TITLE: GCN CIRCULAR NUMBER: 18364 SUBJECT: LIGO/Virgo G184098: LOFAR follow-up DATE: 15/09/24 21:59:56 GMT FROM: Peter Jonker at SRON/RU J. Broderick (ASTRON), P.G. Jonker (SRON/RU), R.P. Fender (Oxford), A. Rowlinson (UvA, ASTRON), R.A.M.J. Wijers (UvA), B.W. Stappers (Manchester) report on behalf of the LOFAR Transients Key Science project: On Sept 21, 2015, starting at 06.00 (UTC), we observed a large fraction of the localization error range at declinations larger than 0 degrees of the Advanced LIGO trigger G184098 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 11.9 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) 132.500000 5.166667 08:50:00.00 +05:10:00.0 2) 135.287125 5.166667 09:01:08.91 +05:10:00.0 3) 129.712875 5.166667 08:38:51.09 +05:10:00.0 4) 131.106458 7.572944 08:44:25.55 +07:34:22.6 5) 131.106458 2.760389 08:44:25.55 +02:45:37.4 6) 133.893542 7.572944 08:55:34.45 +07:34:22.6 7) 133.893542 2.760389 08:55:34.45 +02:45:37.4 8) 128.319333 2.760389 08:33:16.64 +02:45:37.4 The observations cover roughly 50 square degrees in total. Each field was observed for a total of 3 hr with 10s time resolution after pre-processing. These fields will be revisited two times with the same exposures, on provisional time-scales of 1 month and 3 months. Analysis is ongoing. [GCN OPS NOTE(24sep15): This Circular was originally published on 18:05421-Sep-2015 UT.]