Sala 《Astronomische Nachrichten》2010,331(2):227-230
We summarise our optical monitoring program of VY Scl stars with the SMARTS telescopes, and triggered X‐ray as well as optical observations after/during state transitions of V504 Cen and VY Scl (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
The X‐ray emission from accreting black hole (BH) systems displays strong variability. Short reverberation lags are expected between the primary hard X‐ray continuum and the reprocessed disk emission. These lags depend on light‐travel distances, thus offering the opportunity to map the geometry of the innermost accretion flow. X‐ray reverberation lags have been observed in several BH accreting systems. In radio‐quiet active galactic nuclei (AGN), these lags scale with BH mass and point to a reprocessing region located close to the comptonizing X‐ray corona. On the other hand, reverberation lags detected in the hard state of some BH X‐ray binaries (BHXRB) suggest a different accretion flow geometry than in AGN, showing evidence of evolution as a function of luminosity. 相似文献
11.
G. Matt 《Astronomische Nachrichten》2006,327(10):949-956
General Relativity effects (gravitational redshift, light bending, …) strongly modify the characteristics of the lines emitted close to the Black Hole in Active Galactic Nuclei and Galactic Black Hole systems. These effects are reviewed and illustrated, with particular emphasis on line emission from the accretion disc. Methods, based on the iron line, to measure the two astrophysically relevant parameters of a Black Hole, the mass and spin, are briefly discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
Using the recently published data of twin kHz quasi‐period oscillations (QPOs) in neutron stars of low‐mass X‐ray binaries (LMXBs), we study the different profiles between bright Z sources and less luminous Atoll sources. The quality factors of upper kHz QPOs show a narrow distribution both for Z sources and Atoll sources, which concentrate at 7.98 and 9.75, respectively. The quality factors of lower kHz QPOs show a narrow distribution for Z sources and a broader distribution for Atoll sources, which concentrate at 5.25 and 86.22, respectively. In order to investigate the relation between the quality factor and the peak frequency of kHz QPOs, we fit the data with power‐law, linear, and exponential functions, respectively. There is an obvious trend that the quality factors increase with the peak frequencies both for upper and lower QPOs. The implications of our results are discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
David M. Russell Daniel M. Bramich Fraser Lewis Aisha AlMannaei Thabet Al Qaissieh Ahlam Al Qasim Aisha Al Yazeedi Maria Cristina Baglio Federico Bernardini Nour Elgalad Aldrin Gabuya Jean‐Pierre Lasota Alejandro Palado Paul Roche Hinna Shivkumar Silviu‐Marian Udrescu Guobao Zhang 《Astronomische Nachrichten》2019,340(4):278-283
Disc instability models predict that for X‐ray binaries in quiescence, there should be a brightening of the optical flux prior to an X‐ray outburst. Tracking the X‐ray variations of X‐ray binaries in quiescence is generally not possible, so optical monitoring provides the best means to measure the mass accretion rate variability between outbursts, and to identify the beginning stages of new outbursts. With our regular Faulkes Telescope/Las Cumbres Observatory (LCO) monitoring we are routinely detecting the optical rise of new X‐ray binary outbursts before they are detected by X‐ray all‐sky monitors. We present examples of detections of an optical rise in X‐ray binaries prior to X‐ray detection. We also present initial optical monitoring of the new black hole transient MAXI J1820+070 (ASASSN‐18ey) with the Faulkes, LCO telescopes, and Al Sadeem Observatory in Abu Dhabi, UAE. Finally, we introduce our new real‐time data analysis pipeline, the “X‐ray Binary New Early Warning System (XB‐NEWS)” which aims to detect and announce new X‐ray binary outbursts within a day of first optical detection. This will allow us to trigger X‐ray and multiwavelength campaigns during the very early stages of outbursts, to constrain the outburst triggering mechanism. 相似文献
14.
We report on two XMM‐Newton and simultaneous INTEGRAL observations of the microquasar GRO J1655‐40 during its 2005 outburst. The source was most probably in its high‐soft state during both observations. There is evidence for the presence of both a relativistically broadened Fe line providing strong support for the existence of a spinning black hole, and a highly photo‐ionized absorber. The photo‐ionized absorber is responsible for strong K absorption lines of Fe XXV and Fe XXVI in the EPIC pn spectra. The parameters of the highly‐ionized absorber were different during the two observations. A less ionized absorber is present in the second observation, where the 0.5–200 keV luminosity of GRO J1655‐40 decreased by around a half. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
. Balman 《Astronomische Nachrichten》2019,340(4):296-301
Flicker noise and its variations in accreting systems have been a diagnostic tool in understanding accretion disk structure and state transitions. I present broadband noise variations of nonmagnetic cataclysmic variables (CVs) in comparison with magnetic CVs (MCV) extrapolating the comparisons into X‐ray binaries (XRB), mostly in the X‐ray wavelengths. CVs demonstrate band‐limited noise in the UV and X‐ray energy bands (and also optical), which can be adequately explained in the framework of the model of propagating fluctuations). The detected frequency breaks in the nonmagnetic CVs are in the range 1–6 mHz in quiescence and indicate an optically thick disk truncation (i.e., transition) showing the existence of advective (ADAF‐like) hot flows in the inner regions. Analysis of other available data (e.g., SS Cyg, SU UMa, WZ Sge, and Z Cha) reveals that during the outburst the inner disk radius moves toward the white dwarf and recedes as the outburst declines (with some exceptions) while changes in the X‐ray energy spectrum are also observed. Cross‐correlations between the simultaneous optical, UV, and X‐ray light curves show time lags consistent with truncated optically thick disk‐like and ADAF‐like hot flows in the inner disk. I also discuss the hysteresis effect in dwarf novae and show that the X‐ray temperatures and break frequencies anticorrelate indicating the energy exchange in the disk flow as the accretion state of the source changes. 相似文献
16.
