The XMM-Newton view of PG quasars

Free access article

Issue		A&A Volume 432, Number 1, March II 2005


Page(s)		15 - 30
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20041621

A&A 432, 15-30 (2005)
DOI: 10.1051/0004-6361:20041621

I. X-ray continuum and absorption

E. Piconcelli, E. Jimenez-Bailón, M. Guainazzi, N. Schartel, P. M. Rodríguez-Pascual and M. Santos-Lleó

XMM-Newton Science Operation Center (ESAC), Apartado 50727, 28080 Madrid, Spain
e-mail: epiconce@xmm.vilspa.esa.es

(Received 8 July 2004 / Accepted 26 October 2004)

Abstract
We present results of a systematic analysis of the XMM-Newton spectra of 40 quasars (QSOs) ( $z\leq1.72$ ) from the Palomar-Green (PG) Bright Quasar Survey sample ( M_B<-23). The sample includes 35 radio-quiet quasars (RQQs) and 5 radio-loud quasars (RLQs). The analysis of the spectra above 2 keV reveals that the hard X-ray continuum emission can be modeled with a power law component with $\langle\Gamma_{\rm 2-12~keV}\rangle = 1.89\pm0.11$ and $\langle\Gamma_{\rm 2-12~keV}\rangle = 1.63^{+0.02}_{-0.01}$ for the RQQs and RLQs, respectively. Below 2 keV, a strong, broad excess is present in most QSO spectra. This feature has been fitted with four different models assuming several physical scenarios. All tested models (blackbody, multicolor blackbody, bremsstrahlung and power law) satisfactorily fitted the majority of the spectra. However, none of them is able to provide an adequate parameterization for the soft excess emission in all QSOs, indicating the absence of a universal shape for this spectral feature. An additional cold absorption component was required only in three sources. On the other hand, as recently pointed out by Porquet et al. (2004) for a smaller sample of PG QSOs, warm absorber features are present in 50% of the QSO spectra in contrast with their rare occurrence (~5-10%) in previous studies. The XMM-Newton view of optically selected bright QSOs therefore suggests that there are no significant differences in the X-ray spectral properties compared with those of the low-luminosity Seyfert 1 galaxies. Properties of the Fe K $\alpha$ emission lines are presented in a companion paper.

Key words: galaxies: active -- galaxies: nuclei -- galaxies quasars: general -- X-rays: galaxies

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