TITLE: GCN CIRCULAR NUMBER: 20760 SUBJECT: LIGO/Virgo G275404: REM optical/NIR observations DATE: 17/02/27 11:33:14 GMT FROM: Andrea Melandri at INAF-OAB A. Melandri, P. D'Avanzo (INAF-OAB), G. Greco (Urbino University/INFN Firenze), D. Fugazza, S. Covino, (INAF-OAB), E. Palazzi (INAF-IASF Bo), M. Branchesi (Urbino University/INFN Firenze), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), M.T. Botticella (INAF-OAC), S. Campana (INAF-OAB), E. Cappellaro (INAF-OAPD), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm (GRAWITA) report: We carried out optical/NIR follow-up observations of the LIGO/Virgo GW trigger G275404 (LVC GCN Circ. 20738) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile). The observations were carried out on 2017 Feb 26 from 00:15:16 UT to 04:52:42 UT (from 5.75 to 10.37 hours after T0, LVC GCN Circ. 20738), simultaneously in the g, r, i, z and H bands. We observed the twenty brightest (according to the B magnitude reported in the GLADE catalogue) galaxies within the bayestar probability sky map visible from La Silla. The galaxies with a catalogued distance in the range 200-360 Mpc (evaluated on the basis of directional distance information, Singer et al. 2016, ApJL 829, 15) and brighter than Mag(B)=15.4 were selected within the 60% containment probability contour of the sky map using the GWsky script (https://github.com/ggreco77/GWsky). RA(J2000) Dec(J2000) Dist(Mpc) Mag(B) --------------------------------------- 166.78835 -18.02376 309.030 14.37 169.72995 -20.43487 275.423 14.83 160.82343 -12.36031 235.505 14.97 164.62923 -15.38000 292.415 15.04 159.06644 -12.72557 229.087 15.07 157.75930 -10.56777 276.694 15.13 165.18204 -19.41204 255.859 15.18 182.20964 -31.44722 204.174 15.21 159.31235 -11.35495 231.560 15.23 168.87087 -20.79923 279.087 15.26 169.93326 -21.97061 354.813 15.29 174.77983 -27.54560 275.423 15.31 160.25761 -11.44282 235.303 15.31 166.36340 -21.09875 280.543 15.35 160.15845 -14.25566 231.206 15.37 166.13525 -18.84047 292.415 15.38 172.93570 -25.07778 280.543 15.38 156.54243 -07.94825 285.508 15.38 173.67679 -24.94764 221.690 15.39 169.13541 -20.90190 297.852 15.40 A preliminary analysis reveals no obvious optical/NIR candidate counterpart in the above galaxies down to the following magnitudes: r > 19.5, H > 17.0 (AB, 3sigma upper limit, calibrated against the APASS and 2MASS catalogues, respectively). Further analysis is in progress.