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Open Access
Issue
A&A
Volume 691, November 2024
Article Number A4
Number of page(s) 9
Section The Sun and the Heliosphere
DOI https://doi.org/10.1051/0004-6361/202449523
Published online 25 October 2024

© The Authors 2024

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.

1. Introduction

Type II solar radio bursts manifest as slender bands gradually shifting from higher to lower frequencies on solar radio dynamic spectra. It is widely accepted that these bursts are excited by energetic electrons accelerated at coronal shocks (Wild & McCready 1950; Nelson & Melrose 1985). The electron beams accelerated by these shocks have the capability to induce Langmuir waves, producing radio emissions at both fundamental (F) and harmonic (H) frequencies of the local plasma (Ginzburg & Zhelezniakov 1958). Consequently, the configuration of type II bursts often exhibits two distinct emission branches, with a frequency ratio of close to 2:1, corresponding to emissions at the F and H frequencies. When coupled with an appropriate coronal density model, the frequency drift rate of type II radio bursts can be leveraged to deduce shock speed by converting emission frequency to local plasma density (Reiner et al. 2003; Cho et al. 2007, 2011). Hence, type II bursts provide a method to forecast the arrival time of shock waves as they approach and impact the Earth.

Coronal mass ejections (CMEs), jets, flares, and other eruptive activities are potential drivers of type II bursts. Among these activities, type II bursts are commonly detected in conjunction with CMEs. Statistical analyses reveal a strong correlation between type II radio bursts and fast CME events (Gopalswamy et al. 2019; Kumari et al. 2023). Radio imaging observations indicate that the sources of type II radio bursts are often situated above the nose and/or flanks of CMEs (Chen et al. 2010; Mäkelä et al. 2018). Furthermore, CMEs can excite type II bursts through interactions with high-density structures in their path, such as coronal steamers and rays (Chen et al. 2014; Kouloumvakos et al. 2021; Koval et al. 2023). With the launch of SDO and STEREO satellites, type II bursts without accompanying CMEs have been continuously reported. These type II bursts are associated with jets, disturbed coronal loops, and other phenomena (Kumar et al. 2016; Hou et al. 2023; Morosan et al. 2023). Although these type II bursts do not accompany CMEs, they are generally associated with wave-like phenomena such as extreme ultraviolet waves or disturbed coronal loops, which may act as shock waves that excite type II bursts.

Occasionally, both the F and H branches of type II bursts can further split into two nearly parallel bands, a process referred to as “band splitting” (Smerd et al. 1974; Vršnak et al. 2001). The widely accepted model for interpreting band splitting suggests that emission occurs at different locations upstream and downstream of the shock front (Smerd et al. 1975). Using the LOw-Frequency ARray (LOFAR) Chrysaphi et al. (2018) quantitatively determined that the upper and lower emission sources were spatially separated by approximately 0.2 solar radii. These authors proposed that considering scattering effects, the sources of band splitting could originate from nearly co-spatial locations, thus supporting the upstream–downstream (UD) scenario. In accordance with this hypothesis, band splitting can be used to deduce the density ratio between upstream and downstream shock regions, as well as the Alfvén Mach number of the shock wave. Additionally, the magnetic fields in the solar corona can be further diagnosed using this hypothesis (Cho et al. 2007; Ma et al. 2011; Vasanth et al. 2014; Su et al. 2016; Mahrous et al. 2018; Kumari et al. 2019).

In this paper, we report a type II burst associated with filament–filament interaction. In accordance with the UD scenario, we inferred the magnetic field strength based on observed band-splitting phenomena.

