TITLE:   GCN CIRCULAR
NUMBER:  29747
SUBJECT: GRB 210402A: Montarrenti Observatory upper limit
DATE:    21/04/03 07:17:41 GMT
FROM:    Simone Leonini at Monarrenti Obs  <s.leonini@iol.it>

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

We observed the field of GRB210402A (Swift trigger 1040123, Fermi trigger 639093861, K.L. Page et al., GCN Circ. 29743) with the automatic 0.53m RC telescope + U47 detector at Montarrenti Observatory (Siena, Italy, IAU code C88).

The observations were started at 2021-04-02 22:48:18 UT (18 minutes post-burst) stacking 4 unfiltered CCD exposures of 40s each.

We have not found optical transient within the error-box given.
Mag. upper limit R = 20.10+/-0.19

Magnitudes were obtained using Astrometrica software using USNO-B1 catalogue and are not corrected for galactic extinction.