Difference: GCNCIRCULAR21565 ( vs. 1)

I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las Cumbres Obs), M. Zalzman, D. Poznanski (TAU), L.P. Singer (NASA/GSFC), S. Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley), W. Fong (Northwestern) and D. Maoz (TAU) report the brightening of SSS17a / DLT17ck, the possible optical counterpart reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) and others.

In the course of Las Cumbres Observatory LIGO followup we observed NGC 4993 from our 1-meter telescopes at the Cerro Tololo Inter-American Observatory in Chile at 2017-08-18 00:15 UT (Arcavi et al.; LCV GCN 21538) and at the Siding Spring Observatory in Australia at 2017-08-18 09:10 UT. Both images were taken in the broad w (=g+r+i) filter.

Preliminary aperture photometry, comparing to 7 nearby stars, indicates a relative increase in brightness of the candidate by 0.11 magnitudes (with an uncertainty of 0.03 magnitudes) in the ~9 hours between the first and second epochs.

Further observations and analysis are ongoing.

-- ShaonGhosh - 18 Aug 2017