Solar Flare Measurements with STIX and MiSolFA

Solar flares are the most powerful events in the solar system and the brightest sources of X-rays, often associated with emission of particles reaching the Earth and causing geomagnetic storms, giving problems to communication, airplanes and even black-outs. X-rays emitted by accelerated electrons are the most direct probe of solar flare phenomena. The Micro Solar-Flare Apparatus (MiSolFA) is a proposed compact X-ray detector which will address the two biggest issues in solar flare modeling. Dynamic range limitations prevent simultaneous spectroscopy with a single instrument of all X-ray emitting regions of a flare. In addition, most X-ray observations so far are inconsistent with the high anisotropy predicted by the models usually adopted for solar flares. Operated at the same time as the STIX instrument of the ESA Solar Orbiter mission, at the next solar maximum (2020), they will have the unique opportunity to look at the same flare from two different directions: Solar Orbiter gets very close to the Sun with significant orbital inclination; MiSolFA is in a near-Earth orbit. To solve the cross-calibration problems affecting all previous attempts to combine data from different satellites, MiSolFA will adopt the same photon detectors as STIX, precisely quantifying the anisotropy of the X-ray emission for the first time. By selecting flares whose footpoints (the brightest X-ray sources, at the chromosphere) are occulted by the solar limb for one of the two detectors, the other will be able to study the much fainter coronal emission, obtaining for the first time simultaneous observations of all interesting regions. MiSolFA shall operate on board of a very small satellite, with several launch opportunities, and will rely on moir\'e imaging techniques.Comment: Invited talk, N30-8, Astrophysics and Space Instrumentation session, 2014 Nuclear Science Symposium and Medical Imaging Conference, 11 Nov 201

Cosmic Ray Astrophysics with AMS-02

The Alpha Magnetic Spectrometer (AMS) is a cosmic ray (CR) experiment that will operate on the International Space Station for three years, measuring the particle spectra in the rigidity range from 0.2 GV to 2 TV. The AMS-02 detector will provide measurements with unprecedented statistics of the hadronic and leptonic cosmic rays, allowing for a better study of the Earth magnetosphere through the secondaries produced by CR interactions in the atmosphere; of the solar system environment through the measurement of the solar modulation over a long period; of the solar system neighborhood through the measurement of the ratio between unstable isotopes and stable elements; of the interstellar medium of our Galaxy through the ratio between secondary and primary isotopes and the measurement of proton and helium spectra.Comment: Talk given at Lake Louise Winter Institute: 15-21 February 2004 "Fundamental Interactions". 6 pages, 10 figure

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 $\sim25^{\circ}$, 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

The Local Interstellar Spectrum of Cosmic Ray Electrons

The direct measurements of electrons and positrons over the last 30 years, corrected for the solar effect in the force-field approximation, are considered. The resulting overall electron spectrum may be fitted with a single power law above few GeV with spectral index ($\gamma_{-} = 3.41 \pm 0.02$), consistent with the spectral index of the positron spectrum ($\gamma_{+} = 3.40 \pm 0.06$), therefore suggesting a common acceleration process for both species. We propose that the engine was a shock wave originating from the last supernova explosion among those that formed the local bubble. In addition, at low energy, the electron spectrum measured during the last $A+$ solar phase is damped, whereas the positron spectrum is well represented by a single power law down to the lowest inferred local interstellar energy (0.8 GeV). We suggest that this difference arises from a time- and charge-dependent effect of the solar modulation that is not taken into account by the force-field approximation.Comment: 10 pages, 9 figures, 1 table. OBSOLETE: please refer to ApJ 612 (2004) 262-267, that is the final version of this wor