19,289 research outputs found
Measuring X-ray anisotropy in solar flares. Prospective stereoscopic capabilities of STIX and MiSolFA
During the next solar maximum, two upcoming space-borne X-ray missions, STIX
on board Solar Orbiter and MiSolFA, will perform stereoscopic X-ray
observations of solar flares at two different locations: STIX at 0.28 AU (at
perihelion) and up to inclinations of , and MiSolFA in a
low-Earth orbit. The combined observations from these cross-calibrated
detectors will allow us to infer the electron anisotropy of individual flares
confidently for the first time. We simulated both instrumental and physical
effects for STIX and MiSolFA including thermal shielding, background and X-ray
Compton backscattering (albedo effect) in the solar photosphere. We predict the
expected number of observable flares available for stereoscopic measurements
during the next solar maximum. We also discuss the range of useful spacecraft
observation angles for the challenging case of close-to-isotropic flare
anisotropy. The simulated results show that STIX and MiSolFA will be capable of
detecting low levels of flare anisotropy, for M1-class or stronger flares, even
with a relatively small spacecraft angular separation of 20-30{\deg}. Both
instruments will directly measure the flare X-ray anisotropy of about 40 M- and
X-class solar flares during the next solar maximum. Near-future stereoscopic
observations with Solar Orbiter/STIX and MiSolFA will help distinguishing
between competing flare-acceleration mechanisms, and provide essential
constraints regarding collisional and non-collisional transport processes
occurring in the flaring atmosphere for individual solar flares
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UNIQUENESS of the WELDING PROBLEM for SLE and LIOUVILLE QUANTUM GRAVITY
AbstractWe give a simple set of geometric conditions on curves \unicode[STIX]{x1D702}, \widetilde{\unicode[STIX]{x1D702}} in from to so that if \unicode[STIX]{x1D711}:\mathbf{H}\rightarrow \mathbf{H} is a homeomorphism which is conformal off \unicode[STIX]{x1D702} with \unicode[STIX]{x1D711}(\unicode[STIX]{x1D702})=\widetilde{\unicode[STIX]{x1D702}} then \unicode[STIX]{x1D711} is a conformal automorphism of . Our motivation comes from the fact that it is possible to apply our result to random conformal welding problems related to the Schramm–Loewner evolution (SLE) and Liouville quantum gravity (LQG). In particular, we show that if \unicode[STIX]{x1D702} is a non-space-filling \text{SLE}_{\unicode[STIX]{x1D705}} curve in from to , and \unicode[STIX]{x1D711} is a homeomorphism which is conformal on \mathbf{H}\setminus \unicode[STIX]{x1D702}, and \unicode[STIX]{x1D711}(\unicode[STIX]{x1D702}), \unicode[STIX]{x1D702} are equal in distribution, then \unicode[STIX]{x1D711} is a conformal automorphism of . Applying this result for \unicode[STIX]{x1D705}=4 establishes that the welding operation for critical (\unicode[STIX]{x1D6FE}=2) LQG is well defined. Applying it for \unicode[STIX]{x1D705}\in (4,8) gives a new proof that the welding of two independent \unicode[STIX]{x1D705}/4-stable looptrees of quantum disks to produce an \text{SLE}_{\unicode[STIX]{x1D705}} on top of an independent 4/\sqrt{\unicode[STIX]{x1D705}}-LQG surface is well defined.ERC Starting Grant 804166 (SPRS
Variation of the electron flux spectrum along a solar flare loop as inferred from STIX hard X-ray observations
Regularized imaging spectroscopy was introduced for the construction of
electron flux images at different energies from count visibilities recorded by
the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). In this work
we seek to extend this approach to data from the Spectrometer/Telescope for
Imaging X-rays (STIX) on-board the Solar Orbiter mission. Our aims are to
demonstrate the feasibility of regularized imaging spectroscopy as a method for
analysis of STIX data, and also to show how such analysis can lead to insights
into the physical processes affecting the nonthermal electrons responsible for
the hard X-ray emission observed by STIX. STIX records imaging data in an
intrinsically different manner from RHESSI. Rather than sweeping the angular
frequency plane in a set of concentric circles (one circle per detector), STIX
uses collimators, each corresponding to a specific angular frequency. In
