Background electron $v_{\rm 2}$ as a function of $p_{\rm T}$ measured with the invariant mass method (full markers) and with the cocktail simulation (empty markers) in the 0-10% (left panel), 10-20% (middle panel) and 20-40% (right panel) centrality classes in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV.