Perturbations of gyrosynchrotron emission polarization from solar flares by sausage modes: forward modeling

Reznikova, Veronika; Doorsselaere, Tom Van; Kuznetsov, A. A.

doi:10.1051/0004-6361/201424548

Cited by 15 publications

(16 citation statements)

References 33 publications

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“…The sausage oscillations within short periods (<60 s) are often decayless or weakly damping when the cutoff condition and those within long periods (>60 s) are substantially compressible and transverse (Gruszecki et al 2012;Vasheghani Farahani et al 2014;Tian et al 2016). Moreover, they could produce density variation, which can easily modulate the periodic oscillations in microwave emission (Rosenberg 1970;Aschwanden 2005;Antolin & Van Doorsselaere 2013;Reznikova et al 2015). The loop oscillations here are incompressible, damping, and no corresponding intensity fluctuations are detected in EUV and microwave emissions.…”

Section: Mhd Wavesmentioning

confidence: 98%

Doppler Shift Oscillations from a Hot Line Observed by IRIS

Ning

et al. 2017

ApJ

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We present a detailed investigation of the Doppler shift oscillations in a hot loop during an M7.1 flare on 2014 October 27 observed by the Interface Region Imaging Spectrograph. The periodic oscillations are observed in the Doppler shift of Fe XXI 1354.09Å (logT ∼7.05), and the dominant period is about 3.1 minutes. However, such 3.1-min oscillations are not found in the line-integrated intensity of Fe XXI 1354.09Å, AIA EUV fluxes, or microwave emissions. SDO/AIA and Hinode/XRT imaging observations indicate that the Doppler shift oscillations locate at the hot loop-top region (≥11 MK). Moreover, the differential emission measure (DEM) results show that the temperature is increasing rapidly when the Doppler shift oscillates, but the number density does not exhibit the corresponding increases nor oscillations, implying that the flare loop is likely to oscillate in an incompressible mode. All these facts suggest that the Doppler shift oscillations at the shorter period are most likely the standing kink oscillations in a flare loop. Meanwhile, a longer period of about 10 minutes is identified in the time series of Doppler shift and line-integrated intensity, GOES SXR fluxes and AIA EUV light curves, indicating the periodic energy release in this flare, which may be caused by a slow mode wave.

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Section: Mhd Wavesmentioning

confidence: 98%

Doppler Shift Oscillations from a Hot Line Observed by IRIS

Ning

et al. 2017

ApJ

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“…The codes calculate the emission characteristics by numerical integration of the radiative transfer equations for the ordinary and extraordinary electromagnetic modes while taking into account the possible mode-coupling effects, i.e., interaction between the modes in the regions of transverse magnetic field (Cohen, 1960;Zheleznyakov and Zlotnik, 1964). This approach is sufficient to reproduce accurately the emission intensity in both the quasi-longitudinal and quasi-transverse (with respect to the magnetic field) propagation regimes as well as the circular polarization in the quasi-longitudinal regime (Nita et al, 2015), although simulating the polarization in the regions with θ ≃ 90 • may require considering the full set of Stokes parameters (see the upcoming paper of Reznikova, Van Doorsselaere, and Kuznetsov (2015)). Only the emission and absorption processes inside the curved magnetic loop are considered, i.e., the emission outside the loop is assumed to propagate like in vacuum.…”

Section: Electron Parametersmentioning

confidence: 99%

Simulations of Gyrosynchrotron Microwave Emission from an Oscillating 3D Magnetic Loop

2015

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Radio observations of solar flares often reveal various periodic or quasi-periodic oscillations. Most likely, these oscillations are caused by magnetohydrodynamic (MHD) oscillations of flaring loops which modulate the emission. Interpretation of the observations requires comparing them with simulations. We simulate the gyrosynchrotron radio emission from a semi-circular (toroidalshaped) magnetic loop containing sausage-mode MHD oscillations. The aim is to detect the observable signatures specific to the considered MHD mode and to study their dependence on the various source parameters. The MHD waves are simulated using a linear three-dimensional model of a magnetized plasma cylinder; both standing and propagating waves are considered. The curved loop is formed by replicating the MHD solutions along the plasma cylinder and bending the cylinder; this model allows us to study the effect of varying the viewing angle along the loop. The radio emission is simulated using a three-dimensional model and its spatial and temporal variations are analyzed. We consider several loop orientations and different parameters of the magnetic field, plasma, and energetic electrons in the loop. In the model with low plasma density, the intensity oscillations at all frequencies are synchronous (with the exception of a narrow spectral region below the spectral peak). In the model with high plasma density, the emission at low frequencies (where the Razin effect is important) oscillates in anti-phase with the emissions at higher frequencies. The oscillations at high and low frequencies are more pronounced in different parts of the loop (depending on the loop orientation). The layers where the line-of-sight component of the magnetic field changes sign can produce additional peculiarities in the oscillation patterns.

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“…They found that the LOS effect and spatial resolution could significantly affect the intensity modulation and spectral characteristics of the fast sausage mode. Reznikova et al (2014Reznikova et al ( , 2015 used the same model and further investigated the gyrosynchrotron emission intensity variation using the fast gyrosynchrotron codes (Fleishman & Kuznetsov 2010). The radio emission intensity of the fast sausage mode oscillates in phase for all frequencies, while for certain LOS angles, the optically thick and thin radio emissions are antiphase.…”

Section: Introductionmentioning

confidence: 99%

Forward Modeling of Standing Slow Modes in Flaring Coronal Loops

Yuan

Doorsselaere

Banerjee

et al. 2015

ApJ

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Standing slow-mode waves in hot flaring loops are exclusively observed in spectrometers and are used to diagnose the magnetic field strength and temperature of the loop structure. Owing to the lack of spatial information, the longitudinal mode cannot be effectively identified. In this study, we simulate standing slow-mode waves in flaring loops and compare the synthesized line emission properties with Solar Ultraviolet Measurements of Emitted Radiation spectrographic and Solar Dynamics Observatory/Atmospheric Imaging Assembly imaging observations. We find that the emission intensity and line width oscillations are a quarter period out of phase with Doppler shift velocity in both time and spatial domain, which can be used to identify a standing slow-mode wave from spectroscopic observations. However, the longitudinal overtones could only be measured with the assistance of imagers. We find emission intensity asymmetry in the positive and negative modulations;this is because the contribution function pertaining to the atomic emission process responds differently to positive and negative temperature variations. One may detect half periodicity close to the loop apex, where emission intensity modulation is relatively small. The line-of-sight projection affects the observation of Doppler shift significantly. A more accurate estimate of the amplitude of velocity perturbation is obtained by de-projecting the Doppler shift by a factor of 1-2θ/π rather than the traditionally used cos q. If a loop is heated to the hotter wing, the intensity modulation could be overwhelmed by background emission, while the Doppler shift velocity could still be detected to a certain extent.

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Perturbations of gyrosynchrotron emission polarization from solar flares by sausage modes: forward modeling

Cited by 15 publications

References 33 publications

Doppler Shift Oscillations from a Hot Line Observed by IRIS

Doppler Shift Oscillations from a Hot Line Observed by IRIS

Simulations of Gyrosynchrotron Microwave Emission from an Oscillating 3D Magnetic Loop

Forward Modeling of Standing Slow Modes in Flaring Coronal Loops

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