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P. Coppi, T. Maccarone (Yale University, New Haven, US), F.A. Aharonian, H. Krawczynski (Max-Planck-Institut f\"ur Kernphysik, Heidelberg, Germany)
With the arrival of powerful, ground-based \g-ray detectors, we can now begin to seriously probe, via simultaneous X-ray/TeV observations, the origin of the \g-ray emission in the blazars Mkn 421 and 501. If the synchrotron-Compton emission model turns out to work, then we know that the same electrons are responsible for both the X-ray and the \g-ray emission of these objects. In this case, we show that we can use their observed X-ray spectra to robustly estimate their intrinsic \g-ray spectra. Among blazars, Mkn 421/501 are particularly well-suited for this task because the Compton scattering which produces their TeV \g-rays is likely to be in the Klein-Nishina limit, where the outgoing photon has an energy insensitive to the incoming photon energy. With a better handle on their intrinsic TeV spectra, we can then search for evidence of absorption due to \g-ray pair production on diffuse infrared background radiation. Even though Mkn 421/501 are nearby, the emission of these sources extends to sufficiently high energies that we may nevertheless be able to derive interesting constraints on the infrared background. We present results from the detailed modeling of quasi-simultaneous X-ray/TeV observations of Mkn 501 during its 1997 flare state. The detection of Mkn 501 to ~ 20 TeV together with the COBE 140 \mu detection appears to rule out the standard galaxy evolution and star formation models, implying that much of the star formation in the Universe indeed occurs at early times in highly obscured sources that have been missed until now.
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