Shuang-Nan Zhang Collaborators: Nan Liang , Wei-Ke Xiao, Yuan Liu ,

1. A Cosmology Independent Calibration of Gamma-Ray Burst Luminosity Relations and the Hubble Diagram arxiv: 0802.4262v4 [astro-ph] Paper accepted by ApJ Shuang-Nan Zhang Collaborators:Nan Liang, Wei-Ke Xiao, Yuan Liu, Tsinghua Center for Astrophysics , Tsinghua University July 10th, 2008Cosmic Reionization, KIAA, PKU

2. Discovered in 1967 by Los Alamos Several per day Last from ms to ~ 100 seconds Brightest gamma ray phenomenon Isotropic on sky (BATSE/CGRO) No repetitions seconds Gamma Ray Bursts Vela 4a BATSE

3. Isotropy: first sign of cosmological origin

4. Bimodality of GRB duration

5. Hardness ratio distribution

6. Light curves

7. GRB spectra (Schaefer et al. 1992, ApJ) Epeak: peak energy ~several hundred keV

8. 6 hours 48 hours Gamma Ray Burst Breakthrough! X-ray Images from BeppoSax • BeppoSAX combination of wide field and narrow field instruments give 6-hr response to gamma ray burst • observations in 1997 revealed a fading X-ray afterglow • 20 mag optical afterglow identified from X-ray position • Afterglow decays as powerlaw with time X-ray Afterglow HST Image

9. Afterglow detection HST Afterglow Detection

10. Broadband spectrum

11. The fireball model Do you notice a small mistake on this picture?

12. Jet vs spherical geometry: light curve break

13. Opening angle and light curve break

14. Evidence for jet

15. GRB Luminosity Relations as “standard candles” • GRB luminosity/energy relations are connections between measurable properties of the γ-ray emission with the luminosity or energy. • Several GRB luminosity relations as distance indicators have been proposed, for those long and soft GRBs. • Many authors have made use of these GRB luminosity indicators as “standard candles” at very high redshift for cosmology research. see e.g. Ghirlanda, Ghisellini, & Firmani (2006),Schaefer (2007) for reviews

16. Eγ -Epeak relation (Ghirlanda, Ghisellini & Lazzati 2004) Epeak- L relation (Schaefer 2003; Yonetoku et al. 2004) Variability - L relation (Fenimore & Ramirez-Ruiz 2000) τRT - L relation (Schaefer, 2007) Five GRB Relations (Schaefer 2007, 69 GRBs) lag - L relation (Norris, Marani, & Bonnell 2000)

17. Physical Explanations for the Eγ-Epeak relation • Synchrotron radiation + beaming correction (Dai, Liang & Xu 2004; Dai & Lu 2002; Zhang & Meszaros 2002) • Ring-shape jet + viewing angle effect (Levinson & Eichler 2005) • Comptonization of the thermal radiation flux that is advected from the base of an outflow (Rees & Meszaros 2006)

18. Cosmology research Some attempts related to the use of GRBs for cosmology: • Schaefer 2003; • Takahashi et al. 2003; • Dai, Liang, & Xu 2004; • Ghirlanda et al. 2004, 2005, 2006 • Ghirlanda, Ghisellini, & Firmani 2006 • Firmani et al. 2005, 2006, 2007; • Liang & Zhang 2005, 2006; • Xu, Dai, & Liang 2005; • Wang & Dai 2006; Wang, Dai, & Zhu, 2007; • Schaefer 2007 • Qi, Wang, & Lu, 2008; • …

19. The most important point related to GRB cosmology: →The dependence of the cosmological model to the calibration of GRB relations. • SN Ia cosmology:cosmological model-independent ---- The Phillips relation can be calibrated with adequate sample at low-z. • GRB cosmology: cosmological model-dependent ---- Difficult to calibrate the relations using a low-zsample. ---- Calibration of GRB relations : obtained by assuming a particular cosmological model.

