First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum

Dominique, Marie; Zhukov, A. N.; Heinzel, P.; Dammasch, I. E.; Wauters, L.; Dolla, L.; Shestov, S. V.; Kretzschmar, M.; Machol, J. L.; Lapenta, Giovanni; Schmutz, W.

doi:10.3847/2041-8213/aaeace

Cited by 24 publications

(30 citation statements)

References 49 publications

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“…Furthermore, there are observed blueshifts in SXR and EUV emission with upward velocities of up to 1000 km•s −1 (Antonucci et al 1982;Milligan et al 2006a,b;Del Zanna 2008;Milligan & Dennis 2009;Polito et al 2016). In addition, observations of Lyman-α lines by the instruments with low spatial resolution show impulsive brightening of Lyman line emission and the appearance of either red or blue wing asymmetries at different times of flare development (Procházka et al 2017;Druett & Zharkova 2018;Dominique et al 2018). This is also supported by brightening in Lyman continuum intensity, which becomes greatly enhanced from the continuum head at λ = 910 Å along the other wavelengths (Kleint et al 2016;Druett & Zharkova 2019), resulting in strong intensity flattening over the continuum wavelengths reported from observations (Machado et al 2018;Druett & Zharkova 2019).…”

Section: Introductionmentioning

confidence: 95%

Sunquake with a second bounce, other sunquakes, and emission associated with the X9.3 flare of 6 September 2017

Zharkov

Matthews²,

Zharkova

et al. 2020

A&A

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Aims. The 6 September 2017 X9.3 solar flare produced very unique observations of magnetic field transients and a few seismic responses, or sunquakes, detected by the Helioseismic and Magnetic Imager (HMI) instrument aboard Solar Dynamic Observatory (SDO) spacecraft, including the strongest sunquake ever reported. This flare was one of a few flares occurring within a few days or hours in the same active region. Despite numerous reports of the fast variations of magnetic field, and seismic and white light emission, no attempts were made to interpret the flare features using multi-wavelength observations. In this study, we attempt to produce the summary of available observations of the most powerful flare of the 6 September 2017 obtained using instruments with different spatial resolutions (this paper) and to provide possible interpretation of the flaring events, which occurred in the locations of some seismic sources (a companion Paper II). Methods. We employed non-linear force-free field extrapolations followed by magnetohydrodynamic simulations in order to identify the presence of several magnetic flux ropes prior to the initiation of this X9.3 flare. Sunquakes were observed using the directional holography and time–distance diagram detection techniques. The high-resolution method to detect the Hα line kernels in the CRISP instrument at the diffraction level limit was also applied. Results. We explore the available γ-ray (GR), hard X-ray (HXR), Lyman-α, and extreme ultra-violet (EUV) emission for this flare comprising two flaring events observed by space- and ground-based instruments with different spatial resolutions. For each flaring event we detect a few seismic sources, or sunquakes, using Dopplergrams from the HMI/SDO instrument coinciding with the kernels of Hα line emission with strong redshifts and white light sources. The properties of sunquakes were explored simultaneously with the observations of HXR (with KONUS/WIND and the Reuven Ramaty High Energy Solar Spectroscopic Imager payload), EUV (with the Atmospheric Imaging Assembly (AIA/SDO and the EUV Imaging Spectrometer aboard Hinode payload), Hα line emission (with the CRisp Imaging Spectro-Polarimeter (CRISP) in the Swedish Solar Telescope), and white light emission (with HMI/SDO). The locations of sunquake and Hα kernels are associated with the footpoints of magnetic flux ropes formed immediately before the X9.3 flare onset. Conclusions. For the first time we present the detection of the largest sunquake ever recorded with the first and second bounces of acoustic waves generated in the solar interior, the ripples of which appear at a short distance of 5–8 Mm from the initial flare location. Four other sunquakes were also detected, one of which is likely to have occurred 10 min later in the same location as the largest sunquake. Possible parameters of flaring atmospheres in the locations with sunquakes are discussed using available temporal and spatial coverage of hard X-ray, GR, EUV, hydrogen Hα-line, and white light emission in preparation for their use in an interpretation to be given in Paper II.

