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Long-term X-ray/UV variability in ULXs
ABSTRACT The focus of NASA’s Swift telescope has been transients and target-of-opportunity observing, resulting in many observations of ultraluminous X-ray sources (ULXs) over the last ∼20 yr. For the vast majority of these observations, simultaneous data have been obtained using both the X-ray tele...
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Published in: | Monthly notices of the Royal Astronomical Society 2023-07, Vol.524 (3), p.4302-4314 |
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Main Authors: | , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | ABSTRACT
The focus of NASA’s Swift telescope has been transients and target-of-opportunity observing, resulting in many observations of ultraluminous X-ray sources (ULXs) over the last ∼20 yr. For the vast majority of these observations, simultaneous data have been obtained using both the X-ray telescope (XRT) and the ultraviolet and optical telescope (UVOT), providing a unique opportunity to study coupled variability between these bands. Using a sample of ∼40 ULXs with numerous repeat observations, we extract stacked images to characterize the spatial extent of the UV/optical emission and extract long-term light curves to search for first-order linear correlations between the UV and X-ray emission. We find that a small subset may show weakly correlated joint variability, while other sources appear to display non-linear relationships between the bands. We discuss these observations in the context of several theoretical models: precession, irradiation of the outer accretion disc, and irradiation of the companion star. We conclude that more complicated analysis or higher quality data may be required to accurately constrain the nature of the joint X-ray and UV/optical emission in these sources. |
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ISSN: | 0035-8711 1365-2966 |
DOI: | 10.1093/mnras/stad2071 |