We present an analysis of the X-ray properties of the Magellanic-type galaxy NGC 55 based on two contiguous XMM-Newton observations .
We detect a total of 137 X-ray sources in the field of view , down to a flux of \sim 5 \times 10 ^ { -15 } { ~ { } erg~ { } cm ^ { -2 } ~ { } s ^ { -1 } } ( 0.3 – 6 keV ) , 42 of which are located within the optical confines of the galaxy .
On the basis of X-ray colour classification and after correcting for background objects , we conclude that our source sample includes \sim 20 X-ray binaries , 5 supernova remnants and 7 very soft sources ( including 2 good candidate supersoft sources ) associated with NGC 55 .
We also detect an X-ray source coincident with a previously identified globular cluster in NGC 55 .
Detailed spectral and timing analysis was carried out on 4 of the brightest X-ray sources ( excluding the brightest source , which was the subject of a previous paper ) .
One of these objects is identified with a Galactic foreground star and is a possible new RS CVn system .
The other three are persistent X-ray sources with X-ray spectra well described by either a single absorbed power-law ( \Gamma \sim 2 ) or a multicolour disc blackbody ( kT _ { in } \sim 1 keV ) model .
While the observed luminosities of these sources ( L _ { X } \sim 1 - 2 \times 10 ^ { 38 } { ~ { } erg~ { } s ^ { -1 } } ) and their X-ray spectra are consistent with accreting X-ray binaries , further evidence of short term variability is required to confirm this .
Although the observed X-ray emission from NGC 55 is dominated by point sources , we do find evidence of an underlying component , which is concentrated on the bar region but has an extent of at least 6 ^ { \prime } ( 3 kpc ) in the plane of the galaxy and \pm 1 ^ { \prime } ( \pm 500 pc ) perpendicular to it .
This emission is best fitted by a thermal plasma ( mekal ) ( kT \sim 0.2 keV ) plus power-law ( \Gamma \sim 2 ) model but with high intrinsic absorption consistent with its location in the central disc of the galaxy .
We interpret the soft component as diffuse thermal emission linked to regions of current star formation , whilst the hard power-law component may originate in unresolved X-ray binary sources .
The intrinsic luminosity of this residual disc emission may exceed L _ { X } \sim 6 \times 10 ^ { 38 } { ~ { } erg~ { } s ^ { -1 } } ( 0.3–6 keV ) .
A comparison with other Magellanic systems confirms that , in terms of both its discrete X-ray source population and its extended emission , NGC 55 has X-ray properties which are typical of its class .