X-rays:spectra;
galaxies:active;
5TH DATA RELEASE;
D O I:
10.1063/1.3475324
中图分类号:
P1 [天文学];
学科分类号:
0704 ;
摘要:
We present the X-ray properties of a large, optically selected sample of quasars from a cross-correlation of the SDSS DR5 quasar catalogue and the X-ray serendipitous source catalogue 2XMMi. We consider the dependence of photon index on X-ray luminosity and redshift. We find evidence for a correlation of photon index and redshift (decreasing photon indices for higher redshift sources) and propose that this may be due to a Compton reflection component being redshifted into the XMM-Newton observed energy band. We show that this apparent trend can be removed when the spectra are analysed over a reduced range that would exclude any contribution from such a reflection component.