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Unstable eUnstable e±± Photospheres & Photospheres & GRB Spectral RelationsGRB Spectral Relations
Kunihito Ioka (IPNS, KEK)
w/ K.Murase, K.Toma, S.Nagataki, T.Nakamura,
M.Ohno, Suzaku team, P.MészárosOpening of a postdoc in KEK (theoretical cosmophysics)
http://www.kek.jp/ja/jobs/IPNS08-1.html Please search with “KEK”
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ContentsGRB emission mechanism Synchrotron vs. Photosphere Unstable e± photosphere ⇒ Non-thermal Blueshifted e± line (bump) ⇒ GLAST Closure relations between e± line & cutoffSuzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Liso relation for short GRBsHypernova remnants as TeV unID sources Decay of accelerated radioisotope
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Emission mechanismWhat is the GRB emission mechanism?
Reasons:1. Low-energy spectral index
2. Epeak relations (Amati/Yonetoku/Ghirlanda)
⇔ High GRB efficiency (-ray energy/Total energy ≳ 50%)
Internal shock ⇒ GRB: ~ OK, … But,Synchrotron emission?: Possibly No
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Problem 11. Low-energy spectral index
2. Epeak relations (Amati/Yonetoku/Girlanda)
Excluded
Preece+ 00
F
Superposition ofsynchrotron spec.
1/3
High GRB efficiency ⇒ tcool << tdyn-1/2
Ghisellini+ 00Mészáros&Rees 00But, Bosnjak+ 00
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Problem 2
Ep~Liso1/2
Ep~Esyn~B’e2
~B~U1/2~(L/r2)1/2
~L1/2 -2 t-1
(with r~c2t) ⇒ Small ⇒Low GRB efficiency??
1. Low-energy spectral index2. Epeak relations (Amati/Yonetoku/Girlanda)
Synchrotron model:
Yonetoku+ 03, Kodama+ 08Also Willingale+ 07 Kobayashi+ 98
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Photosphere model
Zhang+(04)
Strong dissipationwithin the star
~1 emission ⇒ GRB1. Hard low-energy index F~2
2. Epeak~Thermal peak Stefan-Boltzmann law
Ep~T’~(L/2r2)1/4
~(/r)1/2 L1/4
(if r~rWR*, ~-1, Frail L~-2, then ~L1/2)
Thompson,Mészáros&Rees 06
Weak dependence⇒ High GRB efficiency: OK
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Non-thermal?
~1 ⇒Radiation is thermalized⇔ GRB is nonthermal: Reason that excludes original fireball model
How to make non-thermal(radiation-dominated) fireballs?
F
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Unstable photosphere?High GRB efficiency⇒ Radiation-dom. fireball⇒ Radiative acceleration
22,obs
2151
212com s cm10~ TLg
(g~3x104cm s-2 on the sun)Light
g
Rough Idea
HeavyHeavy
Heavy⇒ Large effective gravity⇒ Heavy parts fall & grow ⇒ Shocks⇒ Non-thermal
ComovingFrame
KI+ 07
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Unstable photosphere?High GRB efficiency⇒ Radiation-dom. fireball⇒ Radiative acceleration
22,obs
2151
212com s cm10~ TLg
(g~3x104cm s-2 on the sun)e±
g
Rough Idea
Proton(+e) Proton
(+e)
Proton(+e)
⇒ Large effective gravity⇒ Heavy parts fall & grow ⇒ Shocks⇒ Non-thermal
ComovingFrame
KI+ 07
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e± pairn±>ne-p is not unlikely since mp~103me
Radiation pushes e± more than e-p
~1
F
thermal
→ e+e-
If E±~Eproton
⇒ n±~103ne-p
Not all e± annihilatesince ~1
Rees&Mészáros 05
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Spontaneous non-thermalization“Proton sedimentation”
KI+ 07
push e± not e-p → Relative V → 2-stream instability→ p inhomogeneity → grow → shock → Non-thermale± heating ≈ cooling without fine-tuning even if tcool<tdyn
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Spectrum
Shock (p-e⇔e±)⇒e± acceleration⇒ Inverse Compton
Non-thermal energy~Proton kinetic energy~Afterglow energy
e~1
N(e) Electronspectrum~e
-p
Observed hardest one
KI+ 07
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Blueshifted e± line (bump)e± bumps are predicted above continua
Proof:If line<continuum,→e± since >1
⇒ line>continuum Check ~L1/2 (Yonetoku)
0.5MeV x ~ 0.53GeV GLAST
KI+ 07Pe’er+ 06
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e± line & cutoff
22~~
cmecutcut
1~'~~ , r
n Tcut →e + e -
Comoving size
Murase&KI 08Lithwick&Sari 01
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Closure relation
22
,,
,
'~~
'~
'
'~~
1~'~
1~'~~
cmcmn
n
L
L
rn
rn
e
cut
e
cutcut
ann
cut
T
Tcut
⇐ e± cutoff
⇐ e± photosphere
Relation betweenonly observables→ Model checking
Luminosity ∝ n (photon density) x (photon energy)
Murase&KI 08Gupta&Zhang 08
⇒ Also, the emission radius r, , e±-p ratioEven non-detection can constrain parameters
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ContentsGRB emission mechanism Synchrotron vs. Photosphere Unstable photosphere ⇒ Non-thermal Blueshifted e± line (bump) ⇒ GLAST Closure relations between e± line & cutoffSuzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Liso relation for short GRBsHypernova remnants as TeV unID sources Decay of accelerated radioisotope
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Time-resolved Ep-LisoSuzaku WAM (50-5000keV)
Ep~Liso1/2 even
for 1sec spectra(~Liang+ 04)
GRB061007
All outliers belong to the pulse rising phase
Synchro: Ep~(L/r2)1/2
Photo: Ep~(/r)1/2L1/4
Ohno,KI+ 08
r expand / decelerate: Fireball dynamics
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Ep-Liso for short GRBsSuzaku WAM (50-5000keV)
Ep
Liso
z-known short GRBs
PRELIMINARY
Ep~Liso1/2
(Yonetoku)
Ohno+ 08
Not satisfy the Yonetoku rela.?… because of no stellar envelope?
