Physics Dept. Seminar

 

 

September 23, Monday

 

All Microflares that Accelerate Electrons to High-Energies are Rooted in Sunspots

 

Dr. Andrea Francesco Battaglia

Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Switzerland

(Solar Physics, Host: Nita)

 

Room: ECE 202

Time: 11:45 am - 12:45 pm with 11:30 am teatime

**Zoom link for those who cannot attend in-person: Check email announcement or request from Ken Ahn (kenahn@njit.edu).

(APPROVAL by Prof Ahn REQUIRED for APPH/MTSE PhD students to attend online)

 

The storage and sudden explosive release of energy in magnetic fields, accompanied by the acceleration of particles, is a widespread phenomenon in plasma across the Universe and it occurs in various contexts, from quasars at cosmological distances to flares from our closest star, the so-called solar flares. In solar flares, generally, the most energetic events are the most efficient at accelerating high-energy electrons. Nonetheless, we sometimes observe microflares (events less energetic than regular flares) that accelerate electrons to high energies. We call these events “hard microflares” because of their strikingly flat spectrum in the hard X-ray (HXR) regime. We statistically characterize these events using observations from the X-ray telescope STIX aboard the Solar Orbiter mission. The key observational result is that all hard microflares have one of the footpoints rooted directly within a sunspot (either in the umbra or the penumbra), which indicates that the underlying magnetic flux densities are large. We therefore conclude that the magnetic field strength plays a key role in efficiently accelerating high-energy electrons, with hard HXR spectra associated with strong fields. This key result will allow us to further constrain our understanding of the electron acceleration mechanisms in flares and space plasmas.