Monday, July 22, 2013

1307.5097 (J. C. Martínez Oliveros et al.)

Transient artifacts in a flare observed by the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory    [PDF]

J. C. Martínez Oliveros, C. Lindsey, H. S. Hudson, J. C. Buitrago Casas
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) provides a new tool for the systematic observation of white-light flares, including Doppler and magnetic information as well as continuum. In our initial analysis of the highly impulsive \gamma-ray flare SOL2010-06-12T00:57 (Mart'{\i}nez Oliveros et al., Solar Phys., 269, 269, 2011), we reported the signature of a strong blueshift in the two footpoint sources. Concerned that this might be an artifact due to aliasing peculiar to the HMI instrument, we undertook a comparative analysis of Global Oscillations Network Group (GONG++) observations of the same flare, using the PArametric Smearing Correction ALgorithm (PASCAL) algorithm to correct for artifacts caused by variations in atmospheric smearing. This analysis confirms the artifactual nature of the apparent blueshift in the HMI observations, finding weak redshifts at the footpoints instead. We describe the use of PASCAL with GONG++ observations as a complement to the SDO observations and discuss constraints imposed by the use of HMI far from its design conditions. With proper precautions, these data provide rich information on flares and transients.
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