Light curves at various frequencies. From top to bottom: γ-rays 0.1–100 GeV from Fermi/LAT with 1 day time bin [10^-7 ph cm^-2 s^-1]; X-ray 0.3–10 keV from Swift/XRT [c s^-1]; U filter (350 nm) from Swift/UVOT [mJy]; H filter (1.65 μm) from INAOE [mJy]; 86 GHz from IRAM [Jy]; 37 GHz from Metsähovi [Jy]; 15 GHz from OVRO, Effelsberg, and MOJAVE [Jy]; 5 GHz from Effelsberg and Medicina. Time starts on 2008 August 1 00:00 UTC (MJD 54 679). Fermi performs an all-sky survey every two orbits (three hours) and thus observed PMN J0948 + 0022 almost continuously. However, for clarity, we do not plot the upper limits. The TS = 4 average sensitivity of LAT for one-day exposure is indicated with the horizontal dotted line in the top panel, which corresponds to  ~2.3 × 10^-7 ph cm^-2 s^-1 (assuming Γ = 2.67). Vertical dashed lines are shown at the beginning of each year (Jan. 1). Vertical dot-dashed lines indicate the days referring to the SED selected as example (see Sect. 4).