Studies of Gamma-Ray Bursts in the Swift Era

Dai Zigao

Department of Astronomy, Nanjing University

物理年会，北京， 09/16/2006

Spectral features: broken power laws

with Ep of a few tens to hundreds of keV Temporal features: diverse and

spiky light curves.

Gamma-Ray Bursts

Bimodal distribution in durations

short

long2 s

Outline

I. Pre-Swift progressII. Recent progress and

implicationsIII. GRB cosmology

Most important discoveries in the pre-Swift era

1967: Klebesadel et al.’s discovery 1992: spatial distribution (BATSE) 1997: observations on

multiwavelength afterglows of GRB970228 and detection of the redshift of GRB970508 (BeppoSAX)

1998: association of GRB980425 with SN1998bw(BeppoSAX)

2003: association of GRB030329 with SN2003dh(HETE-2)

Some important discoveries in the pre-Swift era

1993: sub-classes (Kouveliotou et al.) 1994: MeV-GeV emission from GRB 940217

(Hurley et al.) ； 200 MeV emission from GRB 941017 (Gonzalez et al. 2003)

1997: detection of the iron lines in the X-ray afterglow of GRB 970508 (Piro et al.)

1999: optical flash and broken ligh curve of the R-band afterglow of GRB 990123 (Akerlof et al.; Fruchter et al.; Kulkarni et al.)

2002: X-ray flashes (Heise et al.; Kippen et al.) 2005: X-ray flares of GRBs (Piro et al.)

Theoretical progress in the pre-Swift era

1975: Usov & Chibison proposed GRBs at cosmological distances; Ruderman discussed an optical depth >> 1 problem

1986: Paczynski & Goodman proposed the fireball model of cosmological GRBs

1989: Eichler et al. proposed the NS-NS merger model 1990: Shemi & Piran proposed the relativistic fireball model

to solve the optical depth problem 1992: Rees & Meszaros proposed the external shock model of

GRBs; Usov and Duncan & Thompson proposed the magnetar model

1993: Woosley proposed the collapsar model 1994: Paczynski & Xu and Rees & Meszaros proposed the

internal shock model of GRBs; Katz predicted afterglows from GRBs

1995: Sari & Piran analyzed the dynamics of forward-reverse shocks ； Waxman 和 Vietri discussed high-E cosmic rays from GRBs

1997: Waxman & Bahcall discussed high-E neutrinos from GRBs

1997: Meszaros & Rees predicted light curves of afterglows

1998: Sari,Piran & Narayan established standard afterglow model; Vietri & Stella proposed the supranova model; Paczynski proposed the hypernova model; Dai & Lu and Rees & Meszaros proposed energy injection models; Dai & Lu and Meszaros et al. proposed the wind model; Wei & Lu discussed the IC scattering in afterglows ；

1999: Rhoads and Sari et al. proposed the jet model; Sari & Piran explained the optical flash from GRB 990123; Dai & Lu proposed dense environments —— GMC ； Huang et al. established the generic dynamic model; MacFadyen et al. numerically simulated the collapsar model; Derishev et al. proposed the neutron effect in afterglows

2000: some correlations were found, e.g., Fenimore et al. and Norris et al. ； Kumar & Panaitescu proposed the curvature effect in afterglows

2001: Frail et al. found a cluster of the jet-collimated energies; Panaitescu & Kumar fitted the afterglow data and obtained the model parameters

2002: the Amati correlation was found; Zhang & Meszaros analyzed spectral break models of GRBs; Rossi et al. and Zhang & Meszaros discussed the structured jet models; Fan et al. found the magnetized reverse shock in GRB 990123

2003: Schaefer discussed the cosmological use of GRBs;

2004: the Ghirlanda correlation was found; Dai et al. used this relation to constrain the cosmological parameters

Central engine models

NS-NS merger model (Paczynski 1986; Eichler et al. 1989)

Collapsar models (Woosley 1993; Paczynski 1998; MacFadyen & Woosley 1999)

Magnetar model (Usov 1992; Duncan & Thompson 1992)

NS-SS phase transition models (Cheng & Dai 1996; Dai & Lu 1998a; Paczynski & Haensel 2005)

Supranova models (Vietri & Stella 1998)

Collapsar modelNS-NS merger model

Expectations to Swift

GRB progenitors? Early afterglows? Short-GRB afterglows? Environments? Classes of GRBs? (High-z) GRBs as

astrophysical tools?

