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INTEGRAL/OMC optical photometric observations of multiple flaring from V404 Cyg

ATel #7717; A. Domingo, J. Alfonso-Garzon, J. M. Mas-Hesse (CAB-CSIC/INTA, Spain), J. Rodriguez (SAp-AIM, CEA Paris-Saclay), M. Cadolle Bel (Max Planck Computing and Data Facility, Garching)
on 26 Jun 2015; 10:06 UT
Credential Certification: Albert Domingo (albert@cab.inta-csic.es)

Subjects: Optical, Black Hole, Transient

Referred to by ATel #: 7718, 7721, 7722, 7726, 7734, 7740, 7758, 7959

A target of opportunity INTEGRAL observation (PI Rodriguez, ATel #7702) of the black-hole candidate V 404 Cyg, currently in outburst phase (ATel #7646) and showing large variability at different wavelengths, was executed in revolutions 1555 (20-22 June 2015) and 1556 (23-25 June 2015).

After the INTEGRAL/OMC observations reported on ATel #7662, we report here on the optical photometric data accumulated during revolutions 1555 and 1556. We detect 8 strong flares in revolution 1555 and another one in revolution 1556. A plot of the OMC light curve is available here.

The first two strong optical flares in revolution 1555 occurred around (peak time) MJD 57193.92 and MJD 57194.0 at a time when the source brightness was smoothly increasing. In the first flare it reached an optical brightness of V=11.72, and after that the brightness decayed to around V=13. It re-brightened to V=11.64 in around 1.3 hours, and decayed again below V=12.7. A small gap in our observations prevents us measuring the minimum. After this minimum, the brightness continued increasing up to V=11.5 at the same rate as before the first flare. After a small gap in our observations, the source had a brightness of V=12.3 and it was in a smoothly fading phase, in which it decayed to V=12.5 in less than 4 hours. After that, 6 strong flares with amplitude of the variations ranging from 0.8 to 2 mag occurred. Five of them were single peaked, but the 4th one had a double-peaked structure centred at MJD 57195.02 and showing variations of around 1 mag. The whole event duration was of approximately 2.1 hours. A similar behaviour is found in the IBIS/ISGRI light curve (ATel #7702), showing an X-ray flare event with some structures centred at MJD 57195.

The OMC observations from revolution 1556 started with a slightly variable optical brightness oscillating around V=12.5. On around MJD 57197.0 the brightness of the source started to increase reaching V=11.1 in 5 hours, after which it abruptly decreased to V=14.5 in 1.2 hours. A bright flare took place starting on MJD 57197.28. It was double-peaked and showed asymmetric structure, reaching brightness of V=12.5 and V=11.9 on each peak respectively. This whole event duration was of approximately 3.1 hours.

INTEGRAL will continue monitoring the source over the upcoming revolutions (ATel #7695), so new OMC optical photometric observations will be available in the near future.