Vol 9, No 9 (2009) / Liu

Investigating the disk-corona relation in a blue AGN sample

Jie-Ying Liu, Bi-Fang Liu


We compile a blue AGN sample from SDSS and investigate how the ratio of hard X-ray to bolometric luminosity depends on the Eddington ratio and black hole mass. Our sample comprises 240 radio-quiet Seyfert 1 galaxies and QSOs. We find that the fraction of hard X-ray luminosity (log(L2-10keV/Lbol )) decreases with an increase of the Eddington ratio. We also find that the fraction of hard X-ray luminosity is independent of the black hole mass for radio-quiet AGNs. The relation of log(L2-10keV/Lbol) decreasing with increasing Eddington ratio indicates that X-ray bolometric correction is not a constant, from a larger sample supporting the results of Vasudevan & Fabian.We interpret our results by the disk corona evaporation/condensation model. In the frame work of this model, Compton cooling becomes efficient in cooling the corona at high accretion rates (in units of Eddington rate), leading to condensation of coronal gas to the disk. Consequently, the relative strength of the corona to the disk becomes weaker at higher Eddington ratios. Therefore, the fraction of hard X-ray emission to disk emission and hence to the bolometric emission is smaller at higher Eddington ratios. The independence of the fraction of hard X-ray luminosity with respect to the mass of the black hole can also be explained by the disk corona model since the coronal structure and luminosity (in units of Eddington luminosity) are independent of the mass of black holes.



accretion: accretion disks— galaxies: active— X-rays: galaxies

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