[vsnet-grb-info 27748] GRB 210420B: Montarrenti Observatory optical afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29851
SUBJECT: GRB 210420B: Montarrenti Observatory optical afterglow detection
DATE:    21/04/21 01:21:44 GMT
FROM:    Simone Leonini at Monarrenti Obs  <s.leonini at iol.it>

Simone Leonini, M. Conti, P. Rosi and L.M. Tinjaca Ramirez (Montarrenti Observatory, Siena, Italy) report:

We observed the field of GRB 210420B (Swift trigger 1044382, M.J. Moss et al., GCN Circ. 29844) with the automatic 0.53m RC telescope + U47 detector at Montarrenti Observatory (Siena, Italy, IAU code C88).

The observations were started under good weather conditions at 2021-04-20 23:46:05 UT (approximately 4 hours after notice) stacking 5x60s R filter CCD exposures for each run.

The optical afterglow was clearly detected as follows:

2021 Apr 20.99207 UT (23:48:35 mid-time) R=19.0 +/-0.13
2021 Apr 21.03089 UT (00:44:29 mid-time) R=19.2 +/-0.14

Preliminary magnitudes were obtained using Astrometrica software using USNO-B1 catalogue for positions and photometry. An ensemble between 83 and 76 stars were used for the magnitude and astrometric comparison. Measures are not corrected for galactic dust extinction.

The position of the GRB (within the error box given by Swift) is the following:

RA (J2000.0) 16h 57m 18.05s +/-0.14
Decl. (J2000.0) +42° 34' 12.0" +/-0.13

Our detection is consistent with these reported by MASTER-Net (Lipunov et al, GCNC 29845), Hankasalmi Observatory (Oksanen, GCNC 29846), BOOTES-4 (Hu. et al., GCN 29847) and AST3-3 (Sun et al., GCN 29848).
Further observations are ongoing.