TITLE: GCN CIRCULAR NUMBER: 39576 SUBJECT: EP250302a: SAO RAS optical observations DATE: 25/03/03 16:32:59 GMT FROM: Moskvitin Alexander at SAO RAS mosk@sao.ru

A. S. Moskvitin, O. A. Maslennikova (SAO RAS), A. Pozanenko (IKI) and N. Pankov (HSE, IKI) report on behalf of larger collaboration.

We observed the field of the X-ray transient EP250302a (Dai et al., GCN 39556; Page et al., GCN 39557) with SAO RAS 1-m telescope Zeiss-1000 equipped with CCD-photometer under mediocre weather conditions. We obtained two sets of 300-sec images in Rc band. 1st set: 2025.03.02, 20:33:49 -- 2025.03.02, 22:09:49 UT (t_mid - T0 = 0.24010 days = 5.7625 hours); 2nd set: 2025.03.02, 23:55:53 -- 2025.03.03, 01:00:10 UT, (t_mid - T0 = 0.36942 days = 8.8660 hours).

The OT (Zhu et al., GCN 39550; Busmann et al., GCN 39551; Leonini et al., GCN 39553; Wu et al., GCN 39555; Xin et al., GCN 39558; Adami et al., GCN 39560; Yang et al., GCN 39561; Becerra et al., GCN 39562; Izzo et al., GCN 39564; Pankov et al., GCN 39565; Reguitti, GCN 39568; Komesh et al., GCN 39569; Shilling and Breeveld, GCN 39570; Aryan et al., GCN 39572) is clearly detected in our stacked frames with the following brightness.

Date UT start t-T0 (mid),d Exp.,s Filter OT Err. UL(3sigm) 2025.03.02 20:33:49 0.24010 8x300 R 20.18 0.09 22.5 2025.03.02 23:55:53 0.36942 7x300 R 20.51 0.10 22.5

Above photometry is preliminary and calibrated against R2 magnitudes of nearby USNO-B1 stars and not corrected for the Galaxy extinction.

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