Spectropolarimetry of C-class flare footpoints

TL;DR

This study uses spectropolarimetry to analyze the decay phase of a C-class solar flare, revealing unusual flows and magnetic features at the flare footpoints with high-resolution observations, but finds no clear impact polarization evidence.

Contribution

First detailed spectropolarimetric analysis of C-class flare footpoints combining photospheric and chromospheric data with high spatial resolution.

Findings

Unusual photospheric flows including Doppler shifts and possible inflows.

Variable chromospheric emission and flows observed during the flare.

No definitive detection of impact polarization in the chromospheric line.

Abstract

We investigate the decay phase of a C-class flare in full-Stokes imaging spectropolarimetry with quasi-simultaneous measurements in the photosphere (6302.5 A line) and in the chromosphere (8542 A line) with the IBIS instrument. We analyze data from two fields-of-view, each spanning about 40" \times 80" and targeting the two footpoints of the flare. A region of interest is identified from V/I images: a patch of opposite polarity in the smaller sunspot's penumbra. We find unusual flows in this patch at photospheric levels: a Doppler shift of -4 km/s, but also a possible radial inflow into the sunspot of 4 km/s. Such patches seem to be common during flares, but only high-resolution observations allowed us to see the inflow, which may be related to future flares observed in this region. Chromospheric images show variable overlying emission and flows and unusual Stokes profiles. We also investigate the irregular penumbra, whose formation may be blocked by the opposite polarity patch and flux emergence. The 40 min temporal evolution depicts the larger of the flare ribbons becoming fainter and changing its shape. Measurable photospheric magnetic fields remain constant and we do not detect flare energy transport down from the chromosphere. We find no clear indications of impact polarization in the 8542 A line. We cannot exclude the possibility of impact polarization, because weaker signals may be buried in the prominent Zeeman signatures or it may have been present earlier during the flare.