TITLE:   GCN CIRCULAR
NUMBER:  29577
SUBJECT: GRB 210217A: Mondy optical observations
DATE:    21/02/26 18:35:21 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

N.Pankov (HSE), S. Belkin (IKI),  A. Pozanenko (IKI), E. Klunko (ISTP) 
report  on behalf of IKI GRB FuN:

We observed the field of GRB 210217A (Simpson  et al., GCN  29521) with 
AZT-33IK telescope of Sayan observatory (Mondy)  on 2021-02-19 and XX. 
Within enhanced XRT position (Evans et al., GCN 29525) we do not detect 
afterglow (Simpson  et al., GCNs  29521,29555;  Zhu  et al., GCN  29523; 
Zheng et al., GCN 29533; Shrestha et al., GCN  29535; Kumar et al., GCN 
29539). Preliminary photometry of the filed is following

Date       UT start   t-T0       Filter Exp.    OT    Err.  UL(3sigma)
                       (mid, days)        (s)

2021-02-19 13:10:59   1.58579    R      2190   n/d   n/d   22.2
2021-02-21 16:05:26   3.71250    R      3150   n/d   n/d   22.8
2021-02-19+2021-02-21 2.65193    R      5850   n/d   n/d   22.9

The photometry is based on the nearby USNO-B1.0 star
USNO-B1.0_id R2
1587-088041      17.94

A light curve of afterglow of GRB 210217A (based on published 
photometry) and upper limits can be found in
http://grb.rssi.ru/GRB210217A/GRB210217A_LC.jpg

Using  upper   upper limit we may suggest a possible jet break of the 
light curve we may suggest a jet break between 1.58 and 3.71 days after 
power law decay with index alpha of -0.48 (Shrestha et al., GCN 29535).