Yujin E. Nakagawa - Aoyama Gakuin University, Sagamihara, Kanagawa, Japan

Yujin E. Nakagawa
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Name
Yujin E. Nakagawa
Affiliation
Aoyama Gakuin University, Sagamihara, Kanagawa, Japan
City
Sagamihara
Country
Japan

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High Energy Astrophysical Phenomena (16)
 
Astrophysics (9)
 
Instrumentation and Methods for Astrophysics (2)
 
Solar and Stellar Astrophysics (1)
 
Cosmology and Nongalactic Astrophysics (1)

Publications Authored By Yujin E. Nakagawa

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 present the catalog of high Galactic-latitude ($|b|>10^{\circ}$) X-ray sources detected in the first 37-month data of Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC). To achieve the best sensitivity, we develop a background model of the GSC that well reproduces the data based on the detailed on-board calibration. Source detection is performed through image fit with the Poisson likelihood algorithm. Read More

We present the results of monitoring the Galactic black hole candidate GX 339-4 with the Monitor of All-sky X-ray Image (MAXI) / Gas Slit Camera (GSC) in the high/soft state during the outburst in 2010. All the spectra throughout the 8-month period are well reproduced with a model consisting of multi-color disk (MCD) emission and its Comptonization component, whose fraction is <= 25% in the total flux. In spite of the flux variability over a factor of 3, the innermost disk radius is constant at R_in = 61 +/- 2 km for the inclination angle of i = 46 deg and the distance of d=8 kpc. 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

We present the first unbiased source catalog of the Monitor of All-sky X-ray Image (MAXI) mission at high Galactic latitudes ($|b| > 10^{\circ}$), produced from the first 7-month data (2009 September 1 to 2010 March 31) of the Gas Slit Camera in the 4--10 keV band. We develop an analysis procedure to detect faint sources from the MAXI data, utilizing a maximum likelihood image fitting method, where the image response, background, and detailed observational conditions are taken into account. The catalog consists of 143 X-ray sources above 7 sigma significance level with a limiting sensitivity of $\sim1. Read More

The monitor of all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB\,090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst has peculiarly narrow spectral energy distribution and is represented by Comptonized blackbody model. Read More

Using data with the Suzaku XIS and HXD, spectral studies of short bursts from the soft gamma repeater SGR 0501+4516 were performed. In total, 32 bursts were detected during the ~60 ks of observation conducted in the 2008 August activity. Excluding the strongest one, the remaining 31 bursts showed an average 2--40 keV fluence of 1. Read More

2010Oct
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

Strong X-ray flares from the blazar Mrk 421 were detected in 2010 January and February through the 7 month monitoring with the MAXI GSC. The maximum 2 -- 10 keV flux in the January and February flares was measured as 120 +- 10 mCrab and 164 +- 17 mCrab respectively; the latter is the highest among those reported from the object. A comparison of the MAXI and Swift BAT data suggests a convex X-ray spectrum with an approximated photon index of about 2. Read More

We present the first results on the black hole candidate XTE J1752-223 from the Gas Slit Camera (GSC) on-board the Monitor of All-sky X-ray Image (MAXI) on the International Space Station. Including the onset of the outburst reported by the Proportional Counter Array on-board the Rossi X-ray Timing Explorer on 2009 October 23, the MAXI/GSC has been monitoring this source approximately 10 times per day with a high sensitivity in the 2-20 keV band. XTE J1752-223 was initially in the low/hard state during the first 3 months. Read More

