144 research outputs found
On the Photometric Accuracy of RHESSI Imaging and Spectrosocopy
We compare the photometric accuracy of spectra and images in flares observed
with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)}spacecraft. We
test the accuracy of the photometry by comparing the photon fluxes obtained in
different energy ranges from the spectral-fitting software SPEX with those
fluxes contained in the images reconstructed with the Clean, MEM, MEM-Vis,
Pixon, and Forward-fit algorithms. We quantify also the background fluxes, the
fidelity of source geometries, and spatial spectra reconstructed with the five
image reconstruction algorithms. We investigate the effects of grid selection,
pixel size, field-of-view, and time intervals on the quality of image
reconstruction. The detailed parameters and statistics are provided in an
accompanying CD-ROM and web page. We find that Forward-fit, Pixon, and Clean
have a robust convergence behavior and a photometric accuracy in the order of a
few percents, while MEM does not converge optimally for large degrees of
freedom (for large field-of-views and/or small pixel sizes), and MEM-Vis
suffers in the case of time-variable sources. This comparative study documents
the current status of the RHESSI spectral and imaging software, one year after
launch.Comment: 2 Figures, full version on
http://www.lmsal.com/~aschwand/eprints/2003_photo/index.htm
Fermi-LAT Observations of the 2017 September 10 Solar Flare
The Fermi-Large Area Telescope detection of the X8.2 GOES class solar flare of 2017 September 10 provides for the first time observations of a long-duration high-energy gamma-ray flare associated with a ground-level enhancement (GLE). The >100 MeV emission from this flare lasted for more than 12 hr covering both the impulsive and extended phases. We present the localization of the gamma-ray emission and find that it is consistent with the active region from which the flare occurred over a period lasting more than 6 hr. The temporal variation of the gamma-ray flux and of the proton index inferred from the gamma-ray data seems to suggest three phases in acceleration of the proton population. Based on timing arguments we interpret the last phase to be tied to the acceleration mechanism powering the powering the production of the GLE particles
Variation of the electron flux spectrum along a solar flare loop as inferred from STIX hard X-ray observations
Regularized imaging spectroscopy was introduced for the construction of
electron flux images at different energies from count visibilities recorded by
the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). In this work
we seek to extend this approach to data from the Spectrometer/Telescope for
Imaging X-rays (STIX) on-board the Solar Orbiter mission. Our aims are to
demonstrate the feasibility of regularized imaging spectroscopy as a method for
analysis of STIX data, and also to show how such analysis can lead to insights
into the physical processes affecting the nonthermal electrons responsible for
the hard X-ray emission observed by STIX. STIX records imaging data in an
intrinsically different manner from RHESSI. Rather than sweeping the angular
frequency plane in a set of concentric circles (one circle per detector), STIX
uses collimators, each corresponding to a specific angular frequency. In
this paper we derive an appropriate modification of the previous computational
approach for the analysis of the visibilities observed by STIX. This approach
also allows for the observed count data to be placed into non-uniformly-spaced
energy bins. We show that the regularized imaging spectroscopy approach is not
only feasible for analysis of the visibilities observed by STIX, but also more
reliable. Application of the regularized imaging spectroscopy technique to
several well-observed flares reveals details of the variation of the electron
flux spectrum throughout the flare sources. We conclude that the
visibility-based regularized imaging spectroscopy approach is well-suited to
analysis of STIX data. We also use STIX electron flux spectral images to track,
for the first time, the behavior of the accelerated electrons during their path
from the acceleration site in the solar corona toward the chromospher
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