Spectral features: broken power laws with E p of a few tens to hundreds of keV
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Transcript of Spectral features: broken power laws with E p of a few tens to hundreds of keV
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Studies of Gamma-Ray Bursts in the Swift Era
Dai ZigaoDepartment of Astronomy, Nanjing University
物理年会,北京, 09/16/2006
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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
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Bimodal distribution in durations
short
long2 s
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OutlineI. Pre-Swift progressII. Recent progress and
implicationsIII. GRB cosmology
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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)
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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.)
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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
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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
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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
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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)
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Collapsar modelNS-NS merger model
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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
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Gehrels et al. 2004; Launch on 20 November 2004
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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
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1. Prompt optical-IR emission and very early optical afterglows
Vestrand et al. 2005, Nature, 435, 178Blake et al. 2005, Nature, 435, 181
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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
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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
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3. X-ray flares from long burstsBurrows 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.
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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)
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4. High-z GRB 050904: z=6.295
Tagliaferri et al. 2005, astro-ph/0509766
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Kawai et al. 2006, Nature, 440, 184
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X-ray flares of GRB 050904
Watson et al. 2005, Cusumano et al. 2006, Nature, 440, 164
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Zou, Dai & Xu 2006, ApJ, in press
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5. Afterglow from short GRB050509B
Gehrels et al. 2005, Nature, 437, 851
X-ray afterglow
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Another case - GRB050709
Fox et al. 2005, Nature, 437, 845
X-ray:t-1.3
B-band t-1.25
t-2.8
radio
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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
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GRB050724: Barthelmy et al. 2005, Nature, 438, 994
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Properties of short GRBs
Fox, et al. 2005, Nature, 437, 845
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Ages of the host galaxies
Gorosabel et al. 2005, astro-ph/0510141
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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!
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Rosswog et al., astro-ph/0306418
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Ozel 2006, Nature, in press
Support stiff equations of state
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Morrison et al. 2004, ApJ, 610, 941
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Dai et al. 2006, Science, 311, 1127: differentially-rotating millisecond pulsars, similar to the popular solar flare model.
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Roming et al., astro-ph/0605005, Swift BAT (left), KONUS-Wind (right)
Further evidence: GRB060313 prompt flares + late flattening
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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
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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
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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.
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GRB 060218: prompt emission(Dai, Zhang & Liang 2006)
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OutlineI. Pre-Swift progressII. Recent progress and
implicationsIII. GRB cosmology
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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)
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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)
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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
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Riess et al. (2004, ApJ, 607, 665): 16 SNe Ia discovered by HSTHST.
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Transition from deceleration to acceleration: zT = -q0/(dq/dz) = 0.46
The deceleration factor: q(z) = q0 + z(dq/dz)
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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.
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Daly et al. 2004, ApJ, 612, 652
Pseudo-SNAP SNIa sample
y(z)=H0dL/(1+z)Differential Method, which is model-independent
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Disadvantages in SN cosmology:
1. Dust extinction
2. ZMAX ~ 1.7 - 2
zT~0.5
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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
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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.
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The afterglow jet model (Rhoads 1999; Sari et al. 1999; Dai & Cheng 2001 for 1<p<2):
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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
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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).
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The Hubble diagram of GRBs is consistent with that of SNe Ia.
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Dai, Liang & Xu (2004) assumed a cosmology-independent correlation.
““GRB Cosmology”GRB Cosmology”
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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
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Cosmology-dependent correlation Cosmology-independent correlation
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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.
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Liang & Zhang 2005, ApJ, 633, 611
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Wang & Dai 2006, MNRAS, 368, 371: w=-1 (left); w=w0 (right)
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Wang & Dai 2006, MNRAS, 368, 371: w=w0+w1z (left); w=w0+w1z/(1+z) (right)
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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
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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。
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Thank you !Thank you !