Search

Your search keyword '"Kensei, Shiki"' showing total 14 results
Start Over Author "Kensei, Shiki"
14 results on '"Kensei, Shiki"'

1. Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar

Author

Clark, Colin J., Pletsch, Holger J., Aulbert, Carsten, Orienti, Monica, Orlando, Elena, Palatiello, Michele, Paliya, Vaidehi S., de Palma, Francesco, Paneque, David, Perkins, Jeremy S., Persic, Massimo, Pesce-Rollins, Melissa, Porter, Troy A., Beer, Christian, Principe, Giacomo, Rainò, Silvia, Rando, Riccardo, Ray, Paul S., Razzano, Massimiliano, Reimer, Anita, Reimer, Olaf, Romani, Roger W., Saz Parkinson, Pablo M., Sgrò, Carmelo, Bock, Oliver, Siskind, Eric J., Smith, David A., Spada, Francesca, Spandre, Gloria, Spinelli, Paolo, Thayer, Jana B., Thompson, David J., Torres, Diego F., Troja, Eleonora, Vianello, Giacomo, Cuéllar, Andres, Wood, Kent, Wood, Matthew, Fermi-LAT Collaboration, Eggenstein, Heinz-Bernd, Fehrmann, Henning, Kramer, Michael, Kwang, Shawn A., Machenschalk, Bernd, Nieder, Lars, Wu, Jason, Ackermann, Markus, Ajello, Marco, Baldini, Luca, Ballet, Jean, Barbiellini, Guido, Bastieri, Denis, Bellazzini, Ronaldo, Bissaldi, Elisabetta, Blandford, Roger D., Bloom, Elliott D., Guillemot, Lucas, Bonino, Raffaella, Bottacini, Eugenio, Brandt, Terri J., Bregeon, Johan, Bruel, Philippe, Buehler, Rolf, Burnett, Toby H., Buson, Sara, Cameron, Rob A., Caputo, Regina, Kerr, Matthew, Caraveo, Patrizia A., Cavazzuti, Elisabetta, Cecchi, Claudia, Charles, Eric, Chekhtman, Alexandre, Ciprini, Stefano, Cominsky, Lynn R., Costantin, Denise, Cutini, Sara, D'Ammando, Filippo, Johnson, Tyrel J., De Luca, Andrea, Desiante, Rachele, Di Venere, Leonardo, Di Mauro, Mattia, Di Lalla, Niccolò, Digel, Seth W., Favuzzi, Cecilia, Ferrara, Elizabeth C., Franckowiak, Anna, Fukazawa, Yasushi, Camilo, Fernando, Funk, Stefan, Fusco, Piergiorgio, Gargano, Fabio, Gasparrini, Dario, Giglietto, Nico, Giordano, Francesco, Giroletti, Marcello, Gomez-Vargas, Germán A., Green, David, Grenier, Isabelle A., Salvetti, David, Guiriec, Sylvain, Harding, Alice K., Hewitt, John W., Horan, Deirdre, Jóhannesson, Guðlaugur, Kensei, Shiki, Kuss, Michael, La Mura, Giovanni, Larsson, Stefan, Latronico, Luca, Allen, Bruce, Li, Jian, Longo, Francesco, Loparco, Francesco, Lovellette, Michael N., Lubrano, Pasquale, Magill, Jeffrey D., Maldera, Simone, Manfreda, Alberto, Mazziotta, Mario N., McEnery, Julie E., Anderson, David, Michelson, Peter F., Mirabal, Nestor, Mitthumsiri, Warit, Mizuno, Tsunefumi, Monzani, Maria Elena, Morselli, Aldo, Moskalenko, Igor V., Nuss, Eric, Ohsugi, Takashi, Omodei, Nicola, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Particules de Montpellier (LUPM), Université de Montpellier (UM)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Leprince-Ringuet (LLR), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Centre d'Etudes Nucléaires de Bordeaux Gradignan (CENBG), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Fermi-LAT, Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), ITA, Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Université Montpellier 2 - Sciences et Techniques (UM2)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace ( LPC2E ), Centre National de la Recherche Scientifique ( CNRS ) -Université d'Orléans ( UO ) -Institut national des sciences de