Recent Progress on Gamma-Ray Bursts and GRB Cosmology Zigao Dai Department of Astronomy, Nanjing University Sino-French workshop, Beijing, 08/30/2006

Collaborators Lu Tan, Huang Yongfeng, Wang Xiangyu, Wei Daming, Cheng Kwongsheng Li Zhuo, Wu Xuefeng, Fan Yizhong, Zou Yuanchuan, Shao Lang, Xu Dong, Xu Lei, … Zhang Bing, Liang Enwei, Peter Meszaros

Spectral features: broken power laws with E p of a few tens to hundreds of keV Temporal features: diverse and spiky light curves. Gamma-Ray Bursts

Bimodal distribution in durations shortlong 2 s2 s

Outline I.Pre-Swift progress II.Recent progress and implications III.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 GRB and detection of the redshift of GRB (BeppoSAX)  1998: association of GRB with SN1998bw(BeppoSAX)  2003: association of GRB with SN2003dh(HETE-2)

Some important discoveries in the pre-Swift era  1993: sub-classes (Kouveliotou et al.)  1994: MeV-GeV emission from GRB (Hurley et al.) ； 200 MeV emission from GRB (Gonzalez et al. 2003)  1997: detection of the iron lines in the X-ray afterglow of GRB (Piro et al.)  1999: optical flash and broken ligh curve of the R-band afterglow of GRB (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 ; 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  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 model NS-NS merger model

Summary: fireball + shock model

Basic assumptions in the standard afterglow model ① A spherical, ultrarelativistic fireball is ejected; ② The total energy of the shocks is released impulsively before their formation; ③ The unshocked medium is homogeneous, and its density is of the order of 1 cm -3 ; ④ The electron and magnetic energy-density fractions of the shocked medium and the index p of the electron power-law distribution are constant; ⑤ The emission mechanism is synchrotron radiation.

 Jets (Rhoads 1997, 1999; Sari, Piran & Halpern 1999; Dai & Cheng 2001)  Postburst energy injection (Dai & Lu 1998a, 2000, 2001; Rees & Meszaros 1998; Panaitescu & Meszaros 1998; Kumar & Piran 2000a,b; Zhang & Meszaros 2001a,b; Nakar & Piran 2003; Dai 2004)  Environments including stellar winds and dense media (Dai & Lu 1998b, 1999, 2002; Meszaros, Rees & Wijers 1998; Chevalier & Li 1999, 2000; Dai & Wu 2003; Chevalier et al. 2004)  Model parameters changed (Yost et al. 2003)  Other emission mechanisms including IC scattering (Wei & Lu 1998; Sari & Esin 2001; Panaitescu & Kumar 2001; Zhang & Meszaros 2002) Physical effects in afterglows

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

ν ~(5-18)x10 14 Hz

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 bursts 4.One high-redshift (z=6.295) burst 5.Afterglows and host galaxies of short bursts 6.Nearby GRB / SN2006aj; nearby GRB (z=0.125) / no supernova

1.Prompt optical-IR emission and very early optical afterglows Vestrand et al. 2005, Nature, 435, 178 Blake et al. 2005, Nature, 435, 181

Further evidence: Vestrand et al. 2006, Nature, in press

2. Early steep decay and shallow decay of X-ray afterglows Cusumano et al. 2005, astro-ph/ t -5.5 ν -1.6  0.22 GRB t ν  0.06 t ν  0.08

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.

Halpern et al. (2006): optical flares

Energy source models of X-ray/optical 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 : z=6.295 Tagliaferri et al. 2005, astro-ph/

Kawai et al. 2006, Nature, 440, 184

X-ray flares of GRB 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 － GRB Fox et al. 2005, Nature, 437, 845 X-ray:t -1.3 B-band t t -2.8 radio

X-ray flare from GRB Villasenor et al. 2005, Nature, 437, 855 光学余辉 : t 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/

Summary: Basic features of short GRBs 1. low-redshifts (e.g., GRB050724, z =0.258; GRB050813, z =0.722) 2. E iso ~ – 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/

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/ , Swift BAT (left), KONUS-Wind (right) Further evidence: GRB prompt flares + late flattening

GRB060313: Roming et al., astro-ph/ , Yu Yu’s fitting by the pulsar energy injection model: B  ~10 14 Gauss, P 0 ~1 ms Further evidence: GRB prompt flares + late flattening

6. Nearby GRB /SN2006aj (Campana et al. 17/39, 2006, Nature, in press)  Nearby GRB, z=  SN 2006aj association  Low luminosity ~10 47 ergs/s, low energy ~10 49 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 see J.S. Deng ’ s talk

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

Outline I.Pre-Swift progress II.Recent progress and implications III.GRB cosmology

Einstein equations with  Friedmann equations These equations imply that (1) the expansion of the universe at the present time is accelerating and (2) the universe had once been decelerating.

