GCN Circular 45821

Subject

EP trigger 01709320985: Ondrejov D50 optical upper limits

Date

2026-10-06T20:15:34Z (a day ago)

From

Filip Novotný at Masaryk University <filip.novotny@talentovani.cz>

Via

Web form

F. Novotny, J. Strobl, M. Jelinek and R. Hudec (ASU CAS Ondrejov) report:

We observed the position of the Einstein Probe/WXT trigger 01709320985
(T0 = 2026-10-06 17:50 UT) with the D50 telescope of the Astronomical
Institute Ondrejov, near Prague, Czech Republic. The telescope reacted
automatically to the alert, obtaining an unfiltered exposure starting at
18:09 UT (~20 min after the trigger), followed by a series of 19x300s
Sloan r'-band exposures between 18:26 and 20:07 UT.

We do not detect any new source within the WXT error circle (RA, Dec =
21.806, +12.900, r = 3.1') in comparison to the DESI Legacy Survey DR10
catalog, neither in single images (3-sigma limit r'>19.4-20.0) nor in
the combined 5700s image (mean epoch T0+85 min, 3-sigma limit r'>21.2).
The early unfiltered image reaches ~18.2 mag (3-sigma).

Photometry is calibrated in Sloan r' (AB system) against ATLAS-RefCat2
field stars, not corrected for Galactic extinction.