Ep~L-1/4
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Self-created photosphere?No stellar envelope for short GRB ⇒ rphoto ≠ r*
~n±T(r/)~1Ep~T’~(/r)1/2L1/4
1. Assume energy equipartition (~matter)T’4~npmpc2 (w/o e±) T’4~n±mec2 (w/ e±)
2. Assume the photosphere model~npT(r/)~1Ep~T’~(/r)1/2L1/4
⇒ Ep~2 L-1/4: Anti-correlation?
Self-determined photospheric radius
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ContentsGRB emission mechanism Synchrotron vs. Photosphere Unstable e± photosphere ⇒ Non-thermal Blueshifted e± line (bump) ⇒ GLAST Closure relations between e± line & cutoffSuzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Liso relation for short GRBsHypernova remnants as TeV unID sources Decay of accelerated radioisotope
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Increasing TeV sources“Kifune plot”
Jim Hinton, rapporteurtalk, ICRC 2007
In the TeV sky, most sources are unidentified!
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Observed properties
10010~
kpc10s erg10~4
cm s erg1010~2
135342
211211
N
dFdL
F
TeV unID
kpc102.0pc30~~
ddR
Disk ⇒ Galactic origin d~1-10kpc
Extended
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Radioisotope acceleration
GRB/Hypernova as RI beam factory
56Ni ⇐ SN light curve
e eFeCo *5656
Fe56
~2MeVCould be shock-accelerated before decay (by reverse shock?)
1998bw: M(56Ni)~0.4M◉
KI&Mészáros
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RI decay model
1-346
52
2
36
6
6
s erg10~yr10
erg10
GeV60
MeV2~~
10 10yr110
yr10~~
10TeV2~~
t
E
cmL
N~t
tt
RI
RI
RIRI
RI
SNR disappears: good for explaining unIDs
56Co case
62
10PeV60~
cmRI
Hypernova OK
56Co energy
~unIDs
~unIDsRadioactive Hypernova Remnant ~ TeV unID sources
KI&Mészáros
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SummaryGRB emission mechanism Synchrotron vs. Photosphere Unstable photosphere ⇒ Non-thermal Blueshifted e± line (bump) ⇒ GLAST Closure relations between e± line & cutoffSuzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Liso relation for short GRBsHypernova remnants as TeV unID sources Decay of accelerated radioisotope
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Counter arguments?Steep decay
3.0 and s10for
cm10622
decay
132decay
j
j
t
ctR
Not so much delay
v~c
Residual collision(Li & Waxman 07)
May not be curvature emisssion(Barniol Duran&Kumar 08)
Opt
Prompt optical emissionSelf-absorption is effectiveif the emission radius is smallBut it may be residual collision
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Decay properties
Decay mode Half-life56Ni Electron capture 6.1 day (>104yr: Ion)56Co EC (81%) 77.2 day + (19%) (x5: Ion)57Ni EC 35.60 hr +
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Spectrum
(2-p)-1
F
Exp.cutoff
~TeV
tdecay~1066yr~TeV6
~GeV
Already decayed Now decaying
te eFeCo *5656
Fe56
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High energy e
(2-p)-1F
Exp.cutoff
~TeV
tdecay~1066yr~TeV6
~GeV
Already decayed Now decaying
e eFeCo *5656
Fe56
Similaras -ray
Detection maybe difficult
t
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Swift – Short GRBs
Short GRBs are really few?
Sakamoto+07
Swift :< 150keV⇒short hardare missed?
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Suzaku/WAM – Short GRBs
Tashiro+ 08