TITLE: GCN CIRCULAR NUMBER: 20400 SUBJECT: LIGO/Virgo G268556: Swift/UVOT observations of ATLAS17aeu DATE: 17/01/08 18:31:44 GMT FROM: Samantha Oates at U of Warwick S.R. Oates (Uni. of Warwick), A. A. Breeveld (MSSL-UCL), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), P. Evans (U Leicester), N. Gehrels (NASA/GSFC), P. Giommi (ASI), C. Gronwall (PSU), J. Kennea (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), D. Malesani (DARK/NBI), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), B. Mingo (U. Leicester), J.A. Nousek (PSU), P.T. O'Brien (U. Leicester), 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), E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team: The Swift/UVOT performed targetted observations of the field of ATLAS transient ATLAS17aeu (Tonry et al., LVC Circ. 20382) from 00:00 UT to 01:35 UT on 2017 Jan 7 and again between 16:01 UT on 2017 Jan 7 to 01:30 on 2017 Jan 08. No optical afterglow consistent with the ATLAS position or 'source5' of the XRT follow up of G268556 (Evans et al., GCN Circ. 20390) is detected in the UVOT exposures at more than 3 sigma. We do note however a source at 2.9 sigma in the w2 filter, which in comparison to the second observation appears to have faded. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the exposures are: Filter T_start(UT) T_stop(UT) Exp(s) Mag/3sigUL v 7.007 7.009 144 > 19.1 v 7.667 7.936 1009 > 20.3 u 7.018 7.019 106 > 18.6 u 7.881 8.016 311 > 19.2 w1 7.014 7.018 290 > 19.5 w1 7.876 7.947 801 > 20.2 m2 7.009 7.014 435 > 20.0 m2 7.670 7.943 2413 > 21.2 w2 7.000 7.067 690 > 20.7 (20.76 +/- 0.37 detection at 2.9 sigma) w2 7.658 8.069 5177 > 22.0 (22.41 +/- 0.53 detection at 2.1 sigma) The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the transient (Schlegel et al. 1998). [GCN OPS NOTE(08jan17): Per author's request, PE and JK were added to the author list.]