TITLE: GCN CIRCULAR NUMBER: 32097 SUBJECT: GRB 220521A: MMT Afterglow Imaging DATE: 22/05/23 20:22:56 GMT FROM: Jillian Rastinejad at Northwestern Univ. J. Rastinejad, W. Fong (Northwestern), D. B. Malesani (Radboud Univ. and DAWN/NBI), A. Cucchiara (College of Marin/UVI), and G. Schroeder (Northwestern) report: ''We observed the location of the Fermi and Swift GRB 220521A (Fermi GBM team, GCN 32075, Dichiara et al., GCN 32076; Poolakkil & Meegan, GCN 32089, Strausbaugh et al. GCN 32091) with the Binospec imager and spectrograph mounted on the MMT 6.5-meter telescope on Mount Hopkins, Arizona. We obtain 15x100 s imaging in the z-band at a mid-time of 2022 May 23.423 (1.45 days post-burst) at an average airmass of 1.08. We detect a source at the position of the afterglow reported by Malesani & Pursimo (GCN 32078). Calibrated to PS1, we measure z = 24.04 +/- 0.16 mag (AB system and not corrected for Galactic extinction in the direction of the burst). We thank Ryan Howie and Ben Weiner at the MMT for the rapid scheduling and execution of these observations.''