Transcript Diagnosing Models of Gamma-Ray Bursts through Very High-Energy Gamma-Ray Emission Kohta Murase Tokyo Institute of Technology Center for Cosmology and AstroParticle Physics, OSU Collaborators: R.

Diagnosing Models of Gamma-Ray
Bursts through Very High-Energy
Gamma-Ray Emission
Kohta Murase
Tokyo Institute of Technology
Center for Cosmology and AstroParticle Physics, OSU
Collaborators: R. Yamazaki, K. Toma, K. Ioka, S. Nagataki
Deciphering the Ancient Universe with Gamma-Ray Bursts, Kyoto
Content
• 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 Emission
Chincarini+ 05
• Shallow decay emission: difficult to be explained by
the simplest standard afterglow model
(Talk by Panaitescu)
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 Model
Ghisellini+ 2007
Late prompt:
decelerating jet
shallow+normal AG
break when q~1/G
External shock:
standard AG model
normal decay
Prior Emission Model
Yamazaki 2009
Main jet:
prompt after T0~103-4s
prompt GRB
Prior jet:
late optical AG
g-ray dim precursor
shallow+normal x-ray AG
Prior Emission Model (Contd.)
• Assumption
(AG onset time of prior jet)
< (trigger time T0)
• Afterglow
F(t) ∝ t-a
• t=T+T0
F(T)=(T+T0)-a
→F(T) ~ const. (T<T0)
F(T) ~ T-a (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 Compton
• Those models naturally predict EIC emission
prompt or
late prompt
qsc
“Anisotropic” inverse-Compton emission
→ Contribution from qsc~0 is suppressed
In this talk, we focus on leptonic mechanisms
Predicted Spectrum
• Klein-Nishina effect is important
gm2 Eb ~ TeV (gm/103)2 (Eb/MeV)
>> EKN ~ G gm me c2 ~ 50 GeV (t/1000s)-3/4
n Fn
∝n(3-p)/2
prompt or
late prompt
∝n2-a
EIC
∝n2-b
KN suppression
∝na-q
∝n2-a
Eb
EK
N
q=p-1 or p
gm2 Eb
Prior Emission Model (MeV Prompt + FS)
• electron distribution = standard AG model
• seed photon dist. = observed prompt emission
predicted without introducing further parameters
KM et al. 10 MNRAS 402 L54
Fermi
SSC
EIC
MAGICII
z=0.3
T0=300s
Lg,52=3
Ek,52＝3
ee=0,1
eB=0.01
KM et al. 10 MNRAS 402 L54
EIC duration ~ r(t=T0)/G2c ~ 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~DT~1s
Prediction: shallow decay is not expected for such bursts
Late Prompt Model (keV Prompt + FS)
• Klein-Nishina effect is important
gm2 Eb ~ 0.1 GeV (gm/300)2 (Eb/keV)
<< EKN ~ G gm me c2 ~ 10 GeV (t/1000s)-3/4
• SSC from FS will also contribute to HE emission
EcSSC ~ gc2 Ec ~ TeV (t/1000s)-1/4
n Fn
late prompt
AG
n2-b
n2-a
n(3-p)/2
n1-p/2
n-(3-p)/2
n(3-p)/2
na-q
n1-p/2
q=p-1 or p
n2-a
Ec
Eb
EK
N
KM et al. 2010b, in prep.
Ｆｅｒｍｉ ｒａｎｇｅ
gc2 Ec
SSC
EIC
EIC from Two-Component Models
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 GeVTeV flares or GeV-TeV flashes from RS
(e.g., Wang, Li, & Meszaros 2006)
Connection to Fermi GRBs?
• So far, GeV emission observed by Fermi may
be explained by synchrotron emission in the
standard ext. shock model
(Kumar & Duran 09, Ghisellini+ 10
Wang+ 10, talk by Meszaros, Piran)
•Fermi bursts themselves
do not seem to require
models for shallow decay
emission
Ghisellini+ 10 MNRAS
Synchrotron and SSC emission？
• Radiative AG (e.g., ee, eB~0.1-1， n~1cc-1) (Ghisellini+ 10)
• Adiabatic AG (e.g., eB~10-4, n~10-3 cc-1) (Kumar and Duran 09)
• Unless Y >> 1, it is possible to find parameters where
Ecut is observed
Ecut ~ G (h/2p) (6pe2/sTmec)h-1 ~ G 160 MeV h-1
n Fn
SSC
Ｙ
Synch.
