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[70.05] A Deep ROSAT HRI Observation of NGC 1313

E.M. Schlegel (Harvard-Smithsonian CfA), R. Petre (NASA-GSFC), E.J.M. Colbert, S. Miller (U Maryland)

We describe a series of observations of NGC 1313 using the ROSAT HRI with a combined exposure time of 183.5 ksec. The observations span an interval between 1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray flux of SN1978K, one of several luminous sources in the galaxy. No diffuse emission is detected in the galaxy to a level of ~7\times10³⁶ ergs s^-1 arcmin^-2. A total of eight sources are detected in the summed image within the D₂₅ diameter of the galaxy and an additional seven outside of that region. We present light curves of the five brightest sources. Variability is detected at the 99.9% level from 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 GX339-4, but with considerably higher peak X-ray luminosity. We briefly discuss the large number of super-Eddington sources in this galaxy.

The research was supported by NASA Grant NAG5-4015 to the Smithsonian Astrophysical Observatory.