An X- ray studay of galatic shell- type supernova remnants

Abstract

Observations of synchrotron X-rays can be a useful tool to investigate cosmic-ray acceleration in young supernova remnants (SNRs). Spectral fitting of the synchrotron radiation in an X-ray band gives us information about the cosmic-ray acceleration mechanism. Recently, Galactic cosmic-ray acceleration is widely attributed to SNR shocks. In this thesis, making contribution to search for PeVatron energies (10^15 eV) in SNRs and understand the physical process of this energies were aimed. In line with this objective, the results of the systematic X-ray spectral study of small scale structures on the shocks of five well-known Galactic shell-type SNRs (Cas A, RCW 86, RX J1713.7−3946, SN 1006 and Vela Jr.) with Chandra and XMM-Newton X-ray Observatories were presented. The non-thermal X-ray emission and its contribution with the cosmic-ray acceleration properties with these five SNRs were investigated by extracting the X-ray spectra from different targeted regions. All regions have synchrotron X-ray emission, and the maximum energy of accelerated electrons (Emax,e) and protons (Emax,p) were estimated for each target, which led to search for PeVatron energies. In accordance with this purpose, due to calculate the reliable values, the estimated background subtracted spectra of each SNR were modelled with using a combination of thermal and non-thermal spectral models (e.g., srcut, power-law, cutoffpl, vnei). Analysing extended sources, such as SNRs, with accurately modelled background emission is important since it might be effective on spectral results. Environment of an SNR (e.g., its location on the Galactic latitude) is a key point for background estimation, which could be represented by components such as Cosmic X-ray Background, Galactic Ridge X-ray Emission or Foreground Emission. Such parameters as roll-off frequency or cut-off energy requires accurately modelled background spectra to estimate the reliable values of Emax,e and Emax,p. Thus, the background modelling is a first point to concentrate upon deriving the maximum energies of the particles in this thesis. Briefly stated, analysis of the background spectrum is critical due to characterise the synchrotron emission with sensitive parameters. This process is required to calculate the shock velocities, rolloff frequencies, especially the maximum energies of accelerated particles where they make PeVatron energies searchable. In addition, during these calculations, the magnetic field value is critical while selecting the proper synchrotron models. In this study, it has claimed that the SNRs Cas A and Vela Jr. contain targeted emission regions which have PeVatron energies. But this results require more reliable analysis methods since current synchrotron models need to be retested and improve. Under these circumstances, all these mentioned parameters could be searched reliably with background modelling method, which is suitable for the purpose of determining the nonthermal characteristics of the shell-type SNRs.