Impact of Plasma Instability on Constraint of the Intergalactic Magnetic Field

TL;DR

This study examines how plasma instabilities affect the use of gamma-ray observations from blazars to constrain the intergalactic magnetic field, showing that even with plasma effects, cascade flux can still provide meaningful limits.

Contribution

It introduces the impact of plasma oblique instability on cascade gamma-ray flux calculations and assesses its influence on intergalactic magnetic field constraints.

Findings

Cascade flux remains useful for IGMF constraints even if plasma instability dominates.

The lower limit of IGMF varies with the ratio of plasma instability to ICS cooling rates.

High plasma instability dominance (ratio=30) invalidates IGMF estimates from cascade flux.

Abstract

A relativistic electron-positron pair beam can be produced in the interaction of TeV photons from a blazar with the extragalactic background light (EBL). The relativistic $e^{\pm}$ pairs would loss energy through inverse-Compton scattering (ICS) photons of cosmic microwave background (CMB) or plasma instabilities. The dominant energy-loss process is under debate. Based on the assumption that the dominant energy-loss process is ICS, the resulted cascade GeV radiation is usually used to constrain the intergalactic magnetic field (IGMF). Here, we include the energy-loss due to plasma oblique instability in the calculation of cascade gamma-ray flux, and investigate the impact of the plasma instability on the constraint of IGMF. The up-to-date GeV data and archival TeV data of the blazar 1ES 0229+200 are used. The results indicate that even if the oblique instability cooling is dominating over ICS cooling, the cascade flux could be still used to constrain the IGMF. It is found that with the ratio between the cooling rates of the oblique instability and the ICS varying from 0.1, 1 to 10, the lower limit of the IGMF putted by the cascade flux and the gamma-ray data changes from $8\times10^{-18}\ $G, $5\times10^{-18}\ $G to $10^{-18}\ $G. If the ratio between the two cooling rates is 30, the estimate of IGMF based on the cascade flux is invalid.