Long-Term X-Ray Variability of Quasars in the Lockman Hole Field Observed with ROSAT
Abstract
An improved method has been utilized to estimate the X-ray power spectral densities (PSD) and the variation time scales of three quasars in the Lockman Hole field. Five archival ROSAT PSPC data covering a two-year range were analyzed. To estimate PSD from sparse and unevenly-sampled lightcurves, a forward-method approach with extensive Monte Carlo simulations was adopted. A broken power-law type PSD with a constant Poisson noise component was assumed with a break frequency, fb. Then, assuming the PSD slope, α, to be -2 < α < -1, 1/fb was constrained as >∼ 25 days for one object, while the constraints on the other two objects were very weak. The long-time scale of the one object is consistent with the view that luminous AGNs host massive black holes.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- December 2002
- DOI:
- 10.1093/pasj/54.6.981
- arXiv:
- arXiv:astro-ph/0210451
- Bibcode:
- 2002PASJ...54..981E
- Keywords:
-
- galaxies: active;
- galaxies: quasar : general-- methods: data analysis;
- X-rays: galaxies;
- Astrophysics
- E-Print:
- 8 pages, 3 figures, accepted in PASJ