E＊
Ecut
EpkSC EK
Synchrotron Cutoff by IACTs?
• Ecut only depends on G except acc. coff. h
• In the adiabatic case, Ecut can be seen
EK
ee=0.1
eB=10-5
p=2.4
z=1
n Fn
N
Synch.
SSC
E＊
Ecut
KM & Yamazaki 2010
Ecut E＊
EK
EpkSC
N
Ecut observation → measurement of evolution of G
Summary
VHE 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, ｆor signals from UHE nuclei)
Synchrotron Cutoff?
• Ecut only depends on G except acc. coff.
• For appropriate ee/eB, Ecut may be seen
ee=0.003
eB=0.001
p=2.1
E＊
n Fn
EK
N
SSC
Synch.
EpkSC
Ecut
E＊
Ecut
EpkSC EK
N
Ecut observation → measurement of G!
Issue
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Emission Mechanisms
• Leptonic mechanism
synchrotron
synchrotron self-Compon
external inverse Compton
• Hadronic mechanism
pg
pp
nuclear de-excitation
Various 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 07)
・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?~
High-Energy Spectra from Afterglows
ISMモデル
100s → 10000s → 1000000s
WINDモデル
100s → 10000s → 1000000s
Early Afterglows in the Swift era
Energy injection
dE/dt ∝ t^-0.5
z=1
Time-dependent parameters
εe ∝ t^0.4
High-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)
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)
Flares
(even for SGRBs)
Baryonic (possibly dirty
fireball?) vs non-baryonic?
↑neutrinos!
Burrows et al. (07)
(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 (EGRBg ~ 1051 ergs ~ 0.01 EGRBg,iso, qjet ~ 0.1 rad)
•Related to the deaths of massive stars (association with SNe Ic)
Luminosity
variability~ ms
Afterglow
X-ray、optical、radio
Prompt (GRB)
Gamma-ray～300 keV
Duration: a few s～103s
Time
10-102s
103-104s
Internal-External Shock Model
(Baryonic Jet Model)
r ~ 1014 cm
r > 1016 cm
Interstellar
Medium
Central
Engine
Lorent Factor
G>100
Luminosity
Bulk kinetic energy
↓
Shock dissipation
acceleration
magnetic field
heat
Time
Prompt Gamma-Ray Emission
Amati et al. (2002)
α　~ 1
Isotropic energy
Eγiso ~ 1053 ergs
b ~ 2.2
broken power-law spectrum
e ~ 300 keV
g , pk
N(eg)  eg-a (e<eg,pk)
N(eg)  eg-b (e>eg,pk)
g-ray emission ⇔ radiation from electrons accelerated at
mildly relativistic (Γrel ~ a few) internal shocks
Protons may also be accelerated as well as electrons
Classical Optically Thin Synchrotron Scenario
Fig. from
Guetta (07)
Optically thick ←
→ Optically thin
rph ~ 1012.5 cm
rdec ~ 1016 cm
•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
Cosmic-Ray Acceleration in GRBs
assumption
necessary for UHECRs
Acceleration time scale
η~ (1-10)
Cooling time scale
Criterion for acceleration
tacc < max[tcool, tdyn]
Escape: tdyn < tcool
only if tcool ~ tsyn
r = 1014 cm
Ep,max = Esyn ~ 1020-21 eV
UHECR production is possible
Waxman (95)
For nuclei survival
→ EO,max = Eog ~ 1016-17 eV
E/Γ
Internal-External Shock Model
(Baryonic Jet Model)
r ~ 1014 cm
r > 1016 cm
Interstellar
Medium
Central
Engine
Lorent Factor
G>100
Luminosity
Bulk kinetic energy
↓
Shock dissipation
acceleration
magnetic field
heat
Time
Basics of Prompt Neutrino Emission
Cosmic-ray Spectrum (Fermi)
εp2N(εp)
