Solar radio emissions offer unique diagnostic insights into the solar corona. However, their dynamic and multiscale nature, along with variations spanning several orders of magnitude in intensity, pose significant observational challenges. To date, at gigahertz frequencies, MeerKAT (Jonas & MeerKAT Team 2016) stands out globally for its intrinsic ability to produce high-fidelity, spectroscopic snapshot images of the Sun. This is enabled primarily by its dense core, high sensitivity, and broad frequency coverage. Yet, as a telescope originally designed for observing faint galactic and extragalactic sources, observing the Sun in the MeerKAT primary beam requires customized observing strategies and calibration methods. This work demonstrates the technical readiness of MeerKAT for solar observations in the UHF (580–1015 MHz) and L-band (900–1670 MHz) frequency ranges, including optimized modes, a dedicated calibration scheme, and a tailored, entirely automated Stokes I calibration and imaging pipeline. We have also demonstrated several initial science results using this new solar observing mode of MeerKAT.

Configuring MeerKAT for Solar Observations: From Observing Strategy to Science-Ready Data Products

At GHz frequencies, the Sun is the brightest radio source in the sky and occupies a substantial fraction of the MeerKAT primary beam. Observing such an intense, extended source requires the introduction of additional attenuation at appropriate stages in the signal chain in order to maintain it within its optimal linear regime. We find that attenuation levels of approximately 32 dB in the UHF band and 35 dB in L-band are optimal for solar observations. While this attenuation enables direct observations of the Sun, it renders standard astronomical flux density calibrators too faint for conventional calibration. To overcome this limitation, the attenuators used are  calibrated using a well-characterized noise signal injected directly at the antenna feed.

This dedicated observing strategy for solar observations with MeerKAT has been successfully implemented and validated. However, calibrating and imaging data acquired in this non-standard observing mode requires additional processing steps beyond standard interferometric workflows. To streamline the analysis and to reliably produce science-ready, spectroscopic snapshot solar images, we have developed a fully automated, end-to-end calibration and imaging pipeline, MeerSOLAR, which is publicly distributed via PyPI (https://pypi.org/project/meersolar). The combination of this new observing mode and the MeerSOLAR pipeline has enabled the production of high-fidelity solar images at GHz frequencies with unprecedented quality, opening multiple new avenues for solar radio science.

Demonstration of High Quality Solar Imaging with MeerKAT

MeerKAT solar observations enable unprecedented spectroscopic snapshot imaging of the Sun at centimeter wavelengths. To illustrate the achieved image quality and fidelity, a representative MeerKAT solar image is shown in the left panel of Figure 1, centered at 942 MHz with a bandwidth of 50 MHz and an integration time of 15 minutes. The radio image is compared with a contemporaneous extreme-ultraviolet (EUV) solar image from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, shown in the right panel of Figure 1. Corresponding solar features are identified using colored arrows that are consistent across both panels. A prominent coronal hole (region 7) exhibits closely matching morphology in the radio and EUV images, while a smaller coronal hole is also evident (region 10). On-disk active regions (regions 8 and 9) as well as active regions near the eastern limb (regions 1 and 6) are clearly detected in both bands. Additional extended and filamentary coronal structures are highlighted in regions 2, 3, 4, and 5, further demonstrating the morphological consistency between the MeerKAT radio image and EUV observations.

Figure 1: The left panel shows a solar image at 942 MHz (50 MHz and 15 minutes averaging), observed using the MeerKAT pointing directly at the Sun. Several features are marked by numbered arrows. Corresponding features are also shown in the EUV image from AIA in the right panel.

Glimpses of Early Science Results

High-fidelity spectroscopic snapshot imaging with MeerKAT enables a wide range of new diagnostics of the solar corona, spanning phenomena from the quiescent Sun to coronal mass ejections (CMEs). We present selected examples that illustrate these science cases and highlight the broader potential of MeerKAT solar observations.

