A powerful and highly variable off-nuclear X-ray source in the composite starburst/Seyfert 2 galaxy NGC 4945.
Abstract
The authors report the discovery of 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 ≈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 ⪆8×1038erg s-1, making it brighter than any known persistent X-ray binary in the Milky Way. Its total X-ray luminosity is probably larger than 1.2×1039erg s-1. 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 1996
- DOI:
- 10.1093/mnras/281.3.L41
- arXiv:
- arXiv:astro-ph/9607007
- Bibcode:
- 1996MNRAS.281L..41B
- Keywords:
-
- X-Ray Sources: Spiral Galaxies;
- X-Ray Sources: Seyfert Galaxies;
- X-Ray Sources: Variations;
- X-Ray Sources: X-Ray Luminosities;
- stars: neutron -- supernovae: general -- galaxies: individual: NGC 4945 -- galaxies: Seyfert -- X-rays: galaxies -- X-rays: stars;
- Astrophysics
- E-Print:
- 5 pages, uuencoded compressed tar file, MNRAS in press