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Unstable e ± Photospheres & GRB Spectral Relations

Unstable e ± Photospheres & GRB Spectral Relations. Kunihito Ioka (IPNS, KEK) w/ K.Murase, K.Toma, S.Nagataki, T.Nakamura, M.Ohno, Suzaku team, P.Mészáros. Opening of a postdoc in KEK (theoretical cosmophysics) http://www.kek.jp/ja/jobs/IPNS08-1.html Please search with “KEK”. Contents.

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Unstable e ± Photospheres & GRB Spectral Relations

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  1. Unstable e± Photospheres & GRB Spectral Relations Kunihito Ioka (IPNS, KEK) w/ K.Murase, K.Toma, S.Nagataki, T.Nakamura, M.Ohno, Suzaku team, P.Mészáros Opening of a postdoc in KEK (theoretical cosmophysics) http://www.kek.jp/ja/jobs/IPNS08-1.html Please search with “KEK”

  2. Contents GRB emission mechanism Synchrotron vs. Photosphere Unstable e±photosphere ⇒ Non-thermal Blueshifted e± line(bump) ⇒ GLAST Closure relations between e± line & cutoff Suzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Lisorelation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

  3. Emission mechanism What is the GRB emission mechanism? Internal shock ⇒ GRB: ~ OK, … But, Synchrotron emission?: Possibly No Reasons: 1. Low-energy spectral index 2. Epeak relations (Amati/Yonetoku/Ghirlanda) ⇔ High GRB efficiency (g-ray energy/Total energy ≳ 50%)

  4. Problem 1 Ghisellini+ 00 Mészáros&Rees 00 But, Bosnjak+ 00 1. Low-energy spectral index 2. Epeak relations (Amati/Yonetoku/Girlanda) High GRB efficiency ⇒ tcool << tdyn Fn Excluded n-1/2 n1/3 Superposition of synchrotron spec. n Preece+ 00

  5. Problem 2 1. Low-energy spectral index 2. Epeak relations (Amati/Yonetoku/Girlanda) Synchrotron model: Ep~Esyn~GB’ge2 ~B~U1/2~(L/r2)1/2 ~L1/2G-2 Dt-1 (with r~cG2Dt) Ep~Liso1/2 ⇒ SmallDG⇒ Low GRB efficiency?? Yonetoku+ 03, Kodama+ 08 Also Willingale+ 07 Kobayashi+ 98

  6. Photosphere model t~1 emission ⇒ GRB 1. Hard low-energy index Fn~n2 2. Epeak~Thermal peak Stefan-Boltzmannlaw Ep~GT’~G(L/G2r2)1/4 ~(G/r)1/2 L1/4 (if r~rWR*, G~q-1, Frail L~q-2, then ~L1/2) Thompson,Mészáros&Rees 06 Zhang+(04) Weak G dependence ⇒ High GRB efficiency: OK Strong dissipation within the star

  7. Non-thermal? nFn t~1 ⇒ Radiation is thermalized ⇔ GRB is nonthermal : Reason that excludes original fireball model n How to make non-thermal (radiation-dominated) fireballs?

  8. Unstable photosphere? Rough Idea High GRB efficiency ⇒ Radiation-dom. fireball ⇒ Radiative acceleration Light KI+ 07 Heavy Heavy (g~3x104cm s-2 on the sun) ⇒ Large effective gravity ⇒ Heavy parts fall & grow ⇒ Shocks ⇒ Non-thermal Heavy g Comoving Frame

  9. Unstable photosphere? Rough Idea High GRB efficiency ⇒ Radiation-dom. fireball ⇒ Radiative acceleration e± KI+ 07 Proton (+e) Proton (+e) (g~3x104cm s-2 on the sun) ⇒ Large effective gravity ⇒ Heavy parts fall & grow ⇒ Shocks ⇒ Non-thermal Proton (+e) g Comoving Frame

  10. e± pair n±>ne-p is not unlikely since mp~103me Rees&Mészáros 05 gg→e+e- t~1 If E±~Eproton ⇒ n±~103ne-p nFn thermal Not all e± annihilate since t~1 n Radiation pushes e±more than e-p

  11. Spontaneous non-thermalization “Proton sedimentation” KI+ 07 g push e± not e-p → Relative V → 2-stream instability → p inhomogeneity → grow → shock → Non-thermal e±heating ≈ cooling without fine-tuning even if tcool<tdyn

  12. Spectrum N(ge) Electron spectrum ~ge-p ~1 ge KI+ 07 Observed hardest one Non-thermal energy ~Proton kinetic energy ~Afterglow energy Shock (p-e⇔e±) ⇒e±acceleration ⇒Inverse Compton

