Long-term X-ray variability of quasars in the Lockman Hole field observed with ROSAT

Yu Ichiro Ezoe; Naoko Iyomoto; Kazuo Makishima; Günter Hasinger

doi:10.1093/pasj/54.6.981

Long-term X-ray variability of quasars in the Lockman Hole field observed with ROSAT

Yu Ichiro Ezoe, Naoko Iyomoto, Kazuo Makishima, Günter Hasinger

Research output: Contribution to journal › Article › peer-review

1 Citation (Scopus)

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, f_b. Then, assuming the PSD slope, α, to be -2 < α < -1, l/f_b 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.

Original language	English
Pages (from-to)	981-986
Number of pages	6
Journal	Publications of the Astronomical Society of Japan
Volume	54
Issue number	6
DOIs	https://doi.org/10.1093/pasj/54.6.981
Publication status	Published - 2002
Externally published	Yes

All Science Journal Classification (ASJC) codes

Astronomy and Astrophysics
Space and Planetary Science

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10.1093/pasj/54.6.981

Cite this

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title = "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, l/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.",

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T1 - Long-term X-ray variability of quasars in the Lockman Hole field observed with ROSAT

AU - Ezoe, Yu Ichiro

AU - Iyomoto, Naoko

AU - Makishima, Kazuo

AU - Hasinger, Günter

PY - 2002

Y1 - 2002

N2 - 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, l/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.

AB - 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, l/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.

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Long-term X-ray variability of quasars in the Lockman Hole field observed with ROSAT

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