Japan Aerospace Exploration Agency

About: Japan Aerospace Exploration Agency is a facility organization based out in Tokyo, Japan. It is known for research contribution in the topics: Galaxy & Telescope. The organization has 4327 authors who have published 12054 publications receiving 208330 citations.

Studying the warm hot intergalactic medium with gamma-ray bursts

Abstract: We assess the possibility of detecting and characterizing the physical state of the missing baryons at low redshift by analyzing the X-ray absorption spectra of the gamma-ray burst (GRB) afterglows, measured by a microcalorimeter-based detector with 3 eV resolution and 1000 cm2 effective area and capable of fast repointing, similar to that on board of the recently proposed X-ray satellites EDGE and XENIA. For this purpose we have analyzed mock absorption spectra extracted from different hydrodynamical simulations used to model the properties of the warm hot intergalactic medium (WHIM). These models predict the correct abundance of O VI absorption lines observed in UV and satisfy current X-ray constraints. According to these models space missions such as EDGE and XENIA should be able to detect ~60 WHIM absorbers per year through the O VII line. About 45% of these have at least two more detectable lines in addition to O VII that can be used to determine the density and the temperature of the gas. Systematic errors in the estimates of the gas density and temperature can be corrected for in a robust, largely model-independent fashion. The analysis of the GRB absorption spectra collected in three years would also allow to measure the cosmic mass density of the WHIM with ~15% accuracy, although this estimate depends on the WHIM model. Our results suggest that GRBs represent a valid, if not preferable, alternative to active galactic nuclei to study the WHIM in absorption. The analysis of the absorption spectra nicely complements the study of the WHIM in emission that the spectrometer proposed for EDGE and XENIA would be able to carry out thanks to its high sensitivity and large field of view.

Magnetic Field Amplification in the Thin X-Ray Rims of SN 1006

Abstract: Several young supernova remnants, including SN 1006, emit synchrotron X-rays in narrow filaments, hereafter thin rims, along their periphery. The widths of these rims imply 50-100 μG fields in the region immediately behind the shock, far larger than expected for the interstellar medium compressed by unmodified shocks, assuming electron radiative losses limit rim widths. However, magnetic field damping could also produce thin rims. Here we review the literature on rim width calculations, summarizing the case for magnetic field amplification. We extend these calculations to include an arbitrary power-law dependence of the diffusion coefficient on energy, D∝E {sup μ}. Loss-limited rim widths should shrink with increasing photon energy, while magnetic-damping models predict widths almost independent of photon energy. We use these results to analyze Chandra observations of SN 1006, in particular the southwest limb. We parameterize the FWHM in terms of energy as FWHM ∝E{sub γ}{sup m{sub E}}. Filament widths in SN 1006 decrease with energy; m{sub E} ∼ –0.3 to –0.8, implying magnetic field amplification by factors of 10-50, above the factor of four expected in strong unmodified shocks. For SN 1006, the rapid shrinkage rules out magnetic damping models. It also favors short mean free paths (small diffusion coefficients)more » and strong dependence of D on energy (μ ≥ 1).« less

The GSMaP Precipitation Retrieval Algorithm for Microwave Sounders—Part I: Over-Ocean Algorithm

Abstract: We develop an over-ocean rainfall retrieval algorithm for the Advanced Microwave Sounding Unit (AMSU) based on the Global Satellite Mapping of Precipitation (GSMaP) microwave radiometer algorithm. This algorithm combines an emission-based estimate from brightness temperature (Tb) at 23 GHz and a scattering-based estimate from Tb at 89 GHz, depending on a scattering index (SI) computed from Tb at both 89 and 150 GHz. Precipitation inhomogeneities are also taken into account. The GSMaP-retrieved rainfall from the AMSU (GSMaP_AMSU) is compared with the National Oceanic and Atmospheric Administration (NOAA) standard algorithm (NOAA_AMSU)-retrieved data using Tropical Rainfall Measuring Mission (TRMM) data as a reference. Rain rates retrieved by GSMaP_AMSU have better agreement with TRMM estimates over midlatitudes during winter. Better estimates over multitudes over winter are given by the use of Tb at 23 GHz in the GSMaP_AMSU algorithm. It was also shown that GSMaP_AMSU has higher rain detection than NOAA_AMSU.

Optical - near-infrared catalog for the AKARI north ecliptic pole Deep field

Abstract: Aims. We present an 8-band (u ∗ , g ′, r ′, i ′, z ′, Y , J , K s ) optical to near-infrared deep photometric catalog based on the observations made with MegaCam and WIRCam at the CFHT, and compute photometric redshifts, z p in the north ecliptic pole (NEP) region. AKARI infrared satellite carried out a deep survey in the NEP region at near- to mid-infrared wavelengths. Our optical to near-infrared catalog allows us to identify the counterparts and z p for the AKARI sources. Methods. We obtained seven-band (g ′, r ′, i ′, z ′, Y , J , K s ) imaging data, and we crossmatched them with existing u ∗ -band data (limiting magnitude = 24.6 mag [5σ ; AB]) to design the band-merged catalog. We included all z ′-band sources with counterparts in at least one of the other bands in the catalog. We used a template-fitting methods to compute z p for all the cataloged sources. Results. The estimated 4σ detection limits within a 1 arcsec aperture radius are 26.7, 25.9, 25.1, and 24.1 mag [AB] for the optical g ′, r ′, i ′, and z ′-bands and 23.4, 23.0, and 22.7 mag for the near-infrared Y , J , and K s -bands, respectively. There are a total of 85 797 sources in the band-merged catalog. An astrometric accuracy of this catalog determined by examining coordinate offsets with regard to 2MASS is 0.013 arcsec with a root mean square offset of 0.32 arcsec. We distinguish 5441 secure stars from extended sources using the u ∗ − J versus g ′ − K s colours, combined with the SExtractor stellarity index of the images. Comparing with galaxy spectroscopic redshifts, we find a photometric redshift dispersion, σ Δz /(1 + z ) , of 0.032 and catastrophic failure rate, Δz /(1 + z ) > 0.15, of 5.8% at z > 1. We extend the estimate of the z p uncertainty over the full magnitude/redshift space with a redshift probability distribution function and find that our redshifts are highly accurate with z ′ p ′ p ′z ′K s diagram, (1.4 star-forming galaxies, AKARI mid-infrared detected sources seem to be affected by stronger dust extinction compared with sources with non-detections in the AKARI mid-infrared bands.

The next-generation infrared space telescope SPICA

Abstract: We present the overview and the current status of SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a mission optimized for mid- and far-infrared astronomy with a cryogenically cooled 3.2 m telescope. SPICA has high spatial resolution and unprecedented sensitivity in the mid- and far-infrared, which will enable us to address a number of key problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets. To reduce the mass of the whole mission, SPICA will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system, a combination of which allows us to have a 3-m class cooled (6 K) telescope in space with moderate total weight (3.7t). SPICA is proposed as a Japanese-led mission together with extensive international collaboration. ESA's contribution to SPICA has been studied under the framework of the ESA Cosmic Vision. The consortium led by SRON is in charge of a key focal plane instrument SAFARI (SPICA Far-Infrared Instrument). Korea and Taiwan are also important partners for SPICA. US participation to SPICA is under discussion. The SPICA project is now in the "risk mitigation phase". The target launch year of SPICA is 2022.