IRIS observations of the Mg ii h and k lines during a solar flare

Kerr, Graham S.; Simões, Paulo J. A.; Qiu, Jiong; Fletcher, L.

doi:10.1051/0004-6361/201526128

Cited by 68 publications

(96 citation statements)

References 38 publications

(70 reference statements)

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“…These spectral features are optically thick and often show a strong reversal in the core of the line (e.g., Schmit et al 2015). As we will see, the profiles are not reversed during this flare and the Gaussian moment is an adequate description of the line profile (the lack of a reversal during flaring conditions has been reported previously by Kerr et al 2015 andLiu et al 2015). We take the rest wavelengths for the doublet, 2796.354 Å for the k-line and 2803.531 Å for the h-line, from Murphy & Berengut (2014).…”

Section: Observations Of the Flare Footpointssupporting

confidence: 76%

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Warren

Reep

Crump

et al. 2016

ApJ

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We exploit the high spatial resolution and high cadence of the Interface Region Imaging Spectrograph (IRIS) to investigate the response of the transition region and chromosphere to energy deposition during a small flare. Simultaneous observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager provide constraints on the energetic electrons precipitating into the flare footpoints, while observations of the X-Ray Telescope, Atmospheric Imaging Assembly, and Extreme Ultraviolet Imaging Spectrometer (EIS) allow us to measure the temperatures and emission measures from the resulting flare loops. We find clear evidence for heating over an extended period on the spatial scale of a single IRIS pixel. During the impulsive phase of this event, the intensities in each pixel for the Si IV 1402.770 Å, C II 1334.535 Å, Mg II 2796.354 Å, and O I 1355.598 Å emission lines are characterized by numerous small-scale bursts typically lasting 60 s or less. Redshifts are observed in Si IV, C II, and Mg II during the impulsive phase. Mg II shows redshifts during the bursts and stationary emission at other times. The Si IV and C II profiles, in contrast, are observed to be redshifted at all times during the impulsive phase. These persistent redshifts are a challenge for one-dimensional hydrodynamic models, which predict only short-duration downflows in response to impulsive heating. We conjecture that energy is being released on many small-scale filaments with a power-law distribution of heating rates.

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Section: Observations Of the Flare Footpointssupporting

confidence: 76%

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Warren

Reep

Crump

et al. 2016

ApJ

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“…The ratio at footpoint pixels along all eight slits is around 1.1 (with a standard deviation, σ = 0.068) and does not change during the flare. This is consistent with previous flare observation by OSO-8/LPSP (Lemaire, Choucq-Bruston, and Vial, 1984) and an M class flare observed by IRIS and analyzed by Kerr et al (2015), who found the k to h ratio is 1.07 to 1.19 in flaring pixels and does not change much during flare. Figure 10 shows that there are variations of the k to h ratio at pixels 470-550 before the impulsive phase of the flare and during the flare.…”

Section: Evolution Of Mg II Spectra During the X1 Flaresupporting

confidence: 93%

“…During the observed flare, the LPSP spectrometer was also able to detect an enhanced emission in three subordinate (intersystem) Mg ii lines, which have wavelengths around the Mg ii k line and appear as absorption lines in the quietSun (QS) spectrum. With the observations from IRIS, the Mg ii lines during an M class flare was studied in detail by Kerr et al (2015). They investigated the spatial and temporal behaviour of Mg ii lines and found there were red shifts of line centroids, line broadening, and blue asymmetries in flare ribbons.…”

Section: Introductionmentioning

confidence: 99%

Mg ii Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph

Liu¹,

Heinzel²,

Kleint³

et al. 2016

Solar and Stellar Flares

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Mg ii lines represent one of the strongest emissions from the chromospheric plasma during solar flares. In this article, we studied the Mg ii lines observed during the X1 flare on March 29 2014 (SOL2014-03-29T17:48) by the Interface Region Imaging Spectrograph (IRIS). IRIS detected large intensity enhancements of the Mg ii h and k lines, subordinate triplet lines, and several other metallic lines at the flare footpoints during this flare. We have used the advantage of the slit-scanning mode (rastering) of IRIS and performed, for the first time, a detailed analysis of spatial and temporal variations of the spectra. Moreover, we were also able to identify positions of strongest hard X-ray (HXR) emissions using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations and to correlate them with the spatial and temporal evolution of IRIS Mg ii spectra. The light curves of the Mg ii lines increase and peak contemporarily with the HXR emissions but decay more gradually. There are large red asymmetries in the Mg ii h and k lines after the flare peak. We see two spatially well separated groups of Mg ii line profiles, non-reversed and reversed. In some cases, the Mg ii footpoints with reversed profiles are correlated with HXR sources. We show the spatial and temporal behavior of several other line parameters (line metrics) and briefly discuss them. Finally, we have synthesized the Mg ii k line using our non-LTE code with the Multilevel Accelerated Lambda Iteration (MALI) technique. Two kinds of models are considered, the flare model F2 of Machado et al. (1980, Astrophys. J., 242, 336 ) and the models of Ricchiazzi and Canfield (1983, Astrophys. J., 272, 739, RC). Model F2 reproduces the peak intensity of the unreversed Mg ii k profile at flare maximum but does not account for high wing intensities. On the other hand, the RC models show the sensitivity of Mg ii line intensities to various electronbeam parameters. Our simulations also show that the microturbulence produces a broader line core, while the intense line wings are caused by an enhanced line source function.

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“…Several important characteristics are inferred: (1) in general, the spectra of the ordinary flare ribbon behind the front are brighter than those on the negative front; (2) strong, mainly redshifted emission and line broadening (with a FWHM near or greater than 0.8 Å) are found in the negative front relative to the ribbon behind; and (3) both the Mg II and C II show a central reversal pattern in the ribbon front. This is a common feature for quiet Sun spectra (Leenaarts et al 2013) but unusual for flare regions (Kerr et al 2015).…”

Section: Iris Imaging Spectroscopy Of the Event On 2014 Augustmentioning

confidence: 83%

ULTRA-NARROW NEGATIVE FLARE FRONT OBSERVED IN HELIUM-10830 Å USING THE 1.6 m NEW SOLAR TELESCOPE

Cao

Ding

et al. 2016

ApJ

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Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6m New Solar Telescope at Big Bear Solar Observatory, we show a striking "negative" flare with a narrow but unambiguous "dark" moving front observed in He I 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg II lines. Theoretically, such negative contrast in He I 10830 Å can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects.

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IRIS observations of the Mg ii h and k lines during a solar flare

Cited by 68 publications

References 38 publications

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Mg ii Lines Observed During the X-class Flare on 29 March 2014 by the Interface Region Imaging Spectrograph

ULTRA-NARROW NEGATIVE FLARE FRONT OBSERVED IN HELIUM-10830 Å USING THE 1.6 m NEW SOLAR TELESCOPE

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