OBSERVATION OF A QUASIPERIODIC PULSATION IN HARD X-RAY, RADIO, AND EXTREME-ULTRAVIOLET WAVELENGTHS

Kumar, Pankaj,Nakariakov, Valery M.,Cho, Kyung-Suk American Astronomical Society 2016 The Astrophysical journal Vol.822 No.1

<P>We present a multiwavelength analysis of a quasiperiodic pulsation (QPP) observed in the hard X-ray (HXR), radio, and extreme-ultraviolet (EUV) channels during an M1.9 flare that occurred on 2011 September 23-24. The nonthermal HXR emission in 25-50 keV observed by RHESSI shows five distinct impulsive peaks of decaying amplitude with a period of about 3 minutes. A similar QPP was observed in the microwave emission recorded by the Nobeyama Radioheliograph and Polarimeter in the 2, 3.75, 9.4, and 17 GHz channels. Interestingly, the 3-minute QPP was also observed in the metric and decimetric radio frequencies (25-180, 245, 610 MHz) as repetitive type III bursts. Multiwavelength observations from the Solar Dynamics Observatory/Atmospheric Image Assembly, Hinode/SOT, and Solar TErrestrial RElations Observatory/SECCHI suggest a fan-spine topology at the eruption site, associated with the formation of a quasi-circular ribbon during the flare. A small filament was observed below the fan loops before the flare onset. The filament rose slowly and interacted with the ambient field. This behavior was followed by an untwisting motion of the filament. Two different structures of the filament showed an approximately 3-minute periodic alternate rotation in the clockwise and counterclockwise directions. The 3-minute QPP was found to highly correlate with 3-minute oscillations in a nearby sunspot. We suggest that the periodic reconnection (modulated either by a sunspot slow-mode wave or by an untwisting filament) at a magnetic null point most likely causes the repetitive particle acceleration, generating the QPP observed in HXR, microwave, and type III radio bursts.</P>

Quasi-periodic Radio Bursts Associated with Fast-mode Waves near a Magnetic Null Point

Kumar, Pankaj,Nakariakov, Valery M.,Cho, Kyung-Suk American Astronomical Society 2017 The Astrophysical journal Vol.844 No.2

<P>This paper presents an observation of quasi-periodic rapidly propagating waves observed in the Atmospheric Image Assembly (AIA) 171/193 (A) over circle. channels during the impulsive phase of an M1.9 flare that occurred on 2012 May 7. The instant period was found to decrease from 240 to 120. s, and the speed of the wavefronts was in the range of similar to 664-1416. km s(-1). Almost simultaneously, quasi-periodic bursts with similar instant periods, similar to 70 and similar to 140. s, occur in the microwave emission and in decimetric type IV and type III radio bursts, and in the soft X-ray emission. The magnetic field configuration of the flare site was consistent with a breakout topology, i.e., a quadrupolar field along with a magnetic null point. The quasi-periodic rapidly propagating wavefronts of the EUV emission are interpreted as a fast magnetoacoustic wave train. The observations suggest that the fast-mode waves are generated during the quasi-periodic magnetic reconnection in the cusp region above the flare arcade loops. For the first time, we provide evidence of a tadpole wavelet signature at about 70-140. s in decimetric (245/610 MHz) radio bursts, along with the direct observation of a coronal fast-mode wave train in EUV. In addition, at AIA 131/193 (A) over circle we observed quasi-periodic EUV disturbances with periods of 95 and 240. s propagating downward at apparent speeds of 172-273. km s(-1). The nature of these downward propagating disturbances is not revealed, but they could be connected to magnetoacoustic waves or periodically shrinking loops.</P>

Editorial: solar radiophysics - recent results on observations and theories

Nakariakov, Valery M.,Kashapova, Larisa K.,Yan, Yi-Hua IOP Publishing 2014 Research in astronomy and astrophysics Vol.14 No.7

OSCILLATIONS IN A SUNSPOT WITH LIGHT BRIDGES

Yuan, Ding,Nakariakov, Valery M.,Huang, Zhenghua,Li, Bo,Su, Jiangtao,Yan, Yihua,Tan, Baolin IOP Publishing 2014 The Astrophysical journal Vol.792 No.1

