Photosphere Emission in Gamma-Ray Bursts 4th Fermi Asian Network Workshop, HKU, July 8-12, 2013 Photosphere Emission in Gamma-Ray Bursts Xuefeng Wu Purple Mountain Observatory Chinese Center for Antarctic Astronomy Chinese Academy of Sciences Collaborators: Shujin Hou, Zigao Dai, Bing Zhang, Enwei Liang, Tan Lu et al.

Temporal Characteristics light curve profiles complicated durations ～ ms - 1000 s variabilities ～ 1ms , even ～ 0.1ms

Spectral Characteristics photon energies： 10keV – 10GeV non-thermal GRB090510 GRB090902B multi-color blackbody

GRBs：stellar explosions δT ～ ms  Ri ≤ cδT = 300 km (Ri: emission size) Blackhole： R = 2GM/c2  M ≤ 100 M⊙   GRBs: stellar objects (compact stars)

GRBs：energy bugget DL ~ 3 Gpc Eisotropic = 4DL２Fγ ~ 1051 erg Fγ ~ 10-6 erg/cm2 DL ~ 3 Gpc Eisotropic = 4DL２Fγ ~ 1051 erg EGRB970228 ~ 1051 erg EGRB990123 ~ 1054 erg unisotropic Jet? This redshift indicates the distance. So, we calculate the distance of GRB970228. Furthermore, from the detected gamma-ray fluence, we easily calculate the isotropic-equivalent energies of GRB970228 and GRB990123. These energies vary from 10^51 to 10^54 ergs.

Expanding Fireball Lorentz factor:  >>1 ultra-relativistic The fireball will expand and accelerate to be ultra-relativistic driven by the high radiation temperature and pressure, while the optical depth decreases from extremely thick to thin and produce non-thermal emission. Ri ≤ cδT non-thermal spectrum optically thick  solution  optical thin  ultra-relativistic Lorentz factor:  >>1    

Seminal papers on GRB fireball models

Acceleration of GRB baryonic fireball Ideal hydrodynamic assumption： outside is vacuum (environmental density is low) Photons are coupled (optical depth > 1) Baryons and photons are coupled (lepton-photon scattering depth > 1) Conservations of energy, momentum and particle number： ( energy ) ( momentum ) ( particle number )

Scaling laws of accelerating fireball radiation-dominated epoch matter-dominated epoch

Characteristic radii of GRB fireball-photosphere-internal shocks

Long Way in Discovery of GRB Fireball Emission Since 1997，cosmological GRB internal-external shocks models have been confirmed by many observations； No thermal emission was detected from the energetic GRB 080916C (Fermi GBM/LAT) – evidence of highly magnetization of the initial fireball of this burst! Zhang & Pe’er 2009

Long Way in Discovery of GRB Fireball Emission Thermal emission from GRB fireball photosphere was first discovered (with high confidence level) in GRB 090902B by Fermi Thermal emission have been found in a few GRBs, such as 970828、 081221、090510、090618 GRB 081221 GRB 090902B Ryde et al. 2009 Hou et al. 2013

Static Photosphere (un-relativistic)

Relativistic Photosphere

Relativistic Photosphere Assumptions： （1）do not consider the Equal Arrival Time Surface Effect； （2）impulsive photosphere; （3）uniform fireball

Relativistic Photosphere

Relativistic Photosphere Approximation：

Relativistic Photosphere

Thermal Spectrum from a Relativistic Photosphere wider than Planck function！ we call it“relativistic Planck function”

Realistic Relativistic Photosphere （1）fireball is not isotropic （2）there are many fireballs in a GRB （3）equal arrival time surface effect  multi-color black body (mBB)

multi-color black body Model of multi-color black body (mBB) Single black body see Ryde et al. (2009) A(>Tmin) =1, normalization multi-color black body

Analytical Approach of mBB Model For m<-1

mBB Model: Analytical vs. Accurate

Light Curve of GRB081221

Time-Resolved Spectra in 081221

Summary of Time-Resolved Spectral Fit

Time-Integrated Spectrum of 081221 Time-resolved spectral models are not self-consistent with time-integrated spectrum！

Moments of temperature of mBB For 081221: See Hou Shujin’s Poster ~ (9.9 keV)^4 ~ 7.1 keV

Comparison with 090902B (time-integrated spectrum) Rayleigh – Jeans part not observed m ~ -4 Rayleigh – Jeans part observed ! GRB 090902B GRB 081221 Ryde et al. 2009 Hou et al. 2013

Relativistic Photosphere

High efficiency photosphere

High efficiency photosphere

High efficiency photosphere

Low efficiency photosphere

Low efficiency photosphere

Low efficiency photosphere Constraint-1

Low efficiency photosphere Constraint-2

Low efficiency photosphere Constraint-3

Low efficiency photosphere Constraint-1,2 & 3

GRB 970828 GRB 081221 GRB 090510 GRB 090618 GRB 090902B

Correlations in Luminosities

Luminosity – Lorentz Factor Correlations

Gamma - Luminosity Relation Lv et al 2012; Fan et al 2012

Temperature-Related Correlations

Gamma - Epeak Correlation? Ghirlanda et al 2012

Yonetoku Relation？ Lu et al 2012

Thank You