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Swift UVOT observations of the 2015 outburst of V404 Cygni

Swift UVOT observations of the 2015 outburst of V404 Cygni
Swift UVOT observations of the 2015 outburst of V404 Cygni
The black-hole binary, V404 Cyg, 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 the 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, which affects the X-ray emission. We suggest that 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 emission trace those in the X-ray band, with a time-lag of (0 - 30)s, with the optical/UV generally lagging the X-rays. The amplitude of the variations is correlated with flux in both bands, but less significantly in the optical/UV. The variability in the light curves may be produced by a complex combination of processes. Some of the variability observed only in the X-ray 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 bands 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.
astro-ph.HE
0035-8711
4843-4857
Oates, S. R.
ad6dac21-5a31-4119-a643-849046998b86
Motta, S.
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Beardmore, A. P.
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Gandhi, P.
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Kuin, N. P. M.
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Pasquale, M. De
945718e5-c504-4aee-9732-7310f8ad1f14
Altamirano, D.
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Breeveld, A. A.
b8bbf6f0-4a64-43e6-a6d7-128e5d77f127
Castro-Tirado, A. J.
e86b7d0a-8fd6-41cd-a261-4999ba488179
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Steeghs, Danny
f631b06c-3e33-4daa-8959-c41f188e9c38
Oates, S. R.
ad6dac21-5a31-4119-a643-849046998b86
Motta, S.
461dbdce-0b15-4702-8baf-85b26197ae36
Beardmore, A. P.
d72591c2-c08f-42b6-9f46-645aacb4e3e0
Gandhi, P.
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Kuin, N. P. M.
96233d16-2396-468e-8f22-201a89eee265
Pasquale, M. De
945718e5-c504-4aee-9732-7310f8ad1f14
Altamirano, D.
d5ccdb09-0b71-4303-9538-05b467be075b
Breeveld, A. A.
b8bbf6f0-4a64-43e6-a6d7-128e5d77f127
Castro-Tirado, A. J.
e86b7d0a-8fd6-41cd-a261-4999ba488179
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Steeghs, Danny
f631b06c-3e33-4daa-8959-c41f188e9c38

Oates, S. R., Motta, S., Beardmore, A. P., Gandhi, P., Kuin, N. P. M., Pasquale, M. De, Altamirano, D., Breeveld, A. A., Castro-Tirado, A. J., Knigge, C. and Steeghs, Danny (2019) Swift UVOT observations of the 2015 outburst of V404 Cygni. Monthly Notices of the Royal Astronomical Society, 488 (4), 4843-4857. (doi:10.1093/mnras/stz1998).

Record type: Article

Abstract

The black-hole binary, V404 Cyg, 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 the 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, which affects the X-ray emission. We suggest that 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 emission trace those in the X-ray band, with a time-lag of (0 - 30)s, with the optical/UV generally lagging the X-rays. The amplitude of the variations is correlated with flux in both bands, but less significantly in the optical/UV. The variability in the light curves may be produced by a complex combination of processes. Some of the variability observed only in the X-ray 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 bands 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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Submitted date: 10 September 2018
Accepted/In Press date: 16 July 2019
e-pub ahead of print date: 25 July 2019
Published date: October 2019
Keywords: astro-ph.HE

Identifiers

Local EPrints ID: 423531
URI: http://eprints.soton.ac.uk/id/eprint/423531
ISSN: 0035-8711
PURE UUID: c938ca09-1920-4ecb-920b-e829569011a6
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615
ORCID for D. Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 25 Sep 2018 16:30
Last modified: 07 Oct 2020 02:06

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Contributors

Author: S. R. Oates
Author: S. Motta
Author: A. P. Beardmore
Author: P. Gandhi ORCID iD
Author: N. P. M. Kuin
Author: M. De Pasquale
Author: D. Altamirano ORCID iD
Author: A. A. Breeveld
Author: A. J. Castro-Tirado
Author: C. Knigge
Author: Danny Steeghs

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