Spectral analysis of Fermi-LAT blazars above 50 GeV

TL;DR

This study analyzes the intrinsic gamma-ray spectra of 128 blazars detected by Fermi-LAT above 50 GeV, providing insights into their emission physics and the extragalactic background light (EBL).

Contribution

It offers the first comprehensive analysis of intrinsic spectral indices of VHE blazars and tests models of gamma-ray propagation including EBL attenuation.

Findings

Intrinsic spectral indices have a median of 2.20.

Data are compatible with models including EBL attenuation.

No evolution with redshift in blazar emission physics.

Abstract

We present an analysis of the intrinsic (unattenuated by the extragalactic background light, EBL) power-law spectral indices of 128 extragalactic sources detected up to z~2 with the Fermi-Large Area Telescope (LAT) at very high energies (VHEs, E>50 GeV). The median of the intrinsic index distribution is 2.20 (versus 2.54 for the observed distribution). We also analyze the observed spectral breaks (i.e., the difference between the VHE and high energy, HE, 100 MeV<E<300 GeV, spectral indices). The LAT has now provided a large sample of sources detected both at VHE and HE with comparable exposure that allows us to test models of extragalactic gamma-ray photon propagation. We find that our data are compatible with simulations that include intrinsic blazar curvature and EBL attenuation. There is also no evidence of evolution with redshift of the physics that drives the photon emission in high-frequency synchrotron peak (HSP) blazars. This makes HSP blazars excellent probes of the EBL.