Other
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011acasn..52..536x&link_type=abstract
Acta Astronomica Sinica, vol. 52, no. 6, p.537-538
Other
Polarization, Methods: Observational, Hii Regions, Ism: Magnetic Fields, Supernova Remnants
Scientific paper
Polarization observation provides a useful tool to study the properties of interstellar medium (ISM). It could directly show the orientation of large-scale magnetic fields, and help us understand the structure of large-scale magnetic field in our Galaxy and the evolution of supernova remnants (SNRs). Moreover, combing with polarization observations at other wavelengths, the Faraday rotation could be applied to study the properties of the thermal electron density, filling factor, regular and random magnetic fields in ISM and SNRs.The previous polarization measurements mostly conducted at low frequencies were significantly influenced by the Faraday effects of ISM, while at 6 cm, they are much less affected and polarized emission from larger distances could be detected. By studying Faraday screens, we could explore the physical parameters of the sources as well as the synchrotron emissivities of the Galaxy. The 6 cm total intensity measurements are the key data to clarify the spectrum behavior of diffused emission or individual objects at high frequencies, and help us understand the distribution of relativistic electrons, the disk-halo interaction and the evolution of late-stage SNRs. In August 2009, the project of 6~cm continuum and polarization survey of Galactic plane had been completed successfully using the 25~m radio telescope at Urumqi. The work presented in this thesis is mainly based on data analysis of the second survey region with 60° ≤ l ≤129° and |b|≤5°. We tried to compensate the missing large-scale structures by extrapolating the WMAP K-band polarization data with the spectral index model and simulation of the rotation measures (RMs). By comparing the maps pre- with post-``calibration'', we studied the extended objects in this region. We analyzed the depolarization structure at the periphery of HII region complex using Faraday screen model, and studied the distribution of fluctuation in the entire survey region using structure functions. Besides, we investigated observationally the radio properties of two large-scale SNRs S147 and G65.2+5.7. Using the new 6 cm and Effelsberg 11 cm data,we confirmed the spectral index break of SNR S147. It is found that the spectral break index mainly comes from the diffused emission and the possible mechanism was briefly discussed. In addition, we calculated the RM and the magnetic field in the eastern filamentary shell of the SNR. For the low surface brightness SNR G65.2+5.7, we obtained the spectral index of this SNR using the new 6 cm and 11 cm flux densities. The depolarization at both wavelengths in the northern shell has been discussed, and the RM and the magnetic field in the southern shell of the SNR were calculated. We recognized a HI bubble associated with the SNR. Its mass was estimated and the electron density in this region before the explosion was then inferred. We conclude that the SNR might be expanding in a preblown cavity.
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