GCN Circular 26968
ZTF20aajnksq: Gemini-North optical photometry Leo P. Singer (NASA/GSFC), Tomas Ahumada (UMD), Anna Y. Q. Ho (Caltech) report on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations: Starting at 2020-02-01T12:25:57 UTC, we imaged ZTF20aajnksq/AT2020blt (Ho et al., ATel #13429, GCN 26966) using the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini North 8-meter telescope on Mauna Kea. We combined 8 r-band 200s exposures using DRAGONS, a Python-based data reduction platform provided by the Gemini Observatory. We detect a source at the location of the transient. The aperture photometry calibrated against Pan-STARRS DR1 magnitudes (Chambers et al., 2016) of the object is r = 25.2 +- 0.05 AB mag. We note that for the redshift (z = 2.9) and apparent magnitude (r = 19.6 AB mag) reported in GCN 26966, the absolute magnitude of the source (M_r = -27.4) would be significantly brighter than afterglows of short GRBs at one day: short GRBs are typically M_B = -17.34 +- 0.50 AB mag whereas long GRBs are typically M_B = -23.17 +- 0.21 AB mag (Kann et al., 2011). We therefore suggest three alternative interpretations: (a) GRB 200128A is not a typical short GRB, (b) ZTF20aajnksq is the afterglow of a different (long) GRB, or (c) ZTF20aajnksq is an orphan afterglow. We thank S. Stewart and the Gemini North staff for executing these observations.