TITLE:   GCN CIRCULAR
NUMBER:  33699
SUBJECT: GRB 230427A: GIT optical upper limit
DATE:    23/04/28 09:16:24 GMT
FROM:    Harsh Kumar at Indian Inst of Tech,Bombay <harshkosli13@gmail.com>

T. Roychowdhury(IITB), V. Swain (IITB), A. Suresh (IITB), H. Kumar(IITB),
D. Raman(IITB), Kaysang (IAO), V. Bhalerao(IITB), G. C. Anupama(IIA), S.
Barway(IIA) report on behalf of the GIT team:

We observed GRB 230427A detected by Swift-BAT (Troja et al., GCN 33687)
with 0.7m GROWTH-India Telescope (GIT). The observations started at
14:20:43 UT on 2023-04-27, 3.8 hours after the Swift-BAT trigger. We
obtained 10 images of 300-sec exposures in the r' filter and 5 images of
300-sec exposures in the i', z' and g' filters. We did not detect any new
source in our stacked image within the 2.4 arcsec circle, around R.A.= 10h
13m 15.16s, DEC.=+48d 12' 14.2". The obtained upper limits follow as:

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JD (mid)  |  T_mid-T0(hrs)  |  Exposure (sec)  |  Filter |  Lim_mag
(5-sigma) |

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2460062.1148169  |  4.22  |  10 x 300 (stacked)  |  r' | > 21.70  |

2460062.1433660 |  4.91  |  5 x 300 (stacked) |  i' | > 20.76  |

2460062.1604599 |  5.31 |  5 x 300 (stacked) | z' | > 19.42  |

2460062.1775733  |  5.73  |  5 x 300 (stacked) | g' | > 21.35  |

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Our results are consistent with the upper limit reported by AKO (M. Odeh,
GCN #33693), BOOTES-5/JGT (Y.-D. Hu et al., GCN #33695), OHP/T193 (D.
Turpin et al., GCN #33696), GMG (J. Mao et al., GCN #33697) and Bassano
Bresciano Observatory (U.Quadri et al., GCN #33698). 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/.