GCN Circular 34839
Subject
GRB 231018A: GROWTH-India Follow-Up of a Fermi Long GRB
Date
2023-10-19T07:33:47Z (6 months ago)
From
Varun Bhalerao at IIT Bombay <varunb@iitb.ac.in>
Via
Web form
R. Kumar, Y. Wagh, R. Sharma, A. Salgundi, V. Swain, D. Raman, T. Roychowdhury, V. Bhalerao (IIT Bombay), S. Barway, G. C. Anupama (IIA), K. Angail (IAO)
We observed the field of GRB 231018A detected by Fermi (Fermi GBM Team, GCN Circ. 34826; GCN Circ. 34831) with 0.7m GROWTH-India Telescope (GIT). GIT started observing the field at 2023-10-18 17:28:08.912 UT, i.e., 4.96 hours after the Fermi trigger. We obtained a series of 25 r' band images each of 300s exposure, covering 9.44 square degrees. This corresponds to 21.7% of the probability enclosed in the Fermi GBM Final Real-time Localisation (Fermi GBM Team, GCN Circ. 34826) and 20.17% of the probability enclosed in the BALROG localization (Preis et al., GCN Circ. 34827). Where available, PanSTARRS images (Chambers et al., 2016) were used as references for image subtraction. In other fields, we looked for new point sources absent in the GSC2.3 catalog. We did not find any suitable afterglow candidate, reaching a median limiting magnitude of 18.95 in the r' band. The detailed observing log is:
| Tile ID | RA (deg) | Dec (deg) | Lim Mag (AB) | Method |
| 54910 | 0.12 | 50.1 | 18.54 | Catalog |
| 55565 | 1.25 | 51.5 | 18.93 | Subtraction |
| 55567 | 3.51 | 51.5 | 18.96 | Subtraction |
| 55883 | 0.13 | 51.5 | 18.82 | Catalog |
| 54579 | 3.36 | 49.4 | 18.66 | Subtraction |
| 55238 | 0.12 | 50.1 | 18.25 | Catalog |
| 54912 | 2.32 | 50.1 | 19.02 | Subtraction |
| 55241 | 2.35 | 50.8 | 19.01 | Subtraction |
| 55564 | 0.13 | 51.5 | 18.74 | Catalog |
| 55242 | 3.46 | 50.8 | 18.96 | Subtraction |
| 55240 | 1.24 | 50.8 | 19.02 | Subtraction |
| 55243 | 4.57 | 50.8 | 18.98 | Subtraction |
| 54577 | 1.20 | 49.4 | 18.22 | Subtraction |
| 54914 | 4.51 | 50.1 | 17.48 | Subtraction |
| 54578 | 2.28 | 49.4 | 18.76 | Subtraction |
| 56201 | 2.45 | 52.9 | 15.70 | Subtraction |
| 55885 | 1.27 | 52.2 | 18.97 | Subtraction |
| 55887 | 3.56 | 52.2 | 19.03 | Subtraction |
| 55568 | 4.64 | 51.5 | 18.85 | Subtraction |
| 55886 | 2.42 | 52.2 | 18.97 | Subtraction |
| 54913 | 3.42 | 50.1 | 19.05 | Subtraction |
| 55563 | 0.13 | 50.8 | 18.64 | Catalog |
| 54911 | 1.22 | 50.1 | 19.12 | Subtraction |
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/.