\contentsline {chapter}{Acknowledgments}{xiii}
\contentsline {chapter}{Declaration}{xix}
\contentsline {chapter}{Abstract}{xxi}
\contentsline {chapter}{\numberline {1}Introduction}{1}
\contentsline {section}{\numberline {1.1}Synchrotron Radiation}{4}
\contentsline {section}{\numberline {1.2}Galactic Supernova Remnants}{7}
\contentsline {subsection}{\numberline {1.2.1}Nonthermal Emission from SNRs}{9}
\contentsline {subsection}{\numberline {1.2.2}Continuum Radio Spectra}{10}
\contentsline {subsubsection}{Absorption by the low density ionized medium}{12}
\contentsline {subsection}{\numberline {1.2.3}Thermal emission}{15}
\contentsline {subsection}{\numberline {1.2.4}Radio morphology}{17}
\contentsline {subsection}{\numberline {1.2.5}Galactic distribution}{23}
\contentsline {section}{\numberline {1.3}Effects of the ISM on the observed properties of SNRs}{25}
\contentsline {section}{\numberline {1.4}Why low frequency?}{26}
\contentsline {section}{\numberline {1.5}Aperture synthesis at low frequencies}{27}
\contentsline {subsection}{\numberline {1.5.1}Phase fluctuations}{28}
\contentsline {subsection}{\numberline {1.5.2}Non-coplanar baselines}{31}
\contentsline {subsection}{\numberline {1.5.3}On-line and off-line data analysis}{32}
\contentsline {subsection}{\numberline {1.5.4}Instrumental polarization leakage}{34}
\contentsline {section}{\numberline {1.6}Organization of the thesis}{35}
\contentsline {chapter}{\numberline {2}The Giant Meterwave Radio Telescope}{41}
\contentsline {section}{\numberline {2.1}Principles of aperture synthesis}{41}
\contentsline {subsection}{\numberline {2.1.1}Interferometry in practice}{49}
\contentsline {section}{\numberline {2.2}The Array}{53}
\contentsline {section}{\numberline {2.3}Signal flow}{55}
\contentsline {section}{\numberline {2.4}Telescope parameters}{60}
\contentsline {section}{\numberline {2.5}The GMRT correlator}{60}
\contentsline {subsection}{\numberline {2.5.1}Overview}{61}
\contentsline {subsubsection}{Samplers}{64}
\contentsline {subsubsection}{Long Term Accumulation (LTA) and time keeping}{65}
\contentsline {subsection}{\numberline {2.5.2}Delay compensation}{67}
\contentsline {subsection}{\numberline {2.5.3}Imaging modes}{68}
\contentsline {section}{\numberline {2.6}Baseline and fixed delay calibration}{69}
\contentsline {subsection}{\numberline {2.6.1}Baseline calibration}{70}
\contentsline {subsubsection}{The procedure used}{71}
\contentsline {subsection}{\numberline {2.6.2}Fixed delay calibration}{74}
\contentsline {chapter}{\numberline {3}Data analysis software}{81}
\contentsline {section}{\numberline {3.1}Introduction}{81}
\contentsline {section}{\numberline {3.2}The software design}{83}
\contentsline {subsection}{\numberline {3.2.1}On-line usage of the software}{84}
\contentsline {section}{\numberline {3.3}Data manipulation libraries}{85}
\contentsline {subsection}{\numberline {3.3.1}The {\tt LTAFMT}\ Object}{86}
\contentsline {subsection}{\numberline {3.3.2}The {\tt LTAVIEW}\ object}{86}
\contentsline {subsection}{\numberline {3.3.3}The {\tt LTARec}\ object}{87}
\contentsline {section}{\numberline {3.4}The user interface for off-line programs}{87}
\contentsline {section}{\numberline {3.5}Data analysis and display programs}{88}
\contentsline {subsection}{\numberline {3.5.1}The program {\tt xtract}\ and its variants}{88}
