Long-term X-ray/UV variability in ULXs
Long-term X-ray/UV variability in ULXs
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.
stars: black holes, stars: neutron
4302–4314
Khan, Norman
d5c7df8e-d172-494e-8fc4-4c4ef5cf951f
Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad
1 September 2023
Khan, Norman
d5c7df8e-d172-494e-8fc4-4c4ef5cf951f
Middleton, Matthew
f91b89d9-fd2e-42ec-aa99-1249f08a52ad
Khan, Norman and Middleton, Matthew
(2023)
Long-term X-ray/UV variability in ULXs.
Monthly Notices of the Royal Astronomical Society, 524 (3), .
(doi:10.1093/mnras/stad2071).
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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Evidence_of_UV_X_ray_anticorrelations_in_ULXs-9
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Accepted/In Press date: 4 July 2023
e-pub ahead of print date: 11 July 2023
Published date: 1 September 2023
Additional Information:
Funding Information:
NK acknowledges support via STFC studentship project reference: 2115300. MJM was supported by STFC through grant ST/V001000/1. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. The authors thank the anonymous referee for useful suggestions.
Publisher Copyright:
© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
Keywords:
stars: black holes, stars: neutron
Identifiers
Local EPrints ID: 481970
URI: http://eprints.soton.ac.uk/id/eprint/481970
ISSN: 1365-2966
PURE UUID: 8d987955-796b-4bcb-97ec-1032d1bb4707
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Date deposited: 14 Sep 2023 16:39
Last modified: 09 Apr 2024 21:52
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Author:
Norman Khan
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