EUV Observational consequences of the spatial localisation of nanoflare heating within a multi-stranded atmospheric loop

TL;DR

This study models a multi-stranded solar coronal loop with episodic heating to investigate how the spatial location of heating affects EUV observations, finding that observational signatures of heating location are subtle and often below instrument detection thresholds.

Contribution

It introduces a detailed multi-strand loop model with power-law distributed heating and analyzes the observational consequences of heating location using synthetic EUV data.

Findings

Temperature profiles differ between apex and footpoint heating scenarios.

Broad differential emission measure is consistent with observations.

Observational signatures of heating location are likely below instrument detection limits.

Abstract

Determining the preferred spatial location of the energy input to solar coronal loops would be an important step forward towards a more complete understanding of the coronal heating problem. Following on from Sarkar & Walsh (2008) this paper presents a short 10e9 cm "global loop" as 125 individual strands, where each strand is modelled independently by a one-dimensional hydrodynamic simulation. The strands undergo small-scale episodic heating and are coupled together through the frequency distribution of the total energy input to the loop which follows a power law distribution with index ~ 2.29. The spatial preference of the swarm of heating events from apex to footpoint is investigated. From a theoretical perspective, the resulting emission measure weighted temperature profiles along these two extreme cases does demonstrate a possible observable difference. Subsequently, the simulated output is folded through the TRACE instrument response functions and a re-derivation of the temperature using different filter-ratio techniques is performed. Given the multi-thermal scenario created by this many strand loop model, a broad differential emission measure results; the subsequent double and triple filter ratios are very similar to those obtained from observations. However, any potential observational signature to differentiate between apex and footpoint dominant heating is possibly below instrumental thresholds. The consequences of using a broadband instrument like TRACE and Hinode-XRT in this way are discussed.