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Fast Optical Photometry of V404 Cyg at the MDM Observatory

ATel #7725; D. Terndrup (OSU), R. M. Wagner (LBTO/OSU), S. Starrfield (ASU)
on 28 Jun 2015; 06:16 UT
Credential Certification: R. Mark Wagner (rmw@as.arizona.edu)

Subjects: Optical, Black Hole, Transient, Variables

Referred to by ATel #: 7740, 7959

We obtained continuous fast differential optical photometry of V404 Cyg with the 1.3 m McGraw-Hill Telescope of the MDM Observatory on Kitt Peak on the nights of 2015 June 19.220-19.474, 20.194-20.472, 21.199-21.460, and 22.188-22.421 UT. The observations were performed in the R-band with the Andor frame-transfer CCD camera at an image scale of 0.54 arcsec/pixel and with a field-of-view of 2.3 arcmin. The photometry on June 19 was obtained with a 6 to 10 sec cadence while the photometry on the remaining nights was obtained with a 1 sec cadence. The temporal coverage was 6.096 h (June 19), 6.672 h (June 20), 6.261 h (June 21), and 5.592 h (June 22). A total of 68,374 individual measurements were obtained.

Differential photometry was obtained with respect to the anonymous field star 2MASS J20240718+3350516 (AUID 000-BCL-467 in the AAVSO field photometry database and 620-101865 in the UCA4 catalog). This star has R = 12.384 mag based on photometry obtained by A. Henden and reported in the AAVSO database. We estimate that our differential photometric uncertainty is better than 0.03 mag per bin.

The individual nightly light curves are shown here: June 19, June 20, June 21, and June 22. A comparison of all four nights plotted on the same vertical scale can be found here in a montage. Our photometry overlaps and extends some optical photometry that has been already reported (ATEL #7677, #7681, #7686, #7688, #7696, and #7710).

In particular, the photometry reported by Hynes, Robinson, and Morales (ATEL #7710) overlaps our coverage between June 19.35 and 19.44 UT. The agreement of the two light curves in the overlap region is remarkable right down to variations appearing on the shortest timescales visible in the plot. Although, our sampling on this night was about 6 sec compared to 1 sec in ATEL #7710, we can confirm that based on the combined data as well as our light curve from June 20, that the short episodes of rapid flaring described in ATEL #7710 are intrinsic to the source and may likely be present during some bright optical states.

In addition, our photometry just overlaps and significantly extends the ULTRACAM light curves reported by Gandhi et al. (ATEL #7686) obtained on June 20.174-20.225 and 21.153-21.231 UT. After the conclusion of the ULTRACAM light curve on June 20.225, our extended light curve shows slower and smoother fluctuations comparable to that obtained on June 19 and the presence of rapid flaring down to our time resolution occurring between June 20.400-20.428 UT. The rapid flaring in this time interval is shown here. On June 21, we overlap the ULTRACAM light curve through June 21.2313 UT and the variations are of much lower amplitude and quite smooth for the remainder of the light curve extending through June 21.460 UT.

Additional fast photometry and coordinated observations to improve the temporal coverage are encouraged.