(Fermi observations of) High-energy emissions from gamma-ray bursts

(Fermi observations of) High-energy emissions from gamma-ray bursts Hiroyasu Tajima on behalf of Fermi LAT and GBM Collaborations Kavli Institute of Particle Astrophysics and Cosmology SLAC National Accelerator Laboratory (Stanford Linear Accelerator Center) TeV Particle Astrophysics 9 July 14, 9 SLAC, USA

Gamma-Ray Bursts Overview (1) Discovered in 1967 Cosmological origin Large apparent energy release: 1 5 ~1 54 Energetics consistent with origin of UHECR Peak in ~MeV gamma rays Band function: smoothly joined two power law Synchrotron radiation of ultra-relativistic electrons in jet? 4. 1 5 BATSE Trigger 98 BATSE Trigger 577 BATSE Trigger 97 1.8 1 4 BATSE Trigger 144 1.5 1 4 7. 1 4 Ch: (1: 4) Ch: (1: 4) Ch: (1: 4) ~.5 s Time Res:.64 s ~4 s Time Res:.5 s ~18 s Time Res:.5 s ~8 s 1. 1 4 1.6 1 4 6. 1 4 Ch: (1: 4) Time Res:.64 s 3. 1 5 1.15 1 4 1.4 1 4 5. 1 4 Rate (counts s -1 ). 1 5 Rate (counts s -1 ) 1.1 1 4 1.5 1 4 Rate (counts s -1 ) 1. 1 4 Rate (counts s -1 ) 4. 1 4 1. 1 5 1. 1 4 1. 1 4 3. 1 4 9.5 1 3 8. 1 3. 1 4 - -1 1 Seconds Since Trigger (9169 : 97.1153) 9. 1 3-1 -5 5 1 15 Seconds Since Trigger (9175 : 4756.57) H. Tajima,TeVPA, SLAC, July 14, 9 6. 1 3 5 1 15 Seconds Since Trigger (91116 : 39694.187) 1. 1 4 1 3 Seconds Since Trigger (96 : 978.491) /

Gamma-Ray Bursts Overview (1) 4. 1 5 Discovered in 1967 Cosmological origin Large apparent energy release: 1 5 ~1 54 Energetics consistent with origin of UHECR Peak in ~MeV gamma rays Band function: smoothly joined two power law Synchrotron radiation of ultra-relativistic electrons in jet? Flux (photons cm s 1 MeV 1 ) BATSE Trigger 98 BATSE Trigger 577 BATSE Trigger 97 1.8 1 4 BATSE Trigger 144 1.5 1 4 7. 1 4 Ch: (1: 4) Ch: (1: 4) Ch: (1: 4) Ch: (1: 4) ~.5 s Time Res:.64 s ~4 s 1-4 COMPTEL Burst Mode Time Res:.5 s ~18 EGRET TASC s Time Res:.5 s ~8 s Time Res:.64 s 1. 1 4 1.6 1 4 6. 1 4 1 3 1 1 1 1 1-1 1-1 -3 Low-Energy Index = -.6 ±.7 BATSE SD BATSE SD1 BATSE LAD BATSE SD4 OSSE COMPTEL Telescope F Peak Energy E p = 7 ± 1 kev GRB 9913 High-Energy Index = -3.11 ±.7 Rate (counts s -1 ) 3. 1 5. 1 5 1. 1 5 - -1 1 Seconds Since Trigger (9169 : 97.1153) Rate (counts s -1 ) 1.15 1 4 1.1 1 4 1.5 1 4 1. 1 4 9.5 1 3 9. 1 3-1 -5 5 1 15 Seconds Since Trigger (9175 : 4756.57) H. Tajima,TeVPA, SLAC, July 14, 9 Rate (counts s -1 ) E N E (erg cm s 1 ) 1.4 1 4 1. 1 4 1. 1 4 8. 1 3 6. 1 3 1-6 1-7 1-8 Rate (counts s -1 ) 5. 1 4 4. 1 4 3. 1 4. 1 4.1.1 1. 1 4 1 1 5 1 15 1 3 Seconds Since Trigger (91116 : 39694.187) Seconds Since Trigger (96 : 978.491) Photon Energy (MeV) /