2. Observations and data analysis

Our observation of filament–filament interaction is based on the data from the Chinese Hα Solar Explorer (CHASE; Li et al. 2022) and the Solar Dynamics Observatory (SDO; Pesnell et al. 2012). The CHASE/Hα Imaging Spectrograph (HIS) offers spectroscopic observations of the Sun within the Hα passbands (6559.7–6565.9 Å). The temporal cadence and the spatial and spectral pixel sizes of CHASE/HIS imaging spectral data are 1 minute, 0 . ″ $ \overset{\prime \prime }{.} $52, and 0.024 Å, respectively. Furthermore, we supplemented our analysis with Hα data at 6563 Å from GONG, which have a spatial resolution of ∼1″ and a cadence of ∼1 minute. The SDO/Atmospheric Imaging Assembly (AIA; Lemen et al. 2012) provides seven EUV passbands covering the full disk of the Sun and extending up to 0.5 R⊙ above the limb, with a pixel resolution of 0 . ″ $ \overset{\prime \prime }{.} $6 and a cadence of 12 seconds. In addition, the magnetic field at the two ends of F1 was examined using SDO/Helioseismic and Magnetic Imager (HMI; Scherrer et al. 2012) with a pixel resolution of 0 . ″ $ \overset{\prime \prime }{.} $5. X-ray emissions during the filament–filament interaction were monitored by GOES and the Advanced Space-based Solar Observatory (ASO-S; Gan et al. 2023). ASO-S/Hard X-Ray Imager (HXI; Su et al. 2019) provides the hard x-ray (HXR) data from 10 to 300 keV with a cadence of 4 s in regular observation mode.

The kinematics analysis of the CME was conducted using the data from SDO/AIA, Solar Terrestrial Relations Observatory (STEREO; Howard et al. 2008) A, including its Inner and Outer coronagraphs (COR1 and COR2). On the day of this event, the separated angle between STEREO-A and SDO was only 2.59 degrees.

The type II burst was recorded by the Compound Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatory (CALLISTO), Australia-ASSA Observatory. CALLISTO is dedicated to continuously observing the solar radio spectrum 24 hours a day, year round. In addition, the coronal electron density distribution was deduced by inverting the polarization brightness (pB) data recorded by the COR1 coronagraph based on the spherically symmetric polynomial approximation (SSPA; Wang & Davila 2014) technique.

3. Results

3.1. Filament–filament interaction

On 2023 September 11, two filaments were observed near the northeastern solar limb, and were designated F1 and F2 (the first row of Fig. 1; white and blue arrows). F1 situated within AR 13429 appeared as a curved filament, while F2 presented as an elongated filament adjacent to F1. Within a small field of view (FOV; panel c), the northern ends of F1 were observed to be anchored on negative polarities, while the southern ends were anchored on positive polarities. Additionally, F2 experienced a partial lift in the evolution of previous day, which helps deduce that the northern ends were likely rooted on positive polarities and southern ends were rooted on negative polarities behind the Sun.

thumbnail Fig. 1.

Filament–filament interaction studied here. (a)–(c): Overview of the two filaments in CHASE/HIS and AIA 304 Å maps. The white and blue arrows indicate F1 and F2. The cyan dashed box indicates the AR 13429, and the FOV of panel c. Contours of HMI magnetic field at the closest time are superposed on AIA 304 Å maps with positive (negative) fields in green (blue), and the levels for positive (negative) fields are 150 gauss. (d)–(f): Eruption of F1 and disturbance of F2 in CHASE/HIS, AIA 304 Å, and AIA 171 Å maps. The cyan arrow indicates the erupting F1. The black arrow indicates two parallel flare ribbons. (g)–(i) Filament–filament interaction and formation of loop-like structure in CHASE/HIS, AIA 304 Å, and AIA 171 Å maps. The yellow arrows indicate the loop-like structure. An animation of the filament–filament interaction is available online. The animated sequence runs from 00:55 UT to 02:00 UT on 2023 September 11 and its real-time duration is 13 s.

The eruption of F1 and the disruption of F2 are shown in the second row of Fig. 1. The erupted F1 appeared as a rising bright arch up to about 01:16 UT (cyan arrow in panel e and f), resulting in a two-ribbon flare in the source region (black arrow in panel f). As F1 expanded outward, its northern part likely disturbed nearby F2 at around 01:15 UT. Subsequently, F2 erupted followed by filament materials ejected upward and toward the northern ends (lasting from approximately 01:15 UT to 02:00 UT in animation 1). Interestingly, the ejecta from F1 and F2 likely interacted with each other, forming loop-like structures perpendicular to the erupting filaments (third row of Fig. 1; yellow arrows). These loop-like structures continued to expand, and a blob of material formed in front of them around 01:25 UT, probably as a result of compression; they can be seen to last for several minutes in animation 1. In addition, a third large ejection of material occurred in the southern part of the active region around 01:30 UT.

