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Register a new userTransverse oscillation of a coronal loop induced by a flare-related jet
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In this work, we report our multi-wavelength observations of the transverse oscillation of a large scale coronal loop with a length of 350 Mm. The oscillation was induced by a blowout coronal jet, which was related to a circular ribbon flare (CRF) in AR 12434 on 2015 October 16. We aim to determine the physical parameters in the coronal loop, including the Alfven speed and magnetic field strength. The jet induced kink oscillation was observed in extreme-ultraviolet (EUV) wavelengths by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Line of sight magnetograms were observed by the Helioseismic and Magnetic Imager (HMI) on board SDO. We took several slices along the loop to assemble time-distance diagrams, and used an exponentially decaying sine function to fit the decaying oscillation. The initial amplitude, period, and damping time of kink oscillation were obtained. Coronal seismology of the kink mode was applied to estimate the Alfven speed and magnetic field strength in the oscillating loop. In addition, we measured the magnetic field of the loop through non-linear force free field (NLFFF) modeling using the flux rope insertion method. The oscillation is most pronounced in AIA 171 and 131. The oscillation is almost in phase along the loop with a peak initial amplitude of 13.6 Mm, meaning that the oscillation belong to the fast standing kink mode. The oscillation lasts for 3.5 cycles with an average period of 462 s and average damping time of 976 s. The values of t/P lie in the range of 1.5-2.5. Based on coronal seismology, the Alfven speed in the oscillating loop is estimated to be 1210 km. Two independent methods are applied to calculate the magnetic field strength of the loop, resulting in 30043 G using the coronal seismology and 21123 G using the NLFFF modeling, respectively.
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Coronal jets are ubiquitous in active regions (ARs) and coronal holes. In this paper, we study a coronal jet related to a C3.4 circular-ribbon flare in active region 12434 on 2015 October 16. Two minifilaments were located under a 3D fan-spine structure before flare. The flare was generated by the eruption of one filament. The kinetic evolution of the jet was divided into two phases: a slow rise phase at a speed of $sim$131 km s$^{-1}$ and a fast rise phase at a speed of $sim$363 km s$^{-1}$ in the plane-of-sky. The slow rise phase may correspond to the impulsive reconnection at the breakout current sheet. The fast rise phase may correspond to magnetic reconnection at the flare current sheet. The transition between the two phases occurred at $sim$09:00:40 UT. The blueshifted Doppler velocities of the jet in the Si {sc iv} 1402.80 {AA} line range from -34 to -120 km s$^{-1}$. The accelerated high-energy electrons are composed of three groups. Those propagating upward along open field generate type textrm{III} radio bursts, while those propagating downward produce HXR emissions and drive chromospheric condensation observed in the Si {sc iv} line. The electrons trapped in the rising filament generate a microwave burst lasting for $le$40 s. Bidirectional outflows at the base of jet are manifested by significant line broadenings of the Si {sc iv} line. The blueshifted Doppler velocities of outflows range from -13 to -101 km s$^{-1}$. The redshifted Doppler velocities of outflows range from $sim$17 to $sim$170 km s$^{-1}$. Our multiwavelength observations of the flare-related jet are in favor of the breakout jet model and are important for understanding the acceleration and transport of nonthermal electrons.
