A New Sample of Transient Ultraluminous X-Ray Sources Serendipitously Discovered by Swift/XRT
Abstract
Ultraluminous X-ray sources (ULXs) are our best laboratories for studying extreme super-Eddington accretion. Most studies of these objects are of relatively persistent sources; however, there is growing evidence to suggest a large fraction of these sources are transient. Here we present a sample of five newly reported transient ULXs in the galaxies NGC 4945, NGC 7793, and M81 serendipitously discovered in Swift/XRT observations. Swift monitoring of these sources have provided well-sampled lightcurves, allowing for us to model the lightcurves with the disk-instability model of Hameury & Lasota, which implies durations of 60-400 days and that the mass-accretion rate through the disk is close to or greater than the Eddington rate. Of the three source regions with prior Hubble Space Telescope imaging, color-magnitude diagrams of the potential stellar counterparts show varying ages of the possible stellar counterparts. Our estimation of the rates of these sources in these three galaxies is 0.4-1.3 yr-1. We find that, while persistent ULXs dominate the high end of galaxy luminosity functions, the number of systems that produce ULX luminosities are likely dominated by transient sources.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2023
- DOI:
- 10.3847/1538-4357/acd18a
- arXiv:
- arXiv:2305.01693
- Bibcode:
- 2023ApJ...951...51B
- Keywords:
-
- X-ray transient sources;
- Transient sources;
- X-ray sources;
- Ultraluminous x-ray sources;
- 1852;
- 1851;
- 1822;
- 2164;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in ApJ