To further investigate the eruptions and filament–filament interactions, time–distance plots were created along three slices (S1, S2, and S3). S1 was positioned along the direction of the eruption of F1 (Fig. 2a). F1 erupted around 01:08 UT and entered its impulsive phase at around 01:10 UT, reaching a final speed of ∼324 km s−1 (white dashed line). S2 was along the direction of F2’s eruption (Fig. 2b). It is evident that filament materials from F2 were ejected upwards and towards the northern ends, with an average speed of ∼201 km s−1 (blue dashed line). We note the appearance of bright filament materials from F1 overlapping on F2 (white arrow), possibly indicating interaction between the ejecta from F1 and F2. Thereafter, loop-like structures formed during this filament–filament interaction. Along S3, which passed through the loop-like structure (Fig. 2c), these structures formed around 01:20 UT with an average speed of ∼375 km s−1 (yellow dashed line). The speed of the loop-like structure was faster than that of the ejecting F1 and F2, possibly due to acceleration by magnetic reconnection after the interaction. In addition, the flux of GOES 1–8 Å revealed that the erupting F1 induced a C2.5 two-ribbon flare. The ASO-S/HXI 10–300 keV flux showed two peaks during the F1 and F2 eruptions. A third peak appeared around 01:30 UT, which was caused by the third filament eruption occurring in the southern part of AR 13429, with a speed of ∼357 km s−1 (green arrows and dashed line in panel a and d).

thumbnail Fig. 2.

Time–distance plots along three slices. (a) S1 along the erupt direction of F1 in AIA 171 Å. The white dashed line indicates the speed of erupting F1. The green dashed line indicates the speed of the third filament eruption. (b) S2 along the erupt direction of F2 in AIA 304 Å. The blue dashed line indicates the speed of ejective F2. The white arrow indicates bright material from F1. (c) S3, which passes through the loop-like structures. The yellow dashed line indicates the speed of the loop-like structures. The black arrow indicates the speed of the large-scale expanding loops ahead of the loop-like structures. (d) The GOES 1–8 Å and ASO-S/HXI 10–300 kev flux. The green arrows indicate another filament eruption occurring in the southern part of AR 13429.

Accompanying the formation of loop-like structures, large-scale coronal loops appeared ahead of them and propagated outward (black dashed line in Fig. 3a and animation 2). These expanding loops were much broader than the erupting F1, which had a smaller angular width, and their speed was around 496 km s−1 (black arrow in Fig. 2c). Subsequently, these large expanding loops entered the FOV of COR1 and evolved into a dense CME front at around 01:26 UT (animation 2). The kinematic evolution of the CME is shown in the time–height plots based on measurements by AIA, COR1, and COR2 (Fig. 3d). It can be seen that the extrapolated onset time of the CME was around 01:14 UT (black dashed line and square). The speed of the CME was approximately 499 km s−1 as it propagated within the FOV of AIA and COR1, and around 540 km s−1 within the FOV of COR2. As recorded by the online Coordinated Data Analysis Workshops catalog (CDAW1; Yashiro et al. 2004), the onset time of the CME was around 01:10 UT and the speed was around 545 km s−1. These are in agreement. Additionally, the angular width of the CME was around 166 degrees as recorded by the CDAW catalog, suggesting a broad and strong CME.

thumbnail Fig. 3.

Evolution and kinematics analysis of the CME. (a) The black dashed line indicates the large-scale expanding loops in AIA 193 Å. (b) CME as seen by the COR1 coronagraph. (c) CME as seen by the COR2 coronagraph. (d) Time–height plots of the CME. The asterisk indicates the height. The green and blue lines indicate the lineally fitted speed. The black dashed line and square indicate the extrapolated onset time of the CME to 1 R⊙. An animation of the evolution of the CME is available online. The animated sequence runs from 01:00 UT to 03:00 UT on 2023 September 11 and its real-time duration is 13 s.

