Flaring together: A preferred angular separation between sympathetic flares on the Sun

TL;DR

This study provides strong statistical evidence for the existence of sympathetic solar flares, revealing a preferred angular separation of about 30 degrees, which varies with solar cycle phase and hemisphere, and suggests magnetic field interactions as a driving mechanism.

Contribution

It is the first comprehensive statistical analysis confirming sympathetic flares on the Sun and identifies a characteristic angular separation linked to magnetic field structures.

Findings

Approximately 5% of flares are sympathetic in nature.

A preferred angular separation of about 30 degrees is observed between sympathetic flares.

A deficit of transequatorial events separated by 25-30 degrees in latitude is identified.

Abstract

Sympathetic solar flares are eruptions that occur nearby in space and time, driven by an apparent interaction between the active regions in which they are triggered. Their statistical existence on the Sun has yet to be firmly established. The main goal of this paper is to identify a statistical signature of sympathetic flares, characterize their properties and determine a potential mechanism driving their interaction. We perform a statistical analysis of a large number of flares observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter during solar cycle 24 and 25. We examine the spatiotemporal distribution of consecutive flare pairs across solar cycle phases and hemispheres, along with the propagation velocity of potential causal interactions and the relationship between flare magnitudes. We observe an excess of hemispheric flares separated by about 30 degrees of longitude and triggered in less than 1.5 hours from each other. This peak in angular separation varies with the solar cycle phase and hemisphere. Moreover, we identify a deficit of transequatorial events separated by 25-30 degrees in latitude and less than 5 degrees in longitude, a phenomenon we term unsympathetic flares. We provide strong statistical evidence for the existence of sympathetic flares on the Sun, demonstrating that their occurrence rate reaches approximately 5% across the three instruments used in this study. Additionally, we propose an interpretation of the observed angular scale of the sympathetic phenomenon, based on the separation between magnetic field line footpoints derived from potential field source surface extrapolations.