1. First Stars and GRBs, and their Cosmological Impacts
Masayuki Umemura
University of Tsukuba, Center for Computational Sciences
Collaborators
Susa, Suwa, Mori, Yajima, Nakamoto, Murakami,
Yonetoku, Matsubayashi, Yamazaki , Hirose,
Yonehara, Sato, Hosoda, Aoyama

2. Contents Part I - Reionization by Pop III Stars
Part II - Indicators for Ancient GRBs

3. Part I - Reionization by Pop III Stars
Degeneracy
- Star formation rate in high-z objects
- Escape fraction of ionizing photons

4. Amati -Yonetoku Relation
(Ep‐Eiso,Lp)
Ep‐Eiso relation
Ep‐Lp relation
Amati et al. 2002, A&A, 390, 81
Amati 2006, MNRAS, 372, 233
Yonetoku et al. 2004, ApJ, 609, 935
Ep(1+z)∝ (Eiso)a, a=
L52 = 4.29×10-5 [ Ep (1+z) ]1.94

5. Pop III SFR derived from GRB Events
Murakami, Yonetoku, MU, Matsubayashi, Yamazaki 2005, ApJ, 625, L13
689 GRBs
Ep-Luminosity
relation

6. Reionization criterion
fesc>3-10% at z=10
from GRB event rate
escape
fraction
inhomogeneous IGM reionization
homogeneous IGM reionization

7. Reionization with GRB-derived SFR
Wyithe et al, 2010, MNRAS, 401, 2561
Semi-analytic model + Ly forest + WMAP 5 year
fesc=3-6% (68% confidence)

8. Simulations of Reionization by Pop III Stars
Cen 2003; Ciardi, Ferrara & White 2003;　Somerville & Livio 2003; Fukugita & Kawasaki 2003; Wyithe & Loeb 2003; Sokasian et al. 2004; Ricotti & Ostriker 2004
Sokasian et al. 2004, MNRAS, 350, 47
1 Pop III star per halo of 106M, fesc=1
WMAP 1st year te=0.17±0.04 (Spergel+03)
WMAP Five year te=0.084±0.016 (Komatsu+09)

9. What is the Mass & Number of First Objects ?
Yoshida et al , ApJ, 592, 645
 CDM context
(Yoshida et al. 2003; O’Shea & Norman 2007)
M<MJ
MMJ
M>MJ
Jeans instability
through H2 cooling
runaway
Mhalo,cr  7105 M
Mb,cr  105 M
6h-1Mpc
mass resolution
mb =30 M

10. Collapse of First Objects P3M-GRAPE-SPH Simulations Suwa, MU, Susa
z =30
WMAP CDM cosmology
zin=1200, 60kpc [comoving]3
Baryon mass: 2106M
Dark matter mass: 1107M
z =20
3 x 108 particles
for baryon + dark matter
Maximum mass resolution:
0.07M in DM
0.014M in baryon
No change of mass resolution throughout the simulation
z =16

11. Formation of First Stars
Resolution
Low
P3M SPH Simualtion
(Suwa, MU, Susa 2010)
z=50
z=30
z=40
low resolution
106 particles
mb=2.94M
high resolution
107 particles
mb=0.367M
ultra high resolution
108 particles
mb=0.046M
High

12. Growth of Dark Matter Cusps
low resolution
high resolution
ultra high resolution
N=5×105
mDM=38M
N=4×106 mDM=4.8M
N=3×107 mDM=0.6M
z=16
M(r)
  r -1.5
baryon
Jeans
mass
dark matter
r (kpc)
1pc
1pc
1pc
Collapse driven by dark matter cusps.
Minimm mass Mb,min103M

13. fesc a few % Dark matter cusps can reduce the minimum mass of
firsts objects from Mb,min105M down to 103M.
(Direct collapse to first stars)
The number of first stars could be larger by more than
an order of magnitude than previous prediction.
fesc a few %

14. Escape Fraction from Primordial Galaxies
Yajima, MU, Mori, Nakamoto, 2009, MNRAS, 398, 715
3D Radiative Transfer Calaculation
LAE phase
LBG phase
gas
dust
stars HI

15. Escape Fraction of Ionizing Photons
fesc=0.07–0.47 in LAE phase
fesc=0.06–0.17 in LBG phase
LAE phase
LBG phase
Escape fraction in Pop III objects could be significantly smaller
than that in LAEs.

