BeppoSAX view of NGC 526A: a Seyfert 1.9 galaxy with a flat spectrum

Abstract

In the present work we report the BeppoSAX observation of the Seyfert 1.9 galaxy NGC 526A in the band 0.1-150 keV. The high energy instrument onboard, PDS, has succeeded in measuring for the first time the spectrum of this source in the 13-150 keV range. The combined analysis of all Narrow Field Instruments provides a power law spectral index of ~ 1.6 and confirms the flat spectral nature of this source. Although NGC 526A varies strongly in the 2-10 keV over period of months/years, its spectral shape remains constant over these timescales. An Fe K-alpha line, characterized by a complex structure, has been detected in the 6-7 keV range. The line, which has an equivalent width of 120 eV, is not compatible with being produced in an absorbing torus with N_H ~ 10^22 cm^-2, but most likely originates by reflection in an accretion disk viewed at an intermediate inclination angle of ~ 42 deg. The reflection component is however small (R < 0.7) and so it is not sufficient to steepen the spectrum to photon index values more typical of AGNs. Instead, we find that the data are more consistent with a flat power law spectrum cut-off at around 100 keV plus a small reflection component which could explain the observed iron line. Thus NGC 526A is the only bona-fide Seyfert 2 galaxy which maintains a "flat spectrum" even when broad band data are considered: in this sense its properties, with respect to the general class of Seyfert 2's, are analogous to those of NGC 4151 with respect to the vast majority of Seyfert 1's.Comment: 8 pages, 6 PostScript figures, Latex manuscript, new A&A file style included, accepted for publication on Astronomy and Astrophysic