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Proposed MXGS coded-mask X-ray imager/spectrometer instrument How effective is it for TGF angular and spatial location estimates? What is the effect if a TGF has a significant diffuse structure?
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TGF diffuse imaging and TGF diffuse imaging and spectra as a function of spectra as a function of
altitude and locationaltitude and location
P.H.ConnellP.H.ConnellUniversity of ValenciaUniversity of Valencia
The University of Valencia is part of the phase-B study of a proposed
imager and spectrometer instrument MXGS
to be mounted on the Columbus module of ISS
Nadir↓
Earth horizon
The Columbus model
on Node-2 of the ISS
Proposed MXGS coded-mask X-ray imager/spectrometer instrument How effective is it for TGF angular and spatial location estimates?What is the effect if a TGF has a significant diffuse structure?
Images of X-raysources maybe created bythe method ofphoton back
projection
N photons must come throughN mask holes
How many photons
are required to make
an image of justone X-ray source?
TGF photon beam simulator software
Generates TGF photon energy, altitude, radius, azimuth, angular distribution
Simulates TGF beam azimuth, zenith and photon transport through atmosphere
Uses photoelectric, Klein-Nishina and NPP-EPP scattering statistics
Returns images and spectra observed at any location in or above atmosphere
Does not simulate any coexistent electron accelerator or runaway breakdown
What is the mechanism to generate Terrestrial Gamma-Ray flashes?
Relativistic runaway electrons above thunderstormsPhD Thesis - Nikolai G. Lehtinen – U.S.Inan .et.alDept. Physics - Stanford University - March 2000
Creating a high energy electron avalanche?
Model components and geometry of a Gamma-Ray flash?
Gamma-ray flashes are assumed to originatein the Bremsstrahlung radiation from a streamhigh velocity electrons – coming from where?
TGF photon transport simulation through atmosphere2x2 km Gaussian ball at 20 km altitudeVertical beam - zero angular widthPhoton escape locations – low concentrations enhanced
TGF photon transport simulation through atmosphere2x10 km Gaussian ellipsoid - 20 km altitudeVertical beam - zero angular widthPhoton locations before escaping
TGF photon transport simulation through atmosphere2x10 km Gaussian ellipsoid - 20 km altitudeVertical beam - 30° angular widthPhoton locations before escaping
TGF photon transport simulation through atmosphere2x10 km Gaussian ellipsoid - 20 km altitudeVertical beam - 60° angular widthPhoton locations before escaping
TGF photon transport simulation through atmosphere2x10 km Gaussian ellipsoid - 20 km altitude30° beam tilt – zero angular widthPhoton locations before escaping
TGF photon transport simulation through atmosphere2x10 km Gaussian ellipsoid - 20 km altitude45° beam tilt – zero angular widthPhoton locations before escaping
What does a TGF and its spectrum look like ?
A vertical 2x10 km Gaussian ellipsoid beam
At 350 km altitude in orbit
From various off-axis observation angles
On-axis view of 2x10 km ellipsoid TGF at 350 km altitude
<500 keV <20000 keV
10° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
Vertical asymmetry probably due to HE photons exiting after 1-2 scatters off beam -axis
20° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
30° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
Most photons contained within ~4° circle Most photons contained within ~2° circle
40° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
50° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
Note beam centre shift of ~1° from TGF centrepoint – corresponds to ~13 km altitude
60° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
Beam starting to flatten out
70° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
80° off-axis view at 350 km altitude of 2x10 km ellipsoid TGF
<500 keV <20000 keV
Spectra of TGFs observed over 0,10,20,….80° off-axis at 350 km altitude
Calibrated to an estimate of RHESSI mean photon spectrum
Fitting of mean TGF spectrum over 10-50° off-axis to an estimate of a B-spline deconvolved RHESSI mean photon spectrum. (D.Smith, N.Ostergaard, et.al.)
Beware of f(E) = 1/E TGF spectrum, RHESSI altitude correction and LE efficiency!
What is observed at low altitude?
At 20 km altitude
At 15, 20 km radius from the TGF beam axis
TGF transport simulation in atmosphere2x10 km Gaussian ellipse at 20 km altitudeVertical beam – zero angular widthPhoton locations at absorption – low concentrations enhanced
TGF simulation imaging within lower atmosphereObservation point at 20 km altitude15 and 20 km radius from 2x10 km beam axisObservation direction toward beam axisWill an insect-eye imager detect the beam axis?
TGFs could have significant diffuse structure
Could impact on coded-mask location imaging
High counts at high flight altitudes – the place to be?
Too diffuse at low-altitudes to see beam tilt angle?
Software needs electron accelerator and Bremstrahlung photon generator
Conclusions