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Section: Introductionmentioning

confidence: 95%

Sunquake with a second bounce, other sunquakes, and emission associated with the X9.3 flare of 6 September 2017

Zharkov

Matthews²,

Zharkova

et al. 2020

A&A

Self Cite

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“…The few reports of solar flare observations in Lyα that previously existed were mostly from broadband, disc-integrated irradiance measurements, and often focused on small numbers of events due to the limited duty cycles of instruments capable of observing flares at this wavelength (Kretzschmar, Dominique, and Dammasch, 2013;Raulin et al, 2013;Milligan et al, 2014;Kretzschmar, 2015;Milligan and Chamberlin, 2016;Dominique et al, 2018). However, Milligan et al (2020) recently carried out a statistical study of 477 M-and X-class flares in broadband, disc-integrated Lyα emission, and calculated the distribution of contrasts.…”

Section: Introductionmentioning

confidence: 99%

Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission

Milligan

2021

Sol Phys

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As the Lyman-alpha (Ly$\upalpha $ α ) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Ly$\upalpha $ α of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ≈8500 flares greater than B1 class to determine the contribution that they make to changes in the solar EUV irradiance. Using the peak of the 1 – 8 Å X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Ly$\upalpha $ α emission by the EUV Sensor on the Geostationary Operational Environmental Satellite 15 (GOES-15) were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1 – 0.3% enhancement to the solar Ly$\upalpha $ α irradiance on average. For comparison, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1 – 4% increase in Ly$\upalpha $ α emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Ly$\upalpha $ α at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Ly$\upalpha $ α of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

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“…Solar flare generally shows a sudden brightening feature on the Sun, which is often accompanied by a quick and violent energy release via magnetic reconnection (e.g., Fletcher et al 2011;Benz 2017;Chen et al 2020;Tan et al 2020). The wavelength range of flare radiation is quite broad, i.e., from the radio/microwave through the white light and extreme ultraviolet (UV/EUV) to soft/hard X-rays (SXR/HXR) and even to the γ-ray (e.g., Masuda et al 1994;Su et al 2013;Dominique et al 2018;Yan et al 2018a,b;Lysenko et al 2020;Li et al 2021). In the standard model of a solar flare such as the CSHKP flare model (Carmichael 1964;Sturrock 1966;Hirayama 1974;Kopp & Pneuman 1976), a huge amount of magnetic energies are released via reconnection in the local corona (Shibata & Magara 2011;Li et al 2016;Jiang et al 2021), i.e., as described in the two-dimensional reconnection model (Sturrock & Coppi 1964;Priest & Forbes 2002;Lin et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Simultaneous Observations of Chromospheric Evaporation and Condensation during a C-class Flare

Li,

Hong,

Ning

2021

Preprint

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We explored simultaneous observations of chromospheric evaporation and condensation during the impulsive phase of a C6.7 flare on 9 May 2019. The solar flare was simultaneously observed by multiple instruments, i.e., the New Vacuum Solar Telescope (NVST), the Interface Region Imaging Spectrograph, the Atmospheric Imaging Assembly (AIA), the Fermi, the Mingantu Spectral Radioheliograph, and the Nobeyama Radio Polarimeters. Using the single Gaussian fitting and the moment analysis technique, redshifted velocities at slow speeds of 15−19 km s −1 are found in the cool lines of C II and Si IV at one flare footpoint location. Red shifts are also seen in the Hα line-of-sight (LOS) velocity image measured by the NVST at double footpoints. Those red shifts with slow speeds can be regarded as the low-velocity downflows driven by the chromospheric condensation. Meanwhile, the converging motions from double footpoints to the loop top are found in the high-temperature EUV images, such as AIA 131 Å, 94 Å, and 335 Å. Their apparent speeds are estimated to be roughly 126−210 km s −1 , which could be regarded as the high-velocity upflows caused by the chromospheric evaporation. The nonthermal energy flux is estimated to be about 5.7×10 10 erg s −1 cm −2 . The characteristic timescale is roughly equal to 1 minute. All these observational results suggest an explosive chromospheric evaporation during the flare impulsive phase. While a HXR/microwave pulse and a type III radio burst are found simultaneously, indicating that the explosive chromospheric evaporation is driven by the nonthermal electron.

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First Detection of Solar Flare Emission in Mid-ultraviolet Balmer Continuum

Cited by 24 publications

References 49 publications

Sunquake with a second bounce, other sunquakes, and emission associated with the X9.3 flare of 6 September 2017

Sunquake with a second bounce, other sunquakes, and emission associated with the X9.3 flare of 6 September 2017

Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission

Simultaneous Observations of Chromospheric Evaporation and Condensation during a C-class Flare

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