Constraining the onset height of coronal mass ejection driven shocks using near-Sun observations in visible and radio wavelengths

Abstract

One of the debated issues about the onset of the type II radio bursts near the Sun is the heliocentric distance ($r$) at which the associated magnetohydrodynamic (MHD) shocks are formed, and the association of the latter with the coronal mass ejections (CMEs). The debate is primarily due to the absence of routine CME observations in whitelight at $r\,{<}\,1.5R_{\odot}$. We present here an example for how joint observations with the Visible Emission Line Coronagraph (VELC) onboard the recently launched ADITYA-L1 (the first dedicated Indian space solar mission, \citealp{Parate2025}), and Gauribidanur radio facilities could be useful to address the issue.

Figures (4)

• Figure 1: Brightness of the 5303Å emission line from the solar corona observed along the 1st slit in VELC/ADITYA-L1 as a function of time on 2024 May 27. The position angle range of observations shown is ${\approx}\,90^{\circ}$ - $104^{\circ}$. The enhanced emission near position angle ${\approx}\,100^{\circ}$ whose onset is at ${\approx}$07:04 UT is discussed in the main text. The other enhancement near position angle ${\approx}\,95^{\circ}$ with onset at ${\approx}$08:15 UT is due to coronal loop activity. The vertical black patch near 08:00 UT is due to data error. The VELC data is available from 07:01 UT only. Hence there is a gap in the beginning.
• Figure 2: Time variation of the peak intensity of the emission line, spatially averaged over the region of enhanced emission in Figure \ref{['figone']}. The position angle range is ${\approx}$ 98$^{\circ}$ - 101$^{\circ}$.
• Figure 3: Dynamic spectrum of type III and II bursts observed with GLOSS and GRASP on 2024 May 27 in the frequency range 330 - 30 MHz. The horizontal dotted line is at 174 MHz on the y-axis. The 1st and 2nd vertical dotted lines are at 06:59:30 UT & 07:04 UT on the x-axis, respectively. The fast drifting features during the interval ${\approx}$06:59:30 - 07:03:30 UT are type III bursts. The three comparitively slower drifting features marked 1, 2, & 3 in the period ${\approx}$07:04 - 07:40 UT are the three type II bursts mentioned in the main text. The white lines shown are drawn by joining the mid-points in the respective slow drifting features, at each time interval. The gap in the observed emission in the frequency range ${\approx}$108 - 88 MHz is because of radio frequency interference (RFI) caused by FM transmission and the use of band rejection filter to suppress it. The horizontal patches near 138 MHz & 284 MHz are also due to RFI. Otherwise the observing band is relatively free of RFI, which is one of the advantages with observations from Gauribidanur Monstein2007.
• Figure 4: Close-up view of Figure \ref{['figthree']}. Both the time and frequency ranges in the respective axes are restricted to see more clearly the patchy and weak emission in the frequency range 174 - 108 MHz for the first type II burst mentioned in the main text (Section 2.2). The horizontal dotted line indicates 174 MHz on the frequency axis.