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Multi-thermal dynamics and energetics of a coronal mass ejection in the low solar atmosphere  

Iain Hannah   Submitted: 2013-04-26 09:02

Aims: The aim of this work is to determine the multi-thermal characteristics and plasma energetics of an eruptive plasmoid and occulted flare observed by the Solar Dynamics Observatory?s Atmospheric Imaging Assembly (SDO/AIA). Methods: We study a 2010 Nov. 3 event (peaking at 12:20 UT in GOES soft X-rays) of a coronal mass ejection and occulted flare that demonstrates the morphology of a classic erupting flux rope. The high spatial and time resolution and six coronal channels of the SDO/AIA images allows the dynamics of the multi-thermal emission during the initial phases of eruption to be studied in detail. The differential emission measure is calculated, using an optimized version of a regularized inversion method, for each pixel across the six channels at different times, resulting in emission measure maps and movies in a variety of temperature ranges. Results: We find that the core of the erupting plasmoid is hot (8?11, 11?14 MK) with a similarly hot filamentary "stem" structure connecting it to the lower atmosphere, which could be interpreted as the current sheet in the flux rope model, though is wider than these models suggest. The velocity of the leading edge of the eruption is 597?664 km s-1 in the temperature range ≥3?4 MK and between 1029?1246 km s-1 for ≤2?3 MK. We estimate the density (in 11?14 MK) of the erupting core and stem during the impulsive phase to be about 3e9 cm-3, 6e9 cm-3, 9e8 cm-3 in the plasmoid core, stem, and surrounding envelope of material. This gives thermal energy estimates of 5e29 erg, 1e29 erg, and 2e30 erg. The kinetic energy for the core and envelope is slightly lower. The thermal energy of the core and current sheet grows during the eruption, suggesting continuous influx of energy presumably via reconnection. Conclusions: The combination of the optimized regularized inversion method and SDO/AIA data allows the multi-thermal characteristics (i.e. velocity, density, and thermal energies) of the plasmoid eruption to be determined.

Authors: I. G. Hannah and E. P. Kontar
Projects: SDO-AIA

Publication Status: Published by A&A (movie available in electronic version)
Last Modified: 2013-04-26 10:14
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The effect of turbulent density fluctuations on wave-particle interactions and solar flare X-ray spectrum  

Iain Hannah   Submitted: 2012-11-29 10:07

To demonstrate the effect of turbulent background density fluctuations on flare accelerated electron transport in the solar corona. Using the quasi-linear approximation, we numerically simulate the propagation of a beam of accelerated electrons from the solar corona to chromosphere, including the self-consistent response of the inhomogeneous background plasma in the form of Langmuir waves. We calculate the X-ray spectrum from these simulations using the bremsstrahlung cross-section and fit the footpoint spectrum using the collisional ''thick-target'' model, a standard approach adopted in observational studies. We find that the interaction of the Langmuir waves with the background electron density gradient shifts the waves to higher phase velocity where they then resonate with higher velocity electrons. The consequence is that some of the electrons are shifted to higher energies, producing more high energy X-rays than expected in the cases where the density inhomogeneity is not considered. We find that the level of energy gain is strongly dependent on the initial electron beam density at higher energy and the magnitude of the density gradient in the background plasma. The most significant gains are for steep (soft) spectra which had few electrons initially at higher energies. If the X-ray spectrum of the simulated footpoint emission are fitted using the standard ''thick-target'' model some simulation scenarios produce more than an order-of-magnitude over estimate of the number of electrons >50keV in the source coronal distribution.

