{
  "circularId": 45813,
  "createdOn": 1791240242448,
  "subject": "EP trigger 01709320908: Ondrejov D50 observation, fading star suggests stellar flare",
  "body": "M. Jelinek, J. Strobl, F. Novotny and R. Hudec (ASU CAS Ondrejov) report:\n\nWe observed the position of the Einstein Probe/WXT trigger 01709320908 (T0 =\n2026-10-05 21:32 UT) with the D50 telescope of the Astronomical Institute\nOndrejov, near Prague, Czech Republic. The telescope reacted automatically to\nthe alert, and we obtained so far 9 unfiltered exposures, each a kinetic-mode\naccumulation of 100x1.1s, starting at 21:42 UT, i.e. ~10 min after the trigger\nand covering until ~T0+27 min.\n\nWe find no uncatalogued object within the WXT error circle (r = 3') down to\n~20.5 mag (unfiltered, 3-sigma, single exposure).\n\nThe star PYC J23504+4455 (RA, Dec = 23:50:24.81, +44:55:33.4, J2000), located\n~0.5' from the WXT position, is bright and well detected in all exposures. It\nfades steadily throughout our sequence, by ~0.4 mag over ~15 min, from ~12.2\nmag (unfiltered) at the start. A linear fit gives a decay rate of ~1.5\nmag/hour.\n\nThis fading suggests that the X-ray trigger was caused by a flare on this star\nrather than by a GRB.\n\n",
  "submitter": "Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>",
  "submittedHow": "email"
}