[vsnet-grb-info 22875] LIGO/Virgo S190630ag: no counterpart candidate in the SVOM/GWAC observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24974
SUBJECT: LIGO/Virgo S190630ag: no counterpart candidate in the SVOM/GWAC observations
DATE:    19/07/03 15:25:11 GMT
FROM:    Diego Gotz at CEA  <diego.gotz at cea.fr>

D. Gotz (CEA/AIM), X.H. Han (NAOC), D. Dornic (CPPM), L.P. Xin (NAOC), 
D. Turpin (NAOC), Y.T. Zheng (GXU), C. Wu (NAOC)  on behalf of the SVOM consortium

We observed 52 sky regions (total: 7800 square degrees with overlaps)
to cover the skymap of the advanced LIGO/Virgo trigger S190630ag,
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 = 3.5 cm) and JFOV cameras (FOV~150 square degrees/camera,
aperture = 18 cm). 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). 

The observations were made during two nights (2019.06.30-2019.07.01).
During the night of 2019.06.30, GWAC worked in survey mode. The survey
area covered over 5000 square degrees, including 15.2 % of the 90% c.l. GW error box. 
The images were taken between ~5 hours and ~1 hour before the event trigger
time, and no electromagnetic precursor has been found down to a 15.5
mag 3 sigma limit in the R band.

During the night of 2019.07.01, the GWAC worked on follow-up mode.
Over 5500 square degrees were observed. We estimate a 7.2% prior 
probability that the 19 observed and processed regions contain 
the true location of the source.

The coordinates of the 19 sky regions and observation times are listed below:

No. Ra  Dec start-obs(UTC)  end-obs(UTC)    Camera_ID

1 15:39:28.56 -15:20:36.24 2019-07-01 13:42:36 2019-07-01 14:10:58 034
2 17:06:36.00 -06:00:32.08 2019-07-01 13:37:08 2019-07-01 14:05:27 021
3 17:53:38.64 -06:34:09.05 2019-07-01 13:48:27 2019-07-01 14:08:40 022
4 18:03:11.52 +12:48:53.64 2019-07-01 14:32:56 2019-07-01 14:34:09 031
5 18:45:49.44 +01:11:14.78 2019-07-01 14:47:55 2019-07-01 15:09:24 033
6 18:53:52.32 +18:03:08.64 2019-07-01 13:21:25 2019-07-01 13:55:51 044
7 18:52:12.48 +30:09:05.40 2019-07-01 13:51:48 2019-07-01 13:55:51 041
8 19:16:11.76 +01:05:37.93 2019-07-01 14:09:31 2019-07-01 14:48:26 044
9 20:06:25.68 +01:07:06.78 2019-07-01 14:09:31 2019-07-01 14:57:44 043
10 20:07:04.56 +13:22:56.64 2019-07-01 14:09:32 2019-07-01 14:56:31 042
11 19:16:34.56 +13:12:15.48 2019-07-01 14:23:42 2019-07-01 14:57:44 041
12 21:10:37.92 +15:33:32.76 2019-07-01 14:32:34 2019-07-01 15:06:58 023
13 20:24:27.60 +15:51:24.48 2019-07-01 14:39:51 2019-07-01 15:02:54 024
14 20:22:31.20 +27:54:07.20 2019-07-01 14:41:28 2019-07-01 14:52:24 021
15 21:15:18.72 +27:15:52.92 2019-07-01 14:51:59 2019-07-01 15:08:09 022
16 21:19:04.56 +13:22:06.60 2019-07-01 15:03:19 2019-07-01 15:25:12 042
17 22:25:53.28 +15:31:49.44 2019-07-01 15:13:30 2019-07-01 15:27:40 023
18 21:39:43.20 +15:49:36.84 2019-07-01 15:13:30 2019-07-01 15:26:27 024
19 22:30:33.12 +27:14:10.32 2019-07-01 15:13:30 2019-07-01 15:28:52 022

The sky coverage map of the night 07.01 is available at: 
http://cmm.svom.cn/gwpub/O3/S190630ag/S190630ag_GWAC.png 
(user:svomo3 pwd:gwo3)

The weather conditions were good during the observations. A 3 sigma 
limiting magnitude of about 15.5 mag in R band was obtained in the single 
frames. No credible new source is detected by our online pipeline during follow-up observations.
A more detailed image analysis including co-addition is ongoing with
our offline pipeline to search for transient candidates.