High-energy gamma-ray observations of the accreting black hole V404 Cygni during its 2015 June outburst
We report on Fermi/Large Area Telescope observations of the accreting black hole low-mass X-ray binary V404 Cygni during its outburst in 2015 June–July. Detailed analyses reveal a possible excess of γ-ray emission on 2015 26 June, with a very soft spectrum above 100 MeV, at a position consistent with the direction of V404 Cyg (within the 95 per cent confidence region and a chance probability of 4 × 10−4). This emission cannot be associated with any previously known Fermi source. Its temporal coincidence with the brightest radio and hard X-ray flare in the light curve of V404 Cyg, at the end of the main active phase of its outburst, strengthens the association with V404 Cyg. If the γ-ray emission is associated with V404 Cyg, the simultaneous detection of 511 keV annihilation emission by INTEGRAL reqires that the high-energy γ-rays originate away from the corona, possibly in a Blandford–Znajek jet. The data give support to models involving a magnetically arrested disc where a bright γ-ray jet can re-form after the occurrence of a major transient ejection seen in the radio.
Additional Information© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 July 14. Received 2016 July 13. In original form 2016 April 22. First published online July 19, 2016. We thank J. Miller-Jones, J. Ballet and J. Perkins for useful discussions and T. Siegert for providing the annihilation LC. AL, SC and JR acknowledge funding support from the French Research National Agency: CHAOS project ANR-12-BS05-0009 and the UnivEarthS Labex programme of Sorbonne Paris Cité (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). KM acknowledges funding support from the Hintze Foundation. The Fermi-LAT Collaboration acknowledges support for LAT development, operation and data analysis from NASA and DOE (USA), CEA/Irfu and IN2P3/CNRS (France), ASI and INFN (Italy), MEXT, KEK, and JAXA (Japan), and the K.A. Wallenberg Foundation, the Swedish Research Council and the National Space Board (Sweden). Science analysis support in the operations phase from INAF (Italy) and CNES (France) is also gratefully acknowledged. The OVRO 40-m monitoring programme is supported in part by NASA grants NNX08AW31G and NNX11A043G, and NSF grants AST-0808050 and AST-1109911. We acknowledge with thanks the variable star observations from the AAVSO. We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research.
Published - MNRASLoh,A.etal.pdf
Submitted - 1607.06239v1.pdf