Gamma-Ray Bursts and

Their Cosmological Use

Dai Zigao

Nanjing University

Collaborators: Liang En-Wei, Xu Dong, Wang Fa-Yin

报告目录1.伽玛暴是什么？2.最新进展是什么？3.伽玛暴宇宙学是什么？

报告目录1.伽玛暴是什么？2.最新进展是什么？3.伽玛暴宇宙学是什么？

Gamma-ray bursts are short-duration flashes of gamma rays occurring at cosmological distances.

Temporal features: diverse and spiky light curves

Gamma-Ray Bursts

log

GRB spectra: broken power laws with Ep of a few tens to hundreds of keV

报告目录1.伽玛暴是什么？2.最新进展是什么？3.伽玛暴宇宙学是什么？

Five erasFive eras

1) “Dark” era (1973-1991): discovery

Klebesadel, Strong & Olson’s discovery (1973);

2) BATSE era (1992-1996): spatial distribution

Meegan & Fishman’s discovery (1992),

detection rate: ~1 to 3 /day, ~3000 bursts;

3) BeppoSAX era (1997-2000): afterglows

van Paradijs, Costa, Frail’s discoveries (1997);

4) HETE-2 era (2001-2004): origin of long bursts

Observations on GRB030329/SN2003dh

5) Swift era (2005-): very early afterglows, short-

GRB afterglow, subclasses? GRB cosmology?

Gehrels et al. 2004; Launch on 20 November 2004

ν ~(5-18)x1014 Hz

Discoveries in the Swift eraBefore July 2005

① X-ray afterglow of a short GRB

② Prompt optical-IR emission and very early optical afterglows

③ X-ray flares from three long bursts

④ Early steep decay of X-ray afterglows

⑤ Hard electron energy distribution

Luminous, non star-forming elliptical galaxy at z = 0.225

X-ray afterglow of a short GRB 050509b (T~30 ms, Gehrels et al. 2005, Nature, submitted)

Rosswog et al., astro-ph/0306418

Li H., Dai Z.G., & Zhang X.M. 2005, Phys. Rev. D, 71, 113003

Measuring neutrino mass with short bursts

Prompt optical-IR emission and very early optical afterglows

Vestrand et al. 2005, Nature, 435, 178Blake et al. 2005, Nature, 435, 181

GRB050525A: Shao L. & Dai Z.G. (2005, ApJ, submitted)

X-ray flares from two long bursts

Burrows et al. 2005, Science, submitted

X-ray flares: delayed internal shocks;

Late bumps: delayed central engine activity.

Early steep decay of three X-ray afterglows

Tagliaferri et al. 2005, Nature, in press (also see Chincarini et al. 2005)

Initial steep decay: adiabatic expansion of relativistic shocked matter (Kumar et al. 2000);

Flattening: continuous energy injection (Dai & Lu 1998, PRL, 81, 4301; Dai 2004, ApJ, 606, 1000; Zhang & Meszaros 2001)

Final steepening: forward shock emission

Hard electron energy distribution: GRB041223(Burrows et al. 2005, ApJ, 622, L85)

From Dai & Cheng (2001, ApJ, 558, L109)

Question: Why 1 < p < 2 ?

InnerEngine

Relativistic Wind

ExternalShocks

Afterglow

InternalShocks

gamma-rays

Thanks to rapid localization of Swift,• X-ray afterglow of a short GRB• Very early optical/X-ray afterglows

Confirming the fireball-shock model

Summary: discoveries

报告目录1.伽玛暴是什么？2.最新进展是什么？3.伽玛暴宇宙学是什么？

Gamma-Ray Burst Cosmology

1. High-z star-formation rate

2. High-z intergalactic medium (reionization)

3. Cosmic expansion and dark energy

Studies on cosmic structure, evolution, and dark energy with gamma-ray bursts

Evidence for long GRB-Massive Stars1. GRBs are in star-forming regions.2. The burst rate is proportional to the star-formation

rate.3. The host galaxy is a star-burst one.4. GRB980425/GRB030329 are associated with

SN1998bw/SN2003dh, respectively. 5. Supernova-like components appear in afterglow light

curves. 6. The iron emission line appears in the X-ray afterglow

spectrum.7. Some X-ray afterglows imply high column densities. 8. Prompt soft X-ray absorption requires dense media.

