TITLE: GCN CIRCULAR NUMBER: 18457 SUBJECT: LIGO/Virgo G194575: LOFAR follow-up DATE: 15/10/23 21:34:12 GMT FROM: Antonia Rowlinson at U van Amsterdam A. Rowlinson (UvA, ASTRON), J. Broderick (ASTRON), P.G. Jonker (SRON/RU), R.P. Fender (Oxford), R.A.M.J. Wijers (UvA), B.W. Stappers (Manchester), A. Shulevski (ASTRON) report on behalf of the LOFAR Transients Key Science project On Oct 23, 2015, starting at 11:01 (UTC), we observed a large fraction of the localization error range of the Advanced LIGO trigger G194575 with the ILT (International Low-Frequency Array [LOFAR] Telescope) as part of a test observation. Due to the low elevation and proximity to the Sun of these observations, we note that LOFAR will not be at optimal performance. The quality of these observations will determine the feasibility of further LOFAR follow-up of Advanced LIGO trigger G194575. The observations were obtained with the High-Band Antennas (HBA) at a centre frequency of 145 MHz (bandwidth 7.8 MHz). In this configuration, the ILT can provide 8 simultaneous beams on the sky, where each beam has a field of view of approximately 12 deg^2 (beam FWHM 3.9 degrees). The beam centres are given below: 1) 204.648425 -4.457881 13:38:35.62 -04:27:28.4 2) 207.424367 -4.457881 13:49:41.85 -04:27:28.4 3) 201.872483 -4.457881 13:27:29.40 -04:27:28.4 4) 206.036396 -2.053845 13:44:08.74 -02:03:13.8 5) 203.260454 -2.053845 13:33:02.51 -02:03:13.8 6) 206.036396 -6.861917 13:44:08.74 -06:51:42.9 7) 203.260454 -6.861917 13:33:02.51 -06:51:42.9 8) 196.154938 -15.286953 13:04:37.19 -15:17:13.0 The observations cover roughly 50 square degrees in total. Each field was observed for a total of 0.5 hr with 10s time resolution after pre-processing. Analysis is ongoing.