Interpretation of Radio Wave Scintillation Observed through LOFAR Radio Telescopes

Radio waves propagating through a medium containing irregularities in the spatial distribution of the electron density develop fluctuations in their intensities and phases. In the case of radio waves emitted from astronomical objects, they propagate through electron density irregularities in the interstellar medium, the interplanetary medium, and Earth’s ionosphere. The LOFAR radio telescope, with stations across Europe, can measure intensity across the VHF radio band and thus intensity scintillation on the signals received from compact astronomical objects. Modeling intensity scintillation allows the estimate of various parameters of the propagation medium, for example, its drift velocity and its turbulent power spectrum. However, these estimates are based on the assumptions of ergodicity of the observed intensity fluctuations and, typically, of weak scattering. A case study of single-station LOFAR observations of the strong astronomical source Cassiopeia A in the VHF range is utilized to illustrate deviations from ergodicity, as well as the presence of both weak and strong scattering. Here it is demonstrated how these aspects can lead to misleading estimates of the propagation medium properties, for example, in the solar wind. This analysis provides a method to model errors in these estimates, which can be used in the characterization of both the interplanetary medium and Earth’s ionosphere. Although the discussion is limited to the case of the interplanetary medium and Earth’s ionosphere, its ideas are also applicable to the case of the interstellar medium

Exploring the Circular Polarisation of Low-Frequency Solar Radio Bursts with LOFAR

The Sun is an active star that often produces numerous bursts of electromagnetic radiation at radio wavelengths. Low frequency radio bursts have recently been brought back to light with the advancement of novel radio interferometers. However, their polarisation properties have not yet been explored in detail, especially with the Low Frequency Array (LOFAR), due to difficulties in calibrating the data and accounting for instrumental leakage. Here, using a unique method to correct the polarisation observations, we explore the circular polarisation of different sub-types of solar type III radio bursts and a type I noise storm observed with LOFAR, which occurred during March-April 2019. We analysed six individual radio bursts from two different dates. We present the first Stokes V low frequency images of the Sun with LOFAR in tied-array mode observations. We find that the degree of circular polarisation for each of the selected bursts increases with frequency for fundamental emission, while this trend is either not clear or absent for harmonic emission. The type III bursts studied, that are part of a long-lasting type III storm, can have different senses of circular polarisation, occur at different locations and have different propagation directions. This indicates that the type III bursts forming a classical type III storm do not necessarily have a common origin, but instead they indicate the existence of multiple, possibly unrelated acceleration processes originating from solar minimum active regions.Peer reviewe

Ultra-Low-Frequency Radio Astronomy Observations from a Selenocentric Orbit: first results of the Longjiang-2 experiment

This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) -- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status of the instrumentation. We also present results of a transition observation, which offers unique measurements on several novel aspects. We estimate the RFI suppression required for such a radio astronomy instrumentation at the Moon distances from Earth to be of the order of 80 dB. We analyse a method of separating Earth- and satellite-originated radio frequency interference (RFI). It is found that the RFI level at frequencies lower than a few MHz is smaller than the receiver noise floor.Comment: Accepted for publication in Experimental Astronomy; 22 pages, 11 figure

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Detection of Periodic Disturbances in LOFAR Calibration Solutions

The Earth’s ionosphere is a highly variable medium on a wide range of spatio-temporal scales. The responsiveness of plasma to the geomagnetic field and its changes gives rise to anisotropy, which may introduce wave-like characteristics while scanning the ionosphere with a line-of-sight towards a radio source. Previous studies of LOw Frequency ARray (LOFAR) calibration phase solutions report that the estimated beta parameter of a structure function calculated over 6–8 h of astronomical observation timespan has a range of values from 1.6 to 2.0, with an average of 1.89. Such difference between the observations could result from transient wave-like disturbances within the data. This study aims to present a method of signal processing of ionospheric calibration datasets that allows the extraction of a transient wave-like signal and discuss its possible origin. We use complex Morlet wavelet analysis applied to two 8 h observations corresponding to very quiet geomagnetic conditions. We find a wave-like signal in the interferometric Total Electron Content data even during periods of no geomagnetic activity. We suggest it results from the relative velocity changes between the LOFAR line-of-sight and a convection pattern in the ionospheric F layer. Establishing the relationship between quiet time ionosphere, geomagnetic field changes and LOFAR’s calibration solutions may prove beneficial to determination of the dominant signals in the more disturbed conditions, which we leave for future study

Planetary Science Virtual Observatory: VESPA/Europlanet outcome and prospects

International audienceThe Europlanet-2020 programme, which ended Aug 2019, included anactivity called VESPA (Virtual European Solar and Planetary Access)which focused on adapting Virtual Observatory (VO) techniques to handlePlanetary Science data. We will present some aspects of VESPA at the endof this 4-years development phase and at the onset of the newly selectedEuroplanet-2024 programme in Feb 2020. VESPA currently distributes 54data services which are searchable according to observing conditions andencompass a wide scope including surfaces, atmospheres, magnetospheresand planetary plasmas, small bodies, heliophysics, exoplanets, and labspectroscopy. Versatile online visualization tools have been adapted forPlanetary Science, and efforts were made to connect the Astronomy VOwith related environments, e.g., GIS for planetary surfaces. The newprogramme will broaden and secure the former "data stewardship" concept,providing a handy solution to Open Science challenges in our community.It will also move towards a new concept of "enabling data analysis": arun-on-demand platform will be adapted from another H2020 programme inAstronomy (ESCAPE); VESPA services will be made ready to use for MachineLearning and geological mapping activities, and will also host selectedresults from such analyses. More tutorials and practical use cases willbe made available to facilitate access to the VESPA infrastructure.VESPAportal: http://vespa.obspm.frThe Europlanet 2020/2024 ResearchInfrastructure projects have received funding from the European Union'sHorizon 2020 research and innovation programme under grant agreements No654208 and No 87114

