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GCN Circular 23086

Subject
GRB 180805B: VLT optical and near-infrared observations
Date
2018-08-06T13:01:16Z (6 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@dark-cosmology.dk>
D. B. Malesani (DAWN/NBI and DARK/NBI), G. Pugliese (API/Univ. 
Amsterdam), P. D'Avanzo (INAF/Brera), N. R. Tanvir (Univ. Leicester), K. 
Wiersema (Univ. Warwick), report on behalf of the Stargate consortium:

We observed the field of GRB 180805B, classified as short with extended 
emission (D'Avanzo et al., GCN 23076; Sakamoto et al., GCN 23082), using 
the ESO Telescopes located in Cerro Paranal. Optical and near-infrared 
observations were obtained using the FORS2 and HAWK-I instruments, 
respectively. No counterpart is detected inside the UVOT-enhanced XRT 
error circle (Evans et al., GCN 23077) in either images, with the 
3-sigma upper limits summarized in the table below.

Filter  Mid time (UT)  Time since GRB (hr)  Limiting mag (Vega)
---------------------------------------------------------------
J       Aug 6.245      16.84                23.5
R       Aug 6.363      19.67                25.5

Calibration was carried out against a single 2MASS star for the J band, 
and using archival FORS2 zeropoints for the R band.

We note the presence of four extended objects within a few arcsec of the 
center of the XRT error circle, including a source 3.5" North of the GRB 
(R ~ 22.5) also visible in the Pan-STARRS r and i images. Their 
association with the GRB cannot be assessed at the present time.

We acknowledge excellent support from the ESO observing staff in 
Paranal, especially Stephane Brillant, Joe Anderson, and Bian Fuyan. DBM 
also acknowledges useful discussion with Amy Lien (GSFC/UMBC) about the 
classification of this GRB.
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