Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare

We present Atmospheric Imaging Assembly observations of a structure we interpret as a current sheet associated with an X4.9 flare and coronal mass ejection that occurred on 2014. February. 25 in NOAA Active Region 11990. We characterize the properties of the current sheet, finding that the sheet remains on the order of a few thousand kilometers thick for much of the duration of the event and that its temperature generally ranged between 8 and 10 MK. We also note the presence of other phenomena believed to be associated with magnetic reconnection in current sheets, including supra- arcade downflows and shrinking loops. We estimate that the rate of reconnection during the event was M-A approximate to 0.004- 0.007, a value consistent with model predictions. We conclude with a discussion of the implications of this event for reconnection- based eruption models.