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Time delays in quasi-periodic pulsations observed during the X2.2 solar flare on 2011 February 15  

Laurent Dolla   Submitted: 2012-03-28 04:54

We report observations of quasi-periodic pulsations (QPPs) during the X2.2 flare of 15 February 2011, observed simultaneously in several wavebands. We focus on fluctuations on time scale 1?30 s and find different time lags between different wavebands. During the impulsive phase, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) channels in the range 25x100 keV lead all the other channels. They are followed by the Nobeyama RadioPolarimeters at 9 and 17 GHz and the Extreme Ultra-Violet (EUV) channels of the Euv SpectroPhotometer (ESP) onboard the Solar Dynamic Observatory (SDO). The Zirconium and Aluminum filter channels of the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy (PROBA2) satellite and the SXR channel of ESP follow. The largest lags occur in observations from the Geostationary Operational Environmental Satellite (GOES), where the channel at 1?8 ? leads the 0.5?4 ? channel by several seconds. The time lags between the first and last channels is up to 9 s. We identified at least two distinct time intervals during the flare impulsive phase, during which the QPPs were associated with two different sources in the Nobeyama RadioHeliograph at 17 GHz. The radio as well as the hard X-ray channels showed different lags during these two intervals. To our knowledge, this is the first time that time lags are reported between EUV and SXR fluctuations on these time scales. We discuss possible emission mechanisms and interpretations, including flare electron trapping.

Authors: L. Dolla, C. Marqu?, D. B. Seaton, T. Van Doorsselaere, M. Dominique, D. Berghmans, C. Cabanas, A. De Groof, W. Schmutz, A. Verdini, M. J. West, J. Zender and A. N. Zhukov
Projects: Nobeyama Radioheliograph,PROBA2/LYRA,RHESSI,SDO-AIA,SDO-EVE

Publication Status: ApJ (published)
Last Modified: 2012-03-28 09:04
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On the nature of spectral line broadening in solar coronal dimmings  

Laurent Dolla   Submitted: 2011-02-24 04:34

We analyze the profiles of iron emission lines observed in solarcoronal dimmings associated with coronal mass ejections, using the EUVImaging Spectrometer on board Hinode. We quantify line profiledistortions with empirical coefficients (asymmetry and peakedness)that compare the fitted Gaussian to the data. We find that theapparent line broadenings reported in previous studies are likely tobe caused by inhomogeneities of flow velocities along the line ofsight, or at scales smaller than the resolution scale, or by velocityfluctuations during the exposure time. The increase in the amplitudeof Alfvén waves cannot, alone, explain the observed features. Adouble-Gaussian fit of the line profiles shows that, both for dimmingsand active region loops, one component is nearly at rest while thesecond component presents a larger Doppler shift than that derivedfrom a single-Gaussian fit.

Authors: Dolla, L. R. and Zhukov, A. N.
Projects: Hinode/EIS,STEREO

Publication Status: ApJ 2011, 730, 113
Last Modified: 2011-03-11 11:42
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Time delays in quasi-periodic pulsations observed during the X2.2 solar flare on 2011 February 15
On the nature of spectral line broadening in solar coronal dimmings

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