TITLE: GCN CIRCULAR NUMBER: 28949 SUBJECT: GRB 200826A: TNG and LBT constraints on a supernova bump DATE: 20/11/24 10:54:35 GMT FROM: Andrea Rossi at INAF A. Rossi (INAF-OAS), P. D'Avanzo (INAF-OAB), V. D'Elia (ASI-SSDC), A. Melandri (INAF-OAB) and E.Palazzi (INAF-OAS) on behalf of the CIBO collaboration, and B. Rothberg (LBTO/GMU), O. Kuhn, C. Veillet (LBTO) report: We searched for a supernova bump associated to ZTF20abwysqy/AT2020scz (Ahumada et al. GCN 28295), the afterglow of GRB 200826A (Fermi, GCN 28284; Ridnaia et al., GCN 28294), which energetics are consistent with being a long/soft event (Svinkin et al., GCN 28301). We obtained two series of r-sdss images with the Italian 3.6m TNG telescope equipped with DOLORES. The first set consists in a series of 13 x 240 s obtained on 2020-09-27 at a midtime 02:01 UT (~32 days after the burst). A second set of 26x200 s of exposure time each have been obtained on 2020-11-09. Another two series of r-sdss images have been obtained with the MODS double imager and spectrographs mounted on LBT. Both series consists of 13x180 sec r-band images with the MODS double imager and spectrographs mounted on LBT and otained on 2020-09-28 and 2020-11-13. Image subtraction between the two TNG observing epochs and between the two LBT/MODS observing epochs using HOTPANTS (v5.1.11) does not reveal the source found by Ahumada et al. (GCN 28727) and constrain the presence of a SN bump beyond the conservative 5 sigma limit of r>25 in both TNG and LBT first epochs. Assuming that the supernova responsible for the bump detected by Ahumada et al. is similar to SN1998bw, at the redshift of GRB 200826A z=0.748 (Rothberg et al., GCN 28319) its brightness would be r~24.8, that includes the foreground Galactic extinction on the line of sight of GRB 200826A (A_V=0.184; Schlafly & Finkbeiner 2011). Our non detection then might indicate that the supernova detected by Ahumada et al. was at least 10% faster and/or fainter than SN1998bw. At the position of the afterglow we clearly detect the host galaxy of GRB 200826A, for which we report r=23.33+-0.09 in all observations, calibrated against SDSS field stars. We acknowledge the excellent support from the TNG staff, in particular W. Boschin, and the LBTO and LBT-INAF staff, particularly A. Cardwell, F. Cusano, S. Paiano and D. Paris, in obtaining these observations.