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GCN Circular 33269

Subject
GRB 230204B: GIT discovery of the likely optical afterglow
Date
2023-02-05T05:46:49Z (a year ago)
From
Harsh Kumar at Indian Inst of Tech,Bombay <harshkosli13@gmail.com>
V. Swain (IITB), H. Kumar (IITB), G. Waratkar(IITB), V. Bhalerao (IITB), G.
C. Anupama(IIA), S. Barway (IIA) and K. Angail (IAO) report on behalf of
the GIT team:

We observed the field of GRB 230204B detected by MAXI (Serino et al., GCN
33265) with 0.7m GROWTH-India Telescope (GIT). We started observations at
23:22:37.597 UT, i.e., 1.57 hrs after the Swift/BAT trigger. We obtained 10
frames in the r' band of 300 sec each. We detected an uncatalogued source
at RA 13:10:34.96, Dec: -21:43:05.31 with an uncertainty of 0.67 arcsec.
There is no minor planet present at this position. The photometric results
follow as:

----------------------------------------------------------------------

 JD (mid) | T_mid-T0 (hrs) | Filter | Magnitude (AB) |

----------------------------------------------------------------------

 2459980.47404 | 1.57  | r' | 15.50 +/- 0.04  |

 2459980.50774 | 2.38  | r' | 16.45 +/- 0.05  |

----------------------------------------------------------------------

The candidate decayed by 0.95 magnitude during our observations, separated
by a time span of 48 mins. The fast decay suggests that the candidate is
likely an afterglow of GRB 230204B. We encourage photometric for further
confirmation and spectroscopic follow-up for redshift measurement. The
magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and
not corrected for Galactic extinction.

The GROWTH India Telescope (GIT; Kumar et al. 2022) is a 70-cm telescope
with a 0.7-degree field of view, set up by the Indian Institute of
Astrophysics (IIA) and the Indian Institute of Technology Bombay (IITB)
with funding from DST-SERB and IUSSTF. It is located at the Indian
Astronomical Observatory (Hanle), operated by IIA. We acknowledge funding
by the IITB alumni batch of 1994, which partially supports the operations
of the telescope. Telescope technical details are available at
https://sites.google.com/view/growthindia/.
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