Evidence 4: The supernova (SN1998bw, z=0.0085) associated with GRB980425GRB980425 is type-Ic (Galama et al. 1998).

J. Hjorth, et al., Nature, 423, (2003) 847-850

Strong evidence from GRB030329/SN2003dh tSN-tGRB=±2days.

Evidence 6: The iron emission line implies a pre-burst supernova explosion (Antonelli et al. 2001).

GRB000214: Valentine’s Day Burst

GRBs are believed to be detectable out to very high redshifts up to z~25 (the first stars: Lamb & Reichart 2000; Ciardi & Loeb 2000; Bromm & Loeb 2002). SNe Ia are detected only at redshifts of z ~1.7.

SN

1. Exploring high-z star-formation rateNatarajan et al., astro-ph/0505496

2. Exploring high-z intergalactic medium (reionization)Ciardi & Loeb 2000, ApJ, 540, 687

IGM absorption profiles in GRB optical afterglows: Barkana & Loeb 2004, ApJ, 601, 64

z=7

Cosmic dispersion measure and reionization history

Ioka 2003, ApJ, 598, L79

Supernovae CosmologyWhen the mass of an accreting white dwarf increases to the Chandrasekhar limit, this star explodes as an SN Ia.

Hamuy et al. (1993, 1995)

Observed luminosity distance of a standard candle

DL(z) = [Lp/(4F)]1/2

Supernova Cosmology

More standardized candles from low-z SNe Ia:

1) A tight correlation: Lp ~ Δm15 (Phillips 1993)

2) Multi-color light curve shape (Riess et al. 1995)

3) The stretch method (Perlmutter et al. 1999)

4) The Bayesian adapted template match (BATM) method (Tonry et al. 2003)

5) A tight correlation: Lp ~ ΔC12 (B-V colors after the B maximum, Wang X.F. et al. 2005)

Phillips (1993)

Integral Method for Theoretical DL

Calculate 2 (H0,ΩM,Ω) or 2 (H0,ΩM, w), which is model-dependent, and obtain confidence contours from 1σ to 3σ.

or

Riess et al. (2004, ApJ, 607, 665): 16 SNe Ia discovered by HSTHST.

Riess et al. (2004): ΩM= 0.71, q0 < 0 (3σ), and w = -1.02+0.13

-0.19 (1σ)

Transition from deceleration to acceleration: zT = -q0/(dq/dz) = 0.46

The deceleration factor: q(z) = q0 + z(dq/dz)

Daly et al. 2004, ApJ, 612, 652

Pseudo-SNAP SNIa sample

y(z)=H0dL/(1+z)Differential Method, which is model-independent

Disadvantages in SN cosmology:

1. Redshift < 1.7

2. Dust extinction

3. Measuring cosmic expansion and dark energy with gamma-ray bursts

advantages over SN cosmology

① GRBs can occur at higher redshifts up to z~25;

② Gamma rays suffer from no dust extinction.

So, GRBs are an attractive probe of the universe.

The afterglow jet model (Rhoads 1999; Sari et al. 1999; Dai & Cheng 2001 for 1<p<2):

Ghirlanda et al. (2004a); Dai, Liang & Xu (2004): a tight correlation with a slope of ~1.5 and a reduced \chi2~0.53, suggesting a promising and interesting probe of cosmography.

ΩM=0.27 ΩΛ=0.73

Physical Explanations Synchrotron radiation + beaming correction (Dai, Liang & Xu

2004; Dai & Lu 2002; Zhang & Meszaros 2002) Annular jet + viewing angle effect (Levinson & Eichler 2005) Comptonization of the thermal radiation flux that is advected

from the base of an outflow (Rees & Meszaros 2005) Propagation of relativistic jets in the envelopes of massive stars

an energy limit (compared to the Chandrasekhar limit)

Two Methods of the Cosmological Use

(Ejet/1050 ergs) = C[(1+z)Ep/100 keV]a

Dai et al. (2004) consider a cosmology-independent correlation, in which C and a are intrinsic physical parameters and may be determined by low-z bursts as in the SN cosmology. Our correlation is a rigid ruler.

