Aleksandr Burtovoi

Coronal Mass Ejections (CMEs) are the main drivers of geomagnetic storms. Studying their initial phases is important for understanding their propagation through the heliosphere and the effects they have on the Space Weather. In this work, as a case study, we investigate how SolO/Metis observations improve the accuracy in modeling a geoeffective CME that occurred on 11 April 2022. This event caused a geomagnetic storm of intensity of −81 nT in terms of Disturbance Storm Time (Dst) on 14 April 2022. This moderately geoeffective event serves as a challenging case to model and understand the complex interactions of CMEs with the ambient solar wind. Using coronagraphic data from SOHO/LASCO C2, STEREO/SECCHI COR2‐A along with VL observations from SolO/Metis, a Graduated Cylindrical Shell (GCS) analysis was done for 3D reconstruction of the CME flux rope. This provided the input parameters required for running the physics‐based propagation models (DBM and DBEM, WSA‐Enlil and EUHFORIA) which we have used to calculate the CME arrival times at Earth. SolO/Metis provides an additional viewpoint for the above analysis leading to a more precise determination of the GCS parameters and the 3D speed of the CME. By constraining the initial parameters, the 3D MHD models better resolve the interaction of the CME with the ambient solar wind. Including SolO/Metis data for this particular event leads to a lower error in the predicted arrival times at Earth for WSA‐Enlil and EUHFORIA (≈3 hr) than the typical ≈8–10 hr error estimates found in literature.

Context. Optical pulsations from millisecond pulsars (MSPs) have recently been detected in a transitional MSP and an accreting MSP. Evidence for optical pulsations has also been found for a rotation-powered redback MSP. Observations suggest that optical pulsed emission is produced by different mechanisms depending on whether an accretion disk is present in the system. Aims. We explored a sample of rotation-powered MSPs in close binaries (P _orb < 1 day; redbacks and black widows), searching for optical periodic signals with the SiFAP2 photometer mounted on the Telescopio Nazionale Galileo (TNG). Methods. We performed pulsation searches using the epoch-folding method with the most up-to-date (radio or gamma-ray) orbital solution for each system. These solutions were based either on previously published works or recent observations from Nançay, the Giant Metrewave Radio Telescope, the Parkes Observatory, and Fermi -LAT. Results. We update or confirm radio and gamma-ray ephemerides for five of the presented systems. No optical pulsations were detected with a significance exceeding a 3 σ confidence level in any of our searches, despite achieving sensitivities close to the instrument’s limit. This places correspondingly stringent upper limits on the systems’ optical pulsed magnitude and conversion efficiency. Our upper limits are consistent with the pulsed optical luminosity of optical pulsations from the redback PSR J2339-0533. Compared to accreting and transitional MSPs, redback and black widow systems show much lower efficiency in converting their spin-down power into pulsed optical emission. This supports the recent suggestion that the accretion disk around the neutron star plays a role in accelerating the particles responsible for producing bright optical pulsed emission.

We investigate the main physical characteristics and outward propagation in the solar corona of small-scale coronal transients detected during the rising phase of solar activity cycle 25. They were observed with the Metis coronagraph on Solar Orbiter when the spacecraft was at perihelion, 0.29 au, on October 12, 2022. We compare the results with the Metis observations obtained in February 2021, when Solar Orbiter was at 0.52 au, which revealed intermittent quasi-periodic small-scale structures propagating in a still relatively quiescent corona, between 3.10 and 5.70 R_⊙. The method we adopted is based on the construction of height-time maps of total brightness detected in the Metis white-light channel for three selected angular sectors of the solar corona. We carried out a spectral analysis of the temporal series of the total brightness obtained as a function of heliocentric distance and solar latitude by applying the Lomb-Scargle procedure. Propagating plasma density inhomogeneities are observed above the solar limb within the altitude range 1.76-3.10 R_⊙, in fairly quiet coronal regions that correspond to segments of the warped streamer belt, which is highly inclined relative to the solar equator. This is expected in the ascending-maximum phase of the solar activity cycle. These structures are characterized by radial and transverse sizes of 30-75 ± 8 Mm (0.04-0.10 ± 0.01 R_⊙) and 30-50 ± 8 Mm (0.04-0.07 ± 0.01 R_⊙), respectively. Most of them are fast-evolving structures that rapidly change in shape, dimension, and brightness on a timescale even as short as the observation cadence. The enhanced density structures move into the ambient slow wind with a mean velocity of about 240 ± 70 km s -1 $. They are intermingled with downflows that mainly originate in the range of heliocentric distances 2.0-2.5 R_⊙ and flow inward with speeds ranging over a wide interval, from about 35 ± 1 km s^-1 to about 200 ± 15 km s^-1. The coronal emission integrated over specific latitude intervals of 10^̧irc - 20$^̧irc is characterized by a well-defined periodicity of 42 min. The observations suggest that any dynamical process causing the presence and release of the density structures coherently acts in specific areas according to some periodic clock. The results show that propagating density structures are already present in the corona at 1.76 R_⊙ (the internal occulter edge of the coronagraph). Their concentration in the range of heliocentric distance between 2.0 and 2.4 R_⊙, that is, inside well-defined regions corresponding to streamer belt segments running almost parallel to the limb, is higher. Numerous dark structures moving inward are also present, mainly at the interface between open and closed magnetic lines at the streamer borders. The coronal plasma ejecta is likely released by processes of magnetic reconnection that are triggered in specific locations along the streamer borders in a period of 42 minutes. The driver of the quasi-periodic release of the density structures might be related to the photospheric convective motions and associated emergence of magnetic flux tubes, and also to the propagation of shocks at the boundary of the convection cells.

