A Model for Delayed Emission in a Very-High Energy Gamma-Ray Flare in Markarian 501

Recently, the MAGIC collaboration reported evidence for a delay in the arrival times of photons of different energies during a gamma-ray flare from the blazar Markarian 501 on 2005 July 9. We apply a homogeneous synchrotron self-Compton (SSC) model under the assumption that the blob containing relativistic electrons was observed in its acceleration phase. Such a modified SSC model predicts the appearance of the gamma-ray flare first at lower energies and subsequently at higher energies. Moreover, we argue that the time delay between the flare observed at different energies depends on the gamma-ray energy. Based on the reported time delay of 240 s between the flare observed at about 190 GeV and 2.7 TeV, we predict it should be on the order of 1 h if it was observed between 20 GeV and 200 GeV. Such delay time scales can be tested in the future by simultaneous observations of flares with GLAST and Cherenkov telescopes