Multiwavelength observations of markarian 501 during the 1997 high state

During the observation period 1997, the nearby blazar Mrk 501 showed extrem ely strong emission and high variability. We examine multiwavelength aspect s of this event using radio, optical, soft and hard X-ray, and TeV data. We concentrate on the medium-timescale variability of the broadband spectra, averaged over weekly intervals. We confirm the previously found correlation between soft and hard X-ray emission and the emission at TeV energies, whi le the source shows only minor variability at radio and optical wavelengths . The nonlinear correlation between hard X-ray and TeV fluxes is consistent with a simple analytic estimate based on an SSC model in which Klein-Nishi na effects are important for the highest-energy electrons in the jet, and f lux variations are caused by variations of the electron density and/or the spectral index of the electron injection spectrum. The time-averaged spectr a are fitted with a synchrotron self-Compton (SSC) dominated leptonic jet m odel, using the full Klein-Nishina cross section and following the self-con sistent evolution of relativistic particles along the jet, accounting for y y absorption and pair production within the source as well as due to the in tergalactic infrared background radiation. The contribution from external i nverse-Compton scattering is tightly constrained by the low maximum EGRET f lux and found to be negligible at TeV energies. We find that high levels of the X-ray and TeV fluxes can be explained by a hardening of the energy spe ctra of electrons injected at the base of the jet, in remarkable contrast t o the trend found for gamma-ray flares of the flat-spectrum radio quasar PK S 0528 + 134.