Photon Spectrum (Prompt)
Key parameter
CR loading
2-p~0
total ECR~20EHECR
EHECR≡εp2N(εp)
~εγ,pk2N(εγ,pk)
εγ2N(εγ)
2-β~-0
2-α~1.0
εp
~ΓGeV
1018.5eV 1020.5eV
εγ
εγ,pk~300keV
εmax
Photomeson Production
p + γ → Δ → n + π+ κ p ~ 0.2
Δ-resonance
p + γ → N π± + X
κ p ~ (0.4－0.7)
Δ-resonance approximation
εp εγ ~ 0.3 Γ2 GeV2
multi-pion production
εpb~ 0.3 Γ2/εγ,pk ~ 50 PeV
Photomeson production efficiency
~ effective optical depth for pγ process
(in proton rest frame)
fpγ ~ 0.2 nγσpγ (r/Γ)
Meson Spectrum
pion energy επ~ 0.2 εp
break energy επb~ 0.06 Γ2/εγ,pk ~ 10 PeV
επ2N(επ)
α-1~0
~fpγEHECR
β-1~1
α-3~-2.0
επ
επsyn
επｂ
For charged mesons → sync. cooling
(meson cooling time) ~ (meson life time)
→ break energy in neutrino spectra
Waxman & Bahcall, PRL (1997)
Neutrino Spectrum
εν2N(εν)
p →   n (n ) Gamma-Ray Spectrum
 → e  ne (ne )  n (n )
εg
2N(ε
p0 → g  g
g)
α-1~0
α-1~0
β-1~1
β-1~1
α-3~-2.0
εν
ενb
ενπsyn
neutrino energy εν ~ 0.25 επ ~ 0.05 εp
•ν lower break energy ενb ~ 2.5 PeV
•ν higher break energy ενπsyn ~ 25 PeV
εg
εg b
εgmax
g-ray energy εg ~ 0.5 επ ~ 0.1 εp
•γ lower break energy εgb ~ 5 PeV
•γ maximum energy εgmax ~ 0.1 εpmax
Prompt Neutrino Emission
KM & Nagataki, PRD, 73, 063002 (2006)
z=1.0
A r~1013.5 cm
B r~1014.5 cm
Γ=300, Uγ=UB
Set A: EGRBg,iso=1053 ergs, r ~ 1013-14.5 cm → muon events ~ 0.1
Set B: EGRBg,iso=1053 ergs, r ~ 1014-15.5 cm → muon events ~ 0.01
Set C: EGRBg,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.
We will need to see as many GRBs as possible with time- and space-coincidence.
The Cumulative Background
We cumulate neutrino spectra using GRB rate histories.
for GRB rate models
(e.g., Guetta et al. 04, 07)
KM & Nagataki, PRD, 73, 063002 (2006)
Γ=102.5,
Ug=UB
Current AMANDA limit
Set A - r~1013-14.5cm
Set B - r~1014-15.5cm
The key parameter
CR loading ΕHECR ≡εp2 N(εp)
high CR loading
EHECR ~ 2.5 EGRBg
(Up=50Ug)
moderate CR loading
EHECR ~ 0.5 EGRBg
(Up=10Ug)
• ~10 events/yr by IceCube (moderate CR loading)
• The most optimistic model is being constrained by
AMANDA/IceCube group. (Achterberg et al. 07,08)
fpg(EHECR/EGRBg)<3 → Towards testing the GRB-UHECR hypothesis via νs
Alternative Scenarios?
r~1013-1015.5 cm
Fig. from
Guetta (07)
The optically thin synchrotron scenario has several problems
e.g., epk-Liso correlation, low-energy index problem…
Alternative scenarios
•Photospheric: Emission from the photosphere (t~1, r~1012.5 cm)
•SSC: Emission from around the deceleration radius (r~1016cm)
The Cumulative Background
KM, PRD(R), 78, 101302 (2008)
CR loading
EHECR ~ EGRBg ~ 1051 ergs
(for prompt emission)
Photospheric
~ 20 events/yr
Classical
~ 10 events/yr
SSC
~ 0.1 events/yr
Photospheric: TeV nus from pp (detectable even for h >> 1)
• Important probe of dissipation/acceleration below/around rph
• The most efficient case (min[fpg,1]~1)
SSC: EeV nus from pg (because of optical synchrotron photons)
Remarks
• Key parameters：
CR loading EHECR
(UHECR hypothesis → EHECR ~ 1-10 EGRBg)
Emission radius r
(depending on scenarios)
• Gamma rays should be but more complicated!
