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Plasma dynamics in the flaring loop observed by RHESSI  

Tomasz Mrozek   Submitted: 2022-01-07 03:47

Hard X-rays (HXRs) contain the most direct information about the non-thermal electron population in solar flares. The approximation of the HXR emission mechanism (bremsstrahlung), known as the thick-target model, is well developed. It allows one to diagnose the physical conditions within a flaring structure. The thick-target model predicts that in flare foot points, we should observe lowering of HXR sources' altitude with increasing energy. The foot point of HXR sources result from the direct interaction of non-thermal electron beams with plasma in the lower part of the solar atmosphere, where the density increases rapidly. Therefore, we can estimate the plasma density distribution along the non-thermal electron beam directly from the observations of the altitude-energy relation obtained for the HXR foot point sources. However, the relation is not only density-dependent. Its shape is also determined by the power-law distribution of non-thermal electrons. Additionally, during the impulsive phase, the plasma density and a degree of ionisation within foot points may change dramatically due to heating and chromospheric evaporation. For this reason, the interpretation of observed HXR foot point sources' altitudes is not straightforward and needs detailed numerical modelling of the electron precipitation process. We present the results of numerical modelling of one well-observed solar flare. We used HXR observations obtained by RHESSI. The numerical model was calculated using the hydrodynamic 1D model with an application of the Fokker-Planck formalism for non-thermal beam precipitation. HXR data were used to trace chromospheric density changes during a non-thermal emission burst, in detail. We have found that the amount of mass that evaporated from the chromosphere is in the range of 2.7x1013-4.0x1014{g}. This is in good agreement with the ranges obtained from hydrodynamical modelling of a flaring loop (2.3x1013-3.3x1013{g}), and from an analysis of observed emission measure in the loop top (3.9x1013-5.3x1013{g}). Additionally, we used specific scaling laws which gave another estimation of the evaporated mass around 2x1014{g}. Consistency between the obtained values shows that HXR images may provide an important constraint for models - a mass of plasma that evaporated due to a non-thermal electron beam depositing energy in the chromosphere. High-energy, non-thermal sources' (above 20 keV in this case) positions fit the column density changes obtained from the hydrodynamical model perfectly. Density changes seem to be less affected by the electrons' spectral index. The obtained results significantly improve our understanding of non-thermal electron beam precipitation and allow us to refine the energy balance in solar flare foot points during the impulsive phase.

Authors: Mrozek, T., Falewicz, R., Kołomański, S., Litwicka, M.
Projects: RHESSI

Publication Status: A&A accepted
Last Modified: 2022-01-07 09:36
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Catalog of Solar Failed Eruptions and Other Dynamic Features Registered by SDO/AIA  

Tomasz Mrozek   Submitted: 2021-01-17 03:09

In this paper we present our attempt to constrain the first catalog of solar failed eruptions. We used our automatic algorithm that is able to search for dynamic features in the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) database. We ran the algorithm on the entire SDO/AIA 171 data set. For the time interval from 2010 May 20 to 2019 May 20 we found 12,192 dynamic events. The dynamic events were classified in three groups. Apart from failed eruptions (1214) we obtained a large group of successful eruptions (2064) and other dynamic events (8914). The automatic algorithm enabled us to collect several observational characteristics, which are provided in files that may be downloaded from the catalog web page. In this paper we present the methodology of catalog preparation and preliminary results of the statistical analysis of observational characteristics obtained by the automatic algorithm.

