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

[1] 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 similar to500s 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 similar to4865 m/s(2) within the first 280 Mm of the solar corona.