Post on 13-Jan-2016
Diagnosing Models of Gamma-Ray Diagnosing Models of Gamma-Ray Bursts through Very High-Energy Bursts through Very High-Energy
Gamma-Ray EmissionGamma-Ray Emission
Kohta MuraseKohta Murase Tokyo Institute of TechnologyTokyo Institute of Technology
Center for Cosmology and AstroParticle Physics, OSUCenter for Cosmology and AstroParticle Physics, OSU
Deciphering the Ancient Universe with Gamma-Ray Bursts, KyotoDeciphering the Ancient Universe with Gamma-Ray Bursts, Kyoto
Collaborators: R. Yamazaki, K. Toma, K. Ioka, S. Nagataki
ContentContent• HE emission
discussions motivated by recent Fermi results+ delayed onset, extra component etc.
many models including int.- and ext.- shocks have been discussed leptonic (talks by Meszaros, Dermer, Piran, Wang)hadronic (talks by Meszaros, Dermer, Ioka, Asano)
• Here, I will talk about HE emission at late time from a different motivation
Early X-Ray Afterglow EmissionEarly X-Ray Afterglow Emission
• Shallow decay emission: difficult to be explained by the simplest standard afterglow model(Talk by Panaitescu)
Chincarini+ 05
Many models have been suggested so far…energy injection, time-dependent parameters, long-lasting RS etc.
Multi-component models (e.g., Granot et al. 06, Toma et al. 06, Ghisellini et al. 07, Yamazaki 09)
have been more and more discussed recently
Ex.: two-component model fits by Ghisellini et al. 09
Late Prompt Emission ModelLate Prompt Emission Model
Late promptLate prompt::
decelerating jet
shallow+normal AG
break when ~1/ External shock:External shock:
standard AG model
normal decay
Ghisellini+ 2007
Prior Emission ModelPrior Emission Model
Main jet:Main jet:
prompt after T0~103-4s
prompt GRB
late optical AG
Prior jetPrior jet::
-ray dim precursor
shallow+normal x-ray AG
Yamazaki 2009
Prior Emission Model (Contd.)Prior Emission Model (Contd.)
• Assumption
(AG onset time of prior jet) < (trigger time T0)
• Afterglow
F(t) t∝
• t=T+T0
F(T)=(T+T0)
→F(T) ~ const. (T<T0) F(T) ~ T (T>T0)
consistent with Willingale+ 07
• Motivated by recent interpretations for x-ray afterglows, let us consider consequences of such two-component models for high-energy emission
External Inverse ComptonExternal Inverse Compton
• Those models naturally predict EIC emission
“Anisotropic” inverse-Compton emission→ Contribution from sc~0 is suppressed
sc
In this talk, we focus on leptonic mechanisms
prompt or late prompt
Predicted SpectrumPredicted Spectrum
• Klein-Nishina effect is importantm
2 Eb ~ TeV (m/103)2 (Eb/MeV)
>> EKN ~ m me c2 ~ 50 GeV (t/1000s)-3/4
∝2-
∝(3-p)/2prompt or late prompt
EIC
F
Eb EKN m2 Eb
∝2-
∝2-∝-q
KN suppression
q=p-1 or p
Prior Emission Model (MeV Prompt + FS)Prior Emission Model (MeV Prompt + FS)
• electron distribution = standard AG model
• seed photon dist. = observed prompt emission predicted without introducing further parameters
z=0.3T0=300sL=3E = 3e=0,1B=0.01
KM et al. 10 MNRAS 402 L54
MAGICII
EIC
SSC
Fermi
EIC duration ~ r(t=T0)/2c ~ T0 ~ 1000 s → Follow-up obs. by IACTs would be possible (~ dozens of seconds)
* ~GeV extra comp. of observed Fermi GRBs may be explained for T0~T~1sPrediction: shallow decay is not expected for such bursts
KM et al. 10 MNRAS 402 L54
Late Prompt Model (keV Prompt + FS)Late Prompt Model (keV Prompt + FS)
2-
(3-p)/2
late prompt
EIC
F
Eb EKN c2 Ec
2-
2-
-q
q=p-1 or p
SSC
-(3-p 1-p 1-p/2
Ec
• Klein-Nishina effect is importantm
2 Eb ~ 0.1 GeV (m/300)2 (Eb/keV) << EKN ~ m me c2 ~ 10 GeV (t/1000s)-3/4
• SSC from FS will also contribute to HE emission Ec
SSC ~ c2 Ec ~ TeV (t/1000s)-1/4
(3-p)/2
Fermi rangeKM et al. 2010b, in prep.