<P>The Solar Optical Telescope on board Hinode observed a sunspot (AR 11836) with two light bridges (LBs) on 2013 August 31. We analyzed a two-hour Ca II H emission intensity data set and detected strong five-minute oscillation power on both LBs and in the inner penumbra. The time-distance plot reveals that the five-minute oscillation phase does not vary significantly along the thin bridge, indicating that the oscillations are likely to originate from underneath it. The slit taken along the central axis of the wide LB exhibits a standing wave feature. However, at the center of the wide bridge, the five-minute oscillation power is found to be stronger than at its sides. Moreover, the time-distance plot across the wide bridge exhibits a herringbone pattern that indicates a counter-stream of two running waves, which originated at the bridge's sides. Thus, the five-minute oscillations on the wide bridge also resemble the properties of running penumbral waves. The five-minute oscillations are suppressed in the umbra, while the three-minute oscillations occupy all three cores of the sunspot's umbra, separated by the LBs. The three-minute oscillations were found to be in phase at both sides of the LBs. This may indicate that either LBs do not affect umbral oscillations, or that umbral oscillations at different umbral cores share the same source. It also indicates that LBs are rather shallow objects situated in the upper part of the umbra. We found that umbral flashes (UFs) follow the life cycles of umbral oscillations with much larger amplitudes. They cannot propagate across LBs. UFs dominate the three-minute oscillation power within each core; however, they do not disrupt the phase of umbral oscillation.</P>

Observation of a Short Period Quasi-periodic Pulsation in Solar X-Ray, Microwave, and EUV Emissions

Kumar, Pankaj,Nakariakov, Valery M.,Cho, Kyung-Suk American Astronomical Society 2017 The Astrophysical journal Vol.836 No.1

<P>This paper presents the multiwavelength analysis of a 13 s quasi-periodic pulsation (QPP) observed in hard X-ray (12-300 keV) and microwave (4.9-34 GHz) emissions during a C-class flare that occurred on 2015 September 21. Atmospheric Image Assembly (AIA) 304 and 171 similar to. images show an emerging loop/ flux tube (L1) moving radially outward, which interacts with the preexisting structures within the active region (AR). The QPP was observed during the expansion of and rising motion of L1. The Nobeyama Radioheliograph microwave images in 17/ 34 GHz channels reveal a single radio source that was co-spatial with a neighboring loop (L2). In addition, using AIA 304 similar to. images, we detected intensity oscillations in the legs of L2 with a period of about 26. s. A similar oscillation period was observed in the GOES soft X-ray flux derivative. This oscillation period seems to increase with time. We suggest that the observed QPP is most likely generated by the interaction between L2 and L3 observed in the AIA hot channels (131 and 94 similar to). The merging speed of loops L2 and L3 was similar to 35 km. s-1.. L1 was destroyed possibly by its interaction with preexisting structures in the AR, and produced a cool jet with the speed of similar to 106-118 km. s(-1) associated with a narrow CME (similar to 770 km. s(-1)). Another mechanism of the QPP in terms of a sausage oscillation of the loop (L2) is also possible.</P>

X-RAY AND EUV OBSERVATIONS OF SIMULTANEOUS SHORT AND LONG PERIOD OSCILLATIONS IN HOT CORONAL ARCADE LOOPS

Kumar, Pankaj,Nakariakov, Valery M.,Cho, Kyung-Suk IOP Publishing 2015 The Astrophysical journal Vol.804 No.1

<P>We report decaying quasi-periodic intensity oscillations in the X-ray (6-12 keV) and extreme-ultraviolet (EUV) channels (131, 94, 1600, 304 angstrom) observed by the Fermi Gamma-ray Burst Monitor and Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), respectively, during a C-class flare. The estimated periods of oscillation and decay time in the X-ray channel (6-12 keV) were about 202 and 154 s, respectively. A similar oscillation period was detected at the footpoint of the arcade loops in the AIA 1600 and 304 angstrom channels. Simultaneously, AIA hot channels (94 and 131 angstrom) reveal propagating EUV disturbances bouncing back and forth between the footpoints of the arcade loops. The period of the oscillation and decay time were about 409 and 1121 s, respectively. The characteristic phase speed of the wave is about 560 km s(-1) for about 115 Mm of loop length, which is roughly consistent with the sound speed at the temperature about 10-16 MK (480-608 km s(-1)). These EUV oscillations are consistent with the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Doppler-shift oscillations interpreted as the global standing slow magnetoacoustic wave excited by a flare. The flare occurred at one of the footpoints of the arcade loops, where the magnetic topology was a 3D fan-spine with a null-point. Repetitive reconnection at this footpoint could have caused the periodic acceleration of non-thermal electrons that propagated to the opposite footpoint along the arcade and that are precipitating there, causing the observed 202 s periodicity. Other possible interpretations, e.g., the second harmonics of the slow mode, are also discussed.</P>

