The 22 May 2007 B-class flare: new insights from<i>Hinode</i>observations

Zanna, G. Del; Mitra-Kraev, U.; Bradshaw, S. J.; Mason, H. E.; Asai, Ayumi

doi:10.1051/0004-6361/201014906

Cited by 58 publications

(62 citation statements)

References 56 publications

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“…Surprisingly, the centre component is still found to be blue shifted when adding a second component to the fit, and quite strongly so at 16:01 UT Position 0. This does not fit a situation where high speed upflows found at flare footpoints coincide with stationary background emission (Del Zanna et al 2011).…”

Section: High Velocity Flowsmentioning

confidence: 79%

“…The flexibility of Hinode/EIS allows "sparse" rasters which can scan across an active region several times during a flare, with the slit jumping to non-contiguous positions, thus gaining greater spatial coverage and allowing multiple exposures of a single region, but at the expense of spatial information. Studies of this kind have made significant progress in understanding chromospheric evaporation, see Milligan & Dennis (2009), Watanabe et al (2010), and Del Zanna et al (2011. In this paper we present the results of one such sparse raster observation, which has enabled us to study flare ribbons and footpoints at different times in their evolution.…”

Section: Introductionmentioning

confidence: 99%

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Hinode/EIS plasma diagnostics in the flaring solar chromosphere

Graham

Fletcher

Hannah

2011

A&A

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Context. The impulsive phase of solar flares is a time of rapid energy deposition and heating in the lower solar atmosphere, leading to changes in the temperature, density, ionisation and velocity structure of this region. Aims. We aim to study the lower atmosphere during the impulsive phase of a flare using imaging and spectroscopic data from Hinode/EIS, RHESSI and TRACE. We place these observations in context by using a wide range of temperature observations from each instrument. Methods. We analyse sparse raster data from the Hinode/EIS spectrometer to derive the density and line-of-sight velocity in flare footpoints, in a GOES C6.6 flare observed on 05-June-2007. The raster duration was 150s across the centre of a small active region, allowing multiple exposures of the flare ribbons and footpoints. Using RHESSI and Hinode/XRT we test both non-thermal and thermal models for the HXR emission. Results. During the flare impulsive phase, we find evidence from XRT for flare footpoints at temperatures exceeding 7 MK. We measure the electron number density increasing up to a few ×10 10 cm −3 in the footpoints, at temperatures of ∼1.5−2 MK, accompanied by small downflows at temperatures below Fe XIII and upflows of up to ∼140 km s −1 at temperatures above. This is reasonable in the context of HXR diagnostics of the flare electron beam. The electrons inferred have sufficient energy to affect the chromospheric ionisation structure. Conclusions. EIS sparse raster data coupled with RHESSI imaging and spectroscopy prove useful here in studying the lower atmosphere of solar flares, and in this event suggest heat deposition relatively high in the chromosphere drives chromospheric evaporation while increasing the observed electron densities at footpoints. However, from RHESSI spectral fitting it is not possible to say whether the data are more consistent with a model including a non-thermal beam, or purely thermal model.

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Section: High Velocity Flowsmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Hinode/EIS plasma diagnostics in the flaring solar chromosphere

Graham

Fletcher

Hannah

2011

A&A

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“…In the analysis section of this Letter, we have illustrated that the combined Hinode XRT and EIS data set has a blind spot (Del Zanna 2008;Del Zanna et al 2011). The response curves of a few of the broadband XRT filters are shown in the middle panel of Figure 3.…”

