M31 is one of the best studied galaxies. At a distance of 700 kpc, it provides us with an opportunity to study the global properties of a galaxy which is similar to our Milky Way. We present our Chandra ACIS observations in the central region and along the disk of M31. We include the following. 1) X-ray spectra of point sources: the energy spectrum

A systematic study of the linear thermal stability of a medium subject to cooling, self-gravity, and thermal conduction is carried out for the case when the unperturbed state is subject to global cooling and expansion. A general, recursive WKB solution for the perturbation problem is obtained that can be applied to a large variety of situations in

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Thanks to dedicated X-ray monitoring observations of the Galactic bulge with the Wide Field Cameras on BeppoSAX, several tens of faint X-ray transients have been discovered with peak fluxes that are just a few percent of that of classical X-ray novae. Most of these faint transients exhibit type-I X-ray bursts and, thus, harbor a neutron star. A few

We have obtained I-band images for the new accreting millisecond pulsar XTE J1751-305 (IAUC#7867,#7870,#7872,#7874,#7876) with the 6.5-m Baade telescope and the MagIC CCD camera at the Las Campanas Observatory on 2002 April 14. At the position of the possible infrared counterpart (IAUC#7874), we found no optical sources to a limiting magnitude of I

We analyze very deep X-ray and mid-IR surveys in common areas of the Lockman Hole and the Hubble Deep Field-North (HDF-N) to study the sources of the X-ray background (XRB) and to test the standard obscured accretion paradigm. Observations with XMM-Newton and Infrared Space Observatory (ISO) of a substantial area in Lockman are particularly