Photospheric emission from
Stratified Jets
Hirotaka Ito RIKENCollaborators
Shigehiro Nagataki
RIKEN
Masaomi Ono
Kyushu Univ.
Shiu-Hang Lee
RIKEN
Jirong Mao
RIKEN
Shoichi Yamada
Waseda Univ.
Asaf Pe’er
UCC
Akira Mizuta
RIKEN
Seiji Harikae
Mitsubishi UFJ

＠sngrb 2013 11/12

Model for Emission Mechanism
Internal Shock Modelflaw

・Low efficiency for gamma-ray production
・too hard spectrum in low energy band (α)

Photospheric Emission Model
Natural consequence of fireball model(e.g., Rees & Meszaros 2005, Pe’er et al.2005, Thompson 2007)γγ

photosphere

Internal shock
External shockModel for Emission Mechanism
Internal Shock Modelflaw

・Low efficiency for gamma-ray production
・too hard spectrum in low energy band (α)

Photospheric Emission Model
Natural consequence of fireball model(e.g., Rees & Meszaros 2005, Pe’er et al.2005, Thompson 2007)• High emission efficiency• Peak at ~1 MeV• Non-thermal appearance
E (MeV)Dissipative process
Magnetic recconection
Giannios & Spruit 2007, Giannios 2008

Repeated Shock
Ioka + 2007, Lazzati & Begelman 2010

Proton-neutron collision

Physical broadening

relativistic pairs upscatterthermal photons

Derishev 1999, Beloborodov 2009, Vurm+2011

Geometrical broadening A. Pe’er’s talk: Lundman & Pe’er (2013)
Structure of the jet can give rise to the non-thermal spectra

Mizuta+2011

Multi-dimensional structure of jet may be a key to resolve the difficultyOur focus: Effect of the jet structure on the emission
Find the jet structure that can explain the observation
Pe’er’s talk : Lundman & Pe’er (2013)

Stratified Jet structure

2 effects on the spectra(I) multi-color effect(II) Fermi acceleration ofphotons

Accleration
regionPhotons gain energy bycrossing the boundary layer

photosphere

νfν

t~1
Spine

Sheath

G0 > G1nPropagation of photons are solved by Monte=Carlo methodTwo-component jet
G0=400 qj =1° q0=0.5° qobs=0.4°
Thermal + non-thermal tailSpine

SheathEmax = G0mec2
Klein-Nishina cut-off

Non-thermal tail becomes prominent as the relative
velocity becomes larger-1 ～0.14°G -1
But limited only for small range of |θ
θ|
<Gobs
0400
observer angle

Multi-component jet
G0=400 G1=100

β= -2.3
α=-1dθ

Interval of velocity shear dθ < 2G-1

high energy spectra (β) is reproduced by accelerated photons
Low energy spectra (α) is reproduced by multi-color effect(Lundman & Pe’er 2013)polarization
two-component jet
DOP （％）＝(I+ - I-) / (I+ + I-) ×１００

Spine
edge

0%

qobs (degree)

Degree of polarization (DOP) becomes larger
as the relative velocity becomes large

SheathI+I-DOP（％）＝(I+ - I-) / (I+ + I-) ×１００

polarization
multi-component jet that reproduces Band spectra
G0=400 G1=1005%edge

0%0%dθ5%

qobs (degree)

High polarization degree (>10%) is predicted not onlyin the off-axis region but also in the on-axis region

On-going project2D Hydrodymical simulation of relativistic jet as a background fluid
Mizuta+2011

Distribution the last scattering position

Detail of spectra, polarization and lightcurves for more realistic
case can be obtained

3D Hydrodymical simulation of relativistic jet as a background fluid
simulation by J. MatsumotoSummary
jet can produce a power-law non-thermal tail- Stratified
above the peak energy
non-thermal particle is not required- Multi-component jet can reproduce Band function irrespective tothe observer angle
β is reproduced by the accelerated photons
α is reproduced by the multi-color effect- Degree of polarization tends to increase as the relative velocity
increases
High DOP (>10%) is predicted for the jet structure that
reproduces Band function

Futrure works
・Photon accelerations in various structures
shocks, turbulence・Hydrodymical simulation of relativistic jet as a background fluid