Source Count Distribution of Fermi LAT Gamma-Ray Blazars Using Novel Nonparametric Methods

TL;DR

This study applies novel nonparametric methods to Fermi-LAT data to accurately determine the intrinsic source count distribution of gamma-ray blazars and assess their contribution to the extragalactic gamma-ray background.

Contribution

It introduces nonparametric, unbinned techniques to derive the intrinsic flux distribution of blazars, improving upon previous parametric approaches.

Findings

Blazars contribute 34.5% to the extragalactic gamma-ray background.

The intrinsic flux distribution follows a broken-power-law form.

Photon index distributions are well modeled by Gaussian functions.

Abstract

We utilized a sample from the Fermi-LAT 14-year Source Catalog by adjusting the flux detection threshold, enabling us to derive the intrinsic source count distribution $dN/dF_{25}$ of extragalactic blazars using nonparametric, unbinned methods developed by Efron and Petrosian and Lynden-Bell. Subsequently, we evaluated the contribution of blazars to the extragalactic gamma-ray background. Our findings are summarized as follows: (1) There is no significant correlation between flux and spectral index values among blazars and their subclasses FSRQs and BL Lacs. (2) The intrinsic differential distributions of flux values exhibit a broken-power-law form, with parameters that closely match previous findings. The intrinsic photon index distributions are well described by a Gaussian form for FSRQs and BL Lacs individually, while a dual-Gaussian model provides a more appropriate fit for blazars as a whole. (3) Blazars contribute 34.5\% to the extragalactic gamma-ray background and 16.8\% to the extragalactic diffuse gamma-ray background. When examined separately, FSRQs and BL Lacs contribute 19.6\% and 13\% to the extragalactic gamma-ray background, respectively.