George Kosugi

An optical spectrum of the afterglow of a γ-ray burst at a redshift of z = 6.295

The prompt γ-ray emission from γ-ray bursts (GRBs) should be detectable out to distances of z > 10 (ref. 1), and should therefore provide an excellent probe of the evolution of cosmic star formation, reionization of the intergalactic medium, and the metal enrichment history of the Universe. Hitherto, the highest measured redshift for a GRB has been z = 4.50 (ref. 5). Here we report the optical spectrum of the afterglow of GRB 050904 obtained 3.4 days after the burst; the spectrum shows a clear continuum at the long-wavelength end of the spectrum with a sharp cut-off at around 9,000u2009Å due to Lyman α absorption at z ≈ 6.3 (with a damping wing). A system of absorption lines of heavy elements at z = 6.295 ± 0.002 was also detected, yielding the precise measurement of the redshift. The Si ii fine-structure lines suggest a dense, metal-enriched environment around the progenitor of the GRB.

DARK GRB 080325 IN A DUSTY MASSIVE GALAXY AT z ~ 2

We present optical and near-infrared observations of Swift GRB 080325 classified as a dark gamma-ray burst (GRB). Near-infrared observations with Subaru/MOIRCS provided a clear detection of afterglow in the K s band, although no optical counterpart was reported. The flux ratio of rest-wavelength optical to X-ray bands of the afterglow indicates that the dust extinction along the line of sight to the afterglow is A V = 2.7-10 mag. This large extinction is probably the major reason for the optical faintness of GRB 080325. The J - K s color of the host galaxy, (J — K s = 1.3 in AB magnitude), is significantly redder than those for typical GRB hosts previously identified. In addition to J and K s bands, optical images in B, R c , i, and z bands with Subaru/Suprime-Cam were obtained at about 1 year after the burst, and a photometric redshift of the host is estimated to be Z photo = 1.9. The host luminosity is comparable to L * at z ~ 2 in contrast to the sub-L* property of typical GRB hosts at lower redshifts. The best-fit stellar population synthesis model for the host shows that the red nature of the host is attributed to a large dust extinction (A V = 0.8 mag), and that the host galaxy is massive (M * = 7.0 x 10 10 M ⊙ ), which makes it one of the most massive GRB hosts yet identified. By assuming that the mass-metallicity relation for star-forming galaxies at z ~ 2 is applicable for the GRB host, this large stellar mass suggests the high-metallicity environment around GRB 080325, consistent with inferred large extinction.

Implications for Galaxy Evolution from Cosmic Evolution of the Supernova Rate Density

We report on a comprehensive statistical analysis of observational data of the cosmic evolution of the supernova (SN) rate density, to derive constraints on cosmic star-formation history and the nature of a type Ia supernova (SN Ia) progenitor. We use all available information concerning th em agnitude, SN type, and redshift information of both type Ia and core-collapse (CC) SNe in GOODS and SDF, as well as SN Ia rate densities reported in the literature. We also add 157 SN candidates in the past Subaru/Suprime-Cam data that are newly reported here, to increase the statistics. We find that the current data set of the SN rate density evolution already gives a meaningful constraint on the evolution of the cosmic star formation rate (SFR) at z . 1 ,t hough strong constraints cannot be derived for the delay time distribution (DTD) of SNe Ia. We derive a constraint of ˛ � 3–4 [the evolutionary index of SFR density

Observation scheduling and data acquisition with the Subaru control system

The control system for the Subaru telescope is designed to consist of distributed workstations, local processors, and data acquisition computers, which are interconnected by control LANs and data LANs. The control software achieves its functionality with message-based communication. Two key processes, a scheduler and a status logger cooperating with any other processes, are designed to perform efficiency and security in observation. Control flow of observation scheduling and functionality of sub-processes which constitutes the scheduler and the status logger are described. For data acquisition from instruments, Subaru control system provides a variety of data highway which enable instruments to transfer data by up to 20 Mbytes/second. Functionality and characteristics of other subsystems which compose the Subaru control system are described.