Predictions of DKIST/DL-NIRSP observations for an off-limb kink-unstable coronal loop

TL;DR

This study uses synthetic observations from a 3D kink-unstable flux rope simulation to predict how DKIST/DL-NIRSP can detect fine-scale structures, wave propagation, and magnetic reconnection signatures in off-limb coronal loops.

Contribution

The paper demonstrates, through forward modelling, that DKIST/DL-NIRSP can observe detailed signatures of kink-unstable coronal loops, including small-scale reconnection and wave phenomena.

Findings

Detection of wave propagation and heat redistribution signatures.

Accurate measurement of loop radius and electron density estimation.

Identification of small-scale reconnection events at the loop boundary.

Abstract

Synthetic intensity maps are generated from a 3D kink-unstable flux rope simulation using several DKIST/DL-NIRSP spectral lines to make a prediction of the observational signatures of energy transport and release. The reconstructed large field-of-view intensity mosaics and single tile sit-and-stare high-cadence image sequences show detailed, fine-scale structure and exhibit signatures of wave propagation, redistribution of heat, flows and fine-scale bursts. These fine-scale bursts are present in the synthetic Doppler velocity maps and can be interpreted as evidence for small-scale magnetic reconnection at the loop boundary. The spectral lines reveal the different thermodynamic structures of the loop, with the hotter lines showing the loop interior and braiding, and the cooler lines showing the radial edges of the loop. The synthetic observations of DL-NIRSP are found to preserve the radial expansion and hence the loop radius can be measured accurately. The electron number density can be estimated using the intensity ratio of the Fe~\textsc{xiii} lines at 10747 and 10798~\AA. The estimated density from this ratio is correct to within $\pm10\%$ during the later phases of the evolution, however it is less accurate initially when line-of-sight density inhomogeneities contribute to the Fe~\textsc{xiii} intensity, resulting in an overprediction of the density by $\approx30\%$. The identified signatures are all above a conservative estimate for instrument noise and therefore will be detectable. In summary, we have used forward modelling to demonstrate that the coronal off-limb mode of DKIST/DL-NIRSP will be able to detect multiple independent signatures of a kink-unstable loop and observe small-scale transient features including loop braiding/twisting and small-scale reconnection events occurring at the radial edge of the loop.