High Energy Gamma-ray Emission from GRBs Masanori Ohno(ISAS/JAXA) on behalf of Fermi LAT/GBM collaborations August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワーク ショップ ※ MeV-GeV での話です。

Outline Introduction Fermi Gamma-ray Space Telescope - Instruments - How does Fermi observe GRBs ? Science Result by Fermi - Extra component, delayed/Extended emission - Constraint on jet dynamics - other GRB topics (EBL, QG) - Upper limit on HE emission by Fermi data Summary August 26, 2010 ガンマ線バーストによるダークな宇宙の観測に向けたワーク ショップ 2

Gamma-Ray Bursts Bright gamma-ray pulse in gamma-ray band is discovered in 1967 GRBs originate from All-sky (~1GRBs/day) Bimodal duration distribution: non-thermal spectrum (Band function; synchrotron ?) Short ( 2s) GRB BATSE (1991-) BeppoSAX(1996-) discovery of the X-ray afterglow  This leads a redshift measurement. cosmological origin for long GRBs(z=0.1-8) relativistic jet is required (compactness problem) HETE-2 (2002-) Swift (2004-) Leads many afterglow observations Association with SN and long GRBs Discovery of afterglow from short GRBs Light curve Duration distribution counts 20s shortlong 2s most energetic explosion in the Universe ( E iso ~10 52 erg ) August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Gamma-Ray Bursts Bright gamma-ray pulse in gamma-ray band is discovered in 1967 GRBs originate from All-sky (~1GRBs/day) Bimodal duration distribution: non-thermal spectrum (Band function; synchrotron ?) Short ( 2s) GRB BATSE (1991-) BeppoSAX(1996-) discovery of the X-ray afterglow  This leads a redshift measurement. cosmological origin for long GRBs(z=0.1-8) relativistic jet is required (compactness problem) HETE-2 (2002-) Swift (2004-) Leads many afterglow observations Association with SN and long GRBs Discovery of afterglow from short GRBs Light curve Duration distribution counts 20s shortlong 2s most energetic explosion in the Universe ( E iso ~10 52 erg ) August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ α β E peak Energy(keV) Fv vFv

Standard Model August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Piran 2003 Prompt emission Afterglow

まだ謎は多い August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ emission mechanism, progenitor, short GRB…. etc 高エネルギーガンマ線 (>100MeV) の起源は特によく分かっていない。 8 秒の周期性 ?  SGR と関係 ? 熱的放射 ? (Ryde & Pe’er 2009) Iwakiri et al. in prep (4 月京都会議より） GRB A Band function fit BB + PL fit vFv keV

HE emission from GRBs : Pre-Fermi Era GRB940217v(Hurley et al. 94) -18 to 14 sec 14 to 47 sec 47 to 80 sec sec sec GRB (Gonzaletz et al. 03) GRB080514B AGILE GeV photons up to 90min after the trigger Temporary distinct HE spectral component Giuliani et al. 08 Long-lived HE emission August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

HE emission from GRBs : Pre-Fermi Era August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ 5 EGRET bursts with >50 MeV observations in 7 years –No evidence of cutoff in the summed spectrum Evidence for extended emission –>hour (afterglow?) GeV emission –Extra component at 100 s Composite spectrum of 5 EGRET Bursts Dingus et al No evidence of cutoff

What can we get from HE emission of GRBs? Extra component of the prompt emission ? Extra component of the prompt emission ? Different emission mechanism: Synchrotron self Compton ? Hadronic origin ? Only GRB shows the sign of extra component What is the maximum energy of high energy photon? What is the maximum energy of high energy photon? Constrain the bulk Lorentz factor of the relativistic jet No evidence of the cut-off so far. Delayed or long-lived high energy emission ? Delayed or long-lived high energy emission ? Suggests another emission mechanism Time delay of high energy photon  Limit on the quantum gravity mass :M QG A few GRBs show delayed high energy emission (GRB940217, GRB080714) Need more sensitivity and larger FoV August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor ( GBM ) 12 NaI detectors (8keV-1MeV) - onboard trigger, localization - spectroscopy 2 BGO detectors (150keV-40MeV) - spectroscopy (overlapping LAT band) LAT Silicon-Strip detectors - Identification &direction measurement of γ-rays CsI calolimetor - Energy measurement ACD (plastic scintillators) - background rejection August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

