EDP Sciences
Free Access
Issue
A&A
Volume 410, Number 1, October IV 2003
Page(s) 131 - 138
Section Galactic structure and dynamics
DOI https://doi.org/10.1051/0004-6361:20031195
Published online 17 November 2003


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. Matt4

1  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 $_{\alpha}$ 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 ( $L_{{\rm 5 \ GHz}} \sim 10^{40}$ 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

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.