共查询到20条相似文献，搜索用时 31 毫秒
1.
A significant new development in the study of Anomalous X-ray Pulsars (AXPs) has been the recent discovery by INTEGRAL and RXTE of flat, hard X-ray components in three AXPs. These non-thermal spectral components differ dramatically from the steeper quasi-power-law tails seen in the classic X-ray band in these sources. A prime candidate mechanism for generating this new component is resonant, magnetic Compton upscattering. This process is very efficient in the strong magnetic fields present in AXPs. Here an introductory exploration of an inner magnetospheric model for upscattering of surface thermal X-rays in AXPs is offered, preparing the way for an investigation of whether such resonant upscattering can explain the 20–150 keV spectra seen by INTEGRAL. Characteristically flat emission spectra produced by non-thermal electrons injected in the emission region are computed using collision integrals. A relativistic QED scattering cross section is employed so that Klein–Nishina reductions are influential in determining the photon spectra and fluxes. Spectral results depend strongly on the magnetospheric locale of the scattering and the observer’s orientation, which couple directly to the angular distributions of photons sampled. 相似文献
2.
Ye Lu Wei Wang Yong-Heng ZhaoNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):543-550
We examine the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variati on with the spin-down rate Ω. Based onan accretion-powered model, the influences of both the magnetic field and the mass accretion rate on the spectral properties of AXPs are addressed. We then investigate the relation between the spectral property of AXPs and mass accretion rate M. The result shows that there exists a linear correlation between the photon index and the mass accretion rate: the spectral hardness increases with increasing M. A possible emission mechanism for the explanation of the spectral properties of AXPs is also discussed. 相似文献
3.
We analyze the possibility that anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) originate from radio pulsars subjected to considerable and prolonged glitches. The observed characteristics of such pulsars, their association with supernova remnants, and their evolution in the P-? diagram with allowance made for the actual age of the possible AXP and SGR progenitors are shown to be in conflict with the suggested scenario. 相似文献
4.
Marta Burgay Nanda Rea GianLuca Israel Andrea Possenti Luciano Burderi Tiziana Di Salvo Nichi D’Amico Luigi Stella Elisa Nichelli 《Astrophysics and Space Science》2007,308(1-4):531-534
We have performed deep searches for radio pulsations from four southern anomalous X-ray pulsars (AXPs) to investigate their
physical nature in comparison with the rotation powered pulsars. The data were acquired using the Parkes radio telescope with
the 1.4 GHz multibeam receiver. No pulsed emission with periodicity matching the X-ray ephemeris have been found in the observed
targets down to a limit of ∼0.1 mJy. A blind search has also been performed on all the 13 beams of the multibeam receiver
(the central beam being pointed on the target AXP), leading to the serendipitous discovery of two new radio pulsars and to
the further detection of 18 pulsars. Also a search for single dispersed pulses has been performed in the aim to detect signals
similar to those of the recently discovered rotating radio transients.
相似文献
5.
Cindy R. Tam Victoria M. Kaspi Bryan M. Gaensler Eric V. Gotthelf 《Astrophysics and Space Science》2007,308(1-4):519-523
The population of clearly identified anomalous X-ray pulsars has recently grown to seven, however, one candidate anomalous
X-ray pulsar (AXP) still eludes re-confirmation. Here, we present a set of seven Chandra ACIS-S observations of the transient
pulsar AX J1845.0-0258, obtained during 2003. Our observations reveal a faint X-ray point source within the ASCA error circle
of AX J1845.0-0258’s discovery, which we designate CXOU J184454.6-025653 and tentatively identify as the quiescent AXP. Its
spectrum is well described by an absorbed single-component blackbody (kT∼2.0 keV) or power law (Γ∼1.0) that is steady in flux on timescales of at least months, but fainter than AX J1845.0-0258 was during its 1993 period
of X-ray enhancement by at least a factor of 13. Compared to the outburst spectrum of AX J1845.0-0258, CXOU J184454.6-025653
is considerably harder: if truly the counterpart, then its spectral behavior is contrary to that seen in the established transient
AXP XTE J1810-197, which softened from kT∼0.67 keV to ∼0.18 keV in quiescence. This unexpected result prompts us to examine the possibility that we have observed an
unrelated source, and we discuss the implications for AXPs, and magnetars in general.
