TITLE: GCN CIRCULAR NUMBER: 20953 SUBJECT: LIGO/Virgo G275697: LOFAR follow-up DATE: 17/03/31 11:03:13 GMT FROM: Antonia Rowlinson at U van Amsterdam J.W. Broderick (ASTRON), A. Rowlinson (UvA, ASTRON), A.J. Stewart (Oxford), P.G. Jonker (SRON, RU), R.P. Fender (Oxford), R.A.M.J. Wijers (UvA), B.W. Stappers (Manchester), S. ter Veen (ASTRON), S. Ghosh (RU), A. Shulevski (ASTRON) report on behalf of the LOFAR Transients Key Science project From 2017 March 16-20, we observed a large fraction of the localization error range of the Advanced LIGO trigger G275697 with the ILT (International Low-Frequency Array [LOFAR] Telescope). The observations were obtained with the high-band antennas (HBA) at a centre frequency of 145 MHz (bandwidth 15.8 MHz). We used 6 simultaneous beams on the sky, where each beam has a field of view of approximately 12 deg^2 (beam FWHM 3.9 deg). The observations cover roughly 300 deg^2 in total at optimum sensitivity. Each field was observed for a total of up to 225 min using a number of separate 25 min snapshots. The beam centres are given below (RA & Dec in degrees); analysis is ongoing. Pointing 1 (integration time 225 min over the period 2017-03-16 06:11-13:32 UTC) 1) 325.025000 41.804167 2) 326.746137 44.268755 3) 321.301114 41.682969 4) 323.022251 44.147557 5) 327.027749 39.460777 6) 328.748886 41.925365 Pointing 2 (integration time 225 min over the period 2017-03-16 06:37-13:58 UTC) 1) 328.920158 46.542342 2) 331.030859 48.911430 3) 324.881912 46.615076 4) 326.992613 48.984164 5) 330.847703 44.100521 6) 332.958404 46.469609 Pointing 3 (integration time 225 min over the period 2017-03-17 06:11-13:32 UTC) 1) 319.219737 31.633699 2) 320.468591 34.200728 3) 315.984241 31.271028 4) 317.233096 33.838057 5) 321.206377 29.429341 6) 322.455232 31.996370 Pointing 4 (integration time 225 min over the period 2017-03-17 06:37-13:58 UTC) 1) 321.874437 36.767756 2) 323.340302 39.285962 3) 318.419103 36.525591 4) 319.884968 39.043797 5) 323.863905 34.491716 6) 325.329771 37.009921 Pointing 5 (integration time 200 min over the period 2017-03-18 05:11-12:32 UTC) 1) 314.137598 21.441764 2) 315.303983 23.999416 3) 311.174714 21.103147 4) 312.341099 23.660799 5) 315.934097 19.222730 6) 317.100481 21.780382 Pointing 6 (integration time 200 min over the period 2017-03-18 05:37-12:58 UTC) 1) 316.565036 26.557069 2) 317.828472 29.095384 3) 313.475776 26.266633 4) 314.739212 28.804948 5) 318.390860 24.309189 6) 319.654296 26.847504 Pointing 7 (integration time 175 min over the period 2017-03-20 09:55-15:32 UTC) 1) 333.611809 51.066434 2) 336.179366 53.328480 3) 329.210699 51.332745 4) 331.778257 53.594791 5) 335.445360 48.538078 6) 338.012918 50.800124 Pointing 8 (integration time 200 min over the period 2017-03-20 09:29-15:58 UTC) 1) 8.225000 67.934722 2) 15.175293 68.885036 3) 2.559069 69.720728 4) 9.509362 70.671042 5) 6.940638 65.198402 6) 13.890931 66.148716