IPS survey at 327 MHz for detection of compact radio sources

Abstract

In early 1992 a new feed was installed along the focal line of the 530 m long and 30 m wide parabolic cylinder reflector of the Ooty Radio Telescope (ORT). The new feed consisting of 1056 GaAsFET low noise amplifiers, one behind each dipole, helps reduce the system temperature to about 150 K as compared to about 350 K for the earlier feed. For a receiver bandwidth of 4 MHz and an R-C time constant of 0.5 sec the present system gives a signal to noise ratio per jansky of about 25:1. This implies enough signal to noise ratio to be able to produce an IPS spectrum on every 52 second stretch of data for sources with flux density as small as 1.5 Jansky. Hence it was decided to make a systematic interplanetary scintillation (IPS) survey at 327 MHz with the following aims: (1) To obtain a finding list of compact milli arc second sources for the space VLBI mission 'Radio Astron' due for launch in 1996; (2) To obtain a spatially well distributed list of scintillating sources around the ecliptic plane for interplanetary weather mapping; (3) To have a complete sample ofarc second extragalactic compact sources for cosmological investigations; and (4) For studies of interstellar scattering in the inner galaxy. This paper briefly reports the methodology of the scintillation survey and presents the results from the preliminary analysis of the data obtained so far from the ongoing survey