We present a procedure for obtaining the cluster densities in terms of the probability, P_n_(r), for a randomly placed sphere of radius r to contain n galaxies and the cluster density profiles. We then discuss a method for computing P_n_(r) and use it to obtain the density of Abell clusters in cold dark matter models with different biasing.

Aims:Magnetic elements are thought to be described by flux tube models, and are well reproduced by MHD simulations. However, these simulations are only partially constrained by observations. We observationally investigate the relationship between G-band bright points and magnetic structures to clarify conditions, which make magnetic structures

In this Letter we report the detection of a strong and extremely blueshifted X-ray absorption feature in the 1 Ms Chandra spectrum of CXOCDFS J033260.0-274748, a quasar at z=2.579 with L2-10keV~4×1044 ergs s-1. The broad absorption feature at ~6.3 keV in the observed frame can be fitted either as an absorption edge at 20.9 keV or as a broad

The only way to obtain reliable empirical information on the intensity and topology of the weak magnetic fields of the quiet solar chromosphere is via the measurement and rigorous physical interpretation of polarization signals in chromospheric spectral lines. The observed Stokes profiles reported here are due to the Hanle and Zeeman effects

On 8-9 September 2006, a series of 7 XMM-Newton observations were performed as part of our XMM-Newton/Chandra monitoring campaign of the 1.7 square degree region around Sgr A* (Wijnands et al. 2006, A&A, 449, 1117). Two X-ray transients were active during our observations. A very-faint transient is active with an 2-10 keV X-ray luminosity of

We report a re-brightening of the millisecond X-ray pulsar IGR J00291+5934. In August the source performed an outburst which was detected in X-ray, UV and optical (ATel #1660, #1664, #1665, #1666, #1667, #1668). Since then we have continued to monitor this source with the Faulkes Telescope North in many optical filters as it appeared to be fading