Title: Inverse Compton Catastrophe and Pair Creation in the Intraday-Variable

Title: Inverse Compton Catastrophe and Pair Creation in the Intraday-Variable Sources 0716+714 and 0836+71

Proposal ID: 0120177
Subject category: Extragalactic Object
Principal investigator: Wagner
Institute: Landessternwarte

Abstract

Blazars radiate a large fraction of the total emitted energy at gamma-ray energies. Previous studies have concentrated on GeV and TeV emission, and have been discussed in the context of several models, involving synchrotron-self-Compton emission and Compton-scattering of an external photon field. Inverse-Compton scattering is an unavoidable process in the presence of relativistic electrons, but becomes particularly important at high photon densities. The highest photon densities have been reported in Intra-Day Variable objects, where apparent brightness temperatures exceed the limit for catastrophic inverse Compton cooling by many orders of magnitude. The quasi-periodic and persistent violation of this limit suggests subsequent Compton catastrophes, each leading to outbursts on inverse Compton scattered radiation. Unlike GeV-peaking Blazars the most efficient loss mechanism is via second-order scattering by electrons of moderate Lorentz factors, which leads to brief outbursts in the energy range covered by INTEGRAL. We suggest to search for these signatures of high brightness temperatures in the two best suited IDV sources, which happen to be observable in one IBIS field of view. The high duty cycle of IDV activity in 0716+714 permits unprecedented studies of this radiative signatures at minimum risk of inactivity without demanding TOO strategy. Fortuitously, a second IDV source, 0836+71, will be in the same field of view. Its expected duty cycle is lower, but the amplitudes of flares are likely to be even larger. In addition, for both objects we intend to constrain the mechanisms that lead to the broad-band gamma radiation extending into the GeV regime.