1. 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

3. 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

4. Bimodal distribution in durations shortlong 2 s2 s

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

6. 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)

7. 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.)

8. 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

9.  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

10.  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

11. 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)

12. Collapsar model NS-NS merger model

13. 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

14. Gehrels et al. 2004; Launch on 20 November 2004

15. 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 GRB060218 / SN2006aj; nearby GRB060614 (z=0.125) / no supernova

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

18. 2. Early steep decay and shallow decay of X-ray afterglows Cusumano et al. 2005, astro-ph/0509689 t -5.5 ν -1.6  0.22 GRB 050319 t -0.54 ν -0.69  0.06 t -1.14 ν -0.80  0.08

19. 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

20. 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.

21. 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)

22. 4. High-z GRB 050904: z=6.295 Tagliaferri et al. 2005, astro-ph/0509766

23. Kawai et al. 2006, Nature, 440, 184

24. X-ray flares of GRB 050904 Watson et al. 2005, Cusumano et al. 2006, Nature, 440, 164

25. Zou, Dai & Xu 2006, ApJ, in press

26. 5. Afterglow from short GRB050509B Gehrels et al. 2005, Nature, 437, 851 X-ray afterglow

27. Another case － GRB050709 Fox et al. 2005, Nature, 437, 845 X-ray:t -1.3 B-band t -1.25 t -2.8 radio

28. 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

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

30. Properties of short GRBs Fox, et al. 2005, Nature, 437, 845

31. Ages of the host galaxies Gorosabel et al. 2005, astro-ph/0510141

32. Summary: Basic features of short GRBs 1. low-redshifts (e.g., GRB050724, z =0.258; GRB050813, z =0.722) 2. E iso ~ 10 48 – 10 50 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!

33. Rosswog et al., astro-ph/0306418

35. Ozel 2006, Nature, in press Support stiff equations of state

36. Morrison et al. 2004, ApJ, 610, 941

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

38. Roming et al., astro-ph/0605005, Swift BAT (left), KONUS-Wind (right) Further evidence: GRB060313 prompt flares + late flattening

39. GRB060313: Roming et al., astro-ph/0605005, Yu Yu’s fitting by the pulsar energy injection model: B  ~10 14 Gauss, P 0 ~1 ms Further evidence: GRB060313 prompt flares + late flattening

40. 6. Nearby GRB 060218/SN2006aj (Campana et al. 17/39, 2006, Nature, in press)  Nearby GRB, z=0.0335  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

41. 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.

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

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

44. 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)

45. 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) Phillips (1993)

46. 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

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

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

49. Riess et al. (2004): Ω  = 0.71, q 0 < 0 (3σ), and w = -1.02 +0.13 -0.19 (1σ), implying that Λis a candidate of dark energy.

50. 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

51. Disadvantages in SN cosmology: 1.Dust extinction 2.Z MAX ~ 1.7 - 2 z T ~0.5

52. 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

53. 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.

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

55. 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

56. 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  ).

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

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

59. Conclusions Ω M = 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

60. Cosmology-dependent correlationCosmology-independent correlation

61. 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.

62. Liang & Zhang 2005, ApJ, 633, 611

63. Wang & Dai 2006, MNRAS, 368, 371: w=-1 (left); w=w 0 (right)

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

65. 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

66. 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。

67. Thank you !