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Doppler shift oscillations from a hot line observed by IRIS  

Dong Li   Submitted: 2017-09-28 18:17

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 1354.09 Å (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 1354.09 Å, 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 (> 11MK). 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.

Authors: Dong Li, Zongjun Ning, Yu Huang, N.-H. Chen, Qingmin Zhang, Yingna Su, Wei Su
Projects: IRIS

Publication Status: accept by the Astrophysical Journal
Last Modified: 2017-10-02 12:31
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Quasi-periodic pulsations with multiple periods in hard X-ray emission  

Dong Li   Submitted: 2017-06-06 04:16

We explore the quasi-periodic pulsations (QPPs) with multiple periods in hard X-ray (HXR) emission from Fermi/GBM during the impulsive phase of solar flare (SOL2014-09-10). The completely new observational result is that the shorter periods appear at lower energies of the X-ray photons at the beginning and the longer periods appear at higher energies at the end, with some intersection of the periods at medium energies. We also find the shorter and then the longer periods during the same phase of this flare. Using the wavelet power spectrum and fast Fourier transform (FFT) spectrum, we analyze the normalized rapidly varying signal divided by its slowly varying signal, which is the smoothed original HXR flux. The periods of 27 s and 37 s are derived at lower energy channels between 17:25 UT and 17:29 UT, i.e., 12.0-27.3 keV and 27.3-50.9 keV. Then the periods of 27 s, 46 s and 60 s are observed at medium-energy channel from 17:26 UT to 17:33 UT, such as 50.9-102.3 keV. And the period of 80 s is detected at higher energy channel from 17:28 UT to 17:33 UT, such as 102.3-296.4 keV.

Authors: Li, Dong; Zhang, Qingmin
Projects: Fermi/GBM

Publication Status: MNRAS Letters (in press)
Last Modified: 2017-06-10 19:39
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Explosive chromospheric evaporation driven by nonthermal electrons around one footpoint of a solar flare loop  

Dong Li   Submitted: 2017-05-09 08:32

We explore the temporal relationship between microwave/HXR emission and Doppler velocity during the impulsive phase of a solar flare on 2014 October 27 (SOL2014-10-27), which displays a pulse on the light curves in microwave (34 GHz) and hard X-ray (HXR, 25-50 keV) bands before the flare maximum. Imaging observation shows that this pulse mainly comes from one footpoint of a solar flare loop. The slit of Interface Region Imaging Spectrograph (IRIS) stays at this footpoint during this solar flare. The Doppler velocities of Fe XXI 1354.09 Å and Si IV 1402.77 A are extracted from the Gaussian fitting method. We find that the hot line of Fe XXI 1354.09 Å (logT~7.05) in corona exhibits blue shift, while the cool line of Si IV 1402.77 A (logT~4.8) in transition region exhibits red shift, indicating explosive chromospheric evaporation. The evaporative upflows along the flare loop are also observed in the AIA 131 Å image. To our knowledge, this is the first report of chromospheric evaporation evidence from both spectral and imaging observations in the same flare. Both microwave and HXR pulses are well correlated with the Doppler velocities, suggesting that the chromospheric evaporation is driven by nonthermal electrons around this footpoint of a solar flare loop.

Authors: Li, Dong; Ning, Zongjun; Huang, Yu; Zhang, Qingmin
Projects: IRIS

Publication Status: accept by the Astrophysical Journal Letters
Last Modified: 2017-05-10 09:17
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Abstracts by Author
Doppler shift oscillations from a hot line observed by IRIS
Quasi-periodic pulsations with multiple periods in hard X-ray emission
Explosive chromospheric evaporation driven by nonthermal electrons around one footpoint of a solar flare loop

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