GCN Circular 31868

Amit Kumar, Rahul Gupta, Amit K. Ror, Nikita Rawat, Dimple, Ankur Ghosh,
Amar Aryan, Brajesh Kumar, Shashi B. Pandey and Kuntal Misra (ARIES)
report:

We observed the field of the Swift-BAT (Caputo et al., GCN 31848
Not found
 
 
) and
Fermi-GBM (GBM Team, GCN 31847
Not found
 
 
) detected GRB 220408A with the 1.3m
Devasthal Fast Optical Telescope (DFOT) located at Devasthal observatory of
Aryabhatta Research Institute of Observational Sciences (ARIES), India. We
started the observations on 2022-04-08 at 16:27:57 UT, i.e., ~10.698 hours
after the GBM trigger. We have observed 300s*23 frames in each Bessel R and
I filters. We stacked the images after the pre-processing and alignment. We
did not detect the optical afterglow at the Swift-XRT position (Beardmore
et al., GCN 31852
Not found
 
 
) in our stacked images; see also Caputo et al., GCN
31848
Not found
 
 
; Zheng & Filippenko, GCN 31850
Not found
 
 
; Jiang et al., GCN 31853
Not found
 
 
; Oates &
Caputo, GCN 31855
Not found
 
 
; Kumar et al., GCN 31857
Not found
 
 
; Hu et al., GCN 31859
Not found
 
 
;
Strausbaugh et al., GCN 31862
Not found
 
 
; Zhu et al., GCN 31864
Not found
 
 
; and Gregory et al.,
GCN 31867
Not found
 
 
.


We obtain the following 3-sigma upper limits in the stacked images.

Date Start_UT T_start-T0 (hour) Filter Exp time(s) Limiting magnitude
====================================================
2022-04-08 16:27:57 ~10.698 R 300s*23 >22.5
2022-04-08 18:29:56 ~12.731 I  300s*23 >22.1


The magnitudes are not corrected for the Galactic extinction in the burst
direction. Photometric calibration is performed using the standard stars
from the USNO-B1.0 catalogue.

During our observations, the moon phase and its distance were ~45% and
~55-66 degrees, respectively, which affected our deeper limits
significantly; see Kumar et al. 2021, JAA, arXiv:2111.13018
Not found
 
 
 (
https://ui.adsabs.harvard.edu/abs/2000A%26A...363..705M/abstract) for the
sky brightness of the Devasthal site w.r.t. the moon phase and distance.

Assuming a typical temporal flux decay index of the early afterglows
(alpha~0.7), the extrapolated brightness at the epoch of our observation is
consistent with the quoted non-detection. Deeper observations using the
larger facilities will be useful to establish the fast decaying nature of
the burst and to investigate for this burst to happen in any
distant/background galaxy rather than Whirlpool Galaxy (M51a).

This message may be cited.