Temporal sampling of the GM Aur campaign from September 6, 2021, to March 8, 2022. Bottom: g′-band light curve from LCOGT (black dots) and from REM (magenta crosses). The REM g′-band magnitudes are offset in this figure by +0.1 mag to match the LCOGT measurements. The mean photometric error on both the LCOGT and REM g′-band measurements is 0.025 mag. Vertical arrows: the vertical arrows show the dates of OHP/SOPHIE (red), CFHT/SPIRou (blue), and ESO/ExTrA (black) observations. The core of the campaign took place during October 2021 with contemporaneous measurements from the five instruments.