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) Please search with “KEK”

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 E p -L iso (Yonetoku) relation E p -L iso relation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

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

Problem 1 1. Low-energy spectral index 2. E peak relations (Amati/Yonetoku/Girlanda) Excluded Preece+ 00 F Superposition of synchrotron spec. 1/3 High GRB efficiency ⇒ t cool << t dyn -1/2 Ghisellini+ 00 Mészáros&Rees 00 But, Bosnjak+ 00

Problem 2 E p ~L iso 1/2 E p ~E syn ~  B’  e 2 ~B~U 1/2 ~(L/r 2 ) 1/2 ~L 1/2  -2  t -1 (with r~c  2  t) ⇒ Small  ⇒ Low GRB efficiency?? 1. Low-energy spectral index 2. E peak relations (Amati/Yonetoku/Girlanda) Synchrotron model: Yonetoku+ 03, Kodama+ 08 Also Willingale+ 07 Kobayashi+ 98

Photosphere model Zhang+(04) Strong dissipation within the star  ~1 emission ⇒ GRB 1. Hard low-energy index F ~ 2 2. E peak ~Thermal peak Stefan-Boltzmann law E p ~  T’~  (L/  2 r 2 ) 1/4 ~(  /r) 1/2 L 1/4 (if r~r WR*,  ~  -1, Frail L~  -2, then ~L 1/2 ) 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 (g~3x10 4 cm s -2 on the sun) Light g Rough Idea Heavy ⇒ Large effective gravity ⇒ Heavy parts fall & grow ⇒ Shocks ⇒ Non-thermal Comoving Frame KI+ 07

Unstable photosphere? High GRB efficiency ⇒ Radiation-dom. fireball ⇒ Radiative acceleration (g~3x10 4 cm s -2 on the sun) e±e± g Rough Idea Proton (+e) Proton (+e) Proton (+e) ⇒ Large effective gravity ⇒ Heavy parts fall & grow ⇒ Shocks ⇒ Non-thermal Comoving Frame KI+ 07

e ± pair n ± >n e-p is not unlikely since m p ~10 3 m e Radiation pushes e ± more than e-p  ~1 F thermal  →e + e - If E ± ~E proton ⇒ n ± ~10 3 n e-p Not all e ± annihilate since  ~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-thermal e ± heating ≈ cooling without fine-tuning even if t cool <t dyn

Spectrum Shock (p-e ⇔ e ± ) ⇒ e ± acceleration ⇒ Inverse Compton Non-thermal energy ~Proton kinetic energy ~Afterglow energy ee ~1 N(  e ) Electron spectrum ~  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  ~L 1/2 (Yonetoku) 0.5MeV x  ~ 0.5  3 GeV GLAST  KI+ 07 Pe’er+ 06

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

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

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 E p -L iso (Yonetoku) relation E p -L iso relation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

Time-resolved E p -L iso Suzaku WAM ( keV) E p ~L iso 1/2 even for 1sec spectra (~Liang+ 04) GRB All outliers belong to the pulse rising phase Synchro: E p ~(L/r 2 ) 1/2 Photo: E p ~(  /r) 1/2 L 1/4 Ohno,KI+ 08 r expand /  decelerate : Fireball dynamics

E p -L iso for short GRBs Suzaku WAM ( keV) EpEp L iso z-known short GRBs PRELIMINARY E p ~L iso 1/2 (Yonetoku) Ohno+ 08 Not satisfy the Yonetoku rela.? … because of no stellar envelope? E p ~L -1/4

Self-created photosphere? No stellar envelope for short GRB ⇒ r photo ≠ r *  ~n ±  T (r/  )~1 E p ~  T’~(  /r) 1/2 L 1/4 1. Assume energy equipartition (  ~matter) T’ 4 ~n p m p c 2 (w/o e ± )T’ 4 ~n ± m e c 2 (w/ e ± ) 2. Assume the photosphere model  ~n p  T (r/  )~1 E p ~  T’~(  /r) 1/2 L 1/4 ⇒ E p ~  2 L -1/4 : Anti-correlation? Self-determined photospheric radius

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 E p -L iso (Yonetoku) relation E p -L iso relation for short GRBs Hypernova 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 TeV unID Disk ⇒ Galactic origin d~1-10kpc Extended

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

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

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 E p -L iso (Yonetoku) relation E p -L iso relation for short GRBs Hypernova remnants as TeV unID sources Decay of accelerated radioisotope

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

Decay properties Decay mode Half-life 56 Ni Electron capture 6.1 day (>10 4 yr: Ion) 56 Co EC (81%) 77.2 day  + (19%) (x5: Ion) 57 Ni EC hr  +

Spectrum (2-p)-1 F Exp. cutoff ~TeV t decay ~10 6  6 yr   ~TeV  6 ~GeV Already decayedNow decaying t

High energy e (2-p)-1 F Exp. cutoff ~TeV t decay ~10 6  6 yr   ~TeV  6 ~GeV Already decayedNow decaying Similar as  -ray Detection may be difficult t

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

Suzaku/WAM – Short GRBs Tashiro+ 08