Chinese Acad Sci, Key Lab Particle Astrophys, Inst High Energy Phys, Beijing, Peoples R China
; Chinese Acad Sci, Grad Sch, Beijing, Peoples R China
We present an XMM-Newton EPIC observation of HE 0450-2958, which may be a "naked" quasar as suggested by Magain and coworkers. The XMM-Newton EPIC spectra show a substantial soft X-ray excess and a steep photon index, as well as marginal evidence for a weak Fe K alpha line. The X-ray absorption is consistent with the Galactic level. The 0.3-10 keV EPIC spectra can be fitted by a power-law plus blackbody model; however, the fit by a relativistically blurred photoionized disk reflection model is better. We estimate a black hole mass of 2(-1.3)(+7) x 10(7) M-circle dot from the X-ray variability. This broadly agrees with the value derived from the optical H beta line width. These results support a high-state Seyfert galaxy as the source. HE 0450-2958 shares properties with transitionary objects from ultraluminous infrared galaxies to quasars. We suggest that HE 0450-2958 is just in the beginning of an optical quasar window.