Study of the spatial association between an active region jet and a nonthermal type III radio burst^⋆

¹ Inter-University Centre for Astronomy and Astrophysics (IUCAA), Post Bag-4, Ganeshkhind, Pune 411007, India
e-mail: sargam@iucaa.in
² DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
³ University of Applied Sciences and Arts Northwestern Switzerland, Bahnhofstrasse 6, 5210 Windisch, Switzerland
⁴ University College London, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁵ Instituto de Astronomía y Física del Espacio (IAFE), CONICET-UBA, Argentina
⁶ National Centre for Radio Astrophysics (NCRA), Tata Institute of Fundamental Research, Savitribai Phule Pune University Campus, Pune, Maharashtra, India

Received: 24 July 2019
Accepted: 29 September 2019

Abstract

Aims. We aim to investigate the spatial location of the source of an active region (AR) jet and its relation with associated nonthermal type III radio emission.

Methods. An emission measure (EM) method was used to study the thermodynamic nature of the AR jet. The nonthermal type III radio burst observed at meterwavelength was studied using the Murchison Widefield Array (MWA) radio imaging and spectroscopic data. The local configuration of the magnetic field and the connectivity of the source region of the jet with open magnetic field structures was studied using a nonlinear force-free field (NLFFF) extrapolation and potential field source surface (PFSS) extrapolation respectively.

Results. The plane-of-sky velocity of the AR jet was found to be ∼136 km s⁻¹. The EM analysis confirmed the presence of low temperature 2 MK plasma for the spire, whereas hot plasma, between 5 and 8 MK, was present at the footpoint region which also showed the presence of Fe XVIII emission. A lower limit on the electron number density was found to be 1.4 × 10⁸ cm⁻³ for the spire and 2.2 × 10⁸ cm⁻³ for the footpoint. A temporal and spatial correlation between the AR jet and nonthermal type III burst confirmed the presence of open magnetic fields. An NLFFF extrapolation showed that the photospheric footpoints of the null point were anchored at the location of the source brightening of the jet. The spatial location of the radio sources suggests an association with the extrapolated closed and open magnetic fields although strong propagation effects are also present.

Conclusions. The multi-scale analysis of the field at local, AR, and solar scales confirms the interlink between different flux bundles involved in the generation of the type III radio signal with flux transferred from a small coronal hole to the periphery of the sunspot via null point reconnection with an emerging structure.