Blast wave interaction?

Gehrels et al. 2004, ApJ, 611, 1005

Gehrels et al. 2004; Launch on 20 November 2004

Discoveries in the Swift era

1. Prompt optical-IR emission and very early optical afterglows

2. Early steep decay and shallow decay of X-ray afterglows

3. X-ray flares from long/short bursts4. One high-redshift (z=6.295) burst5. Afterglows and host galaxies of short bursts6. Nearby GRB060218 / SN2006aj; nearby

GRB060614 (z=0.125) / no supernova

1. Prompt optical-IR emission and very early optical afterglows

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

2. Early steep decay and shallow decay of X-ray afterglows

Cusumano et al. 2005, astro-ph/0509689

t -5.5ν-1.60.22

GRB 050319

t -0.54ν-0.690.06

t -1.14ν-0.800.08

Tagliaferri et al. 2005, Nature, 436, 985 (also see Chincarini et al. 2005)

Initial steep decay: tail emission from relativistic shocked ejecta, e.g. curvature effect (Kumar & Panaitescu 2000; Zhang et al. 2006)

Flattening: continuous energy injection (Dai & Lu 1998a,b; Dai 2004; Zhang & Meszaros 2001; Zhang et al. 2006; Nousek et al. 2006), implying long-lasting central engine

Final steepening: forward shock emission

3. X-ray flares from long bursts

Burrows et al. 2005, Science, 309, 1833

Explanation: late internal shocks (Fan & Wei 2005; Zhang et al. 2006; Wu, Dai et al. 2005), implying long-lasting central engine.

Energy source models of X-ray flares

• Fragmentation of a stellar core (King et al. 2005)

• Fragmentation of an accretion disk (Perna Armitage & Zhang 2005)

• Magnetic-driven barrier in an accretion disk (Proga & Zhang 2006)

• Newborn millisecond pulsar (for short GRB) (Dai, Wang, Wu & Zhang 2006)

4. High-z GRB 050904: z=6.295

Tagliaferri et al. 2005, astro-ph/0509766

Kawai et al. 2006, Nature, 440, 184

X-ray flares of GRB 050904

Watson et al. 2005, Cusumano et al. 2006, Nature, 440, 164

Zou, Dai & Xu 2006, ApJ, in press

5. Afterglow from short GRB050509B

Gehrels et al. 2005, Nature, 437, 851

X-ray afterglow

Another case － GRB050709

Fox et al. 2005, Nature, 437, 845

X-ray:t-1.3

B-band t-1.25

t-2.8

radio

X-ray flare from GRB050709

Villasenor et al. 2005, Nature, 437, 855

光学余辉 : t-1.25

t-2.8

射电余辉 : 上限

X-ray flare at t=100 s

GRB050724: Barthelmy et al. 2005, Nature, 438, 994

Properties of short GRBs

Fox, et al. 2005, Nature, 437, 845

Ages of the host galaxies

Gorosabel et al. 2005, astro-ph/0510141

Summary: Basic features of short GRBs

1. low-redshifts (e.g., GRB050724, z=0.258; GRB050813, z=0.722)

2. Eiso ~ 1048 – 1050 ergs ；3. The host galaxies are old and short

GRBs are usually in their outskirts;　 support the NS-NS merger model ！4. X-ray flares challenge this model!

Rosswog et al., astro-ph/0306418

Ozel 2006, Nature, in press

Support stiff equations of state

Morrison et al. 2004, ApJ, 610, 941

Dai et al. 2006, Science, 311, 1127: differentially-rotating millisecond pulsars, similar to the popular solar flare model.

