The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Eduard P Kontar - One of the best experts on this subject based on the ideXlab platform.
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probing Solar Flare accelerated electron distributions with prospective x ray polarimetry missions
Astronomy and Astrophysics, 2020Co-Authors: Natasha L S Jeffrey, P Sainthilaire, Eduard P KontarAbstract:Solar Flare electron acceleration is an extremely efficient process, but the method of acceleration is not well constrained. Two of the essential diagnostics: electron anisotropy (velocity angle to the guiding magnetic field) and the high energy cutoff (highest energy electrons produced by the acceleration conditions: mechanism, spatial extent, time), are important quantities that can help to constrain electron acceleration at the Sun but both are poorly determined. Here, using electron and X-ray transport simulations that account for both collisional and non-collisional transport processes such as turbulent scattering, and X-ray albedo, we show that X-ray polarization can be used to constrain the anisotropy of the accelerated electron distribution and the most energetic accelerated electrons together. Moreover, we show that prospective missions, e.g. CubeSat missions without imaging information, can be used alongside such simulations to determine these parameters. We conclude that a fuller understanding of Flare acceleration processes will come from missions capable of both X-ray flux and polarization spectral measurements together. Although imaging polarimetry is highly desired, we demonstrate that spectro-polarimeters without imaging can also provide strong constraints on electron anisotropy and the high energy cutoff.
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high temperature differential emission measure and altitude variations in the temperature and density of Solar Flare coronal x ray sources
Astronomy and Astrophysics, 2015Co-Authors: Natasha L S Jeffrey, Eduard P Kontar, Brian R DennisAbstract:The detailed knowledge of plasma heating and acceleration region properties presents a major observational challenge in Solar Flare physics. Using the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the high temperature differential emission measure, DEM(T), and the energy-dependent spatial structure of Solar Flare coronal sources were studied quantitatively. The altitude of the coronal X-ray source was observed to increase with energy by ~+0.2 arcsec/keV between 10 and 25 keV. Although an isothermal model can fit the thermal X-ray spectrum observed by RHESSI, such a model cannot account for the changes in altitude, and multi-thermal coronal sources are required where the temperature increases with altitude. For the first time, we show how RHESSI imaging information can be used to constrain the DEM(T) of a flaring plasma. We developed a thermal bremsstrahlung X-ray emission model with inhomogeneous temperature and density distributions to simultaneously reproduce i) DEM(T); ii) altitude as a function of energy; and iii) vertical extent of the flaring coronal source versus energy. We find that the temperature-altitude gradient in the region is ~+0.08 keV/arcsec (~1.3 MK/Mm). Similar altitude-energy trends in other Flares suggest that the majority of coronal X-ray sources are multi-thermal and have strong vertical temperature and density gradients with a broad DEM(T).
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temporal variations of x ray Solar Flare loops length corpulence position temperature plasma pressure and spectra
The Astrophysical Journal, 2013Co-Authors: Natasha L S Jeffrey, Eduard P KontarAbstract:The spatial and spectral properties of three Solar Flare coronal X-ray loops are studied before, during, and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density, and thermal pressure. We observe a decrease in the loop length, width, and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to increasing width. The volume variations are more pronounced than the position variations, often known as magnetic field line contraction. We believe this is the first dedicated study examining the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission, and thermal pressure, with the minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low β plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density. This produces increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.
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temporal variations of x ray Solar Flare loops length corpulence position temperature plasma pressure and spectra
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Natasha L S Jeffrey, Eduard P KontarAbstract:The spatial and spectral properties of three Solar Flare coronal X-ray loops are studied before, during and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density and thermal pressure. We observe a decrease in the loop length, width and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to an increasing width. The volume variations are more pronounced than the position variations, often known as magnetic line contraction. We believe this is the first dedicated study of the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission and thermal pressure, with minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low beta plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density, producing increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.
