The white arc marks the solar limb.
EUV STEREO images (Figure 2) revealed a big rise and an EUV wave. Rise activity was also identified in the Catania Hα images. White light COR1 images from STEREO A & & B reveal a CME with a radial speed of ~ 700 km/s and a streamer interruption.
We determined the 3D structure of the rise through triangulation of STEREO A & & B images. Projection of the surge position on the NRH images showed that the type IIs were not connected with the surge. The same conclusion was reached by projecting the type II positions on the STEREO A images, after estimating the height of the radio emission from the observing frequency and a coronal design (Figure 3). Based on computations for uniform designs (Kontar 2021, personal interaction), we did not apply any refraction and scattering corrections to the position of the radio sources. We keep in mind in Figure 3 that the forecast of the type II positions is near the edge of the 195Å EUV wave, which recommends a possible association.
Figure 3. Derived positions of the type IIs plotted on 195 Å STEREO A running difference images for the first (left) and the second phase of the event. (from Alissandrakis et al. 2021),.
Conclusions.
At first glimpse, the surge appeared to be a great prospect for association with the type II emissions, our analysis revealed that it was not. The association of 2 separate type II bursts with the same EUV wave suggests that each type II was related with various parts of the wave.
In addition to the origin of the type-II emission, our analysis of the radio observations provided a variety of fascinating results: Using cross-correlation we determined the frequency ratio and the time delay between emission at the plasma frequency and its harmonic throughout the very first type II burst; we found worths of 1.95 and 0.23 to 0.6 s, respectively. We likewise observed pulsations superposed on the second type-II burst. The pulsations were broadband with a bandwidth of about 200MHz and they began prior to the type II.
This work highlights the significance of imaging spectroscopy for understanding the physics of solar radio emission.
Based on a recent paper: Alissandrakis, C. E., Nindos, A., Patsourakos, S., Hillaris, A, 2021, A&A, 654, A112. doi:10.1051/ 0004-6361/2021 41672.
References.
Nelson, G. J., & & Melrose, D. B. 1985, in Type II Bursts, eds. D. J. McLean, & & N. R. Labrum, 333.
Nindos, A., Aurass, H., Klein, K.-L., & & Trottet, G. 2008, Sol. Phys., 253, 3.
Choose, M., & & Vilmer, N. 2008, A&AR v, 16, 1.
Vršnak, B., & & Cliver, E.W. 2008, Sol. Phys, 253, 215.
* Full list of authors: Costas Alissandrakis, Alexander Nindos, Spiros Patsourakos, Alexander Hillaris.
Solar type II bursts are sporadic emissions characterized by their narrow bandwidth and sluggish frequency drift in vibrant spectra (Nelson & & Melrose, 1985; Vršnak & Cliver 2008; Nindos et al. 2008; Pick & Vilmer 2008). They are credited to shock waves produced by flare/CME eruptions. Nevertheless, the association of type IIs with optical or EUV functions is unclear; the leading edge or flanks of CMEs, the front of an erupting flux rope, expanding soft X-ray loops, jets, EUV cavities and waves, in addition to CME-streamer interactions have actually been recommended (for a more comprehensive conversation see Alissandrakis et al. 2021).
The association of type IIs with optical or EUV functions is not clear; the leading edge or flanks of CMEs, the front of an emerging flux rope, broadening soft X-ray loops, jets, EUV cavities and waves, as well as CME-streamer interactions have been suggested (for a more comprehensive conversation see Alissandrakis et al. 2021).
Dynamic spectrum of the February 12, 2010 event, taped by the ARTEMIS IV-JLS radio spectrograph. 1F, 1H, B2, b1 and mark branches of type II bursts.
Observations and Analysis.
The event evaluated here happened on February 12, 2010, starting around 11:25 UT, in active region 11046 near the main meridian (N25, E11); it was related to an M9 flare. In addition to ARTEMIS IV-JLS dynamic spectra and NRH images, we utilized information from RHESSI, GOES SXI, Hinode XRT, Catania Hα, along with STEREO A & & B, which saw the occasion near the east and west limb respectively. No EUV images from SOHO were available.
The vibrant spectrum (Figure 1) was abundant in structure. Two stages, confirmed in GOES and RHESSI light curves, show up, every one of which had actually associated type II emission; The type II throughout the first stage had a prominent fundamental-harmonic structure (1F and 1H in the figure), whereas the one throughout the 2nd phase revealed 3 branches, B3, b1 and b2.
The very same conclusion was reached by forecasting the type II positions on the STEREO A images, after estimating the height of the radio emission from the observing frequency and a coronal design (Figure 3). We note in Figure 3 that the forecast of the type II positions is near the edge of the 195Å EUV wave, which recommends a possible association.
The association of 2 different type II bursts with the very same EUV wave suggests that each type II was related with various parts of the wave. In addition to the origin of the type-II emission, our analysis of the radio observations offered a number of intriguing outcomes: Using cross-correlation we measured the frequency ratio and the time delay in between emission at the plasma frequency and its harmonic during the first type II burst; we discovered values of 1.95 and 0.23 to 0.6 s, respectively.