High Energy Gamma-ray Emission from GRBs
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Transcript of High Energy Gamma-ray Emission from GRBs
High EnergyGamma-ray Emission
from GRBs
Masanori Ohno(ISAS/JAXA)
on behalf of Fermi LAT/GBM collaborations
August 26, 2010 1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 BurstsGamma-Ray BurstsBright 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) and Long (>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 curveLight curve
Duration distributionDuration distribution
coun
ts
20s
shortshort longlong
2s2s
most energetic explosion in the Universe (Eiso~1052 erg)
August 26, 2010 3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 BurstsGamma-Ray BurstsBright 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) and Long (>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 curveLight curve
Duration distributionDuration distribution
coun
ts
20s
shortshort longlong
2s2s
most energetic explosion in the Universe (Eiso~1052 erg)
August 26, 2010 4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
Epeak
10 100 1000Energy(keV)
Fv
vFv
Standard Model
August 26, 2010 5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, 2010 6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 090709ABand function fit
BB + PL fit
vFv
vFv
100 1000 keV
HE emission from GRBs : Pre-Fermi EraHE emission from GRBs : Pre-Fermi Era
GRB940217v(Hurley et al. 94)
-18 to 14 sec
14 to 47 sec
47 to 80 sec
80-113 sec
113-211 sec
GRB941017 (Gonzaletz et al. 03)
GRB080514B AGILE
GeV photonsup to 90min after the trigger
Temporary distinct HE spectral component
Giuliani et al. 08Long-lived HE emission
August 26, 2010 7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 EraHE emission from GRBs : Pre-Fermi Era
August 26, 2010 8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. 1997
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 GRB941017 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 jetNo evidence of the cut-off so far.
Delayed or long-lived high energy emission ?Delayed or long-lived high energy emission ?Suggests another emission mechanismTime delay of high energy photon Limit on the quantum gravity mass :MQG
A few GRBs show delayed high energy emission (GRB940217, GRB080714)
Need more sensitivity and larger FoV
August 26, 2010 9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 TelescopeFermi Gamma-ray Space Telescope
GGamma-ray amma-ray BBursturst MMonitor (onitor (GBMGBM)) 12 NaI detectors (8keV-1MeV) - onboard trigger , localization - spectroscopy 2 BGO detectors (150keV-40MeV) - spectroscopy (overlapping LAT
band)
LATLATSilicon-Strip detectors - Identification &direction measurement of γ-raysCsI calolimetor - Energy measurementACD (plastic scintillators) - background rejection
August 26, 2010 10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, 2010 11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
0.540.15Angular resolution (single photon, 10 GeV)
1500 cm29000 cm2Peak 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, 2010 12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
10 107
Energy (keV)103 105
Alpha -1.02 +/- 0.02 Beta -2.21 +/- 0.03Epeak 1170 +/- 142 keV Amp. 0.0354 +/- 0.001 photons/s-cm2-keV REDUCED CHISQ = 0.963, PROB = 0.698
• 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 080916C
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 (1st circular). Final location, high-energy flux and spectrum, afterglow search results (2nd circular).
Onboard Alert and Notices
August 26, 2010 13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, 2010 14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 EarthAvoidance Angle (20. nominal), then slew at constant angle from the Earth limbuntil the the target rises on the other side.
August 26, 2010 15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 090902B ARR
Burst Advocate
August 26, 2010 16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.
1st 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 (E-mail)Alert (E-mail)
Yes
Within 30 min
~ a half of day (typically)
August 26, 2010 17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 090902B: a successful observation sequence
Easily seen in 1 daycounts 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 [T0 + 10 hr]– ASP results ~20 min later, human-in-the-loop localization– Swift ToO request issued at ~21:30 UT, begins at 23:36 UT [T0 + 12.5 hr]
• 21:19:03 UT – 1st GBM circular (GCN 9866)• 22:48:18 UT – 1st 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) [T0 + 21.3 hr]• 09:14:50 UT – GROND localization 3.3 arcmin from LAT position
Fermi GRBs Fermi GRBs
August 26, 2010 18
Detections as of 090904
LAT FoV
GBM FoV
• 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 100724A)– ~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 GRB941017 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 jetNo evidence of the cut-off so far.
Delayed or long-lived high energy emission ?Delayed or long-lived high energy emission ?Suggests another emission mechanismTime delay of high energy photon Limit on the quantum gravity mass :MQG
A few GRBs show delayed high energy emission (GRB940217, GRB080714)
August 26, 2010 20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 GRB941017 shows the sign of extra component
August 26, 2010 21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 090902B (long)GRB 090510 (short)
• First time a low-energy extension of the PL component has been seen
August 26, 2010 22
3 LAT GRBs shows extra PL component(090510, 090902B, 090926A)
First extra component by FermiAt > 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?