It is clear that a filament–filament interaction occurred between erupting F1 and F2, which triggered a strong CME. The timeline of the main phase of these events is presented in Fig. 4. First, F1 erupted and produced a C2.5 two-ribbon flare (starting at around 01:08 UT). Subsequently, F2 erupted, possibly due to the disruption caused by the erupting F1 (starting at around 01:14 UT). Remarkably, filament–filament interaction possibly occurred between ejective materials from F1 and F2, resulting in the formation of loop-like structures perpendicular to the two filaments (starting at around 01:20 UT). Eventually, these loop-like structures triggered a strong CME that appeared above the occulting disk of COR1 at around 01:26 UT. Additionally, a third large filament ejection occurred in the southern part of AR 13429 at around 01:30 UT.

thumbnail Fig. 4.

Timeline of the main phase of the event. The start time of the eruption of F1, the eruption of F2, the formation of loop-like structures, and the CME appearing above the occulting disk of COR1 are marked on the time axis.

3.2. Type II radio burst

Around the formation of loop-like structures and the appearance of CME above the occulting disk of COR1, a type II radio burst appeared on the solar spectrum detected by CALLISTO (Australia-ASSA; Fig. 5). The type II burst shows clear F and H structures (marked “F” and “H”) with band-splitting phenomena. It started around 01:20 UT and ended at around 01:33 UT, lasting for 13 minutes. The start frequency of the F part was around 46 MHz, with a termination frequency of around 17 MHz.

thumbnail Fig. 5.

Type II burst in CALLISTO (Australia-ASSA). The fundamental and harmonic parts are marked “F” and “H”. The relevant phases of the event during the type II burst are marked on the time axis.

By inverting the pB data recorded by the COR1 coronagraph with the SSPA technique, the coronal electron density distribution was deduced along three position angles (PAs) at 60, 75, and 90 degrees (Fig. 6a). Figure 6b presents the profiles of the coronal electron density distribution and the radio frequency converted using the relationship

f = 8.98 × 10 3 n $$ \begin{aligned} f = 8.98 \times 10^{3} \sqrt{n} \end{aligned} $$(1)

thumbnail Fig. 6.

Kinematics analysis of the type II burst. (a) pB data recorded by STEREO COR1 coronagraph at 01:00 UT on 2023 September 11. The soiled, dotted, and dashed lines are separately at the PAs of 60, 75, and 90 degrees. (b) Profile of coronal electron density distribution and corresponding radio frequency along three PAs deduced from STEREO COR1 pB data. (c) Frequency of the type II burst (red asterisk) and deduced shock height (blue asterisk). The lineally fitted shock speed (green and blue lines). The first blue asterisk indicates the extrapolated initial shock height (d) Value of inferred magnetic field strength based on the band-splitting phenomenon in the UD scenario multiplied by 1.5 (blue plus symbol). The empirical model is that proposed by Dulk & McLean (1978) (red curve).

with respect to the coronal height. Thus, the frequency of the type II burst (red asterisk) was converted to coronal height (blue asterisk; Fig. 6c). It can be seen that the extrapolated initial height of the type II burst was around 1.45 R⊙. The frequency drift rates were determined to be in the range of 0.05 MHz/s to 0.017 MHz/s, yielding shock speeds ranging from around 441 km s−1 to 400 km s−1. The deduced formation height of the type II burst is comparable to the observed CME height at that time (around 1.43 R⊙) and is too high to fit the height of the loop-like structures (around 1.2 R⊙). The deduced shock speed from the type II burst was slightly lower than the observed CME speed, possibly due to the source location of the type II burst being located at the flank.

