The Ground-based Wide Angle Cameras (GWACs) project will be a key ground-based observation system for the future space French-Chinese mission SVOM. The GWACs telescopes will be located at two sites, one in China and one in Chile.
GWAC have two kinds of cameras, called JFoV (18cm, f/1.2) equipped with an E2V 4k*4k pixels CCD, and FFoV (3.5cm, f/1.4) with an Apogee U9000X 3k*3K pixels CCD. Each GWAC unit has four JFoV and one FFoV.The cadence is the same for all the cameras, which is 15 seconds,which includes a 10 second exposure and 5 second readout time. The magnitude limit is ~V16 mag for JFoV and V12.5 mag for FFoV in new moon phase in 10 sec exposures.
Every night, in a survey mode, GWACs searches for any optical counterpart to violent phenomena happening in the universe. The main scientific goal is to catch the prompt optical emission and the early afterglows of gamma-ray bursts but also other phenomena as the dMe,Nova, SN, and the counterparts of neutrinos and gravitational waves. For this, it uses its own automatic transient search methods (i.e catalog crossmatch and difference imaging analysis), running independently and whose final results are crossed check by each other. In case of an interesting transient, two dedicated robotics telescopes (60 cm diameter, limiting magnitude 19) are observing the candidates in order to validate their nature.
The complete system of GWAC will have 10 units, covering more than 5000 square degrees simultaneously. Currently, four GWAC units have been installed since 2017 in Xinglong observatory of China to make a full test for the whole system including hardware and data processing system software.
During the next observational campaign of LIGO/Virgo, GWAC follow-up observations are unique in the optical band because they can cover a very large probability region with little latency.
GWACs are funded by National Astronomical Observatories of China,Ministry of Science and Technology of PRC, National Fund Committee (National Natural Science Foundation of China), Chinese Academy of Sciences, Guangxi University, Nanjing University, and Huaibei Normal University.
J.Y. Wei (NAOC), H.B. Cai (NAOC), J.S. Deng (NAOC), W.L. Dong (NAOC), Q.C. Feng (NAOC), X.H. Han (NAOC), L. Huang (NAOC), L. Jia (NAOC), H.L. Li (NAOC), E.W.Liang (GXU), S.F. Liu (NAOC), X.M. Lu (NAOC),Y.L. Qiu (NAOC), D.Turpin (NAOC), J. Wang (NAOC), X.G.Wang (GXU) C. Wu (NAOC), Y.J. Xiao (NAOC), L.P. Xin (NAOC), D.W. Xu (NAOC), Y. Xu (NAOC), Y.G. Yang (HBNU), J, Y.T. Zheng (NAOC), S.C. Zou (NAOC)
Some words about SVOM
SVOM (Space-based multiband astronomical Variable Objects Monitor) is a mission dedicated to the study of the Violent Universe such as the collapse of massive stars or neutrons star coalescence. SVOM is a versatile satellite to be launched in 2021, with built-in multi-wavelength capabilities, autonomous repointing and dedicated ground telescopes. The electromagnetic information from astrophysical violent events can provide useful information about the particle mechanisms at play and the local environment. SVOM can either detect by itself these transient events with ground telescopes or instruments on the satellite as well as observing external alerts found by other facilities including gravitational-wave alerts.