  We discuss the possibility of explaining the extraordinary, correlated
X-ray/TeV flares observed during April 1997 from Mrk 501, by synchrotron-pair
cascades injected by synchrotron radiation from ultra-high energy protons and
muons. Evaluating the jet conditions required to explain the observed features
of the flares, the allowed region for this model in the parameter space of jet
magnetic field and Doppler factor is identified, and compared with the
parameter choices of other, both hadronic and leptonic models presented in the
literature. The present model requires magnetic fields similar to other
hadronic models for gamma-ray blazars (B >~ 30 G), but a lower Doppler factor
(D =~ 3).