Roming et al., astro-ph/0605005, Swift BAT (left), KONUS-Wind (right)

Further evidence: GRB060313 prompt flares + late flattening

GRB060313: Roming et al., astro-ph/0605005, Yu Yu’s fitting by the pulsar energy injection model: B~1014 Gauss, P0~1 ms

Further evidence: GRB060313 prompt flares + late flattening

6. Nearby GRB 060218/SN2006aj(Campana et al. 17/39, 2006, Nature, in press)

Nearby GRB, z=0.0335 SN 2006aj association Low luminosity ~1047 ergs/s,

low energy ~1049 ergs Long duration (~900 s in

gamma-rays, ~2600 s in X-rays)

A thermal component identified in early X-rays and late UV/optical band

GRB 060218: prompt emission(Dai, Zhang & Liang 2006)

Very faint prompt UVOT emission can not be synchrotron emission.

The thermal X-ray component provides a seed photon source for IC.

Steep decay following both gamma-rays and X-rays implies the curvature effect.

Non-thermal spectrum must be produced above the photosphere.

GRB 060218: prompt emission(Dai, Zhang & Liang 2006)

Outline

I. Pre-Swift progressII. Recent progress and

implicationsIII. GRB cosmology

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

Hamuy et al. (1993, 1995)

Luminosity distance of a standard candle

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

Supernova CosmologySupernova 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.

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

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

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

-0.19 (1σ), implying that Λis a candidate of dark energy.

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. Dust extinction

2. ZMAX ~ 1.7 - 2

zT~0.5

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

GRB CosmologyGRB Cosmology Advantages over SNe Ia

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 small scatter of 2~0.53, suggesting a promising and interesting probe of cosmography.

M=0.27, =0.73

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; Firmani et al. 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).

The Hubble diagram of GRBs is consistent with that of SNe Ia.

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

““GRB Cosmology”GRB Cosmology”

Conclusions

ΩM = 0.35 0.15 (1σ)

w = -0.84+0.57-0.83 (1σ)

Many further studies: Ghirlanda et al. (2004b), Friedman & Bloom (2004), Xu, Dai & Liang (2005), Firmani et al. (2005, 2006), Mortsell & Sollerman (2005), Di Girolamo et al (2005), Liang & Zhang (2005, 2006),

…… A larger sample established by Swift

would be expected to provide further constraints (Swift was launched

on 20 Nov 2004)?

Swift

Cosmology-dependent correlation Cosmology-independent correlation

Shortcomings of the Ghirlanda relation

• The collimation-corrected gamma-ray energy is dependent on the environmental number density and the gamma-ray efficiency.

• Thus, the Ghirlanda relation is jet model-dependent.

Liang & Zhang 2005, ApJ, 633, 611

Wang & Dai 2006, MNRAS, 368, 371: w=-1 (left); w=w0 (right)

Wang & Dai 2006, MNRAS, 368, 371: w=w0+w1z (left); w=w0+w1z/(1+z) (right)

Importance: Hopefully, GRBs will provide further constraints on cosmological parameters, complementary to the constraints from CMB and SN —— GRB cosmology.

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

Perlmutter (2003): smallest contours from SNAP

CMB

Clusters

报告总结 Swift 在早期余辉、高红移暴、短暴以及低光度暴上

都有重要发现。 Swift 等关于 XRF 和 Flattening 的观测表明中心

能源很可能长时间释放能量——间断或持续释放。 Swift 等关于短暴的观测表明这些暴很可能起源于致

密双星的合并。 Swift 等关于高红移暴的观测将揭示宇宙早期的物理

性质（恒星形成率和星系际介质物理）。 Swift 等的观测也揭开了许多谜，例如：多波段光变

曲线的解释？中心致密天体？ Swift 与 GLAST 的全波段观测将可能揭示暴本身的

辐射机制。 在未来的几年里，利用 GRB 对宇宙膨胀和暗能量的

研究可望有进展。

Thank you !Thank you !