Probing proton acceleration in W51C with MAGIC

TL;DR

This paper reports the detection and analysis of very high energy gamma-ray emission from the W51C supernova remnant using MAGIC, supporting its role as a cosmic ray accelerator through hadronic interactions.

Contribution

First VHE gamma-ray spectrum measurement of W51C from Fermi energies to TeV range, confirming hadronic origin and pinpointing emission in dense molecular clouds.

Findings

VHE gamma-ray emission spatially coincides with dense molecular clouds.

Spectrum from Fermi to TeV energies fits a hadronic decay model.

W51C is a strong candidate for a cosmic ray accelerator.

Abstract

Located in a dense complex environment, W51C provides an excellent scenario to probe accelerated protons in SNRs and their interaction with surrounding target material. Here we report the observation of extended Very High Energy (VHE) gamma-ray emission from the W51C supernova remnant (SNR) with MAGIC. Detections of extended gamma-ray emission in the same region have already been reported by the Fermi and H.E.S.S. collaborations. Fermi/LAT measured the source spectrum in the energy range between 0.2 and 50 GeV, which was found to be well fit by a hadronic neutral-pion decay model. The VHE observations presented here, obtained with the improved MAGIC stereo system, allow us to pinpoint the VHE gamma-ray emission in the dense shocked molecular cloud surrounding the remnant shell. The MAGIC data also allow us to measure, for the first time, the VHE emission spectrum of W51C from the highest Fermi/LAT energies up to several TeV. The spatial distribution and spectral properties of the VHE emission suggest a hadronic origin of the observed gamma rays. Therefore W51C is a prime candidate for a cosmic ray accelerator.