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RADIO OBSERVATIONS OF SUPERNOVA REMNANTS AT 31 GHZ WITH THE COSMIC BACKGROUND IMAGER
[Thesis]. Manchester, UK: The University of Manchester; 2016.
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Abstract
The explosion of a supernova releases almost instantaneously about 10^51 ergs of mechanical energy, an event that irreversibly changes the physical and chemical properties of large regions of their host galaxy. A supernova remnant (SNR) consists of three components: the stellar ejecta, the nebula resulting from the powerful shock waves, and sometimes a compact stellarremnant. They can radiate their energy across the whole electromagnetic spectrum, but the great majority are strongest in the radio regime. Almost 70 years after the first detection of radio emission coming from a SNR, great progress has been made in fully comprehending their physical characteristics and evolution. The radio spectra of the synchrotron emission from theSNRs has not been studied much at high frequencies (≥ few GHz), hence the motivation behind this research.In this thesis we analyse data from the Cosmic Background Imager (CBI) at 31 GHz. These data were modified and calibrated using the CBI data reduction pipeline. The culled data was then imaged and deconvolved using the CLEAN algorithm. It was decided that we would observe two SNRs, namely G20.0 − 0.2 and G312.5 − 3.0. These two SNRs have different morphologies, as well as spectral properties. To estimate the flux density of the SNRs we used an aperture photometry technique. Using this technique the flux densities of G20.0 − 0.2 and G312.5 − 3.0 at 31 GHz were found to be 3.56 ± 0.2 Jy and 0.49 ± 0.07 Jy, respectively. We estimated various uncertainties, and by taking multi-frequency maps from literature it was possible to fit a power-law spectra and estimate the spectral indices. The value of the spectral indices for G20.0 − 0.2 after fitting a power law was α = −0.36 ± 0.05 and α = −0.8 ± 0.1 after fitting a spectral break at ∼5 GHz. For G312.5 − 3.0 it was estimated to be α = −0.51 ± 0.07. Our results show that the spectrum of G20.0 − 0.2 was flat at low frequencies, similar to Crab SNR, and showing the steepening at high frequency. While the spectrum for G312.5 − 3.0 has a typical value which agrees with most of the SNRs’ spectra.