Study of the diffuse gamma-ray emission from the Galactic plane with ARGO-YBJ

TL;DR

This study analyzes five years of ARGO-YBJ data to measure diffuse gamma-ray emission in the Galactic plane between 350 GeV and 2 TeV, connecting Fermi and Milagro observations, and finds no excess at sub-TeV energies.

Contribution

First detailed analysis of diffuse gamma-ray emission in the specified Galactic regions with ARGO-YBJ data, bridging Fermi and Milagro energy ranges, and confirming model predictions.

Findings

No excess at sub-TeV energies in the analyzed regions.

Results are consistent with Fermi diffuse emission models.

Derived spectral indices and flux at 1 TeV for the diffuse emission.

Abstract

The events recorded by ARGO-YBJ in more than five years of data collection have been analyzed to determine the diffuse gamma-ray emission in the Galactic plane at Galactic longitudes 25{\deg} < l < 100{\deg} and Galactic latitudes . The energy range covered by this analysis, from ~350 GeV to ~2 TeV, allows the connection of the region explored by Fermi with the multi-TeV measurements carried out by Milagro. Our analysis has been focused on two selected regions of the Galactic plane, i.e., 40{\deg} < l < 100{\deg} and 65{\deg} < l < 85{\deg} (the Cygnus region), where Milagro observed an excess with respect to the predictions of current models. Great care has been taken in order to mask the most intense gamma-ray sources, including the TeV counterpart of the Cygnus cocoon recently identified by ARGO-YBJ, and to remove residual contributions. The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding to the excess found by Milagro, and are consistent with the predictions of the Fermi model for the diffuse Galactic emission. From the measured energy distribution we derive spectral indices and the differential flux at 1 TeV of the diffuse gamma-ray emission in the sky regions investigated.