Fast acceleration of a CME‐related X‐ray structure in the low solar corona

We report on a unique observation of the early and rapid acceleration of a fast CME in the low solar corona. The coronal disturbance associated with a LASCO CME and concurrent X1.2 flare on 1998 April 23 was well‐observed by the Yohkoh Soft X‐ray Telescope. The X‐ray observations clearly show an accelerating structure, reaching 800–1100 km/s in ∼500s at a de‐projected height of only 280 Mm, indicating an acceleration well in excess of 1700 m/s 2 . The soft X‐ray observations are coincident with the onset of the CME, which ultimately attained a velocity of 1390 km/s and generated a number of interplanetary radio signatures, frequently associated with fast events. Assuming a constant acceleration, a 0 , throughout the duration of the X‐ray observations, we determine a best‐fit value of a 0 = 1756 m/s 2 , while application of a power‐law acceleration model yields a better fit to the data with a peak acceleration of ∼4865 m/s 2 within the first 280 Mm of the solar corona.