TITLE: GCN CIRCULAR NUMBER: 40289 SUBJECT: EP250427a/GRB250427A: HCT optical follow-up DATE: 25/04/30 12:55:53 GMT FROM: anirudhsalgundi@gmail.com
D. Eappachen (IIA), V. Swain (IITB), A. Salgundi (IITB), D.K. Sahu (IIA), A.P. Saikia (IITB), G. C. Anupama (IIA), V. Bhalerao (IITB), A. Balasubramanian (IIA), S. Barway (IIA), S. Bandari (IAO):
We observed the field of EP250427a (Wang et al., GCN #40257), also detected by Fermi-GBM (Ravasio et al., GCN #40262) with the 2.0m Himalayan Chandra Telescope (HCT) of the Indian Astronomical Observatory (IAO). We obtained multiple exposures in the SDSS r' filter starting at 2025-04-29 22:10:49.88 UT (~2.77 days post trigger). We detected the source in our stacked image and obtained the following photometric result:
| JD (mid) | Filter | Exposure (s) | Mag (AB) | Limiting Magnitude (AB) | | ----------------- | ------- | ------------------ | -------------- |--------------| | 2460795.433742 | r' | 5 x 240 | 21.70 +/- 0.12 | 21.9 |
The magnitudes are calibrated against PanSTARRS DR1 (Chambers et al., 2016) and not corrected for Galactic extinction.
Our result is consistent with BOOTES-7 (Perez-Garcia et al., GCN #40259), TRT (Liu et al., GCN #40260), COLIBRÍ (Becerra et al., GCN #40261), REM (Brivio et al., GCN #40264), LCO (Pérez-Fournon et al., GCN #40267), LT (Qiang Xi et al., GCN #40269), GIT (Swain et al., GCN #40270), COLIBRÍ (Magnani et al., GCN #40271), Lesedi (S. de Wet et al., GCN #40272), FTW (Busmann et al., GCN #40273), OHP/T193 (Amram et al., GCN #40275).
These observations were carried out under the ToO program HCT-2025-C1-P08. We thank the HCT staff for their support during the observations. The Indian Astronomical Observatory is operated by the Indian Institute of Astrophysics, Bengaluru, India.
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