l'Univers ( INSU - CNRS ), Unité Scientifique de la Station de Nançay ( USN ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire AIM, Université Paris Diderot - Paris 7 ( UPD7 ) -Centre d'Etudes de Saclay, Laboratoire Univers et Particules de Montpellier ( LUPM ), Centre National de la Recherche Scientifique ( CNRS ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Université Montpellier 2 - Sciences et Techniques ( UM2 ) -Université de Montpellier ( UM ), Laboratoire Leprince-Ringuet ( LLR ), Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -École polytechnique ( X ) -Centre National de la Recherche Scientifique ( CNRS ), Centre d'Etudes Nucléaires de Bordeaux Gradignan ( CENBG ), Université Sciences et Technologies - Bordeaux 1-Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Centre National de la Recherche Scientifique ( CNRS ), Raunvísindastofnun (HÍ), Science Institute (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland, Clark, Colin J., Pletsch, Holger J., Wu, Jason, Guillemot, Luca, Kerr, Matthew, Johnson, Tyrel J., Camilo, Fernando, Salvetti, David, Allen, Bruce, Anderson, David, Aulbert, Carsten, Beer, Christian, Bock, Oliver, Cuéllar, Andre, Eggenstein, Heinz-Bernd, Fehrmann, Henning, Kramer, Michael, Kwang, Shawn A., Machenschalk, Bernd, Nieder, Lar, Ackermann, Marku, Ajello, Marco, Baldini, Luca, Ballet, Jean, Barbiellini, Guido, Bastieri, Deni, Bellazzini, Ronaldo, Bissaldi, Elisabetta, Blandford, Roger D., Bloom, Elliott D., Bonino, Raffaella, Bottacini, Eugenio, Brandt, Terri J., Bregeon, Johan, Bruel, Philippe, Buehler, Rolf, Burnett, Toby H., Buson, Sara, Cameron, Rob A., Caputo, Regina, Caraveo, Patrizia A., Cavazzuti, Elisabetta, Cecchi, Claudia, Charles, Eric, Chekhtman, Alexandre, Ciprini, Stefano, Cominsky, Lynn R., Costantin, Denise, Cutini, Sara, D'Ammando, Filippo, De Luca, Andrea, Desiante, Rachele, Di Venere, Leonardo, Di Mauro, Mattia, Di Lalla, Niccolò, Digel, Seth W., Favuzzi, Cecilia, Ferrara, Elizabeth C., Franckowiak, Anna, Fukazawa, Yasushi, Funk, Stefan, Fusco, Piergiorgio, Gargano, Fabio, Gasparrini, Dario, Giglietto, Nico, Giordano, Francesco, Giroletti, Marcello, Gomez-Vargas, Germán A., Green, David, Grenier, Isabelle A., Guiriec, Sylvain, Harding, Alice K., Hewitt, John W., Horan, Deirdre, Jóhannesson, Guolaugur, Kensei, Shiki, Kuss, Michael, La Mura, Giovanni, Larsson, Stefan, Latronico, Luca, Li, Jian, Longo, Francesco, Loparco, Francesco, Lovellette, Michael N., Lubrano, Pasquale, Magill, Jeffrey D., Maldera, Simone, Manfreda, Alberto, Mazziotta, Mario N., Mcenery, Julie E., Michelson, Peter F., Mirabal, Nestor, Mitthumsiri, Warit, Mizuno, Tsunefumi, Monzani, Maria Elena, Morselli, Aldo, Moskalenko, Igor V., Nuss, Eric, Ohsugi, Takashi, Omodei, Nicola, Orienti, Monica, Orlando, Elena, Palatiello, Michele, Paliya, Vaidehi S., De Palma, Francesco, Paneque, David, Perkins, Jeremy S., Persic, Massimo, Pesce-Rollins, Melissa, Porter, Troy A., Principe, Giacomo, Rainò, Silvia, Rando, Riccardo, Ray, Paul S., Razzano, Massimiliano, Reimer, Anita, Reimer, Olaf, Romani, Roger W., Parkinson, Pablo M. Saz, Sgrò, Carmelo, Siskind, Eric J., Smith, David A., Spada, Francesca, Spandre, Gloria, Spinelli, Paolo, Thayer, Jana B., Thompson, David J., Torres, Diego F., Troja, Eleonora, Vianello, Giacomo, Wood, Kent, and Wood, Matthew

