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Astron. Astrophys. 359, 471-482 (2000)


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BeppoSAX broad-band observations of low-redshift quasars: spectral curvature and iron [FORMULA] lines

T. Mineo 1, F. Fiore 2,3,4, A. Laor 5, E. Costantini 4,6, W.N. Brandt 7, A. Comastri 6, R. DellaCeca 8, M. Elvis 4, T. Maccacaro 8 and S. Molendi 9

1 Istituto di Fisica Cosmica ed Applicazioni all'Informatica CNR, Via U. La Malfa 153, 90146 Palermo, Italy
2 BeppoSAX Science Data Center, c/o Telespazio, Via Corcolle 19, 00131 Roma, Italy
3 Osservatorio Astronomico di Roma, 00040 Monteporzio (Rm), Italy
4 Harvard Smithsonian Center for Astrophysics, Cambridge, MA, USA
5 Physics Department, Technion, Haifa 32000, Israel
6 Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy
7 Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
8 Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
9 Istituto di Fisica Cosmica e Tecnologia Relative CNR, Via Bassini 15, 20133 Milano, Italy

Received 11 February 2000 / Accepted 22 May 2000

Abstract

We present results from BeppoSAX observations of 10 low redshift quasars. The quasars are part of the Laor et al. (1997) sample of 23 optically selected PG quasars with redshift [FORMULA] and low Galactic absorption along the line of sight. Significant spectral curvature is detected for the 6 quasars with the highest signal to noise ratio in their low energy spectra. The average curvature can be parameterized as a flattening of the underlying power law by [FORMULA] above [FORMULA] 1 keV. We find that quasars with a steeper soft X-ray (0.1-2 keV) spectrum tend to be steeper also at higher (2-10 keV) energies. The distribution of the best fit 2-10 keV slopes is similar to that found for other radio-quiet AGN and characterized by a large dispersion around the mean: [FORMULA] 1.0 [FORMULA] 0.3. Iron [FORMULA] lines are detected in 4 quasars. In the narrow-line quasar PG 1115+407, the rest frame line energy (6.69[FORMULA]0.11 keV) and equivalent width (580[FORMULA]280 eV) are consistent with those found in a few low redshift narrow-line Seyfert 1 galaxies (NLSy1). This, together with the similarity of the 0.1-10 keV X-ray continuum, suggests that this quasar is the higher redshift and luminosity analog of a NLSy1. In the broad line quasar PG 0947+396, the rest-frame line energy suggests fluorescence from cold iron. The line equivalent width ([FORMULA] 400 eV) is however about 2-3 times higher than that usually found in Seyfert 1 galaxies. The high energy power-law slopes and the iron line emission properties seem to be unrelated to the X-ray luminosity.

Key words: galaxies: quasars: general – galaxies: quasars: emission lines – X-rays: galaxies

Send offprint requests to: T. Mineo (mineo@ifcai.pa.cnr.it)

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000

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