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

Pankaj Kumar   Submitted: 2017-07-05 13:05

This paper presents an observation of quasi-periodic rapidly-propagating waves observed in the AIA 171/193 Å channels during the impulsive phase of an M1.9 flare occurred on 7 May 2012. The instant period was found to decrease from 240 s to 120 s, the speed of the wave fronts was in the range of ~664-1416 km s-1. Almost simultaneously, quasi-periodic bursts with similar instant periods, ~70 s and ~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 the 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 Å we observed quasi-periodic EUV disturbances with the periods of 95 s and 240 s propagating downward at the apparent speed of 172-273 km s-1. The nature of these downward propagating disturbances is not revealed, but they could be connected with magnetoacoustic waves or periodically shrinking loops.

Authors: Kumar, Pankaj; Nakariakov, Valery M.; Cho, Kyung-Suk
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2017-07-06 10:45
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Multiwavelength Observations of a Flux Rope Formation by Series of Magnetic Reconnection in the Chromosphere  

Pankaj Kumar   Submitted: 2017-03-29 20:13

Using high-resolution observations from the 1.6 m New Solar Telescope (NST) operating at the Big Bear Solar Observatory (BBSO), we report direct evidence of merging/reconnection of cool Hα loops in the chromosphere during two homologous flares (B- and C-class) caused by a shear motion at the footpoint of two loops. The reconnection between these loops caused the formation of an unstable flux rope which showed counterclockwise rotation. The flux rope could not reach the height of torus instability and failed to form a coronal mass ejection. The HMI magnetograms revealed rotation of the negative/positive (N1/P2) polarity sunspots in the opposite directions, which increased the right and left-handed twist in the magnetic structures rooted at N1/P2. Rapid photospheric flux cancellation (duration~20-30 min, rate≈3.44x1020 Mx h-1) was observed during and even after the first B6.0 flare and continued until the end of the second C2.3 flare. The RHESSI X-ray sources were located at the site of the loop's coalescence. To the best of our knowledge, such a clear interaction of chromospheric loops along with rapid flux cancellation has not been reported before. These high-resolution observations suggest the formation of a small flux rope by a series of magnetic reconnection within chromospheric loops associated with very rapid flux cancellation.

Authors: Pankaj Kumar, Vasyl Yurchyshyn, Kyung-Suk Cho, Haimin Wang
Projects: None

Publication Status: A&A, in press, 12 pages, 12 figures
Last Modified: 2017-03-30 16:18
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Observation of a Short Period Quasi-Periodic Pulsation in Solar X-ray, Microwave and EUV Emissions  

Pankaj Kumar   Submitted: 2017-01-10 08:10

This paper presents the multi-wavelength 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 occurred on 21 September 2015. AIA 304 and 171 Å images show an emerging loop/flux tube (L1) moving radially outward, which interacts with preexisting structures within the active region. The QPP was observed during the expansion and rising motion of L1. The Nobeyama Radioheliograph (NoRH) microwave images in 17/34 GHz channels reveal a single radio source, which was co-spatial with a neighboring loop (L2). In addition, using AIA 304 Å images, we detected intensity oscillations in the legs of loop 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 loops L2 and L3 observed in the AIA hot channels (131 and 94 Å). The merging speed of loops L2 and L3 was ~35 km s-1. Loop L1 destroyed possibly by its interaction with preexisting structures in the active region and produced a cool jet with the speed ~106-118 km s-1 associated with a narrow CME (~770 km s-1). Another mechanism of the QPP in terms of a sausage oscillation of the loop (L2) is also possible.

Authors: Pankaj Kumar, Valery M. Nakariakov, Kyung-Suk Cho
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2017-01-11 12:07
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Flare Generated Shock Wave Propagation Through Solar Coronal Arcade Loops and Associated Type II Radio Burst  

Pankaj Kumar   Submitted: 2016-06-19 18:54

This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II closely match a fast EUV wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the AIA 335 Å images with a speed of ~800 km s-1 and accelerated to ~1490 km s-1 after passing through the arcade loops. A fan-spine magnetic topology was revealed at the flare site. A small, confined filament eruption (~340 km s-1) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan-spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops.