Gamma-Ray Bursts Overview () Bimodal Duration Distribution Short (< s) GRB: progenitor unknown s Merger of compact objects (NS or BH)? Long (> s) GRB: Association with supernovae Core-collapse supernovae Gamma-ray emission mechanism not well understood H. Tajima,TeVPA, SLAC, July 14, 9 3/

High-Energy Emissions from GRB (Past) EGRET observations of delayed HE gamma-ray emissions It is not straightforward to explain by conventional electron synchrotron models Proton acceleration? Origin of UHECR? Gonzalez, Nature 3 44, 749-18 14s BATSE EGRET/TASC 14 47s Hurley et al. 1994 47 8s Two γ >GeV @~T 18 GeV γ @ ~T+75 min 8 113s 113 11s H. Tajima,TeVPA, SLAC, July 14, 9 4/

EGRET High-Energy GRB Spectra 5 EGRET bursts with >5 MeV observations in 7 years No evidence of cutoff or extra HE component in the summed spectrum Dingus et al. 1997 Composite spectrum of 5 EGRET Bursts H. Tajima,TeVPA, SLAC, July 14, 9 5/

GRB Observations by Fermi Improved performance of Fermi LAT (Large Area Telescope) Larger FOV (>.4 sr): more GRB samples Larger effective area: better statistics Less dead time: detailed lightcurve, time-resolved analysis Wider energy coverage: up to > 3 GeV Fermi Gamma-ray Burst Monitor Views entire unocculted sky NaI: 8 kev - 1 MeV BGO: 15 kev - 3 MeV GBM NaI Fermi GBM-LAT covers >7 decades of energy band (8 kev to > 3 GeV) LAT GBM BGO H. Tajima,TeVPA, SLAC, July 14, 9 6/

Fermi Detection of GRBs 41 GBM detection since 7/14/8 9 LAT detections (out of 19 in FOV) GRB885C, GCN8183, Bouvier et al. GRB8916C, GCN846, Tajima et al. Bright GRB with z~4.35, 9Sci...33.1688 GRB814B, GCN947, Omodei et al. First short GRB with >1 GeV photons GRB8115A, GCN8684, McEnery et al. GRB917, GCN893, Ohno et al. GRB933, GCN91, Ohno et al. nd LAT GRB with redshift (z 3.57) Long lived (up to > ks) HE emission GRB938, GCN944, McEnery et al. 3rd LAT GRB with redshift (z=.736) GRB951, GCN9334, Ohno et al. Short and intense GRB with z=.93 GRB966, GCN9584, Piron et al. H. Tajima,TeVPA, SLAC, July 14, 9 Fluence (erg/cm 8-1 kev) 1-4 1-5 1-6 1-7 LAT FOV 8916C 933 951 814B 917 938 885C 8115A 4 6 8 1 1 14 Angle to LAT boresight (deg) Fermi GRBs as of 951 Fermi GRB sky map as of 969 7/

Delayed HE Emission from 8916C Opacity due to γγ e + e in the first peak? 15 1 5 GBM NaI 3 + NaI 4 (8 kev-6 kev). 3.6 a 7.7 b c 15.8 8 5 kev d 54.7 15 1 GRB 8916C 5 5 1 15 e 1.8 3 1 No evidence of spectral cut-off 4 GBM BGO (6 kev-5 MeV) 4.6 5 MeV 6 8 4 5 1 15 1 1 5 4 6 8 1 3 1 LAT (no selection) All LAT events 3 1 5 1 15 6 4 5 LAT (> 1 MeV) > 1 MeV 4 6 8 1 5 5 1 15 1 15 1 5 H. Tajima,TeVPA, SLAC, July 14, 9 3 1 LAT (> 1 GeV) 4 > 1 GeV - 4 6 8 1 13. GeV photon 6 1.5 1.5 8 5 1 15 1 6 4 8/

