The Duration of Energy Deposition on Unresolved Flaring Loops in the Solar Corona

Abstract

Solar flares form and release energy across a large number of magnetic loops. The global parameters of flares, such as the total energy released, duration, physical size, etc., are routinely measured, and the hydrodynamics of a coronal loop subjected to intense heating have been extensively studied. It is not clear, however, how many loops comprise a flare, nor how the total energy is partitioned between them. In this work, we employ a hydrodynamic model to better understand the energy partition by synthesizing Si IV and Fe XXI line emission and comparing to observations of these lines with IRIS. We find that the observed temporal evolution of the Doppler shifts holds important information on the heating duration. To demonstrate this we first examine a single loop model, and find that the properties of chromospheric evaporation seen in Fe XXI can be reproduced by loops heated for long durations, while persistent red-shifts seen in Si IV cannot be reproduced by any single loop model. We then examine a multi-threaded model, assuming both a fixed heating duration on all loops, and a distribution of heating durations. For a fixed heating duration, we find that durations of 100 -200 s do a fair job of reproducing both the red-and blue-shifts, while a distribution of durations, with a median of about 50 -100 s, does a better job. Finally, we compare our simulations directly to observations of an M-class flare seen by IRIS, and find good agreement between the modeled and observed values given these constraints.

Can the Superposition of Evaporative Flows Explain Broad Fe xxi Profiles during Solar Flares?

“…1. Electron energy flux: 1.2×10 11 ergs cm 2 s −1 and energy cut-off E c : 25 keV, within the range of typical values reported in previous observational and theoretical studies (see e.g., Kuridze et al 2015;Kerr et al 2016;Polito et al 2016;Rubio da Costa et al 2016;Reep et al 2018) 2. Power-law index δ: 5, typical for large flares (e.g., Krucker et al 2008;Hannah et al 2011).…”

“…3. Heating duration: 60 s, based on Reep et al (2018), who found that heating durations of ≈50-100 s for each strand are needed to reproduce the observed temporal evolution of Doppler shifts during evaporation.…”

Automated Detection of Rapid Variability of Moss Using SDO/AIA and Its Connection to the Solar Corona

“…The temporal behavior of RMV shows similarities with the standard flare model such as compact footpoints that energize quickly and are connected by loops filling with evaporated material (Falchi et al 1997;Krucker et al 2011). Numerical simulations for flares are available with flexible modes of energy release, e.g., using a single electron beam input (Uitenbroek 2001;Allred et al 2015), or a multi-threaded approach (Reep et al 2018). The RMV events can be modeled using assumptions of non-thermal electron beam fluxes constrained from nanoflare observations (Testa et al 2014).…”

Connecting Chromospheric Condensation Signatures to Reconnection Driven Heating Rates in an Observed Flare

“…Recent data-driven investigations have likewise inferred a beam heating duration of ∼ 20 s from HXR lightcurves (da Costa et al 2016;Graham et al 2020). In contrast, Reep et al (2018) found beam durations of ∼ 50 − 200 s better reproduce redshifts seen in observations of prolonged condensation (Warren et al 2016;Li et al 2017).…”