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TAOS early optical observations of V404 Cyg

ATel #7722; Y. T. Chen (ASIAA), R. Ishioka (ASIAA), S. K. King (ASIAA), C. Y. Wen (ASIAA), S. Y. Wang (ASIAA), M. J. Lehner (ASIAA), M. E. Schwamb (ASIAA) and TAOS team
on 27 Jun 2015; 16:20 UT
Credential Certification: Ying-Tung Chen (ytchen@asiaa.sinica.edu.tw)

Subjects: Optical, Black Hole, Transient

Referred to by ATel #: 7740, 7959

We report early optical observations of the black hole X-ray transient V404 Cyg undergoing an outburst (GCN#17929,#17931, #17933, #17938, #17940,#17944, #17945, #17946, #17948, #17949, #17956; ATel #7646, #7647, #7650, #7655, #7658, #7659, #7661, #7662, #7663, #7665, #7666, #7667, #7669, #7671, #7674, #7677, #7678, #7681, #7686, #7688, #7693, #7694, #7695, #7696, #7699, #7701, #7702, #7708, #7709, #7710, #7714, #7715, #7716, #7717, #7718, #7720, #7721). The first observation with TAOS was started on June 15.7737, 3 min after the Swift/BAT alert at 18:31 UT on June 15(GCN #17929). We also detected a rapid brightening from R=13.8 to R=12.7 within 15 minutes (GCN #17956), with shorter time-scale small amplitude variability. A plot of our preliminary light curve on the first night is available here. On June 18, the second night of our observations, the source brightened from R=13.8 to R=12.7 in 10 min. On June 19, it was R=12.2 with a fading trend during our 2-min observation. The R-band magnitude of nearby stars have been used for calibration. We note that special filter (5000-7200 A) was used in TAOS telescopes.