相似文献
6.
S. Zane N. Rea R. Turolla L. Nobili 《Monthly notices of the Royal Astronomical Society》2009,398(3):1403-1413
Within the magnetar scenario, the 'twisted magnetosphere' model appears very promising in explaining the persistent X-ray emission from soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). In the first two papers of the series, we have presented a 3D Monte Carlo code for solving radiation transport as soft, thermal photons emitted by the star surface are resonantly upscattered by the magnetospheric particles. A spectral model archive has been generated and implemented in xspec . Here, we report on the systematic application of our spectral model to different XMM–Newton and INTEGRAL observations of SGRs and AXPs. We find that the synthetic spectra provide a very good fit to the data for the nearly all the source (and source states) we have analysed. 相似文献
7.
Ian R. Stevens 《Astrophysics and Space Science》1995,224(1-2):367-376
In this paper I will review some recent developments in the field of circumstellar shocks, particularly as they relate to colliding stellar winds. I shall review the basic physics of colliding winds and shocks, and discuss recent developments in hydrodynamic modelling of colliding winds. I shall also report on recent X-ray observations of shock emission in Wolf-Rayet binary systems where high resolution X-ray spectra of colliding wind shock emission is being seen. I will discuss the occurrence of colliding winds to such diverse systems as Wolf-Rayet binaries, pre-main sequence binaries, symbiotic stars as well as the Galactic center object IRS 7, where recent results on interacting winds are yielded insight into the structure of winds in general. 相似文献
8.
In the Quark–Nova model, Anomalous X-ray Pulsars (AXPs) are quark stars surrounded by a degenerate iron-rich Keplerian ring (a few stellar radii away). AXP bursts are caused by accretion of chunks from the inner edge of the ring following magnetic field penetration. For bright bursts, the inner disk is prone to radiation induced warping which can tilt it into counter-rotation (i.e. retrograde). For AXP 1E2259+586, the 2002 burst satisfies the condition for the formation of a retrograde inner ring. We hypothesize the 2002 burst reversed the inner ring setting the scene for the 2012 outburst and “anti-glitch” when the retrograde inner ring was suddenly accreted leading to the basic observed properties of the 2012 event. 相似文献
9.
L. Pavan R. Turolla S. Zane L. Nobili 《Monthly notices of the Royal Astronomical Society》2009,395(2):753-763
There is an increasing theoretical and observational evidence that the external magnetic field of magnetars may contain a toroidal component, likely of the same order of the poloidal one. Such 'twisted magnetospheres' are threaded by currents flowing along the closed field lines which can efficiently interact with soft thermal photons via resonant cyclotron scatterings (RCS). Actually, RCS spectral models proved quite successful in explaining the persistent ∼1–10 keV emission from the magnetar candidates, the soft γ-ray repeaters (SGRs) and the anomalous X-ray pulsars (AXPs). Moreover, it has been proposed that, in the presence of highly relativistic electrons, the same process can give rise to the observed hard X-ray spectral tails extending up to ∼200 keV . Spectral calculations have been restricted up to now to the case of a globally twisted dipolar magnetosphere, although there are indications that the twist may be confined only to a portion of the magnetosphere, and/or that the large-scale field is more complex than a simple dipole. In this paper, we investigate multipolar, force–free magnetospheres of ultramagnetized neutron stars. We first discuss a general method to generate multipolar solutions of the Grad-Schlüter-Shafranov (GSS) equation, and analyse in detail dipolar, quadrupolar and octupolar fields. The spectra and lightcurves for these multipolar, globally twisted fields are then computed using a Monte Carlo code and compared with those of a purely dipolar configuration. Finally, the phase-resolved spectra and energy-dependent lightcurves obtained with a simple model of a locally sheared field are confronted with the International Gamma-Ray Astrophysics Laboratory ( INTEGRAL ) observations of the AXPs 1RXS J1708−4009 and 4U 0142+61. Results support a picture in which the field in these two sources is not globally twisted. 相似文献
10.
