A&A 410, 131-138 (2003)
DOI: 10.1051/0004-6361:20031195

The hard X-ray view of the low-luminosity blazar in the radio galaxy NGC 6251

M. Guainazzi¹, P. Grandi², A. Comastri³ and G. Matt<sup>4

1</sup>  XMM-Newton Science Operations Center, VILSPA, ESA, Apartado 50727, 28080 Madrid, Spain
    e-mail: mguainaz@xmm.vilspa.esa.es
²  Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF-C.N.R.), Sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
³  I.N.A.F., Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁴  Dipartimento di Fisica, Università degli Studi "Roma Tre", via della Vasca Navale 84, 00146 Roma, Italy

(Received 21 February 2003 / Accepted 31 July 2003 )

Abstract
We present results from a BeppoSAX (July 2001) observation of the FR I radio galaxy NGC 6251, together with a re-analysis of archival ASCA (October 1994) and Chandra (September 2000) data. The weak detection above 10 keV and the lack of iron fluorescent K emission lines in the BeppoSAX spectrum rule out that the bulk of the X-ray emission is due to an obscured Seyfert nucleus. The study of the multiwavelength spectral energy distribution suggests instead that X-rays probably originate as inverse-Compton of synchrotron seed photons in a relativistic jet, indicating that NGC 6251 hosts a low radio luminosity (  erg s ^-1) blazar. The BeppoSAX spectrum is flatter than in the earlier ASCA observation. This might be due to the emergence of a different spectral component during phases of lower X-ray flux. In this context, we discuss some possible explanations for the intense and mildly-ionized fluorescent iron line measured by ASCA.

Key words: galaxies: active -- galaxies: individual: NGC 6251 -- galaxies: jets -- galaxies: nuclei -- X-rays: galaxies

Offprint request: M. Guainazzi, mguainaz@scmm.vilspa.esa.es

SIMBAD Objects

© ESO 2003

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.