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

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

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

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

1 Year+ of Fermi Gamma-ray Bursts V. Connaughton (+ 1 LAT GRB  GRB 090926) Andreas von Kienlin 7th AGILE Workshop 01. October 2009

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 01. October 2009 V. Connaughton

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

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

GBM Observation of Short GRBs 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 Band function α = -0.41 ± 0.20 β = -3.2 (-0.3 +0.2) EPeak = 1.97 ± 0.09 MeV GRB 090227B: time integrated spectrum 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 Andreas von Kienlin 7th AGILE Workshop 01. October 2009

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 090227B: GRB 090510: Andreas von Kienlin 7th AGILE Workshop 01. October 2009

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

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

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

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

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

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

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

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

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

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

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

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 01. October 2009 V. Connaughton

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

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