Ultra-impulsive Solar Flare Seismology

We examine a strong, coherent, highly impulsive acoustic transient radiated into the solar interior by the flare SOL20110730T02:04-M9.3. The acoustic spectrum of this transient extends out to 10 mHz. The fine diffraction limit of this high-frequency component of the flare acoustic transient allows us to discriminate different source components in operation during the flare. Acoustic-source power density maps of the 10 mHz component show sources that are compact to within the now 760 km diffraction limit of local helioseismic diagnostics for this frequency. One of the acoustic sources found is bifurcated across a sharp penumbral magnetic boundary, the component in the stronger magnetic field temporally lagging its partner. The facility to discriminate this level of acoustic-source detail could open the door to a long sought after understanding of the mechanics of transient emission from solar flares, still a mystery two decades after its discovery. It also suggests that helioseismic observations of higher cadence and spatial resolution could reveal coherent acoustic emission at even higher frequencies, with proportionately further potential benefits to solar seismology and its growing domain of applications.