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Abstract
Accreting neutron stars and black holes in low-mass X-ray binaries
(LMXBs) radiate across the electromagnetic spectrum. Linking the
emission produced at different wavelengths can provide valuable
information about the accretion process and any associated outflows. In
this work, we study simultaneous X-ray and ultraviolet (UV)/optical
observations of the neutron star LMXB Aql X-1, obtained with the Neil Gehrels Swift Observatory
during its 2013, 2014, and 2016 accretion outbursts. We find that the
UV/optical and X-ray emission are strongly correlated during all three
outbursts. For the 2013 and 2014 episodes, which had the best Swift
sampling, we find that the correlation between the UV/optical and X-ray
fluxes is significantly steeper during the decay (soft state) of the
outburst than during the rise (hard-to-soft state). We observe a
UV/optical hysteresis behaviour that is likely linked to the commonly
known X-ray spectral hysteresis pattern. For the decays of the three
outbursts, we obtain a correlation index that cannot be directly
explained by any single model. We suspect that this is a result of
multiple emission processes contributing to the UV/optical emission, but
we discuss alternative explanations. Based on these correlations, we
discuss which mechanisms are likely dominating the UV/optical emission
of Aql X-1.
Original language | English |
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Pages (from-to) | 940-951 |
Number of pages | 12 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 493 |
Issue number | 1 |
Early online date | 3 Feb 2020 |
DOIs | |
Publication status | Published - Mar 2020 |
Keywords
- Accretion, accretion discs
- Stars: neutron
- X-rays: binaries
- X-rays: individual: (Aql X-1)
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Dive into the research topics of 'The connection between the UV/optical and X-ray emission in the neutron star low-mass X-ray binary Aql X-1'. Together they form a unique fingerprint.Projects
- 1 Finished
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Astronomy at St Andrews 2018-2021: Astronomy at St Andrews 2018-2021
Jardine, M. M. (PI), Bonnell, I. A. (CoI), Cameron, A. C. (CoI), Cyganowski, C. J. (CoI), Dominik, M. (CoI), Helling, C. (CoI), Horne, K. D. (CoI), Scholz, A. (CoI), Tojeiro, R. (CoI), Weijmans, A.-M. (CoI), Wild, V. (CoI), Woitke, P. (CoI), Wood, K. (CoI) & Zhao, H. (CoI)
1/04/18 → 31/03/22
Project: Standard