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Broadband microwave sub-second pulsations in an expanding coronal loop of the 2011 August 10 flare  

Hana Meszarosova   Submitted: 2016-09-15 04:57

We studied the characteristic physical properties and behavior of broadband microwave sub-second pulsations observed in an expanding coronal loop during the GOES C2.4 solar flare on 2011 August 10. We found sub-second pulsations and other different burst groups in the complex radio spectrum. The broadband (bandwidth about 1 GHz) sub-second pulsations (temporal period range 0.07-1.49 s, no characteristic dominant period) lasted 70 s in the frequency range 4-7 GHz. These pulsations were not correlated at their individual frequencies, had no measurable frequency drift, and zero polarization. In these pulsations, we found the signatures of fast sausage magnetoacoustic waves with the characteristic periods of 0.7 and 2 s. The other radio bursts showed their characteristic frequency drifts in the range of -262-520 MHz/s. They helped us to derive average values of 20-80 G for the coronal magnetic field strength in the place of radio emission. It was revealed that the microwave event belongs to an expanding coronal loop with twisted sub-structures observed in the 131, 94, and 193 Å SDO/AIA channels. Their slit-time diagrams were compared with the location of the radio source at 5.7 GHz to realize that the EUV intensity of the expanding loop increased just before the radio source triggering. We reveal two EUV bidirectional flows that are linked with the start time of the loop expansion. Their positions were close to the radio source and propagated with velocities within a range of 30-117 km s-1. We demonstrate that periodic regime of the electron acceleration in a model of the quasi-periodic magnetic reconnection might be able to explain physical properties and behavior of the sub-second pulsations. The depolarization process of the microwave emission might be caused by a plasma turbulence in the radio source. Finally, the observed EUV flows might be linked with reconnection outflows.

Authors: Meszarosova, H., Rybak, J., Kashapova, L., Gömöry, P., Tokhchukova, S., Myshyakov, I.
Projects: SDO-AIA,SDO-HMI

Publication Status: A&A (in press)
Last Modified: 2016-09-17 07:05
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MAGNETOACOUSTIC WAVES PROPAGATING ALONG A DENSE SLAB AND HARRIS CURRENT SHEET AND THEIR WAVELET SPECTRA  

Hana Meszarosova   Submitted: 2014-05-28 08:15

Currently, there is a common endeavor to detect magnetoacoustic waves in solar flares. This paper contributes to this topic using an approach of numerical simulations. We studied a spatial and temporal evolution of impulsively generated fast and slow magnetoacoustic waves propagating along the dense slab and Harris current sheet using two-dimensional magnetohydrodynamic numerical models. Wave signals computed in numerical models were used for computations of the temporal and spatial wavelet spectra for their possible comparison with those obtained from observations. It is shown that these wavelet spectra allow us to estimate basic parameters of waveguides and perturbations. It was found that the wavelet spectra of waves in the dense slab and current sheet differ in additional wavelet components that appear in association with the main tadpole structure. These additional components are new details in the wavelet spectrum of the signal. While in the dense slab this additional component is always delayed after the tadpole head, in the current sheet this component always precedes the tadpole head. It could help distinguish a type of the waveguide in observed data. We present a technique based on wavelets that separates wave structures according to their spatial scales. This technique shows not only how to separate the magnetoacoustic waves and waveguide structure in observed data, where the waveguide structure is not known, but also how propagating magnetoacoustic waves would appear in observations with limited spatial resolutions. The possibilities detecting these waves in observed data are mentioned.

Authors: Meszarosova, H., Karlický, M., Jelinek, P., Rybak, J.
Projects: None

Publication Status: published in The Astrophysical Journal, 788:44, 2014
Last Modified: 2014-05-28 10:14
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Radio fiber bursts and fast magnetoacoustic wave trains  

Hana Meszarosova   Submitted: 2013-03-25 09:40

We present a model for dm-fiber bursts that is based on assuming fast sausage magnetoacoustic wave trains that propagate along a dense vertical filament or current sheet. Eight groups of dm-fiber bursts that were observed during solar flares were selected and analyzed by the wavelet analysis method. To model these fiber bursts we built a semi-empirical model. We also did magnetohydrodynamic simulations of a propagation of the magnetoacoustic wave train in a vertical and gravitationally stratified current sheet. In the wavelet spectra of the fiber bursts computed at different radio frequencies we found the wavelet tadpoles, whose head maxima have the same frequency drift as the drift of fiber bursts. It indicates that the drift of these fiber bursts can be explained by the propagating fast sausage magnetoacoustic wave train. Using new semi-empirical and magnetohydrodynamic models with a simple radio emission model we generated the artificial radio spectra of the fiber bursts, which are similar to the observed ones.