Sausage oscillations in a plasma cylinder with a surface current

Lim, Daye,Nakariakov, Valery M.,Moon, Yong-Jae Elsevier 2018 Journal of Atmospheric and Solar-Terrestrial Physi Vol.175 No.-

<P><B>Abstract</B></P> <P>Linear sausage oscillations of a cylinder embedded in a plasma with an azimuthal magnetic field, created by a current on the surface of the cylinder, are studied. Such a plasma configuration could be applied to modelling flaring loops, and magnetic ropes in coronal mass ejections. The plasma is assumed to be cold everywhere. Dispersion relations demonstrate that the lowest radial harmonic of the sausage mode is in the trapped regime for all values of the parallel wave number. In the long-wavelength limit, phase and group speeds of this mode are equal to the Alfvén speed in the external medium. It makes the oscillation period to be determined by the ratio of the parallel wavelength, e.g. double the length of an oscillating loop, to the external Alfvén speed, allowing for its seismological estimations. The application of the results obtained to the interpretation of long-period (longer than a minute) oscillations of emission intensity detected in solar coronal structures, gives reasonable estimations of the external Alfvén speed. Cutoff values of the parallel wavenumber for higher radial harmonics are determined analytically. Implications of this finding to the observational signatures of fast magnetoacoustic wave trains guided by cylindrical plasma non-uniformities are discussed.</P>

Sausage Waves in a Plasma Cylinder with a Surface Current

Daye Lim,Valery M. Nakariakov,Yong-Jae Moon 한국천문학회 2019 天文學會報 Vol.44 No.1

Origin of the Modulation of the Radio Emission from the Solar Corona by a Fast Magnetoacoustic Wave

Kolotkov, Dmitrii Y.,Nakariakov, Valery M.,Kontar, Eduard P. American Astronomical Society 2018 The Astrophysical journal Vol.861 No.1

<P>Observational detection of quasi-periodic drifting fine structures in a type III radio burst associated with a solar flare SOL2015-04-16T11:22, with the LOw Frequency ARray (LOFAR), is presented. Although similar modulations of the type III emission have been observed before and were associated with the plasma density fluctuations, the origin of those fluctuations was unknown. Analysis of the striae of the intensity variation in the dynamic spectrum allowed us to reveal two quasi-oscillatory components. The shorter component has an apparent wavelength of similar to 2 Mm, phase speed of similar to 657 km s(-1), which gives an oscillation period of similar to 3 s, and a relative amplitude of similar to 0.35%. The longer component has a wavelength of similar to 12 Mm and relative amplitude of similar to 5.1%. The short frequency range of the detection does not allow us to estimate its phase speed. However, the properties of the shorter oscillatory component allowed us to interpret it as a fast magnetoacoustic wave guided by a plasma nonuniformity along the magnetic field outwards from the Sun. The assumption that the intensity of the radio emission is proportional to the amount of plasma in the emitting volume allowed us to show that the superposition of the plasma density modulation by a fast wave and a longer-wavelength oscillation of an unspecified nature could readily reproduce the fine structure of the observed dynamic spectrum. The observed parameters of the fast wave give an absolute value for the magnetic field in the emitting plasma of similar to 1.1 G, which is consistent with the radial magnetic field model.</P>

Nonlinear oscillations of coalescing magnetic flux ropes

Kolotkov, Dmitrii Y.,Nakariakov, Valery M.,Rowlands, George American Physical Society 2016 Physical Review E Vol.93 No.5