Section: Discussionmentioning

confidence: 92%

DEFINING THE “BLIND SPOT” OF HINODE EIS AND XRT TEMPERATURE MEASUREMENTS

Winebarger

Warren

Schmelz

et al. 2012

ApJ

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Observing high-temperature, low emission measure plasma is key to unlocking the coronal heating problem. With current instrumentation, a combination of EUV spectral data from Hinode Extreme-ultraviolet Imaging Spectrometer (EIS; sensitive to temperatures up to 4 MK) and broadband filter data from Hinode X-ray Telescope (XRT; sensitive to higher temperatures) is typically used to diagnose the temperature structure of the observed plasma. In this Letter, we demonstrate that a "blind spot" exists in temperature-emission measure space for combined Hinode EIS and XRT observations. For a typical active region core with significant emission at 3-4 MK, Hinode EIS and XRT are insensitive to plasma with temperatures greater than ∼6 MK and emission measures less than ∼10 27 cm −5 . We then demonstrate that the temperature and emission measure limits of this blind spot depend upon the temperature distribution of the plasma along the line of sight by considering a hypothetical emission measure distribution sharply peaked at 1 MK. For this emission measure distribution, we find that EIS and XRT are insensitive to plasma with emission measures less than ∼10 26 cm −5 . We suggest that a spatially and spectrally resolved 6-24 Å spectrum would improve the sensitivity to these high-temperature, low emission measure plasma.

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“…The Hinode EUV Imaging Spectrometer (EIS), with its two channels (SW: 166-212 Å; LW: 245-291 Å), has provided (since 2006) AR observations in a wide range of temperatures (e.g. from all the iron ionisation stages from Fe vii to Fe xvi and above 10 MK from Fe xxiii and Fe xxiv, as presented in detail in Del Zanna 2009a;Del Zanna 2012b, 2008Del Zanna et al 2011b). We have also recently provided an in-flight calibration for EIS (Del Zanna 2013).…”

Section: Introductionmentioning

confidence: 99%

The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

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155

110

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We present simultaneous SDO AIA and Hinode EIS observations of the hot cores of active regions (ARs) and assess the dominant contributions to the AIA EUV bands. This is an extension of our previous work. We find good agreement between SDO AIA, EVE and EIS observations, using our new EIS calibration and the latest EVE v.3 data. We find that all the AIA bands are multi-thermal, with the exception of the 171 and 335 Å, and provide ways to roughly estimate the main contributions directly from the AIA data. We present and discuss new atomic data for the AIA bands, showing that they are now sufficiently complete to obtain temperature information in the cores of ARs, with the exception of the 211 Å band. We found that the newly identified Fe xiv 93.61 Å line is the dominant contribution to the 94 Å band, whenever Fe xviii is not present. Three methods to estimate the Fe xviii emission in this band are presented, two using EIS and one directly from the AIA data. Fe xviii emission is often present in the cores of ARs, but we found cases where it is formed at 3 MK and not 7 MK, the temperature of peak ion abundance in equilibrium. The best EIS lines for elemental abundance determination and differential emission measure (DEM) analysis are discussed. A new set of abundances for many elements are obtained from EIS observations of hot 3 MK loops. The abundances of the elements with low first ionisation potential (FIP), relative to those of the high-FIP elements, are found to be enhanced by about a factor of three, compared to the photospheric values. A measurement of the path length implies that the absolute abundances of the low-FIP elements are higher than the photospheric values by at least a factor of three. We present a new DEM method customised for the AIA bands, to study the thermal structure of ARs at 1 resolution. This was tested on a few ARs, including one observed during the Hi-C rocket flight. We found excellent agreement between predicted and observed AIA count rates and EIS radiances. Overall we found few differences between the AIA and Hi-C 193 Å images of coronal structures, despite the higher Hi-C resolution (0.25 ). The Hi-C images and the AIA DEM modelling suggest that some of the cooler loops (below 1 MK) are already resolved by AIA, while the hotter (1.5-2.5 MK) "background" emission is in most places still unresolved even at the Hi-C resolution. This unresolved emission is significantly lower than previously observed with TRACE, the SOHO CDS, and Hinode EIS spectrometers. Its enhancement appears to be mostly due to increased iron abundance. We find an ubiquitous presence of emission at different temperatures that is not co-spatial, and suggest that future high-resolution imaging is carried out with isothermal bands.

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The 22 May 2007 B-class flare: new insights fromHinodeobservations

Cited by 58 publications

References 56 publications

Hinode/EIS plasma diagnostics in the flaring solar chromosphere

Hinode/EIS plasma diagnostics in the flaring solar chromosphere

DEFINING THE “BLIND SPOT” OF HINODE EIS AND XRT TEMPERATURE MEASUREMENTS

The multi-thermal emission in solar active regions

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