TITLE:   GCN CIRCULAR
NUMBER:  19770
SUBJECT: GRB 160804A: TNG optical observations, afterglow fading and candidate host galaxy
DATE:    16/08/04 23:12:21 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani@dark-cosmology.dk>

D. Malesani (DARK/NBI and DTU Space), P. D'Avanzo (INAF/OABr), A. Melandri
(INAF/OABr), V. D'Elia (INAF/Roma and ASI/ASDC), A. Garcia de Gurtubai
Escudero (INAF/TNG), and M. Pedani (INAF/TNG), report on behalf of the CIBO
collaboration:

We observed the field of GRB 160804A (Marshall et al., GCN 19761) with 
the Telescopio Nazionale Galileo (TNG) equipped with DOLoRes. 
Observations were carried out in the r and z filters.

At the position of the optical afterglow (Breeveld & Marshall, GCN 
19764), we clearly detect an extended object in both filters. 
Calibrating compared to nearby SDSS stars, we measure AB magnitudes r = 
20.99 +- 0.04 and z = 19.99 +- 0.17. The mid time of the observations is 
Aug 4.89 UT, that is 0.83 days after the trigger.

We note that this object is clearly visible in the SDSS frames, with 
catalog magnitudes of r = 21.22 +- 0.11 and z = 20.74 +- 0.35. It is 
classified as a galaxy with a (fairly uncertain) photometric redshift z 
<~ 0.5  This object is most likely the host galaxy of GRB 160804A.

Our measurements are marginally (2 sigma) brighter than the SDSS values, 
though we caution that aperture effects on a low S/N extended object may 
be responsible for the difference. In any case, the afterglow is only 
contributing little flux at the epoch of the TNG observations.


[GCN OPS NOTE(05aug16): Per author's request, AGdGE was added to the author list.]