TITLE: GCN CIRCULAR NUMBER: 21583 SUBJECT: LIGO/Virgo G298048: Additional Swope Observations of SSS17a DATE: 17/08/19 01:54:36 GMT FROM: Ryan Foley at UCSC C. D. Kilpatrick, D. A. Coulter, M. R. Siebert, R. J. Foley (UCSC), B. J. Shappee, M. R. Drout, J. S. Simon, A. L. Piro (Carnegie), A. Rest (STScI) report on behalf of the One-Meter Two-Hemisphere (1M2H) collaboration: We obtained imaging in B, V, and i bands of SSS17a (Coulter et al., LVC GCN 21529) on 2017 Aug 19 UT with the 1-m Swope telescope at Las Campanas Observatory. We calibrated these data using approximately 90 B, V, and i' APASS standards in the same field as SSS17a and report the following preliminary photometry: B = 18.8 mag +/- 0.1 mag V = 18.1 mag +/- 0.1 mag i = 17.4 mag +/- 0.1 mag Additional photometry is being obtained and analyzed.