《New Astronomy Reviews》2000,44(7-9):503-510
AGNs with narrow Balmer lines show various extreme properties. In particular, rapid X-ray variability, steep X-ray spectra, peculiar optical and UV line ratios, and possibly peculiar line profiles. Since all these phenomena occur together they are likely to be related to one specific underlying physical parameter. I review recent evidence, based on HST imaging of low z quasars, which suggests that the Hβ line width and continuum luminosity of quasars provide a reasonably accurate estimate of the black hole mass. This implies that narrow-line AGN have relatively low black hole masses, and thus high L/LEdd, as independently suggested based on their steep X-ray spectra. I present additional evidence suggesting that the X-ray variability and the radio loudness are primarily driven by the black hole mass. The high mass inflow rate into the core of narrow-line AGNs may produce a denser and more enriched BLR, a high column radiation pressure driven outflow, and a smaller illumination angle for the NLR, as suggested by the observed emission line properties. Narrow-line AGNs may thus provide important clues for understanding the rich overall phenomenology of AGNs. 相似文献
11.
XMM–Newton X-ray spectra of the hard state black hole X-ray binaries (BHXRBs) SWIFT J1753.5−0127 and GX 339−4 show evidence for accretion disc blackbody emission, in addition to hard power laws. The soft and hard band power spectral densities (PSDs) of these sources demonstrate variability over a wide range of time-scales. However, on time-scales of tens of seconds, corresponding to the putative low-frequency Lorentzian in the PSD, there is additional power in the soft band. To interpret this behaviour, we introduce a new spectral analysis technique, the 'covariance spectrum', to disentangle the contribution of the X-ray spectral components to variations on different time-scales. We use this technique to show that the disc blackbody component varies on all time-scales, but varies more, relative to the power law, on longer time-scales. This behaviour explains the additional long-term variability seen in the soft band. Comparison of the blackbody and iron line normalizations seen in the covariance spectra in GX 339−4 implies that the short-term blackbody variations are driven by thermal reprocessing of the power-law continuum absorbed by the disc. However, since the amplitude of variable reflection is the same on long and short time-scales, we rule out reprocessing as the cause of the enhanced disc variability on long time-scales. Therefore, we conclude that the long time-scale blackbody variations are caused by instabilities in the disc itself, in contrast to the stable discs seen in BHXRB soft states. Our results provide the first observational evidence that the low-frequency Lorentzian feature present in the PSD is produced by the accretion disc. 相似文献
12.
R. P. Mignani S. Bagnulo A. De Luca G. L. Israel G. Lo Curto C. Motch R. Perna N. Rea R. Turolla S. Zane 《Astrophysics and Space Science》2007,308(1-4):203-210
In the last years, optical studies of Isolated Neutron Stars (INSs) have expanded from the more classical rotation-powered ones to other categories, like the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray Repeaters (SGRs), which make up the class of the magnetars, the radio-quiet INSs with X-ray thermal emission and, more recently, the enigmatic Compact Central Objects (CCOs) in supernova remnants. Apart from 10 rotation-powered pulsars, so far optical/IR counterparts have been found for 5 magnetars and for 4 INSs. In this work we present some of the latest observational results obtained from optical/IR observations of different types of INSs. 相似文献
13.
