Observation of Supernova Remnant IC443 with the Fermi Large Area Telescope

TL;DR

This paper reports detailed gamma-ray observations of supernova remnant IC443 using the Fermi LAT, revealing extended emission consistent with cosmic-ray acceleration and pion decay, and clarifying the emission's spatial and spectral properties.

Contribution

First detailed gamma-ray characterization of IC443 with broad energy coverage, linking gamma-ray emission to cosmic-ray acceleration and pion decay processes.

Findings

Gamma-ray emission region is extended and overlaps with TeV sources.

The gamma-ray spectrum is consistent with pion decay from a broken power-law proton spectrum.

The centroid displacement suggests the PWN is not the main gamma-ray source.

Abstract

We report observation of the supernova remnant IC443 (G189.1+3.0) with the Fermi Gamma-ray Space Telescope Large Area Telescope (LAT) in the energy band between 200MeV and 50GeV. IC443 is a shell-type supernova remnant with mixed morphology located off the outer Galactic plane where high-energy emission has been detected in the X-ray, GeV and TeV gamma-ray bands. Past observations suggest IC443 has been interacting with surrounding interstellar matter. Proximity between dense shocked molecular clouds and GeV-TeV gamma-ray emission regions detected by EGRET, MAGIC and VERITAS suggests an interpretation that cosmic-ray (CR) particles are accelerated by the SNR. With the high gamma-ray statistics and broad energy coverage provided by the LAT, we accurately characterize the gamma-ray emission produced by the CRs accelerated at IC443. The emission region is extended in the energy band with theta_68 = 0.27 deg +/- 0.01 deg (stat) +/- 0.03 deg (sys) for an assumed 2-dimensional Gaussian profile and overlaps almost completely with the extended source region of VERITAS. Its centroid is displaced significantly from the known pulsar wind nebula (PWN) which suggests the PWN is not the major contributor in the present energy band. The observed spectrum changes its power-law slope continuously and continues smoothly to the MAGIC and VERITAS data points. The combined gamma-ray spectrum (200MeV <E< 2TeV) is reproduced well by decays of neutral pions produced by a broken power-law proton spectrum with a break around 70GeV.