GCN Circular 33547

Amit K. Ror, Rahul Gupta, S. B. Pandey, A. Ghosh, A. Aryan, and K. Misra
(ARIES) report:

GRB 230328B was triggered by Swift-BAT at 14:54:48 UT and Fermi-GBM at
14:54:47.43 UT on 28-03-2023 (Gropp et al. 2023 GCN 33527
Not found
 
 
, Dalessi et al.
2023 GCN 33531
Not found
 
 
). The prompt emission was also detected by other space-based
facilities like AstroSat-CZTI (Waratkar et al. 2023, GCN 33532
Not found
 
 
), GRBAlpha
(Dafcikova et al. 2023, GCN 33543
Not found
 
 
), and Konus-Wind (Svinkin et al. 2023,
GCN 33544
Not found
 
 
). We searched for extended GeV emission for a temporal window of
10 ks since the GBM trigger, based on available LAT data. However, we did
not find the detection of any GeV photons, and an upper limit was obtained
for an energy flux < 5.2 x 10^{-10} erg/cm2/s in the energy range 100 MeV -
100 GeV with TS < 20.

We observed the field of GRB 230328B using the 3.6m Devasthal Optical
Telescope located at the Devasthal observatory of the Aryabhatta Research
Institute of Observational Sciences (ARIES), Nainital, India. We have taken
multiple frames with an exposure time of 300 sec each in several optical
passbands. We clearly detect the optical afterglow discovered by Swift-UVOT
in each individual image. The estimated preliminary magnitude is as follows:

Date Start_UT T_start-T0 (days) Filter  Exp time (sec)       magnitude

==============================================================

2023-03-28 21:51:54.44   ~0.29          R         300 sec  20.30 +/- 0.08

The magnitude quoted is not corrected for the galactic and host extinctions
in the direction of the burst. Photometric calibration is performed using
the standard stars from the USNO-B1 catalog.

The detection of the optical afterglow is consistent with the observation
of Gropp et al. 2023 (GCN 33527
Not found
 
 
), Pankov et al. 2023 (GCN 33528
Not found
 
 
), Belkin et
al. 2023 (GCN 33530
Not found
 
 
), Lu et al. 2023 (GCN 33534
Not found
 
 
), Catapano et al. (33535),
Suresh et al. (GCN 33536
Not found
 
 
), Adami et al. (GCN 33537
Not found
 
 
), Gompertz et al. (GCN
33538
Not found
 
 
), Komesh et al. (GCN 33539
Not found
 
 
), Lu et al. 2023 (GCN 33540
Not found
 
 
)

By combining our R-band magnitude with the observations of Pankov et al.
2023 (GCN 33528
Not found
 
 
) and Belkin et al. 2023 (GCN 33530
Not found
 
 
), we have determined the
preliminary flux decay index of 0.55 +/-0.06.

This circular may be cited. The 3.6m Devasthal Optical Telescope (DOT) is a
recently commissioned facility in the Northern Himalayan region of India
(long: 79 41 04E, lat: 29 21 40N, alt: 2540m) owned and operated by
the Aryabhatta
Research Institute of Observational Sciences (ARIES), Nainital (
https://www.aries.res.in). The authors of this GCN circular thankfully
acknowledge the consistent support from the staff members to run and
maintain the 3.6m DOT.