\contentsline {subsection}{\numberline {3.5.2}The {\tt rantsol}\ and {\tt badbase}\ programs}{91}
\contentsline {subsection}{\numberline {3.5.3}The {\tt closure}\ program}{93}
\contentsline {subsection}{\numberline {3.5.4}Conversion to {\tt FITS} format}{94}
\contentsline {subsection}{\numberline {3.5.5}Miscellaneous programs}{94}
\contentsline {chapter}{\numberline {4}The GMRT Data}{97}
\contentsline {section}{\numberline {4.1}GMRT Observations}{98}
\contentsline {section}{\numberline {4.2}Low frequency specific problems}{100}
\contentsline {subsection}{\numberline {4.2.1}Mapping with non co-planar arrays}{100}
\contentsline {subsubsection}{3D imaging}{103}
\contentsline {subsubsection}{Polyhedron imaging}{104}
\contentsline {subsection}{\numberline {4.2.2}Bandwidth Smearing}{106}
\contentsline {section}{\numberline {4.3}Observational procedure}{107}
\contentsline {subsection}{\numberline {4.3.1}On-line monitoring}{109}
\contentsline {subsubsection}{System monitoring}{109}
\contentsline {subsubsection}{Data monitoring}{110}
\contentsline {section}{\numberline {4.4}Data Analysis}{111}
\contentsline {subsection}{\numberline {4.4.1}Data Editing}{111}
\contentsline {subsection}{\numberline {4.4.2}Data Editing and Calibration in {\tt AIPS}}{113}
\contentsline {subsubsection}{Flux density calibration}{117}
\contentsline {subsubsection}{Phase calibration}{118}
\contentsline {subsubsection}{Bandpass calibration}{119}
\contentsline {section}{\numberline {4.5}Inversion and deconvolution of GMRT data}{119}
\contentsline {section}{\numberline {4.6}The Images}{121}
\contentsline {chapter}{\numberline {5}Observations of Supernova Remnants}{131}
\contentsline {section}{\numberline {5.1}Introduction}{131}
\contentsline {section}{\numberline {5.2}Candidate SNRs}{134}
\contentsline {subsection}{\numberline {5.2.1}G001.4$-$0.1}{135}
\contentsline {subsection}{\numberline {5.2.2}G003.8$+$0.3}{136}
\contentsline {subsection}{\numberline {5.2.3}G004.2$-$0.0}{139}
\contentsline {subsection}{\numberline {5.2.4}G004.8$+$6.2}{142}
\contentsline {subsection}{\numberline {5.2.5}G356.3-1.5}{143}
\contentsline {subsection}{\numberline {5.2.6}G356.2$+$4.5}{146}
\contentsline {subsection}{\numberline {5.2.7}G358.0$+$3.8}{146}
\contentsline {section}{\numberline {5.3}Continuum flux densities of known SNRs}{148}
\contentsline {subsection}{\numberline {5.3.1}G003.7$-$0.2}{148}
\contentsline {subsection}{\numberline {5.3.2}G355.9$-$2.5}{148}
\contentsline {subsection}{\numberline {5.3.3}Kepler's SNR (G004.5$+$6.8)}{152}
\contentsline {section}{\numberline {5.4}Discussion}{152}
\contentsline {chapter}{\numberline {6}Other objects in the fields}{159}
\contentsline {section}{\numberline {6.1}Introduction}{159}
\contentsline {section}{\numberline {6.2}Point sources in the fields}{160}
\contentsline {section}{\numberline {6.3}Extended sources}{164}
\contentsline {subsection}{\numberline {6.3.1}G003.6-0.11}{164}
\contentsline {subsection}{\numberline {6.3.2}Linear structure in the field of G356.3$-$1.5}{172}
\contentsline {section}{\numberline {6.4}Extended emission around Ultra Compact HII regions}{174}
\contentsline {subsection}{\numberline {6.4.1}G004.417$+$0.126}{174}
\contentsline {subsection}{\numberline {6.4.2}G003.349$-$0.076}{176}
\contentsline {section}{\numberline {6.5}Discussion}{178}
\contentsline {chapter}{\numberline {7}Measurement of polarization leakage}{183}
