Characterizing Superflares in HR 1099 using Temporal and Spectral Analysis of XMM-Newton Observations

TL;DR

This study analyzes three superflare events on HR 1099 using XMM-Newton data, revealing their physical properties, coronal abundances, and magnetic fields, and compares these with previous findings to understand stellar flare mechanisms.

Contribution

First detailed spectral and temporal analysis of superflares on HR 1099, highlighting their large loop sizes, energies, and inverse-FIP abundance effects, advancing understanding of stellar flare physics.

Findings

Flares last 2.8 to 4.1 hours with rapid rise and slow decay.

Flare energies range from 10^35.83 to 10^37.03 erg, classifying as superflares.

Loop lengths are 6 to 8.9 x 10^10 cm, larger than solar flares.

Abstract

In the present paper, we analyze three energetic X-ray flares from the active RS CVn binary HR 1099 using data obtained from XMM-Newton. The flare duration ranges from 2.8 to 4.1 h, with e-folding rise and decay times in the range of 27 to 38 minutes and 1.3 to 2.4 h, respectively, indicating rapid rise and slower decay phases. The flare frequency for HR 1099 is one flare per rotation period. Time-resolved spectroscopy reveals peak flare temperatures of 39.44, 35.96, and 32.48 MK, emission measures of $7 \times 10^{53}$ to $8 \times 10^{54}$ cm$^{-3}$, global abundances of 0.250, 0.299, and 0.362 $Z_\odot$, and peak X-ray luminosities of $ 10^{31.21-32.29}$ erg s$^{-1}$. The quiescent state is modeled with a three-temperature plasma maintained at 3.02, 6.96, and 12.53 MK. Elemental abundances during quiescent and flaring states exhibit the inverse-FIP effect. We have conducted a comparative analysis of coronal abundances with previous studies and found evidence supporting the i-FIP effect. The derived flare semi-loop lengths of 6 to 8.9 $\times 10^{10}$ cm were found to be comparable to the other flares detected on HR 1099; however, they are significantly larger than typical solar flare loops. The estimated flare energies, ranging from $10^{35.83-37.03}$ erg, classify these flares as super-flares. The magnetic field strengths of the loops are found to be in the range of 350 to 450 G. We diagnose the physical conditions of the flaring corona in HR 1099 through the observations of superflares and provide inference on the plasma processes.