81,153 research outputs found
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 , 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
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