TITLE:   GCN CIRCULAR
NUMBER:  22651
SUBJECT: LIGO/Virgo G299232: LOFAR follow-up
DATE:    18/04/18 12:16:06 GMT
FROM:    Antonia Rowlinson at U van Amsterdam  <b.a.rowlinson@uva.nl>

J.W. Broderick (ASTRON), K. Gourdji (UvA), A. Rowlinson (UvA, ASTRON),
P.G. Jonker (SRON, RU), A.J. Stewart (SIfA), R.P. Fender (Oxford),
R.A.M.J. Wijers (UvA), B.W. Stappers (Manchester), S. ter Veen
(ASTRON), S. Nissanke (RU), A. Shulevski (UvA) report on behalf of the
LOFAR Transients Key Science Project

From 2018 April 7-15, we observed a large fraction of the localisation
region of the Advanced LIGO/Virgo trigger G299232 (LVC, GCN 21693)
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 245 min using a number of separate 25-min snapshots, as
well as a single 20-min snapshot.

The beam centres are given below (RA and Dec in degrees); the
Bayestar-HLV localisation was used as a basis for calculating the
coordinates of the beams. The pointing setup is identical to the
previous sets of LOFAR follow-up observations described in Broderick
et al., GCN 21809, GCN 21962 and GCN 22172. Two beams in separate
pointings were centred on the IceCube neutrino candidate at RA = 28.2
deg, Dec = 44.8 deg (Bartos et al., GCN 21694; Bartos et al., GCN
21698). Furthermore, one beam was centred on the optical transient
discovered by Swift/UVOT at RA = 25.035625 deg, Dec = 34.567667 deg
(Emery et al., GCN 21733).

Analysis is ongoing. We thank the ASTRON Radio Observatory for
scheduling the observations.

Pointing 1
(integration time 245 min over the period 2018-04-07 08:48 UTC -
2018-04-07 16:56 UTC)

1) 34.039151    46.299866
2) 35.248501    48.949799
3) 28.200000    44.800000
4) 31.322127    48.348415
5) 36.756176    44.251317
6) 37.965526    46.901250

Pointing 2
(integration time 245 min over the period 2018-04-07 08:27 UTC -
2018-04-07 16:35 UTC)

1) 35.780064    51.725205
2) 36.750925    54.437875
3) 31.502071    50.889684
4) 32.472933    53.602354
5) 39.087195    49.848056
6) 40.058057    52.560726

Pointing 3
(integration time 245 min over the period 2018-04-08 08:25 UTC -
2018-04-08 16:33 UTC)

1) 29.306644    35.778068
2) 30.478008    38.389034
3) 25.035625    34.567667
4) 27.105198    37.906547
5) 31.508089    33.649589
6) 32.679454    36.260555

Pointing 4
(integration time 245 min over the period 2018-04-08 08:04 UTC -
2018-04-08 16:12 UTC)

1) 31.825000    41.000000
2) 33.084178    43.610966
3) 28.199341    40.517513
4) 28.200000    44.800000
5) 34.191481    38.871521
6) 35.450659    41.482487

Pointing 5
(integration time 245 min over the period 2018-04-14 08:51 UTC -
2018-04-14 16:59 UTC)

1) 41.738945    68.095823
2) 43.350996    70.808493
3) 34.635623    67.260303
4) 36.247674    69.972972
5) 47.230217    66.218674
6) 48.842268    68.931344

Pointing 6
(integration time 245 min over the period 2018-04-14 08:30 UTC -
2018-04-14 16:38 UTC)

1) 44.937500    79.572222
2) 44.267884    76.796335
3) 31.320689    78.289239
4) 31.990306    81.065126
5) 57.884694    78.079318
6) 58.554311    80.855205

Pointing 7
(integration time 245 min over the period 2018-04-15 08:30 UTC -
2018-04-15 16:38 UTC)

1) 37.337896    57.197845
2) 38.228521    59.934164
3) 32.518303    56.247531
4) 33.408928    58.983851
5) 41.266865    55.411839
6) 42.157490    58.148159

Pointing 8
(integration time 245 min over the period 2018-04-15 08:09 UTC -
2018-04-15 16:17 UTC)

1) 39.119146    62.670484
2) 40.170071    65.406804
3) 33.432096    61.720170
4) 34.483021    64.456490
5) 43.755272    60.884478
6) 44.806196    63.620798