AG
Useful for testing these kinds of two-component models, and quantitative studies of obs. may allow us to discern various theoretical possibilities
Such EIC emission may similarly be expected in such two-component models for prompt emission- MeV prompt + FS/RS (prior emission model)small T0 → extra comp. at GeV-TeV e.g., MeV prompt + IS, Toma, Wu & Meszaros 2010
As was previously suggested , EIC may also lead to GeV-TeV flares or GeV-TeV flashes from RS(e.g., Wang, Li, & Meszaros 2006)
EIC from Two-Component ModelsEIC from Two-Component Models
Connection to Fermi GRBs?Connection to Fermi GRBs?
• So far, GeV emission observed by Fermi may be explained by synchrotron emission in the standard ext. shock model
•Fermi bursts themselves do not seem to require models for shallow decay emission
Ghisellini+ 10 MNRAS(Kumar & Duran 09, Ghisellini+ 10Wang+ 10, talk by Meszaros, Piran)
Synchrotron and SSC emissionSynchrotron and SSC emission ??• Radiative AG (e.g., e, B~0.1-1 , n~1cc-1) (Ghisellini+ 10)
• Adiabatic AG (e.g.,B~10-4, n~10-3 cc-1) (Kumar and Duran 09)
• Unless Y >> 1, it is possible to find parameters where Ecu
t is observedEcut ~ (h/2) (6e2/Tmec)-1 ~ 160 MeV -1
Synch.
SSCF
Ecut EKN Epk
SC
E *
Y
Synchrotron Cutoff by IACTs?Synchrotron Cutoff by IACTs?
• Ecut only depends on except acc. coff. • In the adiabatic case, Ecut can be seen
Synch. SSC
F
Ecut EKN Epk
SC E
*
Ecut observation → measurement of evolution of
Ecut
E *
EKN
e=0.1B=10-5
p=2.4z=1
KM & Yamazaki 2010
SummarySummaryVHE obs.@>10GeV are relevant for diagnosing GRB models• EIC as a diagnosis of multi-component models
VHE observations at ~102-104 s- prior emission model for shallow decay- late prompt emission for shallow decay etc.
• Syn. cutoff or extra components (SSC or hadronic)VHE observations at ~1-102 s for Fermi GeV bursts - e.g., adiabatic AG or radiative AG models
Maybe difficult by Fermi IACTs are better in sensitivities though det. prob. is not large fast follow-up (<100s) & LE thr. (~10GeV) required →CTA (see also my postar #63, f or signals from UHE nuclei)
Synchrotron Cutoff?Synchrotron Cutoff?
• Ecut only depends on except acc. coff.• For appropriate e/B, Ecut may be seen
Synch. SSC
F
Ecut EKN Epk
SC
E *
Ecut observation → measurement of
Ecut
E *
EpkSC
EKN
e=0.003B=0.001p=2.1
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Issue
Emission MechanismsEmission Mechanisms
• Leptonic mechanismsynchrotronsynchrotron self-Componexternal inverse Compton
• Hadronic mechanismpppnuclear de-excitation
Various InterpretationsVarious Interpretations
Many possibilities have been suggested…
For example,Modified Forward Shock Models a. energy injection (e.g., Sari & Meszaros 00) b. time-dependent parameters (e.g., Ioka et al. 06) c. complicated density profile (e.g., Ioka et al. 06)
Long-lasting Reverse Shock Model(Genet et al. 07, Uhm & Beloborodov 0
7) ・ Existence of slow tail of ejecta leads to a long-lasting RS
Multi-component models (e.g., Granot et al. 06, Toma et al. 06, Ghisellini et al. 07, Yamazaki
09)
more and more discussed recently
Ex.: two-component model fits by Ghisellini et al. 09
Plateau Emission ~Late Internal activity?~Plateau Emission ~Late Internal activity?~
High-Energy Spectra from AfterglowsHigh-Energy Spectra from Afterglows
ISM モデル
WIND モデル
100s → 10000s → 1000000s
100s → 10000s → 1000000s
Early Afterglows in the Swift eraEarly Afterglows in the Swift era
Energy injection Time-dependent parametersεe ∝ t^0.4dE/dt ∝ t^-0.5
z=1
High-Energy Gamma-Rays from FlaresHigh-Energy Gamma-Rays from Flares
フレアの high-energy をうけるには近傍のバーストに限られる
Novel Results of Swift (Flares)Novel Results of Swift (Flares)
2. Flares in the early afterglow phase• Energetic (Eflare,γ ~ 0.1 EGRB,γ (Falcone et al. 07)) (Eflare,γ ~ EGRB,γ for some flares such as GRB050502b)•δt >~ 102-3 s, δt/T < 1 → internal dissipation models (e.g. late internal shock model)• Flaring in the (far-UV)/x-ray range (Epeak ~ (0.1-1) keV)• (Maybe) relatively lower Lorentz factors (Γ ~ a few×10)• Flares are common (at least 1/3 ~ 1/2 of LGRBs) (even for SGRBs)
Baryonic (possibly dirty fireball?) vs non-baryonic?↑neutrinos!
