Spektr-R Spacecraft Research Articles

RadioAstron discovery of a mini-cocoon around the restarted parsec-scale jet in 3C 84

We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C 84 (NGC 1275) at the centre of the Perseus cluster. The observations were carried out during a perigee passage of the Spektr-R spacecraft on September 21–22, 2013 and involved a global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz, together with the Space Radio Telescope (SRT). Furthermore, the Very Long Baseline Array (VLBA) and the phased Very Large Array (VLA) observed the source quasi-simultaneously at 15 GHz and 43 GHz. Fringes between the ground array and the SRT were detected on baseline lengths up to 8.1 times the Earth’s diameter, providing unprecedented resolution for 3C 84 at these wavelengths. We note that the corresponding fringe spacing is 125 μas at 5 GHz and 27 μas at 22 GHz. Our space-VLBI images reveal a previously unseen sub-structure inside the compact ∼1 pc long jet that was ejected about ten years earlier. In the 5 GHz image, we detected, for the first time, low-intensity emission from a cocoon-like structure around the restarted jet. Our results suggest that the increased power of the young jet is inflating a bubble of hot plasma as it carves its way through the ambient medium of the central region of the galaxy. Here, we estimate the minimum energy stored in the mini-cocoon, along with its pressure, volume, expansion speed, and the ratio of heavy particles to relativistic electrons, as well as the density of the ambient medium. About half of the energy delivered by the jet is dumped into the mini-cocoon and the quasi-spherical shape of the bubble suggests that this energy may be transferred to a significantly larger volume of the interstellar medium than what would be accomplished by the well-collimated jet on its own. The pressure of the hot mini-cocoon also provides a natural explanation for the almost cylindrical jet profile seen in the 22 GHz RadioAstron image.

Anisotropy of Magnetic Field and Velocity Fluctuations in the Solar Wind

Abstract We present a large statistical study of the fluctuation anisotropy in minimum variance (MV) frames of the magnetic field and solar wind velocity. We use 2, 10, 20, and 40 minute intervals of simultaneous magnetic field (the Wind spacecraft) and velocity (the Spektr-R spacecraft) observations. Our study confirms that magnetic turbulence is a composite of fluctuations varying along the mean magnetic field and those changing in the direction perpendicular to the mean field. Regardless of the length scale within the studied range of spacecraft-frame frequencies, ≈90% of the observed magnetic field fluctuations exhibit an MV direction aligned with the mean magnetic field, ≈10% of events have the MV direction perpendicular to the background field, and a negligible portion of fluctuations has no preferential direction. On the other hand, the MV direction of velocity fluctuations tends to be distributed more uniformly. An analysis of magnetic compressibility and density fluctuations suggests that the fluctuations resemble properties of Alfvénic fluctuations if the MV direction is aligned with background magnetic field whereas slow-mode-like fluctuations have the MV direction perpendicular to the background field. The proportion between Alfvénic and slow-mode-like fluctuations depends on plasma β and length scale: the dependence on the solar wind speed is weak. We present 3D numerical MHD simulations and show that the numerical results are compatible with our experimental results.

Plasma and Magnetic Field Turbulence in the Earth’s Magnetosheath at Ion Scales

Crossing the Earth’s bow shock is known to crucially affect solar wind plasma including changes in turbulent cascade. The present review summarizes results of more than 15 years of experimental exploration into magnetosheath turbulence. Great contributions to understanding turbulence development inside the magnetosheath was made by means of recent multi-spacecraft missions. We introduce the main results provided by them together with first observations of the turbulent cascade based on direct plasma measurements by the Spektr-R spacecraft in the magnetosheath. Recent results on solar wind effects on turbulence in the magnetosheath are also discussed.

Characteristics of Turbulent Solar Wind Flow in Plasma Compression Regions

This work is devoted to the study of properties of spectra of turbulent solar wind fluctuations in plasma compression regions, such as CIR (the plasma compression regions in front of high-speed streams from coronal holes) and SHEATH (the compression regions in front of interplanetary manifestations of coronal mass ejections EJECTA and magnetic clouds MC). The spectra of ion flux fluctuations, on both magnetohydrodynamic and ion-kinetic scales, are considered on the basis of data from the BMSW spectrometer on the SPEKTR-R spacecraft with a high (up to 31 ms) time resolution. The comparison of turbulent characteristics in the plasma compression regions and in the undisturbed solar wind is carried out both on a separate example and using extensive statistical material. It is shown in the paper that the turbulent cascade characteristics on the kinetic interval can significantly change in the plasma compression regions, and the signatures of a change in the main processes that determine the energy dissipation are revealed in them, which may cause increased heating in the regions under consideration.

