Radio obsevation of rapid acceleration in a slow filament eruption/fast coronal mass ejection event Kundu et al ApJ, 607, 530

Introduction the close connection between filament eruptions and coronal mass ejection has long been recognized. A typical CME eruption is now believed to possess a three-part structure (Illing & Hundhausen 1986) ; ① an outer rim carrying the bulk of the ejected material at the highest speed ② a cavity that is dark in coronagraph images but is believed to carry intense magnetic field strengths ③ the filament material, which is generally traveling at speeds slower than the outer front. The relation between erupting filament and CME is an ongoing area of study ; does the filament drive the CME ?, or does the CME release the filament ?, or are the both features consequences of something else ?

In this event, filament is clearly seen as stationary depression prior to its gradual rise and we can follow its evolution in the radio images. Filament Activation constant acceleration rapid acceleration 650 km/s

After 5:00UT, the legs of filaments are still visible in the radio images but the leading edge is no longer discernible above the background.

Soft X-ray observations of the rising filament The brightening feature continues and develops an extension to southwest. A Faint long-looped feature is visible and is extending from active region (this feature is also visible in EIT images). This loop feature is moving outward in the same direction as the filament. The dimmimg feature is shown underneath the long loop. This suggests energy release on the long field lines in the region underneath the filament, disturbed by the passage of the filament materials.

The coronal mass ejection A mean CME speed is ～ 1380 km/s at 3.8R. This image suggests that the event was not simple! ; outer edge of CME consist of two arcs.Both arcs appear to have filamentary materials in their cores. If the filament material continues to move outward at 650 km/s, it would reach a height of 2.4 R above the limb at 05:30 UT while leading edge of CME is at the height of 3.8 R. Since the density of CME material is low, it is likely that the CME material also originates at lower height and also has a slower acceleration period prior to the impulsive phase of the flare.

The flare The 3.75 GHz light curve shows a clear impulsive phase. From the absence of impulsive peak in the 17GHz and 34GHz, they infer that this is due to gyrocyncrotron emission. They note that the Type II burst is not observed until after the filament undergoes its rapid acceleration phase. The emission from northward sunspot in impulsive phase originates nonthermal emission.

The brightest feature in the active region at 17GHz is double sources lying over the sun spot. As the flare develops, the flare radio and SXR emission spread to the northward of the brightest SXR loop, reaching the original location of the filament. They confirms the association between the flare, CME, and filament eruption despite the considerable distance between the original filament location and the active region where the main flare occurs.

constant acceleration 650 km/s Motion of the eruptive filament Zhang et al. argued three phases to the eruption. Zhang et al. had a cadence of no better than 10 min., so they could not investigate the relationship between the flare impulsive phase and CME acceleration on finer timescale. Zhang et al. themselves are careful to note that their data only indicate that CME acceleration “ stops at a time close to the SXR peak time”.

Relationship between filament acceleration and flare The coincident of the impulsive phase of flare and the rapid acceleration of filament despite there are large spatial separation. Two types of mechanism can be envisaged for trigger; a disturbance that propagates from one site to the other at high speed, or large scale event that causes both phenomena to happen together. Any disturbances would propagate from the filament to the active region to cause the flare. (Alfven speed 500 km/s  5minutes ) The old view used to be that the flare blast caused any associated CME, but in this event there is little evidence for impulsive type of blast usually envisaged since the flare diagnostic change relatively gradually.

Conclusion The striking feature of the eruption is rapid acceleration of the filament at the time of impulsive phase, following a very long period of gradual acceleration that led to SXR and EUV emission under the rising filament. Once the rapid acceleration has occurred, apex of the filament propagates outward at high speed, with lesser or no acceleration, while the legs of the filament stretch out. This event shows the same three phases of acceleration that Zhang et al. report. The flare in this event seems to occur well away from the footpint of the erupting filament, which favors model in which a large scale disruption of the coronal magnetic field take place, permitting the simultaneous lance of filament/mass ejection and the release of energy in the flare site. A disturbance propagating from one site to the other to trigger the simultaneous event seems very unlikely.

Radio and multi-wavelength evidence of coronal loop eruption in a flare-coronal mass ejection event on 15 April Haung 2004, JGR, 109, A02105 The radio burst at 1-2GHz were observed with fast frequency drifts with bidirectional drift pairs, which may provide a direct signature of upflow and downflow particle acceleration from the reconnection site. The polarization sense of the microwave bursts suddenly reversed at the GHz, which might have been caused by the fast variation of coronal loops or the magnetic field.

A flare-CME event on 15 April 1998 is studied in this paper. There are strong fluctuations fine structures in both the microwave and HXR.

Photospheric magnetgram One upper positive pole (N2) disappeared gradually. The main configurations is close to a bipolar structure. The positive pole(N1) moved away from the negative pole(S1) at a speed of 700 km/s. Some new polarities (S2-3,N3- 5) started to emerge. Note that the configuration at maximum phase is something like a quadrupolar structure (N1-2,S1-2)

Loop Interaction

The strong fluctuation in the microwave and HXR burst may be considered as the evidence of loop interaction or coalesence. There are two recognized loops (L1,L2 may be rooted in bipolar structure). A bright spot A is located in the cross section of two loops. The location of A is raised before the burst at a speed of about several thousand kilometer per hour.

It is most interesting that the interaction coronal loops L1 and L2 were suddenly opened. The loops open time may correspond to the start time of the CME. The speed of CME is about 600 km/s on average.

The opened loops were closed again about 10 min.

Reverse of radio polarization sense It is well known that the polarization of microwave radiation depends on the coronal magnetic field. The polarization sense was reversed during the time the loops were opened and closed in the event. The reverse of polarization sense took place only in the fast fluctuations with a short timescale and narrow bandwidth, which means that variation of coronal magnetic field does not change the polarization of total gyrocyncrotron radiation in full band. The fine structures may be contributed to some plasma- coherent processes in narrow band.

Fast frequency drift in microwave There is a group of both positive and negative frequency drifts and bidirectional drifts started at GHz, which implied the propagation of nonthermal electrons upward and downward simultaneously from acceleration region at the coronal range corresponding to these frequencies. It is noted that the microwave type III burst were observed at the start time of both flare and CME!

Slow frequency drift in microwave bursts At first, type-U bursts appeared and these bursts are composed two or three parallel loop like structure. The speed of the moving sources is several hundred km/s, which is comparable with the speed of the CME

The frequency drift of Type III bursts gradually changes from negative to positive. This is interpreted with the movement of nonthermal electrons along closed field lines.

There are also two or three parallel loop-like structures at the high frequency edge. It is easy to understand the relation of type U and IV with the CMEs. The type U bursts may be contributed to the energetic electrons moving along the closed field lines. After the magnetic loops are opened the mass ejection as well as the type IV burst start along the open field lines.

Summary The radio bursts wit fast frequency drift were observed, followed by the bulk energy release or flares. X-ray and EUV loops were suddenly opened and closed again in the high corona, which correspond to start time of the CMEs. The polarization of microwave bursts was suddenly reversed. In the decay phase, the microwave with slow frequency drift may be associated with the initial phase of CMEs or shocks. From the observation of this event, it is suggested that falres and CMEs may be triggered simultaneously by some MHD instabilities or reconnection.