TITLE:   GCN CIRCULAR
NUMBER:  29846
SUBJECT: GRB 210420B: Optical observations
DATE:    21/04/20 20:37:21 GMT
FROM:    Arto Oksanen at Nyrola Obs., Finland  <oksanen@nyrola.jklsirius.fi>

A. Oksanen (Hankasalmi observatory) report on behalf a larger collaboration:

We observed the field of the Swift GRB 210420B (Page et al., GCN 29844)
using the 0.40 m remote controlled RC telescope of Hankasalmi observatory 
equipped with the SBIG STX-16803 CCD camera. Total of 25 exposures of 60 s 
each were secured in the clear filter, starting on 2021 April 19:44:58 UT. 

A candidate afterglow is clearly detected in the XRT error circle with 
coordinates (J2000):

RA = 16:57:18.0
DEC = +42:34:12.6

Its magnitude is r = 17.97 +- 0.05 , calibrated against a nearby star
from SDSS. This object is not visible in the Digitized Sky Survey R band
images.

We consider this object as a viable afterglow candidate to GRB 210420B,
but a confirmation is necessary to assess variability. Further
observations are planned.