EVIDENCE OF WIDESPREAD HOT PLASMA IN A NONFLARING CORONAL ACTIVE REGION FROM<i>HINODE/X-RAY TELESCOPE</i>

Reale, F.; Testa, Paola; Klimchuk, J. A.; Parenti, S.

doi:10.1088/0004-637x/698/1/756

Cited by 93 publications

(111 citation statements)

References 20 publications

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“…See, e.g., Reale et al (2009aReale et al ( , 2009b, and Schmelz et al (2009) for initial reports of detections, Reale (2014) for a review of subsequent efforts, and O' Dwyer et al (2011) andWinebarger et al (2012) for reports of negative results and the difficulties of observing the appropriate temperature range. Notwithstanding these problems, measurements of non-thermal velocities at high temperatures (and any trend with temperature) are clearly significant for establishing whether the nanoflare-heated corona model is viable.…”

Section: Introductionmentioning

confidence: 99%

Measurements of Non-Thermal Line Widths in Solar Active Regions

Brooks

Warren

2016

ApJ

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Spectral line widths are often observed to be larger than can be accounted for by thermal and instrumental broadening alone. This excess broadening is a key observational constraint for both nanoflare and wave dissipation models of coronal heating. Here we present a survey of non-thermal velocities measured in the high temperature loops (1-4 MK) often found in the cores of solar active regions. This survey of Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) observations covers 15 non-flaring active regions that span a wide range of solar conditions. We find relatively small non-thermal velocities, with a mean value of 17.6 ± 5.3 km s −1 , and no significant trend with temperature or active region magnetic flux. These measurements appear to be inconsistent with those expected from reconnection jets in the corona, chromospheric evaporation induced by coronal nanoflares, and Alfvén wave turbulence models. Furthermore, because the observed non-thermal widths are generally small, such measurements are difficult and susceptible to systematic effects.

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Section: Introductionmentioning

confidence: 99%

Measurements of Non-Thermal Line Widths in Solar Active Regions

Brooks

Warren

2016

ApJ

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“…This choice was motivated by the results of the DEM and EM calculations in active regions (see e.g. Urnov et al 2007b;Reale et al 2009). The model DEM curves were convoluted with the kernels G(l, T ) for the channels l in each spectral set to obtain the corresponding artificial fluxes.…”

Section: Artificial Dems Reconstructed To Compare the Three Spectral mentioning

confidence: 99%

“…Here we apply the forward modeling described above to both all nine and only five XRT filters to test the diagnostic ability of the BIM technique under different data conditions. In particular, we aim to test the BIM under the conditions of Reale et al (2009), where only five XRT filters were used (Al_poly, C_poly, Be_thin, Be_med, Al_med) for an EM analysis of an AR. In Sect.…”

Section: Tests On Different Number Of Xrt Channelsmentioning

confidence: 99%

“…To calculate the synthetic fluxes in the case of five channels, we adopted both the standard calibration and a new one developed by Reale et al (2009) DEM distribution is isothermal and of width Δ log T = 0.1. We made the position of the peak vary from log T = 6.0 to 7.0.…”

Section: Tests On Different Number Of Xrt Channelsmentioning

confidence: 99%

“…In Sect. 4, we apply the BIM to the DEM analysis of spectroscopic data from SUMER , SPIRIT (Shestov et al 2010), and XRT (Reale et al 2009) ARs and compare them with other diagnostic techniques. In Sect.…”

Section: Introductionmentioning

confidence: 99%

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An iterative method in a probabilistic approach to the spectral inverse problem

Goryaev

Parenti

Urnov

et al. 2010

A&A

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Context. Inverse problems are of great importance in astrophysics, e.g., for deriving information about the physical characteristics of hot optically thin plasma sources from their extreme ultraviolet and X-ray spectra. Aims. We describe and test an iterative method developed within the framework of a probabilistic approach to the spectral inverse problem for determining the thermal structures of the emitting plasma. We also demonstrate applications of this method to both high resolution line spectra and broadband imaging data. Methods. Our so-called Bayesian iterative method (BIM) is an iterative procedure based on Bayes' theorem and is used to reconstruct differential emission measure (DEM) distributions. Results. To demonstrate the abilities of the BIM, we performed various numerical tests and model simulations establishing its robustness and usefulness. We then applied the BIM to observable data for several active regions (AR) previously analyzed with other DEM diagnostic techniques: both SUMER/SOHO (Landi & Feldman 2008, ApJ, 672, 674) and SPIRIT/CORONAS-F (Shestov et al. 2010, Astron. Lett., 36, 44) line spectra data, and XRT/Hinode (Reale et al. 2009, ApJ, 698, 756) broadband imaging data. The BIM calculations confirmed the main results for SUMER/SOHO data showing very good quantitative agreement between both DEMs at log T ≈ 6.5 (T is the temperature in units of Kelvin) and a slight shift for two maxima at lower temperatures with ≈30−50% difference in the DEM values for the coolest peak. For the SPIRIT data, we revised and validated AR DEM results including the inference of hot plasma in ARs with an emission measure (EM) at temperatures ≈9−15 MK comparable to the EM at ≈2−4 MK. In the case of XRT broadband data, the BIM solutions provided evidence of hot plasma at temperatures ≈4−6 MK with EM up to ∼30% as compared to that at ≈2−4 MK in a non-flaring AR on 2006 November 12.Conclusions. The BIM results show that this method is an effective tool for determining the thermal structure of emitting plasma and can be successfully used for the DEM analysis of both line spectra and broadband imaging data. The BIM calculations correlate with recent studies confirming the existence of hot plasma in solar ARs. The BIM results also indicate that the coronal plasma may have the continuous distributions predicted by the nanoflare paradigm.

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