Additionally, the type II burst shows clear band-splitting phenomena. It is widely accepted that the emission frequencies of band splitting are originating from regions of different densities ahead (upstream) of and behind (downstream from) the shock front (UD scenario). These regions are characterized separately by electron densities [n1], [n2], as well as plasma frequencies [fL], [fU]. Using the relation between the plasma frequency [f] and electron density [n] given by Eq. (1), the density jump [X] can be written as

X = n 2 n 1 = ( f U f L ) 2 , $$ \begin{aligned} X= \frac{n_2}{n_1}=\left(\frac{f_U}{f_L}\right)^2, \end{aligned} $$(2)

and thus the [X] was estimated to be at a range of 1.32–1.38. From density jump [X], Alfvén Mach number MA was derived using a simplified Rankine–Hugoniot jump relation,

M A = X ( X + 5 ) / 2 ( 4 − X ) , $$ \begin{aligned} M_{A}=\sqrt{X(X+5)/2(4-X)}, \end{aligned} $$(3)

where a perpendicular shock geometry and β → 0 was assumed (Vršnak et al. 2002). The values of Alfvén Mach numbers MA were determined to be in the range of 1.25–1.30. Then, the Alfvén speed [VA] can be converted from an Alfvén Mach number using the relation:

V A = V s M A , $$ \begin{aligned} {V_A} = \frac{V_s}{M_A}, \end{aligned} $$(4)

where the deduced shock speed [Vs] was around 400–440 km s−1. The Alfvén speed [VA] was determined to vary within approximately 340–373 km s−1. Finally, the magnetic field strength was determined using the Alfvén speed [VA] and [fL]:

B = 5.1 × 10 − 5 × f L V A . $$ \begin{aligned} B = 5.1 \times 10^{-5} \times {f_L}{V_A}. \end{aligned} $$(5)

Magnetic field strengths were around 0.87–0.30 G at the height of 1.45–1.87 R⊙. However, the deduced shock speed was estimated to be lower than the actual shock speed, which accounts only for the component along the radial direction. After multiplying by a coefficient of 1.5, the estimated strength of the coronal magnetic field ranged from 1.30 to 0.45 G, showing a strong correlation with the empirical model (Fig. 6d; Dulk & McLean 1978).

4. Discussion and conclusions

Combing with the observations from CHASE, SDO, STEREO, and CALLISTO, we report a type II radio burst associated with filament–filament interaction. The interaction occurred when an erupting filament (F1) interacted with a nearby eruptive filament, F2. This interaction led to a possible magnetic reconnection, forming loop-like structures perpendicular to the two filaments. Subsequently, the expansion of the loop-like structures triggered a strong CME. Interestingly, a type II burst occurred around the time when the loop-like structures formed and the CME appeared above the occulting disk of COR1. By converting the type II burst’s frequency to coronal height using the SSPA technique and pB data recorded by STEREO COR1, we determined the formation height of the type II burst to be around 1.45 R⊙, with a speed of approximately 440 km s−1. This is comparable to the observed height of the CME (∼1.43 R⊙) at that time, although slightly lower in speed (∼540 km s−1).

The phenomenon of filament–filament interaction is of particular interest, often associated with magnetic reconnection (Török et al. 2011; Jiang et al. 2013, 2014; Joshi et al. 2014; Zhu et al. 2015; Yang et al. 2017). In this event, the northern ends of erupting filament F1 were rooted on negative polarities, while the southern ends of filament F2 were possibly rooted on positive polarities, creating favorable conditions for magnetic reconnection. It is possible that the northern part of erupting F1 interacted with the southern ejective part of F2, forming loop-like structures perpendicular to the two erupting filaments, connecting with the southern ends of F1 and northern ends of F2. It is noteworthy that the loop-like structures were significantly broadened from the initial erupting F1 and experienced acceleration after the interaction. In addition, the formation time of loop-like structures was close to the extrapolated onset time of the CME. Therefore, it is possible that the filament–filament interaction played an important role in triggering the subsequent strong CME.

