HESSI Science Objective  Impulsive Energy Release in the Corona  Acceleration of Electrons, Protons, and Ions  Plasma Heating to Tens of Millions of degrees  Energy and Particle Transport and Dissipation To explore the basic physics of particle acceleration and explosive energy release in Solar Flares A

HESSI Non-Solar Science Objectives ŸThe Crab Nebula – Imaging spectroscopy with 2” resolution ŸGamma Ray Bursts and Cosmic Transient Sources – Detected over a large fraction of the sky – High resolution spectroscopy – Search for cyclotron line features ŸSteady X-ray and gamma-ray sources (point and diffuse) – Detect by Earth occultation or through the rear grids – Obtain high resolution spectra – Search for line features A

HESSI Primary Observations  Hard X-ray Images – Angular resolution as fine as 2 arcseconds – Temporal resolution as fine as 10 ms – Energy resolution of <1 keV from 3 keV to 400 keV  High Resolution X-ray and Gamma-ray Spectra – keV energy resolution –To energies as high as 15 MeV A

Complementary Observations SOHOEUV images and spectra Coronagraph images Particle spectra and abundances GOESImages from the Soft X-ray Imager ACEEnergetic particle spectra and abundances TRACEUV & XUV high resolution images CGROX-ray and gamma-ray spectra and time histories Ground-based Observatories Radio and optical images and spectra Magnetograms A

HESSI Firsts  Hard X-Ray Imaging Spectroscopy  High Resolution Spectroscopy of Solar Gamma-Ray Lines  Hard X-Ray and Gamma-Ray Imaging above 100 keV  Imaging of Narrow Gamma-Ray Lines  High Resolution X-ray and Gamma-Ray Spectra of Cosmic Sources  Hard X-Ray Images of the Crab Nebula with 2-arcsecond Resolution A

Relevance to Strategic Plan  Part of the Solar Connections Program - in the Roadmap for the next solar maximum.  Seeks to understand fundamental physics of solar flare energy release and particle acceleration.  Relevant to understanding relation between flares and coronal mass ejections and their effects on the Earth and its environs. A

Expected Numbers of Flares MicroflaresTens of thousands Hard X-ray flares with crude imaging and spectra>1000 to >100 keV Hard X-ray flares with >10 3 counts s -1 detector -1 Hundreds above 20 keV allowing spatial scales to be followed on timescales of 0.1 s Flares sufficiently intense to allow the finestTens possible imaging spectroscopy Flares with the detection of gamma-ray linesUp to 100 Flares with detailed gamma-ray line spectroscopyTens and the location and extent of the source determined to ~40 arcseconds

HESSI Observational Characteristics  Energy Range3 keV to 15 MeV  Energy Resolution~1 keV from 3 keV to 1 MeV Increasing to 5 keV at 15 MeV  Angular Resolution2 arcseconds to 100 keV 7 arcseconds to 400 keV 36 arcseconds to 15 MeV  Temporal ResolutionTens of ms for basic image 2 s for detailed image  Field of ViewFull Sun  Effective Area - cm at 3 keV, 1 at 10 keV 100 at 100 keV, 50 at 10 MeV  Numbers of flares~1000 imaged to >100 keV. ~100 with spectroscopy to ~10 MeV

HESSI Summary Instrument9 germanium detectors (7-cm dia. x 8 cm) Cooled to 75 K with Sunpower cooler Grid pitches from 34 microns to 2.75 mm 1.55-m grid separation Solar Aspect System to <1 arcsecond Roll Angle System to 1 arcminute Weight120 kg Power110 watts Telemetry<11 Gbits/day SpacecraftSpinning at rpm Pointing to within 0.1° of Sun center Launch VehiclePegasus XL from KSC Orbit38° inclination 600 km altitude, >3-year life Launch Datemid-2000 Operations3 years A

HESSI PI and Co-Is Robert LinUniversity of California, BerkeleyPI Brian DennisGSFC/682Mission Scientist Carol CrannellGSFC/682Education & Outreach Gordon HolmanGSFC/682Flare Theory Reuven RamatyGSFC/661Flare Theory Tycho von RosenvingeGSFC/661ACE Collaboration Patricia BornmannNOAAGOES Collaboration Richard CanfieldMontana State UniversityGround-based Observations Gordon EmslieHuntsvilleFlare Theory Hugh HudsonSolar Physics Research Corp.Imaging Gordon HurfordCaltechImaging Norman MaddenLBNLGermanium Detectors Arnold BenzInst. of Astronomy, Zurich, SwitzerlandRadio Observations John BrownUniv. of Glasgow, ScotlandFlare Theory Shinzo EnomeNAO, JapanRadio Observations Takeo KosugiNAO, JapanImaging Frank van BeekDelft Univ., The NetherlandsGrids and Imaging Nicole VilmerObservatoire de Paris, Meudon, FranceData Analysis Alex ZehnderPaul Scherrer Inst. SwitzerlandTelescope design and fabrication A

HESSI Prime Responsibilities UC BerkeleyGermanium detectors & electronics I & T Ground station, MOC/SOC Data Analysis GSFCGrid characterization & testing Cooler, cryostat design Data analysis, distribution, and archiving PSI (Switzerland)Telescope & aspect system Thermo Electron TecometFinest grids (#1 - 4) van Beek (The Netherlands)Coarser grids (#5 - 9) & mounts Spectrum AstroSpacecraft A

GSFC Involvement Science Dennis (682)Mission Scientist Hurford (Caltech)Imaging Scientist Holman (682), Ramaty (661)Solar flare physics von Rosenvinge (661)ACE/HESSI coordination Crannell (682)Education & Public Outreach Imaging Clark (547), Amato (544)Grid environmental testing Orwig (682), Lang (CUA), Uribe (Raytheon ITSS)Optical & X-ray grid characterization Schmahl (UMd)Image reconstruction Spectrometer Boyle (713)Cryostat design, cooler evaluation Provide flight-qualified Sunpower cooler Schwartz (Raytheon ITSS) Spectral deconvolution Data Analysis Gurman (682), Zarro (ARC)Solar Data Analysis Center Tolbert (Raytheon ITSS) Data archiving and distribution A

HESSI Imaging Parameters

Test Fine Grids A

Tecomet Grid #1 Material:Molybdenum Pitch:34 microns Slit width:15 microns Total thickness:1.2 mm Layer thickness:15 microns No. of layers:75 Active area:9 cm diameter Aspect ratio:>50:1 Second of two identical grids fabricated by Thermo Electron Tecomet in Woburn, MA. Finest, high-aspect-ratio X-ray collimator ever made. Provides modulation to X-ray energies in excess of 100 keV. Allows imaging on HESSI with an angular resolution of 2 arcseconds. Picture shows circular active area with fiducial and mounting features in the integral rim. Direction of slits is revealed by the white bar at 45º resulting from light transmitted from below through the ~1º opening angle of each slit.

Tecomet Grid #1

HESSI Top Grid Tray

Germanium Detector A

Sunpower M77 Stirling-Cycle Cooler

Instrument Sensitivity

Angular Coverage vs. Photon Energy

Relative Modulation Amplitude vs. Photon Energy

Composite Flare Spectrum

Energy Resolution vs. Photon Energy A

Count Rates in Each Detector for One Rotation A

Prelaunch Twist Monitoring System (TMS) A