![]() | ![]() |
Astron. Astrophys. 331, 925-933 (1998) 1. IntroductionStudies of the soft X-ray excess were done preferentially with low
redshift AGN because this spectral feature will be shifted out of the
observed energy windows of the ROSAT, EXOSAT and Einstein
satellites for higher redshifts. The existence of the soft X-ray
excess was first detected for the RX J0947.0+4721 was first detected in the RASS 1 (Bade et al. 1995). It appeared to be a very soft source, but the photon statistics were insufficient to determine the spectral shape. Besides that, RX J0947.0+4721 is the brightest and steepest source in a medium deep ROSAT survey in the field HS 47.5/22 (Molthagen 1996). The field is part of the Hamburg Quasar Survey (Hagen et al. 1995), an objective prism based survey of the northern hemisphere. Due to its brightness, RX J0947.0+4721 can be found in 16 of the 48 pointings which form the survey. Strong variations, already suggested in the RASS data, were clearly seen in the pointed data. RX J0947.0+4721 shows striking similarity in optical and X-ray
behaviour with NLS1 objects such as IRAS 13224-3809 (Boller et al.
1993). Both RX J0947.0+4721 and IRAS 13224-3809 have exceptionally
steep soft X-ray spectra, narrow Balmer lines, and strong optical
Fe II emission. RX J0947.0+4721 is also an IRAS source (Moshir et al.
1990). Its optical and X-ray luminosities, computed with
![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: March 3, 1998 ![]() |