1. Quasi-periodic pulsations in stellar flares observed with XMM-Newton
Alexey Kuznetsov, Robert Sych
Institute of Solar-Terrestrial Physics (Irkutsk, Russia)

2. Example of observations (AD Leo, started on 14 May 2001, 21:04:21 UT):
XMM-Newton:
imaging spectroscopic observations in the soft X-ray range (0.1–12 keV), FOV 30′×30′.
Image
Spectrum
XMM-Newton Serendipitous Source Catalogue (Rosen, Webb, Watson, et al., 2016):
3XMM-DR7 Interface – Observatory of Strasbourg:
Light curve

3. ... Pye, Rosen, Fyfe, & Schroder (2015):
correlation of the XMM-Newton Serendipitous Source Catalogue with the Hipparcos-Tycho catalogue;
years;
search for flares;
F-M stars selected.
~130 flares on ~70 stars were found.
Our subset:
single (or wide binaries) main-frequency stars only (no RS CVn, T Tau, etc.)
 45 light curves with flares on 40 stars were selected.
Time resolution: ≥10 s.
...

4. Analysis:
Fourier analysis (to obtain integral power spectra of oscillations);
wavelet analysis (to study the dynamics of oscillations).
Aim: search for oscillations and analyze their parameters.
Significance level: 90%.

5. Features found in the XMM light curves
“Slow flare” without pulsations
GSC (G5)
70 Oph (K0+K5)

6. Features found in the XMM light curves
“Fast flare” without pulsations
NU UMa (G5)
HD (F6)

7. Features found in the XMM light curves
“Slow flare” with QPPs
chi01 Ori (G0?)
EQ Peg (M3.5+M4.5)
Periods: 0.9, 5.6, 15 min.
Periods: 10, 33, 61 min.

8. Features found in the XMM light curves
Drifting QPPs before/after flare
HK Aqr (M0)
47 Cas B (G0)
Periods: 61, 107, 307 min.
Periods: 15, 34, 92 min.

9. Features found in the XMM light curves
QPPs with frequency jump
CD (K6)
Periods: 45, 64, 103 min.

10. Features found in the XMM light curves
QPPs with increasing/decreasing intensity
HD (F4)
HD (G6)
Periods: 16, 45, 205 min.
Periods: 116 min.

11. Features found in the XMM light curves
Quasi-periodic bursts (flares)
DG CVn (M4)
AD Leo (M3.5)
Periods: 35, 50, 102 min.
Periods: 60, 118, 199 min.

12. Summary Among 45 light curves: “slow flares” without QPPs: 6 (14.3%);
“fast flares” without QPPs: 11 (26.2%);
“slow flares” with QPPs: 6 (14.3%);
flares with QPPs with drifting frequency: 6 (14.3%);
damping QPPs at the decay phase of the flare: 2 (4.5%);
growing QPPs at the pre-flare phase: 1 (2.2%);
quasi-periodic flares: 10 (23.8%).
In some “slow flares”, high-frequency pulsations (with periods of ~5 min) were detected. Such pulsations may be caused by the processes similar to the solar P-mode oscillations. Impulsive flares make the high-frequency pulsations unobservable, and only the relatively slow pulsations were detected.