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high resolution imaging of Solar Flare ribbons and its implication on the thick target beam model
The Astrophysical Journal, 2011Co-Authors: Sam Krucker, Eduard P Kontar, A. O. Benz, H S Hudson, Natasha L S Jeffrey, Marina Battaglia, A CsillaghyAbstract:We report on high-resolution optical and hard X-ray observations of Solar Flare ribbons seen during the GOES X6.5 class white-light Flare of 2006 December 6. The data consist of imaging observations at 430 nm (the Fraunhofer G band) taken by the Hinode Solar Optical Telescope with the hard X-rays observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. The two sets of data show closely similar ribbon structures, strongly suggesting that the Flare emissions in white light and in hard X-rays have physically linked emission mechanisms. While the source structure along the ribbons is resolved at both wavelengths (length ~ 30''), only the G-band observations resolve the width of the ribbon, with values between ~05 and ~18. The unresolved hard X-ray observations reveal an even narrower ribbon in hard X-rays (the main footpoint has a width perpendicular to the ribbon of 5 × 1012 erg s–1 cm–2 provided by an electron flux of 1 × 1020 electrons s–1 cm–2 above 18 keV. This requires that the beam density of electrons above 18 keV be at least 1 × 1010 cm–3. Even if field lines converge toward the chromospheric footpoints, the required beam in the corona has too high a density to be described as a dilute tail population on top of a Maxwellian core. We discuss this issue and others associated with this extreme event, which poses serious questions to the standard thick target beam interpretation of Solar Flares.
Sam Krucker - One of the best experts on this subject based on the ideXlab platform.
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measurement of magnetic field and relativistic electrons along a Solar Flare current sheet
Nature Astronomy, 2020Co-Authors: Bin Chen, Sam Krucker, Chengcai Shen, Dale E. Gary, Katharine K Reeves, Jun Lin, Gregory D Fleishman, Fan Guo, Gelu M NitaAbstract:In the standard model of Solar Flares, a large-scale reconnection current sheet is postulated to be the central engine for powering the Flare energy release1–3 and accelerating particles4–6. However, where and how the energy release and particle acceleration occur remain unclear owing to the lack of measurements of the magnetic properties of the current sheet. Here we report the measurement of the spatially resolved magnetic field and Flare-accelerated relativistic electrons along a current-sheet feature in a Solar Flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the current sheet above the Flare loop-top, referred to as a ‘magnetic bottle’. This spatial structure agrees with theoretical predictions1,7 and numerical modelling results. A strong reconnection electric field of about 4,000 V m−1 is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. These electrons instead concentrate at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest that the loop-top magnetic bottle is probably the primary site for accelerating and confining the relativistic electrons. Observations of the X8.2 Solar Flare, which happened on 2017 September 10, could spatially resolve the distribution of the energetic electrons along the reconnection current sheet. More than 99% of them are concentrated at the bottom of the current sheet, not at the reconnection X point.
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measurement of magnetic field and relativistic electrons along a Solar Flare current sheet
arXiv: Solar and Stellar Astrophysics, 2020Co-Authors: Bin Chen, Sam Krucker, Chengcai Shen, Dale E. Gary, Katharine K Reeves, Jun Lin, Gregory D Fleishman, Fan Guo, Gelu M NitaAbstract:In the standard model of Solar Flares, a large-scale reconnection current sheet is postulated as the central engine for powering the Flare energy release and accelerating particles. However, where and how the energy release and particle acceleration occur remain unclear due to the lack of measurements for the magnetic properties of the current sheet. Here we report the measurement of spatially-resolved magnetic field and Flare-accelerated relativistic electrons along a current-sheet feature in a Solar Flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the current sheet above the Flare loop-top, referred to as a "magnetic bottle". This spatial structure agrees with theoretical predictions and numerical modeling results. A strong reconnection electric field of ~4000 V/m is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. These electrons concentrate instead at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest that the loop-top magnetic bottle is likely the primary site for accelerating and/or confining the relativistic electrons.
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Particle acceleration by a Solar Flare termination shock.
Science (New York N.Y.), 2015Co-Authors: Bin Chen, Sam Krucker, T. S. Bastian, Chengcai Shen, Dale E. Gary, Lindsay GlesenerAbstract:Solar Flares--the most powerful explosions in the Solar system--are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of Solar Flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a Solar Flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in Solar Flares.
