1. Yong-Yeon Keum (Seoul National University) APCTP/IEU-Focus-Program on Cosmology and Fundamental Physics

2.  Long-duration GRBs (> 2 sec) can be the longest cosmic ladder in the universe because they are the most powerful and brightest explosions in the universe  Because of their brightness (isotropic-equivalent radiated energies up to more than 10 54 erg) and distance distribution (z up to 8.2, ~2.3) (see Fig. 1), GRBs are promising candidates to constrain cosmological parameters if, similarly to Supernovae (SN), they (or a subclass of them) can be proven to be used as standard candles.  Long GRBs may be useful to measure the cosmological parameters as well as Type Ia supernovae, Baryonic Oscillation(BAO), and Cosmic Microwave Background (CMB).  Long GRBs can be used to probe the Star Formation Rate(SFR) history in the red-shift universe since they are born from the death of massive stars.

4.  Baryon Acoustic Oscillation (BAO)  Type -1a Supernovae  Galaxy Cluster Counting  Weak Gravitational Lensing

5. How can we obtain the information of time evolution of EoS beyond z=1.73 ?

6.  A) GRBs are the most brilliant events in the universe.  B) Very recently, relation between the peak energy of the burst spectrum, the isotropic-equivalent energy, the radiated energy of the bust-all in the rest frame of the burst source- have been found.  C) In a way that is exactly analogous to the way in which the relation between the peak luminosity and the rate of decline of the light curve of Type Ia supernovae can be used to make Type Ia SN excellent standard candles for cosmology, so too, the relations between Epeak, Eiso, E  point toward a methodology for using GRBs as excellent standard candles for cosmology.  D) In addition, since GRBs occur over the broad redshift range( 0.1<z<~20), GRBs show great promise as cosmological “Yardsticks” to measure the rate of expansion of universe over time and the properties of dark-energy.

7.  GRBs provide information complementing that derived from SN only on early epochs of the Universe, when dark energy was supposedly starting to counterbalance the gravitational pull of dark matter. This requires that the energy or the luminosity is precisely estimated from observable quantities.  It was shown (Frail et al. 2001) that by accounting for the GRB jet opening angle the true collimation corrected energies Eγ clusters around ~ 10 51 erg but they are still too dispersed for precision cosmology (Bloom et al. 2003). Even by considering the (rest frame) peak spectral energy of the EFE spectrum, Ep, which was discovered to be strongly correlated with Eiso (Amati et al. 2002, 2006), GRBs are not standard candle due to the significant dispersion of the Ep- Eiso correlation.

8.  GRB F spectra typically show a peak at a characteristic photon energy E p  measured spectrum + measured redshift -> intrinsic peak enery and radiated energy E p,i = E p x (1 + z) Amati (2009) The Ep,i – Eiso correlation Ep

9.  Ep,i – Eiso correlation for long GRBs with known redshift confirmed and extended by measurements of ALL other GRB detectors with spectral capabilities 120 long GRBs as of Oct. 2010 BeppoSAX GRBs

10.  definite evidence that short GRBs DO NOT follow the Ep.i – Eiso correlation: a tool to distinguish between short and long events and to get clues on their different nature (e.g., Amati 2006, Piranomonte et al. 2008, Ghirlanda et al. 2009)

11.  claims (2004): the E p,i -E iso correlation becomes tighter when adding a third observable: the jet opening angle derived from the afterglow break time tb, (  jet -> E  = [1-cos(  jet )]*E iso, (Ghirlanda et al. 2004) or directly tb (Liang & Zhang 2004) 3-parameters spectrum-energy correlations: prompting investigation of GRBs as cosmological probes

12.  fit the correlation and construct an Hubble diagram for each set of c osmological parameters -> derive c.l. contours based on chi-square  Method (e.g., Ghirlanda et al, Firmani et al., Dai et al., Zhang et al. ): E p,i = E p,obs x (1 + z), t b,i = t b / /1 + z) D l = D l (z, H 0,  M,  ,…)

13.  lack of jet breaks in several Swift X-ray afterglow light curves, in s ome cases, evidence of achromatic break  challenging evidences for Jet interpretation of break in afterglow li ght curves or due to present inadequate sampling of optical light c urves w/r to X-ray ones and to lack of satisfactory modeling of jets ?  “Crisis” of 3-parameters spectrum-energy correlations

14.  There are two empirical relations that relate prompt emission property with Ep. 1) Ep-Eiso relation was the first one found by Amati et al. (2002) which connects Ep with the isotropic equivalent energy Eiso. 2) Ep-Lp relation found by Yonetoku et al. (2004).

17.  analysis of the most updated sample of 120 GRBs shows significant improvements w/r to the sample of 70 GRBs of Amati et al. (2008)  this evidence supports the reliability and perspectives of the use of the Ep,i – Eiso correlation for the estimate of cosmological parameters  m (flat universe) 68% 90% 70 GRBs (Amati 08)0.04 – 0.430.02 – 0.71 120 GRBs (Amati 10)0.06 – 0.340.03 – 0.54 70 GRBs 114 GRBs 120 GRBs

23.  Given their huge radiated energies and redshift distribution extending from ~ 0.1 up to > 8, GRBs are potentially a very powerful cosmological probe, complementary to other probes (e.g., SN Ia, clusters, BAO)  The Ep,i – Eiso correlation is one of the most robust (no firm evidence of significant selection / instrumental effects) and intriguing properties of GRBs and a promising tool for cosmological parameters  Analysis in the last years (>2008) provide already evidence, independent on, e.g., SN Ia, that if we live in a flat  CDM universe,  m is 99.9% c.l. (  2 minimizes at  m ~ 0.25, consistent with “standard” cosmology)  the simulatenous operation of Swift, Fermi/GBM, Konus-WIND is allowing an increase of the useful sample (z + Ep) at a rate of 15-20 GRB/year, providing an increasing accuracy in the estimate of cosmological parameters  future GRB experiments (e.g., SVOM) and more investigations (statistical tools, simulations, calibration) will improve the significance and reliability of the results

26. GRB

27.  The Phenomenological relations(Amati, Yonetoku, Fundamental) has no solid theoretical basis yet. So we propose to use numerical simulations of GRBs to understand the relations from the first principle. In other words, we would like to understand why these relations hold in GRBs with a help of numerical simulations. If we understand the relation from the first principle, we can rely on the relation and use them as cosmic ladder even before the confirmation of future observations  Japanese Collaborators developed a General Relativisitic Magneto- Hydro-Dynamics(GRMHD) code to study the formation and propagation of GRB jets. Successfully they reproduce the spectrum of a typical long GRB in low-energy band by superposition of thermal radiation from the photosphere.

28.  Now we are developing a Monte-Carlo radiation-transfer code to calculate the Compton up-scattering effects. We are expecting that the spectrum in high energy band is modified so that the observed spectrum of a typical GRBs in the high energy band can be explained too.  Finally we can reproduce the observed GRB’s spectrum and reproduce the phenomenological relations on the absolute luminosity and typical energy of GRBs.  This project will bring a great impact to not only the field of GRB but also to the field of cosmology. We may measure the evolution of euation of state of the universe, amount of dark-matter in the universe, and SFR history at high red-shift universe.

29. We describe a concept for a possible MIDEX- class mission dedicated to using GRBs to constrain the properties of dark-energy that would obtain these quantities for > 800 bursts in the redshift range 0.1 < z < 10 during 2 years mission. This burst sample would enable both Omega_M and w_0 to be determined to 0.07 and 0.06 (68% CL), respectively.