TITLE: GCN CIRCULAR NUMBER: 21586 SUBJECT: LIGO/Virgo G298048: HSC observations of the OT candidate of G298048 DATE: 17/08/19 06:52:33 GMT FROM: Nozomu Tominaga at Konan U Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Tajitsu, A., Fujiyoshi, T. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima U.), Tominaga, N. (Konan U.), Motohara, K., Ohsawa, R., Morokuma, T. (Univ. of Tokyo), Kawai, N. (Tokyo Tech.), and Asakura, Y. (Nagoya Univ.) on behalf of the J-GEM collaboration We performed follow-up observations for the gravitational wave event G298048 with Hyper Suprime-Cam attached to the Subaru telescope from 5:20 to 6:00 on August 19 2017 UT. We surveyed the same sky area as our previous observation (GCN 21549) with HSC-z band filter. SSS17a, which is the most promising candidate of the optical counterpart of G298048 (GCN 21529), was still bright. The rough estimation of the z-band magnitude of the object was ~17.7 (AB). Further analysis is ongoing. The sky fields observed by this survey are listed below: ID Time                RA          DEC          Exp  Filter ----------------------------------------------------------- 28 2017-08-19T05:21:42 13h10m14.4s -23d19m20.0s  2.0s HSC-z 04 2017-08-19T05:22:21 13h07m25.6s -26d36m51.9s 10.0s HSC-z 05 2017-08-19T05:23:02 13h10m14.3s -27d17m02.1s 10.0s HSC-z 06 2017-08-19T05:23:46 13h13m03.0s -27d57m27.1s 10.0s HSC-z 07 2017-08-19T05:24:28 13h15m51.8s -28d38m07.2s 10.0s HSC-z 08 2017-08-19T05:25:11 13h18m40.5s -29d19m03.0s 10.0s HSC-z 09 2017-08-19T05:25:57 13h21m29.2s -30d00m15.5s 10.0s HSC-z 28 2017-08-19T05:26:44 13h10m14.4s -23d19m20.0s 30.0s HSC-z 10 2017-08-19T05:27:44 13h04m36.9s -24d37m43.0s 30.0s HSC-z 11 2017-08-19T05:28:45 13h07m25.6s -25d17m13.0s 30.0s HSC-z 12 2017-08-19T05:29:47 13h10m14.4s -25d56m55.7s 30.0s HSC-z 13 2017-08-19T05:30:48 13h13m03.1s -26d36m52.0s 30.0s HSC-z 28 2017-08-19T05:31:49 13h10m14.4s -23d19m20.0s 30.0s HSC-z 14 2017-08-19T05:32:51 13h01m48.2s -22d40m26.0s 30.0s HSC-z 15 2017-08-19T05:33:54 13h15m51.8s -27d17m02.0s 30.0s HSC-z 16 2017-08-19T05:34:55 13h18m40.5s -27d57m27.0s 30.0s HSC-z 17 2017-08-19T05:35:59 13h04m36.9s -23d19m20.1s 30.0s HSC-z 18 2017-08-19T05:37:00 13h07m25.7s -23d58m25.6s 30.0s HSC-z 19 2017-08-19T05:38:02 12h58m59.5s -20d44m48.0s 30.0s HSC-z 20 2017-08-19T05:39:03 13h10m14.4s -24d37m43.1s 30.0s HSC-z 22 2017-08-19T05:40:05 13h13m03.1s -25d17m12.9s 30.0s HSC-z 23 2017-08-19T05:41:06 13h15m51.9s -25d56m55.6s 30.0s HSC-z 24 2017-08-19T05:42:15 12h56m10.8s -18d50m37.3s 30.0s HSC-z 25 2017-08-19T05:43:15 13h04m37.0s -22d01m43.1s 30.0s HSC-z 26 2017-08-19T05:44:15 13h07m25.7s -22d40m26.2s 30.0s HSC-z 29 2017-08-19T05:45:16 13h01m48.3s -20d06m35.2s 30.0s HSC-z 28 2017-08-19T05:46:17 13h10m14.4s -23d19m20.1s 30.0s HSC-z 28 2017-08-19T05:47:17 13h10m14.4s -23d19m20.1s 120.0s HSC-z 28 2017-08-19T05:49:48 13h10m14.4s -23d19m20.0s 120.0s HSC-z 28 2017-08-19T05:52:20 13h10m17.5s -23d18m06.5s 60.0s HSC-z -----------------------------------------------------------