TITLE: GCN CIRCULAR NUMBER: 29029 SUBJECT: GRB 200826A: GMOS-N detected source magnitude (Correction) DATE: 20/12/11 23:06:21 GMT FROM: Tomas Ahumada at U. of Maryland Tomas Ahumada (UMD), Harsh Kumar (IITB), Christoffer Fremling (Caltech), Leo Singer (NASA GSFC) report on behalf of the ZTF and GROWTH collaborations: Reanalysing the data used in Ahumada et al. GCN 28727, we provide a revised magnitude of the source detected in the Gemini Multi-Object Spectrograph (GMOS-N) i-band image of ZTF20abwysqy/AT2020scz (Ahumada et al. GCN 28295). We imaged the region of GRB 200826A (GCN 28284) with GMOS-N, mounted on the Gemini-North 8-meter telescope on Mauna Kea, on three nights: 2020-09-23 (2459115.9675 mjd), 2020-10-10 (2459133.8039 mjd) and 2020-11-08 (2459167.9342 mjd). Each epoch consisted of 14 r- and i- band 200s exposures. We reduced and co-added the images from each epoch using DRAGONS, a Python-based data reduction platform provided by the Gemini Observatory. We subtracted the coadded images using HOTPANTS and PyZOGY independently. We now present the revised magnitudes using a zero-point calculated using 23 stars in the field from the SDSS catalog. We apologize for any possible confusion caused by the erroneously reported photometry in GCN 28727. In the 2020-09-23 images, a source is detected at the position of the afterglow with i = 25.49 +- 0.15 mag, but not in r-band up to r > 25.6 AB mag. In the 2020-10-10 images, we do not detect a transient in either filter up to a 5-sigma limit of i > 25.4 mag and r > 25.5 mag. At the host galaxy's redshift of z = 0.7481 (GCN 28319) and assuming Planck 2015 cosmological parameters, the absolute magnitude of the GMOS-N detection is M_i = -17.9 AB mag. We thank the Gemini Observatory Director for awarding this observing time and the Gemini staff for help with planning and executing the observations. -- Tomas Ahumada (he/him) Ph.D. Student Department of Astronomy University of Maryland, College Park NASA Goddard Space Flight Center, Code 661 B.Sc. Astronomy, Pontificia Universidad Católica de Chile