Authors: I. G. Hannah, E. P. Kontar, H. A. S. Reid
Projects: RHESSI

Publication Status: Accepted for publication in A&A
Last Modified: 2012-12-01 23:51
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Differential Emission Measures from the Regularized Inversion of Hinode and SDO data  

Iain Hannah   Submitted: 2012-01-23 11:24

We develop and apply an enhanced regularization algorithm, used inRHESSI X-ray spectral analysis, to constrain the ill-posed inverseproblem that is determining the DEM from solar observations. Wedemonstrate this computationally fast technique applied to a range ofDEM models simulating broadband imaging data from SDO/AIA and highresolution line spectra from Hinode/EIS, as well as actual activeregion observations with Hinode/EIS and XRT. As this regularizationmethod naturally provides both vertical and horizontal (temperatureresolution) error bars we are able to test the role of uncertaintiesin the data and response functions. The regularization method is ableto successfully recover the DEM from simulated data of a variety ofmodel DEMs (single Gaussian, multiple Gaussians and CHIANTI DEMmodels). It is able to do this, at best, to over four orders ofmagnitude in DEM space but typically over two orders of magnitude frompeak emission. The combination of horizontal and vertical error barsand the regularized solution matrix allows us to easily determine theaccuracy and robustness of the regularized DEM. We find that thetypical range for the horizontal errors is DeltalogTapprox 0.1-0.5 and this is dependent on the observed signal to noise,uncertainty in the response functions as well as the source model andtemperature. With Hinode/EIS an uncertainty of 20% greatly broadensthe regularized DEMs for both Gaussian and CHIANTI models althoughinformation about the underlying DEMs is still recoverable. Whenapplied to real active region observations with Hinode/EIS and XRT theregularization method is able to recover a DEM similar to that foundvia a MCMC method but in considerably less computational time.

Download page contains links to both the preprint in arXiv as well as the codes used.

Authors: I. G. Hannah, E. P. Kontar
Projects: Hinode/EIS,Hinode/XRT,SDO-AIA,SDO-EVE

Publication Status: A&A (accepted)
Last Modified: 2012-01-24 11:24
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The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions  

Iain Hannah   Submitted: 2011-03-14 09:07

Investigate the spatial and spectral evolution of hard X-ray (HXR)emission from flare accelerated electron beams subject to collisionaltransport and wave-particle interactions in the solar atmosphere. Wenumerically follow the propagation of a power-law of acceleratedelectrons in 1D space and time with the response of the backgroundplasma in the form of Langmuir waves using the quasilinearapproximation. We find that the addition of wave-particleinteractions to collisional transport for a transient initiallyinjected electron beam flattens the spectrum of the footpoint source.The coronal source is unchanged and so the difference in the spectralindices between the coronal and footpoint sources is Δ γ >2, which is larger than expected from purely collisional transport. Asteady-state beam shows little difference between the two cases, ashas been previously found, as a transiently injected electron beam isrequired to produce significant wave growth, especially at highervelocities. With this transiently injected beam the wave-particleinteractions dominate in the corona whereas the collisional lossesdominate in the chromosphere. The shape of the spectrum is differentwith increasing electron beam density in the wave-particle interactioncase whereas with purely collisional transport only the normalisationis changed. We also find that the starting height of the sourceelectron beam above the photosphere affects the spectral index of thefootpoint when Langmuir wave growth is included. This may account forthe differing spectral indices found between double footpoints ifasymmetrical injection has occurred in the flaring loop.

Authors: I. G. Hannah and E. P. Kontar
Projects: RHESSI

Publication Status: Accepted for publication in A&A
Last Modified: 2011-03-14 23:35
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Title: Constraining the hard X-ray properties of the quiet Sun with new RHESSI observations  

Iain Hannah   Submitted: 2010-09-16 07:15

We present new RHESSI upper limits in the 3-200 keV energy range for solar hard X-ray emission in the absence of flares and active regions, i.e. the quiet Sun, using data obtained between July 2005 and April 2009. These new limits, substantially deeper than any previous ones, constrain several physical processes that could produce hard X-ray emission. These include cosmic-ray effects and the generation of axions within the solar core. The data also limit the properties of ''nanoflares'', a leading candidate to explain coronal heating. We find it unlikely for nanoflares involving nonthermal effects to heat the corona because such events would require a steep electron spectrum E-delta with index delta > 5 extending to very low energies (<1 keV), into the thermal energy range. We also use the limits to constrain the parameter space of an isothermal model and coronal thin-target emission models (powerlaw and kappa distributions)

