Piotr Podgorski

X-ray emitting hot plasma in solar active regions observed by the SphinX spectrometer

Aims. The detection of very hot plasma in the quiescent corona is important for diagnosing heating mechanisms. The presence and the amount of such hot plasma is currently debated. The SphinX instrument on-board the CORONAS-PHOTON mission is sensitive to X-ray emission of energies well above 1 keV and provides the opportunity to detect the hot plasma component. Methods. We analysed the X-ray spectra of the solar corona collected by the SphinX spectrometer in May 2009 (when two active regions were present). We modelled the spectrum extracted from the whole Sun over a time window of 17 days in the 1.34− 7k eV energy band by adopting the latest release of the APED database. Results. The SphinX broadband spectrum cannot be modelled by a single isothermal component of optically thin plasma and two components are necessary. In particular, the high statistical significance of the count rates and the accurate calibration of the spectrometer allowed us to detect a very hot component at ∼7 million K with an emission measure of ∼2.7 × 10 44 cm −3 . The X-ray emission from the hot plasma dominates the solar X-ray spectrum above 4 keV. We checked that this hot component is invariably present in both the high and low emission regimes, i.e. even excluding resolvable microflares. We also present and discuss the possibility of a non-thermal origin (which would be compatible with a weak contribution from thick-target bremsstrahlung) for this hard emission component. Conclusions. Our results support the nanoflare scenario and might confirm that a minor flaring activity is ever-present in the quiescent corona, as also inferred for the coronae of other stars.

SphinX Measurements of the 2009 Solar Minimum X-Ray Emission

The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1-15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES. Several intervals are identified when the X-ray flux was exceptionally low, and the flux and solar X-ray luminosity are estimated. Spectral fits to the emission at these times give temperatures of 1.7-1.9 MK and emission measures between 4 × 1047 cm–3 and 1.1 × 1048 cm–3. Comparing SphinX emission with that from the Hinode X-ray Telescope, we deduce that most of the emission is from general coronal structures rather than confined features like bright points. For one of 27 intervals of exceptionally low activity identified in the SphinX data, the Suns X-ray luminosity in an energy range roughly extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby K and M dwarfs.

Soft X-ray variability over the present minimum of solar activity as observed by SphinX

Solar Photometer in X-rays (SphinX) is an instrument designed to observe the Sun in X-rays in the energy range 0.85–15.00 keV. SphinX is incorporated within the Russian TESIS X and EUV telescope complex aboard the CORONAS-Photon satellite which was launched on January 30, 2009 at 13:30 UT from the Plesetsk Cosmodrome, northern Russia. Since February, 2009 SphinX has been measuring solar X-ray radiation nearly continuously. The principle of SphinX operation and the content of the instrument data archives is studied. Issues related to dissemination of SphinX calibration, data, repository mirrors locations, types of data and metadata are discussed. Variability of soft X-ray solar flux is studied using data collected by SphinX over entire mission duration.

Investigation of cosmic ray and solar energetic particle background of STIX using GEANT4 simulation

The Spectrometer/Telescope for Imaging X-rays (STIX) is one of the Solar Orbiter instruments and will operate on heliocentric orbit with a perihelion distance of 0.3 a.u. Such close approach to the Sun is connected with severe influence of Solar Energetic Particle (SEP) event. The paper presents results of simulation of expected X-ray background from SEP and cosmic X-rays (CXB) for Caliste-SO detectors, which are used in STIX. The simulation based on Monte Carlo method was implemented in Geant4 toolkit. We considered also the detector effects which affect measured energy like hole tailing, Fano and electronic noise, by implementing this effects in C++ language complementing Geant4 simulations. We show that the largest background is caused by SEPs electrons, while background from protons is negligibly low. The expected CXB caused background is low and can be detected only during periods of low solar activity.

X-ray spectrophotometer SphinX and particle spectrometer STEP-F of the satellite experiment CORONAS-PHOTON. Preliminary results of the joint data analysis

A joint analysis is carried out of data obtained with the help of the solar X-ray SphinX spectrophotometer and the electron and proton satellite telescope STEP-F in May 2009 in the course of the scientific space experiment CORONAS-PHOTON. In order to determine the energies and particle types, in the analysis of spectrophotometer records data are used on the intensities of electrons, protons, and secondary γ-radiation, obtained by the STEP-F telescope, which was located in close proximity to the SphinX spectrophotometer. The identical reaction of both instruments is noted at the intersection of regions of the Brazilian magnetic anomaly and the Earth’s radiation belts. It is shown that large area photodiodes, serving as sensors of the X-ray spectrometer, reliably record electron fluxes of low and intermediate energies, as well as fluxes of the secondary gamma radiation from construction materials of detector modules, the TESIS instrument complex, and the spacecraft itself. The dynamics of electron fluxes, recorded by the SphinX spectrophotometer in the vicinity of a weak geomagnetic storm, supplements the information about the processes of radial diffusion of electrons, which was studied using the STEP-F telescope.

