R.F. Mushotzky, A.C. Fabian, K. Iwasawa, H. Kunieda, M. Matsuoka, K. Nandra, Y. Tanaka

Abstract

X-ray spectra of Seyfert 1 galaxies obtains by the Ginga satellite showed the presence of a fluorescent iron line and a hard continuum tail, which are commonly interpreted as the signature of cold matter irradiated by the X-ray source. This matter could be in the form of either an accretion disc immediately around the central black hole or an outer torus at a radius of about a parsec. Here we use spectra of two such active galaxies taken with the ASCA satellite at higher spectral resolution to show, clearly, that the Fe lines are broad. Gaussian model fits show for IC4329A (z=0.016) that the line is centred at 6.19 keV in the observer's frame and has a FWHM of >20 000 km s^-1, and for NGC 5548 (z=0.017) that the line is at 6.15 keV with a FWHM of >35 000 km s^-1. The line centroids are shifted by >0.2 keV with respect to the expected rest-frame energy of a fluorescent line from cold material. The widths are considerably larger than the full widths of the optical or UV lines found in these objects of ~15 000 km s^-1. The intrinsic line profiles are not well determined, but are consistent with models of lines from the inner regions (<100 Schwarzschild radii) of accretion discs inclined at ~20 deg-30 deg. The discovery of such broad lines now opens up the immediate surroundings of accreting black holes for detailed study.