Nuclear and global X-ray properties of LINER galaxies: Chandra and BeppoSAX results for Sombrero and NGC 4736

¹ Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, 40127 Bologna, Italy
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: pepi@head-cfa.harvard.edu
³ Osservatorio Astronomico di Roma, via Frascati 33, 00044 Monteporzio Catone, Italy e-mail: fiore@quasar.mporzio.astro.it; angelo@coma.mporzio.astro.it
⁴ Osservatorio Astronomico di Brera, via Brera 28, 20121 Milan, Italy e-mail: ginevra@brera.mi.astro.it

Corresponding author: S. Pellegrini, pellegrini@bo.astro.it

Received: 23 July 2001
Accepted: 22 October 2001

Abstract

We report on the 0.1–100 keV BeppoSAX observations of two nearby LINER galaxies, Sombrero and NGC 4736. Chandra ACIS-S observations supplement this broad-beam spectral study with a high resolution look into the nuclear region, and show a dominating central point source in Sombrero and a complex X-ray binary dominated/starburst region in NGC 4736. A compact non-thermal radio source, present in the nucleus of both galaxies, coincides with the central source in Sombrero, while in NGC 4736 its X-ray counterpart is a much fainter point source, not the brightest of the central region. On the basis of these and other results, we conclude that the LINER activity is linked to the presence of a low luminosity AGN in Sombrero and to a recent starburst in NGC 4736, and that Chandra's spectroscopic capabilities coupled to high resolution imaging are essential to establish the origin of the nuclear activity.