  The last years have seen a revolution in ground-based gamma-ray detectors. We
can now detect the spectra of nearby TeV blazars like Mrk 421 and 501 out to
approximately 20 TeV, and during the strongest flares, we can now follow
fluctuations in these spectra on timescales close to the shortest ones likely
in these objects. We point out that this represents a unique opportunity. Using
these and future detectors in combination with broadband X-ray satellites like
SAX and RXTE, we will be able to simultaneously follow all significant
X-ray/gamma-ray variations in a blazar's emission. This will provide the most
stringent test yet of the synchrotron-Compton emission model for these objects.
In preparation for the data to come, we present sample SSC model calculations
using a fully self-consistent, accurate code to illustrate the variability
behavior one might see (the range of behavior is wider than many expect) and to
show how good timing information can probe physical conditions in the source.
If the model works, i.e., if X-ray/TeV variations are consistent with being
produced by a common electron distribution, then we show it is possible to
robustly estimate the blazar's intrinsic TeV spectrum from its X-ray spectrum.
Knowing this spectrum, we can then determine the level of absorption in the
observed spectrum. Constraining this absorption, due to gamma-ray pair
production on diffuse radiation, provides an important constraint on the
infrared extragalactic background intensity. Without the intrinsic spectrum, we
show that detecting absorption is very difficult and argue that Mrk 421 and
501, as close as they are, may already be absorbed by a factor 2 at
approximately 3 TeV. This should not be ignored when fitting emission models to
the spectra of these objects.
