M. Bozkurt

Origin of gamma-ray emission in the shell of Cassiopeia A

Context. Non-thermal X-ray emission from the shell of Cassiopeia A (Cas A) has been an interesting subject of study, as it provides information about relativistic electrons and their acceleration mechanisms in shocks. The Chandra X-ray observatory revealed the detailed spectral and spatial structure of this supernova remnant in X-rays. The spectral analysis of the Chandra X-ray data of Cas A shows unequal flux levels for different regions of the shell, which can be attributed to different magnetic fields in those regions. Additionally, the GeV gamma-ray emission observed by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope showed that the hadronic processes are dominating in Cas A, which is a clear signature of acceleration of protons. Aims. The aim of this study is to locate the origin of gamma-rays based on the X-ray data of the shell of Cas A. We also aim to explain the GeV−TeV gamma-ray data in the context of both leptonic and hadronic scenarios. Methods. We modelled the multi-wavelength spectrum of Cas A. We use a synchrotron emission process to explain the observed non-thermal X-ray fluxes from different regions of the shell. This results in estimates of the model parameters which are then used to explain TeV gamma-ray emission spectrum. We also use a hadronic scenario to explain both GeV and TeV fluxes simultaneously. Results. Based on this analysis, it has been shown that the southern part of the remnant is bright in TeV gamma-rays. We also show that the leptonic model alone cannot explain the GeV−TeV data. Therefore, we need to invoke a hadronic model to explain the observed GeV−TeV fluxes. We found that the lepto-hadronic model provides the best fit to the data although the pure hadronic model is able to explain the GeV−TeV data.

Locating the TeV γ-rays from the shell regions of Cassiopeia A

We have analyzed Chandra X-ray data from different parts of the shell of young supernova remnant (SNR) in the energy range of 0.7 - 8 keV. We observed that X-ray flux level varies over different shell regions of the source. Implications of X-ray observation will be discussed here. We also analyzed Fermi-LAT data in the energy range 0.5 - 50 GeV for the source. The differential spectrum obtained in this way fits with simple power-law. We also present here multi-wavelength modeling of the source considering archival radio and TeV data along with Chandra and Fermi-LAT data.

Structural formation of the universe: As observed by X-ray satellites

Most celestial bodies emit their energy in the 0.5–5 keV range, thus the universe is very bright in X-rays. The Earths atmosphere protects life on earth from being burned out by the high energy UV and X-ray, while blocking the precious information from the universe. Therefore, the X-ray satellites should be placed either at high altitudes in order to have a clear vision of stars, galaxies and unveil the cosmic mystery. According to structural formation hierarchy of the universe, stars form galaxies and galaxies form clusters. Galaxy clusters are the largest gravitational entities of the universe, and yet one of the brightest X-ray sources in the universe. In this paper, we review the large-scale structural formation of the universe based on the analysis results of our TÜBİTAK scientific research project on clusters of galaxies with X-ray data, which is obtained from the scientific satellites facing outer space such as NASAs Chandra, ESAs XMM-Newton and ISAS/JAXAs Suzaku.