A statistical study of the relation between soft X-ray excess and accretion disk  

作　　者：LIU JieYing1,2,3 & QIAO ErLin1,2 1 National Astronomical Observatories/Yunnan Observatory,Chinese Academy of Science,Kunming 650011,China 2 Key Laboratory for the Structure and Evolution of Celestial Objects,Chinese Academy of Sciences,Kunming 650011,China 3 Graduate University of Chinese Academy of Sciences,Beijing 100049,China 

出　　处：《Science China(Physics,Mechanics & Astronomy)》2010年第S1期102-105,共4页中国科学：物理学、力学、天文学（英文版）

基　　金：supported by the National Basic Research Program of China (Grant No. 2009CB824800);the National Natural Science Foundation of China (Grant Nos. 10533050 and 10773028)

摘　　要：To study the origin of the soft X-ray excess,we compile a sample of 94 unobscured,radio-quiet QSOs and Seyfert galaxies with available data from GALEX and ROSAT.We find that 50 sources show strong soft X-ray excess and the other 44 show weak/no soft X-ray excess.Systematic analyses of the data indicate that the difference in soft X-rays is mainly but not only resulting from different accretion rates(in units of Eddington rate).The statistical study of the sources with soft X-ray excess shows that the strength of soft X-ray excess weakly and positively correlates with the Eddington ratio and increases with the increase of the strength of UV radiations relative to the X-rays.Provided that the UV emissions are from the thin disk,the correlations imply that the origin of soft X-ray excess is associated with the thin disk,either by means of Comptonization of the disk photons or in some other ways.To study the origin of the soft X-ray excess,we compile a sample of 94 unobscured,radio-quiet QSOs and Seyfert galaxies with available data from GALEX and ROSAT.We find that 50 sources show strong soft X-ray excess and the other 44 show weak/no soft X-ray excess.Systematic analyses of the data indicate that the difference in soft X-rays is mainly but not only resulting from different accretion rates(in units of Eddington rate).The statistical study of the sources with soft X-ray excess shows that the strength of soft X-ray excess weakly and positively correlates with the Eddington ratio and increases with the increase of the strength of UV radiations relative to the X-rays.Provided that the UV emissions are from the thin disk,the correlations imply that the origin of soft X-ray excess is associated with the thin disk,either by means of Comptonization of the disk photons or in some other ways.

关 键 词：accretion:accretion DISKS ultraviolet:galaxies X-rays:galaxies 

分 类 号：P172.2[天文地球—天文学]