Tracking a beam of electrons from the low solar corona into interplanetary space with the Low Frequency Array, Parker Solar Probe and 1 au spacecraft

TL;DR

This study combines space and ground radio observations to track electron beams from the low solar corona into interplanetary space, revealing that small-scale flux emergence can produce electron injections without major flares.

Contribution

It demonstrates the effectiveness of combining LOFAR, PSP, and other spacecraft data to trace electron beam trajectories from the corona into the heliosphere, highlighting the role of small-scale flux emergence.

Findings

Type III radio burst sources are located on open magnetic fields at 1.6-3 R☉.

Electron enhancements detected in situ at STEREO-A are linked to the radio burst.

Small-scale flux emergence can inject electrons into the heliosphere without strong flares.

Abstract

Type III radio bursts are the result of plasma emission from mildly relativistic electron beams propagating from the low solar corona into the heliosphere where they can eventually be detected in situ if they align with the location of a heliospheric spacecraft. Here we observe a type III radio burst from 0.1-16 MHz using the Parker Solar Probe (PSP) FIELDS Radio Frequency Spectrometer (RFS), and from 20-80 MHz using the Low Frequency Array (LOFAR). This event was not associated with any detectable flare activity but was part of an ongoing type III and noise storm that occurred during PSP encounter 2. A deprojection of the LOFAR radio sources into 3D space shows that the type III radio burst sources were located on open magnetic field from 1.6-3 R$_\odot$ and originated from a near-equatorial active region around longitude E48$^o$. Combining PSP/RFS observations with WIND/WAVES and STEREO/WAVES, we reconstruct the type III radio source trajectory in the heliosphere interior to PSP's position, assuming ecliptic confinement. An energetic electron enhancement is subsequently detected in situ at the STEREO-A spacecraft at compatible times although the onset and duration suggests the individual burst contributes a subset of the enhancement. This work shows relatively small-scale flux emergence in the corona can cause the injection of electron beams from the low corona into the heliosphere, without needing a strong solar flare. The complementary nature of combined ground and space-based radio observations, especially in the era of PSP, is also clearly highlighted by this study.