Authors: Mrozek, Tomasz; Kołomański, Sylwester; Stęślicki, Marek; Gronkiewicz, Dominik
Projects: SDO-AIA

Publication Status: ApJSS: accepted
Last Modified: 2021-01-17 12:58
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The non-Fourier image reconstruction method for the STIX instrument  

Tomasz Mrozek   Submitted: 2021-01-17 03:07

In this work we aimed to develop the image reconstruction algorithm without any analytical simplifications and restrictions. In our method we abandon Fourier's approach to image reconstruction, and instead use the number of counts recorded in each detector pixel, and then reconstruct each image using a classical Richardson-Lucy algorithm. Among similar works performed in the past, our approach is based, for the first time, on the real geometry of STIX. We made a preliminary analysis of expected differences in STIX imaging which may occur due to usage of slightly different geometries. The other difference is that we use single-pixel-response maps. Namely, knowing the instrument geometry we are able to calculate the detector response for point sources covering entire the solar disc. Next, we iteratively combine them with varying weights until the best match between reconstructed and observed detector responses is achieved. Preliminary tests revealed that the developed algorithm reproduces high quality images. The algorithm is moderately fast, but the result comparable to CLEAN algorithm is obtained within 20-50 iteration steps which takes less than 2 seconds on typical portable computer configuration. The location, size and intensity of reconstructed sources are very close to simulated ones. Therefore the algorithm is very well suited for the detailed photometry of the solar HXR sources. Moreover, its simplicity allows to improve photon transmission calculation in case of any grids uncertainties measured after the launch.

Authors: Siarkowski, Marek; Mrozek, Tomasz; Sylwester, Janusz; Litwicka, Michalina; Dąbek, Magdalena
Projects: SO/STIX

Publication Status: Open Astronomy: accepted
Last Modified: 2021-01-17 12:58
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Solar Microflares Observed by SphinX and RHESSI  

Tomasz Mrozek   Submitted: 2018-07-12 02:19

In 2009 the Russian Complex Orbital Observations Near-Earth of Activity of the Sun (CORONAS-Photon) satellite was launched carrying the Polish Solar PHotometer In X-rays (SphinX). The SphinX was the most sensitive in the spectral range 1.2-15 keV thus an excellent opportunity appeared for comparison with low-energy end of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectra. Common spectral measurements with these instruments cover the range where most of the flare energy is accumulated. We have chosen four consecutive small solar events observed on 4 July 2009 at 13:43 UT, 13:48 UT, 13:52 UT, and 13:55 UT, ( RHESSI flare peak times) and used them for comparison of the data and results from both instruments. Moreover, we included Geostationary Operational Environmental Satellite (GOES) records in our analysis. In practice the range of comparison performed for SphinX and RHESSI is limited roughly to 3-6 keV. RHESSI's fluxes measured with a use of one, four, and nine detectors in the 3-4 keV energy band agree with SphinX measurements. However, we observed that SphinX spectral irradiances are three times higher than RHESSI in the 4-6 keV energy band. This effect contributes to the difference in obtained emission measures, but the derived temperatures of plasma components are similar. RHESSI spectra were fitted using a model with two thermal components. We have found that RHESSI hot component is in agreement with GOES and RHESSI hotter component fits well with the SphinX flaring component.Moreover, we calculated the so-called thermodynamic measure and the total thermal energy content in the four microflares studied. The results obtained show that SphinX is a very sensitive complementary observatory for RHESSI and GOES.

Authors: Tomasz Mrozek, Szymon Gburek, Marek Siarkowski, Barbara Sylwester, Janusz Sylwester, Anna Kepa, Magdalena Gryciuk

Publication Status: published
Last Modified: 2018-07-17 10:51
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Coronal Mass Ejections Associated with Slow Long Duration Flares  