Context. The study of the kinematic and dynamic evolution of fast, eruptive events from the middle to the high solar corona is one of the primary scientific objectives of the Metis coronagraph on board the Solar Orbiter satellite. During the spacecraft’s perihelion passages, Metis operates in an observational mode that acquires visible light images at a cadence of 20 seconds, achieving a spatial resolution of around 2000 km at a solar distance of 0.28 au. This capability enables the detailed capture of coronal structures and transient events, such as coronal mass ejections (CMEs), with unprecedented spatial and temporal resolution. Aims. Between October 8 and 9, 2022, an extensive CME was observed in the Metis plane of the sky while Solar Orbiter was at a distance of 0.3 au, allowing for a spatial resolution in the visible channel of 4.4⋅10 ³ km/pixel. We aim to exploit the unprecedented high resolution of Metis observations to resolve multiple substructures within the CME front, revealing plasma elements propagating at different speeds and along distinct trajectories, enabling a detailed kinematic characterisation of the eruption. Methods. To highlight the complex morphology of the solar eruption observed in Metis images, a normalisation-based running difference enhancement algorithm was applied. Height-time diagrams were implemented to estimate the propagation speeds and frequency variations of newly emerging features. In addition, a three-dimensional reconstruction model of the flux rope structure, combined with data from other space-based coronagraphs and disk imagers, enabled tracking of the entire CME evolution from its early phase in the lower corona up to the middle corona (approximately 5 solar radii). Joint observations with Solar Orbiter/EUI-FSI provided insights into the eruption’s initiation in the inner corona, while Metis’ high resolution imaging captured its development into the middle corona, allowing a comprehensive view of CME kinematics across multiple coronal layers. Results. The high spatial and temporal resolution observations provided by Metis make it possible to study the fine structure of the CME, highlighting the internal motions of the coronal plasma and characterising its kinematic evolution. The results obtained from this study contribute to a deeper understanding of the morphology and kinematics of CMEs. Furthermore, the detection of circular, fast-propagating wavefronts (travelling at ∼500 km/s with a characteristic period of ∼3 minutes) at the western flank of the CME front opens new interpretative scenarios, suggesting the involvement of wave excitation and magnetic field reconfiguration processes in shaping the CME evolution. Multiple interpretations are proposed for the observed coronal plasma wave trains, including the presence of quasi-periodic propagating fast modes, providing new insights into wave generation and energy transport in the solar corona.

Context. We investigate the physical conditions of erupting prominences embedded in coronal mass ejection (CME) cores. Aims. The physical parameters of interest were derived by combining the hydrogen Lyman α (L α ) and visible-light (VL) images simultaneously observed by Solar Orbiter/Metis. In particular, we focus on the bright CME event that occurred on April 25-26, 2021. Methods. Our method is based on 2D non-LTE (i.e. non-local thermodynamic equilibrium) modeling of moving structures to derive the integrated intensity of the L α line ( E _L α ), together with VL emission. Our method is based on a novel diagnostic tool that combines the emission measure ( EM ) at a given temperature derived from the observed L α intensity with the electron column density ( N _e ) obtained from VL Stokes I and Q data. This approach determines the electron density ( n _e ) and the effective thickness ( D _eff ) inside the prominence structure. Here, we use a similar diagnostic tool to the one that we proposed for solar eclipses by combining hydrogen Balmer α (H α ) and VL data in previous studies. Results. We analyzed 32 spatial points within the northern part of the prominence. We ran a 2D non-LTE transfer code for these points by assuming a uniform prominence temperature. The results are presented as 2D maps of the electron density and effective thickness at a given temperature. For the brightest pixel, we also estimated the temperature by assuming collisional ionization equilibrium and compared the result with our value obtained using the emission-measure method. Conclusions. We demonstrate how n _e and D _eff inferences depend on the temperature of the structure. The higher the temperature, the lower the effective thickness, and the higher the electron density. This study creates foundation for future diagnostics of eruptive prominences with the Solar Orbiter/Metis coronagraph. It shows that combined UV and VL diagnostics provides a powerful tool for analyzing such events. But it also confirms that the consideration of the helium D ₃ line emission within the VL channel is essential to obtain accurate results.

