Seismic Emission from A M9.5-Class Solar Flare

Abstract

Following the discovery of a few significant seismic sources at 6.0 mHz from the large solar flares of October 28 and 29, 2003, we have extended SOHO/MDI helioseismic observations to moderate M-class flares. We report the detection of seismic waves emitted from the βγ δ active region NOAA 9608 on September 9, 2001. A quite impulsive solar flare of type M9.5 occurred from 20:40 to 20:48 UT. We used helioseismic holography to image seismic emission from this flare into the solar interior and computed time series of egression power maps in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show an acoustic source associated with the flare some 30 Mm across in the East -West direction and 15 Mm in the North -South direction nestled in the southern penumbra of the main sunspot of AR 9608. This coincides closely with three white-light flare kernels that appear in the sunspot penumbra. The close spatial correspondence between white-light and acoustic emission adds considerable weight to the hypothesis that the acoustic emission is driven by heating of the lower photosphere. This is further supported by a rough hydromechanical model of an acoustic transient driven by sudden heating of the low photosphere. Where direct heating of the low photosphere by protons or high-energy electrons is unrealistic, the strong association between the acoustic source and co-spatial continuum emission can be regarded as evidence supporting the back-warming hypothesis, in which the low photosphere is heated by radiation from the overlying chromosphere. This is to say that a seismic source coincident with strong, sudden radiative emission in the visible continuum spectrum indicates a photosphere sufficiently heated so as to contribute significantly to the continuum emission observed. 114A.-C. DONEA ET AL.

ANATOMY OF A SOLAR FLARE: MEASUREMENTS OF THE 2006 DECEMBER 14 X-CLASS FLARE WITH GONG,HINODE, ANDRHESSI

“…This is in spite of a limited bandpass of the egression acoustic power computations (e.g., the egression power signatures is temporally smeared by ≈500 s) imposed by the filtering in 5-7 mHz frequency band used in the processing for GONG data . Furthermore, the peaks approach the magnitudes of 2.5 and 3.85 for the frequencies 3 and 6 mHz, respectively, very close to the peak magnitudes (2.5 and 4) reported by Donea et al (2006) Again following the analysis of Donea et al (2006) and Martínez-Oliveros et al (2008a), we also estimate the rms deviations, σ , from the mean in the strongest seismic source detected in the location of the flare and compare them with those detected in quiet Sun locations. In the Appendix we produce a statistical analysis of the quiet Sun region located on the same latitude but at plus 180 • of the flare longitude.…”

“…Such a situation is not uncommon even with MDI data (Donea et al 2006), but in the majority of MDI measurements there is clearly visible suppression of seismic sources inside a sunspot which provides a high contrast background beneficial for easier identification of flare-induced acoustic kernels. This unfortunately is not the case for GONG observations, which require corrections for atmospheric contribution (Lindsey & Donea 2008;Zharkov et al 2011).…”

“…On the other hand, the acoustic holography technique appears to be more sensitive to noisy signals present in Dopplergrams compared to the TD one, even when using the better quality SOHO/MDI data, thus detecting a greater The fact that we see acoustic signatures at the same location in the north derived from both the TD diagram and egression power snapshot methods leads us to believe that such signatures can be real and not generated by background noise, as we demonstrate in the Appendix. In order to test this argument, we, similarly to Donea et al (2006;their Figure 5), plot the egression powers at 3 and 6 mHz versus time integrated over the rectangular region indicated in Figure 10 centered on acoustic source 3. It can be seen in Figure 10 that the peak of the egression power at 6 mHz corresponds to the time of the strongest HXR source in the north, which is observed around 22:10 UT, i.e., slightly later than the start of integrated HXR emission (see Figure 2).…”

“…The first observations of a "sunquake" were reported by Kosovichev & Zharkova (1998) during the flare of 1996 July 9, which strongly reinforced the foundations of local helioseismology and provided an additional stimulus for developing its methods further. Since that first identification by time-distance (TD) methods, the development of helioseismic holography has led to the identification of many more seismic sources during flares of GOES-class M and X (e.g., Donea et al 2006;Zharkova & Zharkov 2007;Martínez-Oliveros et al 2008b). Solar quake observations provide us with unique opportunities to study the excitation of solar oscillations in detail, and raise new questions about the underlying physical processes as well as the properties of the excited waves and sources producing them.…”

Advances in Global and Local Helioseismology: An Introductory Review

“…13a), [90][91][92][93], or indirectly by calculating integrated acoustic emission [94][95][96]. Solar flares are sources of high-temperature plasma and strong hydrodynamic motions in the solar atmosphere.…”