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Register a new userThe Solar Orbiter SPICE instrument -- An extreme UV imaging spectrometer
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The Spectral Imaging of the Coronal Environment (SPICE) instrument is a high-resolution imaging spectrometer operating at extreme ultraviolet (EUV) wavelengths. In this paper, we present the concept, design, and pre-launch performance of this facility instrument on the ESA/NASA Solar Orbiter mission. The goal of this paper is to give prospective users a better understanding of the possible types of observations, the data acquisition, and the sources that contribute to the instruments signal. The paper discusses the science objectives, with a focus on the SPICE-specific aspects, before presenting the instruments design, including optical, mechanical, thermal, and electronics aspects. This is followed by a characterisation and calibration of the instruments performance. The paper concludes with descriptions of the operations concept and data processing. The performance measurements of the various instrument parameters meet the requirements derived from the missions science objectives. The SPICE instrument is ready to perform measurements that will provide vital contributions to the scientific success of the Solar Orbiter mission.
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The Spectrometer/Telescope for Imaging X-rays (STIX) will look at solar flares across the hard X-ray window provided by the Solar Orbiter cluster. Similarly to the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), STIX is a visibility-based imaging instrument, which will ask for Fourier-based image reconstruction methods. However, in this paper we show that, as for RHESSI, also for STIX count-based imaging is possible. Specifically, here we introduce and illustrate a mathematical model that mimics the STIX data formation process as a projection from the incoming photon flux into a vector made of 120 count components. Then we test the reliability of Expectation Maximization for image reconstruction in the case of several simulated configurations typical of flare morphology.
The goal of this paper is to study the smallest brightening events observed in the EUV quiet Sun. We use commissioning data taken by the EUI instrument onboard the recently launched Solar Orbiter mission. On 2020 May 30, EUI was situated at 0.556AU from the Sun. Its HRIEUV telescope 17.4nm passband reached an exceptionally high two-pixel spatial resolution of 400km. The size and duration of small-scale structures is determined in the HRIEUV data, while their height is estimated from triangulation with the simultaneous SDO/AIA data. This is the first stereoscopy of small scale brightenings at high resolution. We observed small localised brightenings (campfires) in a quiet Sun region with lengthscales between 400km and 4000km and durations between 10 and 200s. The smallest and weakest of these HRIEUV brightenings have not been observed before. Simultaneous HRILYA observations do not show localised brightening events, but the locations of the HRIEUV events correspond clearly to the chromospheric network. Comparison with simultaneous AIA images shows that most events can also be identified in the 17.1nm, 19.3nm, 21.1nm, and 30.4nm passbands of AIA, although they appear weaker and blurred. DEM analysis indicates coronal temperatures peaking at log(T)~6.1-6.15. We determined the height of a few campfires, which is between 1000 and 5000km above the photosphere. We conclude that campfires are mostly coronal in nature and are rooted in the magnetic flux concentrations of the chromospheric network. We interpret these events as a new extension to the flare/microflare/nanoflare family. Given their low height, the EUI campfires could be a new element of the fine structure of the transition region/low corona: apexes of small-scale loops that are internally heated to coronal temperatures.
The 3D fine structure of the solar atmosphere is still not fully understood as most of the available observations are taken from a single vantage point. The goal of the paper is to study the 3D distribution of small-scale brightening events (campfires) discovered in the EUV quiet Sun by the Extreme Ultraviolet Imager (EUI) aboard Solar Orbiter. We used a first commissioning data set acquired by the EUIs High Resolution EUV telescope on 30 May 2020 in the 174 {AA} passband and we combined it with simultaneous data taken by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory in a similar 171 {AA} passband. The two-pixel spatial resolution of the two telescopes is 400 km and 880 km, respectively, which is sufficient to identify the campfires in both data sets. The two spacecraft had an angular separation of around 31.5 degrees (essentially in heliographic longitude), which allowed for the 3D reconstruction of the campfire position. These observations represent the first time that stereoscopy was achieved for brightenings at such a small scale. Manual and automatic triangulation methods were used to characterize the campfire data. The height of the campfires is located between 1000 km and 5000 km above the photosphere and we find a good agreement between the manual and automatic methods. The internal structure of campfires is mostly unresolved by AIA; however, for a particularly large campfire, we were able to triangulate a few pixels, which are all in a narrow range between 2500 and 4500 km. The low height of EUI campfires suggests that they belong to the previously unresolved fine structure of the transition region and low corona of the quiet Sun. They are probably apexes of small-scale dynamic loops heated internally to coronal temperatures. This work demonstrates that high-resolution stereoscopy of structures in the solar atmosphere has become feasible.
Solar X-ray Monitor (XSM) is one of the scientific instruments on-board Chandrayaan-2 orbiter. The XSM along with instrument CLASS (Chandras Large Area Soft x-ray Spectrometer) comprise the remote X-ray fluorescence spectroscopy experiment of Chandrayaan-2 mission with an objective to determine the elemental composition of the lunar surface on a global scale. XSM instrument will measure the solar X-rays in the energy range of 1-15 keV using state-of-the-art Silicon Drift Detector (SDD). The Flight Model (FM) of the XSM payload has been designed, realized and characterized for various operating parameters. XSM provides energy resolution of 180 eV at 5.9 keV with high time cadence of one second. The X-ray spectra of the Sun observed with XSM will also contribute to the study of solar corona. The detailed description and the performance characteristics of the XSM instrument are presented in this paper.
Electric field measurements of the Time Domain Sampler (TDS) receiver, part of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter, often exhibit very intense broadband wave emissions at frequencies below 20~kHz in the spacecraft frame. In this paper, we present a year-long study of electrostatic fluctuations observed in the solar wind at an interval of heliocentric distances from 0.5 to 1~AU. The RPW/TDS observations provide a nearly continuous data set for a statistical study of intense waves below the local plasma frequency. The on-board and continuously collected and processed properties of waveform snapshots allow for the mapping plasma waves at frequencies between 200~Hz and 20~kHz. We used the triggered waveform snapshots and a Doppler-shifted solution of the dispersion relation for wave mode identification in order to carry out a detailed spectral and polarization analysis. Electrostatic ion-acoustic waves are the common wave emissions observed between the local electron and proton plasma frequency in the soler wind. The occurrence rate of ion-acoustic waves peaks around perihelion at distances of 0.5~AU and decreases with increasing distances, with only a few waves detected per day at 0.9~AU. Waves are more likely to be observed when the local proton moments and magnetic field are highly variable. A more detailed analysis of more than 10000 triggered waveform snapshots shows the mean wave frequency at about 3 kHz and wave amplitude about 2.5 mV/m. The wave amplitude varies as 1/R^(1.38) with the heliocentric distance. The relative phase distribution between two components of the E-field shows a mostly linear wave polarization. Electric field fluctuations are closely aligned with the directions of the ambient field lines. Only a small number (3%) of ion-acoustic waves are observed at larger magnetic discontinuities.
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