A. Kotrlov E. &#x;rmkov G. Trk K. Goluchov J. Hork O. Straub 《Astronomische Nachrichten》2019,340(1-3):112-115
We study frequencies of axisymmetric and non‐axisymmetric epicyclic modes of accretion disk oscillations and explore the influence of pressure forces present in the disk. We utilize both approximate analytic methods and methods dealing with exact numerical solutions. Our investigation implies consequences for estimations of black hole spin in the three Galactic microquasars, namely GRS 1915+105, GRO J1655‐40, and XTE J1550‐564, which have been carried out based on several models of 3:2 high‐frequency quasiperiodic oscillations (QPOs). In the particular case of 3:2 epicyclic resonance model, the presence of pressure forces affects the predicted QPO frequencies only slightly when a < 0.9. On the contrary, when a > 0.9, the influence of pressure forces is nonnegligible. Our findings indicate that for several models this influence can be quite significant even for low values of spin. 相似文献
17.
W. H. Lee 《Astronomische Nachrichten》2005,326(9):838-844
The kilo‐Hertz Quasi‐Periodic Oscillations in X‐ray binaries could originate within the accretion flow, and be a signature of non–linear fluid oscillations and mode coupling in strong gravity. The possibility to decipher these systems will impact our knowledge of fundamental parameters such as the neutron star mass, radius, and spin. Thus they offer the possibility to constrain the nuclear equation of state and the rotation parameter of stellar–mass black holes. We review the general properties of these oscillations from a hydrodynamical point of view, when the accretion flow is subject to external perturbations and summarize recent results. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
We have identified three possible ways in which future XMM‐Newton observations can provide significant constraints on the equation of state of neutron stars. First, using a long observation of the neutron star X‐ray transient Cen X‐4 in quiescence one can use the RGS spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X‐ray spectral fitting of the pn and MOS spectra and allows us to investigate whether the variability observed in the quiescent X‐ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in NH. This will test whether the soft thermal spectral component can indeed be due to the hot thermal glow of the neutron star. Potentially such an observation could also reveal redshifted spectral lines from the neutron star surface. Second, XMM‐Newton observations of radius expansion type I Xray bursts might reveal redshifted absorption lines from the surface of the neutron star. Third, XMM‐Newton observations of eclipsing quiescent low‐mass X‐ray binaries provide the eclipse duration. With this the system inclination can be determined accurately. The inclination determined from the X‐ray eclipse duration in quiescence, the rotational velocity of the companion star and the semi‐amplitude of the radial velocity curve determined through optical spectroscopy, yield the neutron star mass. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
J. Yang D. R. Wik A. Zezas S. G. T. Laycock J. Hong R. Xu 《Astronomische Nachrichten》2019,340(1-3):46-49
To understand the progenitor of rotation‐powered pulsars, we compare them with accreting High‐Mass X‐ray binary pulsars, (hereafter X‐ray pulsars), in the small magellanic cloud. The diagram of spin period vs. period derivative shows that isolated neutron stars could be evolved from X‐ray pulsars. The pulsars with long spin period might spin up to 0.001–1 s. The binary orbit is disrupted by a third body in the universe, and the binaries are detached. Therefore, some of the pulsars become isolated neutron stars. 相似文献
20.
A.C. Fabian 《Astronomische Nachrichten》2008,329(2):155-161
Iron line emission is common in the X‐ray spectra of accreting black holes. When the line emission is broad or variable then it is likely to originate from close to the black hole. X‐ray irradiation of the accretion flow by the power‐law X‐ray continuum produces the X‐ray ‘reflection’ spectrum which includes the iron line. The shape and variability of the iron lines and reflection can be used as a diagnostic of the radius, velocity and nature of the flow. The inner radius of the dense flow corresponds to the innermost stable circular orbit and thus can be used to determine the spin of the black hole. Studies of broad iron lines and reflection spectra offer much promise for understanding how the inner parts of accretion flows (and outflows) around black holes operate. There remains great potential for XMM‐Newton to continue to make significant progress in this work. The need for high quality spectra and thus for long exposure times is paramount. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献