Spatial Correlation Study of RX J1713.7-3946

Within our galaxy, high-energy gamma rays are thought to be produced via interactions of cosmic rays with the interstellar medium. In a hadronic scenario, cosmic rays collide with the interstellar medium, typically in a proton-proton interaction. In leptonic scenarios, electrons interact via inverse Compton scattering of low-energy photons and via Bremsstrahlung with nuclei. The detection of a correlation or anti-correlation between the morphology of gamma rays, X rays and the interstellar medium may therefore reveal the production scenario. The interstellar medium is typically measured within a wide range of velocities along the line of sight. The distance to a supernova remnant - which corresponds to a specific velocity range - is often not precisely known. Therefore, a 3d spatial correlation study can be exploited to obtain an unbiased distance measure by selecting the velocity range with the maximum correlation or anti-correlation. A new method to derive the correlation coefficient and its p-value is using a bootstrap method to provide uncertainties for the correlation and to take into account the uncertainties of the measurements. Based on the bootstrap distribution, an optimistic correlation coefficient and the corresponding p-value can also be obtained. This may be important if small regions in the morphology are to be studied, where only a few number of data points are available. This approach has been applied to study the spatial correlation of the famous supernova remnant RX J1713.7-3946 using measurements from the HESS Galactic Plane Survey (gamma rays), XMM-Newton (X-ray) and MOPRA (CO). In this contribution, the bootstrap method will be explained and results for RX J1713.7-3946 will be discussed.