TITLE:   GCN CIRCULAR
NUMBER:  29414
SUBJECT: GRB 210204A: Optical Observations from HCT
DATE:    21/02/07 04:46:24 GMT
FROM:    Anirban Dutta at Indian Inst. of Astrophysics  <anirban.dutta@iiap.res.in>

Teja, R.S.; Dutta, Anirban (IIA, Bengaluru); Kumar, Harsh (IIT, Bombay);
Sujith, D.S.; Sahu, D.K.; Anupama, G.C.; Barway, Sudhansu (IIA,
Bengaluru); Bhalerao, Varun (IIT, Bombay) 

We observed the field of GRB 210204A / ZTF21aagwbjr (Fermi-GBM, GCN
#29390; Li et al., GCN #29392; Izzo et al., GCN #29411) with the
Himalayan Faint Object Spectrograph and Camera (HFOSC) mounted on the
2-m Himalayan Chandra Telescope (IAO, Hanle, India). Multiple frames
(each 300 sec) of the GRB field in Bessell R and I bands were obtained
with an average airmass of 1.21 under good seeing conditions.
Preliminary PSF photometry on the stacked images was performed and
calibrated against USNO-B1 catalogue. We clearly detected an OT in the
stacked images in both the bands. The estimated magnitudes of the OT
(not corrected for the Galactic extinction) are as under - 

-------------------------------------------------------------------------------------
Date | UT (mean) | Filter | Exp. time x No. of frames | Magnitude (err)
-------------------------------------------------------------------------------------
2021-02-06 15:11:11    R             300 sec x 4                   20.07
(0.13)
2021-02-06 15:40:29    I              300 sec X 4                  19.79
(0.15)
-------------------------------------------------------------------------------------
The observations were carried out under the ToO program HCT-2021-C1-P2.
We thank the staff at IAO and CREST for helping us with the
observations.