GCN Circular 24659

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 9 sky regions (total: 147.3 square degrees) to cover the
initial skymap of the LIGO/Virgo trigger S190521r (GCN24632
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 30.2% prior probability that these 9 regions contain the
true location of the source.
The coordinates of the 9 regions and observation time are listed below:

# Ra[deg] Dec[deg] start-obs(UTC) end-obs(UTC) FoV
1 277.934 18.1817 2019-05-22 15:48:27 2019-05-22 17:58:07 12.5x12.5 deg
2 264.736 18.0991 2019-05-22 15:56:09 2019-05-22 17:58:07 12.5x12.5 deg
3 278.536 30.4064 2019-05-22 16:10:35 2019-05-22 17:58:08 12.5x12.5 deg
4 264.327 30.1808 2019-05-22 17:50:50 2019-05-22 17:58:07 12.5x12.5 deg
5 334.381 18.0954 2019-05-22 18:20:31 2019-05-22 19:02:15 12.5x12.5 deg
6 321.183 18.0074 2019-05-22 18:22:32 2019-05-22 19:02:15 12.5x12.5 deg
5 332.268 18.1257 2019-05-22 18:24:45 2019-05-22 19:04:27 12.5x12.5 deg
6 321.343 18.5382 2019-05-22 18:25:58 2019-05-22 18:34:28 12.5x12.5 deg
7 320.76 30.1094 2019-05-22 18:29:25 2019-05-22 18:59:00 12.5x12.5 deg
7 320.628 29.7237 2019-05-22 18:31:38 2019-05-22 18:56:45 12.5x12.5 deg
8 334.97 30.349 2019-05-22 18:35:30 2019-05-22 19:02:15 12.5x12.5 deg
9 342.46 35.0794 2019-05-22 19:15:29 2019-05-22 19:19:32 12.5x12.5 deg

The covering map is available at:
http://cmm.svom.cn/gwpub/O3/S190521r/S190521r_GWAC.png
(user:svomo3 pwd:gwo3)

The first image was taken ~1.3 days 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.