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

Alexander J. van der HorstAlexander J. van der HorstNASA Postdoctoral Progam FellowNASA Postdoctoral Progam Fellow

On behalf of theOn behalf of theFermi GBM & LAT TeamsFermi GBM & LAT Teams

Fermi GBM & LATFermi GBM & LAT

Gamma-ray Burst Monitor (GBM):Gamma-ray Burst Monitor (GBM):Views entire unocculted skyViews entire unocculted skyGamma-ray Burst Monitor (GBM):Gamma-ray Burst Monitor (GBM):Views entire unocculted skyViews entire unocculted sky

NaI: 8 keV – 1 MeVNaI: 8 keV – 1 MeVBGO: 200 keV – 40 MeVBGO: 200 keV – 40 MeVNaI: 8 keV – 1 MeVNaI: 8 keV – 1 MeVBGO: 200 keV – 40 MeVBGO: 200 keV – 40 MeV

Large Area Telescope (LAT):Large Area Telescope (LAT):Full sky every 3 hours (FoV ≈ 2.4 sr)Full sky every 3 hours (FoV ≈ 2.4 sr)20 MeV – 300 GeV20 MeV – 300 GeV

Large Area Telescope (LAT):Large Area Telescope (LAT):Full sky every 3 hours (FoV ≈ 2.4 sr)Full sky every 3 hours (FoV ≈ 2.4 sr)20 MeV – 300 GeV20 MeV – 300 GeV

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GBM TriggersGBM Triggers

• Gamma-Ray Bursts:Gamma-Ray Bursts:• 180 so far, 17% short GRBs, 250 GRBs/year180 so far, 17% short GRBs, 250 GRBs/year• 20% also detected by Swift20% also detected by Swift

• Soft-Gamma RepeatersSoft-Gamma Repeaters• Anomalous X-ray PulsarsAnomalous X-ray Pulsars• Cygnus X-1Cygnus X-1• Solar FlaresSolar Flares• Terrestrial Gamma-ray FlashesTerrestrial Gamma-ray Flashes

““We detect everything”We detect everything”

GBM+LAT GRB HighlightsGBM+LAT GRB Highlights

First LAT GRB withFirst LAT GRB withevents above 100 MeVevents above 100 MeVFirst LAT GRB withFirst LAT GRB withevents above 100 MeVevents above 100 MeV

First short GRBFirst short GRBwith >1 GeV eventswith >1 GeV eventsFirst short GRBFirst short GRBwith >1 GeV eventswith >1 GeV events

145 events above 100 MeV145 events above 100 MeV14 events above 1 GeV14 events above 1 GeVHighest energy event: 13.2 GeVHighest energy event: 13.2 GeV

145 events above 100 MeV145 events above 100 MeV14 events above 1 GeV14 events above 1 GeVHighest energy event: 13.2 GeVHighest energy event: 13.2 GeV

First 3 out of 7First 3 out of 7LAT GRBs so farLAT GRBs so farFirst 3 out of 7First 3 out of 7LAT GRBs so farLAT GRBs so far

GRB 080916C: The Big OneGRB 080916C: The Big OneDelayed high-Delayed high-energy emissionenergy emission

z ≈ 4.35 :z ≈ 4.35 :13.2 13.2 70.6 GeV 70.6 GeVMMQGQG > 1.3 10 > 1.3 101818 GeV/c GeV/c22

EEisoiso ≈ 8.8 10 ≈ 8.8 105454 ergs ergs narrow jetnarrow jet

Γ (bin b) ≥ 900Γ (bin b) ≥ 900Γ (bin d) ≥ 600Γ (bin d) ≥ 600

GRB 080916C – Spectral ResultsGRB 080916C – Spectral Results

α = -1.02 +/- 0.02α = -1.02 +/- 0.02β = -2.21 +/- 0.03β = -2.21 +/- 0.03EEpeakpeak = 1170 +/- 142 keV = 1170 +/- 142 keV

Band function over 6 decades in energyBand function over 6 decades in energy

GRB 080916C – Time EvolutionGRB 080916C – Time Evolution

Spectral evolution:1st – 2nd bin: soft to hard2nd – 5th bin: hard to soft

Spectral evolution:1st – 2nd bin: soft to hard2nd – 5th bin: hard to soft

Extended LAT emissionContinuous decay (1400 s)Constant power-law index

Extended LAT emissionContinuous decay (1400 s)Constant power-law index

GRB 090323: The Long One(?)GRB 090323: The Long One(?)

Index = -1.00 +/- 0.03Index = -1.00 +/- 0.03EEpeakpeak = 1173 +/- 175 keV = 1173 +/- 175 keV

EEpeak,restpeak,rest = 5.36 +/- 0.80 MeV = 5.36 +/- 0.80 MeV

Index = -1.00 +/- 0.03Index = -1.00 +/- 0.03EEpeakpeak = 1173 +/- 175 keV = 1173 +/- 175 keV

EEpeak,restpeak,rest = 5.36 +/- 0.80 MeV = 5.36 +/- 0.80 MeV

Index = -0.83 +/- 0.03Index = -0.83 +/- 0.03EEpeakpeak = 574 +/- 34 keV = 574 +/- 34 keV

EEpeak,restpeak,rest = 2.62 +/- 0.16 MeV = 2.62 +/- 0.16 MeV

Index = -0.83 +/- 0.03Index = -0.83 +/- 0.03EEpeakpeak = 574 +/- 34 keV = 574 +/- 34 keV

EEpeak,restpeak,rest = 2.62 +/- 0.16 MeV = 2.62 +/- 0.16 MeV

GBM NaI 9

Detected from several GHz to GeV 15 decades in energy

Detected from several GHz to GeV 15 decades in energy

GRB 090328: The Latest OneGRB 090328: The Latest One

α = -0.93 +/- 0.02α = -0.93 +/- 0.02β = -2.2 +/- 0.1 β = -2.2 +/- 0.1 EEpeakpeak = 653 +/- 45 keV = 653 +/- 45 keV

α = -0.93 +/- 0.02α = -0.93 +/- 0.02β = -2.2 +/- 0.1 β = -2.2 +/- 0.1 EEpeakpeak = 653 +/- 45 keV = 653 +/- 45 keV

GBM NaI 8 GBM BGO 1

Detected from several GHz to GeV 15 decades in energy

Detected from several GHz to GeV 15 decades in energy

ConclusionsConclusions• Fermi extends the broadband GRB spectrumFermi extends the broadband GRB spectrum

• Spectra fitted with single Band function over up Spectra fitted with single Band function over up to 6 energy decades to 6 energy decades suggests single dominant suggests single dominant emission mechanismemission mechanism

• GRB 080916C: largest apparent energy output in GRB 080916C: largest apparent energy output in gamma-rays & lower limit on bulk Lorentz factorgamma-rays & lower limit on bulk Lorentz factor

• Common features in high-energy emission?Common features in high-energy emission?• Delayed high-energy (>100 MeV) onsetDelayed high-energy (>100 MeV) onset• High-energy extended emissionHigh-energy extended emission