The Long‐Term Variability of a Population of ULXs Monitored by Chandra

Earnshaw, Hannah P.; Patti, Gauri; Brightman, Murray; Sathyaprakash, Rajath; Walton, Dominic J.; Fürst, Felix; Roberts, Timothy P.; Harrison, Fiona A.

Abstract

We present preliminary results of a Chandra Large Program to monitor the ultraluminous x-ray source (ULX) populations of three nearby, ULX-rich galaxies over the course of a year, finding the ULX population to show a variety of long-term variability behaviours. Of a sample of 36 ULXs, some show persistent or moderately variable flux, often with a significant relationship between hardness and luminosity, consistent with a supercritically accreting source with varying accretion rates. Six show very high-amplitude variability with no strong relationship between luminosity and hardness, though not all of them show evidence of any long-term periodicity, nor of the bimodal distribution indicative of the propeller effect. We find evidence of additional eclipses for two previously-identified eclipsing ULXs. Additionally, many sources that were previously identified as ULXs in previous studies were not detected at ULX luminosities during our monitoring campaign, indicating a large number of transient ULXs.

Citation

Earnshaw, H. P., Patti, G., Brightman, M., Sathyaprakash, R., Walton, D. J., Fürst, F., Roberts, T. P., & Harrison, F. A. (online). The Long‐Term Variability of a Population of ULXs Monitored by Chandra. Astronomische Nachrichten, https://doi.org/10.1002/asna.20240103

• Journal Article Type: Article
• Acceptance Date: Oct 28, 2024
• Online Publication Date: Nov 22, 2024
• Deposit Date: Jan 10, 2025
• Publicly Available Date: Jan 10, 2025
• Journal: Astronomische Nachrichten
• Print ISSN: 0004-6337
• Electronic ISSN: 1521-3994
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• DOI: https://doi.org/10.1002/asna.20240103
• Public URL: https://durham-repository.worktribe.com/output/3329290
• Related Public URLs: https://arxiv.org/abs/2411.07459