Shahbaz, T., Paice, J.A. orcid.org/0000-0003-1149-1741, Rajwade, K.M. orcid.org/0000-0002-8043-6909 et al. (8 more authors) (2023) A rapid optical and X-ray timing study of the neutron star X-ray binary Swift J1858.6–0814. Monthly Notices of the Royal Astronomical Society, 520 (1). pp. 542-559. ISSN 0035-8711
Abstract
We present a rapid timing analysis of optical (HiPERCAM and ULTRACAM) and X-ray (NICER) observations of the X-ray transient Swift J1858.6−0814 during 2018 and 2019. The optical light curves show relatively slow, large amplitude (∼1 mag in gs) ‘blue’ flares (i.e. stronger at shorter wavelengths) on time-scales of ∼minutes as well as fast, small amplitude (∼0.1 mag in gs) ‘red’ flares (i.e. stronger at longer wavelengths) on time-scales of ∼seconds. The ‘blue’ and ‘red’ flares are consistent with X-ray reprocessing and optically thin synchrotron emission, respectively, similar to what is observed in other X-ray binaries. The simultaneous optical versus soft- and hard-band X-ray light curves show time- and energy-dependent correlations. The 2019 March 4 and parts of the June data show a nearly symmetric positive cross-correlations (CCFs) at positive lags consistent with simple X-ray disc reprocessing. The soft- and hard-band CCFs are similar and can be reproduced if disc reprocessing dominates in the optical and one component (disc or synchrotron Comptonization) dominates both the soft and hard X-rays. A part of the 2019 June data shows a very different CCFs. The observed positive correlation at negative lag in the soft band can be reproduced if the optical synchrotron emission is correlated with the hot flow X-ray emission. The observed timing properties are in qualitative agreement with the hybrid inner hot accretion flow model, where the relative role of the different X-ray and optical components that vary during the course of the outburst, as well as on shorter time-scales, govern the shape of the optical/X-ray CCFs.
Metadata
Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2023 The author(s). Reproduced in accordance with the publisher's self-archiving policy. | ||||||||
Keywords: | accretion; accretion discs; stars: neutron; X-rays: binaries; X-rays: individual: Swift J1858.6−0814 | ||||||||
Dates: |
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Institution: | The University of Sheffield | ||||||||
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Department of Physics and Astronomy (Sheffield) | ||||||||
Funding Information: |
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Depositing User: | Symplectic Sheffield | ||||||||
Date Deposited: | 01 Feb 2023 15:52 | ||||||||
Last Modified: | 01 Feb 2023 16:01 | ||||||||
Status: | Published | ||||||||
Publisher: | Oxford University Press (OUP) | ||||||||
Refereed: | Yes | ||||||||
Identification Number: | https://doi.org/10.1093/mnras/stad163 |