SCHLEGEL E.M., PETRE R., COLBERT E.J.M. and MILLER S.
Abstract (from CDS):
We describe a series of observations of NGC 1313 using the ROSAT HRI with a combined exposure time of 183.5 ks. The observations span an interval between 1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray flux of SN 1978K, one of several luminous sources in the galaxy. No diffuse emission is detected in the galaxy to a level of i ∼1-2x1037 ergs.s–1.arcmin–2. A total of eight sources are detected in the summed image within the D25 diameter of the galaxy. The luminosities of five of the eight range from ∼6x1037 to ∼6x1038 ergs.s–1; these sources are most likely accreting X-ray binaries, similar to sources observed in M31 and M33. The remaining three sources all emit above 1039 ergs.s–1. We present light curves of the five brightest sources. Variability is detected at the 99.9% level in four of these. We identify one of the sources as an NGC 1313 counterpart of a Galactic X-ray source. The light curve, though crudely sampled, most closely resembles that of a Galactic black hole candidate such as GX 339-4 but with considerably higher peak X-ray luminosity. An additional seven sources lie outside the D25 diameter and are either foreground stars or background active galactic nuclei.