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Flares, wind and nebulae : the 2015 December mini-outburst of V404 Cygni.

Muñoz-Darias, T. and Casares, J. and Mata Sánchez, D. and Fender, R. P. and Armas Padilla, M. and Mooley, K. and Hardy, L. and Charles, P. A. and Ponti, G. and Motta, S. E. and Dhillon, V. S. and Gandhi, P. and Jiménez-Ibarra, F. and Butterley, T. and Carey, S. and Grainge, K. J. B. and Hickish, J. and Littlefair, S. P. and Perrott, Y. C. and Razavi-Ghods, N. and Rumsey, C. and Scaife, A. M. M. and Scott, P. F. and Titterington, D. J. and Wilson, R. W. (2017) 'Flares, wind and nebulae : the 2015 December mini-outburst of V404 Cygni.', Monthly notices of the Royal Astronomical Society : letters., 465 (1). L124-L128.


After more than 26 years in quiescence, the black hole transient V404 Cyg went into a luminous outburst in 2015 June, and additional activity was detected in late December of the same year. Here, we present an optical spectroscopic follow-up of the December mini-outburst, together with X-ray, optical and radio monitoring that spanned more than a month. Strong flares with gradually increasing intensity are detected in the three spectral ranges during the ∼10 d following the Swift trigger. Our optical spectra reveal the presence of a fast outflowing wind, as implied by the detection of a P-Cyg profile (He I–5876 Å) with a terminal velocity of ∼2500 km s−1 . Nebular-like spectra – with an Hα equivalent width of ∼500 Å – are also observed. All these features are similar to those seen during the main 2015 June outburst. Thus, the fast optical wind simultaneous with the radio jet is most likely present in every V404 Cyg outburst. Finally, we report on the detection of a strong radio flare in late 2016 January, when X-ray and optical monitoring had stopped due to Sun constraints.

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Publisher statement:This article has been accepted for publication in Monthly notices of the Royal Astronomical Society letters. ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:21 October 2016
Date deposited:06 July 2017
Date of first online publication:27 October 2016
Date first made open access:06 July 2017

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