CASE STUDY OF A MAGNETIC TRANSIENT IN NOAA 11429 OBSERVED BY<i>SDO</i>/HMI DURING THE M7.9 FLARE ON 2012 MARCH 13

Abstract

NOAA 11429 was the source of an M7.9 X-ray flare at the western solar limb (N18° W63°) on 2012 March 13 at 17:12 UT. Observations of the line-of-sight magnetic flux and the Stokes I and V profiles from which it is derived were carried out by the Solar Dynamics Observatory Helioseismic and Magnetic Imager (SDO/HMI) with a 45 s cadence over the full disk, at a spatial sampling of 05. During flare onset, a transient patch of negative flux can be observed in SDO/HMI magnetograms to rapidly appear within the positive polarity penumbra of NOAA 11429. We present here a detailed study of this magnetic transient and offer interpretations as to whether this highly debated phenomenon represents a "real" change in the structure of the magnetic field at the site of the flare, or is instead a product of instrumental/algorithmic artifacts related to particular SDO/HMI data reduction techniques.