The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT.

We present high‐resolution, high‐sensitivity radio continuum observations of the nearby spiral galaxy NGC 2997 at 332, 616 and 1272 MHz using the Giant Metrewave Radio Telescope (GMRT). The integrated spectrum of this galaxy has a spectral index of −0.92 (Sν ∝ να) and we place an upper limit to the thermal fraction at 1272 MHz of ∼ 10 per cent. Our multifrequency study shows a relatively flat spectrum source (α ∼ −0.6) at the centre of the galaxy. This leads to the radio detection of a circumnuclear ring in the high‐resolution map at 1272 MHz. We detect five hotspots in the ring, with an average star formation rate of ∼0.024 M⊙ yr−1, a median supernova (SN) rate of ∼0.001 yr−1 and luminosity of 1020 W Hz−1. We estimate an equipartition field in the central nuclear region of diameter ∼750 pc to be about G. We also report several interesting features along the spiral arms. In this paper, we present the low‐frequency radio continuum maps, the spectral index distribution, the circumnuclear ring and the derived physical properties.

No abstract