1. Quiescent Sun plasma above the chromosphere — MeerKAT’s observing frequencies and spectroscopic imaging capability enable unique probes of the solar atmosphere above the chromosphere, potentially including the transition region, which remains difficult to access with existing techniques. We compare observed on-disk spectroscopic radio images with simulations that include only coronal emission constrained by extreme-ultraviolet observations. As shown in Figure 2, the observed spectra exhibit a steeper spectral slope (green curve) and systematically higher flux densities than the coronal-only simulations (black curve) (Kansabanik et al., 2024). This discrepancy indicates the presence of additional, cooler plasma emission absent from the simulations but captured by MeerKAT. These results provide the first evidence that MeerKAT may be sensitive to transition-region plasma and open a new diagnostic avenue for characterizing its multi-thermal properties.
2. Non-thermal emission during the erupting phase of a CME — During a science verification observation on 10 June 2024, MeerKAT captured the eruptive phase of a CME, as shown in Figure 3. The observations reveal reconnection signatures in the current sheet accompanied by enhanced radio emission, in the region highlighted by the red box in the right panel. The associated radio spectra exhibit broadband non-thermal characteristics, consistent with gyrosynchrotron emission. Detailed modeling of the spatially resolved spectra and their temporal evolution will enable quantitative constraints on the magnetic field structure during the CME eruption.

Figure 2: Comparison of observed and simulated on-disk radio spectra. The simulated spectrum (black) includes only coronal emission, while the observed spectrum (green) shows significantly higher flux density and a steeper slope, indicating additional emission from plasma below the coronal layer.

Figure 3: Left panel: CME observed by MeerKAT on 10 June 2024. Right panel: radio contours from a spectroscopic MeerKAT solar image overlaid on an EUV image from the GOES-SUVI instrument. The red box highlights the reconnection site and associated bright non-thermal radio emission.

Conclusion

This study demonstrates tha$t MeerKAT is technically ready for solar observations at the telescope boresight, overcoming key limitations of earlier approaches that relied on sidelobe observations of the Sun (Kansabanik et al., 2024). The successful implementation of this capability has already enabled several unique early science results, highlighting its significant diagnostic potential. Once fully commissioned and made operational, this mode will unlock new opportunities for solar research, substantially broaden MeerKAT’s scientific portfolio, and establish a strong foundation for solar observations with the mid-frequency array of the Square Kilometre Array Observatory, for which MeerKAT serves as a key precursor.

Additional info

Based on a recent paper by Kansabanik, D. et al., 2025, Front. Astron. Space Sci. 12:1666743, https://doi.org/10.3389/fspas.2025.1666743

Keywords

MEERKAT, SOLAR RADIO EMISSION, QUIET SUN, CORONAL MASS EJECTION

Full list of authors: Devojyoti Kansabanik^1,2, Marcel Gouws³, Deepan Patra⁴, Angelos Vourlidas², Pieter Kotzé^3,5, Divya Oberoi⁴, Shaheda Begum Shaik^6,7, Sarah Buchner³, Fernando Camilo³

1. NASA Jack Eddy Fellow, University Corporation for Atmospheric Research, Boulder, CO, United States
2. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States
3. South African Radio Astronomy Observatory, Liesbeek House, Cape Town, South Africa
4. National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, S. P. Pune University Campus, Pune, India
5. National Radio Astronomy Observatory, Charlottesville, VA, United States
6. George Mason University, Fairfax, VA, United States
7. U.S. Naval Research Laboratory, Washington, DC, United States

References

1. Jonas, J., and MeerKAT Team (2016). “The MeerKAT radio telescope,” in MeerKATscience: on the Pathway to the SKA, 1. doi:10.22323/1.277.0001
2. Kansabanik, D., Mondal, S., Oberoi, D., Chibueze, J. O., Engelbrecht, N. E., Strauss, R.D., et al. (2024). Spectroscopic imaging of the sun with meerkat: Opening a new frontierin solar physics. Astrophysical J. 961, 96. doi:10.3847/1538-4357/ad0b7f