Extended X-ray emission in the radio-loud galaxy 3C 382

ROSAT /HRI observations of the powerful radio-loud galaxy 3C 382 reveal extended X-ray emission associated with the source. On the basis of this new spatial component, a previous ROSAT /PSPC spectral analysis of the source is revised. Allowing for the presence of an additional thermal component in the PSPC spectrum, the non-thermal component is found to be compatible with the extrapolation of the well-defined 3C 382, 2–10 keV, power-law spectrum into the soft X-ray region. The thermal – extended – component would then account for the soft excess emission previously reported for this source. The origin of this thermal component is not clear. Its luminosity compares with that of rich Abell clusters; yet, the galaxy environment in 3C 382 appears of moderate optical richness. An alternative is that it is the result of a massive extended gaseous atmosphere sustained by the deep gravitational potential well of 3C 382.     

Magnetic flares and the optical variability of the X-ray transient XTE J1118+480

The simultaneous presence of a strong quasi-periodic oscillation, of period ∼10 s, in the optical and X-ray light curves of the X-ray transient XTE J1118+480 suggests that a significant fraction of the optical flux originates from the inner part of the accretion flow, where most of the X-rays are produced. We present a model of magnetic flares in an accretion disc corona where thermal cyclo-synchrotron emission contributes significantly to the optical emission, while the X-rays are produced by inverse Compton scattering of the soft photons produced by dissipation in the underlying disc and by the synchrotron process itself. Given the observational constraints, we estimate the values for the coronal temperature, optical depth and magnetic field intensity, as well as the accretion rate for the source. Within our model we predict a correlation between optical and hard X-ray variability and an anticorrelation between optical and soft X-rays. We also expect optical variability on flaring time-scales (∼tens of ms), with a power-density spectrum similar to that observed in the X-ray band. Finally, we use both the available optical/extreme-ultraviolet/X-ray spectral energy distribution and the low-frequency time variability to discuss limits on the inner radius of the optically thick disc.     

Mark 421天体多波段辐射机制研究

基于对数抛物线型电子分布,用单区、均匀同步自康普顿(Synchrotron Self-Compton,SSC)辐射模型计算BL Lac天体S5 0716+714的多波段能谱,并与Paggi等人的结果进行了比较.模型的计算结果与Paggi等人直接用δ函数近似得到的结果不同,导致该差异的主要原因可能是由于单电子同步辐射的δ函数近似丢失了电子的部分能量而影响逆康普顿散射结果.把该模型分别应用于Mark 421天体的高、中、低3种不同状态下的多波段观测结果,理论计算结果能与不同状态下的观测结果符合得很好.分析认为,观测到的Mark 421天体的不同状态可能是由于喷流内电子分布变化引起的.     

Recent sedimentation and suspended matter in Erhai Lake, Yunnan Province, China

INTR0DUCnONErhailake,thesecondlargestlakeintheYUnnanPlateauinS0uthWstChina,islo-catedinDaliDefecthe25035'to25"58'N,looo05't0l(X)o07'E(Fig.l)-The40kInlong3-9kInwidelakeisnaInedafteritsearlikeshape.ItsbasicchimteristicsaregiveninTablel.EtheibeeisampicalriftlakeintheDalibasinwhichdeveloPedalongtheYuaniangHongheThewestsideofthebasinisformedbytheDiancangMountainwhichconsists0frock(PrecaInbrianschistandgneissandMiocenemetaInrphiclimestone).TheseisndcallystillactivemoUntainrangrisab0ut…     

Towards a new standard model for black hole accretion

We briefly review recent developments in black hole accretion disk theory, emphasizing the vital role played by magnetohydrodynamic (MHD) stresses in transporting angular momentum. The apparent universality of accretion-related outflow phenomena is a strong indicator that large-scale MHD torques facilitate vertical transport of angular momentum. This leads to an enhanced overall rate of angular momentum transport and allows accretion of matter to proceed at an interesting rate. Furthermore, we argue that when vertical transport is important, the radial structure of the accretion disk is modified at small radii and this affects the disk emission spectrum. We present a simple model demonstrating how energetic, magnetically-driven outflows modify the emergent disk emission spectrum with respect to that predicted by standard accretion disk theory. A comparison of the predicted spectra against observations of quasar spectral energy distributions suggests that mass accretion rates inferred using the standard disk model may be severely underestimated.     