LAT Performance August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ 100 ms27 usDeadtime per event 0.4 sr>2.2 srField of view 0.54  0.15  Angular resolution (single photon, 10 GeV)‏ 1500 cm cm 2 Peak effective area 10%<10%Energy resolution (on axis, 100 MeV – 10 GeV)‏ 20 MeV – 30 GeV20 MeV to >300 GeVEnergy range EGRETLAT Major improvements in capabilities for GRB observation – Efficient observing mode (don’t look at Earth)‏ – Wide FoV – Low deadtime (exploring dt’s down to µsec)‏ Studies of short bursts possible – Large effective area – Good angular resolution – Increased energy coverage (to hundreds of GeV)‏ Many GRBs More photons detected from each GRB Good GRB locations

Fermi GRB spectrum August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ GBM/NaI GBM/BGO LAT Energy (keV) Alpha-1.02+/-0.02 Beta-2.21+/-0.03 Epeak1170+/-142keV Amp /-0.001photons/s-cm 2 -keV REDUCED CHISQ = 0.963, PROB = Consistent with Band function from 10 keV to 10 GeV No evidence for any other component No evidence for any roll-off (Abdo et al. 2009, Science 323, 1688) GRB C

 GBM/LAT on-board processing (10—15 s): GCN alert within 10—15 s from the trigger time through TDRSS (alert, location).  GBM ground processing of prompt data (few minutes): Updated GBM position, preliminary light curve.  LAT ground processing (a few hours after data downlink) Final location, spectrum (1 st circular). Final location, high-energy flux and spectrum, afterglow search results (2 nd circular). Onboard Alert and Notices August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Autonomous Repoint Request August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Fermi S/C can be repointed for LAT observations of extended emission from bright GRBs Track the target direction while above the horizon by at least the Earth Avoidance Angle (20. nominal), then slew at constant angle from the Earth limb until the the target rises on the other side.

August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ GRB B ARR

Burst Advocate August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Fermi or other satellites detected GRB. No Notify analysis results to the team when the data is available. 1 st GCN Circulars !! Significant detection !! Japanese members : ISAS/JAXA, Hiroshima U. and TITEC LAT onboard alert ? BA covers 24 hrs/day and 7day/week by an international collaboration. Alert ( ) Yes Within 30 min ~ a half of day (typically)

August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ GRB B: a successful observation sequence Easily seen in 1 day counts maps 11:05:15 UT = T0 – GBM GCN alert – ARR initiated –15:05 UT – GBM human-in-the-loop localization LAT data monitoring and processing –14:44 UT – GRB is seen in the telemetry –18:24 UT – data ingest –19:54 UT – GRB is seen in datamon plots 20:59:48 UT – FT1 file available [T hr] –ASP results ~20 min later, human-in-the-loop localization –Swift ToO request issued at ~21:30 UT, begins at 23:36 UT [T hr]‏ 21:19:03 UT – 1 st GBM circular (GCN 9866)‏ 22:48:18 UT – 1 st LAT circular (GCN 9867)‏ –(RA,Dec=265.00, 27.33) with a 90% containment radius of 0.06 deg (statistical; 68% containment radius: 0.04 deg, systematic error <0.1 deg) 03:00:57 UT – Swift/XRT afterglow candidate (GCN 9868)‏ [T0 + 16hr] –Estimated uncertainty of 4.2 arcseconds radius (90% confidence) –XRT position 3.2 arcmin from LAT position, inside error radius 04:57:44 UT – Swift/UVOT observations, no afterglow confirmation (GCN 9869)‏ 04:57:44 UT – enhanced Swift/XRT position (GCN 9871)‏ 07:36:42 UT – Fermi LAT and GBM refined analysis (GCN 9872)‏ 08:23:17 UT – Gemini-N absorption redshift (GCN 9873) z=1.822 (GMOS spectro) [T hr] 09:14:50 UT – GROND ‏localization 3.3 arcmin from LAT position

