Journal Article

<i>ASCA</i> observations of two steep soft X-ray quasars

F. Fiore, G. Matt, M. Cappi, M. Elvis, K. M. Leighly, F. Nicastro, L. Piro, A. Siemiginowska and B. J. Wilkes

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 298, issue 1, pages 103-113
Published in print July 1998 | ISSN: 0035-8711
Published online July 1998 | e-ISSN: 1365-2966 | DOI:
ASCA observations of two steep soft X-ray quasars

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Steep soft X-ray (0.1–2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe II emission, large and fast X-ray variability, and a rather steep 2–10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026.

Both objects show similar variations (factor of ∼ 2 in 10 ks), despite a factor of ∼ 10 difference in the 0.5–10 keV luminosity (7.3 × 1043 erg s−1 for PG 1244 + 026 and 6.4 × 1044 erg s−1 for NAB 0205 + 024, assuming isotropic emission, H0 = 50.0 and q0 = 0.0).

The X-ray continuum of the two quasars flattens by 0.5–1 going from the 0.1–2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei.

PG 1244 + 026 shows a significant feature in the ‘1-keV’ region, which can be described either as a broad emission line centred at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3–0.6 c).

Keywords: line: formation; line: identification; galaxies: individual: NAB 0205 + 024; galaxies: individual: PG 1244 + 026; galaxies: Seyfert; X-rays: galaxies

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Subjects: Astronomy and Astrophysics

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