TITLE:   GCN CIRCULAR
NUMBER:  31893
SUBJECT: GRB 220408A: HCT optical upper limit
DATE:    22/04/13 08:52:20 GMT
FROM:    Harsh Kumar at Indian Inst of Tech,Bombay  <harshkosli13@gmail.com>

H. Kumar (IITB), V. Swain (IITB), R. Norbu (IAO), G. C. Anupama (IIA), S.
Barway (IIA), V. Bhalerao (IITB), A. Dutta (IIA), R. Gupta (ARIES), K.
Misra (ARIES), D. Panchal (ARIES), S.B. Pandey (ARIES), D.K. Sahu (IIA)
report on behalf of the HCT team:


We observed GRB 220408A detected by the Fermi-GBM (GCN # 31847), Swift-BAT
(R. Caputo et al., GCN #31848) and optical afterglow discovered by Swift-UVOT
(GCN #31848) with the 2.0m Himalayan Chandra Telescope (HCT) of the Indian
Astronomical Observatory (IAO). We obtained multiple exposures in the Rc
and Ic filters. We did not detect any new source in our stacked image at
the afterglow location.

The obtained upper limit follows as:

-------------------------------------------------------------------------

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

-------------------------------------------------------------------------

 2459678.203981 | 11.13 | 300 x 3 (stacked) | Rc | > 22.51 |

 2459678.225509 | 11.64 | 300 x 3 (stacked) | Ic | > 22.46 |

-------------------------------------------------------------------------

Our upper limits are consistent with results from R. Caputo et al. (GCN
#31848), W. Zheng and A.V. Filippenko (GCN #31850), S.Q. Jiang et al. (GCN
#3185), S.R. Oates & R. Caputo (GCN #31855), H. Kumar et al. (GCN #31857),
Y.-D. Hu et al. (GCN #31859), R. Strausbaugh et al. (GCN #31862), Z. Zhu et
al. (GCN #31864), G.S.H. Paek et al. (GCN #31867), A. Kumar et al. (GCN
#31868), A.M. Watson et al. (GCN #31870), B. O'Connor et al. (GCN #31875),
S. Beradze et al. (GCN #31884).

The magnitudes are in the AB system of magnitude, calibrated against
PanSTARRS (Flewelling et al., 2018) using Lupton's transformation equations
available at
http://classic.sdss.org/dr4/algorithms/sdssUBVRITransform.html#Lupton2005.
The magnitudes are not corrected for galactic extinction.


These observations were carried out under the ToO program HCT-2022-C1-P14
(PI: Harsh Kumar). 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.