Context. Transitional millisecond pulsars are old, rapidly rotating neutron stars spun up by accretion from a low-mass companion star. These objects can switch between two emission regimes: rotation-powered radio pulsars and accreting X-ray pulsars. The mechanism responsible for these pulsations remains debated, with one prominent model suggesting that optical and X-ray pulsations arise from synchrotron emission produced by a shock resulting from the interaction between the pulsar wind and the accretion disk. This scenario is supported by the minimal phase lag between optical and X-ray pulses in PSR J1023+0038, and by their detection in the high-mode (flaring state) of the system. Aims. We present a new measurement of the phase lag between optical and X-ray pulse profiles of PSR J1023+0038 and investigate the recent evolution of the binary system (until 2023), monitoring the variation in the time of passage at the ascending node ( T _asc ). Methods. We performed a timing analysis of the optical observations of PSR J1023+0038 taken with Aqueye+ from 2021 through 2023 and NICER X-ray observations taken in 2023. We used the optical and X-ray data to derive new measurements for the variation in T _asc and employed simultaneous Aqueye+ and NICER observations to measure the phase lag between optical and X-ray pulses. Results. We find the shift in T _asc increases by ∼20 s each year, and in January 2023 we measured a phase lag between optical and X-ray data of 0.067 ± 0.018, or 112.3 ± 30.7 μs. Conclusions. After 2017, the variation in the time of passage at the ascending node follows a well-defined parabolic increasing trend, suggesting a corresponding increment in the orbital period and orbital separation of the system. This evolution is consistent with a scenario in which the binary system is evolving through nonconservative Roche lobe overflow and the donor is interacting with the pulsar wind, losing mass at a rate much higher than the inferred accretion rate. The measurement of the phase lag between optical and X-ray data confirms the common origin of such pulsations.

Context. Galactic cosmic rays (GCRs) and solar energetic particles (SEPs) with energies greater than tens of megaelectron volts are at the origin of spacecraft deep charging. The High Energy Telescope of the Energetic Particle Detector instrument measures the particle flux incident on the Solar Orbiter spacecraft. An algorithm implemented in the processing electronics of the visible light (VL) instrument of the Metis coronagraph generates cosmic-ray matrices containing the pixels fired by high-energy particles. These independent observations allow us to monitor the secondary particle production into the spacecraft. Aims. We studied the GCR flux long-term variations during the ascending phase of solar cycle 25 and the evolution of two SEP events observed on July 24–26, 2023, and on February 9–14, 2024, above 80 MeV with the aim of evaluating the impact of galactic and solar high-energy particles on Metis. Methods. A Python tool named REBECCA has been developed for the automated analysis of the Metis cosmic-ray matrices. The number of observed particle tracks is compared to Monte Carlo simulations of the Metis VL bidimensional CMOS sensor used as a particle detector. Results. We present the modulation of the GCR energy spectrum from 2020 through 2024 above 100 MeV. The dynamics of two intense SEP events is also reported. Monte Carlo simulations indicate that the composition of particles in the cosmic-ray matrices is dominated by protons. Going from solar minimum to maximum, an increase in particles produced by cosmic rays in the spacecraft material surrounding Metis was observed. Conversely, during the whole evolution of SEP events, protons made up more than 90% of the particles. These observations were gathered near the ecliptic during a positive polarity epoch of the global solar magnetic field. Analogous studies will be conducted during the negative polarity epoch, within 1 au, both above and below the ecliptic plane, throughout the remaining duration of the mission.

On 2022 March 26, the ESA Solar Orbiter mission observed the early evolution of a coronal mass ejection (CME). On that day, the spacecraft was at a heliocentric distance of 0.32 au and a longitude separation from Earth of 74 . ° 5. The CME source region, observed with the Solar Orbiter Polarimetric and Helioseismic Imager magnetometer, shows no preexisting filament or flux rope. The event was first observed in the inner corona by the Solar Orbiter Extreme Ultraviolet Imager instrument with the Full Sun Imager telescope, showing the initial propagation of a flux rope seen face-on in the EUV, and formed during the eruption. Higher up, the event was observed by Metis with the Visible Light channel with an unprecedented time cadence of 20 s and a spatial resolution of 20” corresponding to about 4600 km bin⁻¹. The sequence of total brightness images shows the existence of small-scale circular flows inside the expanding flux rope, surrounded by multiple nested arch-shaped features. These motions, never reported so far, occur inside the void of the CME, with projected speed ∼40% higher than the CME propagation speed. The formation of the flux rope during the eruption suggests that these motions can be interpreted as a signature of conversion of magnetic writhe into twist, starting from the shearing of a preexisting arcade.