2009Jun
Affiliations: 1ISS Science Project Office, ISAS, JAXA, 2ISS Science Project Office, ISAS, JAXA, 3ISS Science Project Office, ISAS, JAXA, 4ISS Science Project Office, ISAS, JAXA, 5ISS Science Project Office, ISAS, JAXA, 6ISS Science Project Office, ISAS, JAXA, 7ISS Science Project Office, ISAS, JAXA, 8ISS Science Project Office, ISAS, JAXA, 9Cosmic Radiation Laboratory, RIKEN, 10Cosmic Radiation Laboratory, RIKEN, 11Cosmic Radiation Laboratory, RIKEN, 12Cosmic Radiation Laboratory, RIKEN, 13Department of Earth and Space Science, Osaka University, 14Department of Earth and Space Science, Osaka University, 15Department of Physics, Tokyo Institute of Technology, 16Department of Physics, Tokyo Institute of Technology, 17Department of Physics, Tokyo Institute of Technology, 18Department of Physics and Mathematics, Aoyama Gakuin University, 19Department of Physics, Nihon University, 20Department of Physics, Nihon University, 21Department of Astronomy, Kyoto University, 22Cosmic Radiation Laboratory, RIKEN, 23Department of Physics and Mathematics, Aoyama Gakuin University, 24Department of Physics and Mathematics, Aoyama Gakuin University, 25Department of Physics and Mathematics, Aoyama Gakuin University, 26Department of Physics and Mathematics, Aoyama Gakuin University, 27Department of Physics, Nihon University, 28Department of Physics, Nihon University, 29Department of Astronomy, Kyoto University, 30Department of Astronomy, Kyoto University, 31Earth Observation Research Center, JAXA, 32ISAS, JAXA

The MAXI (Monitor of All-sky X-ray Image) mission is the first astronomical payload to be installed on the Japanese Experiment Module-Exposed Facility (JEM-EF) on the ISS. It is scheduled for launch in the middle of 2009 to monitor all-sky X-ray objects on every ISS orbit. MAXI will be more powerful than any previous X-ray All Sky Monitor (ASM) payloads, being able to monitor hundreds of AGN. Read More

We perform a time-resolved spectral analysis of bright, long Gamma-ray burst GRB 061007 using Suzaku/WAM and Swift/BAT. Thanks to the large effective area of the WAM, we can investigate the time evolution of the spectral peak energy, Et_peak and the luminosity Lt_iso with 1-sec time resolution, and we find that luminosity Lt_iso with 1-sec time resolution, and we find that the time-resolved pulses also satisfy the Epeak-Liso relation, which was found for the time-averaged spectra of other bursts, suggesting the same physical conditions in each pulse. Furthermore, the initial rising phase of each pulse could be an outlier of this relation with higher Et_peak value by about factor 2. Read More

Spectral and timing studies of Suzaku ToO observations of two SGRs, 1900+14 and 1806-20, are presented. The X-ray quiescent emission spectra were well fitted by a two blackbody function or a blackbody plus a power law model. The non-thermal hard component discovered by INTEGRAL was detected by the PIN diodes and its spectrum was reproduced by the power law model reported by INTEGRAL. Read More

2007Nov
Affiliations: 1ISAS/JAXA, Japan, 2ISAS/JAXA, Japan, 3Department of Physics, Tokyo Institute of Technology, Tokyo, Japan, 4ISAS/JAXA, Japan, 5ISAS/JAXA, Japan, 6Rikkyo University, Tokyo, Japan, 7RIKEN, Japan, 8University of Tokyo, Japan, 9University of Tokyo, Japan, 10Kanazawa University, Kanazawa, Japan, 11Aoyama Gakuin University, Sagamihara, Kanagawa, Japan, 12Hiroshima University, Japan, 13RIKEN, Japan, 14Aoyama Gakuin University, Sagamihara, Kanagawa, Japan
Category: Astrophysics

Suzaku TOO observation of the anomalous X-ray pulsar CXOU J164710.2-455216 was performed on 2006 September 23--24 for a net exposure of 38.8 ks. Read More

The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-WIND, RHESSI, Suzaku-WAM, and \textit{Swift}-BAT. We detail the results of joint spectral fits with Konus and RHESSI data. Read More

Spectral studies of quiescent emission and bursts of magnetar candidates using XMM-Newton, Chandra and Swift data are presented. Spectra of both the quiescent emission and the bursts for most magnetar candidates are reproduced by a photoelectrically absorbed two blackbody function (2BB). There is a strong correlation between lower and higher temperatures of 2BB (kT_LT and kT_HT) for the magnetar candidates of which the spectra are well reproduced by 2BB. Read More

We present the results of temporal and spectral studies of the short burst (less than a few hundred milliseconds) from the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 detected 50 bursts which were localized to SGR 1806-20 and 5 bursts which were localized to SGR 1900+14. Especially SGR 1806-20 was active in 2004, and HETE-2 localized 33 bursts in that year. Read More