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A. D. Falcone (Purdue University / Whipple Observatory)
By using ground-based observatories, some active galactic nuclei belonging to the blazar class have been observed to emit very high energy gamma rays at TeV energies. Traditionally, blazars have been classified as either flat spectrum radio quasars, which have broad emission lines, or BL Lacs, which are featureless or have very narrow lines. At this time, the small list of TeV emitting blazars is restricted to nearby BL Lacs. In particular, all of the known TeV emitting blazars fall into the category of high-peaked BL Lacs, which have the first peak of the characteristic two-component spectral energy distribution (SED) in the X-ray energy region. By studying the variability of these blazars, which have TeV flaring timescales shorter than those at any other wavelength, it is possible to place strong constraints on properties such as the size of the emission region, the strength of the magnetic field at the acceleration site, and the doppler factor in the jet. The commonly invoked mechanisms for the high energy gamma ray emission are inverse compton processes (with either external seed photons or with seed photons from the electron synchrotron emission), proton cascades, and/or proton synchrotron. By observing the extreme high energy region of the SED and combining this with data at other wavelengths, the acceleration mechanism/s can be constrained. Additionally, inferences can be made about the extragalactic background. Currently operating telescopes have made significant progress with studies of TeV blazar variability, and the next generation of more sensitive instruments will increase the source statistics, and therefore our understanding, of these enigmatic objects.
The author(s) of this abstract have provided an email address for comments about the abstract: afalcone@purdue.edu
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.