Analysis of the Supernova Remnant IC 443 using H.E.S.S. Data

TL;DR

IC 443 is studied as a Galactic SNR interacting with a dense molecular cloud to test hadronic cosmic-ray acceleration. The paper analyzes archival H.E.S.S. data to characterize morphology and spectrum, finding extended VHE gamma-ray emission with a disk-like morphology and a steep proton-induced spectrum. A hadronic model with a broken-power-law proton injection best fits the broadband SED, with $\alpha_1 = 2.32 \pm 0.02$, $\alpha_2 = 2.89 \pm 0.04$, and $E_{\mathrm{break}} = 168^{+57}_{-40}$ GeV. The inferred total CR proton energy above 1 GeV is of order $10^{50}$ erg for $n_H \sim 20~\mathrm{cm}^{-3}$, compatible with a canonical SN energy release, supporting SNRs as Galactic CR sources and demonstrating reproducibility with independent data and analysis; future observations will further constrain the GeV–TeV transition.

Abstract

IC 443 is a well-known supernova remnant that stands out due to its interaction with a dense molecular cloud, creating a complex environment where shocks can efficiently accelerate particles to high energies. This makes it a key target for investigating the mechanisms of cosmic-ray acceleration and gamma-ray production, particularly in the context of supernova remnants as potential sources of PeV cosmic rays. This work presents a first analysis of the region as observed by H.E.S.S.. We detect extended very-high-energy gamma-ray emission from IC 443, consistent with previous observations by VERITAS and MAGIC. A multi-wavelength comparison incorporating data from Fermi-LAT, MAGIC, and VERITAS strongly supports a hadronic origin of the observed emission, and highlights the presence of relativistic protons interacting with the surrounding molecular cloud. These findings reinforce the role of IC 443 as a key laboratory for studying supernova remnants as cosmic-ray accelerators and their interaction with their surrounding mediums.

Figures (3)

• Figure 1: Left: Li&Ma significance map of the region around IC 443, computed with a correlation radius of $0.16\deg$. The best-fit morphology of the Gaussian and Disk models are shown by the purple and black circle. Right: The best-fit morphology of both models compared to the emission observed by other instruments. The uncertainties, depicted as error bars for the position and shaded regions for the extension, include both statistical and systematic uncertainties (H.E.S.S. systematics from collaboration_resolving_2019).
• Figure 2: SED of the emission detected from IC 443, assuming a Disk morphology.
• Figure 3: SED derived in this work compared to the SED derived by EGRET esposito_egret_1996, MAGIC MAGIC_2007, VERITAS VERITAS_2009, and Fermi-LAT Fermi_2013. Additionally shown is the expected $\gamma$-ray spectrum produced by a proton population injected into the region. The injection parameters of this population have been derived through a fit to the SED. The SED derived by EGRET has not been used in the fitting process.