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MASTER OT J095503.19-355149.4 - a probable Dwarf Nova

ATel #8745; D. A.H. Buckley, A. Kniazev, S. B. Potter (SAAO), V. Lipunov, N. Tiurina, E. Gorbovskoy (Lomonosov MSU)
on 27 Feb 2016; 18:20 UT
Credential Certification: David Buckley (dibnob@saao.ac.za)

Subjects: Optical, Gamma Ray, Cataclysmic Variable, Transient

Followup optical imaging and spectroscopic observations with SALT of the optical transient MASTER OT J095503.19-355149.4, tentatively identified (ATel #8741) as the optical counterpart of the Fermi GBM trigger 478121068 (GCN #19092), were conducted on 2016-02-26.78 UT. From un-calibrated g', r' and i' exposures (30 sec each) with the SALTICAM CCD camera, the transient appeared to be approximately 1 mag brighter (V ~ 17) than the MASTER-SAAO observations of the previous night (reported in ATel #8741) and was also seen to be a relatively red object compared to other stars in the field. Two 900 sec exposure spectra were obtained with RSS using the PG900 grating, covering the region 380-680 nm at a resolution of 700. The spectra showed strong blue Balmer lines in absorption, with typical FWHM of 1.5-2 nm, narrower Ca II K absorption, weak HeI 447.1 nm absorption and a very weak H-alpha absorption line. We conclude that this transient is a Dwarf Nova in outburst, still on the rise, and is unlikely to be associated with the purported Fermi source.

MASTER OT J095503.19-355149.4 discovery - possible optical counterpart of Fermi trigger 478121069