Subjects
Einstein@Home, Gammageislar, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], Astronomy, Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, law.invention, Telescope, Computer Science::Hardware Architecture, Bulge, Millisecond pulsar, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010306 general physics, education, 010303 astronomy & astrophysics, Research Articles, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), education.field_of_study, Line-of-sight, Multidisciplinary, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Nifteindastjörnur, Astrophysics::Instrumentation and Methods for Astrophysics, SciAdv r-articles, Computer Science::Computers and Society, Stjörnusjónaukar, Neutron star, ddc:500, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Fermi Gamma-ray Space Telescope, Research Article
Abstract

Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date, radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs, we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs, one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations, raising hopes for detecting MSPs from a predicted Galactic bulge population., This work was supported by the Max-Planck-Gesellschaft, the Deutsche Forschungsgemeinschaft through an Emmy Noether Research Grant [no. PL 710/1-1 (H.J.P.)], and NSF award 1104902. C.J.C. acknowledges support from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 715051; Spiders). W.M. was partially supported by the Thailand Research Fund (grants TRG5880173 and RTA5980003). M.R. was funded by the Italian Ministry of Education, University and Research (contract no. FIRB-2012-RBFR12PM1F). Work at the Naval Research Laboratory is supported by NASA. The Parkes Observatory is part of the Australia Telescope, funded by the Commonwealth of Australia for operation as a National Facility managed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT, as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France; the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan; and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Études Spatiales in France. This work performed in part under DOE Contract DE-AC02-76SF00515.

Published
2018

2. Multiband optical variability of the blazar OJ 287 during its outbursts in 2015–2016

Author

Kensei Shiki, Yuka Kanda, Haritma Gaur, Jun-Hui Fan, Givi N. Kimeridze, Makoto Uemura, Z. Zhang, R. A. Chigladze, Alka Mishra, Tatsuya Nakaoka, Minfeng Gu, Georgi Latev, M. G. Nikolashvili, Miho Kawabata, Lorand A. Sigua, Rumen Bachev, Aditi Agarwal, O. M. Kurtanidze, Paul J. Wiita, Ryosuke Itoh, Ashwani Pandey, O. Vince, Goran Damljanović, Evgeni Semkov, J. Hirochi, A. Strigachev, Sofia O. Kurtanidze, Pankaj Kushwaha, R. G. Chanishvili, R. V. Munoz Dimitrova, Taisei Abe, Alok C. Gupta, Beatriz Villarroel, and B. Spassov

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Blazar, 010303 astronomy & astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

We present recent optical photometric observations of the blazar OJ 287 taken during September 2015 -- May 2016. Our intense observations of the blazar started in November 2015 and continued until May 2016 and included detection of the large optical outburst in December 2016 that was predicted using the binary black hole model for OJ 287. For our observing campaign, we used a total of 9 ground based optical telescopes of which one is in Japan, one is in India, three are in Bulgaria, one is in Serbia, one is in Georgia, and two are in the USA. These observations were carried out in 102 nights with a total of ~ 1000 image frames in BVRI bands, though the majority were in the R band. We detected a second comparably strong flare in March 2016. In addition, we investigated multi-band flux variations, colour variations, and spectral changes in the blazar on diverse timescales as they are useful in understanding the emission mechanisms. We briefly discuss the possible physical mechanisms most likely responsible for the observed flux, colour and spectral variability., 11 pages, 6 figures, 4 tables; Accepted for publication in MNRAS

Published
2016

3. Low-luminosity Type IIP Supernova 2016bkv with early-phase circumstellar interaction

Author

Hiroki Mori, Hiroshi Akitaya, Michitoshi Yoshida, Ryosuke Itoh, Kensei Shiki, Takahiro Nagayama, Miho Kawabata, Keiichi Maeda, Tomoki Morokuma, Nozomu Tominaga, H. Hanayama, Yuki Moritani, T. Urano, Naoki Kawahara, Takashi J. Moriya, Issei Ueno, Koji S. Kawabata, Tatsuya Nakaoka, Taisei Abe, M. Isogai, Makoto Uemura, Masaomi Tanaka, Masayuki Yamanaka, J. Hirochi, and Katsutoshi Takaki

