Difference: GCNCIRCULAR21572 ( vs. 1)

S. B. Cenko (NASA/GSFC), S.W.K. Emery (UCL-MSSL), S. Campana (INAF-OAB), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.A. Breeveld (UCL-MSSL), E. Troja (NASA/GSFC/UMCP), P.T. O'Brien (U. Leicester), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U. Warwick), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) report on behalf of the Swift team:

We obtained a second epoch of UV and X-ray imaging of SSS17a (Coulter et al.; GCN 21529), the candidate optical counterpart of G298048 (LVC; GCN 21509) with the Swift Gamma-Ray Burst Explorer. Observations began at 13:30 UT on 2017 August 18. Compared with our previous epoch of imaging (Evans et al.; GCN 21550), the source has faded significantly at UV wavelengths. Specifically we measure the following magnitudes (with no host subtraction):

Filter T_start(s) T_stop(s) Exp(s) Mag (Vega)

u 90029 90164 133 17.42 +/- 0.09
uvw1 89755 90024 265 18.50 +/- 0.15
uvm2 89346 94665 1045 20.40 +/- 0.27
uvw2 90170 90674 496 20.37 +/- 0.32

Given the relatively flat evolution in the optical and NIR, this suggests significant cooling in the source.

The source remains undetected in the X-rays, with comparable limits to our previous epoch.

Further observations are planned.

-- ShaonGhosh - 18 Aug 2017