D. Xu, Z.P. Zhu, B.Y. Yu, H.J. Wang, L. Ge, T.M. Zhang, X. Zhou, C.Z.
Cui, Y.F. Xu (NAOC), H.B. Zhao, B. Li (PMO), J.Z. Liu (XAO), J.R. Mao
(YNAO), X. Gao (Urumqi No.1 Senior High School) report:
We observed the ZTF19acyldun/AT 2019wrt discovered by PTF (Stein et al.,
GCN 26437), a counterpart candidate of LIGO/Virgo S191213g (GCN 26402),
using the UKIRT telescope. Observations started at 09:32:22 UT on
2019-12-16 in H- and K-filters, with ~30min exposure for either filter.
Sky was clear and seeing was ~0.9 arcsec.
ZTF19acyldun/AT 2019wrt is detected in our stacked H-band and K-band
images. The object is extended in the East-West direction, which might
be affected by an arm of the background host galaxy. Preliminary
photometry gives m(H) ~ 18.70 +/- 0.34 and m(K) ~ 17.82 +/- 0.26,
contaminated by the host galaxy and calibrated with nearby 2MASS stars.
Compared with the measurement of m(g) = 19.97 +/- 0.17 in 2019-12-13
(GCN 26437), the optical/NIR behaviour is largely not consistent with a
decaying afterglow of a short GRB. Other scenarios for S191213g would be
more self-consistent, such as a supernova or an emerging kilonova.
We thank the great support of the UKIRT staff/observer, in particular
Michael Pohlen, Watson Varricatt, and Jessica Stasik.