2013/10/01 by K. P. Singh, Singh, K. P.
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #astro-ph.CO #astro-ph.HE
paper · pdf · doi:10.48550/arxiv.1310.0270
Accepted for publication in the Bulletin of the Astronomical Society of India (22 pages, 6 figures)
openalex publication_date 2013/10/01 · arxiv created 2013/10/04 · arxiv updated 2013/10/07 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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.