Particle Acceleration in the Cygnus Superbubble

TL;DR

This study uses HAWC data to analyze the Cygnus Cocoon at energies above 1 TeV, providing insights into its spectral properties and particle acceleration limits up to 100 TeV.

Contribution

First detailed spectral and morphological analysis of the Cygnus Cocoon above 1 TeV using HAWC data, revealing a softer spectrum at higher energies.

Findings

Spectrum softens above 10 TeV indicating decreased acceleration efficiency

Highest-energy protons may escape the region after acceleration

Provides new constraints on cosmic-ray acceleration in superbubbles

Abstract

The Cygnus Cocoon is the first gamma-ray superbubble powered by a massive stellar association, the OB2 association. It was postulated that the combined effects of the stellar winds of all the massive O-type stars of the OB2 association can accelerate the cosmic rays to PeV energy in the Cocoon. The conclusive proof of acceleration to PeV energy in the Cocoon will identify the stellar association as a PeV cosmic-ray accelerator, known as PeVatron. However, the Cocoon has been previously studied only up to 10 TeV. In this contribution, using 1343 days of High Altitude Water Cherenkov (HAWC) observatory data, we present the morphological and spectral study of the Cocoon above 1 TeV to beyond 100 TeV. The analysis at higher TeV energies reveals a softer spectrum compared to the GeV gamma-ray observation. This result suggests that the accelerator's efficiency decreases around hundreds of TeV, or after being accelerated, the highest-energy protons escape the region. The study above 10 TeV presented here demonstrates how CR accelerators operate in these extreme energies and how particle transport impacts high-energy emission.