Delayed HE Emission from 8916C Opacity due to γγ e + e in the first peak? 15 1 5 GBM NaI 3 + NaI 4 (8 kev-6 kev). 3.6 a 7.7 b c 15.8 8 5 kev d 54.7 15 1 GRB 8916C 5 5 1 15 e 1.8 3 1 No evidence of spectral cut-off 4 GBM BGO (6 kev-5 MeV) 4.6 5 MeV 6 8 4 5 1 15 1 1 5 4 6 8 1 3 1 LAT (no selection) All LAT events 3 1 5 1 15 6 4 5 LAT (> 1 MeV) > 1 MeV 4 6 8 1 5 5 1 15 1 15 1 5 H. Tajima,TeVPA, SLAC, July 14, 9 3 1 LAT (> 1 GeV) 4 > 1 GeV - 4 6 8 1 13. GeV photon 6 1.5 1.5 8 5 1 15 1 6 4 8/

Delayed HE Emission from Other LAT GRBs 6 4 Apparent delay of high-energy emissions (coincident with nd GBM pulse) Common origin for this emission in low and high energies Separate region from initial GBM emission Highest energy is very late (GRB 885C) 1 5 No detectable low energy emission a b c d e GRB 885C + NaI 1 GBM NaI 9 (8 kev-6 kev) Preliminary -1 1 3 4 5 + GBM BGO 1 GBM BGO (6 kev-5 MeV) 6 4 1 15 1 5 6 4-1 + NaI 9 GBM NaI 6 (8 kev-6 kev) -4-4 6 8 1 GBM BGO 1 (6 kev-5 MeV) LAT (All events) GRB 814B Preliminary -4-4 6 8 1 15 1 5 6 4-1 -1 1 3 4 5 1 LAT (> 8 MeV) -1 1 3 4 5 Time since GBM Trigger (s) H. Tajima,TeVPA, SLAC, July 14, 9 6 5 4 3 1 Energy [MeV] 3 1-4 - 4 6 8 1 LAT (> 1 MeV) -4-4 6 8 1 Time since (46576161.8) (s) 35 3 5 15 1 5 Energy [MeV] 9/

Extra Component in GRB 8916C? No conclusive evidence of extra HE component Probability of no extra component is ~1% Effect of EBL GRB 8916C Time bin ʻdʼ HE absorption Transparency:.3 1. (model dependent) Single Band-function dominant for 6 decades of energy band Lack of prominent SSC component implies High magnetic field εe/εb.1 Epeak,SSC 1 GeV (γe 1) H. Tajima,TeVPA, SLAC, July 14, 9 GBM NaI ν F ν synchrotron GBM BGO LAT Band function E p,syn γ e ~ε e /ε B Band + power law E p,ssc SSC ν 1/

Spectral Evolution of GRB 8916C Rapid soft to hard evolution in (a) to (b) Gradual decrease of Epeak from (b) to (d) Epeak GRB 8916C 3 1 /s) (kev/cm F 1 α β a c e b d 1 1 1 3 1 1 1 Energy (kev) 4 5 6 1 7 1 H. Tajima,TeVPA, SLAC, July 14, 9 11/

Spectral Evolution of GRB 8916C Rapid soft to hard evolution in (a) to (b) Gradual decrease of Epeak from (b) to (d) Epeak GRB 8916C 3 1 /s) (kev/cm F 1 α β a c e b d 1 1 1 3 1 1 1 Energy (kev) 4 5 6 1 7 1 H. Tajima,TeVPA, SLAC, July 14, 9 11/

Spectral Evolution of Other LAT GRBs Common trends Soft to hard evolution Long-lived HE emission GRB 885C GRB 814B H. Tajima,TeVPA, SLAC, July 14, 9 1/

Long-Lived HE Emission in 8916C HE (>1 MeV) emission shows different temporal behavior Temporal break in LE emission while no break in HE emission Indication of cascades induced by ultra-relativistic ions? or angle-dependent scattering effects? GRB 8916C H. Tajima,TeVPA, SLAC, July 14, 9 13/