this paper we derive an appropriate modification of the previous computational
approach for the analysis of the visibilities observed by STIX. This approach
also allows for the observed count data to be placed into non-uniformly-spaced
energy bins. We show that the regularized imaging spectroscopy approach is not
only feasible for analysis of the visibilities observed by STIX, but also more
reliable. Application of the regularized imaging spectroscopy technique to
several well-observed flares reveals details of the variation of the electron
flux spectrum throughout the flare sources. We conclude that the
visibility-based regularized imaging spectroscopy approach is well-suited to
analysis of STIX data. We also use STIX electron flux spectral images to track,
for the first time, the behavior of the accelerated electrons during their path
from the acceleration site in the solar corona toward the chromospher
STIX X-ray microflare observations during the Solar Orbiter commissioning phase
Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is the hard X-ray instrument onboard Solar Orbiter designed to observe solar flares over a broad range of flare sizes. Aims. We report the first STIX observations of solar microflares recorded during the instrument commissioning phase in order to investigate the STIX performance at its detection limit. Methods. STIX uses hard X-ray imaging spectroscopy in the range between 4-150 keV to diagnose the hottest flare plasma and related nonthermal electrons. This first result paper focuses on the temporal and spectral evolution of STIX microflares occuring in the Active Region (AR) AR12765 in June 2020, and compares the STIX measurements with Earth-orbiting observatories such as the X-ray Sensor of the Geostationary Operational Environmental Satellite (GOES/XRS), the Atmospheric Imaging Assembly of the Solar Dynamics Observatory, and the X-ray Telescope of the Hinode mission. Results. For the observed microflares of the GOES A and B class, the STIX peak time at lowest energies is located in the impulsive phase of the flares, well before the GOES peak time. Such a behavior can either be explained by the higher sensitivity of STIX to higher temperatures compared to GOES, or due to the existence of a nonthermal component reaching down to low energies. The interpretation is inconclusive due to limited counting statistics for all but the largest flare in our sample. For this largest flare, the low-energy peak time is clearly due to thermal emission, and the nonthermal component seen at higher energies occurs even earlier. This suggests that the classic thermal explanation might also be favored for the majority of the smaller flares. In combination with EUV and soft X-ray observations, STIX corroborates earlier findings that an isothermal assumption is of limited validity. Future diagnostic efforts should focus on multi-wavelength studies to derive differential emission measure distributions over a wide range of temperatures to accurately describe the energetics of solar flares. Conclusions. Commissioning observations confirm that STIX is working as designed. As a rule of thumb, STIX detects flares as small as the GOES A class. For flares above the GOES B class, detailed spectral and imaging analyses can be performed
The Spectrometer/Telescope for Imaging X-rays (STIX)
Aims. The Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter is a hard X-ray imaging spectrometer, which covers the energy range from 4 to 150 keV. STIX observes hard X-ray bremsstrahlung emissions from solar flares and therefore provides diagnostics of the hottest (⪆10 MK) flare plasma while quantifying the location, spectrum, and energy content of flare-accelerated nonthermal electrons.
Methods. To accomplish this, STIX applies an indirect bigrid Fourier imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated CdTe detectors to provide information on angular scales from 7 to 180 arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of STIX has intrinsically low telemetry and it is therefore well-suited to the limited resources available to the Solar Orbiter payload. To further reduce the downlinked data volume, STIX data are binned on board into 32 selectable energy bins and dynamically-adjusted time bins with a typical duration of 1 s during flares.
