X-Ray Observations of the Seyfert 1 Galaxy Markarian 464

Abstract

In this paper we present results of EXOSAT (0.05-10 keV) and hard X- ray (25-45 keV) balloon observations (XG-8 1) of the Seyfert 1 galaxy Mrk 464. The spectrum observed with EXOSAT is well fitted by a power law with a photon spectral index 1.70+/-0.15, in agreement with a previous measurement by HEAO 1 A-2. The absorption column density is found consistent with the galactic column density. Both the EXOSAT and the HEAO 1 upper limit (N_H_ < 10^22^ cm^-2^) are in disagreement with the very high column density of 2.5 x 10^23^ cm^-2^ observed by Ariel 5. The XG-81 experiment detected a bright hard X-ray source in a field of view centered on Mrk 464. This measurement is most likely explained by an outburst of this Seyfert galaxy, with a peak luminosity one order of magnitude greater than the average one. Similar variations have been observed already in two other objects of this class, namely Centaurus A and NGC 4151.