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high resolution imaging of Solar Flare ribbons and its implication on the thick target beam model
The Astrophysical Journal, 2011Co-Authors: Sam Krucker, Eduard P Kontar, A. O. Benz, H S Hudson, Natasha L S Jeffrey, Marina Battaglia, A CsillaghyAbstract:We report on high-resolution optical and hard X-ray observations of Solar Flare ribbons seen during the GOES X6.5 class white-light Flare of 2006 December 6. The data consist of imaging observations at 430 nm (the Fraunhofer G band) taken by the Hinode Solar Optical Telescope with the hard X-rays observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. The two sets of data show closely similar ribbon structures, strongly suggesting that the Flare emissions in white light and in hard X-rays have physically linked emission mechanisms. While the source structure along the ribbons is resolved at both wavelengths (length ~ 30''), only the G-band observations resolve the width of the ribbon, with values between ~05 and ~18. The unresolved hard X-ray observations reveal an even narrower ribbon in hard X-rays (the main footpoint has a width perpendicular to the ribbon of 5 × 1012 erg s–1 cm–2 provided by an electron flux of 1 × 1020 electrons s–1 cm–2 above 18 keV. This requires that the beam density of electrons above 18 keV be at least 1 × 1010 cm–3. Even if field lines converge toward the chromospheric footpoints, the required beam in the corona has too high a density to be described as a dilute tail population on top of a Maxwellian core. We discuss this issue and others associated with this extreme event, which poses serious questions to the standard thick target beam interpretation of Solar Flares.
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measurements of the coronal acceleration region of a Solar Flare
The Astrophysical Journal, 2010Co-Authors: Sam Krucker, H S Hudson, Lindsay Glesener, R P Lin, Simon D M White, S Masuda, J P WuelserAbstract:The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph (NoRH) are used to investigate coronal hard X-ray and microwave emissions in the partially disk-occulted Solar Flare of 2007 December 31. The STEREO mission provides EUV images of the Flare site at different viewing angles, establishing a two-ribbon Flare geometry and occultation heights of the RHESSI and NoRH observations of {approx}16 Mm and {approx}25 Mm, respectively. Despite the occultation, intense hard X-ray emission up to {approx}80 keV occurs during the impulsive phase from a coronal source that is also seen in microwaves. The hard X-ray and microwave source during the impulsive phase is located {approx}6 Mm above thermal Flare loops seen later at the soft X-ray peak time, similar in location to the above-the-loop-top source in the Masuda Flare. A single non-thermal electron population with a power-law distribution (with spectral index of {approx}3.7 from {approx}16 keV up to the MeV range) radiating in both bremsstrahlung and gyrosynchrotron emission can explain the observed hard X-ray and microwave spectrum, respectively. This clearly establishes the non-thermal nature of the above-the-loop-top source. The large hard X-ray intensity requires a very large number (>5 x 10{sup 35} above 16 keV for themore » derived upper limit of the ambient density of {approx}8 x 10{sup 9} cm{sup -3}) of suprathermal electrons to be present in this above-the-loop-top source. This is of the same order of magnitude as the number of ambient thermal electrons. We show that collisional losses of these accelerated electrons would heat all ambient electrons to superhot temperatures (tens of keV) within seconds. Hence, the standard scenario, with hard X-rays produced by a beam comprising the tail of a dominant thermal core plasma, does not work. Instead, all electrons in the above-the-loop-top source seem to be accelerated, suggesting that the above-the-loop-top source is itself the electron acceleration region.« less
Kyoko Watanabe - One of the best experts on this subject based on the ideXlab platform.
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re evaluation of the neutron emission from the Solar Flare of 2005 september 7 detected by the Solar neutron telescope at sierra negra
The Astrophysical Journal, 2015Co-Authors: L X Gonzalez, Kyoko Watanabe, Y Muraki, T Sako, Y Matsubara, J F Valdesgalicia, Federico Sanchez, Yuya Nagai, S Shibata, T SakaiAbstract:The X17.0 Solar Flare of 2005 September 7 released high-energy neutrons that were detected by the Solar Neutron Telescope (SNT) at Sierra Negra, Mexico. In three separate and independent studies of this Solar neutron event, several of its unique characteristics were studied; in particular, a power-law energy spectra was estimated. In this paper, we present an alternative analysis, based on improved numerical simulations of the detector using GEANT4, and a different technique for processing the SNT data. The results indicate that the spectral index that best fits the neutron flux is around 3, in agreement with previous works. Based on the numerically calculated neutron energy deposition on the SNT, we confirm that the detected neutrons might have reached an energy of 1 GeV, which implies that 10 GeV protons were probably produced; these could not be observed at Earth, as their parent Flare was an east limb event.
