SIMBAD references

Major outbursts have been observed from the well known high-energy-peaked blazar Markarian 501 since its discovery in 1996. Two episodes of very-high-energy gamma-ray flaring events during 2005 May-July and 2012 June are of special significance, as the source exhibited extreme HBL-like behavior. The successful standard photohadronic model does not adequately explain these extraneous behaviors. We propose a two-zone photohadronic scenario to overcome this problem. In this picture, the low-energy regime (zone-1) of the spectrum follows the standard photohadronic interpretation, while the high-energy regime (zone-2) of the spectrum is new, with a spectral index δ₂ >= 3.1, which is solely due to the extreme nature of the flaring event. We also estimate the bulk Lorentz factor corresponding to these extreme flaring events. By analyzing many flaring events before and after these extreme events we argue that the extreme HBL-like events are transient and may repeat in the future.