1. Fermi Gamma-ray Burst Monitor
GRB and TGF detections
Andreas von Kienlin - MPE
on behalf of the Fermi GBM Science Team

2. Fermi GBM LAT (high-E spectrum) NaIs (location & low-E spectrum)
Orbit: 565 km, 25.6°
whole unocculted
sky at any time !
BGOs (mid-E spectrum)
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

3. Fermi GBM LAT (high-E spectrum) NaIs (location & low-E spectrum)
NaIs: 8 keV – 1 MeV
BGOs: 150 keV – 40 MeV
LAT: 20 MeV – >300 GeV
BGOs (mid-E spectrum)
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

4. Fermi GBM - Detectors 5“ × 0.5“ NaI 5“ × 5“ BGO
C. Meegan et al. 2009, ApJ, 702, 791
effective area  160 cm2
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

5. 1 Year+ of Fermi Gamma-ray Bursts
V. Connaughton
(+ 1 LAT GRB  GRB )
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

6. GBM Triggering
GBM triggers when 2 or more detectors exceed background by n sigma over t timescale in e energy band.
62 algorithms operating simultaneously.
4.5 ≤ n ≤ 7.5
16 ms ≤ t ≤ s
e = one of keV, keV, keV, > 300 keV
What does GBM trigger on?
Andreas von Kienlin
7th AGILE Workshop
3CAS3 August 2009
01. October 2009
V. Connaughton

7. GBM Triggers Aug 08 – Sept 09 GRBs >300 TGFs 17 SGRs ~170 Particles
Weekly Triggers
Aug 08 – Sept 09
GRBs >300
TGFs 17
SGRs ~170
Particles
Other
Other: Cyg X-1 rises, solar- flare(1x), accidentals
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

8. What can GBM GRBs add? GRB 090227B Short GRB EPeak  2 MeV
Source of EPeak for Swift bursts
spectroscopy from 8 keV - 40 MeV.
Time-resolved spectra for under- standing central engine of GRBs.
Trigger for LAT  Joint spectral fits.
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

9. GBM Observation of Short GRBs
Short & Bright GRB Sample: t50 < 1 s, Fluence > 2E−6 erg cm-2 ( keV)
3 GRBs: B, ,
Analysis & results by Sylvain Guiriec and the GBM team
GBM Results:
short GRBs have very high Epeak values, with modestly steep β values
Band function preferred in 2 of the 3 GRBs over cutoff power law
Band function
α = ± 0.20
β = ( )
EPeak = 1.97 ± 0.09 MeV
GRB B:
time integrated
spectrum
GRB :
time integrated
spectrum
Band function
α = ± 0.02
β = -2.9 ( )
EPeak = 3.95 ± 0.25 MeV
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

10. GBM Observation of Short GRBs
Spectral evolution:
Complex, multi-peaked time histories
GBM allows to follow the spectral evolution on short timescales
Indication of a pattern of differences in spectral evolution between long and short GRBs
(observed up to now only for a very small sample)
GRB B:
GRB :
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

11. The GBM TGF detections
FSW trigger algorithm #43: 16 ms window, 300 keV – 1 MeV
detected 17 TGFs (Jul. 08 – Sep. 09)
GBM is only able to trigger on the brightest TGFs  selection effects
BGO detectors: effective area  160 cm2
for all energies > 300 keV up to ~40 MeV!
Time-tagged events (TTE) data type, records individual counts with:
2μs time resolution and
128 channel spectral resolution (-30 to +300s time coverage)
Absolute timing accuracy: 20 s (derived from GPS)
TGF #14
16 ms trigger window
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

12. TGF #5: Separate Detectors
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

13. TGF #7: 12 × NaI 2 × BGO 12 × NaI + 2 × BGO Andreas von Kienlin
7th AGILE Workshop
01. October 2009

14. TGF #3: Dead time analysis
BGO 0
BGO 1
Simulation:
106 photons
Gaussian TGF pulse profile
2.6 s deadtime filtered
BGO 0 +1
Simulation
+deadtime
Estimated deadtime effect:
GBM processed only 47% of the incident photons
36% during peak 40 s bin
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

15. TGF #6 + #14: two-pulse events
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

16. 12 short TGFs observed with GBM
data from all detectors are summed - binned with 20μs resolution
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

17. Characteristics of TGF pulses#1
#12
#14a
#13
#14b #9
#6a
#6b
Duration: T90
Risetime
Falltime
Overlapping
pulses?
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

18. TGF earth map Correlations with thunderstorm lightning sferics
World Wide Lightning Network (WWLLN)
Locations of lightning with high temporal (~ 30 ms) and positional accuracy (~ 10 km). Detection efficiency: ~ 4%
Location of Fermi spacecraft at the time GBM triggered on a TGF
TGFs correlated with WWLLN sferics (within 5 ms & 500 km)
10 TGFs with no correlation (some are correlated with a storm system)
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

19. Summary: Fermi GBM GRB & TGF detections
GRBs:
GBM detected more than 300 GRBs up to now
BGO detectors have high “photopeak” efficiency and effective area
good spectral capabilities for short burst
Source of EPeak for Swift bursts
spectroscopy from 8 keV - 40 MeV.
Trigger for LAT  Joint spectral fits.
TGFs:
GBM has good capabilities for TGF detection  17 TGFs
detects photons up to 40 MeV (BGO detectors)
Dedicated GBM TGF trigger algorithm: 16 ms, > 300 keV
Soon: more TGF-specific algorithms on BGO rates  weaker TGFs
Status of spectral analysis:
Investigation on possible pile-up effects for strong events
Improvement GBM instrument response determination for TGFs
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

20. Thank you!
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

21. Back-up slides
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

22. GBM Yearly Trigger Summary
253 GRBs
242 between keV
67 on timescales > 1 s of which 37 did not also trigger ≤ 1 s
21 on timescales < 64 ms of which 0 did not also trigger ≥ 64 ms
11 between keV, 4 of which failed to trigger keV
No GRBs triggered on hard energy ranges.
i.e. 212 BATSE-like GRBs in 1 year.
62 commanded (test)
168 SGRs -- most on soft, short trigger algorithms.
14 TGFs -- all on hard, short trigger algorithms.
1 solar flare
Others are Cyg X-1 rises, accidentals, and particle events.
Andreas von Kienlin
7th AGILE Workshop
3CAS3 August 2009
01. October 2009
V. Connaughton

23. 4 longer duration TGFs observed with GBM
data from all detectors are summed - binned with 40μs resolution
Andreas von Kienlin
7th AGILE Workshop
01. October 2009

24. 2 well-separated, double pulseTGFs
data from all detectors are summed
Andreas von Kienlin
7th AGILE Workshop
01. October 2009