A New Sample of Transient Ultraluminous X-Ray Sources Serendipitously Discovered by Swift/XRT
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Author
Brightman, Murray
Hameury, Jean-Marie
Lasota, Jean-Pierre
Baldi, Ranieri D.
Bruni, Gabriele
Cann, Jenna M.
Earnshaw, Hannah
Fürst, Felix
Heida, Marianne
Jaodand, Amruta
Lazzarini, Margaret
Middleton, Matthew J.
Walton, Dominic J.
Weaver, Kimberly A.
Attention
2299/26464
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 date
2023-07-03Published in
The Astrophysical JournalPublished version
https://doi.org/10.3847/1538-4357/acd18aOther links
http://hdl.handle.net/2299/26464Metadata
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