Tomasz Mrozek   Submitted: 2013-02-28 02:11

It is well known that there is temporal relationship between coronal mass ejections (CMEs) and associated flares. The duration of the acceleration phase is related to the duration of the rise phase of a flare. We investigate CMEs associated with slow long duration events (LDEs), i.e. flares with the long rising phase. We determined the relationships between flares and CMEs and analyzed the CME kinematics in detail. The parameters of the flares (GOES flux, duration of the rising phase) show strong correlations with the CME parameters (velocity, acceleration during main acceleration phase and duration of the CME acceleration phase). These correlations confirm the strong relation between slow LDEs and CMEs. We also analyzed the relation between the parameters of the CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a duration of the acceleration phase, and a height of a CME at the end of the acceleration phase. The CMEs associated with the slow LDEs are characterized by high velocity during the propagation phase, with the median equal 1423 km s-1. In half of the analyzed cases, the main acceleration was low (a<300 m s-2), which suggests that the high velocity is caused by the prolongated acceleration phase (the median for the duration of the acceleration phase is equal 90 minutes). The CMEs were accelerated up to several solar radii (with the median 7 Rsun), which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may potentially precede extremely strong geomagnetic storms. The analysis of slow LDEs and associated CMEs may give important information for developing more accurate space weather forecasts, especially for extreme events.

Authors: U. Bak-Steslicka, S. Kolomanski, T. Mrozek
Projects: GOES X-rays ,Other,SoHO-EIT,SoHO-LASCO,Yohkoh-SXT

Publication Status: Solar Physics, accepted
Last Modified: 2013-02-28 12:33
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Extreme-ultraviolet and hard X-ray signatures of electron acceleration during the failed eruption of a filament  

Tomasz Mrozek   Submitted: 2012-11-28 06:47

Aims. We search for extreme-ultraviolet (EUV) brightenings in TRACE 171 Å images and hard X-ray (HXR) bursts observed during failed eruptions. We expect that if an eruption is confined by interaction with overlaying magnetic structures, we should observe effects caused by reconnection between magnetic structures and acceleration of particles. Methods. We used TRACE observations of three well-observed failed eruptions. A semi-automated method was used to search for abrupt brightness changes in the TRACE field of view. The EUV images were compared to the HXR spatial distribution reconstructed from YOHKOH/HXT and RHESSI data. The EUV light curves of a selected area were compared to height profiles of eruption, HXR emission, and the HXR photon spectral index of a power-law fit to the HXR data. Results. We have found that EUV brightenings are closely relatedto the eruption velocity decrease, to HXR bursts, and to episodes of hardening of the HXR spectra. The EUV-brightened areas are observed far from the flaring structure, in footpoints of large systems of loops observed 30?60 min after the maximum of a flare. These are not ?post-flare? loops, which are also observed, but at significantly lower heights. The high-lying systems of loops are observed at heights equal to the height at which the eruption was observed to stop. We observed only one HXR source that was spatially correlated with EUV brightening. For other EUV-brightened areas we estimated the expected brightness of HXR sources. Conclusions. We find that EUV brightenings are produced by interaction between the erupting structure with overlaying loops. The interaction is strong enough to heat the system of high loops. These loops cool and are visible in the EUV range about 30?60 min later. The estimated brightness of HXR sources associated with EUV brightenings shows that they are too weak to be detected with present instruments. However, next-generation instruments will have sufficient dynamic range and sensitivity to enable such observations.

Authors: A. Netzel, T. Mrozek, S. Kołomański, and S. Gburek
Projects: None

Publication Status: A&A 548, A89
Last Modified: 2012-11-28 09:41
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Failed Eruption of a Filament as a Driver for Vertical Oscillations of Coronal Loops  

Tomasz Mrozek   Submitted: 2011-05-12 08:28

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.

Authors: T. Mrozek
Projects: TRACE

Publication Status: Solar Physics, accepted
Last Modified: 2011-05-12 15:06
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Abstracts by Author
Plasma dynamics in the flaring loop observed by RHESSI
Catalog of Solar Failed Eruptions and Other Dynamic Features Registered by SDO/AIA
The non-Fourier image reconstruction method for the STIX instrument
Solar Microflares Observed by SphinX and RHESSI
Coronal Mass Ejections Associated with Slow Long Duration Flares
Extreme-ultraviolet and hard X-ray signatures of electron acceleration during the failed eruption of a filament
Failed Eruption of a Filament as a Driver for Vertical Oscillations of Coronal Loops

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