16 research outputs found
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
First-trimester diagnosis and management of Cesarean scar pregnancies after in vitro fertilization-embryo transfer: a retrospective clinical analysis of 12 cases
Ectopic pregnancy secondary to in vitro fertilisation-embryo transfer: pathogenic mechanisms and management strategies
Plasma dynamics in the flaring loop observed by RHESSI
Context. Hard X-rays (HXRs) contain the most direct information about the non-thermal electron population in solar flares. The approximation of the HXR emission mechanism (bremsstrahlung), known as the thick-target model, is well developed. It allows one to diagnose the physical conditions within a flaring structure. The thick-target model predicts that in flare foot points, we should observe lowering of HXR sourcesâ altitude with increasing energy.
Aims. The foot point of HXR sources result from the direct interaction of non-thermal electron beams with plasma in the lower part of the solar atmosphere, where the density increases rapidly. Therefore, we can estimate the plasma density distribution along the non-thermal electron beam directly from the observations of the altitude-energy relation obtained for the HXR foot point sources. However, the relation is not only density-dependent. Its shape is also determined by the power-law distribution of non-thermal electrons. Additionally, during the impulsive phase, the plasma density and a degree of ionisation within foot points may change dramatically due to heating and chromospheric evaporation. For this reason, the interpretation of observed HXR foot point sourcesâ altitudes is not straightforward and needs detailed numerical modelling of the electron precipitation process.
Methods. We present the results of numerical modelling of one well-observed solar flare. We used HXR observations obtained by RHESSI. The numerical model was calculated using the hydrodynamic 1D model with an application of the Fokker-Planck formalism for non-thermal beam precipitation.
Results. HXR data were used to trace chromospheric density changes during a non-thermal emission burst, in detail. We have found that the amount of mass that evaporated from the chromosphere is in the range of 2.7â
Ăâ
1013â
ââ
4.0â
Ăâ
1014 g. This is in good agreement with the ranges obtained from hydrodynamical modelling of a flaring loop (2.3â
Ăâ
1013â
ââ
3.3â
Ăâ
1013 g), and from an analysis of observed emission measure in the loop top (3.9â
Ăâ
1013â
ââ
5.3â
Ăâ
1013 g). Additionally, we used specific scaling laws which gave another estimation of the evaporated mass around 2â
Ăâ
1014 g.
Conclusions. Consistency between the obtained values shows that HXR images may provide an important constraint for models â a mass of plasma that evaporated due to a non-thermal electron beam depositing energy in the chromosphere. High-energy, non-thermal sourcesâ (above 20 keV in this case) positions fit the column density changes obtained from the hydrodynamical model perfectly. Density changes seem to be less affected by the electronsâ spectral index. The obtained results significantly improve our understanding of non-thermal electron beam precipitation and allow us to refine the energy balance in solar flare foot points during the impulsive phase
Intracytoplasmatic sperm injection (ICSI) outcome versus intracytoplasmatic morphologically selected sperm injection (IMSI) outcome: a prospective trial
The relationship between male age, sperm quality and sperm DNA damage in an unselected population of 1566 men attending a fertility centre for the first time.
The impact of thyroid autoantibodies on the cycle outcome and embryo quality in women undergoing intracytoplasmic sperm injection
STIX X-ray microflare observations during the Solar Orbiter commissioning phase
The Spectrometer/Telescope for Imaging X-rays (STIX) is the HXR instrument
onboard Solar Orbiter designed to observe solar flares over a broad range of
flare sizes, between 4-150 keV. We report the first STIX observations of
microflares recorded during the instrument commissioning phase in order to
investigate the STIX performance at its detection limit. This first result
paper focuses on the temporal and spectral evolution of STIX microflares
occuring in the AR12765 in June 2020, and compares the STIX measurements with
GOES/XRS, SDO/AIA, and Hinode/XRT. 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 SXR 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. 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.Comment: 19 pages, 11 figure