A [ITAL]CHANDRA[/ITAL][ITAL]Chandra[/ITAL] Study of the Circinus Galaxy Point-Source Population

We have used the Chandra X-ray Observatory to resolve spatially andspectrally the X-ray emission from the Circinus Galaxy. We report here on thenature of the X-ray emission from the off-nuclear point sources associated withthe disk of Circinus. We find that many of the serendipitous X-ray sources areconcentrated along the optical disk of the galaxy, but few have opticalcounterparts within 1" of their X-ray positions down to V=23-25. At 3.8 Mpc,their intrinsic 0.5-10 keV luminosities range from approx. 2E37 erg/s to 4E39erg/s. One quarter of the sources are variable over the duration of the 67 ksobservation, and spectral fitting of these off-nuclear sources shows a diverserange of spectral properties. The properties of the two strongest off-nuclearsources are remarkable, with average X-ray luminosities of 3.7E39 erg/s and3.4E39 erg/s. The former displays large and periodic flux variations every 7.5hr and is well fit by a multicolor blackbody accretion-disk model withT_in=1.35 keV, properties consistent with an eclipsing >50 M_sun black-holebinary. The latter appears to be a young supernova remnant, as it coincideswith a non-thermal radio counterpart and an H\alpha-detected HII region. Thissource exhibits both long-term (approx. 4 yr) X-ray variability and a 6.67-6.97keV iron emission-line blend with a 1.6 keV equivalent width. These two objectsfurther support the notion that super-Eddington X-ray sources in nearbygalaxies can be explained by a mixture of intermediate-mass black holes inX-ray binaries and young supernova remnants. (abridged)