Fermi GRBs August 26, Detections as of The GBM detects ~250 GRBs/year (~400 total) – ~18% short – ~50% in the LAT FoV The LAT detects ~10 GRBs/year – 19 total as of today (recent detection : GRB A) – ~10% of GBM GRBs observed ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Only one case, LAT onboard notice has been issued (GRB090510)  onboard algolythm has been updated, now we can expect 5 notices/year

LAT GRB detection rate ~9.3 GRBs/year with >10 photons >100 MeV ~2.7 GRBs/year with >10 (100) photons >1 (0.1) GeV Comparable to estimates based on Band spectrum fits to bright BATSE GRBs Suggests that on average, GRBs don't have much excess (HE component) or deficit (cutoff) in the LAT energy range w.r.t. the extrapolated Band spectrum from <2 MeV Band et al., ApJ 701, 1673 (2009)

What can we get from HE emission of GRBs? Extra component of the prompt emission ? Extra component of the prompt emission ? Different emission mechanism: Synchrotron self Compton ? Hadronic origin ? Only GRB shows the sign of extra component What is the maximum energy of high energy photon? What is the maximum energy of high energy photon? Constrain the bulk Lorentz factor of the relativistic jet No evidence of the cut-off so far. Delayed or long-lived high energy emission ? Delayed or long-lived high energy emission ? Suggests another emission mechanism Time delay of high energy photon  Limit on the quantum gravity mass :M QG A few GRBs show delayed high energy emission (GRB940217, GRB080714) August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

What can we get from HE emission of GRBs? Extra component of the prompt emission ? Extra component of the prompt emission ? Different emission mechanism: Synchrotron self Compton ? Hadronic origin ? Only GRB shows the sign of extra component What is the maximum energy of high energy photon? What is the maximum energy of high energy photon? Constrain the bulk Lorentz factor of the relativistic jet No evidence of the cut-off so far. Delayed or long-lived high energy emission ? Delayed or long-lived high energy emission ? Suggests another emission mechanism Time delay of high energy photon  Limit on the quantum gravity mass :M QG A few GRBs show delayed high energy emission (GRB940217, GRB080714) August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Extra PL component in short and long GRBs Abdo, A. A. et al., ApJL 706, 138 (2009) Abdo, A. A. et al., ApJ submitted GRB B (long)GRB (short) First time a low-energy extension of the PL component has been seen August 26, LAT GRBs shows extra PL component (090510, B, A) First extra component by Fermi At > 5 sigma level ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ T0+4.6s to T0+9.6s

What can we get from HE emission of GRBs? Extra component of the prompt emission ? Extra component of the prompt emission ? Different emission mechanism: Synchrotron self Compton ? Hadronic origin ? Only GRB shows the sign of extra component What is the maximum energy of high energy photon? What is the maximum energy of high energy photon? Constrain the bulk Lorentz factor of the relativistic jet No evidence of the cut-off so far. Delayed or long-lived high energy emission ? Delayed or long-lived high energy emission ? Suggests another emission mechanism Time delay of high energy photon  Limit on the quantum gravity mass :M QG A few GRBs show delayed high energy emission (GRB940217, GRB080714) August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Limit on bulk Lorentz factor Due to large luminosity and small emitting region, optical depth for the γ-γ -> e+e- pair production is too large to observe the non-thermal emission from GRB  compactness problem. Relativistic motion (Γ>>1) could avoid this compactness problem Γ min can be derived using observed highest energy photon August 26, Γ min ~1000 for short and long GRBs z Γ min ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ E=31 GeV B E=33 GeV C E=3 GeV

