Several research studies show that CMEs are accountable for the coronal type II bursts too, but flares and numerous other eruptive activity have actually likewise been reported as drivers of the shocks that create these bursts. Any result that individually constrains the shock chauffeur of the near-Sun type II bursts would be essential and beneficial. We carried out a statistical research study of twenty 6 type II radio bursts from the Sun observed with the Gauribidanur LOw-frequency Solar Spectrograph (GLOSS) in the frequency variety 85– 35 MHz throughout the period 2009– 2019.
A number of studies show that CMEs are accountable for the coronal type II bursts too, however flares and various other eruptive activity have actually likewise been reported as motorists of the shocks that produce these bursts. Any result that individually constrains the shock chauffeur of the near-Sun type II bursts would be useful and essential. Reports indicate that the shock geometry in the low corona might be quasi-perpendicular at several areas on the shock (Gopalswamy et al. 2012), and sub-critical quasi-perpendicular shocks could likewise create coronal type II bursts (Mann et al., 1995). Multi-frequency radio imaging information reveal that the centroids of the type II bursts observed at different frequencies at the very same time are laterally displaced (Kouloumvakos et al., 2021) This recommends co-temporal occurrence of the type II radio bursts from an extended region with various electron density, and hence plasma frequency values, on the shock ahead of a CME. We examined twenty 6 low frequency (85– 35 MHz) type II solar radio bursts observed with the GLOSS throughout the duration 2009– 2019, along with the associated CMEs and flares.
Figure 1– Bandwidth of the type II bursts observed with the GLOSS versus the angular width of the associated CMEs. The straight line is the linear least squares fit to the information points.
Analysis and Results:.
Figure 1 indicates a significant correlation (~ 71%) between the bandwidth of the type II bursts and the angular width of the associated CMEs. Both the above amounts are straight measurable from the respective observations (i.e. radio and white light) without any presumptions. This suggests that the type II bursts in our information set are likely due to shocks driven by the associated CMEs. The different locations from the nose to the flanks of the shock will be at various heliocentric distances. Therefore the electron density (and thus plasma frequency) at the respective places will be various. It was reported just recently that type II radio emission takes place at locations where the shock is super-critical with quasi-perpendicular geometry (Jebaraj et al., 2021; Kouloumvakos et al. 2021). These conditions can be unique to different parts of the shock. Keep in mind that a shock is stated to be quasi-perpendicular if the angle between the shock normal and the upstream electromagnetic field is >> 45 degrees. The important Alfven-Mach number for such a shock is usually in the variety ~ 1.1– 2.8 depending on the regional plasma specifications (Benz & & Thejappa 1988; Mann et al., 1995). Shocks whose Alfven-Mach number goes beyond the vital Alfven-Mach number representing that specific area are said to be super-critical. Reports indicate that the shock geometry in the low corona could be quasi-perpendicular at several areas on the shock (Gopalswamy et al. 2012), and sub-critical quasi-perpendicular shocks might also generate coronal type II bursts (Mann et al., 1995). Presuming that all of the abovementioned conditions are beneficial for the generation of type II emission, it is highly likely that they would be satisfied at multiple locations or along a prolonged area on the shock. Multi-frequency radio imaging data show that the centroids of the type II bursts observed at various frequencies at the exact same time are laterally displaced (Kouloumvakos et al., 2021) This suggests co-temporal event of the type II radio bursts from an extended area with different electron density, and for this reason plasma frequency worths, on the shock ahead of a CME. There are reports of modeling of type II burst vibrant spectra assuming parabola shaped worldwide shock with multiple electron velocity regions with quasi-perpendicular geometry (Knock & & Cairns 2005). The correlation between typical rapid bandwidths of type II bursts and angular widths of the associated CMEs in today case follows these results.
Conclusions:.
We examined twenty six low frequency (85– 35 MHz) type II solar radio bursts observed with the GLOSS throughout the period 2009– 2019, along with the associated CMEs and flares. This shows that: (i) the coronal type II bursts reported in the present work are most likely due to shocks driven by the CMEs, and (ii) the velocity of electrons leading to the bursts occurs at the same time at multiple locations or over an extended area on the shock which in turn has a bearing on the rapid bandwidth of the bursts.
Based on a recently published article: R. Ramesh, C. Kathiravan, and S. Surya Natarajan (2022 ). New Results from the Spectral Observations of Solar Coronal Type II Radio Bursts, Astrophysical Journal, 926, 38 DOI: 10.3847/ 1538-4357/ ac4bd6.
Referrals:.
Benz, A. O., & & Thejappa, G., 1988, Astron. Astrophys., 202, 267.
Gopalswamy, N., Nitta, N. Akiyama, S. Makela, P., & & Yashiro, S., 2012, Astrophys. J., 744, 72.
Jebaraj, I. C., Kouloumvakos, A., Magdalenic, J., et al., 2021, Astron. Astrophys., 654, A64.
Knock, S. A., & & Cairns, I. H., 2005, J. Geophys. Res., 110, A01101.
Kouloumvakos, A., Rouillard, A., Warmuth, A., et al., 2021, Astrophys. J., 913, 99.
Mann, G., Classen, T., & & Aurass, H., 1995, Astron. Astrophys., 295, 775.
* Full list of authors: R. Ramesh. C. Kathiravan, and S. Surya Natarajan.
