Taro Kotani - Tokyo-tech

Taro Kotani
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Taro Kotani

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Astrophysics (8)
High Energy Astrophysical Phenomena (6)
Solar and Stellar Astrophysics (1)
Instrumentation and Methods for Astrophysics (1)

Publications Authored By Taro Kotani

23 giant flares from 13 active stars (eight RS CVn systems, one Algol system, three dMe stars and one YSO) were detected during the first two years of our all-sky X-ray monitoring with the gas propotional counters (GSC) of the Monitor of All-sky X-ray Image (MAXI). The observed parameters of all of these MAXI/GSC flares are found to be at the upper ends for stellar flares with the luminosity of 10^(31-34) ergs s-1 in the 2-20 keV band, the emission measure of 10^(54-57) cm-3, the e-folding time of 1 hour to 1.5 days, and the total radiative energy released during the flare of 10^(34-39) ergs. Read More

We report on X-ray spectral and timing results of the new black hole candidate (BHC) MAXI J1659-152 with the orbital period of 2.41 hours (shortest among BHCs) in the 2010 outburst from 65 Rossi X-ray Timing Explorer (RXTE) observations and 8 simultaneous Swift and RXTE observations. According to the definitions of the spectral states in Remillard & McClintock (2006), most of the observations have been classified into the intermediate state. Read More

Cygnus X-3 (Cyg X-3) is a well-known microquasar with relativistic jets. Cyg X-3 is especially famous for its giant radio outbursts, which have been observed once every few years since their first discovery. Each giant outburst presumably consists of a series of short-duration flares. Read More

We present a large X-ray flare from a nearby weak-lined T Tauri star TWA-7 detected with the Gas Slit Camera (GSC) on the Monitor of All-sky X-ray Image (MAXI). The GSC captured X-ray flaring from TWA-7 with a flux of $3\times10^{-9}$ ergs cm$^{-2}$ s$^{-1}$ in 2--20 keV band during the scan transit starting at UT 2010-09-07 18:24:30.The estimated X-ray luminosity at the scan in the energy band is 3$\times10^{32}$ ergs s$^{-1}$,indicating that the event is among the largest X-ray flares fromT Tauri stars. Read More

Authors: Tadayuki Takahashi, Kazuhisa Mitsuda, Richard Kelley, Felix Aharonian, Fumie Akimoto, Steve Allen, Naohisa Anabuki, Lorella Angelini, Keith Arnaud, Hisamitsu Awaki, Aya Bamba, Nobutaka Bando, Mark Bautz, Roger Blandford, Kevin Boyce, Greg Brown, Maria Chernyakova, Paolo Coppi, Elisa Costantini, Jean Cottam, John Crow, Jelle de Plaa, Cor de Vries, Jan-Willem den Herder, Michael DiPirro, Chris Done, Tadayasu Dotani, Ken Ebisawa, Teruaki Enoto, Yuichiro Ezoe, Andrew Fabian, Ryuichi Fujimoto, Yasushi Fukazawa, Stefan Funk, Akihiro Furuzawa, Massimiliano Galeazzi, Poshak Gandhi, Keith Gendreau, Kirk Gilmore, Yoshito Haba, Kenji Hamaguchi, Isamu Hatsukade, Kiyoshi Hayashida, Junko Hiraga, Kazuyuki Hirose, Ann Hornschemeier, John Hughes, Una Hwang, Ryo Iizuka, Kazunori Ishibashi, Manabu Ishida, Kosei Ishimura, Yoshitaka Ishisaki, Naoki Isobe, Masayuki Ito, Naoko Iwata, Jelle Kaastra, Timothy Kallman, Tuneyoshi Kamae, Hideaki Katagiri, Jun Kataoka, Satoru Katsuda, Madoka Kawaharada, Nobuyuki Kawai, Shigeo Kawasaki, Dmitry Khangaluyan, Caroline Kilbourne, Kenzo Kinugasa, Shunji Kitamoto, Tetsu Kitayama, Takayoshi Kohmura, Motohide Kokubun, Tatsuro Kosaka, Taro Kotani, Katsuji Koyama, Aya Kubota, Hideyo Kunieda, Philippe Laurent, Francois Lebrun, Olivier Limousin, Michael Loewenstein, Knox Long, Grzegorz Madejski, Yoshitomo Maeda, Kazuo Makishima, Maxim Markevitch, Hironori Matsumoto, Kyoko Matsushita, Dan McCammon, Jon Miller, Shin Mineshige, Kenji Minesugi, Takuya Miyazawa, Tsunefumi Mizuno, Koji Mori, Hideyuki Mori, Koji Mukai, Hiroshi Murakami, Toshio Murakami, Richard Mushotzky, Yujin Nakagawa, Takao Nakagawa, Hiroshi Nakajima, Takeshi Nakamori, Kazuhiro Nakazawa, Yoshiharu Namba, Masaharu Nomachi, Steve O' Dell, Hiroyuki Ogawa, Mina Ogawa, Keiji Ogi, Takaya Ohashi, Masanori Ohno, Masayuki Ohta, Takashi Okajima, Naomi Ota, Masanobu Ozaki, Frits Paerels, St├ęphane Paltani, Arvind Parmer, Robert Petre, Martin Pohl, Scott Porter, Brian Ramsey, Christopher Reynolds, Shin-ichiro Sakai, Rita Sambruna, Goro Sato, Yoichi Sato, Peter Serlemitsos, Maki Shida, Takanobu Shimada, Keisuke Shinozaki, Peter Shirron, Randall Smith, Gary Sneiderman, Yang Soong, Lukasz Stawarz, Hiroyuki Sugita, Andrew Szymkowiak, Hiroyasu Tajima, Hiromitsu Takahashi, Yoh Takei, Toru Tamagawa, Takayuki Tamura, Keisuke Tamura, Takaaki Tanaka, Yasuo Tanaka, Yasuyuki Tanaka, Makoto Tashiro, Yuzuru Tawara, Yukikatsu Terada, Yuichi Terashima, Francesco Tombesi, Hiroshi Tomida, Miyako Tozuka, Yoko Tsuboi, Masahiro Tsujimoto, Hiroshi Tsunemi, Takeshi Tsuru, Hiroyuki Uchida, Yasunobu Uchiyama, Hideki Uchiyama, Yoshihiro Ueda, Shinichiro Uno, Meg Urry, Shin Watanabe, Nicholas White, Takahiro Yamada, Hiroya Yamaguchi, Kazutaka Yamaoka, Noriko Yamasaki, Makoto Yamauchi, Shigeo Yamauchi, Yoichi Yatsu, Daisuke Yonetoku, Atsumasa Yoshida