Long-Lived HE Emission in Other LAT GRBs GRB 933 HE emission up to a few GeV lasted ~ s. Made possible by ARR (autonomous repoint recommendation) by GBM Otherwise GRB would have been out of FOV GRB 938 Planned orbit GRB 933 HE emission lasted ~9 s ARR was also issued H. Tajima,TeVPA, SLAC, July 14, 9 LAT 6 hour automated science processing 14/

Long-Lived HE Emission in Other LAT GRBs GRB 933 HE emission up to a few GeV lasted ~ s. Made possible by ARR (autonomous repoint recommendation) by GBM Otherwise GRB would have been out of FOV GRB 938 Planned orbit Actual orbit due to ARR GRB 933 HE emission lasted ~9 s ARR was also issued H. Tajima,TeVPA, SLAC, July 14, 9 LAT 6 hour automated science processing 14/

Long-Lived HE Emission in Other LAT GRBs GRB 933 HE emission up to a few GeV lasted ~ s. Made possible by ARR (autonomous repoint recommendation) by GBM Otherwise GRB would have been out of FOV GRB 938 Planned orbit Actual orbit due to ARR GRB 933 HE emission lasted ~9 s ARR was also issued H. Tajima,TeVPA, SLAC, July 14, 9 LAT 6 hour automated science processing 14/

Long-Lived HE Emission in Other LAT GRBs GRB 933 HE emission up to a few GeV lasted ~ s. Made possible by ARR (autonomous repoint recommendation) by GBM Otherwise GRB would have been out of FOV GRB 938 Planned orbit Actual orbit due to ARR GRB 933 HE emission lasted ~9 s ARR was also issued H. Tajima,TeVPA, SLAC, July 14, 9 LAT 6 hour automated science processing 14/

GRB 8916C Detection and Follow-up GBM trigger at :1:45 UT September 16, 8 (GCN845) Localized at RA = 11.8, Dec= -61.3 (±1 at 68% C.L., syst. -3 ) LAT localization @ 16 hours+t RA = 119.88, Dec = 56.59 (±.9 @ 68%, ±.13 @ 9% C.L.) systematic error<.1 GCN846 was circulated @ 18 hours+t Swift/XRT follow-up @ 17 hours+t RA = 119.8468, Dec = 56.638 (±1.9 at 9% C.L.) (GCN861) GROND follow-up @ 3 hours+t (GCN857) RA = 119.847, Dec = 56.6383 (±.5 at 68% C.L.) z = 4.35±.15 (Greiner et al. 9 ApJ) H. Tajima,TeVPA, SLAC, July 14, 9 15/

Redshift Determinations GROND measured redshift of GRB 8916C at z=4.35±.15 using Lyα break Simultaneous 7-filter observation VLT/FORS measured redshift of GRB 951 at z=.93±.3 using [OII] and Hβ emission lines flux density [µjy] 1 H. Tajima,TeVPA, SLAC, July 14, 9 z = 4.35 ±.15 gʼ GRB 8916C rʼ iʼ photons / (cm s kev) residuals 1 1 1 1 1 1 1 1 3 1 4 1 5.5..5 zʼ J (Greiner et al. 9) H Ks 1 3 3 1 1 1 1 1 1 energy [kev] 3 1 3 observed wavelength [nm] 1 brightness [magab] 16/

Constraints on Bulk Lorentz Factor Large luminosity and short variability time imply large optical depth due to γγ e + e Small emission region: R ~ cδt τγγ(e) ~ (11/18)σTN>1/E/4πR τγγ(1 GeV) ~ 7x1 11 for fluence=1 6 erg/cm, z=1, Δt=1 s Relativistic motion (Γ 1) can reduce optical depth Lager emission region: R ~ Γ cδt Reduced # of target photons: N>1/E Γ β+ (note: β ~ -.) Blue shift of energy threshold: Eth Γ Blue shift of spectrum: N(E) = (ΓE) β+1 Overall reduction of optical depth: Γ β- ~ Γ -6.4 Limit from GRB 8916C: Γ 89±1 H. Tajima,TeVPA, SLAC, July 14, 9 min 1 11 1 9 8 7 6 5 4 3 1 GRB 8916C bin-b ( t=5 ms) bin-b ( t= s) bin-d ( t= s) 1 z 3 4 5 17/

