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Fermi Gamma-ray Burst Monitor

Fermi Gamma-ray Burst Monitor. GRB and TGF detections. Andreas von Kienlin - MPE on behalf of the Fermi GBM Science Team. Fermi GBM. Orbit: 565 km, 25.6 °. whole unocculted sky at any time !. LAT (high-E spectrum). NaIs (location & low-E spectrum). BGOs (mid-E spectrum). Fermi GBM.

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Fermi Gamma-ray Burst Monitor

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

  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

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

  5. (+ 1 LAT GRB  GRB 090926) V. Connaughton 1 Year+ of Fermi Gamma-ray Bursts Andreas von Kienlin 7th AGILE Workshop

  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 ≤ 8.096 s • e = one of 25 - 50 keV, 50 - 300 keV, 100 - 300 keV, > 300 keV • What does GBM trigger on? Andreas von Kienlin 7th AGILE Workshop 3CAS3 August 2009 V. Connaughton

  7. GBM Triggers 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

  8. What can GBM GRBs add? • 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. GRB 090227B Short GRB EPeak  2 MeV Andreas von Kienlin 7th AGILE Workshop

  9. GRB 090227B: time integrated spectrum Band function α = -0.41 ± 0.20 β = -3.2 (-0.3 +0.2) EPeak = 1.97 ± 0.09 MeV GBM Observation of Short GRBs GRB 090510: time integrated spectrum Band function α = -0.63 ± 0.02 β = -2.9 (-0.3 +0.2) EPeak = 3.95 ± 0.25 MeV • Short & Bright GRB Sample: t50 < 1 s, Fluence > 2E−6 erg cm-2 ( 8-1000 keV) • 3 GRBs: 090227B, 090228, 090510 • 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 Andreas von Kienlin 7th AGILE Workshop

  10. GRB 090227B: GRB 090510: 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) Andreas von Kienlin 7th AGILE Workshop

  11. TGF #14 16 ms trigger window 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) Andreas von Kienlin 7th AGILE Workshop

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

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

  14. BGO 0 BGO 1 TGF #3: Dead time analysis 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

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

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

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

  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

  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

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

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

  22. GBM Yearly Trigger Summary • 253 GRBs • 242 between 50 -- 300 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 25 -- 50 keV, 4 of which failed to trigger 50 -- 300 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 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

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

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