Emitting electrons and source activity in Markarian 501

We study the variation of the broadband spectral energy distribution (SED) of the BLLac object Mrk501 as a function of source activity, from quiescent to flaring. Through \u3c72-minimization we model eight simultaneous SED data sets with a one-zone synchrotron self-Compton (SSC) model, and examine how model parameters vary with source activity. The emerging variability pattern of Mrk501 is complex, with the Compton component arising from \u3b3-e scatterings that sometimes are (mostly) Thomson and sometimes (mostly) extreme Klein-Nishina. This can be seen from the variation of the Compton to synchrotron peak distance according to source state. The underlying electron spectra are faint/soft in quiescent states and bright/hard in flaring states. A comparison with Mrk421 suggests that the typical values of the SSC parameters are different in the two sources: however, in both jets the energy density is particle-dominated in all states