TITLE: GCN CIRCULAR NUMBER: 41030 SUBJECT: EP250704a/GRB250704B : HCT optical and NIR upper limits DATE: 25/07/08 15:06:08 GMT FROM: V. Swain at IIT Bombay vishwajeet.s@iitb.ac.in
V. Swain (IITB), D. Eappachen (IIA), T. Mohan (IITB), A.P. Saikia (IITB), D.K. Sahu (IIA), A. Balasubramanian (IIA), G. C. Anupama (IIA), V. Bhalerao (IITB), S. Barway (IIA), M. Nayana (IAO), S. Bandari (IAO) :
We observed the field of EP250704a (Li et al., GCN 40941) also detected by SVOM (GRB 250704B; Wang et al., GCN 40940), with the 2.0m Himalayan Chandra Telescope (HCT) of the Indian Astronomical Observatory (IAO). We obtained multiple exposures in J and r' filters. We obtained the following upper limits:
| JD (mid) | Date-Time (UTC)| Filter | Total Exposure (s) | tmid-t0 (days) | 5-sigma Upper Limit (AB) | | ---------------- |---------------- | ------ | ------------------ | -------------- | ---------------- | | 2460862.386666 | 2025-07-05T21:16:47.94 | J | 1170 | 1.54 | 18.9 | | 2460864.216936 | 2025-07-07T17:12:23.27 | r' | 3600 | 3.37 | 21.8 |
The magnitudes are calibrated against PanSTARRS DR1 for SDDS r' filter (Chambers et al., 2016) and against 2MASS catalog (Skrutskie et al., 2006) for J-filter. The magnitudes are not corrected for Galactic extinction.
The result is consistent with other optical observations.
These observations were carried out under the ToO program HCT-2025-C2-P010. 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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