Imaging Spectroscopy of a White-Light Solar Flare

TL;DR

This study presents the first high-resolution space-based imaging spectroscopy of a white-light solar flare, revealing magnetic and spectral signatures, and analyzing the flare's impact on the photospheric FeI line and magnetic field.

Contribution

It provides novel high-resolution spectroscopic observations of a white-light flare using HMI and RHESSI, including magnetic, Doppler, and continuum data, with insights into line shifts and magnetic field changes.

Findings

White-light kernel appears in magnetic footpoints during impulsive phase

FeI line shifts to blue but remains in absorption, not emission

No seismic wave detected from the event

Abstract

We report observations of a white-light solar flare (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). The HMI data give us the first space-based high-resolution imaging spectroscopy of a white-light flare, including continuum, Doppler, and magnetic signatures for the photospheric FeI line at 6173.34{\AA} and its neighboring continuum. In the impulsive phase of the flare, a bright white-light kernel appears in each of the two magnetic footpoints. When the flare occurred, the spectral coverage of the HMI filtergrams (six equidistant samples spanning \pm172m{\AA} around nominal line center) encompassed the line core and the blue continuum sufficiently far from the core to eliminate significant Doppler crosstalk in the latter, which is otherwise a possibility for the extreme conditions in a white-light flare. RHESSI obtained complete hard X-ray and \Upsilon-ray spectra (this was the first \Upsilon-ray flare of Cycle 24). The FeI line appears to be shifted to the blue during the flare but does not go into emission; the contrast is nearly constant across the line profile. We did not detect a seismic wave from this event. The HMI data suggest stepwise changes of the line-of-sight magnetic field in the white-light footpoints.