GRB 230427A: GIT optical upper limit

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