Terrestrial Gamma-Ray Flashes (TGFs)
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Terrestrial Gamma-Ray Flashes (TGFs) Observed with Fermi-GBM G. J. Fishman 1 , M. S. Briggs 2 , and V. Connaughton 2 for the GBM TGF Team 1 NASA-Marshall Space Flight Center Huntsville, AL USA 2 Univ. Alabama in Huntsville Huntsville, AL USA

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Terrestrial Gamma-Ray Flashes (TGFs) Observed with Fermi-GBM

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  • Terrestrial Gamma-Ray Flashes (TGFs)

  • Observed with Fermi-GBM

  • G. J. Fishman1, M. S. Briggs2, and V. Connaughton2

  • for the GBM TGF Team

  • 1NASA-Marshall Space Flight Center

  • Huntsville, AL USA

  • 2Univ. Alabama in Huntsville

  • Huntsville, AL USA

  • Thunderstorms and Elementary Particle Acceleration

  • (TEPA 2010)

  • Nor Amberd, Armenia

  • 6-11 September 2010

  • ( -for TEPA Web site posting)


  • TGFs - Overview &

  • Some New Results

  • History; Spacecraft observations

  • Observations from Fermi-GBM

  • Future Space Missions


  • Observations of TGFs

  • with

  • Four Spacecraft:

  • BATSE /Compton Observatory:1991-2000

  • Solar Spectroscopic Imager

  • AGILE Gamma-ray Telescope

  • Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope (this talk)


  • Burst and Transient Source Experiment (BATSE) - Compton Observatory (CGRO) 1991-2000


  • BATSE TGFs:

    • Determined rough spectral properties (extremely energetic)

    • Associated with thunderstorms

    • Observed 78 in 9 years


TGFs from BATSE (showing saturation at ~300,000 cps)


II. RHESSI(Ramaty High-Energy Solar Spectroscopic Imager)

- Solar Observatory

- Launched 2002; currently operational


  • RHESSI Observations of TGFs:

  • Doesn’t require trigger; all data are transmitted

  • Detected many more TGFs than BATSE, but they were much weaker

  • Determined very hard spectra (> 20 MeV)

Time Profiles of some RHESSI TGFs:


Hi Bkgnd - Low Sensitivity Region

SAA Region

High Background, Low Sensitivity Region

Map of RHESSI TGFs (820 events)


GLOBAL FLASH RATE – ANNUAL (from LIS-TRMM data)

H. Christian et al.


III. AGILE

- Italian Gamma-ray Astronomy Satellite

- 100kg Experiment

- Launched: April 2007

Large CsI Scintillator

Can Detect TGFs


IV. GBM

(Gamma-ray Burst Monitor)

Launched June 11, 2008

NASA Kennedy Space Center

Fermi

Gamma-Ray Space Telescope


BGO Det.

(1 of 2)

NaI Det.

(3 of 12)

GBM

Detector Locations on the

Fermi Spacecraft – Launched June 2008


GBM(Gamma-ray Burst Monitor)

on theFermiObservatory

- Launched June 11, 2008

- Primary Objective: GRBs

Fermi

Gamma-Ray

Space Telescope


Gamma-Ray Burst Monitor (GBM) Sodium Iodide (NaI) Detectors (12)

1.27 cm thick

12.7 cm dia.

8 keV to 1 MeV


GBM Bismuth Germinate (BGO) Detectors (2)

12.7 cm thick

12.7 cm dia.

150 keV to 45 MeV


NaI Detectors (all 12 combined)

TGF

“Overflow” Chan. (127)

Gamma-ray Energy Chan.

(~1 MeV max.)

milliseconds (rel. to trigger time)


MeV

Spectral Differences

TGF #1:

Low energies dominate

TGF #7:

High energies dominate

45

40

20

7

5.5

4.2

2.0

1.3

0.3

1

MeV

45

40

20

7

5.5

4.2

2.0

1.3

0.3

7


6 of the fastest TGFs

Risetimes & Falltimes

~7 μs to 15 μs

(4 μs per bin)

(400 μs , total span}


Two Well-separated, Double-Pulse TGFs

seen with GBM (all detectors summed)

Narrowest Pulse

seen with GBM, ~ 50 μs


Fermi – GBM

Locations of 85 TGFs


TGF & Lightning are usually Simultaneous


How simultaneous?

