Signatures of the impact of flare-ejected plasma on the photosphere of a sunspot light bridge^⋆

¹ Instituto de Astrofísica de Canarias, 38205, C/ Vía Láctea, s/n, La Laguna, Tenerife, Spain
e-mail: tobias@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³ Indian Institute of Astrophysics, Bangalore-34, 560034 Karnataka, India
⁴ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

Received: 14 June 2017
Accepted: 21 August 2017

Abstract

Aims. We investigate the properties of a sunspot light bridge, focusing on the changes produced by the impact of a plasma blob ejected from a C-class flare.

Methods. We observed a sunspot in active region NOAA 12544 using spectropolarimetric raster maps of the four Fe i lines around 15 655 Å with the GREGOR Infrared Spectrograph, narrow-band intensity images sampling the Fe i 6173 Å line with the GREGOR Fabry-Pérot Interferometer, and intensity broad-band images in G-band and Ca ii  H-band with the High-resolution Fast Imager. All these instruments are located at the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The data cover the time before, during, and after the flare event. The analysis is complemented with Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager data from the Solar Dynamics Observatory. The physical parameters of the atmosphere at differents heights were inferred using spectral-line inversion techniques.

Results. We identify photospheric and chromospheric brightenings, heating events, and changes in the Stokes profiles associated with the flare eruption and the subsequent arrival of the plasma blob to the light bridge, after traveling along an active region loop.

Conclusions. The measurements suggest that these phenomena are the result of reconnection events driven by the interaction of the plasma blob with the magnetic field topology of the light bridge.