THE PROFILE AND EQUIVALENT WIDTH OF THE X-RAY IRON EMISSION-LINE FROMA DISC AROUND A KERR BLACK-HOLE

Recent X-ray observations have shown broad, skewed iron line emission from Seyfert 1 galaxies, which is explained by the emission being fluo rescence on a disc close to a black hole. During one interval, the lin e in MCG-6-30-15 was so broad and redshifted that a Kerr black hole is implied. We are therefore studying the effects of the Kerr metric on the Line profile, and extending the work by Laor and Kojima which deal t only with extreme values of the spin parameter. Here we report that the spin parameter of the black hole in MCG-6-30-15 is high (a/M>0.94) , and invert the line profile to obtain the disc emissivity profile, w hich approximates a power law. Continuum radiation returning to the di sc because of the Kerr metric does not enhance the equivalent width of the line seen above 3 keV by more than about 20 per cent if the conti nuum source corotates with the disc.