A powerful and highly variable off-nuclear X-ray source in the composite starburst/Seyfert 2 galaxy NGC 4945

Abstract

We report on a powerful and variable off-nuclear X-ray source in the nearby spiral galaxy NGC 4945. Two ROSAT PSPC observations show the source to brighten in 0.5--2.0 keV flux by a factor of about 9 on a time-scale of 11 months or less. It is seen by ASCA about one month after the second PSPC pointing, and is seen to have dimmed by a factor of > 7 in a ROSAT HRI pointing about one year after the second PSPC pointing. Its maximum observed 0.8--2.5 keV luminosity is about 8E38 erg/s, making it brighter than any known persistent X-ray binary in the Milky Way. Its total X-ray luminosity is probably larger than 1.2E39 erg/s. The observed variability argues against a superbubble interpretation, and the off-nuclear position argues against a low-luminosity active galactic nucleus. The source is therefore probably either an ultra-powerful X-ray binary or an ultra-powerful supernova remnant. Optical monitoring has not identified any supernovae in NGC 4945 during the time of the X-ray observations, and any supernova would have had to have been either very highly absorbed or intrinsically optically faint.

5 pages, uuencoded compressed tar file, MNRAS in press

Cited by in corpus (8)

• Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
• ASCA observations of Seyfert 1 galaxies: I. Data Analysis, Imaging and Timing
• The variable hard X-ray emission of NGC4945 as observed by NuSTAR
• An X-ray investigation of powerful far-infrared galaxies
• Structure of the Circumnuclear Region of Seyfert 2 Galaxies Revealed by RXTE Hard X-ray Observations of NGC 4945
• The XMM deep survey in the CDF-S II. a 9-20 keV selection of heavily obscured active galaxies at z>1.7
• Discovery of a bright transient ultraluminous X-ray source Suzaku J1305-4931 in NGC 4945
• A new sample of transient ultraluminous X-ray sources serendipitously discovered by Swift/XRT