Probing cosmic plasma with giant radio pulses

Abstract

Very Long Baseline Interferometry (VLBI) observations of the Crab pulsar with the 64-m radio telescope at Kalyazin (Russia) and the 46-m radio telescope of the Algonquin Radio Observatory (Canada) at 2.2 GHz and single-dish observations of the millisecond pulsar B1937+21 with the GBT at 2.1 GHz were conducted to probe the interstellar medium and study the properties of giant pulses. The VLBI data were processed with a dedicated software correlator, which allowed us to obtain the visibility of single giant pulses. Two frequency scales of 50 and 450 kHz were found in the diffraction spectra of giant pulses from the Crab pulsar. The location of the scattering region was estimated to be close to the outer edge of the nebula. No correlation was found between the power spectra of giant pulses at the left- and right-hand circular polarisation. We explain this lack of correlation through the influence of the strong magnetic field on circularly polarised emission in the region close to the Crab pulsar.

Combining the measurement of the decorrelation bandwidths with that of scattering time of giant pulses for B1937+21, we found three frequency scales of 1.7, 3.8, and 16.5 MHz. The scattering time of giant pulses of B1937+21 at 2.1 GHz was found to be 40±4 ns. We obtained an upper limit of the intrinsic width of giant pulses from B1937+21 of less than 8 ns. The frequency dependences of the scattering times for the Crab pulsar and PSR B1937+21 were found to be different. They are characterized by exponents of−3.5 and−4.2, respectively. We attribute the difference to the large influence of scattering in the Crab nebula.

Keywords:

• Interstellar medium
• Pulses

Acknowledgements

We thank Frank Ghigo for extraordinary help in the preparation of the observations with the GBT and Konstantin Belousov and Andrey Chibisov for providing the operational S2-RDR play-back system. The Robert C. Byrd Green Bank Telescope (GBT) is operated by the National Radio Astronomy Observatory, which is a facility of the US National Science Foundation operated under cooperative agreement by Associated Universities, Inc. ARO is operated by the Geodetic Survey Division of Natural Resources Canada. V.I. Kondratiev was a postdoctoral fellow at York University at the beginning of this project. Part of the project was done while Y.Y. Kovalev was a Jansky Fellow of the National Radio Astronomy Observatory and a research fellow of the Alexander von Humboldt Foundation. This project was supported in part by grants from the Canadian NSERC, the Russian Foundation for Basic Research (project number 07-02-00074) and the Presidium of the Russian Academy of Sciences ‘Origin and evolution of stars and galaxies’.