An X-ray view of quasars

I present an overview of observational studies of quasars of all types, with particular emphasis on X-ray observational studies. The presentation is based on the most popularly accepted unified picture of quasars - collectively referred to as AGN (active galactic nuclei) in this review. Characteristics of X-ray spectra and X-ray variability obtained from various X-ray satellites over the last 5 decades have been presented and discussed. The contribution of AGN in understanding the cosmic X-ray background is discussed very briefly. Attempt has been made to provide up-to-date information; however, this is a vast subject and this presentation is not intended to be comprehensive.Comment: Accepted for publication in the Bulletin of the Astronomical Society of India (22 pages, 6 figures

Study of X-ray emission from the old open cluster, M67

We present an X-ray analysis of a 4 Gyr old open cluster, M67, using archival XMM-Newton data. The aim of this study was to find new X-ray members of M67, and to use the updated member list for studying X-ray variability, and derive the X-ray luminosity functions (XLFs) of different stellar types and compare them with other star clusters of similar age. We report the detection of X-ray emission from 25 members of M67, with membership based primarily on their proper motion, of which one X-ray source is a new member. Supplementing this study with previous ROSAT and Chandra studies of M67, and using the most recent proper motion study by Vereshchagin et al., we have compiled a revised list of X-ray emitting members of M67 consisting of 43 stars. Sixteen of these are known RS CVn type binaries having orbital periods $<$ 10 days, and near-circular orbits, 5 are contact binaries with orbital periods $<$ 6 hours, 5 are yellow and blue stragglers, 2 are Algol-type binaries, and one source is a cataclysmic variable. Fourteen members do not have any orbital information and cannot be classified. Fourteen of the X-ray sources detected do not have any optical counterpart down to a magnitude of $V\simeq22$, and their membership is uncertain. Finally, we report the X-ray luminosity functions of RS CVn type and other types of stars in M67 and compare them with other open clusters of intermediate-to-old age.Comment: 13 pages, 8 figures, 5 tables. Accepted for publication in MNRA