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Published in

Oxford University Press, Monthly Notices of the Royal Astronomical Society, 1(304), p. 52-60, 1999

DOI: 10.1046/j.1365-8711.1999.02359.x

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The X-ray properties of the nearby LINER galaxy, NGC 4736

Journal article published in 1998 by Tp P. Roberts ORCID, Rs S. Warwick, T. Ohashi
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Data provided by SHERPA/RoMEO

Abstract

NGC 4736 is a nearby Sab spiral galaxy, hosting one of the closest examples of a LINER nucleus. We have utilized recent observations by ROSAT and ASCA to characterise the X-ray properties of this galaxy. Twelve discrete X-ray sources are detected within the region subtended by its optical disk, the majority of which are likely to be X-ray binaries associated with the galaxy. By far the brightest source in the X-ray band is positionally coincident with the nucleus of the galaxy and is spatially resolved into a component with a radial extent of ~ 3 kpc plus a point-like core. The broad band (0.1-10 keV) spectrum of this nuclear source is composed of a hard continuum with a spectral slope characteristic of that observed in classical Seyfert nuclei (i.e. power-law photon index, Gamma ~ 1.7), with thermal emission (kT = 0.1-0.6 keV) dominant below 2 keV. An Fe K alpha line may also be present at ~ 6.8 keV. There is no evidence for X-ray temporal variability on timescales of hours to years. A plausible model is that the hard continuum originates in a near-quiescent active galactic nucleus (with L_x ~ 6 x 10^39 erg/s, 0.5-10 keV) embedded in the LINER at the centre of NGC 4736. However, an alternative explanation, namely that the LINER is the site of a dense population of X-ray binary sources, cannot be completely excluded. ; Comment: 11 pages including 4 embedded figures, uses graphicx.sty and mn.sty, accepted for publication in MNRAS