Comparison of Magnetic and Plasma Overshoots of Interplanetary Shocks

The structure of interplanetary shock fronts was studied based on the data from the BMSW plasma spectrometer, installed on the SPEKTR-R spacecraft, supplemented by magnetic field measurements on the WIND spacecraft. Special attention was paid to periodic growths (overshoots) in the value of the ion flux or magnetic field relative to their mean values outside the ramp. A comparison was performed with the overshoot in the magnetic field, with the Mach number, and with the β parameter. Based on an analysis of 18 intersections of interplanetary shock fronts, in which the overshoots in the ion flux and magnetic field value were observed, it was shown that the value of the magnetic field overshoot is, on the average, less than a similar value in the solar wind’s ion flux, which is associated with different time resolution of measurements. The ion flux overshoot value is found to grow with the growth of the Mach number, in the same way, as the value of the magnetic field overshoot. It is shown that overshoots are formed not only in the supercritical shocks, but also in those with Mach numbers that are less than the value of the first critical Mach number. It is also found that the estimates of the wavelength of the ion flux and magnetic field oscillations behind the ramp well correlate with the value of a gyroradius of captured ions.

Dynamics of Plasma Turbulence at Earth’s Bow Shock and through the Magnetosheath

Abstract Earth’s magnetosheath can be treated as a natural laboratory to study turbulence development in confined space. The present study focuses on the characteristics of turbulent cascade downstream of the bow shock, where properties of turbulence are known to differ from those in the upstream solar wind. Characteristics of the turbulent spectrum are considered in two distinct points of the magnetosheath for two case studies. The analysis is based on high-resolution measurements of plasma parameters by the Spektr-R spacecraft and magnetic field data by the Themis/Arthemis mission. The measurements are performed for two distinct cases: in the dayside magnetosheath behind the quasi-perpendicular bow shock and in the nightside flank of the magnetosheath behind the quasi-parallel bow shock. The study focuses on the scales at which kinetic effects in plasma become significant and the turbulent spectrum is known to break. The analysis reveals that modification of the fluctuation spectrum at the bow shock is controlled by the distance of the measurement point from the bow shock’s nose. Also, performed statistical results suggest the influence of the large-scale parameters of the upstream solar wind and the type of the bow shock on the turbulent spectrum’s modification in the downstream region.

Small-Scale Plasma Fluctuations in Fast and Slow Solar Wind Streams

This study gives a comparison of characteristics of small-scale ion flux fluctuations based on measurements of the SPEKTR-R spacecraft in slow and fast solar wind streams. Fast quasi-stationary streams and fast disturbed streams, associated with transient phenomena in the solar corona, are considered separately. The use of high-time-resolution data from the Bright Monitor of Solar Wind (BMSW) instrument makes it possible to analyze plasma fluctuations in a wide range of scales, including small scales, where kinetic effects can make a significant contribution. It is shown in the study that the nature of small-scale fluctuations can significantly differ in fast streams with the same mean solar wind velocity but having a different nature.

The space VLBI mission RadioAstron: AGN results

AbstractThe RadioAstron Space VLBI mission utilized the 10-m radio telescope on board the dedicated Spektr-R spacecraft to observe cosmic radio sources with an unprecedented angular resolution at centimeter wave lengths in total and polarized light. The longest baseline of the space-ground interferometer is about 350000 km. It operated in 2011–2019 together with 58 largest ground radio telescopes. Resolution as high as 10 microarcsec has been achieved. An overview of its AGN science results will be presented in the talk. It includes a probe of jet emission mechanism through brightness temperature measurements, reconstruction of magnetic field structure close to the jet origin using polarization data, jet formation and collimation study for well resolved nearby AGN, as well as observations and analysis of jet precession and plasma instabilities. We will also discuss a new scattering effect which was discovered by RadioAstron to affect high resolution radio measurements of AGN and SgrA*.

Features of the Spectral Characteristics of Plasma Fluctuations in Different Large-Scale Streams of the Solar Wind

The turbulent characteristics of plasma fluctuations in the solar wind (SW) may substantially change depending on the SW conditions. Large-scale streams of different types, such as undisturbed slow solar wind, fast solar wind, interplanetary coronal mass ejection (EJECTA), magnetic cloud (MC), the compression region at the boundary between fast and slow streams (CIR), and the compression region in front of the EJECTA/MC (SHEATH), are usually characterized by specific plasma parameter values, which may influence turbulent cascade formation. In this paper, we analyze the properties of the spectra of ion flux fluctuations in the SW in the region of transition from the magnetohydrodynamic (MHD) scale to the kinetic one. The analysis is based on measurements carried out with the BMSW plasma spectrometer onboard the SPEKTR-R spacecraft with a high time resolution. The observational intervals inside the SW streams of different large-scale types are considered, and the main turbulence characteristics in these streams are compared. It was shown that the properties of the fluctuation spectra may strongly depend on the SW type; in particular, the spectrum of kinetic-scale fluctuations usually becomes much steeper inside the MC regions and the compression regions in front of them, as well as in the CIR. The characteristics of the fluctuation spectra on MHD scale are less dependent on the type of large-scale SW structures, and, on average, they correspond to the Kolmogorov spectra. However, it can be noted that the smallest spectral slopes are observed in the slow undisturbed solar wind, which is indicative of the differences from the traditional Kolmogorov model of the developed turbulence.

