Investigating Pre-flare Signatures in Spectroscopic Observations of an X9-class Solar Flare

TL;DR

This study analyzes spectroscopic data from an X9-class solar flare to identify pre-flare signatures such as oscillations and velocity changes, providing insights into the magnetic destabilization process before eruption.

Contribution

It presents the first detailed spectroscopic analysis of pre-flare phenomena associated with an X9-class solar flare, revealing oscillations and velocity patterns indicative of magnetic destabilization.

Findings

Detected ~7-10 min and ~18-21 min oscillations during pre-flare phase.

Observed a steady rise in Si IV line parameters 3 hours before flare.

Identified strong non-thermal velocities and blueshifts 15 minutes before flare onset.

Abstract

On October 3rd, 2024, the Sun emitted an X9.0-class flare from active region NOAA 13842. The event was recorded by multiple space-based instruments, beginning hours before the eruption, granting a unique opportunity to provide insight into the flare's pre-flare phase. In this study, we employ analysis of Interface Region Imaging Spectrograph (IRIS) spectroscopic data to investigate pre-flaring phenomena associated with this flare. We present time-series and wavelet analysis of non-thermal velocity, Doppler velocity, and line intensity quantities of the IRIS Si IV 1403 angstrom line. We find two ranges of periodic oscillations during the pre-flare phase: ~7-10 min and ~18-21 min oscillations, with local enhancements occurring near the polarity inversion line. We also find a steady rise in Si IV line parameters beginning 3 hours before the flare in the same region, transitioning into strong non-thermal velocities and blueshifts ~15 minutes before onset. These findings are consistent with a slow destabilization of the coronal magnetic field, possibly driven by the gradual activation of a flux rope, followed by a rapid shift to intense reconnection activity leading to flare onset.