XRT Picture of the Week (XPOW)

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2014 December 16

Click for movie. Also available on YouTube.

An M3.2 flare and XRT's New Co-alignment Database

On November 15, 2014, XRT observed two M-class flares from active region 12209. XRT first observed this active region during the annular eclipse on October 23, near the center of the sun. One month older, AR12209 was still very active and XRT had excellent data coverage of a M3.2 flare that started around noon. In the GOES plot, the red bar indicates XRT's flare response was activated and a special observation program was run.

We made a movie of this event using our recently developed co-alignment database. Because XRT is on a satellite, small shifts in the pointing can happen while the satellite orbits the Earth, called spacecraft jitter. These tiny shifts need to be taken into account when analyzing data, especially for collaborating with other instruments.

The co-alignment database allows for quick alignment of XRT images. In the movie, the left images are aligned only with XRT's pointing information. Whereas, the images on the right have been aligned using the co-alignment database. Throughout the movie, you can see the effects of spacecraft jitter in the left image as the bright area's dart around between frames. The right images appear smoother as the movie evolves. Near the end of the movie, a frame is lost due to erroneous pointing information but after alignment the frame is in the correct location. You will also notice that the location of the flare is different between the left and right images because the alignment also corrects for a pointing offset.

The co-alignment database uses Hinode's Ultra Fine Sun Sensor output to improve the pointing information (the area of the Sun observed) or by taking the cross-correlation with SDO/AIA images observed close in time. The co-alignment database has been included in XRT's standard analysis software and you can also download the database from MSU's Coalignment Database website.

Keywords: Flare, AR Tracking
Filters: Be_thin

(Prepared by Aki Takeda & Keiji Yoshimura)

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