Scale-dependent Polarization of Solar Wind Velocity Fluctuations at the Inertial and Kinetic Scales

Abstract We study the polarization properties of the velocity fluctuations in solar wind turbulence using high-resolution data from the Spektr-R spacecraft. The ratio of perpendicular to parallel velocity fluctuations in the inertial range is smaller than the equivalent ratio for magnetic fluctuations, but gradually increases throughout this range. In the kinetic range, there is a large decrease in the ratio, similar to the magnetic fluctuations. We compare the measurements to numerical solutions for a combination of kinetic Alfvén waves and slow waves, finding that both the slow increase and sharp decrease in the ratio are consistent with a majority population of Alfvén waves and minority population of slow waves in critical balance. Furthermore, the beta-dependence of this scale-dependent ratio can be successfully captured in the model when incorporating a beta-dependent Alfvén to slow wave ratio similar to that observed in the solar wind.

Temperature spectra in the solar wind turbulence

We study Alfvenic turbulent fluctuations and their spectral properties from MHD to kinetic scales and compare with recent measurements of the Spektr-R spacecraft. An apparent contradiction is found between the temperature spectra derived from the Spektr-R data and the temperature spectra predicted theoretically. To resolve this contradiction, we show that the temperature fluctuations can be correctly estimated from the Spektr-R data only if the mean temperature is isotropic. Since the mean temperature in the solar wind is usually anisotropic, the derived fluctuations appear to be pseudo-temperature rather than temperature. These pseudo-temperature fluctuations are driven by the high-amplitude magnetic fluctuations in Alfven waves rather than the fluctuations of temperature or thermal velocity. That is why their amplitudes are usually significantly larger than the amplitudes of authentic temperature fluctuations.

Do we detect interplanetary dust with Faraday cups?

Transient clouds of a plasma generated by hypervelocity dust particles impacting onto the spacecraft were observed in-situ by many experiments over the last 20 years. The reported observations analyze sensitive measurements of plasma waves that are transmitted to the Earth with a sufficient time resolution. The detection is based on a fact that hypervelocity impacts generate plumes of the ionized gas expanding into a space. The present paper analyzes five years of the operation of the Bright Monitor of the Solar Wind (BMSW) onboard the Spektr-R spacecraft with a motivation to demonstrate that such type of the instruments is capable to observe the dust impacts into its detectors. The results of analysis are compared with Wind electric field measurements used for a detection of hypervelocity dust impacts.

Fine structure of interplanetary shock fronts from the data of the BMSW instrument of the PLASMA-F experiment

The paper is concerned with studying the thickness of fronts of 38 interplanetary shocks detected by the BMSW instrument, which is a part of the scientific payload of the SPEKTR-R spacecraft, which was launched into a highly elliptical orbit in 2011. The main parameters of the interplanetary shocks have been calculated as follows: the ratio of thermal pressure to magnetic pressure before the front β, the angle between the shock front normal and the undisturbed magnetic field θBn, the ratio of the shock propagation velocity to the magnetosonic velocity in the undisturbed region Mms, and the shock front velocity relative to the Earth. It has been shown that the front thickness determined from the plasma parameters approximately matches the front thickness obtained from the magnetic field measurements and lies between 0.5 and 5 proton inertial lengths. In some events, the oscillations have been observed (upstream and downstream of the shock) in plasma parameters and in the magnetic field data. The length has been found to be between 0.5 and 6 proton inertial lengths for the preceding oscillations and between 0.5 and 10 proton inertial lengths for the following oscillations. The average value of the proton inertial length is 62 km.

