A 151.5 MHz southern sky survey covering the RA range 0h < RA < 6h and the declination range −70 DEC −10

The Mauritius Radio Telescope has been built with the main objective of carrying out an equivalent of 6C survey in the southern hemisphere. The present work is a step in this direction. MRT data processing is both complex and challenging due to the non-coplanarity of the array and the heterogeneous nature of its database containing 20,000 hours of observations carried out over a span of five years. This thesis summarizes the important out comes of the present work, challenges faced and methodologies developed to meet those challenges. The main outcome of the present work is a set of images of the sky at 151.5 MHz with a resolution of 4 × 4.6 sec(DEC + 20.14) and a sensitivity of ∼ 300 mJy covering DEC range −75◦ ≤ DEC ≤ −10◦ and RA range 0 < RA < 6 (Set II images), a source catalog containing 3000 sources, a subset of this catalog giving the flux density at 151.5 MHz of ≈ 100MS4sourcesandacompendiumofseveralextendedsourcesseeninSetIIimages. The present work began with the investigation of systematics in the positional errors of sources seen in the MRT source catalog extracted from set I images covering DEC range −75◦ ≤ DEC ≤ −10◦ and RA range 18 < RA < 24the RA range (Pandey & Udaya Shankar, 2006). Systematics in positional errors were found when the positions of sources common to MRT and MRC catalogues were compared. The positional errors in declination were found to be significant (up to about 50% of the MRT beamwidth in declination). We applied two-dimensional homography to correct for systematic positional errors in the image domain and thereby avoid re-processing the visibility data. Positions of bright point sources, common to MRT catalogue and MRC, were used to set up an over determined system to solve for the homography matrix. After correction the errors were found to be within 10% of the beamwidth for these bright sources and the systematics are eliminated from the images. We are of the view that this technique will be of relevance to the new generation radio telescopes where, owing to huge data rates, only images after certain integration would be recorded as opposed to raw visibilities. Our investigations cued to possible errors in the array geometry. We re-estimated the array geometry using the astrometry principle. The estimates show an error of 1 mm/m, which results in an error of about half a wavelength at 150 MHz for a 1 km north-south baseline. The estimates also indicate that the east-west arm is inclined by an angle of 4 to the true east-west direction. We re-imaged regions of sky common to set I images using the re estimated array geometry and proved that the systematic positional errors disappear by incorporating the new array geometry. To provide the right hardware and software environments to meet the challenges of processing MRT data, we assembled a set of 8 computers inter-connected using a 100 Mbps Ethernet link to store the intermediate products of analysis and developed a set of software pipelines to run MARMOSAT (The Mauritius Minimum Operating System for Array Telescopes) effectively on this MRT cluster. The main focus of the new development was inter-process communication and homogenization of the database, which had kept changing in structure along with system development and commissioning. We also paid attention to the fact that one required the final products in FITS image format to be able to distribute the images to the astronomical community. Armed with good hardware and software environments, we examined the quality of data for the RA range 0 to 18 hours. We found that the data quality decreased as one moved away from the calibrators used for phase/amplitude calibration of the array. In view of this we designed and developed a field of view based calibration procedure to facilitate calibration. This helped us to get calibration very close to the proximity of the sky area being analyzed and helped us include several files which were earlier excluded for imaging due to lack of calibrators. With feed back from data quality assessment we analyzed the MRT data for the RA range 0 to 6 hr (Set II images), covering approximately one steradian of the sky. We have been able to detect 3837 sources in Set II images. 1500 of these sources have matching MRC sources. By carrying out a statistical analysis of positional errors and flux densities of sources common to MRC and MRT, we have carefully corrected for positional errors in our images and have revised our flux density scale. This shows that the median spectral index of sources between 150 and 408 MHz to be 0.87. This is along the expected lines. From the catalog we have made a list of sources, which have steep spectral indices (α < 1.3) for further studies. The MRT has a very good uv coverage with baselines going down to 2m both along EW and S directions. With this we were indeed expecting to detect extended sources in the images. We were able to detect all the 71 SUMSS extended sources listed in the ? paper in the RA range 0 to 6 hr. 33 of these sources show extended emission at 151.5 MHz. In addition we find 16 extended sources in MRT not listed by them. The median spectral index of the 33 extended sources common to MRT and SUMSS is -0.74. We have prepared a source list including the integrated flux densities and spectral indices of these sources. We envisage a follow-up study of these sources in our future work.