pair creation in the source
contribution from leptonic components
GeV Gamma Rays
Relative small r → VHE g rays (e.g., ｆｒｏｍ p0) cannot escape
r ~ 1014 cm
p 100%
r~1014 cm
EHECR/EGRBg = 0.05
r~1014 cm
EHECR/EGRBg =5
EHECR/EGRBg = １.5
EHECR/EGRBg = 0.5
Asano & Inoue (2007)
Asano, Inoue, & Meszaros (2008)
*Here e index (pe=3) is assumed to be steeper than p index (pp=2)
EM cascades in the source (modification for high CR loading)
GeV g rays → Fermi, MAGIC (e.g., possibly GRB 090510B)
TeV Gamma Rays
Relative large r → VHE g rays (e.g., ｆｒｏｍ p0) can escape
r ~ 1015 cm (HL GRB)
EHECR/EGRBg =1
r ~ 1016 cm (LL GRB)
EHECR/EGRBg = 0.5
KM, Ioka, Nagataki, & Nakamura, PRD (2008)
*p0 g rays are attenuated by CMB (their detection is not easy)
Non-cascades in the source (CR synch. emission can be important)
TeV g rays → MAGIC, VERITAS (for nearby/energetic GRBs)
Remarks
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)
Meszaros (2001)
Classical Afterglows
External Shock Model
EeV ν, GeV-TeV γ
(Waxman & Bahcall 00)
(Dai & Lu 01)
(Dermer 02)
(Li, Dai & Lu 02)
Early Afterglows
EeV ν, GeV-TeV γ
(Dermer 07)
(KM 07)
Reverse-Forward Shock Model
Γ~ 100-1000
afterglow
Reverse shock
Forward shock
ejecta
CBM
Forward Shock vs Reverse Shock
• Forward-shock acceleration of protons (Dermer 02)
Ultra-relativistic shock
For typical parameters, Emax ~ Z 1015eV BISM,-6 (t/104 s)-1/8
Very strong amplification of upstream B is required
UHECR acceleration at G >> 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 shock
The 1st order Fermi acceleration seems possible
It might relatively easy to produce UHECRs
UHECRs + optical/IR photons (~ T ~ 100 s) → EeV neutrinos
UHECRs and GRBs
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Photospheric Emission Scenario
e.g., Meszaros & Rees (00), Rees & Meszaros (05)
Photosphere
Epeak ~ kT (characterized)
kT ~
100keV
Peer, Meszaros, & Rees (06)
Significance of thermal emission (r<rph) → High radiation efficiency
Dissipation/acceleration occurs below/around the photosphere
Nonthermal component comes from electrons at r ~ rph
Synchrotron 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)
νFν
B ~ 100 G
~ 10 GeV
~ 300 keV
synchrotron
opt
bright optical!
Racusin et al. (08)
ν
High-Energy Spectra in the Internal Shock Model
(Asano & Inoue 07)
Up=Ug=UB
No proton signature
UB>>Ug=Up
proton signature
Plateau Emission ~Late Internal activity?~
Issues of Prompt Emission
r~1013-1015.5 cm
Fig. from
Guetta (07)
DO not belive the synchrotron scenario.
•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)
Magnetic Dissipation - External Shock Model
(Magnetic Jet Model)
Meszaros (2001)
Prompt Emission
from Classical (High-Luminosity) GRBs
Internal Shock Model
PeV ν, GeV-TeV γ
(Waxman & Bahcall 97)
Classical Afterglows
External Shock Model
EeV ν, GeV-TeV γ
(Waxman & Bahcall 00)
(Dai & Lu 01)
(Dermer 02)
(Li, Dai & Lu 02)