Implications of High Redshift for 8916C Eiso ~ 8.3 x 1 54 ergs Largest energy release ever ~5 solar mass Indicates strong beaming (jet) 15 1 5 4 + NaI 4 GBM NaI 3 (8 kev-6 kev) GBM BGO (6 kev-5 MeV). 16.5 s 3.6 a 7.7 b c 15.8 d 4 54.7 15 1 GRB 8916C 5 5 1 15 e 6 8 1 4 5 1 15 1.8 3 1 1 5 Lorentz invariance violation Dispersion relation: 3 1 LAT (no selection) 4 6 8 3 1 5 1 15 1 6 4 t = (1 + n) H (E n h En l ) (M QG,n c ) n z (1 + z ) n Ωm (1 + z ) 3 + Ω Λ dz 5 LAT (> 1 MeV) 4 6 8 1 5 5 1 15 1 15 1 5 Eh ~ 13. GeV @ Δt~16.5 s MQG,1 > 1.3 x 1 18 GeV/c 3 1 LAT (> 1 GeV) 4-4 6 8 1 6 1.5 1.5 8 5 1 15 1 6 4 Pulsar (Kaaret 99) GRB (Ellis 6/7) AGN (Biller 99) GRB (Boggs 4) AGN 1 16 1 17 (Albert 8) H. Tajima,TeVPA, SLAC, July 14, 9 AGN (Aharonian 8) GRB8916C Planck mass min M QG (GeV) 1 18 1 19 18/

Probing EBL at High Redshift HE gamma rays are sensitive to EBL (Extragalactic Background Light) in IR to UV band via γγ e + e process Observation of 13. GeV gamma ray from GRB 8916C τγγ highly model dependent:.3 5 Requires more bright GRBs like 8916C in various redshifts to untangle EBL models and gamma-ray emission models 1 1 1 1-1 z = 4.35 Stecker et al. (6) Baseline Stecker et al. (6) Fast Evolution Kneiske et al. (4) Best Fit Gilmore et al. (8) Razzaque et al. (8) 1 - H. Tajima,TeVPA, SLAC, July 14, 9 1 1 1 1 E [GeV] 19/

Latest Bright Short GRB 951 Short GRB lasting < 1 s in GBM band Significant HE emission 1 s 1st second 1st minute E > 1 MeV > 5 events > 15 events E > 1 GeV > 1 events > events Long-lived HE emission Relatively high redshift (z=.93±.3) for short GRB Constraints on Lorentz invariance and bulk Lorentz factor? H. Tajima,TeVPA, SLAC, July 14, 9 /

Summary of LAT GRBs GRB duration # of events > 1 MeV # of events > 1 GeV delayed HE onset Long-lived HE emission 885C long ~1 Redshift 8916C long ~1 >1 4.35 814B short ~1 8115A long 917 long 933 long >1 > 3.57 938 long >1.736 951 short >15 >.93 966 long H. Tajima,TeVPA, SLAC, July 14, 9 1/

Summary Single Band-function dominates 6 decades of energy band Implications on SSC model of high-energy emission The delayed onset of the LAT emission suggests a separate region from initial GBM emission Different behaviors of HE emission from LE emission may indicate separate emission mechanisms In GRB 8916C (@ z~4.35): Largest energy release ever observed Highest bulk Lorentz factor measured ( 89) Most stringent constraint on violation of Lorentz invariance Further constraints on origin of HE emission expected with future Fermi GRB observations H. Tajima,TeVPA, SLAC, July 14, 9 /

backup slides H. Tajima,TeVPA, SLAC, July 14, 9 3/

GRB Afterglow X-ray afterglow iʼ (Greiner et al. 9) zʼ J H Ks rʼ gʼ IR/visible light afterglow z = 4.35 ±.15 H. Tajima,TeVPA, SLAC, July 14, 9 4/