Flares
Burrows et al. (07)
(Long) Gamma-Ray Bursts(Long) Gamma-Ray Bursts
•The most violent phenomena in the universe (L~1051-52 ergs s-1)•Cosmological events (z~1-3)•~1000 per year (⇔ apparent rate of ~ 1/10000 of SNe Ibc rate)•Jet hypothesis (EGRB~ 1051 ergs ~ 0.01 EGRB,iso, jet ~ 0.1 rad)•Related to the deaths of massive stars (association with SNe Ic)
Gamma-ray ~ 300 keVDuration: a few s ~ 103s
Prompt (GRB)
AfterglowX-ray 、 optical 、 radio
variability~ ms
Time
Luminosity
10-102s103-104s
Internal-External Shock Model(Baryonic Jet Model)
Lorent Factor
>100
InterstellarMedium
Bulk kinetic energy↓
Shock dissipation
acceleration magnetic field heat
CentralEngine
Time
Luminosity
r ~ 1014 cm r > 1016 cm
Prompt Gamma-Ray EmissionPrompt Gamma-Ray Emission
-ray emission ⇔ radiation from electrons accelerated at
mildly relativistic (Γrel ~ a few) internal shocks Protons may also be accelerated as well as electrons
1~α 2.2~
Amati et al. (2002)
keV300~pk,
broken power-law spectrum
N(∝,pk
N(∝,pk
Isotropic energyEγ
iso ~ 1053 ergs
•Peak energy of ~ 300 keV is identified with synchrotron peak•The typical required magnetic field is B ~ 104-5 G for Γ ~ 300•The typical emission radius is r~1013-1015.5 cm
Fig. fromGuetta (07)
Classical Optically Thin Synchrotron ScenarioClassical Optically Thin Synchrotron Scenario
Optically thick ← → Optically thin
rph ~ 1012.5 cm rdec ~ 1016 cm
Cosmic-Ray Acceleration in GRBsCosmic-Ray Acceleration in GRBs assumption
necessary for UHECRs
η~ (1-10)
Criterion for acceleration
tacc < max[tcool, tdyn] Escape: tdyn < tcool
Ep,max = Esyn ~ 1020-21 eVUHECR production is possible
For nuclei survival→ EO,max = Eo ~ 1016-17 eV
E/Γ
Waxman (95)
Acceleration time scale
Cooling time scale only if tcool ~ tsyn
r = 1014 cm
Internal-External Shock Model(Baryonic Jet Model)
Lorent Factor
>100
InterstellarMedium
Bulk kinetic energy↓
Shock dissipation
acceleration magnetic field heat
CentralEngine
Time
Luminosity
r ~ 1014 cm r > 1016 cm
Basics of Prompt Neutrino EmissionBasics of Prompt Neutrino Emission
2.0~κπ+n→Δ→γ+p p+
εp
Cosmic-ray Spectrum (Fermi)
Key parameterCR loading
1018.5eV1020.5eV
εγ
Photon Spectrum (Prompt)
εγ,pk~300keV εmax
Photomeson production efficiency~ effective optical depth for pγ process
fpγ ~ 0.2 nγσpγ (r/Γ)
Δ-resonance Δ-resonance approximation
εp εγ ~ 0.3 Γ2 GeV2
εpb~ 0.3 Γ2/εγ,pk ~ 50 PeV
εp2N(εp)
2-α~1.0
2-β~-02-p~0
~ΓGeV
εγ2N(εγ)
EHECR≡εp2N(εp)
~εγ,pk2N(εγ,pk)
multi-pion production
Photomeson Production
)7.04.0(~κX+πN→γ+p p± -
(in proton rest frame)
total ECR~20EHECR
pion energy επ~ 0.2 εp
break energy επb~ 0.06 Γ2/εγ,pk ~ 10 PeV
επ
