TITLE:   GCN CIRCULAR
NUMBER:  21055
SUBJECT: GRB 170428A: TNG optical observations
DATE:    17/05/01 14:24:23 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>

P. D'Avanzo (INAF-OAB), V. D'Elia (INAF/OAR & ASI/ASDC), Daniele Malesani (DARK/NBI), S. Campana, G. Tagliaferri (INAF/OAB), 
G. Andreuzzi, D. Carosati (INAF-TNG) report on behalf of the CIBO collaboration: 

We observed the field of GRB 170428A (Beardmore et al., GCN 21042) with the 3.6m Telescopio Nazionale Galileo (TNG) 
equipped with DOLoRes. Observations were carried out in the i-sdss and z-sdss filters. Observations started on May 01 at 
03:55:46 UT (~2.78 days after the burst) under a seeing of ~ 1.5". 

We clearly detect the candidate host galaxy reported by Xu et al. (GCN 21048). Some emission is also visible at the position 
of the optical afterglow (Bolmer et al., GCN 21050; Troja et al., GCN 21051; Cenko et al., GCN 21053), blended with the 
candidate host galaxy light. For the whole complex (afterglow and candidate host galaxy) we measure the following magnitudes: 

i(AB) = 22.1 +/- 0.1 at t-t0 = 2.79 d
z(AB) = 21.9 +/- 0.1 at t-t0 = 2.81 d

(calibrated against nearby SDSS stars). It is not possible, at this stage, to evaluate the afterglow contribution to the observed 
optical emission. Further observations are planned.