The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument is a balloon-borne telescope designed to study solar- are particle acceleration and transport. We describe GRIPS's first Antarctic long-duration flight in January 2016 and report preliminary calibration and science results. Electron and ion dynamics, particle abundances and the ambient plasma conditions in solar flares can be understood by examining hard X-ray (HXR) and gamma-ray emission (20 keV to 10 MeV). Enhanced imaging, spectroscopy and polarimetry of are emissions in this energy range are needed to study particle acceleration and transport questions. The GRIPS instrument is specifically designed to answer questions including: What causes the spatial separation between energetic electrons producing hard X-rays and energetic ions producing gamma-ray lines? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why? GRIPS's key technological improvements over the current solar state of the art at HXR/gamma-ray energies, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), include 3D position-sensitive germanium detectors (3D-GeDs) and a single-grid modulation collimator, the multi-pitch rotating modulator (MPRM). The 3D-GeDs have spectral FWHM resolution of a few hundred keV and spatial resolution <1 mm3. For photons that Compton scatter, usually ⪆150 keV, the energy deposition sites can be tracked, providing polarization measurements as well as enhanced background reduction through Compton imaging. Each of GRIPS's detectors has 298 electrode strips read out with ASIC/FPGA electronics. In GRIPS's energy range, indirect imaging methods provide higher resolution than focusing optics or Compton imaging techniques. The MPRM gridimaging system has a single-grid design which provides twice the throughput of a bi-grid imaging system like RHESSI. The grid is composed of 2.5 cm deep tungsten-copper slats, and quasi-continuous FWHM angular coverage from 12.5-162 arcsecs are achieved by varying the slit pitch between 1-13 mm. This angular resolution is capable of imaging the separate magnetic loop footpoint emissions in a variety of are sizes. In comparison, RHESSI's 35-arcsec resolution at similar energies makes the footpoints resolvable in only the largest ares.
Aline Meuris, Olivier Limousin, Olivier Gevin, Marie-Cécile Vassal, Fabrice Soufflet, Nicolas Fiant, Martin Bednarzik, Christopher Wild, Stefan Stutz, Guy Birrer, Claire Blondel, Isabelle Le Mer, Duc-Dat Huynh, Modeste Donati, Oliver Grimm, Volker Commichau, Gordon Hurford, Säm Krucker, François Gonzalez, Marc Billot
Caliste-SO is a hybrid detector integrating in a volume of 12 × 14 × 18 mm3 a 1 mm-thick CdTe pixel detector, a frontend IDeF-X HD ASIC and passive parts to perform high resolution spectroscopy in the 4-200 keV energy range with high count rate capability (104-105 photons/s/cm2). The detector hybridization concept was designed by CEA and 3DPlus to realize CdTe cameras for space astronomy missions with various pixel patterns. For the STIX instrument onboard the Solar Orbiter mission, the imaging system is made by 32 collimators that sample the visibilities of the spatial Fourier transform and doesn’t require fine pitch pixels. The Al-Schottky CdTe detectors produced by Acrorad are then patterned and tested by the Paul Scherrer Institute to produce 12 pixels surrounded by a guard ring within 1 cm2. Electrical and spectroscopic performance tests of the Caliste-SO samples are performed in France at key manufacturing steps, before sending the samples to the principal investigator to mount them in the Detector Electronics Module of STIX in front of each collimator. Four samples were produced in 2013 to be part of the STIX engineering model. Best pixels show an energy resolution of 0.7 keV FWHM at 6 keV (1 keV resolution requirement for STIX) and a low-level detection threshold below 3 keV (4 keV requirement for STIX). The paper describes the design and the production of Caliste-SO and focuses on main performance tests performed so far to characterize the spectrometer unit.
KEYWORDS: Sensors, Device simulation, Photons, Field programmable gate arrays, Signal detection, Solar processes, X-rays, Temperature sensors, Data modeling, Data storage
The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10 instruments on-board Solar Orbiter mission of the European Space Agency (ESA) scheduled to be launched in 2017. STIX is aimed to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 keV to 150 keV using a Fourier-imaging technique. The instrument employs a set of tungsten grids in front of 32 pixelized CdTe detectors. These detectors are source of data collected and analyzed in real time by Instrument Data Processing Unit (IDPU). In order to support development and implementation of on-board algorithms a dedicated detector hardware simulator is designed and manufactured as a part of Electrical Ground Support Equipment (EGSE) for STIX instrument. Complementary to the hardware simulator is data analysis software which is used to generate input data and to analyze output data. The simulator will allow sending strictly defined data from all detectors’ pixels at the input of the IDPU for further analysis of instrument response. Particular emphasis is given here to the simulator hardware design.