Meson Spectrum
επb επ
syn
β-1~1
α-1~0
επ2N(επ)
Neutrino Spectrum
ενb
β-1~1
α-1~0
εν2N(εν)
)(→
)()(e→ ee
For charged mesons → sync. cooling(meson cooling time) ~ (meson life time)→ break energy in neutrino spectra
~fpγEHECR
α-3~-2.0
ενπsyn
εν
α-3~-2.0
neutrino energy εν ~ 0.25 επ ~ 0.05 εp
•ν lower break energy ενb ~ 2.5 PeV
•ν higher break energy ενπsyn ~ 25 PeV
→0
Gamma-Ray Spectrum
εb
β-1~1
α-1~0
ε2N(ε)
εmax
ε
-ray energy ε ~ 0.5 επ ~ 0.1 εp
•γ lower break energy εb ~ 5 PeV
•γ maximum energy εmax ~ 0.1 εp
max
Waxman & Bahcall, PRL (1997)
Prompt Neutrino EmissionPrompt Neutrino Emission
Γ=300, Uγ=UB
Set A: EGRB,iso=1053 ergs, r ~ 1013-14.5 cm → muon events ~ 0.1Set B: EGRB,iso=1053 ergs, r ~ 1014-15.5 cm → muon events ~ 0.01
Set C: EGRB,iso=1054 ergs, r ~ 1013-14.5 cm → muon events ~ 1(Note: C is a very extreme case with α=0.5 and β=1.5)
We expect ν signals from one GRB for only nearby/energetic bursts.
A r~1013.5 cm
B r~1014.5 cm
z=1.0
We will need to see as many GRBs as possible with time- and space-coincidence.
KM & Nagataki, PRD, 73, 063002 (2006)
The Cumulative BackgroundThe Cumulative Background
• ~10 events/yr by IceCube (moderate CR loading)• The most optimistic model is being constrained by
AMANDA/IceCube group. (Achterberg et al. 07,08)
moderate CR loadingEHECR ~ 0.5 EGRB
(Up=10U)
high CR loadingEHECR ~ 2.5 EGRB
(Up=50U)
The key parameter CR loading ΕHECR ≡εp
2 N(εp)
Set A - r~1013-14.5cm Set B - r~1014-15.5cm
Γ=102.5, U=UB
KM & Nagataki, PRD, 73, 063002 (2006)
Current AMANDA limit
fp(EHECR/EGRB)<3 → Towards testing the GRB-UHECR hypothesis via νs
We cumulate neutrino spectra using GRB rate histories. for GRB rate models
(e.g., Guetta et al. 04, 07)
r~1013-1015.5 cm
Alternative scenarios •Photospheric: Emission from the photosphere (rcm)•SSC: Emission from around the deceleration radius (r~1016cm)
Fig. fromGuetta (07)
Alternative Scenarios?Alternative Scenarios?
The optically thin synchrotron scenario has several problems e.g., pk-Liso correlation, low-energy index problem…
The Cumulative BackgroundThe Cumulative Background
Photospheric: TeV nus from pp (detectable even for >> 1)• Important probe of dissipation/acceleration below/around rph
• The most efficient case (min[fp,1]~1)SSC: EeV nus from p (because of optical synchrotron photons)
CR loadingEHECR ~ EGRB~ 1051 ergs(for prompt emission)
Photospheric~ 20 events/yrClassical~ 10 events/yrSSC~ 0.1 events/yr
KM, PRD(R), 78, 101302 (2008)
RemarksRemarks
• Key parameters : CR loading EHECR
(UHECR hypothesis → EHECR ~ 1-10 EGRB)
Emission radius r
(depending on scenarios)
• Gamma rays should be but more complicated!
