Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 28022

GRB 200623A: OAJ deep multi-color imaging, XRT #2 is pre-detected
2020-06-24T01:07:31Z (4 years ago)
Alexander Kann at IAA-CSIC <>
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 
CEFCA) report:

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.
Looking for U.S. government information and services? Visit