Swift UVOT observations of the 2015 outburst of V404 Cygni

DOI: 
10.1093/mnras/stz1998
Publication date: 
01/07/2019
Main author: 
Oates, S. R.
IAA authors: 
Oates, S. R.;Castro-Tirado, A. J.
Authors: 
Oates, S. R.;Motta, S.;Beardmore, A. P.;Russell, D. M.;Gandhi, P.;Kuin, N. P. M.;De Pasquale, M.;Altamirano, D.;Breeveld, A. A.;Castro-Tirado, A. J.;Knigge, C.;Page, M. J.;Steeghs, D.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Pages: 
4843-4857
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.
Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85078756130&doi=10.1093%2fmnras%2fstz1998&partnerID=40&md5=803ce4a1a5a4896e0110e8201aa111e7
ADS Bibcode: 
2019MNRAS.488.4843O
Keywords: 
X-rays: binaries;X-rays: bursts;X-rays: individual: V404 Cyg;Astrophysics - High Energy Astrophysical Phenomena