A Hot Microflare Observed With RHESSI and Hinode

TL;DR

This study combines RHESSI and Hinode data to analyze a microflare, revealing that high-temperature plasma results from direct coronal heating rather than nonthermal electron acceleration, challenging existing flare models.

Contribution

It provides observational evidence supporting coronal heating as the primary mechanism in microflares, contrasting with traditional models emphasizing electron precipitation.

Findings

No detectable hard X-ray emission observed.

High-temperature plasma likely due to direct coronal heating.

Unusual redshifts indicating downward flows at high temperatures.

Abstract

RHESSI and Hinode observations of a GOES B-class flare are combined to investigate the origin of 15 MK plasma. The absence of any detectable hard X-ray emission coupled with weak blueshifted emission lines (indicating upward velocities averaging only 14 km/s) suggests that this was a result of direct heating in the corona, as opposed to nonthermal electron precipitation causing chromospheric evaporation. These findings are in agreement with a recent hydrodynamical simulation of microflare plasmas which found that higher temperatures can be attained when less energy is used to accelerate electrons out of the thermal distribution. In addition, unusual redshifts in the 2 MK Fe XV line (indicating downward velocities of 14 km/s) were observed cospatial with one of the flare ribbons during the event. Downflows of such high temperature plasma are not predicted by any common flare model.