20. The circularity problem • In order to investigate cosmology, the relations of standard candles should be calibrated in a cosmological model independent way. → Otherwise the circularity problem can not be avoided easily • Many previous works treated this problem by means of statistical methods. ---- A simultaneous fit of the parameters in the calibration curves and the cosmology should be carried out. ---- Because a particular cosmology is required in doing the joint fitting, the problem can not be avoided completely.

21. The Cosmic Distance Ladder 1929: Discovery of cosmic expansion Extra- galactic Cepheids M-z GRB Standard Candle H-z GRB Cosmology Galactic Cepheids   L-z SN Ia Standard Candle M-z SN Ia Cosmology  1998: Discovery of Dark Energy 1.7 6.3 z 13.5 billion yrs 3.5 1 age

22. A new method to calibrate GRB relations • The distances of SN Ia obtained directly from observations are completely cosmological model independent. • SNe Ia → GRBs :If the luminosity distance of GRBs can be obtained directly from the SN Ia data,we can calibrate the GRB relations in a cosmological model independent way.

23. Calibration of GRB relations: cosmology independent • All types of sources at the same redshift should have the same luminosity distancefor any certain cosmology. • So many SN Ia samples →the luminosity distance for any object at any redshift (in SN Ia redshift range) can be obtained by interpolating from the Hubble diagram of SNe Ia. → If regarding SNe Ia as the first order standard candles, we can obtain the luminosity distance of GRBs (in SN Ia redshift range) and calibrate the relations in a completely cosmology independent way.

24. We calibrate seven GRB relations with the sample at z<1.4 (Amati et al. 2002) (Liang & Zhang 2005)

25. Calibration results Table 1.Calibration results for the 7 GRB relations with the sample at z<1.4. → Results obtained by using the two interpolation methods are almost identical. → Results obtained by assuming the two cosmological models with the samesample differ only slightlyfrom those obtained by using interpolation methods.

26. Hubble Diagram of SNe Ia and GRBs Fig. 1. The Hubble Diagram of 192 SNe Ia and 69 GRBs z=1.4 Concordance model → GRB high-z “data” , obtained from the calibrated GRB “standard” candles (weighted average over 5 relations used in Schaefer 2007); These data are used to fit cosmological parameters at high-z. SN1997ff(z = 1.755) → GRB low-z “data”, interpolated from SN Ia data, (thus also cosmology independent). These data are used to calibrate the GRB “standard” candles. → SNe Ia data(Davis et al. 2007), directly from observations, cosmology independent. These data used to interpolate the distance moduli of GRB low-z “data”,

27. Cosmological results from GRBs (for ΛCDM model) Fig. 2.ΩM -ΩΛ joint confidence contours from42 GRBs (z>1.4)

28. Dark Energy model with a constant EoS (w0) Fig. 3. Confidence region in (ΩM –w0 ) plane

29. Summary and Discussion • With the basic assumption that objects at the same redshift should have the same luminosity distance, the distance modulus of a GRB can be obtained by interpolating from the Hubble diagram of SNe Ia at z <1.4. • We construct the GRB Hubble diagram and constrain cosmological parameters for 42 GRBs at 1.4<z<6.6 →ΩM = 0.25+0.04−0.05 (for the flat ΛCDM model) →w0 = −1.05+0.27−0.40(for DE model with a constant EoS) Which are consistent withthe concordance model (w0 = −1,ΩM = 0.27, ΩΛ = 0.73)

30. Our method avoids the circularity problem completely, compared to previous cosmology-dependent calibration methods. • Further examinations to the possible evolution effects and selection bias, as well as some unknown biases of SN Ia luminosity relations should be required for considering GRBs as standard candles to cosmological use.

31. We predicted that many GRBs should be produced at z > 10

32. Brighter GRBs produces harder photons, and are thus detectable from higher redshift The Amati relation for Long/Soft GRBs (Amati, 2006, MNRAS; 2002, A&A; Yonetoku et al., 2004, ApJ, 609, 935; Sakamoto et al., 2004, ApJ, 602, 875)

33. GRB as probe of cosmic reionization SN Ia range Future GRB range Current GRB range