High-Energy Gamma-Ray Burst Observations with the Fermi Gamma-ray Space Telescope

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High-Energy Gamma-Ray Burst Observations with the
Fermi Gamma-ray Space Telescope
Alexander J. van der Horst NASA Postdoctoral
Progam Fellow
On behalf of the Fermi GBM LAT Teams
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Fermi GBM LAT
Large Area Telescope (LAT) Full sky every 3
hours (FoV 2.4 sr) 20 MeV 300 GeV
Gamma-ray Burst Monitor (GBM) Views entire
unocculted sky
NaI 8 keV 1 MeV BGO 200 keV 40 MeV
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GBM Triggers

• Gamma-Ray Bursts
• 180 so far, 17 short GRBs, 250 GRBs/year
• 20 also detected by Swift
• Soft-Gamma Repeaters
• Anomalous X-ray Pulsars
• Cygnus X-1
• Solar Flares
• Terrestrial Gamma-ray Flashes
• We detect everything

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GBMLAT GRB Highlights
145 events above 100 MeV 14 events above 1
GeV Highest energy event 13.2 GeV
First 3 out of 7 LAT GRBs so far

• First LAT GRB with
• events above 100 MeV

First short GRB with gt1 GeV events
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GRB 080916C The Big One

• Delayed high-
• energy emission
• z 4.35
• 13.2 ? 70.6 GeV
• MQG gt 1.3 1018 GeV/c2
• Eiso 8.8 1054 ergs
• narrow jet
• G (bin b) 900
• G (bin d) 600

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GRB 080916C Spectral Results

• a -1.02 /- 0.02
• ß -2.21 /- 0.03
• Epeak 1170 /- 142 keV

Band function over 6 decades in energy
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GRB 080916C Time Evolution
Extended LAT emission Continuous decay (1400
s) Constant power-law index
Spectral evolution 1st 2nd bin soft to
hard 2nd 5th bin hard to soft
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GRB 090323 The Long One(?)
GBM NaI 9

• Index -1.00 /- 0.03
• Epeak 1173 /- 175 keV
• Epeak,rest 5.36 /- 0.80 MeV

Index -0.83 /- 0.03 Epeak 574 /- 34
keV Epeak,rest 2.62 /- 0.16 MeV
Detected from several GHz to GeV ? 15 decades in
energy
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GRB 090328 The Latest One
GBM NaI 8
GBM BGO 1
a -0.93 /- 0.02 ß -2.2 /- 0.1 Epeak 653
/- 45 keV
Detected from several GHz to GeV ? 15 decades in
energy
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Conclusions

• Fermi extends the broadband GRB spectrum
• Spectra fitted with single Band function over up
  to 6 energy decades ? suggests single dominant
  emission mechanism
• GRB 080916C largest apparent energy output in
  gamma-rays lower limit on bulk Lorentz factor
• Common features in high-energy emission?
• Delayed high-energy (gt100 MeV) onset
• High-energy extended emission