To investigate the excitation of kink oscillations in coronal loops and filaments, a C3.4 circular-ribbon flare (CRF) associated with a blowout jet in active region 12434 on 2015 October 16 is analyzed. The flare excited small-amplitude kink oscillation of a remote coronal loop. The oscillation lasted for $ge$4 cycles without significant damping. The amplitude and period are 0.3$pm$0.1 Mm and 207$pm$12 s. Interestingly, the flare also excited transverse oscillation of a remote filament. The oscillation lasted for $sim$3.5 cycles with decaying amplitudes. The initial amplitude is 1.7$-$2.2 Mm. The period and damping time are 437$-$475 s and 1142$-$1600 s. The starting times of simultaneous oscillations of coronal loop and filament were concurrent with the hard X-ray peak time. Though small in size and short in lifetime, the flare set off a chain reaction. It generated a bright secondary flare ribbon (SFR) in the chromosphere, remote brightening (RB) that was cospatial with the filament, and intermittent, jet-like flow propagating in the northeast direction. The loop oscillation is most probably excited by the flare-induced blast wave at a speed of $ge$1300 km s$^{-1}$. The excitation of the filament oscillation is more complicated. The blast wave triggers secondary magnetic reconnection far from the main flare, which not only heats the local plasma to higher temperatures (SFR and RB), but produces jet-like flow (i.e., reconnection outflow) as well. The filament is disturbed by the secondary magnetic reconnection and experiences transverse oscillation. The findings give new insight into the excitation of transverse oscillations of coronal loops and filaments.
In this paper, multiwavelength observations of remote coronal dimmings related to an M1.1 circular-ribbon flare (CRF) in active region (AR) 12434 are reported. The confined flare without a CME was observed by AIA and HMI on board SDO on 2015 October 16. Global three-dimensional (3D) magnetic fields before flare were obtained using the potential field source surface modeling. A few minutes before the flare hard X-ray peak time (06:13:48 UT), small-scale, weak dimming appeared $sim$240$arcsec$ away from the flare site, which can be observed by AIA only in 131 and 171 {AA}. Afterwards, long and narrow dimmings became evident in all AIA EUV passbands except 304 {AA}, while localized core dimming was not clearly observed near the flare site. The large-area dimmings extended southeastward and the areas increased gradually. The total area of dimmings reaches (1.2$pm0.4$)$times$10$^4$ Mm$^2$ in 193 {AA}. The maximal relative intensity decreases in 171 and 193 {AA} reach 90% and 80%, respectively. Subsequently, the dimmings began to replenish and the area decreased slowly, lasting for $geq$3 hr. The remote dimmings and AR 12434 were connected by large-scale coronal loops. The remote dimmings were associated with the southwest footpoints of coronal loops with weak negative polarities. Possible origins of remote dimmings are discussed.
Jets are defined as impulsive, well-collimated upflows, occurring in different layers of the solar atmosphere with different scales. Their relationship with coronal mass ejections (CMEs), another type of solar impulsive events, remains elusive. Using the high-quality imaging data of AIA/SDO, here we show a well-observed coronal jet event, in which part of the jets, with the embedding coronal loops, runs into a nearby coronal hole (CH) and gets bounced towards the opposite direction. This is evidenced by the flat-shape of the jet front during its interaction with the CH and the V-shaped feature in the time-slice plot of the interaction region. About a half-hour later, a CME initially with a narrow and jet-like front is observed by the LASCO C2 coronagraph, propagating along the direction of the post-collision jet. We also observe some 304 A dark material flowing from the jet-CH interaction region towards the CME. We thus suggest that the jet and the CME are physically connected, with the jet-CH collision and the large- scale magnetic topology of the CH being important to define the eventual propagating direction of this particular jet-CME eruption.
Evidence of flare induced, large-amplitude, decay-less transverse oscillations is presented. A system of multi-thermal coronal loops as observed with the Atmospheric Imaging Assembly (AIA), exhibit decay-less transverse oscillations after a flare erupts nearby one of the loop footpoints. Measured oscillation periods lie between 4.2 min and 6.9 min wherein the displacement amplitudes range from 0.17 Mm to 1.16 Mm. A motion-magnification technique is employed to detect the pre-flare decay-less oscillations. These oscillations have similar periods (between 3.7 min and 5.0 min) like the previous ones but their amplitudes (0.04 Mm to 0.12 Mm) are found to be significantly smaller. No phase difference is found among oscillating threads of a loop when observed through a particular AIA channel or when their multi-channel signatures are compared. These features suggest that the occurrence of a flare in this case neither changed the nature of these oscillations (decaying vs decay-less) nor the oscillation periods. The only effect the flare has is to increase the oscillation amplitudes.
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