TITLE: GCN CIRCULAR NUMBER: 41112 SUBJECT: EP270713a: Kitab and AbAO Optical Observations DATE: 25/07/17 20:04:29 GMT FROM: Nicolai Pankov at HSE, IKI RAS colinsergesen@gmail.com
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Schmalz (KIAM), R. Ya. Inasaridze (AbAO) and A. Volnova (IKI) report on behalf of IKI-GRB-FuN:
We observed the field of GRB 250713A detected by SVOM/ECLAIRs (Maggi et. al, GCN 41078) using the RC-36 telescope of the ISON-Kitab Observatory and the AS-32 telescope of the Abastumani Observatory (AbAO). The observations at Kitab began on 2025-07-13 at 19:29 UT, i.e. ~0.13 days after the trigger, while AS-32 started observations 2025-07-13 at 19:59 UT, i.e. ~0.14 days since trigger. We obtained a series of 120x60 sec images in the clear light with RC-36 and a series of 71x60 sec images in the R-band with AS-32. We have inspected the co-added images from both telescopes for any new optical sources spatially consistent with the X-ray candidates found by EP-FXT (Liang et. al, GCN 41085) and Swift/XRT (Evans et. al, GCN 41086). No new optical sources were found in our observations. However, our searches revealed one known, but brightened optical source J222746.80+384743.9 from the SDSS-DR12 catalog found within the localization of EPF_J222746.7+384738 (90% error radius is 10 arcsec). The magnitudes of J222746.80+384743.9 in SDSS-DR12 are g = 21.54 +/- 0.06 and r = 20.58 +/- 0.04, and i = 20.13 +/- 0.04, which can be transformed by Lupton 2005 transformation into R = 20.31 +/- 0.11. The preliminary photometry of SDSS J222746.80+384743.9 is provided below:
Date UT start t-T0 Exp. Filter OT Err. UL Telescope (mid, days) (n*s) (3sigma) 2025-07-13 19:29:20 0.13431 101*60 R n/d n/d 18.5 Kitab 2025-07-13 19:59:02 0.14313 67*60 R 19.28 0.14 19.7 AS-32
The photometry was calibrated using nearby stars from the SDSS-DR12 catalog (R-mags obtained with Lupton 2005 transformations) and not corrected for the Galactic extinction. We can tentatively assume that SDSS J222746.80+384743.9 is a stellar flare if indeed the gamma-ray and X-ray emission came from SDSS J222746.80+384743.9. The optical source reported by NOT (Saccardi et. al, GCN 41091) was not detected by our telescopes.
Ref. stars SDSS-DR12 RA Dec R(Lupton 2005 transformation) 336.9314 38.7641 14.28 336.9030 38.7712 16.08 336.9267 38.7809 15.76 336.9080 38.7704 16.35
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