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Astrophysics - Astrophysics of Galaxies, Luminosity, Supernova, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Early phase, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

We present optical and near-infrared observations of a low-luminosity Type IIP supernova (SN) 2016bkv from the initial rising phase to the plateau phase. Our observations show that the end of the plateau is extended to $\gtrsim 140$ days since the explosion, indicating that this SN takes one of the longest time to finish the plateau phase. among Type IIP SNe (SNe IIP), including low-luminosity (LL) SNe IIP. The line velocities of various ions at the middle of the plateau phase are as low as 1,000--1,500 km s$^{-1}$, which is the lowest even among LL SNe IIP. These measurements imply that the ejecta mass in SN 2016bkv is larger than that of the well-studied LL IIP SN 2003Z. In the early phase, SN 2016bkv shows a strong bump in the light curve. In addition, the optical spectra in this bump phase exhibit a blue continuum accompanied with a narrow H$\alpha$ emission line. These features indicate an interaction between the SN ejecta and the circumstellar matter (CSM) as in SNe IIn. Assuming the ejecta-CSM interaction scenario, the mass loss rate is estimated to be $\sim 1.7 \times 10^{-2} M_{\odot}$ yr$^{-1}$ within a few years before the SN explosion. This is comparable to or even larger than the largest mass loss rate observed for the Galactic red supergiants ($\sim 10^{-3} M_{\odot}$ yr$^{-1}$ for VY CMa). We suggest that the progenitor star of SN 2016bkv experienced a violent mass loss just before the SN explosion., Comment: 9 pages, 12 figures. Accepted for publication in ApJ

Published
2018

4. No Ly$\alpha$ emitters detected around a QSO at z=6.4: Suppressed by the QSO?

Author

Kensei Shiki, Satoshi Kikuta, Tomotsugu Goto, Yousuke Utsumi, Satoshi Miyazaki, and Tetsuya Hashimoto

Subjects
Physics, Number density, Field (physics), 010308 nuclear & particles physics, Order (ring theory), Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Astrophysics - Astrophysics of Galaxies, Galaxy, Redshift, Space and Planetary Science, 0103 physical sciences, Galaxy formation and evolution, Halo, 010303 astronomy & astrophysics, Reionization, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

Understanding how QSO's UV radiation affects galaxy formation is vital to our understanding of reionization era. Using a custom made narrow-band filter, $NB906$, on Subaru/Suprime-Cam, we investigated the number density of Ly$\alpha$ emitters (LAE) around a QSO at z=6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field-of-view of Suprime-Cam, our survey area is $\sim$5400~cMpc$^2$, much larger than previously studies at z=5.7 ($\sim$200 cMpc$^2$). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies (LBGs). Based on this, we expected to detect $\sim$100 LAEs down to $NB906$=25 ABmag. However, our 6.4 hour exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 $p$Mpc across. A simple argument suggests a strong UV radiation from the QSO can suppress star-formation in halos with $M_{vir}, Comment: Accepted for publication in MNRAS Letters. https://academic.oup.com/mnrasl/article-lookup/doi/10.1093/mnrasl/slx088

Published
2017

5. A measurement of interstellar polarization and an estimation of Galactic extinction for the direction of the X-ray black hole binary V404 Cygni

Author

Hiroshi Akitaya, Yasushi Fukazawa, Kensei Shiki, Miho Kawabata, Yasuyuki T. Tanaka, R. Itoh, Tatsuya Nakaoka, Makoto Uemura, Yuki Moritani, Makoto Watanabe, Michitoshi Yoshida, Yumiko Oasa, Jun Takahashi, Koji S. Kawabata, and Yuka Kanda

Subjects
010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Extinction (astronomy), FOS: Physical sciences, Synchrotron radiation, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Astrophysical jet, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Astronomy and Astrophysics, Optical polarization, Polarization (waves), Interstellar medium, Stars, Space and Planetary Science, Spectral energy distribution, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

