Stereoscopic Observations of Solar Hard X‐Ray Flares Made by<i>Ulysses</i>and<i>Yohkoh</i>

Kane, S. R.; Hurley, K.; McTiernan, J.; Boër, M.; Niel, M.; Kosugi, T.; Yoshimori, M.

doi:10.1086/305738

Cited by 26 publications

(25 citation statements)

References 17 publications

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“…The difference could be caused by one or both of the following two factors: (1) directivity (anisotropy) of the hard X-ray source, and (2) partial occultation of the hard X-ray source by the photosphere from the view of the RHESSI instrument. Extensive stereoscopic observations of the directivity of flareassociated hard X-ray sources during the last solar activity cycle have shown that it is small (Kane et al 1980(Kane et al , 1988(Kane et al , 1998. The good agreement between the observed and expected counting rates during the rise and small maximum confirm this earlier finding.…”

Section: The Small Hard X-ray Burstsupporting

confidence: 69%

“…An on-board 241 Am X-ray source provides 60 keV X-rays for daily in-flight calibrations. The instrument has also been inter-calibrated in the past with other hard X-ray spectrometers such as the one on Yohkoh (Kane et al 1998). A recent comparison with RHESSI measurements indicates that the inter-calibration of these two instruments is also satisfactory.…”

Section: Hard X-ray Instruments On Ulysses and Rhessimentioning

confidence: 99%

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Multispacecraft observations of the hard X-ray emission from the giant solar flare on 2003 November 4

Kane

McTiernan

Hurley

2005

A&A

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Abstract. The hard X-ray emission from the "giant" solar flare on 4 November 2003 (∼1947 UT) was observed by the hard X-ray/gamma ray spectrometer on the Ulysses spacecraft located at ∼114 degrees west of the Sun-Earth line at a distance of 5.28 AU from the Sun. A "small" hard X-ray burst during the early rise of the giant flare and a part of the decay of the hard X-ray emission associated with the giant flare were also observed by the hard X-ray imager on the RHESSI satellite located near the Earth. The maximum of the hard X-ray emission during the giant flare could not be observed by the RHESSI instrument because of satellite night. The flare view angles for Ulysses and RHESSI were ∼31• West and 83 • East respectively. The H-α flare (importance 3B) was located at S19 W83 in the active region NOAA 10486. GOES observations of the associated soft X-ray emission saturated during the period 1943-1958 UT. It has been estimated that the soft X-ray maximum occurred at ∼1947 UT with peak flux equivalent to NOAA class > = X28. OVSA radio observations show that the flare produced intense microwave emission, the peak flux at 15.4 GHz being ∼60 000 sfu at ∼1945 UT. Intense type II, III and IV radio bursts have also been reported at metric and decimetric wavelengths. RHESSI has provided 10-100 keV X-ray images and spectra for 1930-1936 UT (the early rise of the flare) and 10-30 keV images and spectra for 2016-2114 UT (a part of the late decay of the flare). Ulysses observed an increase in 25-150 keV X-rays from 1933 UT to 2015 UT with the maximum at ∼1944 UT, almost simultaneously with the maximum in 15.4 GHz radio emission and ∼3 min before the maximum in the soft X-ray emission. This indicates that the X-ray emission observed by Ulysses was mostly non-thermal. An assumed hard X-ray spectrum of ∼E −3.5 photons cm −2 s −1 keV −1 for >20 keV photons leads to an energy dissipation rate of ∼6.4 × 10 31 erg s −1 at the time of the hard X-ray maximum. The total energy in >20 keV electrons released during the flare is estimated to be ∼1.3 × 10 34 erg.

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Section: The Small Hard X-ray Burstsupporting

confidence: 69%

Section: Hard X-ray Instruments On Ulysses and Rhessimentioning

confidence: 99%

Multispacecraft observations of the hard X-ray emission from the giant solar flare on 2003 November 4

Kane

McTiernan

Hurley

2005

A&A

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“…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. Deep-space observations contribute to the detection of flares occulted by the solar limb, a good method for isolating X-ray sources in the corona rather than at the chromospheric footpoints of the flare loop system (Frost and Dennis, 1971;Hudson, 1978;Kane et al, 1998).…”

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confidence: 99%

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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“…Such previous stereoscopic studies (e.g. Kane et al 1998) found no clear evidence for directivity at large X-ray energies. However, past direct measurements by multiple spacecrafts suffered greatly from calibration issues, owing to the use of different types of detectors, therefore the results were questionable at best.…”

Section: Introductionmentioning

confidence: 74%

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 Observations of Solar Hard X‐Ray Flares Made byUlyssesandYohkoh

Cited by 26 publications

References 17 publications

Multispacecraft observations of the hard X-ray emission from the giant solar flare on 2003 November 4

Multispacecraft observations of the hard X-ray emission from the giant solar flare on 2003 November 4

The Ulysses Catalog of Solar Hard X-Ray Flares

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

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