EVENTS LEADING UP to the 2015 JUNE OUTBURST of V404 CYG

F. Bernardini, Dave Russell, A. W. Shaw, F. Lewis, P. A. Charles, K. I.I. Koljonen, J. P. Lasota, J. Casares

Research output: Contribution to journalArticle

Abstract

On 2015 June 15 the burst alert telescope (BAT) on board Swift detected an X-ray outburst from the black hole (BH) transient V404 Cyg. We monitored V404 Cyg for the last 10 years with the 2-m Faulkes Telescope North in three optical bands (V, R, and i′). We found that, one week prior to this outburst, the optical flux was 0.1-0.3 mag brighter than the quiescent orbital modulation, implying an optical precursor to the X-ray outburst. There is also a hint of a gradual optical decay (years) followed by a rise lasting two months prior to the outburst. We fortuitously obtained an optical spectrum of V404 Cyg 13 hr before the BAT trigger. This too was brighter than quiescence, and showed spectral lines typical of an accretion disk, with characteristic absorption features of the donor being much weaker. No He II emission was detected, which would have been expected had the X-ray flux been substantially brightening. This, combined with the presence of intense Hα emission, about seven times the quiescent level, suggests that the disk entered the hot, outburst state before the X-ray outburst began. We propose that the outburst is produced by a viscous-thermal instability triggered close to the inner edge of a truncated disk. An X-ray delay of a week is consistent with the time needed to refill the inner region and hence move the inner edge of the disk inwards, allowing matter to reach the central BH, finally turning on the X-ray emission.

Original languageEnglish (US)
Article numberL5
JournalAstrophysical Journal Letters
Volume818
Issue number1
DOIs
StatePublished - Feb 10 2016

Fingerprint

outburst
x rays
telescopes
bursts
thermal instability
accretion disks
line spectra
optical spectrum
actuators
modulation
orbitals
accretion
decay

Keywords

  • accretion, accretion disks
  • black hole physics
  • X-rays: individual (V404 Cyg, GS 2023+338)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Bernardini, F., Russell, D., Shaw, A. W., Lewis, F., Charles, P. A., Koljonen, K. I. I., ... Casares, J. (2016). EVENTS LEADING UP to the 2015 JUNE OUTBURST of V404 CYG. Astrophysical Journal Letters, 818(1), [L5]. https://doi.org/10.3847/2041-8205/818/1/L5

EVENTS LEADING UP to the 2015 JUNE OUTBURST of V404 CYG. / Bernardini, F.; Russell, Dave; Shaw, A. W.; Lewis, F.; Charles, P. A.; Koljonen, K. I.I.; Lasota, J. P.; Casares, J.

In: Astrophysical Journal Letters, Vol. 818, No. 1, L5, 10.02.2016.

Research output: Contribution to journalArticle

Bernardini, F, Russell, D, Shaw, AW, Lewis, F, Charles, PA, Koljonen, KII, Lasota, JP & Casares, J 2016, 'EVENTS LEADING UP to the 2015 JUNE OUTBURST of V404 CYG', Astrophysical Journal Letters, vol. 818, no. 1, L5. https://doi.org/10.3847/2041-8205/818/1/L5
Bernardini F, Russell D, Shaw AW, Lewis F, Charles PA, Koljonen KII et al. EVENTS LEADING UP to the 2015 JUNE OUTBURST of V404 CYG. Astrophysical Journal Letters. 2016 Feb 10;818(1). L5. https://doi.org/10.3847/2041-8205/818/1/L5
Bernardini, F. ; Russell, Dave ; Shaw, A. W. ; Lewis, F. ; Charles, P. A. ; Koljonen, K. I.I. ; Lasota, J. P. ; Casares, J. / EVENTS LEADING UP to the 2015 JUNE OUTBURST of V404 CYG. In: Astrophysical Journal Letters. 2016 ; Vol. 818, No. 1.
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