A study of high energy emission from the TeV blazar Mrk 501 during multiwavelength observations in 1996 Original Research Article

We present the results of a multiwavelength campaign for Mrk 501 performed in March 1996 with ASCA, EGRET, Whipple, and optical telescopes. We report here for the first time the detection of GeV γ ray flux from Mrk 501 with EGRET with 3.5 σ significance (E > 100MeV). Higher flux was also observed in April/May 1996, with 4.0 σ for E > 100MeV, and 5.2 σ for E > 500MeV. We find that the multiband spectrum in March 1996 is consistent with that calculated from a one-zone SSC model, except for the extremely ‘flat’ TeV spectrum. We show that this flat spectrum cannot be explained by either 2nd order Comptonization or the contribution of the ‘seed’ IR photons from the host galaxy.