Hard X-ray and gamma-ray emission during solar flares encode information about electron/ion dynamics and provide a proxy to deduce solar atmospheric parameters. Enhanced imaging, spectroscopy and polarimetry of HXR/gamma-ray are emissions over ~20 keV to greater than or approx. equal to 10MeV is needed to study particle transport; the Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS) instrument is designed to meet these goals. GRIPS' key technological improvements over the current solar state of the art in HXR/gamma-ray energies (RHESSI) include 3D position-sensitive germanium detectors (3D-GeDs) and a single-grid modulation collimator, the Multi-Pitch Rotating Modulator (MPRM). The 3D-GeDs allow GRIPS to reconstruct Compton-scatter tracks of energy deposition, providing enhanced background reduction and polarization measurements. Each of GRIPS' sixteen detectors has 298 electrode strips, each of which has dedicated ASIC/FPGA electronics. In GRIPS' energy range, indirect Fourier imaging provides higher resolution than focusing optics or Compton imaging techniques. The MPRM grid-imaging system has a single-grid design which provides 2x the throughput of a bigrid imaging system like RHESSI. Quasi-continuous resolution from 12.5 - 162 arcsecs is achieved by varying the grid pitch between 1 - 13mm. This spatial resolution will be capable of imaging the separate footpoints in a variety of flare sizes. In comparison, RHESSI's minimum 35 arcsec resolution at the same energy makes footpoints resolvable
in only the largest flares. We discuss GRIPS' science goals, the instrument overall, and recent developments in GRIPS' detector and imaging systems. GRIPS is scheduled for an engineering flight from Fort Sumner in September 2014, followed by two long-duration balloon flights from Antarctica in 2015/16.
Konrad Skup, A. Cichocki, R. Graczyk, M. Michalska, M. Mosdorf, W. Nowosielski, P. Orleański, A. Przepiórka, K. Seweryn, M. Stolarski, M. Winkler, J. Sylwester, M. Kowalinski, T. Mrozek, P. Podgorski, A. Benz, S. Krucker, G. Hurford, N. Arnold, H. Önel, A. Meuris, O. Limousin, O. Grimm
KEYWORDS: Sensors, X-rays, Space operations, Attenuators, Imaging systems, X-ray imaging, Field programmable gate arrays, Control systems, Data processing, Electronics
The Spectrometer/Telescope for Imaging X-rays (STIX) is one of 10 instruments on board Solar Orbiter, an M-class
mission of the European Space Agency (ESA) scheduled to be launch in 2017. STIX applies a Fourier-imaging
technique using a set of tungsten grids in front of 32 pixelized CdTe detectors to provide imaging spectroscopy of solar
thermal and non-thermal hard X-ray emissions from 4 to 150 keV. These detectors are source of data collected and
analyzed in real-time by Instrument Data Processing Unit (IDPU). Besides the data processing the IDPU controls and
manages other STIX’s subsystems: ASICs and ADCs associated with detectors, Aspect System, Attenuator, PSU and
HK. The instrument reviewed in this paper is based on the design that passed the Instrument Preliminary Design Review
(IPDR) in early 2012 and Software Preliminary Design Review (SW PDR) in middle of 2012. Particular emphasis is
given to the IDPU and low level software called Basic SW (BSW).
P. Kaufmann, A. Abrantes, E. C. Bortolucci, E. Correia, J. A. Diniz, G. Fernandez, L. O. T. Fernandes, C. G. Giménez de Castro, R. Godoy, G. Hurford, A. S. Kudaka, M. Lebedev, R. Lin, N. Machado, V. S. Makhmutov, R. Marcon, A. Marun, V. Nicolaev, P. Pereyra, J.-P. Raulin, C. M. da Silva, A. Shih, Y. Stozhkov, J. Swart, A. Timofeevsky, A. Valio, T. Villela, M. B. Zakia
A new solar flare spectral component has been found with intensities increasing for larger sub-THz frequencies,
spectrally separated from the well known microwaves component, bringing challenging constraints for interpretation.
Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A twofrequency
THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons
or satellites, or at exceptionally transparent ground stations. 76 mm diameter telescopes were designed to observe the
whole solar disk detecting small relative changes in input temperature caused by flares at localized positions at 3 and 7
THz. Golay cell detectors are preceded by low-pass filters to suppress visible and near IR radiation, band-pass filters,
and choppers. It can detect temperature variations smaller than 1 K with time resolution of a fraction of a second,
corresponding to small burst intensities. The telescopes are being assembled in a thermal controlled box to which a data
conditioning and acquisition unit is coupled. While all observations are stored on board, a telemetry system will forward
solar activity compact data to the ground station. The experiment is planned to fly on board of long-duration
stratospheric balloon flights some time in 2013-2015. One will be coupled to the GRIPS gamma-ray experiment in
cooperation with University of California, Berkeley, USA. One engineering flight will be flown in the USA, and a 2
weeks flight is planned over Antarctica in southern hemisphere summer. Another long duration stratospheric balloon
flight over Russia (one week) is planned in cooperation with the Lebedev Physics Institute, Moscow, in northern
hemisphere summer.
The balloon-borne Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument will provide a near-optimal
combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions
from ~20 keV to >~10 MeV. GRIPS will address questions raised by recent solar flare observations regarding particle
acceleration and energy release, such as: What causes the spatial separation between energetic electrons producing hard
X-rays and energetic ions producing gamma-ray lines? How anisotropic are the relativistic electrons, and why can they
dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and
why? The spectrometer/polarimeter consists of sixteen 3D position-sensitive germanium detectors (3D-GeDs), where
each energy deposition is individually recorded with an energy resolution of a few keV FWHM and a spatial resolution
of <0.1 mm3. Imaging is accomplished by a single multi-pitch rotating modulator (MPRM), a 2.5-cm thick tungstenalloy
slit/slat grid with pitches that range quasi-continuously from 1 to 13 mm. The MPRM is situated 8 meters from the
spectrometer to provide excellent image quality and unparalleled angular resolution at gamma-ray energies (12.5 arcsec
FWHM), sufficient to separate 2.2 MeV footpoint sources for almost all flares. Polarimetry is accomplished by
analyzing the anisotropy of reconstructed Compton scattering in the 3D-GeDs (i.e., as an active scatterer), with an
estimated minimum detectable polarization of a few percent at 150–650 keV in an X-class flare. GRIPS is scheduled for
a continental-US engineering test flight in fall 2013, followed by long or ultra-long duration balloon flights in
Antarctica.
A. Benz, S. Krucker, G. Hurford, N. Arnold, P. Orleanski, H.-P. Gröbelbauer, S. Klober, L. Iseli, H. Wiehl, A. Csillaghy, L. Etesi, N. Hochmuth, M. Battaglia, M. Bednarzik, R. Resanovic, O. Grimm, G. Viertel, V. Commichau, A. Meuris, O. Limousin, S. Brun, N. Vilmer, K. Skup, R. Graczyk, M. Stolarski, M. Michalska, W. Nowosielski, A. Cichocki, M. Mosdorf, K. Seweryn, A. Przepiórka, J. Sylwester, M. Kowalinski, T. Mrozek, P. Podgorski, G. Mann, H. Aurass, E. Popow, H. Önel, F. Dionies, S. Bauer, J. Rendtel, A. Warmuth, M. Woche, D. Plüschke, W. Bittner, J. Paschke, D. Wolker, H. Van Beek, F. Farnik, J. Kasparova, A. Veronig, I. Kienreich, P. Gallagher, D. Bloomfield, M. Piana, A. Massone, B. Dennis, R. Schwarz, R. Lin
The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10 instruments on board Solar Orbiter, a confirmed Mclass mission of the European Space Agency (ESA) within the Cosmic Vision program scheduled to be launched in 2017. STIX applies a Fourier-imaging technique using a set of tungsten grids (at pitches from 0.038 to 1 mm) in front of 32 pixelized CdTe detectors to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 to 150 keV. The status of the instrument reviewed in this paper is based on the design that passed the Preliminary Design Review (PDR) in early 2012. Particular emphasis is given to the first light of the detector system called Caliste-SO.