Authors: I. G. Hannah, H. S. Hudson, G. J. Hurford, R. P. Lin
Projects: RHESSI

Publication Status: Accepted by ApJ
Last Modified: 2010-09-17 08:54
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The effect of wave-particle interactions on low energy cutoffs in solar flare electron spectra  

Iain Hannah   Submitted: 2009-11-02 19:41

Solar flare hard X-ray spectra from RHESSI are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this paper we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-particle interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than coulomb collisions. From these simulations we derive the mean electron flux spectrum, comparable to such spectra recovered from high resolution hard X-rays observations of solar flares with RHESSI. We find that a negative spectral index (i.e. a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when coulomb collisions are only considered. The inclusion of wave-particle interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step towards a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0 to 1) down to thermal energies maybe a better approximation instead of a sharp cut-off in the injected electron spectrum.

Authors: I. G. Hannah, E. P. Kontar, O. K. Sirenko
Projects: RHESSI

Publication Status: Accepted by ApJL
Last Modified: 2009-11-03 09:18
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Subject will be restored when possible  

Iain Hannah   Submitted: 2008-01-03 12:16

We present X-ray imaging and spectral analysis of all microflares the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observed between March 2002 and March 2007, a total of 25,705 events. These microflares are small flares, from low GOES C Class to below A Class (background subtracted) and are associated with active regions. They were found by searching the 6-12 keV energy range during periods when the full sensitivity of RHESSI's detectors was available (see paper I). Each microflare is automatically analyzed at the peak time of the 6-12 keV emission: the thermal source size is found by forward-fitting the complex visibilities for 4-8 keV, and the spectral parameters (temperature, emission measure, power-law index) are found by forward fitting a thermal plus non-thermal model. The combination of these parameters allows us to present the first statistical analysis of the thermal and non-thermal energy at the peak times of microflares. ################## This article is part 2 of a RHESSI microflare statistics study. Part 1 is Christe et al. 2008.

Authors: I. G. Hannah, S. Christe, S. Krucker, G. J. Hurfod, H. S. Hudson and R. P. Lin
Projects: RHESSI

Publication Status: ApJ Accepted
Last Modified: 2008-01-03 14:00
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Subject will be restored when possible  

Iain Hannah   Submitted: 2008-01-03 12:15

We present X-ray imaging and spectral analysis of all microflares the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observed between March 2002 and March 2007, a total of 25,705 events. These microflares are small flares, from low GOES C Class to below A Class (background subtracted) and are associated with active regions. They were found by searching the 6-12 keV energy range during periods when the full sensitivity of RHESSI's detectors was available (see paper I). Each microflare is automatically analyzed at the peak time of the 6-12 keV emission: the thermal source size is found by forward-fitting the complex visibilities for 4-8 keV, and the spectral parameters (temperature, emission measure, power-law index) are found by forward fitting a thermal plus non-thermal model. The combination of these parameters allows us to present the first statistical analysis of the thermal and non-thermal energy at the peak times of microflares. ################## This article is part 2 of a RHESSI microflare statistics study. Part 1 is Christe et al. 2008.

Authors: I. G. Hannah, S. Christe, S. Krucker, G. J. Hurfod, H. S. Hudson and R. P. Lin
Projects: RHESSI

Publication Status: ApJ Accepeted
Last Modified: 2008-01-03 12:15
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Subject will be restored when possible  

Iain Hannah   Submitted: 2007-12-03 18:23

Aims: Investigate particle acceleration and heating in a solar microflare. Methods: In a microflare with non-thermal emission to remarkably high energies (>50 keV), we investigate the hard X-rays with RHESSI imaging and spectroscopy and the resulting thermal emission seen in soft X-rays with Hinode/XRT and in EUV with TRACE. Results: The non-thermal footpoints observed with RHESSI spatially and temporally match bright footpoint emission in soft X-rays and EUV. There is the possibility that the non-thermal spectrum extends down to 4 keV. The hard X-ray burst clearly does not follow the expected Neupert effect, with the time integrated hard X-rays not matching the soft X-ray time profile. So although this is a simple microflare with good X-ray observation coverage it does not fit the standard flare model.

