Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars

Namekata, Kosuke; Sakaue, Takahito; Watanabe, Kyoko; Asai, Ayumi; Maehara, Hiroyuki; Notsu, Yuta; Notsu, Shota; Honda, Satoshi; Ishii, Takako T.; Ikuta, Kazumasa; Nogami, Daisaku; Shibata, Kazunari

doi:10.3847/1538-4357/aa9b34

Cited by 139 publications

(148 citation statements)

References 73 publications

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“…In both cases, a weak correlation is found considering only the M stars. In the Kepler band we find that Article number, page 18 of 25 kep,flare , which is significantly different from the relation found by Namekata et al (2017). In X-rays we find a steeper relation (t xray =E 0.52 xray,flare ) than the one found for solar flares (t xray =E 0.2−0.33 xray,flare ; Veronig et al 2002).…”

Section: Discussioncontrasting

confidence: 84%

“…In X-rays we find a steeper relation (t xray =E 0.52 xray,flare ) than the one found for solar flares (t xray =E 0.2−0.33 xray,flare ; Veronig et al 2002). These differences are likely due to the poor statistical sample of superflares analyzed in this paper and the limited range of emitted energy (32.9≤log(E K2,flare )≤34.7 in our sample, 33≤log(E K2,flare )≤36 in Namekata et al (2017)). We however extend the results obained by Hawley et al (2014) on the flares occurring in GJ 1243, where the energy of the observed flares reached 10 33 erg in the Kepler band, smaller than most of the flares analyzed in this paper.…”

Section: Discussionmentioning

confidence: 83%

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Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

Guarcello

Micela

Sciortino

et al. 2019

A&A

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Context. Flares are powerful events ignited by a sudden release of magnetic energy which triggers a cascade of interconnected phenomena, each resulting in emission in different electromagnetic bands. In fact, in the Sun flares are observed across the whole electromagnetic spectrum. Multi-band observations of stellar flares are instead rare. This limits our ability to extend what we learn from solar flares to the case of flares occurring in stars with different properties. Aims. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. The objective of this paper is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We also aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. Methods. We selected bright X-ray/optical flares that occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Results. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-versus-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares. Conclusions.

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Section: Discussioncontrasting

confidence: 84%

Section: Discussionmentioning

confidence: 83%

Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

Guarcello

Micela

Sciortino

et al. 2019

A&A

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“…The timescales and energies of the two GJ 1243 flare events are strikingly similar to the largest solar flares (Woods et al 2004); thus, HST-1 and HST-2 may be suitable for establishing connections and differences (e.g., in the slow rise and decay of Ca II K) between dMe and dG flares. Recently, Namekata et al (2017) compared the durations and energies of flares on GJ 1243 (from Kepler ) to whitelight flares on the Sun (from SDO/HMI). They found that both GJ 1243 and the Sun exhibited similar power-law scalings between flare energy and duration as found in Maehara et al (2015), but that for a given duration, the flares on GJ 1243 were 10x larger energy (all bolometric flare energies were calculated assuming a blackbody; see Section 9).…”

Section: Future Modeling Directions and Connection To Dg Flaresmentioning

confidence: 99%

The Near-ultraviolet Continuum Radiation in the Impulsive Phase of HF/GF-type dMe Flares. I. Data

Kowalski

Wisniewski

Hawley

et al. 2019

ApJ

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We present NUV flare spectra from the Hubble Space Telescope/Cosmic Origins Spectrograph during two moderateamplitude U -band flares on the dM4e star GJ 1243. These spectra are some of the first accurately flux-calibrated, NUV flare spectra obtained over the impulsive phase in M dwarf flares. We observed these flares with a fleet of nine ground-based telescopes simultaneously, which provided broadband photometry and low-resolution spectra at the Balmer jump. A broadband continuum increase occurred with a signal-to-noise > 20 in the HST spectra, while numerous Fe II lines and the Mg II lines also increased but with smaller flux enhancements compared to the continuum radiation. These two events produced the most prominent Balmer line radiation and the largest Balmer jumps that have been observed to date in dMe flare spectra. A T = 9000 K blackbody under-estimates the NUV continuum flare flux by a factor of two and is a poor approximation to the white-light in these types of flare events. Instead, our data suggest that the peak of the specific continuum flux density is constrained to U -band wavelengths near the Balmer series limit. A radiative-hydrodynamic simulation of a very high energy deposition rate averaged over times of impulsive heating and cooling better explains the λ > 2500Å flare continuum properties. These two events sample only one end of the empirical color-color distribution for dMe flares, and more time-resolved flare spectra in the NUV, U -band, and optical from 2000 − 4200Å are needed during more impulsive and/or more energetic flares.

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“…One important exception is the lack of the detection of QPP in solar flares in the white light emission, while QPP are confidently detected in this band in stellar flares. However, we should point out that solar flares are rarely detected in the white light anyway, see [6] for a recent discussion.…”

Section: Introductionmentioning

confidence: 99%

Non-stationary quasi-periodic pulsations in solar and stellar flares

Nakariakov

Kolotkov

Kupriyanova

et al. 2018

Plasma Phys. Control. Fusion

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Often the enhanced electromagnetic radiation generated in solar and stellar flares shows a pronounced (quasi)-oscillatory pattern-quasi-periodic pulsations (QPP), with characteristic periods ranging from a fraction of a second to several tens of minutes. We review recent advances in the empirical study of QPP in solar and stellar flares, addressing the intrinsic nonstationarity of the signal, i.e. the variation of its amplitude, period or phase with time. This nonstationarity could form a basis for a classification of QPP, necessary for revealing specific physical mechanisms responsible for their appearance. We could identify two possible classes of QPP, decaying harmonic oscillations, and trains of symmetric triangular pulsations. Apparent similarities between QPP and irregular geomagnetic pulsations Pi offer a promising avenue for the knowledge transfer in both analytical techniques and theory. Attention is also paid to the effect of the flare trend on the detection and analysis of QPP.

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Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars

Cited by 139 publications

References 73 publications

Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades

The Near-ultraviolet Continuum Radiation in the Impulsive Phase of HF/GF-type dMe Flares. I. Data

Non-stationary quasi-periodic pulsations in solar and stellar flares

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