Results. Through hard X-ray diagnostics, STIX provides critical information for understanding the acceleration of electrons at the Sun and their transport into interplanetary space and for determining the magnetic connection of Solar Orbiter back to the Sun. In this way, STIX serves to link Solar Orbiter’s remote and in-situ measurements
Evaluation of Faraday-shielded Stix coils for ion cyclotron resonance heating of a plasma Technical report no. 3
Faraday-shielded Stix coil evaluation including electric field waveform for ion cyclotron resonance heating of plasm
Forward fitting STIX visibilities
Aims. We seek to determine to what extent the problem of forward fitting visibilities measured by the Spectrometer/Telescope Imaging X-rays (STIX) on board Solar Orbiter becomes more challenging with respect to the same problem in the case of previous hard X-ray solar imaging missions. In addition, we aim to identify an effective optimization scheme for parametric imaging for STIX. Methods. This paper introduces a global search optimization for forward-fitting STIX visibilities and compares its effectiveness with respect to the standard simplex-based optimization used so far for the analysis of visibilities measured by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We made this comparison by considering experimental visibilities measured by both RHESSI and STIX, as weel as synthetic visibilities generated by accounting for the STIX signal formation model. Results. We found that among the three global search algorithms for parametric imaging, particle swarm optimization (PSO) exhibits the best performances in terms of both stability and computational effectiveness. This method is as reliable as the simplex method in the case of RHESSI visibilities. However, PSO is significantly more robust when applied to STIX simulated and experimental visibilities. Conclusions. A standard optimization based on local search of minima is not effective enough for forward-fitting the few visibilities sampled by STIX in the spatial frequency plane. Therefore, more sophisticated optimization schemes based on global search must be introduced for parametric imaging in the case of the Solar Orbiter X-ray telescope. The forward-fitting routine based on PSO proved to be significantly robust and reliable, and it could be considered as an effective candidate tool for parametric imaging in the STIX context
cyberaCTIve: a STIX-based Tool for Cyber Threat Intelligence in Complex Models
Cyber threat intelligence (CTI) is practical real-world information that is
collected with the purpose of assessing threats in cyber-physical systems
(CPS). A practical notation for sharing CTI is STIX. STIX offers facilities to
create, visualise and share models; however, even a moderately simple project
can be represented in STIX as a quite complex graph, suggesting to spread CTI
across multiple simpler sub-projects. Our tool aims to enhance the STIX-based
modelling task in contexts when such simplifications are infeasible. Examples
can be the microgrid and, more in general, the smart grid.Comment: 11 pages, 8 figures, technical repor
Cyber Threat Intelligence Platform
Cieľom práce je vytvoriť webovú platformu, ktorá poskytne zjednodušený popis, spracovanie a výmenu bezpečnostných incidentov za pomoci dostupných štandardov STIX, TAXII, CybOX, IDEA. Platforma poskytuje restové API pre zhromažďovanie externých udalostí vo fomráte IDEA, nástroj pre vytvárenie STIX formátovaných modelov udalostí a mechanizmus pre výmenu spracovaných udalostí s využitím služieb popísaných štandardom TAXII.Main goal of this thesis is to create an web application platform, which provides simplified characterization, adaptation and exchange of cyber threat incidents using the STIX, TAXII, CybOX and IDEA standards. Platform has implemented rest API to collect external events in IDEA format, tool for creating STIX formatted models of events and model exchange mechanism based on TAXII described services.
Layered Interpretation of Street View Images
We propose a layered street view model to encode both depth and semantic
information on street view images for autonomous driving. Recently, stixels,
stix-mantics, and tiered scene labeling methods have been proposed to model
street view images. We propose a 4-layer street view model, a compact
representation over the recently proposed stix-mantics model. Our layers encode
semantic classes like ground, pedestrians, vehicles, buildings, and sky in
addition to the depths. The only input to our algorithm is a pair of stereo
images. We use a deep neural network to extract the appearance features for
semantic classes. We use a simple and an efficient inference algorithm to
jointly estimate both semantic classes and layered depth values. Our method
outperforms other competing approaches in Daimler urban scene segmentation
dataset. Our algorithm is massively parallelizable, allowing a GPU
implementation with a processing speed about 9 fps.Comment: The paper will be presented in the 2015 Robotics: Science and Systems
Conference (RSS
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