Article

Living on a Flare: Relativistic Reflection in V404 Cyg Observed by NuSTAR during Its Summer 2015 Outburst

D. J. WaltonJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USAK. P. MooleyDepartment of Physics, Oxford University, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UKA. L. KingEinstein Fellow, Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305, USAJohn A. TomsickSpace Sciences Laboratory, University of California, Berkeley, CA 94720, USAJ. M. MïllerDepartment of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI, 49109-1107, USAThomas DauserJavier A. GarcíaHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USAMatteo BachettiINAF/Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047 Selargius (CA), ItalyMurray BrightmanSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAA. C. FabianInstitute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UKKarl FörsterSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAFelix FürstSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAP. GandhiDepartment of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UKBrian W. GrefenstetteSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAFiona A. HarrisonSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAKristin K. MadsenSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAD. L. MeierSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USAMatthew MiddletonDepartment of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UKL. NatalucciIstituto di Astrofisica e Planetologia Spaziali, INAF, Via Fosso del Cavaliere 100, I-00133 Roma, ItalyF. RahouiEuropean Southern Observatory, K. Schwarzschild-Str. 2, D-85748 Garching bei Munchen, GermanyVikram RanaSpace Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USADaniel SternJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

2017en

ABI

Abstract

Abstract We present first results from a series of 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 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 (99% statistical uncertainty, based on an idealized lamp-post geometry).

Identifiers

DOI: 10.3847/1538-4357/aa67e8

Citations and references

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