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Increased optical flaring activity of V404 Cyg

ATel #7681; Liam Hardy (Sheffield), Stuart Littlefair (Sheffield), Vik Dhillon (Sheffield), Tim Butterley (Durham), Richard Wilson (Durham)
on 21 Jun 2015; 15:10 UT
Credential Certification: Stuart Littlefair (s.littlefair@shef.ac.uk)

Subjects: Optical, Black Hole, Transient

Referred to by ATel #: 7686, 7688, 7702, 7708, 7714, 7718, 7721, 7722, 7725, 7726, 7734, 7740, 7959

We report nightly monitoring of the outbursting black hole X-ray transient V404 Cyg (GCN #17929, #17931, #17933, #17938, #17940, #17944, #17945, #17946, #17948; ATel #7646, #7647, #7650, #7655, #7658, #7659, #7661, #7662, #7663, #7665, #7666, #7667, #7669, #7671, #7674, #7677, #7678) in the V-band. Observations were made on the nights 2015 Jun 16th, 17th, 18th, 19th and 20th with durations between 3 and 5 hours using pt5m - a 0.5m robotic telescope at the Roque de los Muchachos Observatory on La Palma. Exposures of 20s were obtained with 5s deadtime between frames.

The baseline brightness of V404 Cyg appears to be increasing, and the optical flaring reported in Atel #7650, #7659, #7662, #7666, #7669, #7677 is seen to be increasing in amplitude. On the first night, the source was varying between V-band magnitudes of V=16.1 and V=14.1. By the fifth night the baseline brightness had reached V=12.9, with flares of up to V=12.2. Taking into account the increased baseline flux, the amplitude of the flaring activity has increased by roughly a factor of four. A plot of our light curve is available here.