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