Living on a Flare: Relativistic Reflection in V404 Cyg Observed by NuSTAR during Its Summer 2015 Outburst
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Authors
Mooley, K
King, AL
Tomsick, JA
Miller, JM
Dauser, T
García, JA
Bachetti, M
Brightman, M
Forster, K
Fürst, F
Gandhi, P
Grefenstette, BW
Harrison, FA
Madsen, KK
Meier, DL
Middleton, MJ
Natalucci, L
Rahoui, F
Rana, V
Stern, D
Publication Date
2017-04-21Journal Title
The Astrophysical Journal
ISSN
0004-637X
Publisher
IOP Publishing
Volume
839
Number
110
Language
English
Type
Article
This Version
VoR
Metadata
Show full item recordCitation
Walton, D., Mooley, K., King, A., Tomsick, J., Miller, J., Dauser, T., García, J., et al. (2017). Living on a Flare: Relativistic Reflection in V404 Cyg Observed by NuSTAR during Its Summer 2015 Outburst. The Astrophysical Journal, 839 (110)https://doi.org/10.3847/1538-4357/aa67e8
Abstract
We present first results from a series of $\textit{NuSTAR}$ observations of the black hole X-ray binary V404 Cyg obtained during its summer 2015 outburst, primarily focusing on observations during the height of this outburst activity. The $\textit{NuSTAR}$ data show extreme variability in both the flux and spectral properties of the source. This is partly driven by strong and variable line-of-sight absorption, similar to previous outbursts. The latter stages of this observation are dominated by strong flares, reaching luminosities close to Eddington. During these flares, the central source appears to be relatively unobscured and the data show clear evidence for a strong contribution from relativistic reflection, providing a means to probe the geometry of the innermost accretion flow. Based on the flare properties, analogies with other Galactic black hole binaries, and also the simultaneous onset of radio activity, we argue that this intense X-ray flaring is related to transient jet activity during which the ejected plasma is the primary source of illumination for the accretion disk. If this is the case, then our reflection modeling implies that these jets are launched in close proximity to the black hole (as close as a few gravitational radii), consistent with expectations for jet launching models that tap either the spin of the central black hole, or the very innermost accretion disk. Our analysis also allows us to place the first constraints on the black hole spin for this source, which we find to be ${a}^{* }\gt 0.92$ (99% statistical uncertainty, based on an idealized lamp-post geometry).
Keywords
black hole physics, X-rays: binaries, X-rays: individual (V404 Cyg)
Sponsorship
D.J.W., P.G., and M.J.M. acknowledge support from STFC Ernest Rutherford fellowships (grant ST/J003697/2). K.P.M. acknowledges support from the Hintze Foundation. A.L.K. acknowledges support from NASA through an Einstein Postdoctoral Fellowship (grant number PF4-150125) awarded by the Chandra X-ray Center, operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. A.C.F. acknowledges support from ERC Advanced Grant 340442. L.N. wishes to acknowledge the Italian Space Agency (ASI) for Financial support by ASI/INAF grant I/037/12/0-011/13. This research has made use of data obtained with NuSTAR, a project led by Caltech, funded by NASA and managed by NASA/JPL, and has utilized the NUSTARDAS software package, jointly developed by the ASDC (Italy) and Caltech (USA). This research has also made use of data from AMI, which is supported by the ERC, and we thank the AMI staff for scheduling these radio observations.
Funder references
European Research Council (340442)
SCIENCE & TECHNOLOGY FACILITIES COUNCIL (ST/N000927/1)
Identifiers
External DOI: https://doi.org/10.3847/1538-4357/aa67e8
This record's URL: https://www.repository.cam.ac.uk/handle/1810/264556
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