Krauss, L. M. 1999, Scientific American deceleration acceleration

Type-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 D L (z) = [L p /(4  F)] 1/2 Supernova Cosmology More standardized candles from low-z SNe Ia: 1)A tight correlation: L p ~ Δm 15 (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: L p ~ ΔC 12 (B-V colors after the B maximum, Wang X.F. et al. 2005) see X.F. Wang’s talk Phillips (1993)

Integral Method for Theoretical D L Calculate  2 (H 0,Ω M,Ω  ) or  2 (H 0,Ω M, w), which is model-dependent, and obtain confidence contours from 1σ to 3σ. or

Accelerating Universe Riess et al. (1998): 50 SNe Ia Dotted: excluding SN1997ck (z=0.97)

Accelerating Universe Perlmutter et al. (1999): 42 high-z SNe Ia

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

Transition from deceleration to acceleration: z T = -q 0 /(dq/dz) = 0.46 The deceleration factor: q(z) = q 0 + z(dq/dz)

Riess et al. (2004): Ω  = 0.71, q 0 < 0 (3σ), and w = (1σ), implying that Λis a candidate of dark energy.

Daly et al. 2004, ApJ, 612, 652 Pseudo-SNAP SNIa sample y(z)=H 0 d L /(1+z) Differential Method, which is model- independent

Disadvantages in SN cosmology: 1.Dust extinction 2.Z MAX ~ 1.7 z T ~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

High-z GRB : z=6.3 Tagliaferri et al. 2005, astro-ph/

GRB Cosmology GRB Cosmology Advantages over SNe Ia  GRBs can occur at higher redshifts up to z~25;  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

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; Thompson, Meszaros & Rees 2006) Propagation of relativistic jets in the envelopes of massive stars  an energy limit (compared to the Chandrasekhar limit)

Two Methods of the Cosmological Use (E jet /10 50 ergs) = C[(1+z)E p /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 (Ω M, Ω  ).

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

Dai, Liang & Xu (2004) assumed a cosmology-independent correlation. “GRB Cosmology”

Conclusions Ω M = 0.35  0.15 (1σ) w = (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 correlationCosmology-independent correlation

Xu D., Dai Z.G. & Liang E.W. (2005, ApJ, 633, 603): method 2 cosmology-dependent 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=w 0 (right)

Wang & Dai 2006, MNRAS, 368, 371: w=w 0 +w 1 z (left); w=w 0 +w 1 z/(1+z) (right)

Schaefer 2006

w=w0+w’zw=w0+w’zw=w0+w’zw=w0+w’z

Other works  Calibration of GRB luminosity indicators (Liang & Zhang 2006, MNRAS)  Very recently, a new correlation: L iso, E pk and T 0.45, and its cosmological use (Firmani et al. 2006a, b, c)

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

Explosions SNe IaGRBs Astrophysical energy sources Thermonuclear explosion of accreting white dwarfs Core collapse of massive stars Standardized candles Colgate (1979): L p constant Frail et al. (2001): E jet constant More standardized candles Phillips (1993): L p ~Δm 15 (9 low-z SNe Ia) Ghirlanda et al. (2004a): E jet ~E p (14 high-z bursts) Other correlationsRiess et al. (1995); Perlmutter et al. (1999) … Liang & Zhang (2005); Firmani et al. (2006) Recent or future observations 16 HST-detected SNe Ia up to z~1.7 (Riess et al. 2004) SVOM A large SVOM-detected sample up to higher z Comments on research status From infancy to childhood (1998) to adulthood (SNAP) At babyhood (to childhood by future missions?) Comparison of Cosmological Probes

Summary: GRB cosmology 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. some subclass Prospect: In the future, the GRB cosmology would progress from its infancy to childhood, if a large sample of some subclass (including low- & high-z bursts) and a more standardized candle are found. Experience: “Chance favors (only) the prepared mind” (said Trimble V on the GRB meeting in Santa Fe). Proposal: Lamb et al proposed a satellite project for GRB cosmology (gamma- & X-ray and optical detectors), and the Sino-French GRB mission ……

Requirements to future missions from GRB cosmology Based on –Ghirlanda relation –Liang & Zhang luminosity indicator –Firmani et al. relation Science: –Constraints on cosmological parameters –properties of dark energy –Systematics different from SNe Requirements (broadband observations): –Full set of spectral parameters: α, β, E peak –Jet break time (optical, X-ray) –Redshift –A large sample of GRBs…

Thank you !