SOFT-X-RAY EMISSION FROM THE SPIRAL GALAXY NGC-1313

The nearby barred spiral galaxy NGC 1313 has been observed with the PS PC instrument on board the ROSAT X-ray satellite. Ten individual sourc es are found. Three sources (X-1, X-2, and X-3 [SN 1978K]) are very br ight (similar to 10(40) ergs s(-1)) and are unusual in that analogous objects do not exist in our Galaxy. We present an X-ray image of NGC 1 313 and X-ray spectra for the three bright sources. The emission from the nuclear region (R less than or similar to 2 kpc) is dominated by s ource X-1, which is located similar to 1 kpc north of the photometric (and dynamical) center of NGC 1313. Optical, far-infrared, and radio i mages do not indicate the presence of an active galactic nucleus at th at position; however, the compact nature of the X-ray source (X-1) sug gests that it is an accretion-powered object with central mass M great er than or similar to 10(3) M.. Additional emission (L(x) similar to 1 0(39) ergs s(-1)) in the nuclear region extends out to similar to 2.6 kpc and roughly follows the spiral arms. This emission is from four so urces with luminosity of several x 10(38) ergs s(-1) two of which are consistent with emission from Population I sources (e.g., supernova re mnants, and hot interstellar gas which has been heated by supernova re mnants). The other two sources could be emission from Population II so urces (e.g., low-mass X-ray binaries). The bright sources X-2 and SN 1 978K are positioned in the southern disk of NGC 1313. X-2 is variable and has no optical counterpart brighter than 20.8 mag (V-band). It is likely that it is an accretion-powered object in NGC 1313. The Type II supernova SN 1978K (Ryder et al. 1993) has become extraordinarily lum inous in X-rays similar to 13 yr after optical maximum.