High Energy Solar Spectroscopic Imager HESSI

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High Energy Solar Spectroscopic Imager HESSI
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HESSI Science Objective
To explore the basic physics of particle
acceleration and explosive energy release in
solar flares

• 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

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What is a Solar Flare ?

• A solar flare occurs when magnetic energy that
  has built up in the solar atmosphere (Corona) is
  suddenly released.
• Radiation is emitted across virtually the entire
  electromagnetic spectrum (radio, optical, (E)UV,
  X- and gamma Ray).
• The amount of energy released is very large
  1027-1032 ergs
• 3 Stage
• Precursor trigger of magnetic energy release
  (soft-xray)
• Impulsive protons, ions and electrons are
  accelerated,
• Heating of plasma to Millions of degree in time
  scale minutes to hours
• Many models exist, but impulsive energy release
  is poorly understood
• Solar flare activities are correlated with the 11
  year solar cycle

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The Sun at Solar Minimum and Maximum
EUV Images Telescope (EIT)
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How are Flares seen in the EUV (171A) by the
TRACE Satellite?
M. Aschwanden et al, Lockheed Martin Advanced
Technology
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Example of a SMM Observation
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Composite Flare Energy Spectrum
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Problems to be solved with HESSI

• Needed
• Large energy range (3kev to 15MeV), good energy
  resolution (better than 1)
• Good spatial resolution (up to 2 arcsec), Images
• Good time resolution (2 sec for an image)
• Low energy threshold (3keV)

• How can a large fraction of magnetically stored
  energy (30) to be converted into kinetic energy
  in such a very short time?
• Are loops in a quasi-steady hydrodynamic
  equilibrium?
• Where does the heating and acceleration occur?
• How are such high electron and ion energy
  possible?
• Why are the electrons and ions quasi
  simultaneously accelerated?
• Is the Corona heated by micro flares? (yes if
  NE-a and agt2 and nano flares exist)

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HESSI Non-Solar Science Objectives

• The Crab Nebula
• Imaging spectroscopy with 2 resolution
• Gamma Ray Bursts and Cosmic Transient Sources
• Detected over a large fraction of the sky
• High resolution spectroscopy
• Search for cyclotron line features
• Steady 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

A1309.04
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HESSI Prime Responsibilities

• UC Berkeley Germanium detectors, cryostat,
  electronics
• I T
• Ground station, MOC/SOC
• Data Analysis
• GSFC Grid characterization testing
• Cryocooler
• Data analysis, distribution, and archiving
• PSI (Switzerland) Telescope
• Aspect system
• Twist Monitoring System
• Spectrum Astro Spacecraft
• ETH-Zurich European Data Center
• Data Analysis and archiving

A1309.013
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PSI Involvement

• Instrument
• Fritz Burri Technician
• Reinhold Henneck RAS, SAS
• Martin Fivan PhD Student, Simulation, Aspect
  System S/W
• Aliko Mchedlshishvili Electronic, Aspect Data
  Processor
• Peter Ming Manager
• Knud Thomsen Mechanical Design, Qualification
• Joerg Welte Designer
• Alex Zehnder Co-I, TMS
• Science
• Kaspar Arzner
• Manuel Guedel
• PSI Infrastructure
• total about 30 well motivated collaborators

A1309.014
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HESSI Imaging Technique Rotation Grid
Collimators (RMC)
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Imaging Simulation

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Box 1 is a map of the sky near the assumed
point-like X-ray source.
Box 2 represents what the detectorr see as a
function of time as X-ray photons from the
off-axis point source indicated in Box 1 pass
through the grids.
Box 3 shows the number of X-ray photons that pass
through both grids and reach the detector as a
function of time while the instrument rotates.
Box 4 and 5 show how the image can be
reconstructed from the probability distributions
shown in Box 1 and the counting rate in the
detector shown in Boxes 2 and 3. The point source
can be clearly seen in the bottom left corner. A
second "ghost" source appears in the upper right
corner and faint rings, referred to as
"side-lobes" appear around both "source"
locations. These artifacts can be removed.
Animation made by Ed Schmahl, GSFC
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(No Transcript)
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Example Yohko Flare
Countrate in the 9 HESSI grids
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HESSI Imaging

• Requirement
• Mechanical twist stability to be better than 20
  arcsec. (achieved 5 arcsec)
• Solar aspect (pointing) to be better than 0.4
  arcsec for each photon (Solar Aspect System SAS)
• Roll Angle (RAS) to be better than 1 armin
  1arcsec at limb

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HESSI FM Imager at Contraves
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End-to-End Test
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Solar Aspect System

• Operation Principle
• The Sun is imaged on 3 linear CCD 120o spaced.
• The CCD are readout at 128Hz
• Onboard processing of limb position, download
  needed data.
• On-ground aspect reconstruction.
• Calibration on ground. Result

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Roll Aspect System (RAS)
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RAS
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PSI Twist Monitor System
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Results TMS
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HESSI at JPL 2nd Vibration Tests
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HESSI at VAFB (April 01)
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Launch Date 1. June 01 !?
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3D Model of HESSI
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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

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HESSI Observational Characteristics

• Energy Range 3 keV to 15 MeV
• Energy Resolution (FWHM) lt1 keV FWHM at 3 keV
• increasing to 5 keV at 15 MeV
• Angular Resolution 2 arcseconds to 100 keV
• 7 arcseconds to 400 keV
• 36 arcseconds to 15 MeV
• Temporal Resolution Tens of ms for basic image
• 2 s for detailed image
• Field of View Full Sun
• Effective Area - cm2 10-3 at 3 keV, 50 at 10 keV
• (with attenuators out) 60 at 100 keV, 20 at
  10 MeV
• Numbers of flares 1000 imaged to gt100 keV.
• 100 with spectroscopy to 10 MeV

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Instrument Sensitivity
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Angular Coverage vs. Photon Energy
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Relative Modulation Amplitudevs. Photon Energy
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Composite Flare Spectrum
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Energy Resolution vs. Photon Energy
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Prelaunch Twist Monitoring System (TMS)
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