X-RAY-SPECTRA OF 8 SEYFERT-GALAXIES

Analyses of the low- (LE) and medium-energy (ME) X-ray (0.1 - 10 keV) spectra of eight Seyfert galaxies (ESO 012-G21, Mkn 352, Mkn 374, Mkn 766, Mkn 279, Mkn 464, Mkn 290 and ESO 140-G43), obtained from the EXOSAT data base, are presented. For seven of these galaxies, power-law plus absorption models fit the LE plus ME spectra well, although the low-energy absorption (N(H)) values are smaller than the corresponding galactic N(H) values. For ESO 140-G43, a power-law plus fixed-absorption model is unacceptable, because of the large values of the reduced chi2 (chi(r)2 much greater than 1.0). Seven of the galaxies (ESO 012-G21, Mkn 352, 374, 766, 279, 464 and 290) have soft excesses in their spectra when they are fitted with the fixed power-law (obtained from the fits to the ME data) plus fixed-absorption model. For six of them, this is a new result. Models involving two power laws, thermal bremsstrahlung and broken power laws were tried in attempts to fit the soft excesses, but they were fitted best by the broken power-law model. A highly significant (99.9 per cent) emission line near 6.0 keV has been detected in the spectra of Mkn 766, Mkn 464, Mkn 290 and ESO 140-G43.