The primary scientific objective of RHESSI Small Explorer mission is to investigate the physics of particle acceleration and energy release in solar flares, through imaging and spectroscopy of X-ray/gamma-ray continuum and gamma-ray lines emitted by accelerated electrons and ions, respectively. RHESSI utilizes rotating modulator collimators together with cooled germanium detectors to image X-rays/gamma-rays from 3 keV to 17 MeV. It provides the first hard X-ray imaging spectroscopy, the first high resolution spectroscopy of solar gamma-ray liens, and the first imaging of solar gamma-ray lines and continuum. Here we briefly describe the mission and instrumentation, and illustrate its capabilities with solar and cosmic observations obtained in the first 17 months of operation.
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a
NASA Small Explorer satellite designed to study hard x-ray and
gamma-ray emission from solar flares. In addition, its
high-resolution array of germanium detectors can see photons
from high-energy sources throughout the Universe. Here we discuss
the various algorithms necessary to extract spectra, lightcurves,
and other information about cosmic gamma-ray bursts, pulsars,
and other astrophysical phenomena using an unpointed, spinning
array of detectors. We show some preliminary results and discuss
our plans for future analyses. All RHESSI data are public, and
scientists interested in participating should contact the
principal author.
Alex Zehnder, Jacek Bialkowski, F. Burri, Martin Fivian, Reinhold Henneck, A. Mchedlishvili, P. Ming, J. Welte, Knud Thomsen, David Clark, Brian Dennis, Gordon Hurford, David Curtis, Peter Harvey, David Pankow
RHESSI uses nine Rotating Modulation Collimators (RMCs) for imaging, each consisting of a pair of grids mounted on the rotating spacecraft. The angular resolutions range from 2.3 arcsec to 3arcmin. The relative twist between the two grids of each pair is the most critical parameter. It must be less than 20 arcsec for the finest grid. After precision alignment, it is monitored by the Twist Monitoring System (TMS) to a few arcsec. The Sun-pointing must be known better than 0.4 arcsec for the image reconstruction. This is achieved by the Solar Aspect System (SAS), which consists of a set of three Sun sensors. Each sensor is focusing the filtered Sun light onto a linear CCD. The onboard Aspect Data Processor (ADP) selects the 6 limb positions, which over-define the pointing offset of the Sun center in respect to the imaging axis of the imager. The Roll Angle System (RAS) continuously measures the roll angle of RHESSI within arcmin accuracy. The RAS is a continuously operating CCD star scanner. The time of the passage of a star image over the CCD is recorded and defines the roll angle, comparing its pixel position and amplitude with a star map.
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA SMall EXplorer (SMEX) mission to study the acceleration and transport of high-energy electrons and nuclei in solar flares. This is done using high spatial (2.3 arcsec) and high spectral (~1 keV) resolution imaging spectroscopy of X-rays and gamma rays between 3 keV and 17 MeV. Such an energy range includes ~10-30MK thermal emission, non-thermal hard X-ray bremsstrahlung from accelerated electrons, and gamma-ray lines from accelerated nuclei.
RHESSI's imaging is based on a set of rotating modulation collimators. Each of the nine subcollimators uses a pair of widely separated (1.55m) grids, mounted on a rotating spacecraft. Each grid in turn consists of a large number of parallel, equispaced, X-ray-opaque slats. A corresponding set of nine high-resolution cooled germanium detectors determines the energy and arrival time of each detected photon. As the spacecraft rotates at ~15 rpm, the grid pairs time-modulate the detected X-ray flux in a manner sensitive to the morphology and location of the X-ray source(s). Post-analysis then reconstructs the image from the set of time-modulated light curves. This paper reviews the RHESSI imaging instrumentation, data analysis approach, imaging concept and early indications of in-flight performance.
In response to the recent NASA-SMEX Announcement of Opportunity, our collaboration proposed Cyclone, the Cyclotron/Nuclear Explorer. Cyclone is a broadband pointed astrophysical observatory, combining the highest spectral resolutions (E/(Delta) E approximately 30 - 300) and angular resolutions (15') achieved in the optimized hard X-ray range (10 - 200 keV). The instrument consists of 19 co-aligned rotation modulation collimator (RMC) telescopes, each with a high spectral resolution, 6-cm diameter germanium detector (GeD) covering energies from 3 keV to 600 keV. Both the optics and detectors are actively shielded with 15-mm BGO to gain low background an high sensitivity to astrophysical sources. A 550-km altitude, circular equatorial orbit also minimizes background. Building strongly upon instrumental heritage from the High-Energy Solar Spectroscopic Imager (HESSI) program, Cyclone would be ready for launch by September 2003. The instrument design and expected performance are discussed, as well as a brief overview of scientific goals.
