B.C.Joshi¹ and Sunil Ramakrishna^{2,3 1} National Centre for Radio Astrophysics (TIFR), Pune 411 007, India ²
International Institute of Information Technology (I2IT), Pune - 411 057, India
³ Intoto Software(I) Pvt Ltd., Hyderabad 500 082, India

Abstract. A variety of pulsar studies, ranging from high precision astrometry to tests for theories of gravity, require high time resolution data. Few such observations at more than two frequencies below 1 GHz are available. Giant Meterwave Radio Telescope (GMRT) has the unique capability to provide such multi-frequency pulsar data at low observation frequencies, but the quality and time resolution of pulsar radio signals is degraded due to dispersion in the interstellar medium at these frequencies. Such degradation is usually taken care of by employing specialized digital hardware, which implement coherent dedispersion algorithm. In recent years, a new alternative is provided by the availability of cheap computer hardware. In this approach, the re- quired signal processing is implemented in software using commercially off-the-shelf available computing hardware. This makes such a receiver flexible and upgradeable unlike a hardware implementation. The salient features and the modes of operation of a high time resolution pulsar instrument for GMRT based on this approach is described in this paper. The capability of the instrument is demonstrated by illustrations of test observations. We have obtained the average profile of PSR B1937+21 at 235 MHz for the first time and this profile indicates a scattering timescale of about 300 µs. Lastly, the possible future extensions of this concept are discussed.

Keywords: : instrumentation : radio pulsars - instrumentation : polarimeter - instrumentation : spectrograph - coherent dedispersion - pulsars : general

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