A Chandra observation of the X-ray environment and jet of 3C 31

We have used a deep Chandra observation of the central regions of the twin-jet Fanaroff–Riley class I (FRI) radio galaxy 3C 31 to resolve the thermal X-ray emission in the central few kpc of the host galaxy, NGC 383, where the jets are thought to be decelerating rapidly. This allows us to make high-precision measurements of the density, temperature and pressure distributions in this region, and to show that the X-ray emitting gas in the centre of the galaxy has a cooling time of only  5×10⁷ yr  . In a companion paper, these measurements are used to place constraints on models of the jet dynamics.
A previously unknown one-sided X-ray jet in 3C 31, extending up to 8 arcsec from the nucleus, is detected and resolved. Its structure and steep X-ray spectrum are similar to those of X-ray jets known in other FRI sources, and we attribute the radiation to synchrotron emission from a high-energy population of electrons. In situ particle acceleration is required in the region of the jet where bulk deceleration is taking place.
We also present X-ray spectra and luminosities of the galaxies in the Arp 331 chain of which NGC 383 is a member. The spectrum and spatial properties of the nearby bright X-ray source 1E 0104+3153 are used to argue that the soft X-ray emission is mostly due to a foreground group of galaxies rather than to the background broad absorption-line quasar.     

Jet breaks in the X-ray light-curves of Swift gamma-ray burst afterglows

In the set of 236 gamma-ray burst (GRB) afterglows observed by Swift between 2005 January and 2007 March, we identify 30 X-ray light-curves that have power-law fall-offs that exhibit a steepening ('break') at 0.1–10 d after they are triggered, to a decay steeper than t ^−1.5. For most of these afterglows, the X-ray spectral slope and the decay indices before and after the break can be accommodated by the standard jet model although a different origin of the breaks cannot be ruled out. In addition, there are 27 other afterglows which have X-ray light-curves that may also exhibit a late break to a steep decay, but the evidence is not that compelling. The X-ray emissions of 38 afterglows decay slower than t ^−1.5 until after 3 d, half of them exhibiting such a slow decay until after 10 d. Therefore, the fraction of well-monitored Swift afterglows with potential jet breaks is around 60 per cent, whether we count only the strongest cases for each type or all of them. This fraction is comparable to the 75 per cent of pre-Swift afterglows which have optical light-curves that displayed similar breaks at ∼1 d. The peak energy of the GRB spectrum of Swift afterglows with light-curve breaks shows the same correlations with the burst isotropic output (Amati relation) and with the burst collimated output (Ghirlanda relation) as previously found for pre- Swift optical afterglows with light-curve breaks. However, we find that the Ghirlanda relation is largely a consequence of Amati's and that the use of the jet-break time leads to a stronger Ghirlanda correlation only when the few objects that do not satisfy the Amati relation are included.     

The X-ray spectrum of Cyg X-2

The spectra of disc accreting neutron stars generally show complex curvature, and individual components from the disc, boundary layer and neutron star surface cannot be uniquely identified. Here we show that much of the confusion over the spectral form derives from inadequate approximations for Comptonization and for the iron line. There is an intrinsic low-energy cut-off in Comptonized spectra at the seed photon energy. It is very important to model this correctly in neutron star systems as these have expected seed photon temperatures (from either the neutron star surface, inner disc or self-absorbed cyclotron) of ≈1 keV, clearly within the observed X-ray energy band. There is also reflected continuum emission which must accompany the observed iron line, which distorts the higher energy spectrum. We illustrate these points by a reanalysis of the Ginga spectra of Cyg X-2 at all points along its Z track, and show that the spectrum can be well fitted by models in which the low-energy spectrum is dominated by the disc, while the higher energy spectrum is dominated by Comptonized emission from the boundary layer, together with its reflected spectrum from a relativistically smeared, ionized disc.