University of Hertfordshire

From the same journal

From the same journal

By the same authors


  • 1507.06659

    Accepted author manuscript, 2.82 MB, PDF document


  • J. Rodriguez
  • M. Cadolle Bel
  • J. Alfonso-Garzón
  • T. Siegert
  • X.-L. Zhang
  • V. Grinberg
  • V. Savchenko
  • J.~A. Tomsick
  • J. Chenevez
  • M. Clavel
  • S. Corbel
  • R. Diehl
  • A. Domingo
  • C. Gouiffès
  • J. Greiner
  • P. Laurent
  • A. Loh
  • S. Markoff
  • J.~M. Mas-Hesse
  • J.~C.~A. Miller-Jones
  • D.~M. Russell
  • J. Wilms
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Original languageEnglish
Article numberL9
Pages (from-to)5
JournalAstronomy & Astrophysics
Publication statusPublished - 23 Sep 2015


After 25 years of quiescence, the microquasar V404 Cyg entered a new period of activity in June 2015. This X-ray source is known to undergo extremely bright and variable outbursts seen at all wavelengths. It is therefore an object of prime interest to understand the accretion-ejection connections. These can, however, only be probed through simultaneous observations at several wavelengths. We made use of the INTEGRAL instruments to obtain long, almost uninterrupted observations from 2015 June 20th, 15:50 UTC to June 25th, 4:05 UTC, from the optical V-band, up to the soft γ-rays. V404 Cyg was extremely variable in all bands, with the detection of 18 flares with fluxes exceeding 6 Crab (20--40 keV) within 3 days. The flare recurrence can be as short as ∼ 20~min from peak to peak. A model-independent analysis shows that the >6 Crab flares have a hard spectrum. A simple 10--400 keV spectral analysis of the off-flare and flare periods shows that the variation in intensity is likely to be due to variations of a cut-off power law component only. The optical flares seem to be at least of two different types: one occurring in simultaneity with the X-ray flares, the other showing a delay greater than 10 min. The former could be associated with X-ray reprocessing by either an accretion disk or the companion star. We suggest that the latter are associated with plasma ejections that have also been seen in radio.


Reproduced with permission from Astronomy & Astrophysics. © 2015 ESO.

ID: 10546582