An XMM‐Newton survey of broad iron lines in AGN

We report on the iron Kα line properties of a sample of Seyfert galaxies observed with the XMM‐Newton EPIC pn instrument. Using a systematic and uniform analysis, we find that complexity at iron‐K is extremely common in the XMM‐Newton spectra. Once appropriate soft X‐ray absorption, narrow 6.4 keV emission and associated Compton reflection are accounted for, ∼75% of the sample show an improvement when a further component is introduced. The typical properties of the broad emission are both qualitatively and quantitatively consistent with previous results from ASCA. The complexity is in general very well described by relativistic accretion disk models. In most cases the characteristic emission radius is constrained to be within ∼50R _g, where strong gravitational effects become important. We find in about 1/3 of the sample the accretion disk interpretation is strongly favoured over competing models. In a few objects no broad line is apparent. We find evidence for emission within 6R _g in only two cases, both of which exhibit highly complex absorption. Evidence for black hole spin based on the X‐ray spectra therefore remains tentative. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Collimation of extragalactic radio jets in compact steep-spectrum and larger sources

We study the collimation of radio jets in the high-luminosity Fanaroff–Riley class II sources by examining the dependence of the sizes of hotspots and knots in the radio jets on the overall size of the objects for a sample of compact steep-spectrum (CSS) and larger-sized objects. The objects span a wide range in overall size from about 50 pc to nearly 1 Mpc. The mean size of the hotspots increases with the source size during the CSS phase, which is typically taken to be about 20 kpc, and the relationship flattens for the larger sources. The sizes of the knots in the compact as well as the larger sources are consistent with this trend. We discuss possible implications of these trends. We find that the hotspot closer to the nucleus or core component tends to be more compact for the most asymmetric objects where the ratio of separations of the hotspots from the nucleus r _d>2. These highly asymmetric sources are invariably CSS objects, and their location in the hotspot size ratio–separation ratio diagram is possibly the result of their evolution in an asymmetric environment. We also suggest that some sources, especially of lower luminosity, exhibit an asymmetry in the collimation of the oppositely directed radio jets.     

贺兰山地区云凝结核浓度的测量及分析

利用热扩散型云凝结核计数器在贺兰山地区进行地面和空中云凝结核(CCN)观测。结果表明,在该地区夏季地面平均CCN浓度为610 cm^-3,最大浓度达10⁴ cm^-3。沙尘天气现象没有明显地增加CCN浓度。层状云中CCN浓度随高度变化不大。     

Observations of the gamma-ray flux from the galaxy Mk 501

We present two-year-long observations of the flux of very-high-energy (～10¹² eV) gamma rays from the active galactic nucleus Mk 501 performed with a Cherenkov detector at the Crimean Astrophysical Observatory. A gamma-ray flux from the object was shown to exist at confidence levels of 11 and 7 standard deviations for 1997 and 1998, respectively. The flux varied over a wide range. The mean flux at energies >10¹² eV, as inferred from the 1997 and 1998 data, is (5.0±0.6)×10^?11 and (3.7±0.6)×10^?11 cm^?2 s^?1, respectively. The errors are the sum of statistical observational and modeling errors. The mean power released in the form of gamma rays is ～2×10⁴³ erg s^?1 sr^?1.     

An ultrasoft X-ray source (RX 215319−1514) and discovery of a narrow‐line Seyfert 1 galaxy

We present results on the identification of the optical counterpart of an ultrasoft X-ray source discovered with ROSAT . Two optical candidates – a galaxy and a star – are found within the error circle of the X-ray source position. Optical spectroscopy of the two candidates reveals that (a) the galaxy is a narrow-line Seyfert type 1 galaxy, and (b) the star is a late A-type or an early F-type. The F _x F _v ratio is too high for the star to be the counterpart of the X-ray source, but consistent with that for an active galaxy. Although higher-resolution X-ray imaging of the region is needed to definitely settle the question of the counterpart of the X-ray source, the narrow-line Seyfert 1 galaxy is the best candidate. The spectral properties of the newly discovered narrow-line Seyfert 1 galaxy are also presented, including its extreme X-ray power-law spectral index of Γ≥4.     

The structure of black hole magnetospheres I. Schwarzschild black holes

We introduce a multipolar scheme for describing the structure of stationary, axisymmetric, force-free black hole magnetospheres in the '3+1' formalism. We focus here on Schwarzschild spacetime, giving a complete classification of the separable solutions of the stream equation. We show a transparent term-by-term analogy of our solutions with the familiar multipoles of flat-space electrodynamics. We discuss electrodynamic processes around disc-fed black holes in which our solutions find natural applications: (i) 'interior' solutions in studies of the BlandfordZnajek process of extracting the rotational energy of holes, and of the formation of relativistic jets in active galactic nuclei and 'microquasars'; (ii) 'exterior' solutions in studies of accretion disc dynamos, disc-driven winds and jets. On the strength of existing numerical studies, we argue that the poloidal field structures found here are also expected to hold with good accuracy for rotating black holes, except for the cases of the maximum possible rotation rates. We show that the closed-loop exterior solutions found here are not in contradiction with the MacdonaldThorne theorem, as these solutions, which diverge logarithmically on the horizon of the hole , only apply to those regions that exclude .     

The black hole mass–galaxy age relation

We present evidence that there is a significant correlation between the fraction of the mass of a galaxy that lies in its central black hole and the age of the galactic stellar population. Since the absorption-line indices that are used to estimate the age are luminosity-weighted, they essentially measure the time since the last significant episode of star formation in the galaxy. The existence of this correlation is consistent with several theories of galaxy formation, including the currently favoured hierarchical picture of galaxy evolution, which predicts just such a relation between the black hole mass and the time since the last burst of merger-induced star formation. It is not consistent with models in which the massive black hole is primordial, and hence uncoupled from the stellar properties of the galaxy.     

Compton-thick X-ray absorption in the Seyfert galaxies Tololo 0109383 and ESO 138G1

We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo 0109383 and ESO 138G1. In both cases, spectral fitting reveals two statistically acceptable continuum models: Compton reflection and partial covering. Both spectra have strong iron K lines, with equivalent widths greater than 1.5 keV. These large equivalent widths are suggestive of heavier obscuration than that directly indicated by the partial-covering models (  210²³ cm^-2),  with the actual column densities being 'Compton-thick' (i.e.   N _H1.510²⁴ cm^-2).  We use the hard X-ray/[O  iii ] flux correlation for Seyferts and data from the literature to provide additional support for this hypothesis. Since Tololo 0109383 is known to have optical type 1 characteristics such as broad Balmer line components and Fe  ii emission, this result marks it as a notable object.     

Using Hubble Space Telescope images to identify straight segments in galaxy nuclear spirals

This Letter reports the discovery of straight segments of nuclear spiral arms. Hubble Space Telescope images of Seyfert galaxies are used. The morphology of the straight features on scales of few hundred parsecs proves to be similar to the morphology of disc-wide polygonal spirals and rings. This suggests that the straight structures on both nuclear and disc scales may have a common physical nature.