Extreme HBL-like Behavior of Markarian 421 and Its Two-zone Photohadronic Interpretation

Abstract

Abstract Markarian 421 is the nearest high-energy peaked blazar and is also the first extragalactic source to be detected in multi-TeV γ-rays. It has been observed in multiwavelength for an exceptionally long period of time with dense monitoring and several major outbursts have been detected from this source. In 2010 March, the source was in a high state of activity and was observed in multiwavelength by various telescopes for 13 consecutive days. During this period the position of the synchrotron peak was found to be above 1017 Hz and also the position of the second peak was shifted toward higher energy, a signature of extreme HBL-like behavior. We observed that the standard photohadronic model is inadequate to explain the observed spectra. However, a recently proposed two-zone photohadronic model explains very well the GeV–TeV flaring events observed by both MAGIC and VERITAS telescopes. From the observation of the highest energy γ-ray event on MJD 55266 we also estimated the minimum bulk Lorentz factor.