  13. Blueshifted e± line (bump) e± bumps are predicted above continua 0.5MeV x G ~ 0.5G3GeV GLAST KI+ 07 Pe’er+ 06 Proof: If line<continuum, gg→e± since t>1 ⇒ line>continuum G Check G~L1/2 (Yonetoku)

  14. e± line & cutoff Murase&KI 08 Lithwick&Sari 01 gg→e＋e－ Comoving size

  15. Closure relation Murase&KI 08 Gupta&Zhang 08 ⇐ e± cutoff ⇐ e± photosphere Relation between only observables → Model checking Luminosity ∝ n (photon density) x e (photon energy) ⇒ Also, the emission radius r, t, e±-p ratio Even non-detection can constrain parameters

  16. Contents GRB emission mechanism Synchrotron vs. Photosphere Unstable photosphere ⇒ Non-thermal Blueshifted e± line(bump) ⇒ GLAST Closure relations between e± line & cutoff Suzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Lisorelation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

  17. Time-resolved Ep-Liso Suzaku WAM (50-5000keV) Ep~Liso1/2 even for 1sec spectra (~Liang+ 04) All outliers belong to the pulse rising phase GRB061007 Ohno,KI+ 08 Synchro: Ep~(L/r2)1/2 Photo: Ep~(G/r)1/2L1/4 r expand / G decelerate : Fireball dynamics

  18. Ep-Liso for short GRBs Suzaku WAM (50-5000keV) Ep~Liso1/2 (Yonetoku) Ep z-known short GRBs Ep~L-1/4 Not satisfy the Yonetoku rela.? … because of no stellar envelope? PRELIMINARY Ohno+ 08 Liso

  19. Self-created photosphere? No stellar envelope for short GRB ⇒ rphoto ≠ r* 1. Assume energy equipartition (g~matter) T’4~npmpc2 (w/o e±) T’4~n±mec2 (w/ e±) 2. Assume the photospheremodel t~npsT(r/G)~1 Ep~GT’~(G/r)1/2L1/4 t~n±sT(r/G)~1 Ep~GT’~(G/r)1/2L1/4 Self-determined photospheric radius ⇒ Ep~G2 L-1/4: Anti-correlation?

  20. Contents GRB emission mechanism Synchrotron vs. Photosphere Unstable e±photosphere ⇒ Non-thermal Blueshifted e± line(bump) ⇒ GLAST Closure relations between e± line & cutoff Suzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Lisorelation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

  21. Increasing TeV sources “Kifune plot” In the TeV sky, most sources are unidentified! Jim Hinton, rapporteurtalk, ICRC 2007

  22. Observed properties TeV unID Disk ⇒ Galactic origin d~1-10kpc Extended

  23. Radioisotope acceleration 56Ni ⇐ SN light curve 1998bw: M(56Ni)~0.4M◉ ~2MeV Could be shock-accelerated before decay (by reverse shock?) KI&Mészáros GRB/Hypernova as RI beam factory

  24. RI decay model 56Co case KI&Mészáros 56Co energy Hypernova OK ~unIDs SNR disappears: good for explaining unIDs ~unIDs Radioactive Hypernova Remnant ~ TeV unID sources

  25. Summary GRB emission mechanism Synchrotron vs. Photosphere Unstable photosphere ⇒ Non-thermal Blueshifted e± line(bump) ⇒ GLAST Closure relations between e± line & cutoff Suzaku/WAM + Swift/BAT Time-resolved Ep-Liso (Yonetoku) relation Ep-Lisorelation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

  26. Counter arguments? Steep decay Residual collision (Li & Waxman 07) May not be curvature emisssion (Barniol Duran&Kumar 08) g Prompt optical emission Self-absorption is effective if the emission radius is small But it may be residual collision v~c g Opt Not so much delay

  27. Decay properties Decay mode Half-life 56Ni Electron capture 6.1 day (>104yr: Ion) 56Co EC (81%) 77.2 day b+ (19%) (x5: Ion) 57Ni EC 35.60 hr b+

  28. Spectrum tdecay~106g6yr eg~TeVg6 t nFn n(2-p)-1 Exp. cutoff Already decayed Now decaying ~GeV n ~TeV

  29. High energy ne tdecay~106g6yr eg~TeVg6 t nFn n(2-p)-1 Exp. cutoff Similar as g-ray Already decayed Now decaying Detection may be difficult ~GeV n ~TeV

  30. Swift – Short GRBs Swift：＜150keV ⇒short hard are missed? Sakamoto+07 Short GRBs are really few?

  31. Suzaku/WAM – Short GRBs Tashiro+ 08

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