The role of radiative losses in the late evolution of pulse-heated coronal loops/strands

TL;DR

This study examines how updated radiative loss functions influence the late-phase cooling behavior of pulse-heated coronal loops, revealing faster cooling rates and steeper emission measure slopes at temperatures below 2 MK.

Contribution

It demonstrates the significant impact of recent spectral code updates on the plasma evolution predictions in coronal loop models, especially during late cooling phases.

Findings

Faster plasma cooling at 1-2 MK with new radiative loss functions.

Cooling rate increases when plasma density exceeds a threshold.

Steepening of the emission measure distribution slope below 2 MK.

Abstract

Radiative losses from optically thin plasma are an important ingredient for modeling plasma confined in the solar corona. Spectral models are continuously updated to include the emission from more spectral lines, with significant effects on radiative losses, especially around 1 MK. We investigate the effect of changing the radiative losses temperature dependence due to upgrading of spectral codes on predictions obtained from modeling plasma confined in the solar corona. The hydrodynamic simulation of a pulse-heated loop strand is revisited comparing results using an old and a recent radiative losses function. We find significant changes in the plasma evolution during the late phases of plasma cooling: when the recent radiative loss curve is used, the plasma cooling rate increases significantly when temperatures reach 1-2 MK. Such more rapid cooling occurs when the plasma density is larger than a threshold value, and therefore in impulsive heating models that cause the loop plasma to become overdense. The fast cooling has the effect of steepening the slope of the emission measure distribution of coronal plasmas with temperature at temperatures lower than ~2 MK. The effects of changes in the radiative losses curves can be important for modeling the late phases of the evolution of pulse-heated coronal loops, and, more in general, of thermally unstable optically thin plasmas.