Photo voltaic flares speed up energetic electrons. Whereas a few of them escape into interplanetary house and produce interplanetary Sort III photo voltaic radio bursts, the electrons interacting with the photo voltaic ambiance produce Exhausting X-ray emission (HXR). Many research relating the observations of sort III radio bursts and HXR emissions have been carried out because the first observations of their temporal affiliation (e.g., Kane 1972, 1981). Extra lately, statistical research have been achieved by https://www.aanda.org/articles/aa/full_html/2025/02/aa52278-24/aa52278-24.html and James & Vilmer (2023) on the hyperlink between the electrons producing HXR emissions and the properties of coronal sort III bursts and the affiliation with interplanetary sort III bursts. With STIX and RPW now observing repeatedly on the identical spacecraft (Photo voltaic Orbiter), we’re in a novel place to pursue the exploration of the affiliation between HXR flares and interplanetary sort III bursts.
The current research by Paipa-Leon et al. (2025) is predicated on 5 days of observations (17 November- 21 November) in 2020, when STIX and RPW supplied the primary simultaneous observations of X-ray flares and sort III radio bursts on Photo voltaic Orbiter (Determine 1).
Determine 1. RPW/STIX observations from November 18 at 00:00 UT to November 19 at 18:00 UT. (High curve) From prime to backside: RPW-TNR (100–425 kHz) and RPW-HFR spectrograms (425 kHz- 8 MHz), and STIX rely price gentle curves. The vertical traces point out the time of sort III onsets. (Backside curve) For six flares, X-ray contours overlaid on EUV photographs (EUI) within the 174 Å band. The colour-coding of the vitality band of the contours is identical as within the prime panels.
Determine 1 exhibits that the affiliation between the 2 forms of emission will not be one-to-one, as already identified from earlier research. The strongest X-ray flare detected as much as 80 keV has no sort III counterpart. Probably the most intense IP sort III burst (occasion 8) is related to a comparatively weak flare (no counts above 16 keV). Throughout the entire interval of observations, 21 IP sort III bursts and HXR flares have been discovered to be temporally related (with a complete of 232 HXR flares noticed by STIX and 32 IP sort III bursts noticed by RPW).
Determine 2: Occasion on November 17 ∼ 01:25 UT. (Left from prime to backside): RPW spectrograms and STIX rely price spectrogram and light-weight curves in numerous vitality ranges overlayed. The X-ray flare onset time, the IP sort III burst onset time and the time of the related X-ray peak are marked with vertical traces in magenta, blue, and purple. (Proper) X-ray contours at chosen time intervals overlaid on the EUI/FSI picture within the 174 Å band.
Determine 2 exhibits that the onset of IP sort III burst will not be essentially related to the primary HXR peak of the flare nor essentially the most energetic one, however it might be related to later peaks. That is the case for many of the flares of our pattern. Solely in six circumstances is the IP sort III burst temporally related to the primary HXR peak. The delays between the onset of IP sort III bursts and the time of related HXR peaks differ from a couple of seconds as much as round 5 minutes, with most of them below three minutes. These delays are according to the propagation time of electrons with velocities round 0.1 c (typical of electrons producing sort III bursts) between the injection time from the low corona to the place the place they will produce radio emissions within the frequencies vary from 6.52 MHz to 675 kHz). Determine 2 (proper) additionally exhibits that modifications within the morphology of HXR sources are noticed near the onset of IP sort III bursts. That is noticed in all flares of our pattern. Both further X-ray sources seem close to pre-existing X-rays sources on the disk or on the limb (see determine 2b) or an elongation of the X-ray supply is noticed when the lively area is behind the limb (see flares 12 and 13 in determine 1).
Conclusions
Determine 3 describes a potential state of affairs to clarify the looks of latest X-ray sources or elongation of X-ray sources for flares near the limb. Successive reconnection episodes produce energetic electrons in magnetic configurations with totally different connectivity to the higher photo voltaic ambiance. A primary reconnection occasion happens within the low corona and produces HXR emitting energetic electrons. This primary episode will not be related to a radio burst since energetic particles haven’t any entry to open subject traces. Because the magnetic configuration evolves, a brand new reconnection occasion happens larger within the corona between closed and open subject traces. Some accelerated electrons produce X-rays and a few of them propagate within the open subject line and produce sort III bursts. If the flaring lively area remains to be on the disk, the brand new reconnection occasion results in the looks of latest footpoints. Faint coronal sources can also be produced on the loop-tops close to the reconnection websites. When the footpoints are occulted (lively area near the limb or behind), these coronal sources will be detected and new sources showing larger within the corona will be noticed in reference to the brand new reconnection episode. Given the restricted spatial decision or lengthy integration occasions, the looks of the brand new coronal supply can seem as an elongation.
Our outcomes affirm the numerous position of interchange reconnection within the entry of flare-accelerated electrons to open magnetic subject traces, as beforehand in e.g. Krucker et al., 2008.
Determine 3: Cartoon for the proposed reconnection state of affairs (tailored from Glesener et al. 2012). Energy launch is triggered by an rising loop within the lively area embedded in open subject traces. Reconnection happens between the closed rising loop and the open magnetic subject line. Energetic electrons touring alongside the reconnected subject traces (orange arrows) produce laborious X-ray emissions at footpoints (in blue; they are often occulted if the lively area is behind the limb) and in coronal sources (in magenta) close to the reconnection web site (in purple). They’ll additionally escape alongside the open magnetic subject line within the corona towards the IP medium and produce sort III bursts (in inexperienced).
Based mostly on the current paper by Paipa-Leon, D., et al. Connecting energetic electrons on the Solar and within the heliosphere by way of X-ray and radio diagnostics, Astronomy & Astrophysics, Quantity 694, id.A111, DOI: 10.1051/0004-6361/202452278
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