Martin Fivian, Jacek Bialkowski, W. Hajdas, Reinhold Henneck, A. Mchedlishvili, P. Ming, Knud Thomsen, Alex Zehnder, Gordon Hurford, David Curtis, David Pankow, Brian Dennis
HESSI will image Solar flares with spatial resolution ranging from 2 and 190 arcsec over the energy range from 3 keV to approximately equals 100 keV and as low as 35 arcsec for energies up to 20 MeV, respectively. The system is based on Fourier- transform imaging in connection with high-resolution Ge- detectors. In order to achieve arcsec-quality images with an instrument having only arcmin alignment requirements one needs in addition two precise aspect systems: (1) The Solar Aspect System (SAS) will provide Sun aspect data with high precision (< 0.2 arcsec relative and 1 arcsec absolute) and at high frequency (100 Hz). It consists of three identical lens/filter assemblies with focus Sun images on three 2048 X (13 micrometers )2 linear CCDS at 1.55 m focal distance. Simultaneous exposures of three chords of the focused solar images are made and the pixels spanning each solar limb are recorded. (2) The Roll Angle System (RAS) will provide precise (arcmin) information on the roll angle of the rotating spacecraft. The RAS is a star scanner which points out radially and observes stars at 75 degrees from the Sun direction using a commercial lens and a fast CCD. The passage of a star image over the CCD will induce a signal in one or several pixels and the timing of this signal defines the roll angle, once the star has been identified by comparing its pixel position and amplitude with a star map. With a limiting magnitude of mv equals 3 we expect to observe at least 1 star per revolution (during direct Sun view) over 1 year; on the average we will detect about 10 stars/revolution. We report on the design, construction and calibration measurements of the SAS and RAS flight-model instruments.
Reinhold Henneck, Jacek Bialkowski, F. Burri, Martin Fivian, W. Hajdas, A. Mchedlishvili, P. Ming, Knud Thomsen, J. Welte, Alex Zehnder, M. Dettwyler, F. Buerki, Gordon Hurford, David Curtis, David Pankow
The purpose of the HESSI RAS is to provide information on the roll angle of the rotation spacecraft. Precise knowledge of the roll angle is a necessary ingredient for image reconstruction. The RAS is a continuously operating star scanner that points out radially and observes stars at 75 degrees from the Sun direction using a commercial lens and a fast CCD. The passage of a star image over the CCD charges one or several pixels above threshold and the timing of this signal defines the roll angle, once the star has been identified by comparing its pixel position and amplitude with a star map. Roll angles at intermediate times are inferred by assuming uniform rotation. With a limiting star magnitude of mv equals 3 we expect to observe at least 1 star per revolution over 1 year; on the average we will detect about 10 stars/revolution.
Reinhold Henneck, Jacek Bialkowski, F. Burri, Martin Fivian, W. Hajdas, A. Mchedlishvili, P. Ming, Knud Thomsen, J. Welte, Alex Zehnder, Brian Dennis, Gordon Hurford, David Curtis, David Pankow
KEYWORDS: Charge-coupled devices, Sun, Imaging systems, Space operations, Solar energy, Fermium, Frequency modulation, Data processing, Light emitting diodes, Imaging spectroscopy
The HESSI SAS is a set of three Sun sensors, which shall provide high bandwidth information on the solar pointing of the rotating spacecraft. The precision of <EQ 0.4 arcsec relative is necessary in order to obtain the HESSI imaging resolution of 2 arcsec; the absolute accuracy of 1 arcsec is required for comparison with other measurements. Each SAS is based on focusing the Sun through a narrow bandwidth filter on to a 2048-element x (13(mu) )2 linear CCD. A digital threshold algorithm is used to select N pixels that span each solar limb for inclusion in the telemetry. Determination of the 6 limb crossing locations provided by the 3 subsystems defines the position offset of the Sun in the rotating frame. In this paper we describe the mechanical and electronic configuration of the SAS FM and the results of the first test measurements.
