Spectral response of the solar atmosphere to an X-class flare event

The only X-class flare of 2015 observed by IRIS occurred at 16:22 UT on 11 March 2015, in AR 12297. This flare generated significant seismic transients in the photosphere at the eastern location of the flare. IRIS observations of the chromosphere and transition region help us understand the physics of the sunquake. In this work we will analyse this event using data from IRIS, SDO, and RHESSI. The IRIS rasters scanned the area between the main footpoints of the solar flare, and a wealth of chromospheric information has been inferred about the dynamics of the event. The main X-ray emission dominates the eastern flare footpoint, being missed by the IRIS slit. Significant enhancements in the chromospheric and TR lines intensities were identified. The forbidden line of Fe XXI 1354.1 Å is detected after the flare peak revealing the coronal responses to the flare. Plasma downflows of up to 300 km/s were identified in the majority of the observed lines, consistent with magnetic field local reconfiguration. We have also analysed an erupting filament developing at an earlier time, which moved rapidly towards the eastern part of the active region. We discuss the possibility that this filament might have pre-conditioned the chromosphere for the flare process.