Consider a cosmology-dependent correlation (Ghirlanda et al.

2004b; Friedman & Bloom 2005). Because C and a are always

given by best fitting for each cosmology, this correlation is an elastic ruler, which is dependent of (ΩM, Ω).

Dai, Liang & Xu (2004) assumed a cosmology-independent correlation.

Conclusions and Implications

For a flat universe, ΩM = 0.35 0.15 (1σ) w = -0.84+0.57

-0.83 (1σ) A larger sample established by

Swift and WIMS is expected to provide further constraints.

Our work stimulated some studies:

Ghirlanda et al. (2004), Friedman & Bloom (2004), Firmani et al. (2005), Mortsell & Sollerman (2005), Di Girolamo et al (2005), Liang & Zhang (2005), ……

WIMS: Wide-sky Image Multiband Spectrometry (PI: 张双南教授 )

Swift

Cosmology-dependent correlation Cosmology-independent correlation

A larger sample including X-ray, optical, and radio light curve breaks ?

Cosmology-dependent correlation

Different error analysis X

Still, the correlation is so striking that just 15 gamma ray bursts already reveal the mass content of the universe and its expansion nearly as well as type Ia supernovae and other techniques, Ghirlanda says. His team confidently calls gamma ray bursts “new rulers to measure the universe” in the 20 September Astrophysical Journal Letters. A team from Nanjing University in China, led by Zigao Dai, reached a similar conclusion. ……Swift’s cornucopia of bursts should settle the debate …

Xu D., Dai Z.G. & Liang E.W. (2005, ApJ, submitted)

Future Observations

Xu, Dai & Liang (2005): red contours based on a simulated 157-GRB sample

Perlmutter (2003): smallest contours from SNAP

CMB

Clusters

A recent improvement: astro-ph/0504404

Wang F.Y. & Dai Z.G. (2005): only SN (solid contours), SN+GRB (dashed contours) following LZ05.

Cosmological constraints from 157 SN + 15 GRB

Explosions SNe Ia GRBsAstrophysical energy sources

Thermonuclear explosion of accreting white dwarfs

Core collapse of massive stars

Standardized candles

Colgate (1979): Lp constant

Frail et al. (2001): E jet constant

More standardized candles

Phillips (1993): Lp~Δm15 (9 low-z SNe Ia)

Ghirlanda et al. (2004a): E jet~Ep (14 high-z bursts)

Other correlations Riess et al. (1995); Perlmutter et al. (1999) …

Schaefer (2003); Wu et al. (2004); Liang & Zhang 05

Recent or future observations

16 HST-detected SNe Ia up to z~1.7 (Riess et al. 2004)

A large Swift-detected sample up to higher z~25

Comments on research status

From infancy to childhood (1998) to adulthood (SNAP)

At babyhood (to childhood by Swift and WIMS …)

Comparison of Cosmological Probes

Wu X.F., Dai Z.G. & Liang E.W. 2004, ApJ, 615, 359 Phillips (1993)

Conclusions• Finding: GRBs appear to provide an independent,

promising probe of the early universe (high-z SFR and IGM) and dark energy—one of the most enigmatic clouds.

• Status: The current GRB cosmology is at babyhood because of the small sample and model assumptions.

• Prospect: In the Swift and WIMS eras, the GRB cosmology would progress from its infancy to childhood, if a large sample (including low- & high-z bursts) and a more standardized candle are found.

• Experience: “Chance favors (only) the prepared mind” (said Trimble V. 2003 on the GRB meeting in Santa Fe): Don Lamb (Chicago U) is proposing a satellite project for GRB cosmology (gamma- & X-ray and optical detectors).

Thank you