Ying, B. ; Feng, L. ; Lu, L. ; Zhang, J. ; Magdalenic, J. ; Su, Y. ; Su, Y. ; Gan, W.

published in The Astrophysical Journal, 856 issue 1 (2018)

Abstract: Large-scale solar eruptions have been extensively explored over many years. However, the properties of small-scale events with associated shocks have rarely been investigated. We present analyses of a small-scale, short-duration event originating from a small region. The impulsive phase of the M1.9-class flare lasted only four minutes. The kinematic evolution of the CME hot channel reveals some exceptional characteristics, including a very short duration of the main acceleration phase (<2 minutes), a rather high maximal acceleration rate (˜50 km s-2), and peak velocity (˜1800 km s-1). The fast and impulsive kinematics subsequently results in a piston-driven shock related to a metric type II radio burst with a high starting frequency of ˜320 MHz of the fundamental band. The type II source is formed at a low height of below 1.1 R ⊙ less than ˜2 minutes after the onset of the main acceleration phase. Through the band-split of the type II burst, the shock compression ratio decreases from 2.2 to 1.3, and the magnetic field strength of the shock upstream region decreases from 13 to 0.5 Gauss at heights of 1.1-2.3 R ⊙. We find that the CME (˜4 × 1030 erg) and flare (˜1.6 × 1030 erg) consume similar amounts of magnetic energy. The same conclusion for large-scale eruptions implies that small- and large-scale events possibly share a similar relationship between CMEs and flares. The kinematic particularities of this event are possibly related to the small footpoint-separation distance of the associated magnetic flux rope, as predicted by the Erupting Flux Rope model.

DOI: 10.3847/1538-4357/aaadaf
Funding: BRAIN.be/CCSOM/CCSOM