GWAC 181017A: Independently discovery of an outburst of a dwarf nova with an amplitude of 5.5 mag by GWAC

ATel #12140; Liping Xin (NAOC), Jing Wang (NAOC), Junbo Zhang (NAOC), Zhongyi Lin (NCU), Hongbo Cai (NAOC), Zigao Dai (NJU), Turpin Damien(NAOC), Jingsong Deng(NAOC), Wenlong Dong(NAOC), Qichen Feng(NAOC), Xuhui Han (NAOC), Lei Huang (NAOC), Huali Li (NAOC), Enwei Liang(GXU), Xiaomeng Lu (NAOC), Shunfang Liu (NAOC), Xianmin Meng(NAOC), Yulei Qiu(NAOC), Xianggao Wang(GXU), XiangYu Wang(NJU), Chao Wu (NAOC), Yujie Xiao(NAOC), Dawei Xu(NAOC), Yang Xu(NAOC), Yuangui Yang(HNU), Pinpin Zhang(NAOC), Yatong Zheng(NAOC), Ruosong Zhang(NAOC) and Jianyan Wei (NAOC) on behalf of GWAC/SVOM team
on 23 Oct 2018; 03:23 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Liping Xin (xlp@nao.cas.cn)

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GWAC (Wei et al., 2016) auto-discovery system discover an outburst of the source, whose coordinates are RA=02:25:06.4 DEC=+08:06:39 J2000 on 2018-10-17T13:55:00 UT. There is a source in VIZIER database within an error circle radius of 0.5 arcsec. The brightness of the counterpart in USNO B1.0 catalog is R1=19.93 mag.

The multi wavelength photometry observations were performed with 0.6m GWAC_F60B telescope 65sec after the event at Xinglong observatory, operated by the National Observatories of China and the Guangxi University. The brightness of this optical transient is about 14.4 mag in R band during the observation epoch and has a variation of about 0.4 mag. All these magnitudes are calibrated by the nearby USNO B1.0 magnitudes.

The spectrum of the transient was obtained by the 2.16m telescope of Xinglong observatory, National Astronomical Observatories, CAS, on 2018-10-17. The beginning time of the spectrum was 16:35:13UT. The exposure time was 30 min. The OMR spectrograph was used in the observation. The spectral resolution is ~10A, and is blazed at 6000A. The transient shows a very blue continuum superposed by evident Ha, Hb, and HeII4686A emission lines. The Ha emission line is double peaked. The spectrum is consistent with the feature of a dwarf nova.