TITLE:   GCN CIRCULAR
NUMBER:  34833
SUBJECT: GRB231017A: GROWTH-India upper limits on the optical afterglow
DATE:    23/10/18 20:23:19 GMT
FROM:    Anirudh Salgundi <salgundi.anirudh@gmail.com>

R. Kumar, A. Salgundi, R. Sharma, Y. Wagh, V. Swain, V. Bhalerao (IIT Bombay), S. Barway, G. C. Anupama (IIA), K. Angail (IAO)

We observed the field of GRB 231017A detected by Fermi (Fermi GBM team GCN 34822) with 0.7m GROWTH-India Telescope (GIT). GIT was triggered at 2023-10-18 15:49:46.29 UT, i.e., 1.32 days after the Fermi trigger, as a response to the Swift/GUANO trigger (J DeLaunay et al., GCN 34824). We obtained multiple frames in the g' and r' bands, covering the localisation reported by Swift/XRT (P. A. Evans et al., GCN 34825). We searched individual images and the stacked image for an afterglow, but do not detect any. Our upper limits on the magnitude of the afterglow are:

JD (mid) | t_mid-t0 (days)| Filter | Exposure (s) | Limiting Magnitude (5 sigma) |

2460236.187750 | 1.351 | g' | 3 x 300 | 19.27 |
2460236.171885 | 1.335 | r' | 6 x 300 | 21.08 |
2460236.250104 | 1.413 | g' | 2 x 400 | 19.98 |

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/.