Open AccessThe X‐ray properties of the nearby LINER galaxy NGC 4736
Author(s) -
Roberts T. P.,
Warwick R. S.,
Ohashi T.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02359.x
Subject(s) - physics , astrophysics , galaxy , astronomy
NGC 4736 is a nearby Sab spiral galaxy, hosting one of the closest examples of a low‐ionization nuclear emission‐line region (LINER) nucleus. We have utilized recent observations by ROSAT and ASCA to characterize the X‐ray properties of this galaxy. 12 discrete X‐ray sources are detected within the region subtended by its optical disc, 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, γ≈ 1.7), with thermal emission ( kT = 0.1 ‐‐0.6 keV) dominant below 2 keV. An Fe K α line may also be present at ∼ 6.8 keV. There is no evidence for X‐ray temporal variability on time‐scales of hours to years. A plausible model is that the hard continuum originates in a near‐quiescent active galactic nucleus (with L X ∼ 6 × 10 39 erg s ‐1 , 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.