京大天体核 D3 山崎 了
共同研究者 : 井岡 邦仁(阪大)、中村 卓史(京大)
Ref. Yamazaki et al., astro-ph/0401044
Light Curves of XRFs &
GRBs
X-ray flash (XRF)
γ-ray burst (GRB)
X-ray band
γ- ray band
Spectral properties of XRFs and
GRBs
Double power-low form fits spectra of XRFs and GRBs.
XRF
Ep=19 keV
GRB
Ep=126 keV
Photon indices α, β (スペクトルの傾き) は GRB と XRF で同じ。
XRF の Ep (peak energy) は GRB のものよりも小さい。
Rest frame Ep - Eiso
relation
(for GRBs and XRFs
with known redshifts)
XRF(X-ray rich GRB) と GRB GRB
の
･ スペクトル以外の性質(duration, event rate 等)
は同じ。
･ 観測量の分布は連続的。
X-ray rich GRB
⇒ 両者の起源は同一であると考えられている。
XRF
(1+z) Ep ∝ Eiso1/2
Theoretical Models of the X-ray
flash
1. High redshift GRBs (Heise et al. 2001)
2. External shocks with small Lorentz factors
(Dermer et al. 1999; Rossi et al. 2001)
3. Internal shocks with high Lorentz factors
(Mochkovitch et al. 2003)
4. Photosphere-dominated fireball
’ ’
(Meszaros
et al. 2002; Drenkahn 2002)
5. Jets with wide opening angles (Lamb et al. 2003)
6. Off-Axis GRBs (Yamazaki et al. 2002, 2003)
Ｏff-Axis Jet Model of XRFs
The X-ray flashes (and the soft GRBs) are the typical GRBs
observed from off-axis viewing angle.
relativistic beaming
effect
νFν
X-ray band
γ-ray band
XRFs
GRB
GRBs
XRF
jet
(γ～100)
relativistic Doppler
effect
ν
Ep - Eiso relation in off-axis jet
model
Ep ～ ν0δ
ν0 : frequency in the jet-comoving frame
δ-1 = γ(1-βcosθ) ～[1+ (γθ)2]/(2γ)
γ= 100 : Lorentz factor of the jet
θ= θｖ- Δθ (<< 1 )
Eiso ∝δ1-α
α= -1～-2 : photon index
⇒ Ep ∝ Eiso1/(1-α)
～ Eiso1/3～1/2
LOS
Jet Emission Model (Yamazaki et al.
2003)
・Spontaneous emission from
instantaneously thin shell.
Line of sight
・Normalization of emissivity;
isotropic γ-ray energy from the
source with z = 1 and θｖ= 0 satisfies
Eγ= Eiso (Δθ)2 /2 = 1×1051 ergs (Bloom et al. 2003)
where Eiso = 4πdL2 (1+z)-1 Sγ ( Sγ; obs. fluence )
・Emission spectrum in the comoving frame
zmax : maximum redshift
Maximum redshift to be detected by
HETE
Δθ/γ-1 =10
γ = 100
α = -1
β = -2.5
γν’０ = 500 keV
Δθ/γ-1 = 5
Slim(2-400 keV)
= 5×10-8 erg/cm2
Viewing angle θV / γ-1
Input parameters (10,000
events)
α
β
z
Δθ
for z=0, θV=0
Result of Simulation : Ep – Eiso
relation
HETE detects 288 events among 10000 simulated bursts.
Soft events (<100 keV)
are off-axis emissions!
obs.
best fit
209 on-axis events
79 off-axis events
62 GRBs
192 XRR-GRBs
34 XRFs
＋ : detected by HETE (on-axis)
× : detected by HETE (off-axis)
･ : not detected by HETE
Summary
Off-axis emission from z～1 can be observable.
The Ep-Eiso relation may be reproduced by the off-axis
jet model : off-axis emission represents large portion
of the X-ray flash.
The Ep-Eiso relation, the Ep-distribution, the hardness
distribution etc. depend on the unknown functional
form of the opening angle distribution.
⇒ Ep-Eiso relation constrains the jet opening angle
distribution, and therefore the ratio of GRBs to
core-collapse SNe !!!

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