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

¹ Dipartimento di Fisica, Università di Bologna, via Irnerio 46, 40127 Bologna, Italy
² ITeSRE/CNR, via Piero Gobetti 101, 40129 Bologna, Italy
³ Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁴ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
⁵ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy

Corresponding author: R. Landi, landi@tesre.bo.cnr.it

Received: 11 April 2001
Accepted: 6 August 2001

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 range over a 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 medium with N_H ~ 10²² cm^-2, but most likely originates by reflection in an accretion disk viewed at an intermediate inclination angle of ~42°. The reflection component is however small () 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.