TITLE: GCN CIRCULAR NUMBER: 44412 SUBJECT: EP260321a/SN 2026gzf: spectroscopy at Mondy observatory DATE: 26/04/27 15:01:46 GMT FROM: Alexander Moskvitin at SAO RAS <mosk@sao.ru> A. Moskvitin (SAO RAS), I. Zaznobin (IKI), M. Eselevich (ISTP), A. Volnova (IKI), N. Pankov (IKI), A. Pozanenko (IKI), report on behalf of IKI-GRB-FuN: We observed the optical counterpart of the fast X-ray transient EP260321a (Huang et al., GCN 44068; GCN 44075) identified early as SN 2026gzf (Lee et al., GCN 44070; Ma et al., GCN 44074; Aguilar-Ruiz et al., GCN 44076; Aryan et al., GCN 44081; Tanvir et al., GCN 44082; Moran et al., GCN 44083; Ahumada et al., GCN 44084; Liu et al., GCN 44087; Sankar et al., GCN 44089; de Ugarte Postigo et al., GCN 44091; Xu et al., GCN 44092; Pankov et al., GCN 44103; Corcoran et al., GCN 44105; Rastinejad et al., GCN 44107; Gao et al., GCN 44110; Zhang et al., GCN 44171; Li et al., GCN 44284; Gupta et al., GCN 44348; also detected as NIR source: He et al., GCN 44117; Volnova et al., GCN 44295) with AZT-33IK telescope (Mondy) equipped with the ADAM spectrograph (Afanasiev et al., Astrophysical Bulletin, 2015, Vol. 71, Issue 4, p. 479; Burenin et al., Astronomy Letters, 2016, Vol. 42, Issue 5, p. 295). We obtained 4 x 900 sec spectra with VPHG600G grism (range 3600--7250AA, dispersion 3.6 A/pix) on 2026-04-13, 15:02:08--16:02:47 UT(t_mid - T0 = 23.1265 days). In the spectra we clearly detected host galaxy emission lines of Balmer series, [O III] 4959A, 5007A, 4363A, [O II] 3727A, [S II] 6717A and 6731A, He I 5876A at the redshift of z = 0.0343 which is consistent with other reported measurements (Tanvir et al., GCN 44082; Xu et al., GCN 44092; Corcoran et al., GCN 44105; Rastinejad et al., GCN 44107). We also detected broad lines of supernova SN 2026gzf which we interpreted as Fe II and Si II with the velocity of about 10000 km/s. Comparison with the SNID (Blondin & Tonry, 2007, ApJ, 666, 1024) showed best fit with SN 1997ef, SN 2006aj, SN 2002ap and SN 1998bw supernovae. View this GCN Circular online at https://gcn.nasa.gov/circulars/44412. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...