GRB A: the first HE spectral cutoff Preliminary ! - Delay in HE onset: ~3 s - The extra component shows at >4 σ spectral break at ~1.4 GeV - First direct measurement of Γ ~ 720 (if cutoff due to γ-γ absorption) August 26, keV keV MeV LAT all event >100 MeV >1GeV ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Time-integrated photon spectrum( s) νF ν (erg/cm 2 /s) Energy (keV)

What can we get from HE emission of GRBs? Extra component of the prompt emission ? Extra component of the prompt emission ? Different emission mechanism: Synchrotron self Compton ? Hadronic origin ? Only GRB shows the sign of extra component What is the maximum energy of high energy photon? What is the maximum energy of high energy photon? Constrain the bulk Lorentz factor of the relativistic jet No evidence of the cut-off so far. Delayed or long-lived high energy emission ? Delayed or long-lived high energy emission ? Suggests another emission mechanism Time delay of high energy photon  Limit on the quantum gravity mass :M QG A few GRBs show delayed high energy emission (GRB940217, GRB080714) August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Long-lived GeV emission ~ Swift and Fermi view of GRB ~ De Pasquale et al., ApJL 709, 146 (2010) Forward shock model can reproduce the spectrum from the optical up to GeV energies Extensions needed to arrange the temporal properties t  1.38  0.07 Simultaneous fit of the SED at 5 different times LAT emission until 200 s No spectral evolution (photon index -2.1 ± 0.1) August 26, GRB (short GRB) UVOT XRT Fermi/LAT ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

HE delayed onset in short and long GRBs The first few GBM peaks are missing in the LAT but later peaks coincide Delay in HE onset: s Abdo et al. 2009, Science 323, 1688 The first LAT peak coincides with the second GBM peak Delay in HE onset: ~4-5 s Abdo et al. 2009, Nature 462, 331 GRB C (long) GRB (short) HE delayed onset can be seen from almost all LAT GRBs August 26, keV MeV LAT all events >100 MeV >1GeV ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Constraint on QG and EBL models August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Constraints on the quantum gravity mass (M QG ) by direct measurement of photon arrival time M QG,1 /M plank > 1.19 Disfavors quantum gravity models which linearly alters the speed of light (n=1) Most models are optically thin for 33 GeV photon from GRB B (z=1.822) “baseline” and “fast evolution” models are rejected at 3.6 σ level Abdo et al. 2009, Nature 462, 331 GRB GRB B Abdo, A. A. et al., ApJL 706, 138 (2009) 31 GeV GBM NaI GBM BGO LAT (>1MeV) 0.83 s

