Search Publications
Can the relativistic light-bending model explain X-ray spectral variations of Seyfert galaxies?
Tsujimoto, Masahiro; Ebisawa, Ken; Mizumoto, Misaki +3 more
Many Seyfert galaxies are known to exhibit Fe-K broad emission line features in their X-ray energy spectra. The observed lines have three distinct features: (1) the line profiles are skewed and show significant low-energy tails, (2) the Fe-K band has low variability, which produces a broad and deep dip in the root-mean-square (rms) spectra, and (3…
Is the infrared background excess explained by the isotropic zodiacal light from the outer solar system?
Tsumura, Kohji
This paper investigates whether an isotropic zodiacal light from the outer solar system can account for the detected background excess in the near-infrared. Assuming that interplanetary dust particles are distributed in a thin spherical shell at the outer solar system (>200 au), thermal emission from such cold (<30 K) dust in the shell has a…
Suzaku observations of low surface brightness cluster Abell 1631
Matsumoto, Hironori; Mitsuishi, Ikuyuki; Ota, Naomi +5 more
We present analysis results for a nearby galaxy cluster Abell 1631 at z = 0.046 using the X-ray observatory Suzaku. This cluster is categorized as a low X-ray surface brightness cluster. To study the dynamical state of the cluster, we conduct four-pointed Suzaku observations and investigate physical properties of the Mpc-scale hot gas associated w…
High entropy and evidence for a merger in the low surface brightness cluster Abell 2399
Mitsuishi, Ikuyuki; Ota, Naomi; Babazaki, Yasunori +4 more
We present results of the X-ray analyses of the nearby cluster of galaxies Abell 2399 (z = 0.058) using the XMM-Newton and Suzaku satellites. This cluster is classified as a low surface brightness (LSB) cluster. It has a bimodal structure in X-rays, and the X-ray-emission peaks are significantly offset from the peaks in gas temperature. By de-proj…
Membership determination of open clusters based on a spectral clustering method
Gao, Xin-Hua
We present a spectral clustering (SC) method aimed at segregating reliable members of open clusters in multi-dimensional space. The SC method is a non-parametric clustering technique that performs cluster division using eigenvectors of the similarity matrix; no prior knowledge of the clusters is required. This method is more flexible in dealing wi…
Search for companions in visual binary systems using precise radial-velocity measurements
Sato, Bun'ei; Itoh, Yoichi; Katoh, Noriyuki
The frequency of triple and quadruple systems is considered to be high in the early phase of star formation. Some multiple systems decay in the pre-main-sequence phase. The multiplicity of main-sequence stars provides clues about the evolution of binary systems. This work searched for companions of five components of visual binary systems using pr…
Detection of the thermal component in GRB 160107A
Yamaoka, Kazutaka; Yoshida, Atsumasa; Sakamoto, Takanori +14 more
We present the detection of a blackbody component in gamma-ray burst GRB 160107A emission by using the combined spectral data of the CALET Gamma-ray Burst Monitor (CGBM) and the MAXI Gas Slit Camera (GSC). MAXI/GSC detected the emission ∼45 s prior to the main burst episode observed by the CGBM. The MAXI/GSC and the CGBM spectrum of this prior emi…
Searches for H2O masers toward narrow-line Seyfert 1 galaxies
Hagiwara, Yoshiaki; Doi, Akihiro; Hachisuka, Kazuya +1 more
We present searches for 22 GHz H2O masers toward 36 narrow-line Seyfert 1 galaxies (NLS1s), selected from known NLS1s with vsys ≲ 41000 km s-1. Out of the 36 NLS1s in our sample, 11 have been first surveyed in our observations, while the observations of other NLS1s were previously reported in literature. In our sur…
Energy-dependent intensity variation of the persistent X-ray emission of magnetars observed with Suzaku
Enoto, Teruaki; Ebisawa, Ken; Nakagawa, Yujin
The emission mechanism of magnetars is still controversial even though various observational and theoretical studies have been made. In order to investigate mechanisms of both the persistent X-ray emission and the burst emission of the magnetars, we propose a model in which the persistent X-ray emission consists of numerous micro-bursts of various…
X-ray-bright optically faint active galactic nuclei in the Subaru Hyper Suprime-Cam wide survey
Greene, Jenny E.; Ueda, Yoshihiro; Terashima, Yuichi +8 more
We construct a sample of X-ray-bright optically faint active galactic nuclei by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source catalogs. Fifty-three X-ray sources satisfying i-band magnitude fainter than 23.5 mag and X-ray counts with the EPIC-PN detector larger than 70 are selected from 9.1 deg2, and their spectral…