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N. D. R. Bhat (NAIC, Arecibo Observatory, USA), M. Kramer (JBO, University of Manchester, UK), Y. Gupta (NCRA-TIFR, Pune, India), H. C. Lambert (Raytheon, MA, USA)
The Effelsberg 100-m radio telescope is a unique instrument for high quality pulsar observations at frequencies above 1 GHz. In this paper, we report on recent observations of centi-metre (cm) wave Interstellar Scintillation (ISS) carried out with this instrument, with the goals of (1) investigation of the cm-wave ISS phenomenon itself, (2) studying the structure and dynamics of the Local Interstellar Medium (LISM), and (3) direct determination of the interstellar electron density spectrum. Observations were made for seven nearby pulsars (distance ~ 100--500 pc) at 13 cm, 6 cm and 3.6 cm in quasi-simultaneous, multi-wavelength mode by frequently switching between the receivers. From the time scales of fading of pulse intensity at these frequencies, we infer the distance to the scattering screen. Our findings are compared with the results from other recent investigations based on cm-wave ISS studies of radio sources, intra-day variable (IDV) quasars, and low-frequency pulsar scintillation studies. Further, constraints are placed on the nature of the electron density spectrum based on a structure function analysis of the time series of pulse intensity. Our results, along with those from from low-frequency pulsar scintillation observations, are used to infer the nature of the spectrum over a much wider range of length scales.