Authors: Karlický, M., Meszarosova, H., Jelinek, P.
Projects: None

Publication Status: A&A (2013) 550, A1 (published)
Last Modified: 2013-03-26 10:36
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Fast Magnetoacoustic Waves in a Fan Structure Above a Coronal Magnetic Null Point  

Hana Meszarosova   Submitted: 2013-03-25 09:29

We analyze the 26 November 2005 solar radio event observed interferometrically at frequencies of 244 and 611 MHz by the Giant Metrewave Radio Telescope (GMRT) in Pune, India. These observations are used to make interferometric maps of the event at both frequencies with the time cadence of 1 s from 06:50 to 07:12 UT. These maps reveal several radio sources. The light curves of these sources show that only two sources at 244 MHz and 611 MHz are well correlated in time. The EUV flare is more localized with flare loops located rather away from the radio sources. Using SoHO/MDI observations and potential magnetic field extrapolation we demonstrate that both the correlated sources are located in the fan structure of magnetic field lines starting from a coronal magnetic null point. Wavelet analysis of the light curves of the radio sources detects tadpoles with periods in the range P = 10 ? 83 s. These wavelet tadpoles indicate the presence of fast magnetoacoustic waves that propagate in the fan structure of the coronal magnetic null point. We estimate the plasma parameters in the studied radio sources and find them consistent with the presented scenario involving the coronal magnetic null point.

Authors: Meszarosova, H., Dudik, J., Karlický, M., Madsen, F.R.H., Sawant, H.S.
Projects: Other

Publication Status: Solar Phys (2013) 283:473?488 (published)
Last Modified: 2013-03-26 10:36
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"Drifting tadpoles" in wavelet spectra of decimetric radio emission of fiber bursts  

Hana Meszarosova   Submitted: 2009-08-05 03:30

For the first time, we have found drifting tadpoles in the wavelet spectra of the decimetric radio emission associated with the fiber bursts observed in July 11, 2005. These tadpoles were detected at all radio frequencies in the 1602-1780 MHz frequency range. The characteristic period of the wavelet tadpole patterns was found to be 81.4 s and the frequency drift of the tadpole heads is -6.8 MHz s-1 . These tadpoles are interpreted as a signature of the magnetoacoustic wave train moving along a dense flare waveguide and their frequency drift as a motion of the wave train modulating the radio emission produced by the plasma emission mechanism. Using the Aschwanden density model of the solar atmosphere, only low values of the Alfvén speed and the magnetic field strength in the loop guiding this wave train were derived which indicates a neutral current sheet as the guiding structure. The present analysis supports the model of fiber bursts based on whistler waves.

Authors: Meszarosova, H., Karlický, M., Rybak, J., Jiricka, K.
Projects: None

Publication Status: A&A 502, L13 (2009)
Last Modified: 2009-08-05 14:22
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TADPOLES IN WAVELET SPECTRA OF A SOLAR DECIMETRIC RADIO BURST  

Hana Meszarosova   Submitted: 2009-05-12 04:26

In the solar decimetric type IV radio event observed on 2001 June 13, we have found wavelet tadpole patterns for the first time. They were detected simultaneously at all radio frequencies in the 1.1?4.5 GHz frequency range. The characteristic period of the wavelet tadpole patterns was found to be 70.9 s. The parameters of the tadpoles on different frequencies are very similar and the correlations between individual radio fluxes are high. These tadpoles are interpreted as a signature of the magnetoacoustic wave train moving along the flare loop through the radio source and modulating its gyrosynchrotron emission.

Authors: Meszarosova, H., Karlický, M., Rybak, J., Jiricka, K.
Projects: None

Publication Status: ApJ 697 (2009), L108
Last Modified: 2009-05-12 07:28
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Abstracts by Author
Broadband microwave sub-second pulsations in an expanding coronal loop of the 2011 August 10 flare
MAGNETOACOUSTIC WAVES PROPAGATING ALONG A DENSE SLAB AND HARRIS CURRENT SHEET AND THEIR WAVELET SPECTRA
Radio fiber bursts and fast magnetoacoustic wave trains
Fast Magnetoacoustic Waves in a Fan Structure Above a Coronal Magnetic Null Point
?Drifting tadpoles? in wavelet spectra of decimetric radio emission of fiber bursts
TADPOLES IN WAVELET SPECTRA OF A SOLAR DECIMETRIC RADIO BURST

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