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emission height and temperature distribution of white light emission observed by hinode sot from the 2012 january 27 x class Solar Flare
The Astrophysical Journal, 2013Co-Authors: Kyoko Watanabe, S Masuda, Toshifumi Shimizu, Kiyoshi Ichimoto, M OhnoAbstract:White-light emissions were observed from an X1.7 class Solar Flare on 2012 January 27, using three continuum bands (red, green, and blue) of the Solar Optical Telescope on board the Hinode satellite. This event occurred near the Solar limb, and so differences in the locations of the various emissions are consistent with differences in heights above the photosphere of the various emission sources. Under this interpretation, our observations are consistent with the white-light emissions occurring at the lowest levels of where the Ca II H emission occurs. Moreover, the centers of the source regions of the red, green, and blue wavelengths of the white-light emissions are significantly displaced from each other, suggesting that those respective emissions are emanating from progressively lower heights in the Solar atmosphere. The temperature distribution was also calculated from the white-light data, and we found the lower-layer emission to have a higher temperature. This indicates that high-energy particles penetrated down to near the photosphere, and deposited heat into the ambient lower layers of the atmosphere.
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emission height and temperature distribution of white light emission observed by hinode sot from the 2012 january 27 x class Solar Flare
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Kyoko Watanabe, S Masuda, Toshifumi Shimizu, Kiyoshi Ichimoto, M OhnoAbstract:White-light emissions were observed from an X1.7 class Solar Flare on 27 January 2012, using three continuum bands (red, green, and blue) of the Solar Optical Telescope (SOT) onboard the Hinode satellite. This event occurred near the Solar limb, and so differences in locations of the various emissions are consistent with differences in heights above the photosphere of the various emission sources. Under this interpretation, our observations are consistent with the white-light emissions occurring at the lowest levels of where the Ca II H emission occurs. Moreover, the centers of the source regions of the red, green, and blue wavelengths of the white-light emissions are significantly displaced from each other, suggesting that those respective emissions are emanating from progressively lower heights in the Solar atmosphere. The temperature distribution was also calculated from the white-light data, and we found the lower-layer emission to have a higher temperature. This indicates that high-energy particles penetrated down to near the photosphere, and deposited heat into the ambient lower layers of the atmosphere.
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physics of ion acceleration in the Solar Flare on 2005 september 7 determines γ ray and neutron production
Advances in Space Research, 2009Co-Authors: Kyoko Watanabe, R P Lin, S Krucker, R J Murphy, G H Share, M J Harris, M Gros, Y Muraki, T Sako, Y MatsubaraAbstract:Abstract Relativistic neutrons were observed by the neutron monitors at Mt. Chacaltaya and Mexico City and by the Solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in association with an X17.0 Flare on 2005 September 7. The neutron signal continued for more than 20 min with high statistical significance. Intense emissions of γ -rays were also registered by INTEGRAL , and during the decay phase by RHESSI . We analyzed these data using the Solar-Flare magnetic-loop transport and interaction model of Hua et al. [Hua, X.-M., Kozlovsky, B., Lingenfelter, R.E. et al. Angular and energy-dependent neutron emission from Solar Flare magnetic loops, Astrophys. J. Suppl. Ser. 140, 563–579, 2002], and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch-angle scattering parameters. These results indicate that Solar neutrons were produced at the same time as the γ -ray line emission and that ions were continuously accelerated at the emission site.
A G Kosovichev - One of the best experts on this subject based on the ideXlab platform.
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dynamics of electric currents magnetic field topology and helioseismic response of a Solar Flare
The Astrophysical Journal, 2015Co-Authors: I N Sharykin, A G KosovichevAbstract:The Solar Flare on 2011 July 30 was of a modest X-ray class (M9.3), but it made a strong photospheric impact and produced a ?sunquake,? which was observed with the Helioseismic and Magnetic Imager on board NASA's Solar Dynamics Observatory. In addition to the helioseismic waves, the Flare caused a large expanding area of white-light emission and was accompanied by the rapid formation of a sunspot structure in the Flare region. The Flare produced hard X-ray (HXR) emission less then 300 keV and no coronal mass ejection (CME). The absence of CME rules out magnetic rope eruption as a mechanism of helioseismic waves. The sunquake impact does not coincide with the strongest HXR source, which contradicts the standard beam-driven mechanism of sunquake generation. We discuss the connectivity of the Flare energy release with the electric currents dynamics and show the potential importance of high-speed plasma flows in the lower Solar atmosphere during the Flare energy release.
