Towards an all-sky continuum survey with a new K-band multi-feed receiver: system characterization, calibration, software development and pilot survey

This thesis has been carried out in the framework of the EU FP6 Marie Curie Early Stage Training programme ‘ESTRELA’. In this thesis, the design and the commissioning of the K-band 7-horn multi-feed receiver (MF) on the Medicina 32-m telescope is described. The MF receiver currently undergoing commissioning on Medicina telescope, has been designed and built for the upcoming Sardinia Radio Telescope. The MF receiver, based on the heterodyne receiver technology, is a 7-horn focal plane array arranged in a hexagonal geometry with a central feed and operates in the frequency band 18-26.5 GHz with an instantaneous bandwidth of 2 GHz. A total power analogue backend (2 GHz bandwidth, 7×2 channels) was designed and built for continuum observations with the MF. This thesis presents several sets of measurements performed as part of the MF receiver commissioning to test the receiver performance on the Medicina antenna. The optical alignment of the MF receiver attached to the Medicina antenna was optimized to gain the maximum power in the main lobe of the antenna beam, at the same time minimizing the sidelobes. The system temperature together with other antenna parameters were measured and found to be in agreement with the expected values. In parallel I calculated precise values for the MF Tcal as a function of frequency in the entire 18-26.5 GHz operational range. A mathematical approach was developed to achieve this goal using Tcal laboratory measurements as reference values. A dedicated calibration campaign was carried out to assess the pointing precision i of the MF receiver coupled with the total power analogue backend on the Medicina antenna and to obtain a list of suitable pointing and flux calibrators for 21 GHz observations. The pointing of the MF receiver was found to be within the pointing accuracy of the Medicina telescope (1/10 of the antenna beamsize) and is not affected by antenna speed. The pointing of the receiver was found to be stable for weak sources as well (≈ 1 Jy). A method was developed to calibrate the MF receiver in absence of a noise source. A list of pointing and flux calibrators was obtained both for Medicina and SRT telescopes. A pilot survey at 21 GHz was conducted as part of the commissioning and in the framework of an international collaboration aimed to map the entire Northern sky in K-band. An area of 1000 square degrees covering the Northern polar cap was mapped using the On The Fly fast scanning observing strategy. A list of 151 source candidates was obtained from the pilot survey maps. Follow-up observations of a subsample of 104 ‘reliable’ sources candidates extracted from the candidate list were performed at 30 GHz in the framework of the ‘ESTRELA’ collaboration at the Toruń telescope. 57 sources were confirmed and the flux densities of these sources are presented in Chapter 5. Follow-up observations at 5, 8 and 21 GHz have been carried out at Medicina. Preliminary results indicate 70 sources are confirmed as real at 21 and 5 GHz, and 66 of them were also detected at 8 GHz. All the sources detected at 30 GHz were also detected at 21 GHz. The results presented in this thesis prove the MF receiver scientific capabilities and address its high sensitivity. This thesis was submitted by Rashmi Verma, to the University of Bologna, Italy for the degree of Doctoral of Philosophy in Dipartimento di Astronomia on 15 March 2011. This thesis work was carried out at INAF Istituto di Radioastronomia (Bologna, Italy) by extensively using the Medicina 32-m dish.