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GCN Circular 28949

Subject
GRB 200826A: TNG and LBT constraints on a supernova bump
Date
2020-11-24T10:54:35Z (3 years ago)
From
Andrea Rossi at INAF <andrea.rossi@inaf.it>
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.
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