\contentsline {section}{\numberline {7.1}Introduction}{183}
\contentsline {section}{\numberline {7.2}Motivation}{184}
\contentsline {section}{\numberline {7.3}Algorithm and simulation}{186}
\contentsline {subsection}{\numberline {7.3.1}The {\tt leaky\nobreakspace {}{\tt antsol}}}{187}
\contentsline {subsection}{\numberline {7.3.2}Results of the simulations}{188}
\contentsline {section}{\numberline {7.4}Real data}{189}
\contentsline {subsection}{\numberline {7.4.1}150 MHz data}{189}
\contentsline {subsection}{\numberline {7.4.2}L-band data with circular feed}{190}
\contentsline {subsubsection}{Results and Interpretation}{191}
\contentsline {section}{\numberline {7.5}Closure phase and the Poincar\'e sphere}{194}
\contentsline {section}{\numberline {7.6}Non-uniqueness of solutions}{196}
\contentsline {section}{\numberline {7.7}Conclusions}{198}
\contentsline {chapter}{\numberline {8}Conclusions}{199}
\contentsline {section}{\numberline {8.1}Using the Giant Meterwave Radio Telescope}{199}
\contentsline {subsection}{\numberline {8.1.1}Testing and debugging}{200}
\contentsline {subsection}{\numberline {8.1.2}Software development}{200}
\contentsline {section}{\numberline {8.2}Candidate Galactic SNRs}{202}
\contentsline {section}{\numberline {8.3}Other sources in the fields}{204}
\contentsline {section}{\numberline {8.4}Future directions}{205}
\contentsline {section}{\numberline {8.5}Some thoughts on the role of software for the GMRT}{206}
\contentsline {chapter}{\numberline {A}The user interface for off-line applications}{211}
\contentsline {section}{\numberline {A.1}The User interface commands}{211}
\contentsline {subsection}{\numberline {A.1.1}De-referencing mechanism}{214}
\contentsline {subsection}{\numberline {A.1.2}File name convention}{215}
\contentsline {section}{\numberline {A.2}Customization}{215}
\contentsline {subsection}{\numberline {A.2.1}The {\tt help} keyword}{217}
\contentsline {chapter}{\numberline {B}The {\tt xtract}\ macro language}{219}
\contentsline {section}{\numberline {B.1}The macro language}{219}
\contentsline {section}{\numberline {B.2}Output filters}{222}
\contentsline {section}{\numberline {B.3}Internal design}{223}
\contentsline {subsection}{\numberline {B.3.1}Macro compilation}{223}
\contentsline {subsection}{\numberline {B.3.2}Macro execution}{226}
\contentsline {section}{\numberline {B.4}Programming with the {\tt xtract} library}{227}
\contentsline {subsection}{\numberline {B.4.1}Interpretation and compilation of the format string}{227}
\contentsline {subsection}{\numberline {B.4.2}Execution of the compiled macro}{228}
\contentsline {subsection}{\numberline {B.4.3}The {\tt Parameters} structure }{229}
\contentsline {section}{\numberline {B.5}Adding new {\it elements}\ to the syntax}{231}
\contentsline {chapter}{\numberline {C}Antenna/baseline naming convention}{233}
\contentsline {section}{\numberline {C.1}Antenna naming convention}{233}
\contentsline {section}{\numberline {C.2}Baseline naming convention}{234}
\contentsline {subsection}{\numberline {C.2.1}Examples}{234}
\contentsline {chapter}{\numberline {D}Computation of antenna based complex gains}{237}
\contentsline {section}{\numberline {D.1}Interpretation of the equation}{240}
\contentsline {section}{\numberline {D.2}Estimation of the system temperature ($T^s$)}{240}
\contentsline {section}{\numberline {D.3}Derivation of $g_i$ using real and imaginary parts}{242}