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First detection of metric emission from a photo voltaic surge by Costas Alissandrakis et al.* – Group of European Photo voltaic Radio Astronomers

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Virtually all photo voltaic phenomena noticed in radio wavelengths have their counterpart in different areas of the electromagnetic spectrum. Metric photo voltaic bursts are an exception to the above assertion. Though we now have a fundamental understanding of their origin, a few of their counterparts in different spectral ranges haven’t been recognized, apart from the so known as “radio CMEs”. That is apparently as a result of metric bursts end result from coherent plasma emission, which has no observable signature exterior the radio vary. Right here we report the detection of surge-associated metric emission that occurred after the tip of the majority of a big radio burst that occurred on February 12, 2010 close to the central meridian (N25, E11), and was described by Alissandrakis et al. 2021 (Paper I, see additionally CESRA nugget) .   

Determine 1. NRH photos in whole depth of the surge in any respect ten frequencies throughout the first (prime) and the second (backside) part of the occasion. The white arc marks the photo voltaic limb, the insert exhibits the NRH beam (decision), whereas the crosshair is positioned on the most of the decrease supply at 445 MHz throughout the first part. The photographs are normalized in order that the utmost depth at every frequency is white and the minimal is black, with a linear scale. An Hα picture from Catania and a protracted publicity SXR picture from SXI are given for reference within the left column (from Alissandrakis et al. 2022). 

Observations and Evaluation

We used photos from the Nançay Radioheliograph (NRH) at ten frequencies with a cadence of 250 ms and a spatial decision of 1.20′ by 1.80′ at 432 MHz, dynamic spectra from the ARTEMIS-JLS radiospectrograph  and CALLISTO; gentle curves from GOES, Hα photos from Catania, tender X-ray photos from the GOES Mushy X-ray Imager (SXI), EUV photos at 304 Å with a cadence of 10 min from STEREO SECCHI A and B and coronagraph photos from STEREO COR1, with a cadence of 5 min. Seen from STEREO-A, the occasion was very near the E limb, whereas it was close to the W limb for STEREO-B. No EIT knowledge have been accessible throughout the occasion. The three-dimensional place of the surge options was computed from triangulation of STEREO A and B photos at 304 Å and, from that, the projection of the surge on the aircraft of the sky, as seen from the Earth.

Outcomes

Radio emission from the surge was detected by the NRH throughout two intervals: from 11:49 to 11:51 UT (part A) and from 12:00 to ~13:00 UT (part B). There was no hint of surge emission both in Hα or in SXR. We additional observe that in each phases two sources seem within the high-frequency NRH photos the place the decision is greater (Determine 1); furthermore, throughout part B the higher supply is clearly displaced upwards, in comparison with part A, which is seemingly a results of the growth of the surge. Enlargement velocities of the order of 150 km/s have been measured primarily based on the NRH and STEREO knowledge. The scale and place of the supply are markedly completely different within the two lowest frequencies, indicating completely different buildings or completely different emission mechanisms.   

Determine 2. Stokes I cuts (depth as a perform of time and place alongside the surge), at full time decision, for 445.0, 432.0, and 408.0 MHz, throughout part A of the surge. Zero place is on the center of the lower. The width of the cuts is marked on the pictures at left (from Alissandrakis et al. 2022)

Brief-scale time variations have been discovered throughout each phases of the surge. An instance is proven in Determine 2, which provides photos (cuts) of the depth as a perform of time and place alongside the axis of the surge throughout the part A. Curiously, the variations within the higher decrease and higher supply are extremely correlated, with a slight time delay, which seems as an inclination of the options within the Determine. Taken at face worth, this delay interprets to propagation at superluminal pace. Nevertheless, when the geometry is correctly taken under consideration (left panel of Determine 3), a extra believable clarification is that this delay is because of scattering of radiation from the decrease supply by the higher supply.

NRH photos confirmed a excessive diploma of round polarization, confirmed by dynamic spectra; the latter additionally confirmed spikes and pulsations. All these level in direction of kind IV-like plasma emission from the elemental. The positions of the NRH decrease supply, from 327 to 435 MHz, computed for emission on the elementary, projected very near the bottom of the surge on the sky aircraft as seen from STEREO-A (proper panels of Determine 3).

Determine 3. Left: NRH supply positions on a aircraft perpendicular to the sky aircraft (open circles). A and B check with the corresponding phases of the emission. The boundaries of the 304Å surge derived from triangulation are additionally plotted in purple for reference. Dotted strains with arrows level in direction of the observer. The black arc marks the photo voltaic limb. Proper: Computed NRH supply positions from 327 to 435 MHz (purple crammed circles) projected on the sky aircraft as seen from STEREO-A, on prime of base-difference 304 Å photos close to part A (left) and through part B (proper). Greater-frequency sources are at decrease radial distances. (from Alissandrakis et al. 2022),

Conclusions

We reported the detection of metric radio emission from a surge, related to a secondary power launch throughout the late part of the M9-class flare of February 12, 2010, that was beforehand analyzed in Paper I. That is the primary time that direct imaging of a surge is reported. The detection of surge-associated emission provides yet another manifestation to the record of flare-associated metric radio emissions.

The NRH photos confirmed that the surge occurred in two phases and consisted of two sources. Brief-scale time variations appeared in each, with a slight delay suggesting superluminal velocities; a correct consideration of the geometry revealed that scattering of radiation from the decrease supply by the higher supply is the more than likely clarification.

The noticed excessive diploma of round polarization, in addition to the presence of spikes and pulsations within the dynamic spectrum, might be accommodated by plasma emission from the elemental. Furthermore, radio supply positions computed beneath this mechanism are according to the surge place as seen from STEREO-A. Therefore, we take into account kind IV-like plasma emission with a low depth gyrosynchrotron part as probably the most believable mechanism.

Based mostly on a current paper by Alissandrakis, C. E., Patsourakos, S., Nindos, A., Bouratzis, C., Hillaris, A., 2022, A&A, 662, A14. https://doi.org/10.1051/0004-6361/202243169

References

Alissandrakis, C. E., C. E., Nindos, A., Patsourakos, S., Hillaris, A, 2021, A&A, 654, A112. doi:10.1051/0004-6361/202141672 (Paper I)

*Full record of authors: Costas Alissandrakis, Spiros Patsourakos, Alexander Nindos, Costas Bouratzis and Alexander Hillaris

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