Authors: Kumar, Pankaj; Innes, D. E.; Cho, K. S.
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2016-06-22 09:13
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Observation of a Quasi-periodic Pulsation in Hard X-ray, Radio and Extreme-ultraviolet Wavelengths  

Pankaj Kumar   Submitted: 2016-03-14 20:13

We present multi-wavelength analysis of a quasi-periodic pulsation (QPP) observed in the hard X-ray, radio, and extreme-ultraviolet (EUV) channels during an M1.9 flare occurred on 23-24 September 2011. The non-thermal hard X-ray emission in 25-50 keV observed by RHESSI shows five distinct impulsive peaks of decaying amplitude with a period of about three minutes. Similar QPP was observed in the microwave emission recorded by the Nobeyama Radioheliograph and Polarimeter in the 8.8, 15, 17 GHz channels. Interestingly, the 3-min QPP was also observed in the metric and decimetric radio frequencies (25-180, 245, 610 MHz) as repetitive type III bursts. Multi-wavelength observations from the SDO/AIA, Hinode/SOT, and STEREO/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 behaviour was followed by an untwisting motion of the filament. Two different structures of the filament showed ~3-min periodic alternate rotation in the clockwise and counterclockwise directions. The 3-min QPP was found to highly correlate with 3-min oscillations in a nearby sunspot. We suggest that the periodic reconnection (modulated either by sunspot slow-mode wave or by untwisting filament) at a magnetic null-point most likely causes the repetitive particle acceleration, generating the QPP observed in hard X-ray, microwave and type III radio bursts.

Authors: Pankaj Kumar, Valery M. Nakariakov, Kyung-Suk Cho
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2016-03-15 11:24
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X-ray and EUV Observations of Simultaneous Short and Long Period Oscillations in Hot Coronal Arcade Loops  

Pankaj Kumar   Submitted: 2015-02-25 18:35

We report decaying quasi-periodic intensity oscillations in the X-ray (6-12 keV) and extreme ultraviolet (EUV) channels (131, 94, 1600, 304 Å) observed by the Fermi GBM (Gamma-ray Burst Monitor) and SDO/AIA, respectively, during a C-class flare. The estimated period of oscillation and decay time in the X-ray channel (6-12 keV) was about 202 s and 154 s, respectively. A similar oscillation period was detected at the footpoint of the arcade loops in the AIA 1600 and 304 Å channels. Simultaneously, AIA hot channels (94 and 131 A) 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 s and 1121 s, respectively. The characteristic phase speed of the wave is about 560 km s-1 for about 115 Mm 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 SOHO/SUMER 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 cause the periodic acceleration of non-thermal electrons that propagated to the opposite footpoint along the arcade and precipitating there, causing the observed 202-s periodicity. Other possible interpretations, e.g. the second harmonics of the slow mode are also discussed.

Authors: Pankaj Kumar, Valery M. Nakariakov, Kyung-Suk Cho
Projects: None

Publication Status: ApJ (in press)
Last Modified: 2015-03-02 09:53
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Evolution of Solar Magnetic Field and Associated Multiwavelength Phenomena: Flare Events on 2003 November 20  

Pankaj Kumar   Submitted: 2010-01-29 05:23

We analyze Hα images, soft X-ray profiles, magnetograms, extreme ultra-violet images and, radio observations of two homologous flare events (M1.4/1N and M9.6/2B) on 2003 November 20 in the active region NOAA 10501 and study properties of reconnection between twisted filament systems, energy release, and associated launch of coronal mass ejections. During both events twisted filaments observed in Hα approached each other and initiated the flare processes. However, the second event showed the formation of cusp as the filaments interacted. The rotation of sunspots of opposite polarities, inferred from the magnetograms likely powered the twisted filaments and injection of helicity. Along the current sheet between these two opposite polarity sunspots, the shear was maximum, which could have caused the twist in the filament. At the time of interaction between filaments, the reconnection took place and flare emission in thermal and nonthermal energy ranges attained the maximum. The radio signatures revealed the opening of field lines resulting from the reconnection. The Hα images and radio data provide the inflow speed leading to reconnection and the scale size of the particle acceleration region. The first event produced a narrow and slow CME, whereas the later one was associated with a fast full halo CME. The halo CME signatures observed between the Sun and Earth using white-light and scintillation images and in situ measurements indicated the magnetic energy utilized in the expansion and propagation. The magnetic cloud signature at the Earth confirmed the flux rope ejected at the time of filament interaction and reconnection.

Authors: Pankaj Kumar, P. K. Manoharan, Wahab Uddin
Projects: None

Publication Status: published in ApJ, 2010 January 28
Last Modified: 2010-01-29 09:59
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Abstracts by Author
Quasi-Periodic Radio Bursts Associated with Fast-mode Waves near a Magnetic Null Point
Multiwavelength Observations of a Flux Rope Formation by Series of Magnetic Reconnection in the Chromosphere
Observation of a Short Period Quasi-Periodic Pulsation in Solar X-ray, Microwave and EUV Emissions
Flare Generated Shock Wave Propagation Through Solar Coronal Arcade Loops and Associated Type II Radio Burst
Observation of a Quasi-periodic Pulsation in Hard X-ray, Radio and Extreme-ultraviolet Wavelengths
X-ray and EUV Observations of Simultaneous Short and Long Period Oscillations in Hot Coronal Arcade Loops
Evolution of Solar Magnetic Field and Associated Multiwavelength Phenomena: Flare Events on 2003 November 20

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