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