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe by performing high-resolution, high-throughput spectroscopy with moderate angular resolution. ASTRO-H covers very wide energy range from 0. Read More

Cyg X-3 is a well-known microquasar with a bipolar relativistic jet. Its famous giant radio outbursts have been repeated once every several years. However, the behavior of the millimeter wave emission has remained unclear because of limitations of time resolution in previous observations. Read More

We report results of the 2006 April multi-wavelengths campaign of SS 433, focusing on X-ray data observed with Suzaku at two orbital phases (in- and out-of- eclipse) and simultaneous optical spectroscopic observations. By analyzing the Fe25 K_alpha lines originating from the jets, we detect rapid variability of the Doppler shifts, dz/dt ~ 0.019/0. Read More

Highly supercritical accretion discs are probable sources of dense optically thick axisymmetric winds. We introduce a new approach based on diffusion approximation radiative transfer in a funnel geometry and obtain an analytical solution for the energy density distribution inside the wind assuming that all the mass, momentum and energy are injected well inside the spherization radius. This allows to derive the spectrum of emergent emission for various inclination angles. Read More

We present the results of optical panoramic and long-slit spectroscopy of the nebula MF16 associated with the Ultraluminous X-ray Source NGC6946 ULX-1. More than 20 new emission lines are identified in the spectra. Using characteristic line ratios we find the electron density n_e ~ 600cm^{-3}, electron temperature in the range from ~9000K to ~20 000K (for different diagnostic lines) and the total emitting gas mass M ~ 900 Msolar. Read More

The Galactic black-hole binary GRO J1655$-$40 was observed with Suzaku on 2005 September 22--23, for a net exposure of 35 ks with the X-ray Imaging Spectrometer (XIS) and 20 ks with the Hard X-ray Detector (HXD). The source was detected over a broad and continuous energy range of 0.7--300 keV, with an intensity of $\sim$50 mCrab at 20 keV. Read More

Affiliations: 1RIKEN, 2ISAS/JAXA, 3NASA/GSFC, 4Tokyo-tech, 5Durham university, 6Kyoto University, 7Cambridge university, 8Hiroshima university, 9Hiroshima university, 10Hiroshima university, 11Aoyama university, 12University of Tokyo, RIKEN, 13University of Tokyo, 14Kogakuin university, 15NASA/GSFC
Category: Astrophysics

We present the results of six Suzaku observations of the recurrent black hole transient 4U1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50keV band, roughly described by an optically thick disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above \~20keV. The disk temperature decreases from 1. Read More

High-resolution X-ray spectra of SS 433 obtained after a binary egress with the Chandra High Energy Transmission Grating Spectrometer (HETGS) were studied. Many Doppler-shifted X-ray emission lines from highly ionized elements were detected. The initial temperature of the jets is estimated to be 20 keV. Read More

We briefly review the Galactic microquasar SS 433/W50 and present a new RXTE spectral and timing study. We show that the X-ray flux decreases during radio flares, a behavior seen in other microquasars. We also find short time-scale variability unveiling emission regions from within the binary system. Read More

We have discovered errors in the calculation of some of the Einstein coefficients in Table 5 and some plots in Figure 3. Due to the errors, the square-root section of the curves of growth of Fe xxvi Ka and Kb, and Ni xxviii Ka in Figure 3 were a few times underestimated. We correct Table 5 and re-plot Figure 3 together with the unaffected curves. Read More

Affiliations: 1RIKEN, 2ISAS, 3ISAS, 4University of Tasmania, 5JPL, 6NASA/GSFC
Category: Astrophysics

The X-ray binary pulsar GX 1+4 was observed with Ginga every year from 1987 to 1991, and with ASCA in 1994. During the Ginga observations, GX 1+4 was in the steady spindown phase, while the X-ray flux was not steady. The X-ray luminosity decreased down to L = 2. Read More