1. 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.

2. Temporal Characteristics
light curve
profiles
complicated
durations
～ ms s
variabilities
～ 1ms ,
even ～ 0.1ms

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

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

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

7. 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

9. Seminal papers on GRB fireball models

10. 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 )

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

12. Characteristic radii of GRB
fireball-photosphere-internal shocks

13. 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 C (Fermi GBM/LAT) – evidence of highly magnetization of the initial fireball of this burst!
Zhang & Pe’er 2009

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

15. Static Photosphere
(un-relativistic)

16. Relativistic Photosphere

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

18. Relativistic Photosphere

19. Relativistic Photosphere
Approximation：

20. Relativistic Photosphere

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

22. 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)

23. 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

25. Analytical Approach of mBB Model
For m<-1

26. mBB Model: Analytical vs. Accurate

27. Light Curve of GRB081221

28. Time-Resolved Spectra in 081221

29. Summary of Time-Resolved Spectral Fit

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

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

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

34. Relativistic Photosphere

38. High efficiency photosphere

39. High efficiency photosphere

40. High efficiency photosphere

41. Low efficiency photosphere

42. Low efficiency photosphere

44. Low efficiency photosphere
Constraint-1

45. Low efficiency photosphere
Constraint-2

46. Low efficiency photosphere
Constraint-3

47. Low efficiency photosphere
Constraint-1,2 & 3

48. GRB
GRB
GRB
GRB
GRB B

59. Correlations in Luminosities

66. Luminosity – Lorentz Factor Correlations

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

71. Temperature-Related Correlations

75. Gamma - Epeak Correlation?
Ghirlanda et al 2012

77. Yonetoku Relation？
Lu et al 2012

78. Thank You