We review how the recent increase in X-ray and radio data from black hole and neutron star binaries can be merged together with theoretical advances to give a coherent picture of the physics of the accretion flow in strong gravity. Both long term X-ray light curves, X-ray spectra, the rapid X-ray variability and the radio jet behaviour are consistent with a model where a standard outer accretion disc is truncated at low luminosities, being replaced by a hot, inner flow which also acts as the launching site of the jet. Decreasing the disc truncation radius leads to softer spectra, as well as higher frequencies (including quasi periodic oscillations, QPOs) in the power spectra, and a faster jet. The collapse of the hot flow when the disc reaches the last stable orbit triggers the dramatic decrease in radio flux, as well as giving a qualitative (and often quantitative) explanation for the major hard–soft spectral transition seen in black holes. The neutron stars are also consistent with the same models, but with an additional component due to their surface, giving implicit evidence for the event horizon in black holes. We review claims of observational data which conflict with this picture, but show that these can also be consistent with the truncated disc model. We also review suggested alternative models for the accretion flow which do not involve a truncated disc. The most successful of these converge on a similar geometry, where there is a transition at some radius larger than the last stable orbit between a standard disc and an inner, jet dominated region, with the X-ray source associated with a mildly relativistic outflow, beamed away from the disc. However, the observed uniformity of properties between black holes at different inclinations suggests that even weak beaming of the X-ray emission may be constrained by the data. After collapse of the hot inner flow, the spectrum in black hole systems can be dominated by the disc emission. Its behaviour is consistent with the existence of a last stable orbit, and such data can be used to estimate the black hole spin. By contrast, these systems can also show very different spectra at these high luminosities, in which the disc spectrum (and probably structure) is strongly distorted by Comptonization. The structure of the accretion flow becomes increasingly uncertain as the luminosity approaches (and exceeds) the Eddington luminosity, though there is growing evidence that winds may play an important role. We stress that these high Eddington fraction flows are key to understanding many disparate and currently very active fields such as ULX, Narrow Line Seyfert 1’s, and the growth of the first black holes in the Early Universe. 相似文献
14.
J. S. Clark I. A. Steele M. J. Coe & P. Roche 《Monthly notices of the Royal Astronomical Society》1998,297(3):657-666
We present infrared spectroscopy of the Be/X-ray binary HDE 245770/A0535+26 obtained over the period 1992–1995. The spectra show significant variability, reflecting changes in the circumstellar environment during this time. A reduction in the flux observed in the Paschen series lines between 1993 December and 1994 September correlates with a similar reduction in both the strength of Hα and the optical continuum emission, which can be attributed to a reduction in the emission measure of the disc. A turnover between optically thin and thick emission is seen for both Paschen and Brackett series lines, and allows an estimate of the disc density as ∼1012 cm−3 . Echelle spectroscopy reveals strong similarities between the He I 1.008, 2.058 μm, Hα and Paschen series line profiles, suggesting their formation in a similar (and asymmetric) region of the disc. In contrast, the line profile of He I 6678 Å indicates that it is formed at smaller radii than the other transitions. 相似文献
15.
M. Birkinshaw D. M. Worrall M. J. Hardcastle 《Monthly notices of the Royal Astronomical Society》2002,335(1):142-150
Chandra ACIS observations of PKS 0521−365 find that the X-ray emission of this BL Lac object consists of emission from an unresolved core, a diffuse halo and a 2-arcsec jet feature coincident with the inner radio/optical jet. A comparison with a new ATCA 8.6-GHz map also finds X-ray emission from the bright hotspot south-east of the nucleus. The jet spectrum, from radio to X-ray, is probably synchrotron emission from an electron population with a broken power-law energy distribution, and resembles the spectra seen from the jets of low-power (FR I) radio galaxies. The hotspot X-ray flux is consistent with the expectations of synchrotron self-Compton emission from a plasma close to equipartition, as seen in studies of high-power (FR II) radio galaxies. While the angular structure of the halo is similar to that found by an analysis of the ROSAT High Resolution Imager image, its brightness is seen to be lower with Chandra , and the halo is best interpreted as thermal emission from an atmosphere of similar luminosity to the haloes around FR I radio galaxies. The X-ray properties of PKS 0521−365 are consistent with it being a foreshortened, beamed, radio galaxy. 相似文献
16.
