Multiwavelength investigation of the candidate Galactic PeVatron MGRO J1908+06

TL;DR

This study uses multiwavelength data to analyze the complex gamma-ray source MGRO J1908+06, revealing it likely comprises multiple emission regions including a pulsar wind nebula and supernova remnant interactions.

Contribution

It provides a comprehensive multiwavelength analysis and introduces a two-zone model to explain the source's emission, advancing understanding of Galactic PeVatrons.

Findings

Dense molecular clouds are spatially correlated with the source.

A hard spectrum counterpart was identified in Fermi-LAT data.

A two-zone model explains the multiwavelength emission.

Abstract

The candidate PeVatron MGRO J1908+06, which shows a hard spectrum beyond 100 TeV, is one of the most peculiar $\gamma$-ray sources in the Galactic plane. Its complex morphology and some possible counterparts spatially related with the VHE emission region, preclude to distinguish between a hadronic or leptonic nature of the $\gamma$-ray emission. In this paper we illustrate a new multiwavelength analysis of MGRO J1908+06, with the aim to shed light on its nature and the origin of its ultra high-energy emission. We performed an analysis of the $^{12}$CO and $^{13}$CO molecular line emission demonstrating the presence of dense molecular clouds spatially correlated with the source region. We also analyzed 12-years of Fermi-LAT data between 10 GeV and 1 TeV finding a counterpart with a hard spectrum ($\Gamma \sim 1.6$). Our reanalysis of XMM-Newton data allowed us to put a more stringent constraint on the X-ray flux from this source. We demonstrate that a single accelerator cannot explain the whole set of multiwavelength data, regardless of whether it accelerates protons or electrons, but a 2-zone model is needed to explain the emission from MGRO J1908+06. The VHE emission seems most likely the superposition of a TeV PWN powered by PSR J1907+0602, in the southern part, and of the interaction between the supernova remnant G40.5-0.5 and the molecular clouds towards the northern region.