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

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 lowand high-energy bands is offset from zero by more than 3σ (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. The offset in the first peak in the cross-correlation of the detrended residuals of two non-congruent energy bands (0.5 − 1.0 keV and 4.5 − 12.0 keV) is found to be even larger (10 ± 2 min). However, the signal-to-noise in the higher of these two energy-bands, covering the range 4.5 − 12.0 keV, is low. Conclusions. The presence of QPPs similar to those observed on the Sun, and other stars, suggests that the physics of flares on this young solar analogue is similar to the physics of solar flares. It is possible that the differences in the QPPs detected in the two energy bands are seen because each band observes a different plasma structure. However, the phase difference, which differs more significantly between the two energy bands than the period, could also be explained in terms of the Neupert effect. This suggests that QPPs are caused by the modulation of the propagation speeds of charged particles.

Quasi-Periodic Pulsations in Solar and Stellar Flares: A Review of Underpinning Physical Mechanisms and Their Predicted Observational Signatures

“…To date, stellar flare QPPs at several wavelengths within the same spectral range have been observed in optical (e.g. Zhilyaev et al, 2000, see Section 3.1.1), radio (see Section 3.2) and soft Xrays (Broomhall et al, 2019b, see Section 3.3.2). However, no QPPs occurring simultaneously in different spectral ranges (e.g.…”

“…The two consecutive flares were consistent with the reheating of the same magnetic structure where the first flare occurred. The large-scale magnetic structure and the periodicity of the multiple gigantic stellar flares suggested that the reheating events of the same magnetic stellar loop could develop during an interaction between the star and the disk of the star owing to their differential rotation Broomhall et al (2019b). detected QPPs in a flare on EK Draconics in the Xray bands of low-energy (0.2 -1.0 keV) with a period of 76±2 min and high-energy (1.0 -12.0 keV) with a period of 82±2 min.…”

The Independence of Oscillatory Reconnection Periodicity from the Initial Pulse

“…The term describes a series of reconnection events associated with periodic changes in the magnetic connectivity and topology of the field, the periodicity of which is derived from the relaxation of a perturbed field from a finite, aperiodic driver. As a mechanism, oscillatory reconnection has been proposed as a possible driving force behind quasi-periodic pulsations (QPPs) of solar flares (e.g., Kupriyanova et al 2016;Van Doorsselaere et al 2016;Pugh et al 2017;Yuan et al 2019;Hayes et al 2020;Li et al 2020aLi et al , 2020bLi et al , 2021Clarke et al 2021) and stellar flares (e.g., Broomhall et al 2019;Guarcello et al 2019;Jackman et al 2019;Notsu et al 2019;Vida et al 2019;Mancuso et al 2020;Ramsay et al 2021). Detailed reviews of a wide variety of suggested mechanism(s) behind QPPs can be found in McLaughlin et al (2018), Kupriyanova et al (2020), and Zimovets et al (2021).…”

Multi-wavelength quasi-periodic pulsations in a stellar superflare

“…Empirical properties of QPP in solar and stellar flares have similarities (Cho et al 2016) which could indicate the analogy in underlying physical processes. In particular, QPP in stellar flares have been detected at different wavelengths within the same spectral band: in optics (Zhilyaev et al 2000), in radio (Stepanov et al 2001), and in SXR (Broomhall et al 2019a). Guarcello et al (2019) analysed simultaneous observations of stellar superflares in the WL (with Kepler) and SXR (with XMM-Newton), and found 500-s QPP in an SXR flare lightcurve on the M2 class star HCG 273.…”