# Multi-waveband detection of quasi-periodic pulsations in a stellar flare on EK Draconis observed by XMM-Newton

## TL;DR

This study detects and characterizes quasi-periodic pulsations in an X-ray stellar flare on EK Draconis, revealing energy-dependent periodicities and phase differences, thus linking stellar flare physics to solar phenomena.

## Contribution

It provides the first detailed analysis of QPPs in a stellar flare across multiple energy bands, demonstrating energy-dependent periodicities and phase shifts using wavelet and modeling techniques.

## Key findings

- QPPs with ~76 min period detected in EK Draconis flare
- Energy-dependent QPP periods: 73 min (low-energy) and 82 min (high-energy)
- Significant phase difference and high-energy lead in the pulsations

## Abstract

Context. Quasi-periodic pulsations (QPPs) are time variations in the energy emission during a flare that are observed on both the Sun and other stars and thus have the potential to link the physics of solar and stellar flares. Aims. To characterise the QPPs detected in an X-ray flare on the solar analogue, EK Draconis, which was observed by XMM-Newton. Methods. We use wavelet and autocorrelation techniques to identify the QPPs in a detrended version of the flare. We also fit a model to the flare based on an exponential decay combined with a decaying sinusoid. The flare is examined in multiple energy bands. Results. A statistically significant QPP is observed in the X-ray energy band of 0.2-12.0 keV with a periodicity of 76+/-2 min. When this energy band is split, a statistically significant QPP is observed in the low-energy band (0.2-1.0 keV) with a periodicity of 73+/-2 min and in the high-energy band (1.0-12.0 keV) with a periodicity of 82+/-2 min. When fitting a model to the time series the phases of the signals are also found to be significantly different in the two energy bands (with a difference of 1.8+/-0.2 rad) and the high-energy band is found to lead the low-energy band. Furthermore, the first peak in the cross-correlation between the detrended residuals of the low- and high-energy bands is offset from zero by more than 3{\sigma} (4.1+/-1.3 min). Both energy bands produce statistically significant regions in the wavelet spectrum, whose periods are consistent with those listed above. However, the peaks are broad in both the wavelet and global power spectra, with the wavelet showing evidence for a drift in period with time, and the difference in period obtained is not significant. etc...