Effect of reflected ions on the formation of the structure of interplanetary quasi-perpendicular shocks for Mach numbers lower than the first critical mach number

Based on the data of the BMSW instrument installed on the of SPEKTR-R spacecraft, as well as according to the data of instruments of the WIND spacecraft, etc., using two examples, the paper has studied the role of ions reflected from the front and associated structural features of quasi-perpendicular interplanetary shocks (IS) with the Alfven Mach number М A lower than the first critical Mach number М c1 . It has been shown that BSs with the finite parameter 0.1 < β1 < 1 contain a small fraction of reflected protons, which play a significant role in forming the front structure (β1 is the ratio of gas-to-magnetic pressure before the shock front). In particular, in the case of a perpendicular shock recorded on August 24, 2013 (the angle between the magnetic field direction and the normal to the front θBn ≈ 85°), an IS with a small Mach number (МA ≈ 1.4) and small β1 ≈ 0.2 is shown that the interactions of reflected ions with inflowing solar wind may result in the collisionless heating of ions in front of and behind it. The case of the oblique (θBn = 63°) IS on April 19, 2014 with a small Mach number (М A ≈ 1.2) and small β1 ≈ 0.5 has been investigated. It has been found that, before the front, there is a sequence of trains of magnetosonic waves, the amplitude of which decreases to zero upon increasing their distance from the front. The mechanism of their formation is associated with the development of instability caused by the ions reflected from the front.

Decay of Solar Wind Turbulence behind Interplanetary Shocks

Abstract We investigate the decay of magnetic and kinetic energies behind IP shocks with motivation to find a relaxation time when downstream turbulence reaches a usual solar wind value. We start with a case study that introduces computation techniques and quantifies a contribution of kinetic fluctuations to the general energy balance. This part of the study is based on high-time (31 ms) resolution plasma data provided by the Spektr-R spacecraft. On the other hand, a statistical part is based on 92 s Wind plasma and magnetic data and its results confirm theoretically established decay laws for kinetic and magnetic energies. We observe the power-law behavior of the energy decay profiles and we estimated the power-law exponents of both kinetic and magnetic energy decay rates as −1.2. We found that the decay of MHD turbulence does not start immediately after the IP shock ramp and we suggest that the proper decay of turbulence begins when a contribution of the kinetic processes becomes negligible. We support this suggestion with a detailed analysis of the decay of turbulence at the kinetic scale.

Designing corrections for the trajectory of the Spektr-R spacecraft in the event of immersions into the Moon’s sphere of influence

The results of updating the parameters of motion of the Spektr-R spacecraft at the end of 2016 have shown that, in January 2018, with a probability close to unity, the condition that a spacecraft stay in the Earth’s shadow is violated; however, in May of the same year, the ballistic life of the spacecraft will be terminated. Thus, in 2017, the question arose of how to design the correction of flight of this spacecraft using its onboard propulsion system. The correction was designed with allowance for the fact that, for the first time since it was launched, the spacecraft in the course of several years, beginning with 2017, repeatedly approaches the Moon, deeply immersing into its sphere of influence. This paper presents the technologically and organizationally convenient, allowable versions of upcoming correction of the Spektr-R spacecraft trajectory and justifies the particular scheme of its implementation.

Improvement of the orbit of the Spektr-R spacecraft in the RadioAstron mission and required conditions for improvement using a Kalman filter

This paper is concerned with improvement of the state vector of the Spektr-R spacecraft of the RadioAstron mission. The state vector includes three coordinates of the position of the spacecraft and three components of its velocity in the Geocentric Celestial Reference System. Improvement of the orbit of the spacecraft is understood as improvement of the state vector. The results are compared with the original orbits determined at the Keldysh Institute of Applied Mathematics (IAM). The paper considers both using the Kalman filter based on a single set of radio-range and Doppler data from ground-based stations and the analysis of conditions that will lead to improvement of the orbit. It has been shown that using three ground-based stations that perform simultaneous measurements the problem is solved completely, even when a poor initial approximation is used. Based on the results, a list of requirements is obtained that will provide more accurate information on the orbit of the Spektr-R spacecraft.

Improvement of the orbit of the Spektr-R spacecraft in the RadioAstron mission on the basis of radio range and Doppler measurements

The first results of the improvement of the state vector of the Spektr-R spacecraft of the RadioAstron mission, which is a part of an earth–space radio interferometer, are presented. The state vector includes three components for the spacecraft position and three components for its velocity in the Geocentric Celestial Reference System. Kalman filtering on the basis of radio range and Doppler data allows refinement of the components at each iteration. It is shown that orbit improvement increases the accuracy of the orbit determined at the Keldysh Institute of Applied Mathematics.

Analysis of SPEKTR-R spacecraft operating modes for various algorithms of high gain antenna drive control

The paper considers some operational modes of a high gain antenna drive in order to determine the minimum perturbing influences that impact precision equipment of the SPEKTR-R spacecraft.

System of maintaining the thermal regime of a space radio telescope

We present the results of developing a system of thermal regime maintenance for the onboard complex of scientific instruments of the space radio telescope installed on the Spektr-R spacecraft. The structure of the system of thermal regime maintenance is presented that includes a set of autonomous systems of constructive elements of the radio telescope. Basic schemes and composition of aggregates are presented, and main principles of operation of the autonomous systems supporting the thermal regime of the radio telescope are considered.