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dynamics of electric currents magnetic field topology and helioseismic response of a Solar Flare
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: I N Sharykin, A G KosovichevAbstract:The Solar Flare on July 30, 2011 was of a modest X-ray class (M9.3), but it made a strong photospheric impact and produced a "sunquake," observed with the Helioseismic and Magnetic Imager (HMI) on NASA's Solar Dynamics Observatory (SDO). In addition to the helioseismic waves (also observed with the SDO/AIA instrument), the Flare caused a large expanding area of white-light emission and was accompanied by substantial restructuring of magnetic fields, leading to the rapid formation of a sunspot structure in the Flare region. The Flare produced no significant hard X-ray emission and no coronal mass ejection. This indicates that the Flare energy release was mostly confined to the lower atmosphere. The absence of significant coronal mass ejection rules out magnetic rope eruption as a mechanism of helioseismic waves. We discuss the connectivity of the Flare energy release with the electric currents dynamics and show the potential importance of high-speed plasma flows in the lower Solar atmosphere during the Flare energy release.
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helioseismic response to the x2 2 Solar Flare of 2011 february 15
The Astrophysical Journal, 2011Co-Authors: A G KosovichevAbstract:The X2.2-class Solar Flare of 2011 February 15 produced a powerful "sunquake" event, representing a helioseismic response to the Flare impact in the Solar photosphere, which was observed with the Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO). The impulsively excited acoustic waves formed a compact wave packet traveling through the Solar interior and appearing on the surface as expanding wave ripples. The initial Flare impacts were observed in the form of compact and rapid variations of the Doppler velocity, line-of-sight magnetic field, and continuum intensity. These variations formed a typical two-ribbon Flare structure, and are believed to be associated with thermal and hydrodynamic effects of high-energy particles heating the lower atmosphere. The analysis of the SDO/HMI and X-ray data from RHESSI shows that the helioseismic waves were initiated by the photospheric impact in the early impulsive phase, observed prior to the hard X-ray (50-100 keV) impulse, and were probably associated with atmospheric heating by relatively low-energy electrons (~6-50 keV) and heat flux transport. The impact caused a short motion in the sunspot penumbra prior to the appearance of the helioseismic wave. It is found that the helioseismic wave front traveling through a sunspot had a lower amplitude and was significantly delayed relative to the front traveling outside the spot. These observations open new perspectives for studying the Flare photospheric impacts and for using the Flare-excited waves for sunspot seismology.
Natasha L S Jeffrey - One of the best experts on this subject based on the ideXlab platform.
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probing Solar Flare accelerated electron distributions with prospective x ray polarimetry missions
Astronomy and Astrophysics, 2020Co-Authors: Natasha L S Jeffrey, P Sainthilaire, Eduard P KontarAbstract:Solar Flare electron acceleration is an extremely efficient process, but the method of acceleration is not well constrained. Two of the essential diagnostics: electron anisotropy (velocity angle to the guiding magnetic field) and the high energy cutoff (highest energy electrons produced by the acceleration conditions: mechanism, spatial extent, time), are important quantities that can help to constrain electron acceleration at the Sun but both are poorly determined. Here, using electron and X-ray transport simulations that account for both collisional and non-collisional transport processes such as turbulent scattering, and X-ray albedo, we show that X-ray polarization can be used to constrain the anisotropy of the accelerated electron distribution and the most energetic accelerated electrons together. Moreover, we show that prospective missions, e.g. CubeSat missions without imaging information, can be used alongside such simulations to determine these parameters. We conclude that a fuller understanding of Flare acceleration processes will come from missions capable of both X-ray flux and polarization spectral measurements together. Although imaging polarimetry is highly desired, we demonstrate that spectro-polarimeters without imaging can also provide strong constraints on electron anisotropy and the high energy cutoff.
