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Probing the Plasma Tail of Interstellar Comet 2I/Borisov

Presentation #227.01 in the session The Sun and Solar System I.

Published onJun 29, 2022
Probing the Plasma Tail of Interstellar Comet 2I/Borisov

We present an occultation study of compact radio sources by the plasma tail of the interstellar Comet 2I/Borisov (C/2019 Q4) using the Arecibo and Green Bank radio telescopes both at pre-perihelion and near-perihelion distances. We employed the remote-sensing, interplanetary scintillation (IPS) technique to probe the plasma tail at P-band, 820 MHz, and L-band. The presence and absence of scintillation at different perpendicular distances from the central part of the plasma tail suggests a narrow tail width of less than 6 arcmin at a distance of ~10 arcmin from the nucleus of the comet. The data recorded during the occultation of two of the sources, on 31 October 2019 at 327 MHz and L-band, covered the width of the plasma tail from its outer region to close to the center part. The profiles of systematic increase in scintillation provide the plasma properties associated with the tail, when the comet was located at its pre-perihelion distance. The excess level of scintillation observed at L-band indicates a plasma density enhancement to be in the range of ~15 – 20 times higher than the background solar wind. The evolution of the shape of the observed scintillation power spectra across the tail from its edge to the central axis suggests a density spectrum flatter than Kolmogorov, and that the plasma-density irregularity scales present in the tail range between 10 and 700 km. In particular, the result on the high-frequency spectral power excess, corresponding to irregularity scales much smaller than than the Fresnel scale, suggests the presence of small-scale density structures in the plasma tail, likely caused by the interaction between the solar wind and the plasma environment formed by the comet.

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