[vsnet-grb-info 24890] GRB 200205A / Swift trigger 954304: VLT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26989
SUBJECT: GRB 200205A / Swift trigger 954304: VLT optical observations
DATE:    20/02/05 18:32:10 GMT
FROM:    Daniele B Malesani at DTU Space  <malesani at space.dtu.dk>

D. B. Malesani (DTU Space), L. Izzo (DARK/NBI), J. Palmerio (GEPI - 
Paris Observatory), N. R. Tanvir (Univ. Leicester), A. J. Levan (Radboud 
Univ.), D. A. Kann (HETH-IAA/CSIC), report on behalf of the Stargate 
consortium:

We observed the optical counterpart of GRB 200205A / Swift trigger 
954304 (Evans et al., GCN 26982), with the ESO VLT UT2 (Kueyen) equipped 
with the X-shooter instrument. Unfortunately, observations could be 
started only late in twilight and no spectroscopy was secured.

We confirm the presence of an optical counterpart just outside the 
currently available (unenhanced) XRT position (Evans et al., GCN 26982; 
Lipunov et al., GCN 26984; Melandri et al., GCN 26986). Its coordinates 
are (calibrated to the Gaia catalog; 0.2" uncertainty):

RA = 08:40:40.94
Dec = -35:16:25.1

In a 60-s image taken in the SDSS r filter at a mid time Feb 5.385 UT 
(2.63 hr after the BAT trigger), we measure for it r = 17.7+-0.1 AB, 
where the error is dominated by the scatter of the calibrators, chosen 
from the SkyMapper catalog (Wolf et al. 2018, PASA, 35, 010; 
https:doi.org/10.4225/41/593620ad5b574).

We note that the MAXI detection for a prolonged time at X-ray energies 
(Niwano et al., GCN 26987), the unusually large optical/gamma-ray 
brightness ratio, and the low Galactic latitude (4 deg above the plane) 
may indicate that this source is not a GRB but a Galactic transient. 
Further analysis of the high-energy data, or ground-based spectroscopic 
observations, will be necessary to distinguish among these options.

We acknowledge support from the ESO observing staff in Paranal, in 
particular Elyar Sedaghati, Eleonora Sani, and Ditte Slumstrup.