Eruption of a plasma blob, associated M-class flare, and large-scale extreme-ultraviolet wave observed by SDO^⋆

¹ Korea Astronomy and Space Science Institute (KASI), 305-348 Daejeon, Republic of Korea
e-mail: pankaj@kasi.re.kr
² Radio Astronomy Centre, National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, 643 001 Udhagamandalam ( Ooty), India
e-mail: mano@ncra.tifr.res.in

Received: 24 August 2012
Accepted: 6 March 2013

Abstract

We present a multiwavelength study of the formation and ejection of a plasma blob and associated extreme ultraviolet (EUV) waves in active region (AR) NOAA 11176, observed by SDO/AIA and STEREO on 25 March 2011. The EUV images observed with the AIA instrument clearly show the formation and ejection of a plasma blob from the lower atmosphere of the Sun at  ~9 min prior to the onset of the M1.0 flare. This onset of the M-class flare happened at the site of the blob formation, while the blob was rising in a parabolic path with an average speed of  ~300 km s. The blob also showed twisting and de-twisting motion in the lower corona, and the blob speed varied from  ~10−540 km s. The faster and slower EUV wavefronts were observed in front of the plasma blob during its impulsive acceleration phase. The faster EUV wave propagated with a speed of  ~785 to 1020 km s, whereas the slower wavefront speed varied in between  ~245 and 465 km s. The timing and speed of the faster wave match the shock speed estimated from the drift rate of the associated type II radio burst. The faster wave experiences a reflection by the nearby AR NOAA 11177. In addition, secondary waves were observed (only in the 171 Å channel), when the primary fast wave and plasma blob impacted the funnel-shaped coronal loops. The Helioseismic Magnetic Imager (HMI) magnetograms revealed the continuous emergence of new magnetic flux along with shear flows at the site of the blob formation. It is inferred that the emergence of twisted magnetic fields in the form of arch-filaments/“anemone-type” loops is the likely cause for the plasma blob formation and associated eruption along with the triggering of M-class flare. Furthermore, the faster EUV wave formed ahead of the blob shows the signature of fast-mode MHD wave, whereas the slower wave seems to be generated by the field line compression by the plasma blob. The secondary wave trains originated from the funnel-shaped loops are probably the fast magnetoacoustic waves.