Oates, SR;
Motta, S;
Beardmore, AP;
Russell, DM;
Gandhi, P;
Kuin, NPM;
Pasquale, MD;
... Steeghs, D; + view all
(2019)
Swift UVOT observations of the 2015 outburst of V404 Cygni.
Monthly Notices of the Royal Astronomical Society
, 488
(4)
pp. 4843-4857.
10.1093/mnras/stz1998.
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Abstract
The black-hole binary, V404 Cygni, went into outburst in June 2015, after 26 years of X-ray quiescence. We observed the outburst with the Neil Gehrels Swift observatory. We present optical/UV observations taken with the Swift Ultra-violet Optical Telescope, and compare them with the X-ray observations obtained with the Swift X-ray Telescope. We find that dust extinction affecting the optical/UV, does not correlate with absorption due to neutral hydrogen that affects the X-ray emission. We suggest there is a small inhomogeneous high density absorber containing a negligible amount of dust, close to the black hole. Overall, temporal variations in the optical/UV appear to trace those in the X-rays. During some epochs we observe an optical time-lag of (15 - 35)s. For both the optical/UV and X-rays, the amplitude of the variations correlates with flux, but this correlation is less significant in the optical/UV. The variability in the light curves may be produced by a complex combination of processes. Some of the X-ray variability may be due to the presence of a local, inhomogeneous and dust-free absorber, while variability visible in both the X-ray and optical/UV may instead be driven by the accretion flow: the X-rays are produced in the inner accretion disc, some of which are reprocessed to the optical/UV; and/or the X-ray and optical/UV emission is produced within the jet.
| Type: | Article |
|---|---|
| Title: | Swift UVOT observations of the 2015 outburst of V404 Cygni |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/stz1998 |
| Publisher version: | http://dx.doi.org/10.1093/mnras/stz1998 |
| Language: | English |
| Additional information: | This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | X-rays: binaries, X-rays: bursts, X-rays: individual: V404 Cyg |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10079511 |
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