tokens: We acknowledge the anonymous referee for suggestions regarding the phase-connection analysis and the position accuracy. We thank Peng Wei and Eugene Magnier for helpful discussion about the search of the optical/IR counterpart. This work was supported by NSFC grants 11503008 and J1210039, and Top-notch Academic Programs Project of Jiangsu Higher Education Institutions. P.Z. acknowledges the support from the NWO Veni Fellowship, grant No. 639.041.647, and NSFC grant 11233001. W.Y. was supported in part by NSFC grant No. 11333005 and by the National Program on Key Research and Development Project (grant No. 2016YFA0400804). X.L. was supported by the National Program on Key Research and Development Project (grant No. 2016YFA0400803), and NSFC grants 11133001 and 11333004. X.X. is grateful for the support of NSFC grant 11303015.
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