unstable e ± photospheres & grb spectral relations kunihito ioka (ipns, kek) w/ k.murase,...
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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”
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
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
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
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
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
Non-thermal?
~1 ⇒Radiation is thermalized⇔ GRB is nonthermal: Reason that excludes original fireball model
How to make non-thermal(radiation-dominated) fireballs?
F
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
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
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
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
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
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
e± line & cutoff
22~~
cmecutcut
1~'~~ , r
n Tcut →e + e -
Comoving size
Murase&KI 08Lithwick&Sari 01
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
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
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
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
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
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
Increasing TeV sources“Kifune plot”
Jim Hinton, rapporteurtalk, ICRC 2007
In the TeV sky, most sources are unidentified!
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
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
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
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
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
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 +
Spectrum
(2-p)-1
F
Exp.cutoff
~TeV
tdecay~1066yr~TeV6
~GeV
Already decayed Now decaying
te eFeCo *5656
Fe56
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
Swift – Short GRBs
Short GRBs are really few?
Sakamoto+07
Swift :< 150keV⇒short hardare missed?
Suzaku/WAM – Short GRBs
Tashiro+ 08