TRACING ELECTRON BEAMS IN THE SUN'S CORONA WITH RADIO DYNAMIC IMAGING SPECTROSCOPY

Abstract

We report observations of type III radio bursts at decimeter wavelengths\n(type IIIdm bursts) -- signatures of suprathermal electron beams propagating in\nthe low corona -- using the new technique of radio dynamic imaging spectroscopy\nprovided by the recently upgraded Karl G. Jansky Very Large Array (VLA). For\nthe first time, type IIIdm bursts were imaged with high time and frequency\nresolution over a broad frequency band, allowing electron beam trajectories in\nthe corona to be deduced. Together with simultaneous hard X-ray (HXR) and\nextreme ultraviolet (EUV) observations, we show these beams emanate from an\nenergy release site located in the low corona at a height below ~15 Mm, and\npropagate along a bundle of discrete magnetic loops upward into the corona. Our\nobservations enable direct measurements of the plasma density along the\nmagnetic loops, and allow us to constrain the diameter of these loops to be\nless than 100 km. These over-dense and ultra-thin loops reveal the\nfundamentally fibrous structure of the Sun's corona. The impulsive nature of\nthe electron beams, their accessibility to different magnetic field lines, and\nthe detailed structure of the magnetic release site revealed by the radio\nobservations indicate that the localized energy release is highly fragmentary\nin time and space, supporting a bursty reconnection model that involves\nsecondary magnetic structures for magnetic energy release and particle\nacceleration.\n