GCN Circular 21236

D. Xu (NAO/CAS), J.Z. Liu, H.B. Niu, S.G. Ma, Y. Zhang, X. Zhang, G.X. 
Pu,T.Z. Yang, F.F. Song (XAO/CAS), H.B. Zhao, B. Li, G.T. Zhaori, H. Lu, 
R.Q. Hong, L.F. Hu (PMO/CAS), H.X. Feng, Z.P. Zhu, T.M. Zhang, X. Zhou, 
H.X. Feng, Z.P. Zhu (NAO/CAS), J. Mao, J.M. Bai (YNAO/CAS) report on 
behalf of the Gravitational Wave Follow-Up Network by NAO-PMO-XAO-YNAO 
in China (GWFUNC):

We have performed tiled observations of LIGO/Virgo G288732 (LVC, GCN 
21221
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) using the Nanshan One-meter Wide field Telescope (NOWT) with a 
FOV of 1.3 x 1.3 deg^2, located in Xinjiang, China. Observations started 
at 18:21:44 UT and ended at 21:31:17 UT on 2017-06-08, covering a total 
area of ~337 deg^2 and with each exposure of 150s in the R-band. Data 
analysis is still underway. We note that the Fermi/LAT error circle 
(Omodei et al., GCN 21227
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) was not covered in the tiled observations, 
because the LAT altitude was too low since the starting of the observations.

However, the NOWT manged to image the Fermi/LAT error circle at the very 
beginning of the following night, and we obtained 3x150s and 2x200s 
R-band images around 15:30:19 UT on 2017-06-09. Five uncatalogued X-ray 
sources by Swift/XRT have been reported, which might be the X-ray 
counterpart candidates of the Fermi/LAT transient (Evans et al. GCN 
21233
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). These five sources, i.e., sources #1, 2, 3, 6, and 7, are within 
the FOV of each Nanshan exposure. Comparison with DSS-II, SDSS, and 
PanSTARRS reveals that sources #1, 3, 6, and 7 have known optical 
counterparts already, and no apparent strong variation in brightness for 
the optical counterparts. Source #2 doesn't have any optical counterpart 
in the DSS-II, SDSS, and PanSTARRS surveys. No optical transient is 
detected at the source #2 position in the Nanshan images, down to a 
limiting magnitude of R>19.2 mag. Therefore, deeper photometry at this 
position is encouraged.