Leptonic models (inverse-Compton or SSC) (Toma et al., 2009) –Hard to produce a delayed onset longer than spike widths –Hard to produce a low-energy (<50 keV) power-law excess – Hard to account for the different photon index values of the Band spectrum at low energie (but photospheric models can) and of the HE component – But, photospheric models could explain these properties (Toma et al. 2010) Hadronic models (pair cascades, proton synchrotron) (Asano et al., 2009) – GRBs as possible sources of Ultra-High Energy Cosmic Rays – Late onset: time to accelerate protons & develop cascades? – Proton synchrotron radiation (requires large B-fields) – Synchrotron emission from secondary e± pairs produced via photo-hadron interactions can naturally explain the power-law at low energies require substantially more energy than observed (GRB : Etotal / Eiso ~ ) – Hard to produce correlated variability at low- and high-energies (e.g. spikes of GRB A) ? Early Afterglow (e+e- synchrotron from external shock) (Kumar et al, 2009) – Can account for possible delayed (~9 s) onset of power-law component in GRB B – Short variability time scales in LAT data (e.g. GRB A) argues against external shock – Requires larger bulk Lorentz factor than measured for GRB A Models for HE delayed onset and extra-PL August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Detections as of Summary of LAT GRBs Detections as of GRB Angle from LAT Duration (or class) # of events > 100 MeV # of events > 1 GeV Delayed HE onset Long-lived HE emission Extra spectral comp. Highest photon Energy Redshift C ~ 60° long~ 100 ? ✔ X~ 600 MeV C 49° long14514 ✔✔ ?~ 13.2 GeV~ B 21° short~ 102 ✔✔ ?3 GeV A ~ 86° long————--— ~ 34° long~ 100XXX~ 1 GeV ~ 55° long~ 20> 0? ✔ ? ~ 64° long~ 20> 0? ✔ ? ~ 14° short> 150> 20 ✔ ✔ ✔ ~ 31 GeV ~ 15° long~ 20> 0? ✔ ? B 51° long> 200> 30 ✔ ✔ ✔ ~ 33 GeV ~ 52° long> 150> 50 ✔ ✔ ✔ ~ 20 GeV A ~ 13° long~ 20> 0? ? ? ~ 22° long~ 20> 0? ? ?~ 1.2 GeV A ~ 29° long~ 103? ? ?~ 2.2 GeV August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Long vs Short GRBs (1) August 26, Property (HE: >0.1GeV) Short GRBs (2)Long GRBs (12) Delayed HE onset 1 out of 2 ✔ (+ 1 likely but inconclusive) 3 out of 4 ✔ (+ 7 inconclusive cases) Long-lived HE emission 2 out of 2 ✔ 7 out of 8 ✔ (+ 3 inconclusive cases) Redshift 1 out of 2 ✔ (z = for GRB090510) 6 out of 12 ✔ (0.74, 0.90, 1.82, 2.11, 3.57, 4.35) Bright 1 out of 2 ✔ >100 (10) events >0.1 (1) GeV 3 out of 12 ✔ >100 (10) events >0.1 (1) GeV Γ min Γ min 1200 for GRB , 1000 (080916C, B) HE spectral component 1 out of 2 ✔ (GRB090510) 2 out of 10 ✔ (GRBs B, ) Similar high energy properties between short and long GRBs ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Long vs Short GRBs (2) August 26, Comparable LE and HE gamma-ray outputs for short GRBs Long GRBs seem to emit ~5-20 times less at HE than at LE w.r.t. short GRBs short Abdo, A. A. et al., ApJ 712, 558 (2010) Preliminary ! ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ short

Upper Limit on LAT GRB Flux August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Fermi GRB statistics up to April 2010 GBM Detections : 427 events - Within LAT FoV (<65 deg from LAT boresight) 213 events (~50 %) - LAT Detection 16 events (~7.5 %) What can we say about remaining 197 events (92.5%)? (1) LAT flux upper limit (2) Expected LAT flux by GBM extrapolation Intrinsic spectral break ? EBL or γ-γ absorption ?  Possible Implication..

GBM Extrapolation August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ Bright GBM sample : GBM events with > 70 BGO cts But no LAT detections Performed spectral fitting 16 events in “Gold” sample beta can be constrained 53 sample  Obtain expected LAT flux from GBM extrapolation  Compare LAT flux upper limit with expected LAT flux

Example: GRB August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Example: GRB August 26, ガンマ線バーストによるダークな宇宙の観測に向けたワークショップ

Summary  Fermi detected ~400 GRBs including 19 LAT GRBs in ~1.5 years => 250 GRBs/year for GBM and ~10 GRBs/year for LAT April 19, Extra component of the prompt emission ? Extra component of the prompt emission ? What is the maximum energy of HE emission ? What is the maximum energy of HE emission ? HE emission is delayed and/or long-lived ? HE emission is delayed and/or long-lived ? -Clear evidence of extra PL component from 3 LAT GRBs -Low-energy excess is also seen -Constraint lower limit of bulk Lorentz factor: Γ min ~1000 -GRB A, first detection of HE spectral cutoff : Γ ~ 720 -Many LAT GRBs show delayed and long-lived high energy emission Many leptonic or hadronic models are proposed for LAT high energy emission No difference of high energy properties between short and long GRBs Deciphering the Ancient Universe with Gamma-Ray Bursts Constraint on QG and EBL models