GCN Circular 24657

LIGO/Virgo S190521g: No optical counterpart from SVOM/GWAC observations.

D. Turpin (NAOC), N. Dagoneau (CEA/AIM), L.P. Xin (NAOC),
X.H. Han (NAOC), J.Y. Wei (NAOC), C. Wu (NAOC),  L. Huang (NAOC),
Y. Xu (NAOC), H.B. Cai (NAOC), J. Wang (NAOC), X.M. Lu (NAOC),
Y.L. Qiu (NAOC), J.S. Deng (NAOC), L. Jia (NAOC), S.C. Zou (NAOC),
S.F. Liu (NAOC), Q.C. Feng (NAOC), H.L. Li (NAOC), D.W. Xu (NAOC),
Y.J. Xiao (NAOC), W.L. Dong (NAOC), Y.T. Zheng (NAOC), P.P. Zhang (NAOC),
R.S. Zhang (NAOC), E.W. Liang (GXU), X.G. Wang (GXU), Z.G. Dai (NJU),
X.Y. Wang (NJU), Y.G. Yang (HBNU), J.R. Mao (YNAO), B. Cordier (CEA/AIM),
S. Basa (CNRS/LAM), J.L. Atteia (UPS/IRAP), D. G�tz (CEA/AIM),
A. Claret (CEA/AIM), N. Leroy (CNRS/LAL), C. Lachaud (CNRS/APC),
E. Le Floc'h (CEA/AIM), S.N. Zhang (IHEP), B.B. Wu (IHEP),
report on behalf of the SVOM Ground Follow-up Group:


We observed 12 sky regions (total: 241.9 square degrees) to cover the
initial skymap of the LIGO/Virgo trigger S190521g (GCN24621
Not found
 
 
), with 
SVOM/GWAC, at Xinglong Observatory, equipped with a set of two types
of wide angle cameras: FFOV cameras (FOV~900 square degrees/camera,
aperture = 3.5cm) and JFOV cameras (FOV~150 square degrees/camera,
aperture = 18cm).
SVOM/GWAC currently comprises 4 FFOV cameras and 16 JFOV cameras,
working with unfiltered band. The observations are operated in time-series
mode, taking one exposure every 15 seconds (10s exposure + 5s readout).
We estimate a 31.6% prior probability that these 12 regions contain the
true location of the source.
The coordinates of the 12 regions and observation time are listed below:

# Ra[deg] Dec[deg] start-obs(UTC) end-obs(UTC) FoV
1 186.062 19.4675 2019-05-21 12:28:04 2019-05-21 13:58:31 12.5x12.5 deg
2 173.651 31.7854 2019-05-21 12:28:04 2019-05-21 13:58:10 12.5x12.5 deg
3 187.313 30.9042 2019-05-21 12:28:55 2019-05-21 13:58:10 12.5x12.5 deg
4 200.866 18.4278 2019-05-21 13:58:51 2019-05-21 16:14:36 12.5x12.5 deg
5 213.618 47.4480 2019-05-21 13:59:55 2019-05-21 16:15:18 12.5x12.5 deg
6 212.232 35.2260 2019-05-21 13:59:55 2019-05-21 16:15:18 12.5x12.5 deg
7 196.883 35.0781 2019-05-21 13:59:55 2019-05-21 16:15:07 12.5x12.5 deg
8 195.536 47.1398 2019-05-21 13:59:55 2019-05-21 16:15:07 12.5x12.5 deg
9 239.028 47.0970 2019-05-21 16:16:18 2019-05-21 17:10:37 12.5x12.5 deg
10 240.266 35.0818 2019-05-21 16:16:18 2019-05-21 17:10:37 12.5x12.5 deg
11 255.613 35.2164 2019-05-21 16:16:18 2019-05-21 17:10:33 12.5x12.5 deg
12 257.022 47.4364 2019-05-21 16:26:48 2019-05-21 17:10:33 12.5x12.5 deg
4 200.45 18.3189 2019-05-22 15:35:57 2019-05-22 15:45:16 12.5x12.5 deg
4 202.637 18.2594 2019-05-22 14:36:21 2019-05-22 14:57:49 12.5x12.5 deg
8 195.53 47.1473 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
7 196.874 35.0868 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
6 212.24 35.2348 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
5 213.618 47.4531 2019-05-22 15:00:14 2019-05-22 15:30:47 12.5x12.5 deg
7 197.187 35.7065 2019-05-22 15:46:41 2019-05-22 15:58:26 12.5x12.5 deg
8 195.659 46.8473 2019-05-22 15:56:00 2019-05-22 15:58:26 12.5x12.5 deg
6 214.626 37.1103 2019-05-22 17:20:03 2019-05-22 17:58:29 12.5x12.5 deg
7 200.666 37.3979 2019-05-22 17:32:10 2019-05-22 17:58:27 12.5x12.5 deg
12 260.506 48.6905 2019-05-22 19:16:41 2019-05-22 19:19:30 12.5x12.5 deg
10 244.148 37.3798 2019-05-22 19:18:42 2019-05-22 19:19:30 12.5x12.5 deg
9 238.995 47.1164 2019-05-22 14:04:56 2019-05-22 14:32:53 12.5x12.5 deg
12 257.088 47.4065 2019-05-22 14:20:44 2019-05-22 14:32:53 12.5x12.5 deg
11 255.657 35.1801 2019-05-22 14:04:56 2019-05-22 14:32:53 12.5x12.5 deg
10 240.333 35.0506 2019-05-22 14:11:49 2019-05-22 14:32:53 12.5x12.5 deg

The covering map is available at:
http://cmm.svom.cn/gwpub/O3/S190521g/S190521g_GWAC.png
(user:svomo3 pwd:gwo3)

The first image was taken ~9.4 hours after the event trigger time. The
weather conditions were partly cloudy during the two consecutive days
of observations. A 3 sigma limiting magnitude of about 16 mag in R band
is typically obtained in our single frames.
No credible new source is detected by our online pipeline.
A more detailed image analysis including co-addition is ongoing with
our offline pipeline to search for faint transient candidates.