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high temperature differential emission measure and altitude variations in the temperature and density of Solar Flare coronal x ray sources
Astronomy and Astrophysics, 2015Co-Authors: Natasha L S Jeffrey, Eduard P Kontar, Brian R DennisAbstract:The detailed knowledge of plasma heating and acceleration region properties presents a major observational challenge in Solar Flare physics. Using the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the high temperature differential emission measure, DEM(T), and the energy-dependent spatial structure of Solar Flare coronal sources were studied quantitatively. The altitude of the coronal X-ray source was observed to increase with energy by ~+0.2 arcsec/keV between 10 and 25 keV. Although an isothermal model can fit the thermal X-ray spectrum observed by RHESSI, such a model cannot account for the changes in altitude, and multi-thermal coronal sources are required where the temperature increases with altitude. For the first time, we show how RHESSI imaging information can be used to constrain the DEM(T) of a flaring plasma. We developed a thermal bremsstrahlung X-ray emission model with inhomogeneous temperature and density distributions to simultaneously reproduce i) DEM(T); ii) altitude as a function of energy; and iii) vertical extent of the flaring coronal source versus energy. We find that the temperature-altitude gradient in the region is ~+0.08 keV/arcsec (~1.3 MK/Mm). Similar altitude-energy trends in other Flares suggest that the majority of coronal X-ray sources are multi-thermal and have strong vertical temperature and density gradients with a broad DEM(T).
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temporal variations of x ray Solar Flare loops length corpulence position temperature plasma pressure and spectra
The Astrophysical Journal, 2013Co-Authors: Natasha L S Jeffrey, Eduard P KontarAbstract:The spatial and spectral properties of three Solar Flare coronal X-ray loops are studied before, during, and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density, and thermal pressure. We observe a decrease in the loop length, width, and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to increasing width. The volume variations are more pronounced than the position variations, often known as magnetic field line contraction. We believe this is the first dedicated study examining the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission, and thermal pressure, with the minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low β plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density. This produces increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.
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temporal variations of x ray Solar Flare loops length corpulence position temperature plasma pressure and spectra
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Natasha L S Jeffrey, Eduard P KontarAbstract:The spatial and spectral properties of three Solar Flare coronal X-ray loops are studied before, during and after the peak X-ray emission. Using observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we deduce the temporal changes in emitting X-ray length, corpulence, volume, position, number density and thermal pressure. We observe a decrease in the loop length, width and volume before the X-ray peak, and an increasing number density and thermal pressure. After the X-ray peak, volume increases and loop corpulence grows due to an increasing width. The volume variations are more pronounced than the position variations, often known as magnetic line contraction. We believe this is the first dedicated study of the temporal evolution of X-ray loop lengths and widths. Collectively, the observations also show for the first time three temporal phases given by peaks in temperature, X-ray emission and thermal pressure, with minimum volume coinciding with the X-ray peak. Although the volume of the flaring plasma decreases before the peak in X-ray emission, the relationship between temperature and volume does not support simple compressive heating in a collapsing magnetic trap model. Within a low beta plasma, shrinking loop widths perpendicular to the guiding field can be explained by squeezing the magnetic field threading the region. Plasma heating leads to chromospheric evaporation and growing number density, producing increasing thermal pressure and decreasing loop lengths as electrons interact at shorter distances and we believe after the X-ray peak, the increasing loop corpulence.
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high resolution imaging of Solar Flare ribbons and its implication on the thick target beam model
The Astrophysical Journal, 2011Co-Authors: Sam Krucker, Eduard P Kontar, A. O. Benz, H S Hudson, Natasha L S Jeffrey, Marina Battaglia, A CsillaghyAbstract:We report on high-resolution optical and hard X-ray observations of Solar Flare ribbons seen during the GOES X6.5 class white-light Flare of 2006 December 6. The data consist of imaging observations at 430 nm (the Fraunhofer G band) taken by the Hinode Solar Optical Telescope with the hard X-rays observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager. The two sets of data show closely similar ribbon structures, strongly suggesting that the Flare emissions in white light and in hard X-rays have physically linked emission mechanisms. While the source structure along the ribbons is resolved at both wavelengths (length ~ 30''), only the G-band observations resolve the width of the ribbon, with values between ~05 and ~18. The unresolved hard X-ray observations reveal an even narrower ribbon in hard X-rays (the main footpoint has a width perpendicular to the ribbon of 5 × 1012 erg s–1 cm–2 provided by an electron flux of 1 × 1020 electrons s–1 cm–2 above 18 keV. This requires that the beam density of electrons above 18 keV be at least 1 × 1010 cm–3. Even if field lines converge toward the chromospheric footpoints, the required beam in the corona has too high a density to be described as a dilute tail population on top of a Maxwellian core. We discuss this issue and others associated with this extreme event, which poses serious questions to the standard thick target beam interpretation of Solar Flares.