V404 Cygni is a well-known black hole binary candidate thought to have relativistic jets. It showed extreme outbursts on June 2015, characterized by a large amplitude and short time variation of flux in the radio, optical, and X-ray bands. Not only disk emission, but also synchrotron radiation from the relativistic jets were suggested by radio observations. However, it is difficult to measure the accurate spectral shape in the optical/near infrared band because there are uncertainties of interstellar extinction. To estimate the extinction value for V404 Cygni, we performed photopolarimetric and spectroscopic observations of V404 Cygni and nearby field stars. Here, we estimate the Galactic extinction using interstellar polarization based on the observation that the origin of the optical polarization is the interstellar medium, and investigate the properties of interstellar polarization around V404~Cygni. We found a good correlation between the color excess and polarization degree in the field stars. We also confirmed that the wavelength dependence of the polarization degree in the highly polarized field stars was similar to that of V404~Cygni. Using the highly polarized field stars, we estimated the color excess and the extinction, $E(B-V)=1.2 \pm 0.2$ and $3.0 < A(V) < 3.6$, respectively. A tendency for a bluer peak of polarization ($��_{\rm max}, 11 pages, 6 figures, 3 tables. Accepted for publication in PASJ

Published
2017

6. Systematic Study of Gamma-ray bright Blazars with Optical Polarization and Gamma-ray Variability

Author

Takashi Ohsugi, Tatsuya Nakaoka, Grzegorz Madejski, Koji S. Kawabata, Yuka Kanda, Miho Kawabata, Hiroshi Akitaya, Krzysztof Nalewajko, Mahito Sasada, Yasushi Fukazawa, Kensei Shiki, Masayuki Yamanaka, Katsutoshi Takaki, Takahiro Ui, Yasuyuki T. Tanaka, Ryosuke Itoh, Koji Takata, Makoto Uemura, Frank K. Schinzel, Yuki Moritani, and Michitoshi Yoshida

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Active galactic nucleus, 010308 nuclear & particles physics, Linear polarization, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, Synchrotron radiation, FOS: Physical sciences, Astronomy and Astrophysics, Optical polarization, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Astrophysical jet, Space and Planetary Science, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Blazar, 010303 astronomy & astrophysics
Abstract

Blazars are highly variable active galactic nuclei which emit radiation at all wavelengths from radio to gamma-rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between Jul. 2008 and Dec. 2014 to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in pc-scale relativistic jets between different types blazars (FSRQs vs. BL Lacs), and consequently between different types of radio galaxies (FR Is vs. FR IIs)., Comment: 17 pages, 30 figures, 6 tables. Accepted for publication in Astrophysical Journal

Published
2016
Full Text
View/download PDF

7. No Evidence of Intrinsic Optical/Near-Infrared Linear Polarization for V404 Cygni During its Bright Outburst in 2015: Broadband Modeling and Constraint on Jet Parameters

Author

Makoto Watanabe, A. Ikebe, Daisuke Kuroda, S. Gouda, Yoshiyuki Inoue, K. Sekiguchi, Kumiko Morihana, Kensuke Hosoya, Masataka Imai, Yumiko Oasa, Tatsuya Nakaoka, Tomoki Morokuma, Makoto Uemura, Tomohito Ohshima, Nobuyuki Kawai, Katsutoshi Takaki, Satoshi Honda, C. C. Cheung, Keisuke Isogai, Michitoshi Yoshida, Jun Takahashi, Taichi Kato, T. Fujiwara, Yoshihiko Saito, Yasuyuki T. Tanaka, Daisaku Nogami, Yasushi Fukazawa, Yuya Gouda, Hiroshi Akitaya, Hinako Akimoto, Takumi Nagayama, Masashi Kimura, Taketoshi Yoshii, Yuhei Takagi, Katsuhiro L. Murata, Yutaro Tachibana, Kyoko Watanabe, Yoichi Yatsu, Kensei Shiki, Ryosuke Itoh, Koji S. Kawabata, and Miho Kawabata

Subjects
Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, law.invention, stars: jets, symbols.namesake, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Blazar, infrared: stars, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, stars: individual: V404 Cyg, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), polarization, 010308 nuclear & particles physics, Linear polarization, stars, Astronomy and Astrophysics, radiation mechanisms: non-thermal, Light curve, Position angle, Synchrotron, Particle acceleration, Lorentz factor, binaries: general, Space and Planetary Science, symbols, Astrophysics - High Energy Astrophysical Phenomena, Flare
Abstract

