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Paper: BeppoSAX Observations of BL Lac Object MKN 501 in an Intermediate State
Volume: 159, BL Lac Phenomenon
Page: 180
Authors: Pian, Elena; Palazzi, E.; Chiappetti, L.; Maraschi, L.; Tavecchio, F.; Ghisellini, G.; Tagliaferri, G.; Fossati, G.; Treves, A.; Urry, C. M.; Vacanti, G.
Abstract: The BL Lac object Mkn 501, which is a source of TeV radiation, was observed with the BeppoSAX satellite on 7, 11, and 16 April 1997 during a phase of high activity at TeV energies, as monitored with the Whipple, HEGRA and CAT Cherenkov telescopes. Over the whole 0.1-200 keV range the spectrum was exceptionally hard, indicating that the X-ray power output peaked at (or above) ~100 keV. This represents a shift of at least two orders of magnitude with respect to previous observations of Mkn 501, a behavior never seen before in this or any other blazar. The correlated variability from soft X-rays to the TeV band points to models in which the same population of relativistic electrons produces the X-ray continuum via synchrotron radiation and the TeV emission by inverse Compton scattering (limited by the Klein-Nishina regime) of the synchrotron photons or other seed photons. For the first time in any blazar the synchrotron power is observed to peak at hard X-ray energies. These findings will be compared with BeppoSAX observations to be taken in spring 1998.
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