Fermi-LAT and Chandra studies of shell-like supernova remnants

Supernova Remnants (SNRs) have long been considered to be the primary source of galactic cosmic rays (CRs) having energies below the so called knee, 10^15 eV. CRs are accelerated by SNRs which transfer some of their internal energies into chargedparticles. Those charged particles in SNRs produce high energy photons up to TeVenergies. Main motivation of this study is to investigate young, shell-like SNRs as high energy (HE) sources and to better understand the origins of main HE emissions. SNRs are observable in GeV energies by means of Fermi Gamma Ray Space Telescope(Fermi). Generally, there are two accepted models for the gamma-ray productionin SNRs: (i) The leptonic model, where emission arises from inverse Compton and relativistic bremsstrahlung, (ii) the hadronic model, where gamma rays are produced from decay of neutral pions originating from proton-proton interactions. Fermi analysis of SNRs, Cassiopeia A (Cas A) and Tycho as point-like sources in gamma-ray, has shown that these young SNRs are GeV sources in the Milky Way. Also, about half of the SNRs in the galaxy are observed in the X-ray band [16]. The X-ray emissionof SNRs results from the interactions of ejecta of the SNR and swept-up interstellarmedium (ISM). Bremsstrahlung and line emissions are the thermal and main X-ray emission mechanisms in SNRs. Synchrotron emission is the non-thermal contribution of X-ray emission and it is produced by charged particles in strong magnetic eld. Chandra-ACIS image and spectral analysis of Cas A and Tycho was performed both to understand shell-like structures of SNRs and, to examine which part of SNRs are responsible for main non-thermal emission. Also Chandra analysis showed that thin filaments at the shell of the remnants associated with reverse shocks are the most important candidate regions, where non-thermal emission is dominant.