Robert Lin, Gordon Hurford, Norman Madden, Brian Dennis, Carol Crannell, Gordon Holman, Reuven Ramaty, Tycho von Rosenvinge, Alex Zehnder, H. Frank van Beek, Patricia Bornmann, Richard Canfield, A. Gordon Emslie, Hugh Hudson, Arnold Benz, John Brown, Shinzo Enome, Takeo Kosugi, Nicole Vilmer, David Smith, Jim McTiernan, Isabel Hawkins, Said Slassi-Sennou, Andre Csillaghy, George Fisher, Chris Johns-Krull, Richard Schwartz, Larry Orwig, Dominic Zarro, Ed Schmahl, Markus Aschwanden, Peter Harvey, David Curtis, David Pankow, David Clark, Robert Boyle, Reinhold Henneck, Akilo Michedlishvili, Knud Thomsen, Jeff Preble, Frank Snow
The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum.
For many years, ground-based radio observations of the Sun have proceeded into two directions: (1) high resolution imaging at a few discrete wavelengths; (2) spectroscopy with limited or no spatial resolution at centimeter, decimeter, and meter wavelengths. Full exploitation of the radio spectrum to measure coronal magnetic fields in both quiescent active regions and flares, to probe the thermal structure of the solar atmosphere, and to study energy release and particle energization in transient events, requires a solar-dedicated, frequency-agile solar radiotelescope, capable of high-time, - spatial, and -spectral resolution imaging spectroscopy. In this paper we summarize the science program and instrument requirements for such a telescope, and present a strawman interferometric array composed of many (greater than 40), small (2 m) antenna elements, each equipped with a frequency- agile receiver operating over the range 1 - 26.5 GHz.
Brian Dennis, Robert Lin, Richard Canfield, Carol Crannell, A. Gordon Emslie, Gordon Holman, Hugh Hudson, Gordon Hurford, James Ling, Norman Madden, Reuven Ramaty
The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) is to understand particle acceleration and explosive energy release in the magnetized plasmas at the Sun. HESSI will provide the first hard X-ray imaging spectroscopy, the first high-resolution spectroscopy of solar gamma-ray lines from a spacecraft, the first imaging above 100 keV, and the first imaging of solar gamma- ray lines. The gamma-ray imaging spectroscopy will provide the first information on the spatial distribution of energetic (>1 MeV) protons, heavy ions, and relativistic electrons, and the first information on the angular distribution of the energetic ions. It will also provide detailed information on elemental abundances for both the accelerated ions and the ambient ions in the interaction region. HESSI uses Fourier-transform imaging spectroscopy to cover the broad energy range from soft X-rays (2 keV) to gamma-rays (20 MeV) with spatial resolutions down to 2 arcseconds and spectral resolutions down to 1 keV. This capability is achieved with 12 bi-grid rotating modulation collimators located in front of a corresponding set of 12 pairs of cooled germanium and silicon (Si(Li)) detectors to provide the wide spectral coverage. HESSI has been selected by NASA as an alternate Medium-class Explorer (MIDEX) mission, for launch in the year 2000. If it does not get funded as a flight mission, it will be descoped and proposed at a Small Explorer mission for launch in 2000 at half the MIDEX cost.
A single high-energy instrument based on rotating modulation collimators with germanium semiconductor
spectrometers as the detectors can provide high angular resolution (< 1 arc sec), high time resolution
(< 1 s), and high spectral resolution (about one keV), all in one package. Such rotating modulation-
collimator optics provide excellent spatial (u,v)-plane coverage for high-contrast images in the hard X-ray
domain, where there will be a large signal-to-noise ratio during even modest flares. The use of thick
modulation plates will make it possible to image gamma rays with < 5 arc sec angular resolution to
energies in excess of 10 MeV during the more energetic flares without compromising the ability of the
germanium detectors to resolve the gamma-ray lines. Energetic neutrons will also be imaged for the first
time with < 20 arc sec angular resolution. This combination of imaging and spectroscopy at high resolution
will be a powerful tool for helping to answer central questions of solar flare physics, especially if such an
instrument were supported by observations at longer wavelengths. The timing of solar activity dictates a
launch of such a High-Energy Solar Physics (HESP) mission by 1998.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.