INTEGRAL/OMC optical photometric observations of V404 Cyg during its last outburst

ATel #8516; Julia Alfonso-Garzon, Albert Domingo, J. Miguel Mas-Hesse (Centro de Astrobiologia, CSIC-INTA)
on 8 Jan 2016; 16:21 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Julia Alfonso-Garzon (julia@cab.inta-csic.es)

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After the past period of activity of the black-hole binary X-ray transient V404 Cyg (GS 2023+338) in the Summer of 2015, this source re-emerged from quiescence again at the end of the year. On 21 December 2015, the Fermi Gamma Ray Burst Monitor (GBM) triggered on a source consistent with V404 Cyg (Jenke 2015, GCN 18719). On 23 December 2015, the Swift Burst Alert Telescope (BAT) triggered and located a source also consistent with V404 Cyg (Barthelmy et al. 2015, GCN 18716).

INTEGRAL performed public Target-of-Opportunity observations of this black-hole from 26 December 2015 to 4 January 2016 (see ATels #8475, #8500, #8510, #8512). We report here on the INTEGRAL/OMC optical photometric data accumulated during these observations.

During revolution 1626, the source was close to the OMC detection limit, showing just a few detections with optical brightness close to V = 15 mag around MJD 57382.5.

On revolution 1627, the source presented a double-peaked flare with peak values of V = 14.97 mag on MJD 57386.3 and of V = 14.61 mag on MJD 57386.4.

On revolution 1628, five optical flares have been identified. On MJD 57387.7, a multiple flare took place during 1.5 hour with peak brightness of V = 13.64 mag and showing variations of almost 1.8 mag. On MJD 57387.8, another multiple flare occurred, lasting 1.1 hour and displaying variations of 1.7 mag and a peak brightness of V = 13.42 mag. Two flares with variations of 2 mag and maximum values of V = 13.25 mag and V = 13.94 mag, happened between MJD 57388.0 and MJD 57388.1. This activity is in agreement with the high-energy activity detected by the INTEGRAL/ISGRI and JEM-X instruments, reported on ATel #8500. Around MJD 57388.9, multiple flaring has also been identified showing variations of around 1 mag during 2.4 hours and with maximum brightness of V = 14.23 mag.

On revolution 1269, the source was too faint to be detected with OMC.

On the other hand, INTEGRAL observed V404 Cyg during a previous public observation of the Cygnus region, performed between 21 and 23 December 2015 (revolution 1624), and the source was under the OMC detection limit.

The complete OMC light curve can be found at here.