The type II burst was closely correlated with the loop-like structures and the CME. These structures and the CME are potential drivers of the excitation of the type II burst. The formation of the loop-like structures was close in time to the onset of the type II burst, and previous studies have revealed that type II bursts can be excited by shock waves driven by the expansion of strongly inclined magnetic loops reconnecting with nearby emerging flux (Su et al. 2015). However, the observed height of the loop-like structures was too low to match the initial height of the type II burst in this event. On the other hand, the initial height of the type II burst was comparable to the observed height of the strong CME. Therefore, the filament–filament interactions did not trigger the excitation of the type II burst directly in this event; instead, they triggered a strong CME that excited the type II burst. Additionally, a third large filament ejection occurring in the southern part of the AR 13429 at around 01:30 UT is also noteworthy. Considering its beginning time (of very close to the termination time of the type II burst), its speed (of around 357 km/s, lower than the CME and the type II burst), and the observed height (around 1.1 R⊙ at around 01:30 UT, which is too low compared to the deduced height of type II (around 1.82 R⊙), we suggest it may not be related to this type II emission.

The relatively long-lasting and initially low-frequency type II burst with band-splitting phenomena provides an opportunity to infer the strength of the coronal magnetic field across a wide range of coronal heights. According to the UD scenario, the density jump [X] and the Alfv’en Mach number [MA] of the shock wave were calculated from the type II burst. The values of [X] range from around 1.32 to 1.38, and [MA] ranges from around 1.25 to 1.30, aligning well with previous studies (Ma et al. 2011; Vasanth et al. 2014). Furthermore, the magnetic field strength was estimated to range from 1.32 to 0.45 G after multiplying by a coefficient of 1.5, decreasing from 1.45 to 1.87 R⊙ in the corona. This result shows reasonable agreement with the empirical models (Dulk & McLean 1978) and previous findings (Cho et al. 2007; Kumari et al. 2019). For a recent review of measurements of coronal magnetic field strength, please refer to Alissandrakis & Gary (2021).

Based on the above results and discussions, a scenario was proposed to interpret the type II burst associated with filament–filament interaction (Fig. 7). An overview of the filament–filament interaction is presented in panel (a). F1 erupted from AR 13429, with its southern ends rooted on positive polarities and northern ends on negative polarities (red line). Simultaneously, F2 erupted upwards with its southern ends rooted on negative polarities (blue lines). Ahead of the two filaments, large-scale coronal loops constrained them (green line). Interestingly, the filament–filament interaction occurred between two erupting filaments (yellow “X”). Consequently, loop-like structures connecting the southern ends of F1 and the northern ends of F2 formed at high latitudes (lines change from red to blue in panel b), and leaving likely small loops at low latitudes (lines change from blue to red). Remarkably, the formation of these loop-like structures triggered the expansion of overlying loops, which subsequently evolved into a strong CME (green line) and excited a type II burst possibly located at the flank of the CME-driven shock (black line). Therefore, filament–filament interaction acted as a piston to initiate a strong CME that excited the type II burst at the flank.

thumbnail Fig. 7.

Scenario of the type II burst associated with filament–filament interaction. (a) Overview of the filament–filament interaction. The red line indicates erupting F1. The blue lines indicate erupting F2. The green line indicates the overlying loops constraining two filaments. The yellow “X” indicates the interaction between the erupting F1 and F2. (b) Formation of the type II burst. The lines change from red to blue and the lines change from blue to red indicate the productions of the magnetic reconnection between F1 and F2. Green and black lines indicate the CME and CME-driven shock, respectively. The possible location of the type II burst is marked on the flank of the shock wave.

In summary, the type II burst was closely associated with the filament–filament interaction and was possibly excited by the associated CME at the flank. We propose that the filament–filament interaction played an important role in producing the type II burst via its action as a piston, triggering a strong CME. Further observations and simulations of the type II burst directly excited by the filament–filament interaction are still needed.

Data availability

Movies associated with Figs. 1 and 3 are available at https://www.aanda.org

Acknowledgments

The authors thank the CHASE, SDO, STEREO, CALLISTO and ASO-S team for the high quality data. CHASE mission is supported by China National Space Administration (CNSA). ASO-S mission is supported by the Strategic Priority Research Program on Space Science, the Chinese Academy of Sciences, grant No. XDA15320000. This work is supported by grants of NSFC 12073016.

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All Figures

thumbnail Fig. 1.

