Spectroscopic and imaging observations of transient hot and cool loops by IRIS and SDO

TL;DR

This study uses multi-wavelength spectroscopic and imaging observations to investigate the formation and properties of transient hot and cool coronal loops, revealing their temperature, density, and magnetic flux characteristics.

Contribution

It presents detailed analysis of small-scale transient loops, linking magnetic flux cancellation to loop formation, and distinguishes between hot and cool loops with their thermodynamic properties.

Findings

Hot transient reaches 8 MK temperature

Cool transient reaches 0.4 MK temperature

Electron densities are approximately 10^11.2 and 10^10.8 cm^-3 for hot and cool loops

Abstract

Coronal loops are basic building blocks of solar atmosphere and are observed on various length scales. However, their formation mechanism is still unclear. In this paper, we present the spectroscopic and imaging observations of small-scale transients and subsequent formation of transient loops. For the purpose, we have utilized the multi-wavelength observations recorded by AIA and IRIS-SJI, along with spectroscopic measurements provided by IRIS. For the photospheric magnetic field data, we obtained line-of-sight magnetogram data provided by HMI. Small-scale transients are simultaneously observed with several EUV and UV passbands of AIA and IRIS-SJI. HMI magnetogram provides evidence of negative flux cancellations beneath these transients. Differential Emission Measure (DEM) analysis shows that one of the transient attains temperature up to 8 MK whereas another one reaches only up to 0.4 MK. These transients further lead to the formation of small-scale loops with similar temperature distributions, and thus termed as hot and cool loops respectively. During the course of events, IRIS slit was rastering the region and thus provided spectroscopic measurements at both transients and associated loops. This enabled us to perform in-depth investigations of hot and cool loops. Using density sensitive O IV line pair, we obtained average electron densities along the hot and cool loop to be $10^{11.2}$ and $10^{10.8}$ cm$^{-3}$ respectively. Energy estimates suggest that flux cancellation can easily power the hot transient whereas is insufficient for cool transient. Life time estimates and magnetic field extrapolation suggest presence of small-scale and fine structures within these loops. Results provide crucial ingredients on the physics of loop formation and involved thermodynamics.