Stereoscopic Measurements of Hard Solar X-Rays, and Related Topics

Hurley, K.

doi:10.1007/978-94-009-4612-5_9

Cited by 4 publications

(2 citation statements)

References 29 publications

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“…One of the scientific objectives of the GRB experiment flown on Ulysses (Hurley et al, 1992) was to make stereoscopic observations of solar flares from its unique high-latitude heliocentric orbit by comparison with data from other X-ray monitors flown on satellites in near-Earth or other interplanetary orbits (Hurley, 1986). Combining simultaneous measurements of solar X-rays from two or more satellites having different vantage points can provide useful information about the directivity of the emission as well as an estimate of the height of the emitting region in the photosphere.…”

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The Ulysses Catalog of Solar Hard X-Ray Flares

2009

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Ulysses was launched in October 1990, and its Solar X-ray/Cosmic Gamma-Ray Burst Experiment (GRB) has provided more than 13 years of uninterrupted observations of solar X-ray flare activity. Due to the large variation of the relative solar latitude and longitude of the spacecraft orbit with respect to the Earth, the perspective of the GRB instrument often differed significantly from that of X-ray instruments on Earth-orbiting satellites. During extended periods the GRB experiment made direct observations of flares on the hidden face of the Sun, providing a unique record of events not visible to other instruments. The small detector area of GRB and its optimization for very high counting rates minimized the effects of pulse pile-up. We interpret the spectra, time histories, and occurrence distribution patterns of GRB data in terms of "thermal feed-through", the confusion of thermal soft X-rays and non-thermal hard X-rays. This effect is a systematic problem for scintillation-counter spectrometers observing the solar hard X-ray spectrum. This paper provides a definitive catalog of the Ulysses X-ray flare observations and discusses various features of this unique database. For the equivalent GOES range X2 -X25, we find a power-law fit for the (differential) occurrence frequency at >25 keV with slope −1.61 ± 0.04, with no evidence for a downturn at the highest event magnitudes (for the relatively small sample of such events available in this study). If the nine most intense events are excluded because of concerns about the effects of pulse pile-up, the slope steepens to −1.75 ± 0.08.

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The Ulysses Catalog of Solar Hard X-Ray Flares

2009

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“…Even without utilizing occultation, a satellite pair with cross-calibrated detectors and different points-of-view could make unambiguous measurements of solar flare electron anisotropy (e.g. Kane 1981, Hurley 1986, Kane et al 1988, McTiernan & Petrosian 1990, Kane et al 1998, Casadei et al 2017). Here, good spectral resolution and detector compatibility are more important than imaging capability.…”

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The Micro Solar Flare Apparatus (MiSolFA) instrument concept

Lastufka

Casadei

Hurford

et al. 2020

Advances in Space Research

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The Micro Solar-Flare Apparatus (MiSolFA) is a compact X-ray imaging spectrometer designed for a small 6U micro-satellite. As a relatively inexpensive yet capable Earth-orbiting instrument, MiSolFA is designed to image the high-energy regions of solar flares from a different perspective than that of Solar Orbiter's STIX, operating from a highly elliptical heliocentric orbit. Two instruments working together in this way would provide a 3-dimensional view of X-ray emitting regions and can bypass the dynamic range limitation preventing simultaneous coronal and chromospheric imaging. Stereoscopic X-ray observations would also contain valuable information about the anisotropy of the flare-accelerated electron distribution. To perform these types of observations, MiSolFA must be capable of imaging sources with energies between 10 and 100 keV, with 10 arcsec angular resolution.MiSolFA's Imager will be the most compact X-ray imaging spectrometer in space. Scaling down the volume by a factor of ten from previous instrument designs requires special considerations. Here we present the design principles of the MiSolFA X-ray optics, discuss the necessary compromises, and evaluate

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Measuring X-ray anisotropy in solar flares. Prospective stereoscopic capabilities of STIX and MiSolFA

Casadei

Jeffrey

Kontar

2017

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Context. During a solar flare, a large percentage of the magnetic energy released goes into the kinetic energy of non-thermal particles, with X-ray observations providing a direct connection to keV flare-accelerated electrons. However, the electron angular distribution, a prime diagnostic tool of the acceleration mechanism and transport, is poorly known. Aims. 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 ∼25• , 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. Methods. 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.Results. 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• . Both instruments will directly measure the flare X-ray anisotropy of about 40 M-and X-class solar flares during the next solar maximum. Conclusions. 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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Stereoscopic Measurements of Hard Solar X-Rays, and Related Topics

Cited by 4 publications

References 29 publications

The Ulysses Catalog of Solar Hard X-Ray Flares

The Ulysses Catalog of Solar Hard X-Ray Flares

The Micro Solar Flare Apparatus (MiSolFA) instrument concept

Measuring X-ray anisotropy in solar flares. Prospective stereoscopic capabilities of STIX and MiSolFA

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