Filament–filament interaction studied here. (a)–(c): Overview of the two filaments in CHASE/HIS and AIA 304 Å maps. The white and blue arrows indicate F1 and F2. The cyan dashed box indicates the AR 13429, and the FOV of panel c. Contours of HMI magnetic field at the closest time are superposed on AIA 304 Å maps with positive (negative) fields in green (blue), and the levels for positive (negative) fields are 150 gauss. (d)–(f): Eruption of F1 and disturbance of F2 in CHASE/HIS, AIA 304 Å, and AIA 171 Å maps. The cyan arrow indicates the erupting F1. The black arrow indicates two parallel flare ribbons. (g)–(i) Filament–filament interaction and formation of loop-like structure in CHASE/HIS, AIA 304 Å, and AIA 171 Å maps. The yellow arrows indicate the loop-like structure. An animation of the filament–filament interaction is available online. The animated sequence runs from 00:55 UT to 02:00 UT on 2023 September 11 and its real-time duration is 13 s.
In the text
thumbnail Fig. 2.

Time–distance plots along three slices. (a) S1 along the erupt direction of F1 in AIA 171 Å. The white dashed line indicates the speed of erupting F1. The green dashed line indicates the speed of the third filament eruption. (b) S2 along the erupt direction of F2 in AIA 304 Å. The blue dashed line indicates the speed of ejective F2. The white arrow indicates bright material from F1. (c) S3, which passes through the loop-like structures. The yellow dashed line indicates the speed of the loop-like structures. The black arrow indicates the speed of the large-scale expanding loops ahead of the loop-like structures. (d) The GOES 1–8 Å and ASO-S/HXI 10–300 kev flux. The green arrows indicate another filament eruption occurring in the southern part of AR 13429.
In the text
thumbnail Fig. 3.

Evolution and kinematics analysis of the CME. (a) The black dashed line indicates the large-scale expanding loops in AIA 193 Å. (b) CME as seen by the COR1 coronagraph. (c) CME as seen by the COR2 coronagraph. (d) Time–height plots of the CME. The asterisk indicates the height. The green and blue lines indicate the lineally fitted speed. The black dashed line and square indicate the extrapolated onset time of the CME to 1 R⊙. An animation of the evolution of the CME is available online. The animated sequence runs from 01:00 UT to 03:00 UT on 2023 September 11 and its real-time duration is 13 s.
In the text
thumbnail Fig. 4.

Timeline of the main phase of the event. The start time of the eruption of F1, the eruption of F2, the formation of loop-like structures, and the CME appearing above the occulting disk of COR1 are marked on the time axis.
In the text
thumbnail Fig. 5.

Type II burst in CALLISTO (Australia-ASSA). The fundamental and harmonic parts are marked “F” and “H”. The relevant phases of the event during the type II burst are marked on the time axis.
In the text
thumbnail Fig. 6.

Kinematics analysis of the type II burst. (a) pB data recorded by STEREO COR1 coronagraph at 01:00 UT on 2023 September 11. The soiled, dotted, and dashed lines are separately at the PAs of 60, 75, and 90 degrees. (b) Profile of coronal electron density distribution and corresponding radio frequency along three PAs deduced from STEREO COR1 pB data. (c) Frequency of the type II burst (red asterisk) and deduced shock height (blue asterisk). The lineally fitted shock speed (green and blue lines). The first blue asterisk indicates the extrapolated initial shock height (d) Value of inferred magnetic field strength based on the band-splitting phenomenon in the UD scenario multiplied by 1.5 (blue plus symbol). The empirical model is that proposed by Dulk & McLean (1978) (red curve).
In the text
thumbnail Fig. 7.

Scenario of the type II burst associated with filament–filament interaction. (a) Overview of the filament–filament interaction. The red line indicates erupting F1. The blue lines indicate erupting F2. The green line indicates the overlying loops constraining two filaments. The yellow “X” indicates the interaction between the erupting F1 and F2. (b) Formation of the type II burst. The lines change from red to blue and the lines change from blue to red indicate the productions of the magnetic reconnection between F1 and F2. Green and black lines indicate the CME and CME-driven shock, respectively. The possible location of the type II burst is marked on the flank of the shock wave.
In the text

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