TITLE:   GCN CIRCULAR
NUMBER:  45813
SUBJECT: EP trigger 01709320908: Ondrejov D50 observation, fading star suggests stellar flare
DATE:    26/10/05 22:44:02 GMT
FROM:    Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>

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

We observed the position of the Einstein Probe/WXT trigger 01709320908 (T0 =
2026-10-05 21:32 UT) with the D50 telescope of the Astronomical Institute
Ondrejov, near Prague, Czech Republic. The telescope reacted automatically to
the alert, and we obtained so far 9 unfiltered exposures, each a kinetic-mode
accumulation of 100x1.1s, starting at 21:42 UT, i.e. ~10 min after the trigger
and covering until ~T0+27 min.

We find no uncatalogued object within the WXT error circle (r = 3') down to
~20.5 mag (unfiltered, 3-sigma, single exposure).

The star PYC J23504+4455 (RA, Dec = 23:50:24.81, +44:55:33.4, J2000), located
~0.5' from the WXT position, is bright and well detected in all exposures. It
fades steadily throughout our sequence, by ~0.4 mag over ~15 min, from ~12.2
mag (unfiltered) at the start. A linear fit gives a decay rate of ~1.5
mag/hour.

This fading suggests that the X-ray trigger was caused by a flare on this star
rather than by a GRB.