Geant4-based simulations of the x-ray luminescence background in the rotating drum spectrometer/SOLPEX

The Rotating Drum Spectrometer (RDS) experiment is planned to be placed onboard Ruscosmos Multipurpose Laboratory Module ”NAUKA” on the International Space Station (ISS) in 2019. The experiment is designed to measure X-ray spectra of Solar flares using Bragg reflection from flat crystals. Additionally to the reflection of X-ray photons crystals produce luminescent light. In order to separate those physical effects during real experiment data analysis, computer simulations are necessary. Using Geant4 toolkit we simulated particle background, which were generated by several processes: photoelectric effect, Compton scattering and Bremsstrahhlung. In this paper we present luminescent light background estimations in the RDS instrument.

Model of flare lightcurve profile observed in soft X-rays

We propose a new model for description of solar flare lightcurve profile observed in soft X-rays. The method assumes that single-peaked ‘regular’ flares seen in lightcurves can be fitted with the elementary time profile being a convolution of Gaussian and exponential functions. More complex, multi-peaked flares can be decomposed as a sum of elementary profiles. During flare lightcurve fitting process a linear background is determined as well. In our study we allow the background shape over the event to change linearly with time. Presented approach originally was dedicated to the soft X-ray small flares recorded by Polish spectrophotometer SphinX during the phase of very deep solar minimum of activity, between 23 rd and 24 th Solar Cycles. However, the method can and will be used to interpret the lightcurves as obtained by the other soft X-ray broad-band spectrometers at the time of both low and higher solar activity level. In the paper we introduce the model and present examples of fits to SphinX and GOES 1-8 A channel observations as well.

Geant4 simulations of STIX Caliste-SO detector's response to solar X-ray radiation

Spectrometer/Telescope for Imaging X-rays (STIX) is a part of Solar Orbiter (SO) science payload. SO will be launched in October 2018, and after three years of cruise phase, it will reach orbit with perihelion distance of 0.3 a.u. STIX is a Fourier imager equipped with pairs of grids that comprise the flare hard X-ray tomograph. Similar imager types were already used in the past (eq. RHESSI, Yohkoh/HXT), but STIX will incorporate Moiré modulation and a new type of pixelized detectors with CdTe sensor. We developed a method of modeling these detectors’ response matrix (DRM) using the Geant4 simulations of X-ray photons interactions with CdTe crystals. Taking into account known detector effects (Fano noise, hole tailing etc.) we modeled the resulting spectra with high accuracy. Comparison of Caliste-SO laboratory measurements of Am decay spectrum with our results shows a very good agreement. The modeling based on the Geant4 simulations significantly improves our understanding of detector response to X-ray photons. Developed methodology gives opportunity for detailed simulation of whole instrument response with complicated geometry and secondary radiation from cosmic ray particles taken into account. Moreover, we are developing the Geant4 simulations of aging effects which decrease detector’s performance.

The Bragg solar x-ray spectrometer SolpeX

Detection of polarization and spectra measurement of X-ray solar flare emission are indispensable in improving our understanding of the processes releasing energy of these most energetic phenomena in the solar system. We shall present some details of the construction of SolpeX – an innovative Bragg soft X-ray flare polarimeter and spectrometer. The instrument is a part of KORTES – Russian instrument complex to be mounted aboard the science module to be attached to the International Space Station (2017/2018). The SolpeX will be composed of three individual measuring units: the soft X-ray polarimeter with 1-2% linear polarization detection threshold, a fast-rotating flat crystal X-ray spectrometer with a very high time resolution (0.1 s) and a simple pinhole soft X-ray imager-spectrometer with a moderate spatial (~20 arcsec), spectral (0.5 keV) and high time resolution (0.1 s). Having a fast rotating unit to be served with power, telemetry and “intelligence” poses a challenge for the designer. Some of the solutions to this will be provided and described.

SolpeX: the soft X-ray flare polarimeter–spectrometer for the ISS

We present an innovative soft X-ray spectro-polarimeter SolpeX. The instrument consists of three functionally independent blocks. They are to be included into the Russian instrument KORTES, to be mounted aboard the ISS. The three SolpeX units are: a simple pin-hole X-ray spectral imager, a polarimeter, and a fast-rotating drum multiple flat crystal Bragg spectrometer. Such a combination of measuring blocks will offer a new opportunity to reliably measure possible X-ray polarization and spectra of solar flares, in particular during the impulsive phase. Polarized Bremsstrahlung and line emission due to presence of directed particle beams will be detected and measurements made of the velocities of evaporated hot plasma. We discuss details of the construction of the SolpeX units. Delivery of KORTES with SolpeX to ISS is expected in 2017/2018.