Bepposax observations of unprecedented synchrotron activity in the BL Lacertae object Markarian 501

摘要

The BL Lacertae object Markarian 501, one of only three extragalactic sources(with Mrk 421 and 1ES 2344 + 514)so far detected at TeV energies, was observed with the BeppoSAX satellite in 1997 April 7, 11, and 16 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(α≤ 1, with F_v ∝ v~-α), indicating that the X-ray power output peaked at (or above) ～ 100 keV. This represents a shift of at least 2 orders of magnitude with respect to previous observations of Mrk 501, a behavior never seen before in this or any other blazar.