# Inverse Compton Cascades in Pair-Producing Gaps: Effects of Triplet Pair Production

## TL;DR

This paper studies how triplet pair production influences inverse Compton cascades in accelerating gaps near supermassive black holes, providing analytical models and implications for gamma-ray observations of active galactic nuclei.

## Contribution

It introduces a detailed analysis of triplet pair production effects on pair cascades in accelerating gaps, with analytical expressions for growth rates and electric fields.

## Key findings

- Triplet pair production can regulate pair cascades in certain astrophysical environments.
- Analytical formulas for cascade growth rate and electric field are derived.
- Implications for gamma-ray emissions from active galactic nuclei are discussed.

## Abstract

Inverse Compton-pair cascades are initiated when gamma-rays are absorbed on an ambient soft photon field to produce relativistic pairs, which in turn up-scatter the same soft photons to produce more gamma-rays. If the Compton scatterings take place in the deep Klein-Nishina regime, then triplet pair production ($e\gamma_b \rightarrow ee^{+}e^{-}$) becomes relevant and may even regulate the development of the cascade. We investigate the properties of pair-Compton cascades with triplet pair production in accelerating gaps, i.e., regions with an unscreened electric field. Using the method of transport equations for the particle evolution, we compute the growth rate of the pair cascade as a function of the accelerating electric field in the presence of black-body and power-law ambient photon fields. Informed by the numerical results, we derive simple analytical expressions for the peak growth rate and the corresponding electric field. We show that for certain parameters, which can be realized in the vicinity of accreting supermassive black holes at the centers of active galactic nuclei, the pair cascade may well be regulated by inverse Compton scattering in the deep Klein-Nishina regime and triplet pair production. We present indicative examples of the escaping gamma-ray radiation from the gap, and discuss our results in application to the TeV observations of radio galaxy M87.