Multi-Te flaring in nearby high energy blazars: a photo hadronic scenario

Blazars are a subclass of Active Galactic Nuclei and flaring in multi-TeV gamma-ray seems to be the major activity in high energy blazars a subgroup of blazars. Flaring is also unpredictable and switches between quiescent and active states involving different time scales and fluxes. While in some high energy blazars a strong temporal correlation between X-ray and multi-TeV gamma ray has been observed, outbursts in some other have no low energy counterparts and explanation of such extreme activity needs to be addressed through different mechanisms, as it is not understood well. The extragalactic background light (EBL) plays an important role in the observation of these high energy gamma-rays as it attenuates through pair production of electron-positron and also changes the spectral shape of the high energy photons. In the context of the photo hadronic model and taking EBL correction into account, flaring can be explained very well. In a series of papers, we have developed this model to explain multi-TeV flaring events form many blazars. In this review, the photo hadronic model is discussed and applied to explain the multi-TeV flaring from nearby high energy blazars: Markarian 421, Markarian 501 and 1 Es-1959 + 650. (Author)