Authors: I. G. Hannah, S. Krucker, H. S. Hudson, S. Christe and R. P. Lin
Projects: RHESSI

Publication Status: Accepted by A&A Letters
Last Modified: 2007-12-04 07:38
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First limits on the 3-200 keV X-ray spectrum of the quiet Sun using RHESSI  

Iain Hannah   Submitted: 2007-02-28 18:33

We present the first results using the Reuven Ramaty High-Energy Solar Spectroscopic Imager, RHESSI, to observe solar X-ray emission not associated with active regions, sunspots or flares (the quiet Sun). Using a newly developed chopping technique (fan-beam modulation) during seven periods of offpointing between June 2005 to October 2006, we obtained upper limits over 3-200 keV for the quietest times when the GOES12 1-8A flux fell below 10-8 Wm-2. These values are smaller than previous limits in the 17-120 keV range and extend them to both lower and higher energies. The limit in 3-6 keV is consistent with a coronal temperature leq 6 MK. For quiet Sun periods when the GOES12 1-8A background flux was between 10-8 Wm-2 and 10-7 Wm-2, the RHESSI 3-6 keV flux correlates to this as a power-law, with an index of 1.08 pm 0.13. The power-law correlation for microflares has a steeper index of 1.29 pm 0.06. We also discuss the possibility of observing quiet Sun X-rays due to solar axions and use the RHESSI quiet Sun limits to estimate the axion-to-photon coupling constant for two different axion emission scenarios.

Authors: Iain G. Hannah, G. J Hurford, H. S. Hudson, R. P. Lin and K. van Bibber
Projects: RHESSI

Publication Status: Accepted by ApJL
Last Modified: 2007-03-01 11:05
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A new method of observing weak extended sources with RHESSI  

Iain Hannah   Submitted: 2007-02-07 17:09

We present a new method, fan-beam modulation, for observing weak extended x-ray sources with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). This space-based solar x-ray and gamma-ray telescope has much greater sensitivity than previous experiments in the 3-25 keV range, but is normally not well suited to detecting extended sources since their signal is not modulated by RHESSI's rotating grids. When the spacecraft is offpointed from the target source, however, the fan-beam modulation time-modulates the transmission by shadowing resulting from exploiting the finite thickness of the grids. In this paper we detail how the technique is implemented and verify its consistency with sources with clear known signals that have occurred during RHESSI offpointing: microflares and the Crab Nebula. In both cases the results are consistent with previous and complementary measurements. Preliminary work indicates that this new technique allows RHESSI to observe the integrated hard x-ray spectrum of weak extended sources on the quiet Sun. The published article appeared in Review of Scientific Instruments 2007, 78, 024501, and may be found at http://link.aip.org/link/?RSI/78/024501/

Authors: Iain G. Hannah, Gordon J. Hurford, Hugh S. Hudson and Robert P. Lin
Projects: RHESSI

Publication Status: Rev. Sci. Instrums (published 2007, 78, 024501)
Last Modified: 2007-02-08 09:38
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Abstracts by Author
Multi-thermal dynamics and energetics of a coronal mass ejection in the low solar atmosphere
The effect of turbulent density fluctuations on wave-particle interactions and solar flare X-ray spectrum
Differential Emission Measures from the Regularized Inversion of Hinode and SDO data
The spectral difference between solar flare HXR coronal and footpoint sources due to wave-particle interactions
Title: Constraining the hard X-ray properties of the quiet Sun with new RHESSI observations
The effect of wave-particle interactions on low energy cutoffs in solar flare electron spectra
Subject will be restored when possible
Subject will be restored when possible
Subject will be restored when possible
First limits on the 3-200 keV X-ray spectrum of the quiet Sun using RHESSI
A new method of observing weak extended sources with RHESSI

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