Distribution of GBM TGF peaks - WWLLN sferic peaks.


2 Exceptions:

TGF

Lightning sferic

TGF

Lightning sferic

Of 15 associated sferics (5 ms, 300 km), 2 are not consistent with being simultaneous with the TGF pulse

Difference: ~few ms.


TGF & Lightning - Summary

  • Simultaneous, no preferred order

  • GBM detects gamma-ray TGFs within 300 km of sub-spacecraft.

  • We need other VLF data to explore shape, size of sferics (Duke, Stanford, LASA groups).


Triggered TGF Rate in GBM: ~1/mo., prior to 11 Nov. 2010

~8/mo., after “ “


Pulse Durations of First 50 GBM TGFs

Median TGF Pulse Duration = 0.11ms

- Does not include 5 longer “electron” TGFs

- Solid column – includes 10 possible un-resolved pulses


Electron TGFs: No Storm in Region Below Spacecraft

Geomagnetic Conjugate Region

Below Spacecraft


Five “Electron” TGFs (in the first 50)

  • Characteristics:

    • Longer than usual

    • Fast rise, then decaying

    • Some are not over thunderstorms


Long “Electron” TGF

31


August 2010 – Implemented “un-triggered” TGF capability

Over selected “America’s Region”:

  • RHESSI TGFs

  • RHESSI TGFs, May-November

est.: ~several TGFs per day in this Reion


First look at a GBM an Un-triggered TGF

Binned Data 20μs/bin

TGFFull-Width: ~0.25ms

Total cts above bkgnd: ~35 cts

Peak ct. rate: ~20kcps

(Spectrum appears similar to strong TGFs)


  • TGFs –

  • Major Observational Questions:

    • Altitude of origin?

    • Extent & volume of the emitting region?

    • Beaming properties of the emission?

    • What is the intensity distribution of TGFs ?

    • Are TGFs related to Gigantic Blue Jets ?


TGF #5 , Individual Detectors, 0.1ms bins

NaI (12) BGO (2)

Plot by M. Briggs


TGF #1 , Individual Detectors, 0.1ms bins

NaI (12) BGO (2)


Properties of 10 Short TGF Pulses

Energies of Single Counts -

BGO Detectors Only

Time Profiles –

All Detectors Combined


Four Longer TGF Pulses (~1-3 ms)

Time Profiles –

All Detectors Combined

Energies of Single Counts -

BGO Detectors Only


Overlapping Double Pulses

- 3 in the first 50 TGFs

(~7 others are less obvious)


Overlapping Double Pulses

- 3 in the first 50 TGFs

(~7 others are less obvious)


TGF #1 , Individual Detectors, 0.1ms bins

NaI (12) BGO (2)


TGF #5 , Individual Detectors, 0.1ms bins

NaI (12) BGO (2)

Plot by M. Briggs


Fermi – GBM

Locations of 85 TGFs


GBM TGF Papers - 2010

  • “First Results on Terrestrial Gamma-ray Flashes from the Fermi Gamma-ray Burst Monitor”, M. S. Briggs, et al., JGR

  • “Associations between Fermi GBM Terrestrial Gamma-ray Flashes and sferics from the WWLLN”, V. Connaughton, et al., in press, JGR

  • “Temporal Properties of Terrestrial Gamma-ray Flashes from the Gamma-ray Burst Monitor on the Fermi Observatory”, G. J. Fishman, submitted to JGR

  • “Positrons observed from Terrestrial Lightning with Fermi GBM”, M. S. Briggs, et al., in preparation

Complete list of Huntsville Gamma-Ray Team Publications: http://gammaray.nsstc.nasa.gov/publications/tgf_journal.html


TGF Simulation - Courtesy J. Dwyer, Florida Tech.Gamma-rays (red); Electrons (blue)

200

150

100

50

20

Altitude (km)

-200 -100 0 100 200

Horizontal Distance (km)


  • Future Spacecraft to Study TGFs:

    • Firefly – NSF cubesat; GSFC; Siena College

    • ASIM – on ISS; ESA, led by Danish

    • TIRANIS – French & others

    • CHIBIS-M – Russian (IKI) & others


End


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