D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC,
DARK/NBI), M. Blazek, C. C. Thoene, J. F. Agui Fernandez (all
HETH/IAA-CSIC), V. Tilve, A. Moreno Signes, and H. Vasquez Ramio (all
We observed the error circle of the short GRB 200623A (Fermi GBM
detection and analysis: Fermi GBM Team, GCN #28011, Veres & Meegan, GCN
#28019; Swift BAT/GUANO localization: DeLaunay et al., GCN #28013) with
the T80 0.8m telescope at the Observatorio de Javalambre (Teruel,
Spain). Observations consisted of 3 x 500 s in g', 3 x 500 s in r', 8 x
180 s in i', and 8 x 180 s in z', at midtimes 0.816779, 0.798439,
0.779694, and 0.755722 days after the GRB, respectively.
At the position of XRT source #1, the known quasar from the Veron-Cetty
& Veron 2006 catalog is clearly detected.
At the position of XRT source #2, we clearly detect the source proposed
by Belkin et al. (GCN #28020) as a candidate afterglow. Measured against
three nearby SDSS comparison stars, we find (AB mags):
g' = 23.70 +/- 0.30 mag;
r' = 22.55 +/- 0.15 mag;
i' = 21.54 +/- 0.15 mag;
z' = 20.74 +/- 0.10 mag,
indicating this is a very red source. We assume that the observations of
Belkin et al. were performed without a filter, this would explain the
brighter magnitude they find (their use of comparison stars from the
USNO catalog may also play a role).
These very red colors are untypical for a GRB afterglow. Furthermore,
comparison with images form PanSTARRS clearly reveals a pre-detection of
the source at a similar magnitude and color, see:
for a comparison. We therefore believe it is unlikely that this source
is associated with GRB 200623A (additionally, the XRT detection is of
low significance for now).
At the position of XRT source #3, we detected multiple sources in the
vicinity also seen in PanSTARRS imaging. The faint source detected by
the TNG (D'Avanzo et al., GCN #28021), may be vaguely detected in our r'
and z' images, but it is unclear how much this could be due to the PSF
of a nearby bright star. We present a second comparison image here:
No other obviously bright afterglow candidate is detected in the BAT
error circle, however, a second epoch of comparable depth would be
needed for a more detailed analysis.