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/

Light Curves of XRFs & GRBs X-ray band γ - ray band X-ray flash (XRF)γ-ray burst (GRB)

Spectral properties of XRFs and GRBs Double power-low form fits spectra of XRFs and GRBs. 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。 Ep=126 keVEp=19 keV XRF GRB

Rest frame Ep - E iso relation XRF GRB X-ray rich GRB XRF(X-ray rich GRB) と 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。 ⇒ 両者の起源は同一であると考えられている。 (1+z) Ep ∝ E iso 1/2 (for GRBs and XRFs with known redshifts)

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) ’ ’

Ｏ ff-Axis Jet Model of XRFs The X-ray flashes (and the soft GRBs) are the typical GRBs observed from off-axis viewing angle. (γ ～ 100) XRFs GRB s jet X-ray band νFν νFν ν γ-ray band relativistic Doppler effect relativistic beaming effect GRB XRF

LOS Ep - E iso relation in off-axis jet model ν 0 : frequency in the jet-comoving frame θ= θ ｖ - Δθ (<< 1 ) γ= 100 : Lorentz factor of the jet Ep ～ ν 0 δ δ -1 = γ(1-βcosθ) ～ [1+ (γθ) 2 ]/(2γ) E iso ∝ δ 1-α α= -1 ～ -2 : photon index ⇒ Ep ∝ E iso 1/(1-α) ～ E iso 1/3 ～ 1/2

Line of sight Jet Emission Model (Yamazaki et al. 2003) ・ Spontaneous emission from instantaneously thin shell. ・ Normalization of emissivity; isotropic γ-ray energy from the source with z = 1 and θ ｖ = 0 satisfies E γ = E iso (Δθ) 2 /2 = 1×10 51 ergs (Bloom et al. 2003) where E iso = 4πd L 2 (1+z) -1 S γ ( S γ ; obs. fluence ) ・ Emission spectrum in the comoving frame

Maximum redshift to be detected by HETE γ = 100 z max : maximum redshift Viewing angle θ V / γ -1 α = -1 β = -2.5 γν ’ ０ = 500 keV S lim (2-400 keV) = 5×10 -8 erg/cm 2 Δθ/γ -1 = 5 Δθ/γ -1 =10

Input parameters (10,000 events) for z=0, θ V =0 z α β Δθ

Result of Simulation : Ep – E iso relation obs. best fit Soft events (<100 keV) are off-axis emissions! HETE detects 288 events among simulated bursts. 79 off-axis events 209 on-axis events 62 GRBs 192 XRR-GRBs 34 XRFs × : detected by HETE (off-axis) ＋ : detected by HETE (on-axis) ･ : not detected by HETE

Summary Off-axis emission from z ～ 1 can be observable. The Ep-E iso relation may be reproduced by the off- axis jet model : off-axis emission represents large portion of the X-ray flash. The Ep-E iso relation, the Ep-distribution, the hardness distribution etc. depend on the unknown functional form of the opening angle distribution. ⇒ Ep-E iso relation constrains the jet opening angle distribution, and therefore the ratio of GRBs to core-collapse SNe !!!