Ryo Tsutsui

Gamma-ray bursts in 1.8 < z < 5.6 suggest that the time variation of the dark energy is small

We calibrated the peak energy–peak luminosity relation of gamma-ray bursts (GRBs; the so-called Yonetoku relation) using 33 events with redshift z < 1.62 without assuming any cosmological models. The luminosity distances to GRBs are estimated from those of large numbers of Type Ia supernovae with z < 1.755. This calibrated Yonetoku relation can be used as a new cosmic distance ladder towards higher redshifts. We determined the luminosity distances of 30 GRBs in 1.8 < z < 5.6 using the calibrated relation, and plotted the likelihood contour in the (Ωm, ΩΛ) plane. We obtained (Ωm, ΩΛ) = (0.37+0.14−0.11, 0.63+0.11−0.14) for a flat universe. Because our method is free from the circularity problem, we can say that our universe in 1.8 < z < 5.6 is compatible with the so-called concordance cosmological model derived for z < 1.8. This suggests that the time variation of the dark energy is small or zero up to z∼ 6.

Possible Origins of Dispersion of the Peak Energy–Brightness Correlations of Gamma-Ray Bursts

We collected and reanalyzed about 200 GRB data of prompt-emission with known redshift observed until the end of 2009, and selected 101 GRBs that were well-observed to have good spectral parameters in order to determine the spectral peak energy (Ep), 1-second peak luminosity (Lp) and isotropic energy (Eiso). Using our newly constructed database with 101 GRBs, we first revised the Ep–Lp and Ep–Eiso correlations. The correlation coefficients of the revised correlations were 0.889 for 99 degrees of freedom for the Ep–Lp correlation and 0.867 for 96 degrees of freedom for the Ep–Eiso correlation. These values correspond to a chance probability of 2.18 � 10 � 35 and 4.27 � 10 � 31 , respectively. It is a very important issue whether these tight correlations are an intrinsic property of GRBs, or are caused by some selection effect of observations. In this paper, we examine how the truncation of the detector sensitivity affects the correlations, and conclude they are surely intrinsic properties of GRBs. Next we investigate origins of the dispersion of the correlations by studying their brightness and redshift dependence. Here, the brightness (flux or fluence) dependence would be regarded as being an estimator of the bias due to the detector threshold. We found a weak fluence-dependence in the Ep–Eiso correlations and a redshift dependence in the Ep– Lp correlation both at the 2 � statistical level. These two effects may contribute to the dispersion of the correlations, which is larger than the statistical uncertainty. We discuss a possible reason of these dependences and give a future prospect to improve the correlations.

Improved Ep-TL-Lp Diagram and a Robust Regression Method

The accuracy and reliability of gamma-ray bursts (GRBs) as distance indicators are strongly restricted by their systematic errors, which are larger than the statistical errors. These systematic errors might come from either intrinsic variations of GRBs, or systematic errors in observations. In this paper, we consider the possible origins of systematic errors in the following observables: (i) the spectral peak energies (Ep) estimated by the cut-off power law (CPL) function and (ii) the peak luminosities (Lp) estimated by 1 s in observer time. By removing or correcting them we can reveal the true intrinsic variation of the Ep–TL–Lp relation of GRBs. Here, TL is the third parameter of

WISH: wide-field imaging surveyor at high redshift

WISH is a new space science mission concept whose primary goal is to study the first galaxies in the early universe. We will launch a 1.5m telescope equipped with 1000 arcmin2 wide-field NIR camera by late 2010s in order to conduct unique ultra-deep and wide-area sky surveys at 1-5 micron. The primary science goal of WISH mission is pushing the high-redshift frontier beyond the epoch of reionization by utilizing its unique imaging capability and the dedicated survey strategy. We expect to detect ~104 galaxies at z=8-9, ~3-6x103 galaxies at z=11-12, and ~50-100 galaxies at z=14-17 within about 5 years of the planned mission life time. It is worth mentioning that a large fraction of these objects may be bright enough for the spectroscopic observations with the extremely large telescopes. By adopting the optimized strategy for the recurrent observations to reach the depth, we also use the surveys to detect transient objects. Type Ia Supernova cosmology is thus another important primary goal of WISH. A unique optical layout has been developed to achieve the diffraction-limited imaging at 1-5micron over the required large area. Cooling the mirror and telescope to ~100K is needed to achieve the zodiacal light limited imaging and WISH will achieve the required temperature by passive cooling in the stable thermal environment at the orbit near Sun-Earth L2. We are conducting the conceptual studies and development for the important components of WISH including the exchange mechanism for the wide-field filters as well as the primary mirror fixation.

The Fundamental Plane of Gamma‐Ray Bursts and Its Prospect for Cosmology

We showed the independence of the Epeak‐Lp from Epeak‐Eiso relations, and using Epeak, Lp, and Eiso as independent parameters, we found the fundamental plane of Gamma‐ray bursts (GRBs). The fundamental plane of GRBs is the tightest correlation only using parameters of prompt emission of GRBs. Thus this correlation have the greatest potential for cosmology among other correlations obtained from GRBs. We calibrated by distances measured by supernovae Ia (SNe Ia). Then we estimated the distance toward high redshift GRBs (z>1.8) with about 30% errors. In this talk, we present cosmological constraints from high redshift GRBs which is as strong as from type Ia supernovae (SNe Ia). Then we show the current status of GRB cosmology and compare them with SNe Ia, clusters of galaxy, and CMB cosmologies. The constraint from high redshift GRBs are consistent with others. This might indicate that the time evolution of dark energy density is not large. Finally, we discuss the future prospect of GRB cosmology.

The Spectral Epeak‐Luminosity and the Epeak‐Eiso Relation: the Origin of Dispersion and Its Improvement

We formed a GRB cosmology project in Japan, and promote the observational cosmology with Gamma‐ray bursts (GRBs). In this paper, we introduce recent result of our project with the spectral Epeak‐Luminosity relations. We show the Hubble diagram up to the redshift of z = 8.2, and the confidence contour of the dark energy (ΩΛ) and the dark matter (Ωm) beyond z>2 beyond the current range measured by the Type Ia supernovae. After that, we investigate the origin of data dispersion of the Epeak‐brightness relations, and suggest a possible improvement of their accuracy.

Testing two‐jet models of GRBs with the orphan afterglow

In the \swift era, two-component jet models were introduced to explain the complex temporal profiles and the diversity of early afterglows. In this paper, we concentrate on the two-component jet model; first component is the conventional afterglow and second is the emission due to the late internal dissipation such as the late-prompt emission. We suggest herein that the two-component jet model can be probed by the existence of two optical peaks for orphan GRB afterglows. Each peak is caused by its respective jet as its relativistic beaming cone widens to encompass the off-axis line of sight. Typically, the first peak appears at

Constraints on w0 and wa of dark energy from high-redshift gamma-ray bursts

10^4-10^5

Redshift-dependent lag–luminosity relation in 565 BATSE gamma-ray bursts

s and the second at

Cosmological constraints from calibrated Yonetoku and Amati relation suggest fundamental plane of gamma-ray bursts

10^5-10^6