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CHANDRA OBSERVATIONS OF THE AKARI NEP DEEP FIELD
T. Miyaji,M. Krumpe,H. Brunner,T. Ishigaki,H. Hanami,A. Markowitz,T. Takagi,T. Goto,M. A. Malkan,H. Matsuhara,C. Pearson,Y. Ueda,T. Wada 한국천문학회 2017 天文學論叢 Vol.32 No.1
The AKARI NEP Deep Field Survey is an international multiwavelength survey over 0.4 deg$^2$ of the sky. This is the deepest survey made by the InfraRed Camera (IRC) of the infrared astronomical satellite AKARI with 9 filters continuously covering the 2-25 μm range, including three filters in the Spitzer gap between the IRAC and MIPS coverages. This enabled us to make sensitive MIR detection of AGN candidates at z ~ 1, based on hot dust emission in the AGN torus. It is also efficient in detecting highly obscured Compton-thick AGN population. In this article, we report the first results of X-ray observations on this field. The field was covered by 15 overlapping Chandra ACIS-I observations with a total exposure of ~ 300 ks, detecting $\approx 450$ X-ray sources. We utilize rest-frame stacking analysis of the MIR AGN candidates that are not detected individually. Our preliminary analysis shows a marginal detection of the rest-frame stacked Fe K$\alpha$ line from our strong Compton-thick candidates.
The AKARI NEP-Deep survey: a mid-infrared source catalogue
Takagi, T.,Matsuhara, H.,Goto, T.,Hanami, H.,Im, M.,Imai, K.,Ishigaki, T.,Lee, H. M.,Lee, M. G.,Malkan, M.,Ohyama, Y.,Oyabu, S.,Pearson, C. P.,Serjeant, S.,Wada, T.,White, G. J. Springer-Verlag 2012 Astronomy and astrophysics Vol.537 No.-
<P>We present a new catalogue of mid-IR sources using the AKARI NEP-Deep survey. The InfraRed Camera (IRC) onboard AKARI has a comprehensive mid-IR wavelength coverage with 9 photometric bands at 2–24?µm. We utilized all of these bands to cover a nearly circular area adjacent to the north ecliptic pole (NEP). We designed the catalogue to include most of sources detected in 7, 9, 11, 15 and 18?µm bands, and found 7284 sources in a 0.67?deg<SUP>2</SUP> area. From our simulations, we estimate that the catalogue is~80 per cent complete to 200µJy at 15–18µm, and ~10 per cent of sources are missed, owing to source blending. Star-galaxy separation is conducted using only AKARI photometry, as a result of which 10 per cent of catalogued sources are found to be stars. The number counts at 11, 15, 18, and 24µm are presented for both stars and galaxies. A drastic increase in the source density is found in between 11 and 15µm at the flux level of~300micro;Jy. This is likely due to the redshifted PAH emission at 8µm, given our rough estimate of redshifts from an AKARI colour–colour plot. Along with the mid-IR source catalogue, we present optical-NIR photometry for sources falling inside a Subaru/Sprime-cam image covering part of the AKARI NEP-Deep field, which is deep enough to detect most of AKARI mid-IR sources, and useful to study optical characteristics of a complete mid-IR source sample.</P>
Structural and Magnetic Properties of Dilute Spinel Ferrites
H. Mamiya,N. Terada,H. Kitazawa,A. Hoshikawa,T. Ishigaki 한국자기학회 2011 Journal of Magnetics Vol.16 No.2
Magnetic properties of highly zinc-substituted manganese ferrites are discussed on the basis of cation distribution. High throughput neutron powder diffractometry indicates that the prepared samples possess a nearly normal spinel structure, where the substitution of nonmagnetic zinc ions mainly causes the dilution of magnetic ions in the A-sublattice and consequently affects bond-randomness in the B-sublattice. On the other hand, the estimated occupancy of manganese ions in the B site indicates that random anisotropy effects due to local Jahn-Teller distortions gradually weaken with the substitution. Bulk magnetometry indicates that the substitution smears the transition from a paramagnetic phase to a soft-magnetic phase. Furthermore, at lower temperatures, such a soft-magnetic phase is destabilized and a magnetic glassy state appears. These features of the magnetic properties of dilute spinel ferrites are discussed from the viewpoint of the above-mentioned various types of disorders.