# VER J2227+608: A Hadronic PeVatron Pulsar Wind Nebula?

## TL;DR

This paper reports the detection of GeV gamma-ray emission from VER J2227+608, suggesting it may be a PeVatron powered by a pulsar wind nebula, with implications for cosmic ray acceleration up to hundreds of TeV.

## Contribution

It provides evidence supporting a hadronic origin of gamma rays and identifies VER J2227+608 as a potential PeVatron candidate, advancing understanding of cosmic ray sources.

## Key findings

- Gamma-ray emission is extended and coincident with molecular clouds.
- The gamma-ray spectrum fits a single power-law with index 1.90.
- The hadronic model suggests proton cutoff energy > 400 TeV.

## Abstract

We report the detection of GeV $\gamma$-ray emission from the very-high-energy (VHE) $\gamma$-ray source VER J2227+608 associated with the "tail" region of SNR G106.3+2.7. The GeV $\gamma$-ray emission is extended and spatially coincident with molecular clouds traced by CO emission. The broadband GeV to TeV emission of VER J2227+608 can be well fitted by a single power-law function with an index of 1.90$\pm$0.04, without obvious indication of spectral cutoff toward high energies. The pure leptonic model for the $\gamma$-ray emission can be marginally ruled out by the X-ray and TeV data. In the hadronic model, the low energy content of CRs and the hard $\gamma$-ray spectrum, in combination with the center-bright source structure, suggest that VER J2227+608 may be powered by the PWN instead of shocks of the SNR. And the cutoff energy of the proton distribution needs to be higher than $\sim$ 400 TeV, which makes it an attractive PeVatron candidate. Future observations by the upcoming Large High Altitude Air Shower Observatory (LHAASO) and the Cherenkov Telescope Array in the north (CTA-North) could distinguish these models and constrain the maximum energy of cosmic rays in supernova remnants.