TITLE:   GCN CIRCULAR
NUMBER:  26470
SUBJECT: LIGO/Virgo S191213g: MASTER OT J064855.37-055545.7 is a dwarf nova
DATE:    19/12/17 13:29:38 GMT
FROM:    Denis Denisenko at SAI MSU  <d.v.denisenko@gmail.com>

D. Denisenko (SAI MSU/Education Center Vorobyovy Gory, Moscow) reports:

MASTER-OAFA has detected an optical transient in the updated error box
of binary NS merger candidate S191213g on 2019-12-16.075 UT (Lipunov
et al., GCN 26467) which was also reported to Transient Name Server as
AT 2019wwg, see https://wis-tns.weizmann.ac.il/object/2019wwg with the
unfiltered magnitudes of 16.6 and 16.3 on 2019-12-16.067 UT and 16.075
UT, respectively.

The object is listed in the Pan-STARRS Survey Data Release 1 (Chambers
et al., 2016) with the following magnitudes: g=22.12, r=21.64,
i=21.47, z=17.68, y=17.44. Checking the PanSTARRS-1 Image Access
website at http://ps1images.stsci.edu/cgi-bin/ps1cutouts for the
position of MASTER OT J064855.37-055545.7 shows the previous outburst
on two images in z and y filters taken on MJD=56597.62894  (2013 Nov.
01) and MJD=56596.63531 (2013 Oct. 31), respectively. The object was
at quiescence on all other images, including r-band image on
MJD=56622.55184 and i-band image on MJD=56622.57154 (25 days after the
outburst). The amplitude of variability (about 5-6 mag) is typical for
the outbursts of dwarf novae (cataclysmic variables of U Gem type).

Given the galactic latitude b=-2.3 and the density of stars in
Monoceros, the detection of the unrelated dwarf nova in the updated
S191213g error box covering 10.9 per cent of the entire sky (G. Mo,
GCN 26417) is more than likely.