《New Astronomy Reviews》2000,44(1-2):63-68
I review some of the more interesting recent results on Intermediate Polars, with an emphasis on the information content of their periodic intensity variations, as provided by power spectra. The current definitions of the class are discussed, and new contenders listed with their properties. Results of the X-ray periodicities seen in IPs and developments in interpreting their light curves and power spectra are discussed. Studies of the morphology of IP X-ray light curves seem to show a bifurcation into single- or double-maxima spin profiles. An explanation for this behaviour, involving faster, weaker field, rotators accreting over a larger area, is discussed. Significant polarization has only been detected in three IPs, and the polarized flux distributions have been used to infer magnetic field strength. The failure to detect any IR cyclotron spectral features in IPs, even for polarized systems, limits our possibilities of direct magnetic field measurements. Recent tomographic results qualitatively support the accretion curtain models for IPs and some progress has been made in modelling the line emission using realistic physics. 相似文献
17.
P. Reig A. S&#;owikowska A. Zezas P. Blay 《Monthly notices of the Royal Astronomical Society》2010,401(1):55-66
SAX J2103.5+4545 is the Be/X-ray binary (BeX) with the shortest orbital period. It shows extended bright and faint X-ray states that last for a few hundred days. The main objective of this work is to investigate the relationship between the X-ray and optical variability and to characterize the spectral and timing properties of the bright and faint states. We have found a correlation between the spectral and temporal parameters that fit the energy and power spectra. Softer energy spectra correspond to softer power spectra. That is to say, when the energy spectrum is soft, the power at high frequencies is suppressed. We also present the results of our monitoring of the Hα line of the optical counterpart since its discovery in 2003. There is a correlation between the strength and shape of the Hα line, originated in the circumstellar envelope of the massive companion and the X-ray emission from the vicinity of the neutron star. Hα emission, indicative of an equatorial disc around the B-type star, is detected whenever the source is bright in X-rays. When the disc is absent, the X-ray emission decreases significantly. The long-term variability of SAX J2103.5+4545 is characterized by fast episodes of disc loss and subsequent reformation. The time-scales for the loss and reformation of the disc (about 2 yr) are the fastest among BeXs. 相似文献
18.
能谱仅反映了高能天体辐射的部分性质，而高能X射线辐射的时变可以反映致密天体的动态性质。因此，在构造高能辐射的理论模型时，既要考虑X辐射的能谱性质，也要考虑其时变性质。特别对高能天体X辐射的快速光变，一般认为其发生在致密天体附近，致密天体快速光变的研究可以揭示出致密天体附近的物理性质，因此，时变可以对X辐射模型给以很强的限制。X射线源不同能量光子到达观测者的时间差称为X射线辐射的时延。介绍了高能X辐射时变中的时延分析方法及其最新发展，综述了致密双星系统中黑洞侯选林和中子星的时延现象，并简单介绍了为解释这些现象所发展的模型，以及时延对模型的限制。 相似文献
19.
Thomas Preibisch 《Astrophysics and Space Science》2004,292(1-4):631-641
I discuss recent observational results on the X-ray properties of young stellar objects, based mostly on Chandra and XMM-Newton observations. The sensitive X-ray data on large, well characterized samples of T Tauri stars (and a number of protostars) allow to study in detail the dependence of magnetic activity on the bulk properties of the young objects and to draw important clues towards the origin of the X-ray emission. The absence of a relation between X-ray activity and rotation for T Tauri stars clearly suggests that their magnetic activity cannot be simply explained by the action of a scaled-up solar-like dynamo. I discuss alternative models for the generation of magnetic fields and also consider the long standing question whether the X-ray properties of the T Tauri stars are related to the presence/absence of circumstellar disks or active accretion. 相似文献
20.
扼要介绍了类太阳恒星星晚射线辐射的研究历史,综述了Ｘ射线辐射与恒星参量的关系,并对星冕的加热机制作了介绍。类太阳恒星的Ｘ射线辐射与表面磁场有关,因此测定晚型星表面的磁场很重要。 相似文献