16. Part II - Indicators for First GRBs
Microlensing of GRBs by an intervening Pop III star
Damping of CMB by TeV- photons from GRBs

17. Microlensing of GRBs by Pop III Stars
Hirose, MU, Yonehara, Sato, 2006, ApJ, 650, 252
Image 1
Observer
GRB
Pop III Star
Image2
Time delay：
intrinsic
light curve
Image 1
lensed
light curve
Photon number
(Point mass)
Image 2 t

18. Auto-correlation 1 (=64msn) lensed light curve C( ) I(t) τlens
τlens τ

19. Test by Artificial Lensing
GRB
(z=0.835)
800
Intrinsic light curve
Intrinsic light curve
700
600
500
110
120
130
140
150
160
170
lensed
Photon number/64ms
3000
Total
1st image
2000
2nd image
1000
500
Time (s)
source redshift

20. Autocorrelation of Artificially Lensed GRB Lightcurves

21. PopIII mass
1 + zL 10
100
zL 10
50
Time delay
Lens Mass
t=1s
Lens Pop III should be at zlens>10, and therefore zGRB>zlens.

22. Bump detection probability for Lensed GRBs

23. SWIFT Data Analysis 111GRB lightcurves (GRB 050401 - GRB 091130B)
Results
98/111GRBs show almost featureless autocorrelation
(suggestive for GRB nature?)
3/111GRBs exhibit bumps in autocorrelation

24. GRB z=8.2
Time resolution is not sufficient to analyze the autocorrelation !

25. Light curve Autocorrelation Light curve Autocorrelation GRB 060105
blue: Windowed Timing (WT) data
red: Photon Counting (PC) data
Light curve
Autocorrelation
Light curve
Autocorrelation
GRB
GRB
GRB
GRB
GRB
GRB

26. GRB 070129 t(bump)=1.9s GRB 090424 t(bump)=2.4s z=0.544 GRB 090904A
*I-band detection
(I=20.60.04)
*Dust scattered X-ray
halo
GRB
t(bump)=2.4s
z=0.544
GRB A
t(bump)=1.8s
z=?

27. On-the-Spot Collision of GRB TeV- with CMB Photons
GRB fireball
pair-production
TeV-
CMB photon
Pair production cross section

28. Model Total energy Fireball radius Energy spectrum
(Aharonian et al. 2005, 2007)
GRB redshift

29. Damping of CMB by High-z GRBs
Differential optical depth
for pair production
Optical depth at zGRB
Damped CMB at zGRB
Damped CMB at z=0
(Observation)

30. Damping of CMB by High-z GRBs
R=3×109 cm, Emax=30TeV
νpeak=1.6×1011Hz : peak frequency of CMB at z=0
100%
z=30
z=20
z=10 1%
Damping factor
νpeak
frequency (Hz)

31. R=3×109 cm, Emax=50TeV 100% Damping factor 1% νpeak frequency (Hz)
νpeak=1.6×1011Hz : peak frequency of CMB at z=0
100%
z=30
z=20
z=10
Damping factor 1%
νpeak
frequency (Hz)

32. SUMMARY Part I - Reionization by Pop III Stars
is concordant with WMAP5 if the escape fraction is
a few %,which may be significantly smaller than LAEs.
Part II - Indicators for Ancient GRBs
Microlensing of GRBs by an intervening Pop III star
needs more data with high time resolution
Damping of CMB by TeV- photons in high-z GRBs
could be detected, if CMB is observed shortly after
GRB event.

33. Thank you