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 CenterHuntsville, AL USA

2Univ. Alabama in HuntsvilleHuntsville, AL USA

Thunderstorms and Elementary Particle Acceleration (TEPA 2010)

Nor Amberd, Armenia6-11 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:

I. BATSE /Compton Observatory: 1991-2000

II. Solar Spectroscopic Imager

III. AGILE Gamma-ray Telescope

IV. Gamma-ray Burst Monitor (GBM) on the Fermi

Gamma-ray Space Telescope (this talk)

I. 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

Time Profiles of some RHESSI TGFs:

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)

SAA Region

Hi Bkgnd - Low Sensitivity Region

High Background, Low Sensitivity Region

Map of RHESSI TGFs (820 events)

GLOBAL FLASH RATE – ANNUAL (from LIS-TRMM data)H. Christian et al.

Large CsI Scintillator

Can Detect TGFs

III. AGILE - Italian Gamma-ray Astronomy Satellite

- 100kg Experiment

- Launched: April 2007

Launched June 11, 2008

NASA Kennedy Space CenterFermi

Gamma-Ray Space Telescope

IV. GBM(Gamma-ray Burst Monitor)

GBMDetector Locations on the

Fermi Spacecraft – Launched June 2008

BGO Det.

(1 of 2)NaI Det.

(3 of 12)

GBM (Gamma-ray Burst Monitor)

on the Fermi Observatory - Launched June 11, 2008- Primary Objective: GRBs

FermiGamma-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

Gam

ma-

ray

Ener

gy C

han.

(~1

MeV

max

.)

milliseconds (rel. to trigger time)

TGFNaI Detectors (all 12 combined)

“Overflow” Chan. (127)

0

20

40

60

80

100

120

140

-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0

0

20

40

60

80

100

120

140

-11 -10 -9 -8 -7

7

1

45

40

20

7

5.5

4.2

2.0

1.3

0.3

45

40

20

7

5.5

4.2

2.0

1.3

0.3

MeV

Spectral Differences

TGF #1:

Low energies dominate

TGF #7:

High energies dominate

MeV

6 of the fastest TGFs

Risetimes & Falltimes ~7 μs to 15 μs

(4 μs per bin)

(400 μs , total span}

Narrowest Pulse seen with GBM, ~ 50 μs

Two Well-separated, Double-Pulse TGFs seen with GBM (all detectors summed)

Fermi – GBMLocations of 85 TGFs

TGF & Lightning are usually Simultaneous

How simultaneous?

Distribution of GBM TGF peaks - WWLLN sferic peaks.

2 Exceptions:

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

Difference: ~few ms.

Lightning sfericLightning sfericTGF TGF

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 “ “

Median TGF Pulse Duration = 0.11ms

- Does not include 5 longer “electron” TGFs

- Solid column – includes 10 possible un-resolved pulses

Pulse Durations of First 50 GBM TGFs

Electron TGFs: No Storm in Region Below Spacecraft

Below Spacecraft

Geomagnetic Conjugate Region

Five “Electron” TGFs (in the first 50)

Characteristics: Longer than usual

Fast rise, then decaying

Some are not over thunderstorms

31

Long “Electron” TGF

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

TGF Full-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 ?

Plot by M. Briggs

TGF #5 , Individual Detectors, 0.1ms binsN

aI (

12)

B

GO

(2)

NaI

(12

)

BGO

(2)

TGF #1 , Individual Detectors, 0.1ms bins

Time Profiles – All Detectors Combined

Energies of Single Counts -BGO Detectors Only

Properties of 10 Short TGF Pulses

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)

NaI

(12

)

BGO

(2)

TGF #1 , Individual Detectors, 0.1ms bins

Plot by M. Briggs

TGF #5 , Individual Detectors, 0.1ms binsN

aI (

12)

B

GO

(2)

Fermi – GBMLocations 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

Altit

ude

(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