High-resolution X-ray imaging of M33

The nearby spiral galaxy M33 was observed for 35 ks with the high-resolution imager on ROSAT in 1992 January and August. We find 27 X-ray sources more luminous than 6 x 10(exp 36) ergs/s within 17.5 arcmin of the nucleus, of which 12 were discovered by the Einstein Observatory. Three of the ROSAT sources are coincident with giant H II regions, and seven are coincident or nearly coincident with supernova remnants. There is evidence for long-term variability between the Einstein and ROSAT observations in three sources, one of which was not detected in the ROSAT observations. Aside from an eclipsing binary X-ray source discovered by the Einstein Observatory, there is no evidence for variability within the ROSAT observations. Of the 120 cataloged holes in the H I layer in the field of view, two have significant X-ray emission. One is coincident with the giant H II region IC 133 while the other appears to be due to the chance superposition of a strong X-ray point source. Such holes are thought to be created by energetic stellar winds and supernovae from massive stars in young associations. We detect diffuse X-ray emission with a luminosity of about 10(exp 39) ergs/s, which may trace the spiral arms within 10 arcmin of the nucleus.