109 research outputs found
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 x 10^47 cm^-3
and 1.1 x 10^48 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
Sun's 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.Comment: Astrophysical Journal, in press. 14 pp, 3 figure
SphinX soft X-ray spectrophotometer: Science objectives, design and performance
The goals and construction details of a new design Polish-led X-ray spectrophotometer are described. The instrument is aimed to observe emission from entire solar corona and is placed as a separate block within the Russian TESIS X- and EUV complex aboard the CORONAS-PHOTON solar orbiting observatory. SphinX uses silicon PIN diode detectors for high time resolution measurements of the solar spectra in the range 0.8–15 keV. Its spectral resolution allows for discerning more than hundred separate energy bands in this range. The instrument dynamic range extends two orders of magnitude below and above these representative for GOES. The relative and absolute accuracy of spectral measurements is expected to be better than few percent, as follows from extensive ground laboratory calibrations
SphinX: The Solar Photometer in X-Rays
Solar Photometer in X-rays (SphinX) was a spectrophotometer developed to observe the Sun in soft X-rays. The instrument observed in the energy range ≈ 1 - 15 keV with resolution ≈ 0.4 keV. SphinX was flown on the Russian CORONAS-PHOTON satellite placed inside the TESIS EUV and X telescope assembly. The spacecraft launch took place on 30 January 2009 at 13:30 UT at the Plesetsk Cosmodrome in Russia. The SphinX experiment mission began a couple of weeks later on 20 February 2009 when the first telemetry dumps were received. The mission ended nine months later on 29 November 2009 when data transmission was terminated. SphinX provided an excellent set of observations during very low solar activity. This was indeed the period in which solar activity dropped to the lowest level observed in X-rays ever. The SphinX instrument design, construction, and operation principle are described. Information on SphinX data repositories, dissemination methods, format, and calibration is given together with general recommendations for data users. Scientific research areas in which SphinX data find application are reviewed
Low-energy cutoffs in electron spectra of solar flares: statistical survey
The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) X-ray data base
(February 2002 -- May 2006) has been searched to find solar flares with weak
thermal components and flat photon spectra. Using a regularised inversion
technique, we determine the mean electron flux distribution from count spectra
of a selection of events with flat photon spectra in the 15--20 keV energy
range. Such spectral behaviour is expected for photon spectra either affected
by photospheric albedo or produced by electron spectra with an absence of
electrons in a given energy range, e.g. a low-energy cutoff in the mean
electron spectra of non-themal particles. We have found 18 cases which exhibit
a statistically significant local minimum (a dip) in the range of 10--20 keV.
The positions and spectral indices of events with low-energy cutoff indicate
that such features are likely to be the result of photospheric albedo. It is
shown that if the isotropic albedo correction was applied, all low-energy
cutoffs in the mean electron spectrum were removed and hence the low energy
cutoffs in the mean electron spectrum of solar flares above 12 keV cannot
be viewed as real features in the electron spectrum. If low-energy cutoffs
exist in the mean electron spectra, the energy of low energy cutoffs should be
less than 12 keV.Comment: 9 pages, 5 figures, submitted to Solar Physic
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
Surface Deposition and Imaging of Large Ag Clusters Formed in He Droplets
The utility of a continuous beam of He droplets for the assembly and surface
deposition of Ag clusters, ~ 300 - 6 000, is studied with transmission
electron microscopy. Images of the clusters on amorphous carbon substrates
obtained at short deposition times have provided for a measure of the size
distribution of the metal clusters. The average sizes of the deposited clusters
are in good agreement with an energy balance based estimate of Ag cluster
growth in He droplets. Measurements of the deposition rate indicate that upon
impact with the surface the He-embedded cluster is attached with high
probability. The stability of the deposited clusters on the substrate is
discussed.Comment: 24 pages, 5 figure
Relationship between haemagglutination-inhibiting antibody titres and clinical protection against influenza: development and application of a bayesian random-effects model
<p>Abstract</p> <p>Background</p> <p>Antibodies directed against haemagglutinin, measured by the haemagglutination inhibition (HI) assay are essential to protective immunity against influenza infection. An HI titre of 1:40 is generally accepted to correspond to a 50% reduction in the risk of contracting influenza in a susceptible population, but limited attempts have been made to further quantify the association between HI titre and protective efficacy.</p> <p>Methods</p> <p>We present a model, using a meta-analytical approach, that estimates the level of clinical protection against influenza at any HI titre level. Source data were derived from a systematic literature review that identified 15 studies, representing a total of 5899 adult subjects and 1304 influenza cases with interval-censored information on HI titre. The parameters of the relationship between HI titre and clinical protection were estimated using Bayesian inference with a consideration of random effects and censorship in the available information.</p> <p>Results</p> <p>A significant and positive relationship between HI titre and clinical protection against influenza was observed in all tested models. This relationship was found to be similar irrespective of the type of viral strain (A or B) and the vaccination status of the individuals.</p> <p>Conclusion</p> <p>Although limitations in the data used should not be overlooked, the relationship derived in this analysis provides a means to predict the efficacy of inactivated influenza vaccines when only immunogenicity data are available. This relationship can also be useful for comparing the efficacy of different influenza vaccines based on their immunological profile.</p
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