Case study of a magnetic transient in NOAA 11429 observed by SDO/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 0.″5. 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. © 2013. The American Astronomical Society. All rights reserved.