Volume 629, September 2019
|Number of page(s)||16|
|Published online||19 September 2019|
Multi-waveband detection of quasi-periodic pulsations in a stellar flare on EK Draconis observed by XMM-Newton
Department of Physics, University of Warwick,
CV4 7AL, UK
2 Institute of Advanced Study, University of Warwick, Coventry, CV4 7HS, UK
3 Centre for Habitability, University of Warwick, Coventry, CV4 7HS, UK
4 School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
5 University of Leicester, Department of Physics & Astronomy, Leicester, LE1 7RH, UK
6 XMM-Newton Science Operations Centre, ESA, Villafranca del Castillo, Apartado 78, 28691 Villanueva de la Cañada, Spain
Accepted: 8 August 2019
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. We characterise the QPPs detected in an X-ray flare on the solar analogue, EK Draconis, which was observed by XMM-Newton.
Methods. We used wavelet and autocorrelation techniques to identify the QPPs in a detrended version of the flare. We also fitted 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 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.
Key words: methods: data analysis / stars: activity / stars: flare / stars: solar-type / X-rays: stars
© ESO 2019
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.