Planetary Science Virtual Observatory: VESPA/Europlanet outcome and prospects

International audienceThe Europlanet-2020 programme, which ended Aug 2019, included anactivity called VESPA (Virtual European Solar and Planetary Access)which focused on adapting Virtual Observatory (VO) techniques to handlePlanetary Science data. We will present some aspects of VESPA at the endof this 4-years development phase and at the onset of the newly selectedEuroplanet-2024 programme in Feb 2020. VESPA currently distributes 54data services which are searchable according to observing conditions andencompass a wide scope including surfaces, atmospheres, magnetospheresand planetary plasmas, small bodies, heliophysics, exoplanets, and labspectroscopy. Versatile online visualization tools have been adapted forPlanetary Science, and efforts were made to connect the Astronomy VOwith related environments, e.g., GIS for planetary surfaces. The newprogramme will broaden and secure the former "data stewardship" concept,providing a handy solution to Open Science challenges in our community.It will also move towards a new concept of "enabling data analysis": arun-on-demand platform will be adapted from another H2020 programme inAstronomy (ESCAPE); VESPA services will be made ready to use for MachineLearning and geological mapping activities, and will also host selectedresults from such analyses. More tutorials and practical use cases willbe made available to facilitate access to the VESPA infrastructure.VESPAportal: http://vespa.obspm.frThe Europlanet 2020/2024 ResearchInfrastructure projects have received funding from the European Union'sHorizon 2020 research and innovation programme under grant agreements No654208 and No 87114

Determining Ionospheric Drift and Anisotropy of Irregularities from LOFAR Core Measurements: Testing Hypotheses behind Estimation

We try to assess the validity of assumptions taken when deriving drift velocity. We give simple formulas for characteristics of the spatiotemporal correlation function of the observed diffraction pattern for the frozen flow and the more general Briggs model. Using Low-Frequency Array (LOFAR) Cassiopeia intensity observation, we compare the experimental velocity scaling factor with a theoretical one to show that both models do not follow observations. We also give a qualitative comparison of our drift velocity estimates with SuperDARN convection maps. The article is essentially an extended version of the conference paper: “Determining ionospheric drift and anisotropy of irregularities from LOFAR core measurements”, Signal Processing Symposium 2021 (SPSympo 2021)

Determining Ionospheric Drift and Anisotropy of Irregularities from LOFAR Core Measurements: Testing Hypotheses behind Estimation

We try to assess the validity of assumptions taken when deriving drift velocity. We give simple formulas for characteristics of the spatiotemporal correlation function of the observed diffraction pattern for the frozen flow and the more general Briggs model. Using Low-Frequency Array (LOFAR) Cassiopeia intensity observation, we compare the experimental velocity scaling factor with a theoretical one to show that both models do not follow observations. We also give a qualitative comparison of our drift velocity estimates with SuperDARN convection maps. The article is essentially an extended version of the conference paper: “Determining ionospheric drift and anisotropy of irregularities from LOFAR core measurements”, Signal Processing Symposium 2021 (SPSympo 2021)

Science goals of the COMPASS instrument consortium on M-MATISSE

International audienceMars-Magnetosphere ATmosphere Ionosphere and Space-weather SciencE (M-MATISSE) is a candidate for the ESA M7 mission opportunity, currently being studied by ESA in Phase A. It consists of two spacecraft with largely identical scientific payloads that will be placed into orbit around Mars in 2037. On inclined elliptical orbits they will encounter all relevant regions of the Mars-induced magnetosphere and upper atmosphere for further refining our understanding of the exchange of material, energy and momentum between the solar wind and space environment, and the Martian system. The Combined Magnetic and Plasma Sensor Suite, COMPASS, consists of dual Fluxgate Magnetometers (MAG), dual Langmuir Probes (LP), a Mutual Impedance eXperiment (MIX) (composed of an electronic card Mutual Impedance Board (MIB) that supplies driving electric signals to the Mutual Impedance Probe (MIP)) and a 3D Velocity of Ion (3DVI) instrument (composed of Ion Drift Meter (IDM) and a Retarding Potential Analyzer (RPA) in a combined instrument package), with redundant integrated Wave Analyzer Processing Unit (WAPU) for handling digital data processing and redundant Low Voltage Power Supply (LVPS). Design heritage for COMPASS is derived from the Dust and Fields Package to be flown on Comet Interceptor and from the Radio And Plasma Wave Investigation on the Jupiter Icy Moons Explorer. By sharing physical and electrical resources where possible, COMPASS provides an integrated suite of sensors and data handling systems that will provide highly configurable measurements of plasma properties (density, temperature, velocity and basic composition), as well as the vector magnetic field, a single component of the electric field, and the spacecraft potential. In this presentation, we will review the initial design, expected performance and scientific goals of the COMPASS consortium within the M-MATISSE mission