MWL lightcurve of B2 1811+31 in a period of approximately 70 days surrounding the Fermi-LAT high-state detection on MJD 59123, marked by the dashed red line. From top to bottom panels: VHE γ-ray flux above 135 GeV from MAGIC, HE γ-ray flux above 100 MeV from Fermi-LAT in daily bins and using the ‘adaptive-binning’ method, X-ray flux in the 0.3−10 keV range from Swift-XRT, optical/UV data in the photometric filters of Swift-UVOT, optical R-band data and radio data. The shaded yellow and light violet bands indicate periods of 48 h and 72 h surrounding the two sets of MAGIC consecutive observation nights, respectively, defined as periods A and B in Section 6.