GCN Circular 29168

H. Kumar (IITB), U. Stanzin (IAO), V. Bhalerao (IITB), G. C. Anupama (IIA),
S. Barway (IIA), report on behalf of the GROWTH-India collaboration:

We observed GRB 201223A detected by Swift-BAT (J.D. Gropp et al., GCN
#29158); optical counterpart first reported by V. Lipunov et al., (GCN
#29157) with 0.7m GROWTH-India Telescope, starting at
2020-12-23T18:30:33.51 UT. We obtained multiple images of 300 sec each in
the r' filter. We clearly detected the afterglow at a position consistent
with Swift-UVOT (GCN #29158) and MASTER-Net OT (GCN #29157) positions.

We obtained the following photometric results:

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 JD (start) | T_start-T0 (hrs) | Filter | Mag (AB)|

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2459207.27122 | 0.5 | r' | 18.52 +/- 0.03

2459207.28623 | 0.9 | r' | 19.12 +/- 0.04

2459207.32568 | 1.8 | r' | 19.98 +/- 0.09

2459207.34029 | 2.2 | r' | 20.15 +/- 0.09

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Combining our photometric results with r band measurements of Z.P. Zhu et.
al., (GCN #29159), we conclude that the source is fading with a power-law
index of 1.04 +/- 0.01. The magnitudes are calibrated against PanSTARRs PS1
data release, (Flewelling et al., 2018) and not corrected for galactic
extinction. Processing of more data is underway.

The GROWTH India Telescope (GIT) is a 70-cm telescope with a 0.7 degree
field of view, set up by the Indian Institute of Astrophysics and the
Indian Institute of Technology Bombay with support from the Indo-US Science
and Technology Forum (IUSSTF) and the Science and Engineering Research
Board (SERB) of the Department of Science and Technology (DST), Government
of India (https://sites.google.com/view/growthindia/). It is located at the
Indian Astronomical Observatory (Hanle), operated by the Indian Institute
of Astrophysics (IIA).