Evidence of hadronic interaction in Tycho Supernova Remnant using Fermi-LAT data

Abstract

The Fermi Large Area Telescope (LAT) has observed Tycho Supernova Remnant in the MeV-GeV energy range. The spectrum has been studied using the first three years of data and new data are being collected. We present a multiwavelength model of the observed spectrum from radio to TeV energy range, based on the hypothesis of hadronic origin of γ-rays. As described by the Fermi acceleration theory, a single proton population was considered, modeled with a simple power-law in momentum. The photon emissivity is computed following Kamae et al (2006) [T. Kamae, et al., ApJ 647 (2006) 692]. The leptonic component is also taken into account according to Giordano et al. (2012) [F. Giordano, et al., ApJ 744 (2012) L2] prescriptions and it turns out to be negligible with respect to the hadronic one. The model returns a spectral index of $2.23(\pm 0.05)$ and an acceleration efficiency of 5% of the total kinetic energy expelled in Supernova explosion and it may provide a hint of the acceleration processes in SNRs up to energies close to the knee of cosmic ray spectrum. This work shows that experimental data can be easily explained with a simple model, representing a good test for the acceleration theory.