# Plasma heating in solar microflares: statistics and analysis

## TL;DR

This study analyzes 481 weak solar flares during low solar activity, examining plasma temperature and energy, and finds that power-law models best describe the temperature distribution across flare sizes, indicating plasma heating in very small flares.

## Contribution

It provides a comprehensive statistical analysis of plasma heating in microflares, extending understanding to very weak flares down to A0.0002 class, and compares exponential and power-law models for temperature distribution.

## Key findings

- Power-law models fit temperature data well across flare sizes.
- Plasma heating evidence starts from A0.0002 X-ray class.
- Weaker flares likely do not heat surrounding plasma.

## Abstract

In this paper, we present the results of an analysis of 481 weak solar flares, from A0.01 to the B \textit{GOES} class, that were observed during the period of extremely low solar activity from 2009 April to July. For all flares we measured the temperature of the plasma in the isothermal and two-temperature approximations and tried to fit its relationship with the X-ray class using exponential and power-law functions. We found that the whole temperature distribution in the range from A0.01 to X-class cannot be fit by one exponential function. The fitting for weak flares below A1.0 is significantly steeper than that for medium and large flares. The power-law approximation seems to be more reliable: the corresponding functions were found to be in good agreement with experimental data both for microflares and for normal flares. Our study predicts that the evidence of plasma heating can be found in flares starting from the A0.0002 X-ray class. Weaker events presumably cannot heat the surrounding plasma. We also estimated emission measures for all flares studied and the thermal energy for 113 events.