期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 488, 期 4, 页码 4843-4857出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stz1998
关键词
X-rays: binaries; X-rays: bursts; X-rays: individual: V404 Cyg
资金
- Leverhulme Trust
- Violette and Samuel Glasstone Research Fellowship program
- UK Science and Technology Facilities Council (STFC)
- STFC
- UKIERI
- UK Space Agency
- [AYA2012-39727-C03-01]
- STFC [ST/N000811/1, ST/P000495/1] Funding Source: UKRI
The black hole binary, V404 Cygni, went into outburst in 2015 June, after 26years 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.
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