[vsnet-grb-info 27780] GRB 210420B: follow-up photometry of the optical afterglow at Konkoly

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29883
SUBJECT: GRB 210420B: follow-up photometry of the optical afterglow at Konkoly
DATE:    21/04/22 17:53:17 GMT
FROM:    Jozsef Vinko at Konkoly Observator  <vinko at konkoly.hu>

J. Vinko (Konkoly/ELTE/U Szeged), L. Kriskovics, R. Szakats, A. Pal and K. Vida (Konkoly)
report on behalf of the "Transient Astrophyical Objects" project:

We observed the field of GRB 210420B (Moss et al., GCN 29833; Lien et al., GCN 29854; 
Osborne et al. GCN 29876; Stamatikos et al., GCN29879) with the 0.8m RC80 robotic telescope at Piszkesteto Mountain Station of Konkoly Observatory through SDSS r' and i' filters on 
2021 Apr 21.85 UT (MJD 59325.85, 1.07 day after the trigger). The total exposure time 
was 1800 s in both filters. 

The frames were tied to PS1-photometry of local stellar sources. We detect the optical 
afterglow (Lipunov et al., GCN 29845; Oksanen et al., GCN 29846; Hu et al., GCN 29847;
Tianrui Sun et al., GCN 29848; Leonini et al., GCN 29851; de Ugarte Postigo et al., 
GCN 29852, 29853; Watson et al., GCN 29858; Zheng et al., GCN 29861; Breeveld et al., 
GCN 29862; Stecklum et al., GCN 29863; Butler et al.,GCN 29864; Jelinek et al., GCN 29866;
Watson, GCN 29867; Leonini et al., GCN 29872) is detected on the stacked r-band images. 
Forced photometry at the position of the GRB, tied to the PS1 photometry of nearby stars, 
resulted in the following AB-magnitudes:

r = 20.76 +/- 0.33 (5-sigma limit 22.18)
i > 22.09 (5-sigma limit)