TITLE:   GCN CIRCULAR
NUMBER:  18826
SUBJECT: GRB 160104A:  GWAC upper limit during prompt emission phase
DATE:    16/01/05 03:05:45 GMT
FROM:    L.P. Xin at NAOC  <xlp@bao.ac.cn>

L. P. Xin,  J. Y. Wei， Y. L. Qiu,   E. W. Liang,  X. H. Han,   
Y. Xu,  L. Huang,  Y. G. Yang,  X. M. Meng,  H. B. Cai,  
J. Wang,  C. Wu,  J. S. Deng  and H. L. Li   report:

The field of SWIFT GRB 160104A (Melandri et al. GCN 18815)
was monitored by Mini-GWAC system continuously 
during about 1.5 hrs before and 1 hrs after the burst trigger time.
The exposure time for each frame is 10 sec.

No any new optical counterpart (Guidorzi et al., GCN 18816; 
Saito GCN 18817; Xin et al., GCN 18823)  in single frame 
was detected  down to the 5 sigma upper limit of 12.3 mag 
during our observations, calibrated by  nearby USNO B1.0 R2 mag, 
at the epoch of prompt emission phase.

Combining 5 frames during and after the burst trigger initially with a total 
exposure time of 50 sec gives a 5 sigma upper limit of 12.8 mag.

Mini-GWAC system is located at Xinglong observatory,
National Astronomical Observatories, China,
including 6 mounts and 12 Canon 85/f1.2 cameras.
Each mount is equipped with 2 cameras.
For each camera, the Apogee U9000X CCD was used, which gives
about 400 square degree of FOV. The total field of view of this system
is about 5000 sq.deg.

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