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Post Info TOPIC: V404 Cygni


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RE: V404 Cygni
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Title: The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence
Author: R. M. Plotkin, J. C. A. Miller-Jones, E. Gallo, P. G. Jonker, J. Homan, J. A. Tomsick, P. Kaaret, D. M. Russell, S. Heinz, E. J. Hodges-Kluck, S. Markoff, G. R. Sivakoff, D. Altamirano, J. Neilsen

We present simultaneous X-ray and radio observations of the black hole X-ray binary V404 Cygni at the end of its 2015 outburst. From 2015 July 11-August 5 we monitored V404 Cygni with Chandra, Swift, and NuSTAR in the X-ray, and with the Karl G. Jansky Very Large Array and the Very Long Baseline Array in the radio, spanning a range of luminosities that were poorly covered during its previous outburst in 1989 (our 2015 campaign covers 2e33<Lx<1e34 erg/s). During our 2015 campaign, the X-ray spectrum evolved rapidly from a hard photon index of Gamma~1.6 (at Lx~1e34 erg/s) to a softer Gamma~2 (at Lx~3e33 erg/s). We argue that V404 Cygni reaching Gamma~2 marks the beginning of the quiescent spectral state, which occurs at a factor of ~3-4 higher X-ray luminosity than the average pre-outburst luminosity of ~8e32 erg/s. V404 Cygni falls along the same radio/X-ray luminosity correlation that it followed during its previous outburst in 1989, implying a robust disk-jet coupling. We exclude the possibility that a synchrotron cooled jet dominates the X-ray emission in quiescence, leaving synchrotron self-Compton from either a hot accretion flow or from a radiatively cooled jet as the most likely sources of X-ray radiation, and/or particle acceleration along the jet becoming less efficient in quiescence. Finally, we present the first indications of correlated radio and X-ray variability on minute timescales in quiescence, tentatively measuring the radio emission to lag the X-ray by 15+/-4 min, suggestive of X-ray variations propagating down a jet of length <3.0 AU.

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Posts: 131433
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Nova Cygni 1938
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Title: The nova-like nebular optical spectrum of V404 Cygni at the beginning of the 2015 outburst decay
Author: F. Rahoui, J. A. Tomsick, P. Gandhi, P. Casella, F. Fürst, L. Natalucci, A. Rossi, A. W. Shaw, V. Testa, D. J. Walton

We report on FORS2 optical spectroscopy of the black hole X-ray binary V404 Cygni, performed at the very beginning of its 2015 outburst decay, complemented by quasi-simultaneous Swift X-ray and ultra-violet as well as REM near-infrared observations. Its peculiar spectrum is dominated by a wealth of emission signatures of HI, HeI, and higher ionisation species, in particular FeII. The spectral features are divided between broad red-shifted and narrow stationary varieties, the latter being emitted in the outer regions. Continuum and line variability at short time scale is high and we find Baldwin effect-like anti-correlations between the full-widths at half-maximum and equivalent widths of the broad lines with their local continua. The Balmer decrement H{\alpha}/H{\beta} is also abnormally large at 4.61±0.62. We argue that these properties hint at the broad lines being optically thick and arising within a circumbinary component in which shocks between faster optically thick and slower optically thin regions may occur. We associate it to a nova-like nebula formed by the cooling remnant of strong accretion disc winds that turned off when the mass-accretion rate dropped following the last major flare. The FeII lines likely arise from the overlap region between this nebula and the companion star winds, whereas we favour the shocks within the nebula as responsible for the optical continuum via self-absorbed optically thin bremsstrahlung. The presence of a near-infrared excess also points towards the contribution of a strongly variable compact jet or a dusty component.

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RE: V404 Cygni
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ATel 8458: INTEGRAL IBIS/ISGRI confirms renewed activity of V404 Cyg



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ATel 8455: Swift triggers on V404 Cyg



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ATel 7959: Swift XRT observations indicates the end of the V404 Cyg 2015 outburst in early August



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ATel 7755: A giant flare of V404 Cyg observed with Swift/BAT 



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ATel 7716: A new giant radio flare of V404 Cyg at centimeter wavelengths



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Monster black hole wakes up after 26 years

Over the past week, ESA's Integral satellite has been observing an exceptional outburst of high-energy light produced by a black hole that is devouring material from its stellar companion.
On 15 June 2015, a long-time acquaintance of X-ray and gamma ray astronomers made its comeback to the cosmic stage: V404 Cygni, a system comprising a black hole and a star orbiting one another. It is located in our Milky Way galaxy, almost 8000 light-years away in the constellation Cygnus, the Swan.

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ATel 7671: Observing V404 Cyg on 2015 June 22 10:49-14:49 UT 



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Posts: 131433
Date:
GS 2023+338
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ATel 7647: Renewed activity of V404 Cyg (GS 2023+338)



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