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GCN Circular 23756

GRB 190114C: UKIRT JHK observation continuation - steady fading?
2019-01-18T13:20:06Z (5 years ago)
Myungshin Im at Seoul Nat U <>
Myungshin Im, Gregory S. H. Paek, Changsu Choi (CEOU/SNU), on behalf of a
larger collaboration

We continued the observation of the NIR afterglow of GRB 190114C (Gropp et
al., GCN 23688, D'Avanzo et al. GCN 23729, 23754, Im et al. GCN 23740,
23747, Watson et al. GCN 2375 ) with the United Kingdom Infrared Telescope
(UKIRT). Our 3rd epoch UKIRT observation started at 2019-01-18 05:04 UT or
about 3.33 days after the initial alert.

Preliminary magnitudes are derived from quick-look data, using nearby 2MASS
stars as photometry references. The afterglow faded by about 0.3 magnitude
in all of the JHK bands with the J-band magnitude given below, consistent
with the ~0.5 mag/day fading rate reported earlier (Im et al. GCN 23747).

Filter Date UT-start Vega_Mag (AB mag)
J      2019-01-18 08:30:12.989 18.3 +- 0.12 (19.2 AB)

In view of the recent correction report by D'Avanzo et al. (GCN 23754),
J-band fading rate is now 0.6 mag/day from 2019-01-15 to 2019-01-16, which
is consistent with the fading rate of ~0.5/day derived from the later epoch
data. However, the most recent result indicates that GRB may be fading a
bit slower as time goes on.
Note that host galaxy light is not subtracted.

Further observations are planned.
We thank the staffs at UKIRT for carrying out the observation.
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