Study of the long-term X-ray variability of a possible quasar RX J0957.9+6903 with ASCA

Yu Ichiro Ezoe, Naoko Iyomoto, Kazuo Makishima

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The long-term variability and spectral properties of a possible quasar, RX J0957.9+6903, were studied utilizing 16 ASCA observations spanning 5.5 years. The average 0.7-10 keV spectrum of RX J0957.9+6903 is well represented by a power-law continuum having a photon index of 1.58 ±0.03 and an absorption column of ∼ 1 × 1021 cm-2. The 2-10 keV flux of RX J0957.9+6903 varied by a factor of four over a period of six years, around a mean of ∼ 8.8 × 10-12 ergs-1 cm-2. Peak-to-peak variability within each observation was less than 25% on ∼ 1 day time scale. These properties support the classification of RX J0957.9+6903 as a quasar. The power spectrum density (PSD) was estimated in a "forward" manner over a frequency range of 10-8.2-10-43 Hz by utilizing the structure function method and a Monte Carlo simulation assuming a broken power-law type PSD. Then, the break frequency fb of the PSD of RX J0957.9+6903 has been constrained as 1/fb = 1600+∞-1100 days, and the logarithmic slope of the high-frequency region of the PSD as α = -1.55 ± 0.2. A comparison of the estimated PSDs is made between RX J0957.9+6903 and the M 81 nucleus, observed in the same field of view.

Original languageEnglish
Pages (from-to)69-77
Number of pages9
JournalPublications of the Astronomical Society of Japan
Issue number1
Publication statusPublished - 2001
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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