The Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS)

Science team :

• Pascal Saint-Hilaire
• Albert Shih (GSFC)
• Samer Al Nussirat
• Meredith Wieber
• Gordon Hurford
• Andreas Zoglauer
• John Tomsick
• Eric Wulf (NRL)

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Engineering team :

• Brent Mochizuki
• Hunter Kanniainen
• Alex Lowell
• Kenyon Schutt
• Constance Angelopoulos
• Parth Behani

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Pascal Saint-Hilaire

SPHERE workshop, 2022-Jul-13

Imaging spectroscopy:

10 keV-10 MeV

3.5 keV spec res

full-sun FOV

12.5” ang. res.

Polarimetry: 150-650 keV

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Long duration high-altitude balloon payload launched from Antarctica

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GRIPS-1: 2016

GRIPS-2: 2024

GRIPS-1 components

(0.17° rms)

1700 kg science payload

2650 kg with parachute, ballast,

& CSBF hardware

3D-GeDs, Compton reconstrution�

3D position-sensitive germanium detectors

• Locate energy depositions to�~0.1 mm³
• Spectral resolution of a few keV FWHM
• Identify the first interaction

Compton probability circles

• >~1 deg angular resolution
• Insufficient for our imaging needs

Monogrid �imaging

• Compton-imaging techniques (>~1 deg) too coarse, but can be used to reject non-solar photons
• Multi-pitch rotating modulator (MPRM)
• 8-meter grid-detector separation, ~10 rpm
• Quasi-continuous slit/slat pitches from 1 to 13 mm
• 2.5 cm-thick tungsten/copper (70%/30%) slats
• Angular resolutions from 12.5” to 162” FWHM

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See Meredith’s poster for all about the grid!

Monogrid �imaging

• Compton-imaging techniques (>~1 deg) too coarse, but can be used to reject non-solar photons
• Multi-pitch rotating modulator (MPRM)
• 8-meter grid-detector separation, ~10 rpm
• Quasi-continuous slit/slat pitches from 1 to 13 mm
• Inch-thick pre-cut tungsten/copper slats
• Angular resolutions from 12.5” to 162” FWHM

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See Meredith’s poster for all about the grid!

High-energy flare spectroscopy

• Thermal plasma emission
• Plasma temperature
• Plasma abundances
• Relativistic bremsstrahlung continuum from electrons
• Electron energy spectrum
• Electron angular distribution
• Nuclear de-excitation lines
• Ambient abundances
• Accelerated abundances
• Shape of the ion energy spectrum�(~3–10 MeV)
• Neutron-capture line
• Higher-energy accelerated ions�(~20 MeV)
• Positron-annihilation line
• Ambient conditions such as temperature

thermal plasma emission

nonthermal bremsstrahlung

ion-associated emission

RHESSI 2002-07-23 spectrum

Atmospheric

cutoff

Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS)

• What causes the spatial separation between energetic electrons producing hard X-rays and energetic ions producing gamma-ray lines?
• GRIPS has the angular resolution�(3× better than RHESSI) to resolve gamma-ray footpoints in many flares
• What is the angular distribution of accelerated electrons and ions?
• GRIPS can measure the redshifts of gamma-ray lines and the polarization of bremsstrahlung emission
• Why do relativistic electrons dominate in the corona?
• GRIPS can produce high-quality gamma-ray images with a point-spread function virtually free of sidelobes

(Hurford et al. 2006)

Polarimetry

The predicted minimum detectable

polarization (MDP, 3σ) in the 150–650 keV

energy range (solid line) versus the total

bremsstrahlung fluence above >300 keV.

The points are 200–400 keV limits on

polarization (Boggs et al. 2006) for two

flares observed by RHESSI

Simulated modulation of counts over

600 seconds from the X4.8 flare on

2002 July 23, for various levels of

linear polarization, as it would be

observed by the GRIPS instrument on

an Antarctic flight

GRIPS-1 flight

• 2016 Jan 19–30�(1 million seconds)
• Engineering success!
• (Solar pointing three times better than required)
• Relatively low solar activity
• 21 C-class flare
• Largest flare: GOES C9.6
• Not imageable ~40 keV atmospheric cutoff (confirmed by RHESSI)
• Magnetospheric activity
• Two extended periods of radiation belt electron precipitation

(Duncan et al. 2016)

2016 Jan 27 precipitation

Anti-coincidence shield

3D-GeDs

background

511 keV

including background

background-subtracted

Summary & GRIPS-2

• Specs:
• Imaging spectroscopy: 10 keV (>~40 keV in atm) – 10 MeV
• 12.5” angular resolution, full sun FOV
• Polarimetry: 150-650 keV band
• Funded for a second high altitude long duration flight: 2024
• GRIPS-3:
• spacecraft?
• 20m boom
• 5” ang res
• 64? GeDs
• part of

COMPLETE?

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