pair creation in the source
contribution from leptonic components
GeV Gamma RaysGeV Gamma Rays
Relative small r → VHE rays (e.g., from 0) cannot escape
r ~ 1014 cmp 100%
Asano, Inoue, & Meszaros (2008)
*Here e index (pe=3) is assumed to be steeper than p index (pp=2)
r~1014 cmEHECR/EGRB = 0.05
r~1014 cm
Asano & Inoue (2007)
EHECR/EGRB =5
EHECR/EGRB = 0.5
EHECR/EGRB = 1 .5
EM cascades in the source (modification for high CR loading)
GeV rays → Fermi, MAGIC (e.g., possibly GRB 090510B)
TeV Gamma RaysTeV Gamma Rays
Non-cascades in the source (CR synch. emission can be important)TeV rays → MAGIC, VERITAS (for nearby/energetic GRBs)
r ~ 1015 cm (HL GRB)EHECR/EGRB =1
r ~ 1016 cm (LL GRB)EHECR/EGRB = 0.5
KM, Ioka, Nagataki, & Nakamura, PRD (2008)
Relative large r → VHE rays (e.g., from 0) can escape
*0 rays are attenuated by CMB (their detection is not easy)
RemarksRemarks
CR acceleration during the prompt phase is testable
But prompt emission mechanism is highly uncertain(magnetic dissipation models → less neutrinos…)
Even if prompt emission is magnetic, GRBs can still be candidates of the UHECR origin
(But large Ekin w. small fe is required)
Because CRs are likely to be accelerated in afterglows caused by shock dissipation
(This situation is similar to AGNs)
Early AfterglowsEeV ν, GeV-TeV γ
(Dermer 07)(KM 07)
Meszaros (2001)
Classical AfterglowsExternal Shock Model
EeV ν, GeV-TeV γ (Waxman & Bahcall 00)
(Dai & Lu 01)(Dermer 02)
(Li, Dai & Lu 02)
Reverse-Forward Shock ModelReverse-Forward Shock Model
afterglow
Reverse shock
Forward shock
ejecta
Γ~ 100-1000
CBM
Forward Shock vs Reverse ShockForward Shock vs Reverse Shock
• Forward-shock acceleration of protons (Dermer 02)
Ultra-relativistic shockFor typical parameters, Emax ~ Z 1015eV BISM,-6 (t/104 s)-1/8
Very strong amplification of upstream B is requiredUHECR acceleration at >> 1 shock is theoretically difficult→Other mechanisms such as the 2nd order Fermi acceleration?
• Reverse-shock acceleration of protons (Waxman & Bahcall 00)
Mildly relativistic or non-relativistic shockThe 1st order Fermi acceleration seems possibleIt might relatively easy to produce UHECRsUHECRs + optical/IR photons (~ T ~ 100 s) → EeV neutrinos
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UHECRs and GRBs
Photospheric Emission ScenarioPhotospheric Emission Scenario
Significance of thermal emission (r<rph) → High radiation efficiencyDissipation/acceleration occurs below/around the photosphereNonthermal component comes from electrons at r ~ rph
kT ~100keV
e.g., Meszaros & Rees (00), Rees & Meszaros (05)Epeak ~ kT (characterized)
Photosphere
Peer, Meszaros, & Rees (06)
Synchrotron Self-Compton ScenarioSynchrotron Self-Compton Scenario
• Some observations of early AGs lead to r ~ 1016 cm
difficulty in synchrotron scenario (Kumar & MacMahon 08)
• e.g., one-zone interpretation of 080319B → SSC model
optical emission implies large r (e.g., Racusin et al., Nature 08)
opt
~ 300 keV
~ 10 GeVνFν
ν
bright optical!
Racusin et al. (08)
synchrotron
B ~ 100 G
(Asano & Inoue 07)
High-Energy Spectra in the Internal Shock Model
UB>>U=Up
proton signature
Up=U=UB
No proton signature
Plateau Emission ~Late Internal activity?~Plateau Emission ~Late Internal activity?~
r~1013-1015.5 cm
•Inner range (~1011-13 cm) pγ efficient, UHECR impossible•Middle range (~1013-15 cm) pγ moderately efficient, UHE proton possible•Outer range (~1015-16 cm) pγ inefficient, UHE nuclei survive
(e.g., KM & Nagataki, 2006)
r-determination is important ← GLAST (e.g., KM & Ioka 08, Gupta & Zhang 08)
Fig. fromGuetta (07)
Issues of Prompt EmissionIssues of Prompt Emission
DO not belive the synchrotron scenario.
Magnetic Dissipation - External Shock Model(Magnetic Jet Model)
Prompt Emission from Classical (High-Luminosity) GRBs
Internal Shock ModelPeV ν, GeV-TeV γ
(Waxman & Bahcall 97)
Meszaros (2001)
Classical AfterglowsExternal Shock Model
EeV ν, GeV-TeV γ (Waxman & Bahcall 00)
(Dai & Lu 01)(Dermer 02)
(Li, Dai & Lu 02)