Transient Acoustic Emission from a Source Submerged Beneath Solar Flare

Some solar flares drive tremors, called “sunquakes,” in the solar surface propagating outward from the site of the flare over the hour succeeding its impulsive phase. These tremors are a manifestation of acoustic transients that have traveled deep into the solar interior from the site of the flare and have thenceforth been refracted back upward to the Sun’s surface tens of thousands of kilometers outside of the flaring region. We have used RHESSI and SDO/HMI to study eighteen sunquakes from solar cycle 24, compiled by Buitrago Casas et al. (2015). Each of these events shows a significant seismic transient, HXR emission observed with RHESSI and significant visible-continuum emission observed with SDO/HMI. The focus of this study is one of these events, SOL20140207T10:28, which shows evidence of a submerged acoustic source some two thousand km beneath the photosphere. We present an analysis of this sunquake utilizing time-depth extrapolations of transient emission from surface and submerged source components at frequencies ranging from 4 to 10 mHz. In the instance of transient acoustic emission from another flare, SOL20110730T02:04, a delay between surface and submerged source components of transient emission was cited to support a model in which some disturbance propagated downward from an overlying surface source component at some 4.75~km/sec to trigger subsequent emission from the submerged source. In the instance of SOL20140207T10:28, the submerged emission is extrapolated to have emanated approximately simultaneously to that from the overlying surface, suggesting a different causal relationship, if any, between the two from that hypothesized between the source components of SOL20110730T02:04.