Multiwavelength investigation of the candidate Galactic PeVatron MGRO J1908+06

Abstract

ABSTRACT The candidate PeVatron MGRO J1908+06, which shows a hard spectrum beyond 100 TeV, is one of the most peculiar γ-ray sources in the Galactic plane. Its complex morphology and some possible counterparts spatially related with the very high energy (VHE) emission region, preclude to distinguish between a hadronic and leptonic nature of the γ-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 12CO and 13CO molecular line emission demonstrating the presence of dense molecular clouds spatially correlated with the source region. We also analysed 12 yr of Fermi-Large Area Telescope (LAT) data between 10 GeV and 1 TeV finding a counterpart with a hard spectrum (Γ ∼ 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 two-zone model is needed to explain the emission from MGRO J1908+06. The VHE emission seems most likely the superposition of a TeV pulsar wind nebula powered by PSR J1907+0602, in the southern region, and of the interaction between the supernova remnant G40.5−0.5 and the molecular clouds, in the northern region.