Probing the Gamma-ray Emission from HESS Source RX J1713.7-3946

Abstract

The origin of Cosmic Rays (CRs) from our the galaxy remains a major mystery in high energy astrophysics. Astronomy techniques, such as 𝛾-ray astronomy, have assisted us in coming closer to solving the problem, but many questions still remain unsolved. CRs are believed to produce 𝛾-rays via interactions with the interstellar medium (ISM) in high energy situations. For this reason 𝛾-rays are often used as a tracer for the parent CRs. The hadronic (𝑝𝑝 interactions) and leptonic processes (IC scattering, synchrotron processes and relativistic Bremsstrahlung) involved in the production of the 𝛾-rays are complex and at times intertwined. Hadronic processes are often favoured as the dominant production channel when there is spatially correlated ISM gas surrounding a source. RX J1713.7- 3946 is a bright source of 𝛾-rays, but is also visible in the radio and X-ray regime. The morphology of the radiation seen from this source is shell like, which leads us to believe that it resembles a supernova remnant (SNR). The high energy environment provided by SNRs is believed to be a great way to accelerate CRs to the energies we observe. In this study we attempt to determine whether the 𝛾-ray production is dominated by hadronic and/or leptonic processes towards RX J1713.7-3946. Using the latest high resolution 𝛾-ray observations from the High Energy Stereoscopic System (HESS) along with X-ray and radio observations from Suzaku and the Southern Galactic Plane Survey (SGPS) respectively, we are able to model the broadband spectra from 29 distinct regions across the SNR. We investigate the resultant parameter space and begin to gain an idea of how the 𝛾-rays are produced in some of these regions. Additionally, using the latest high resolution Mopra CO data we are able to estimate the density of the ISM in each region. This allows us to more accurately model the 𝑝𝑝 spectra and to uncover some regions where the often-negligible Bremsstrahlung emission is of significance. In addition to this spectral study, we use the high resolution 𝛾-ray and CO data to perform a 2D correlation study between the 𝛾-rays and ISM. Spatial correlation is found in 7 regions, suggesting the 𝛾-rays are produced predominantly by hadronic processes. On the other hand, 5 regions display anti-correlation, leading us to favour the leptonic scenario for the 𝛾-ray production. We also find observable and modeled differences between the correlated regions and anti-correlated regions, e.g. the radio synchrotron emission. These differences are investigated and discussed within the scope of the literature.