The main science objective of the Ground-based Wide Angle Camera (GWAC) is to observe in the visible range (between 500 and 850 nm) from the ground, the prompt emission of some of the gamma-ray bursts detected by the camera ECLAIRs.
The instrument consists of 10 mountings, each carrying 4 cameras 18 cm in diameter, covering a field of view of about 5000 degrees2, roughly half of the field of view of the ECLAIRs telescope.
Each of the 40 cameras is equipped with a 4096 × 4096 E2V CCD operating in the 0.5 to 0.85 ?m wavelength band with a field of view (FoV) of 150 deg². GWAC provides source locations up to a visible magnitude mv = 16 with an accuracy of 11 arcsec (for a 10 s exposure).
![Panoramic view of GWAC installation at Xinglong Observatory (Beijing, China) showing 4 GWAC mountings (right) and 60cm and 30cm telescopes (left). @NAOC](http://www.svom.eu/wp-content/uploads/2019/10/UNADJUSTEDNONRAW_thumb_3359-600x170.jpg")
GWAC searches in real time for visible counterparts around the coordinates of bursts provided by the other instruments (ECLAIR, GRM, MXT, VT, GFT and others). In addition to the VT telescope aboard SVOM, GWAC provides a wide field coverage of the sky regions observed by SVOM.
GWAC also has the ability to detect optical transient events itself without external triggers. Two 60 cm telescopes and 30 cm telescopes are installed next to GWAC to confirm transient detections and to verify whether they are real or false events, providing coordinates with an accuracy of 1 arcsec.
It is foreseen that GWAC will be divided into two sub-sets, each of them consisting of 20 cameras and a 60cm diameter follow-up telescope. One set is already installed at the Xinglong Observatory, north of Beijing. The second will be installed at the Muztagh Ata Observatory in western China.
GWAC is designed to observe more than 12% of SVOM gamma-ray bursts in the visible band from 5 minutes prior to 15 minutes after initiation.
