What is the maximum frequency of the Gamma Rays produced during supernovae? And how are these detected by telescopes without getting some serious damage done?
There is the ground based observatory ( nice picture) Veritas.
There is the space based Fermi Large Area Telescope
So the energies detected go fairly high and there are means of measuring the energetic photons, developed for the earth bound accelerators.
A quick Google for "gamma ray burst spectrum" found lots of hits including http://arxiv.org/abs/1201.2981, which contains a collection of spectra from gamma ray bursts in the appendix. The maximum energies detected are around 10MeV, which seems a lot but remember that the LHC accelerates particles to around a million times more energy than this.
Remember that although GRBs are fantastically energetic, they're a long long way away, so by the time the radiation reaches the earth it's so weak that it can't do any damage. Given the debate in the comments about what constitutes a gamma ray telescope you might like to have a look at http://www.nasa.gov/mission_pages/swift/main/index.html. This describe the NASA Swift satellite, which is used to detect GRBs.