Discrete correlation function computed between two energy ranges provided by Fermi-LAT and Swift-XRT with and without the big flare in February using a binning of 3 days. It is computed for a range of time lags between -40 to +40 days. The 1 σ, 2 σ, and 3 σ confidence levels obtained by simulations are shown by the yellow, red, and green lines, respectively. (a) 3-300 GeV versus 0.3-2 keV; (b) 3-300 GeV versus 0.3-2 keV without the flare in February 2010; (c) 0.3-3 GeV versus 0.3-2 keV; (d) 0.3-3 GeV versus 0.3-2 keV without the flare in February 2010; (e) 3-300 GeV versus 2-10 keV; (f) 3-300 GeV versus 2-10 keV without the flare in February 2010; (g) 0.3-3 GeV versus 2-10 keV; (h) 0.3-3 GeV versus 2-10 keV without the flare in February 2010.