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 jetNo evidence of the cut-off so far.
August 26, 2010 23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 factorLimit 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
Γmin can be derived using observed highest energy photon
August 26, 2010 24
Γmin~1000 for short and long GRBs
z
Γmin
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
090510E=31 GeV
090902BE=33 GeV
080916CE=3 GeV
GRB 090926A: 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, 2010 25
8-14.3keV
14.3-260 keV
0.26-5 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(3.3-21.6s)
νFν(
erg
/cm
2/s
)
Energy (keV)10 102 103 104 105 106
What can we get from HE emission of GRBs?
Delayed or long-lived high energy emission ?Delayed or long-lived high energy emission ?Suggests another emission mechanismTime delay of high energy photon Limit on the quantum gravity mass :MQG
A few GRBs show delayed high energy emission (GRB940217, GRB080714)
August 26, 2010 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 090510 ~
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
t1.380.07
Simultaneous fitof the SED at 5 different times
LAT emission until 200 sNo spectral evolution(photon index -2.1 ± 0.1)
August 26, 2010 27
GRB 090510 (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 coincideDelay in HE onset: 0.1-0.2 s
Abdo et al. 2009, Science 323, 1688
The first LAT peak coincides with thesecond GBM peakDelay in HE onset: ~4-5 s
Abdo et al. 2009, Nature 462, 331
GRB 080916C (long)GRB 090510 (short)
HE delayed onset can be seen from almost all LAT GRBsAugust 26, 2010 28
8-260keV
0.26-5MeV
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, 2010 29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 (MQG) by direct measurement of photon arrival time
MQG,1/Mplank > 1.19
Disfavors quantum gravity models which linearly alters the speed of light (n=1)
Most models are optically thin for33 GeV photon from GRB 090902B(z=1.822)
“baseline” and “fast evolution” modelsare rejected at 3.6 σ level
Abdo et al. 2009, Nature 462, 331GRB 090510 GRB 090902B
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 090510: Etotal / Eiso ~ 100-1000)
– Hard to produce correlated variability at low- and high-energies (e.g. spikes of GRB 090926A) ?
• 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 090902B
– Short variability time scales in LAT data (e.g. GRB 090926A) argues against external shock
– Requires larger bulk Lorentz factor than measured for GRB 090926A
Models for HE delayed onset and extra-PL
August 26, 2010 30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 090904
Summary of LAT GRBs
Detections as of 090904
GRBAngle 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
080825C ~ 60° long ~ 10 0 ? ✔ X ~ 600 MeV
080916C 49° long 145 14 ✔ ✔ ? ~ 13.2 GeV ~ 4.35
081024B 21° short ~ 10 2 ✔ ✔ ? 3 GeV
081215A ~ 86° long — — — — -- —
090217 ~ 34° long ~ 10 0 X X X ~ 1 GeV
090323 ~ 55° long ~ 20 > 0 ? ✔ ? 3.57
090328 ~ 64° long ~ 20 > 0 ? ✔ ? 0.736
090510 ~ 14° short > 150 > 20 ✔ ✔ ✔ ~ 31 GeV 0.903
090626 ~ 15° long ~ 20 > 0 ? ✔ ?
090902B 51° long > 200 > 30 ✔ ✔ ✔ ~ 33 GeV 1.822
090926 ~ 52° long > 150 > 50 ✔ ✔ ✔ ~ 20 GeV 2.1062
091003A ~ 13° long ~ 20 > 0 ? ? ? 0.8969
091031 ~ 22° long ~ 20 > 0 ? ? ? ~ 1.2 GeV
100116A ~ 29° long ~ 10 3 ? ? ? ~ 2.2 GeV
August 26, 2010 31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, 2010 32
PropertyProperty(HE: >0.1GeV)(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 = 0.903 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
ΓΓmin min 1200 for GRB090510 900, 1000 (080916C, 090902B)
HE spectral component
1 out of 2 ✔(GRB090510)
2 out of 10 ✔(GRBs 090902B, 090926)
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, 2010 33
• 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
short
Upper Limit on LAT GRB Flux
August 26, 2010 34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 2010GBM 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, 2010 35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 090620.400
August 26, 2010 36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 081207.680
August 26, 2010 37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
SummarySummary
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, 2010 38
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: Γmin ~1000-GRB 090926A, 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