The scintillating tail of comet C/2020 F3 (Neowise)^⋆

¹ ASTRON – the Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
e-mail: rafallows@gmail.com
² Department of Electronic and Electrical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK
³ RAL Space, United Kingdom Research and Innovation – Science & Technology Facilities Council – Rutherford Appleton Laboratory, Harwell Campus, Oxfordshire OX11 0QX, UK
⁴ Dipartimento di Fisica “G. Occhialini”, Università di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
⁵ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
⁶ INAF, Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, Italy

Received: 29 June 2022
Accepted: 17 September 2022

Abstract

Context. The occultation of a radio source by the plasma tail of a comet can be used to probe structure and dynamics in the tail. Such occultations are rare, and the occurrence of scintillation, due to small-scale density variations in the tail, remains somewhat controversial.

Aims. A detailed observation taken with the Low-Frequency Array (LOFAR) of a serendipitous occultation of the compact radio source 3C196 by the plasma tail of comet C/2020 F3 (Neowise) is presented. 3C196 tracked almost perpendicularly behind the tail, providing a unique profile cut only a short distance downstream from the cometary nucleus itself.

Methods. Interplanetary scintillation (IPS) is observed as the rapid variation of the intensity received of a compact radio source due to density variations in the solar wind. IPS in the signal received from 3C196 was observed for five hours, covering the full transit behind the plasma tail of comet C/2020 F3 (Neowise) on 16 July 2020, and allowing an assessment of the solar wind in which the comet and its tail are embedded.

Results. The results reveal a sudden and strong enhancement in scintillation which is unequivocally attributable to the plasma tail. The strongest scintillation is associated with the tail boundaries, weaker scintillation is seen within the tail, and previously-unreported periodic variations in scintillation are noted, possibly associated with individual filaments of plasma. Furthermore, contributions from the solar wind and comet tail are separated to measure a sharp decrease in the velocity of material within the tail, suggesting a steep velocity shear resulting in strong turbulence along the tail boundary.