著者人数: 42名, Accepted: 2016-03-14, 資料番号: SA1160038000

Published
2016
Full Text
View/download PDF

8. X-Ray and GeV Gamma-Ray Variability of the Radio Galaxy NGC 1275

Author

and Hiroshi Nagai, Hiromitsu Takahashi, Fumiya Imazato, Kensei Shiki, Yasuyuki T. Tanaka, Ryosuke Itoh, Roopesh Ojha, Yasushi Fukazawa, Filippo D'Ammando, ITA, USA, and JPN

Subjects
Physics, 010308 nuclear & particles physics, Space and Planetary Science, High energy accelerator, Research council, Astrophysics::High Energy Astrophysical Phenomena, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Library science, Astronomy and Astrophysics, Christian ministry, 010303 astronomy & astrophysics, 01 natural sciences
Abstract

The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include NASA and the Department of Energy in the United States, the Commissariat a l’Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’Etudes Spatiales in France. This work was performed in part under DOE Contract DE- AC02-76SF00515.

Published
2018

9. No Ly α emitters detected around a QSO at z = 6.4: Suppressed by the QSO?

Author

Tomotsugu Goto, Yousuke Utsumi, Satoshi Kikuta, Satoshi Miyazaki, Kensei Shiki, and Tetsuya Hashimoto

Subjects
QUASARS, GALAXY formation, BLACK holes, GALACTIC redshift, ASTRONOMICAL observations
Abstract

Understanding how quasars' (QSOs') ultraviolet (UV) radiation affects galaxy formation is vital to our understanding of the reionization era. Using a custom-made narrow-band filter, NB906, on Subaru/Suprime-Cam, we investigated the number density of Ly α emitters (LAEs) around a QSO at z = 6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field of view of Suprime-Cam, our survey area is ~5400 cMpc², much larger than previous studies at z = 5.7 (~200 cMpc²). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies. Based on this, we expected to detect ~100 LAEs down to NB906 = 25 ABmag. However, our 6.4 h exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 pMpc across. A simple argument suggests that a strong UV radiation from the QSO can suppress star formation in haloes with Mvir < 1010?MΘ within a pMpc from the QSO, but the deficit at the edge of the field (5 pMpc) remains to be explained. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

10. A measurement of interstellar polarization and an estimation of Galactic extinction for the direction of the X-ray black hole binary V404 Cygni.

Author

Ryosuke ITOH, TANAKA, Yasuyuki T., KAWABATA, Koji S., Makoto UEMURA, Makoto WATANABE, Yasushi FUKAZAWA, Yuka KANDA, Hiroshi AKITAYA, Yuki MORITANI, Tatsuya NAKAOKA, Miho KAWABATA, Kensei SHIKI, Michitoshi YOSHIDA, Yumiko OASA, and Jun TAKAHASHI

Subjects
BINARY black holes, X-ray binaries, INTERSTELLAR reddening, SYNCHROTRON radiation, DUST
Abstract

V404 Cygni is a well-known candidate for the black hole binary thought to have relativistic jets. It showed extreme outbursts in 2015 June, characterized by a large amplitude and short time variation of flux in the radio, optical, and X-ray bands. Not only disk emission but also synchrotron radiation from the relativistic jets was suggested by radio observations. However, it is difficult to measure the accurate spectral shape in the optical/near-infrared band because there are uncertainties of interstellar extinction. To estimate the extinction value for V404 Cygni, we performed photopolarimetric and spectroscopic observations of V404 Cygni and nearby field stars. Here, we estimate the Galactic extinction using interstellar polarization based on the observation that the origin of the optical polarization is the interstellar medium, and investigate the properties of interstellar polarization around V404 Cygni. We found a good correlation between the color excess and polarization degree in the field stars. We also confirmed that the wavelength dependence of the polarization degree in the highly polarized field stars was similar to that of V404 Cygni. Using the highly polarized field stars, we estimated the color excess for the (B - V) color and the extinction in the V band to be E(B - V) = 1.2±0.2 and 3.0 < A(V) < 3.6, respectively. A tendency for a bluer peak of polarization (λmax < 5500A° ) was commonly seen in the highly polarized field stars, suggesting that the dust grains toward this region are generally smaller than the Galactic average. The corrected spectral energy distribution of V404 Cygni in the near-infrared and optical bands in our results indicated a spectral break between 2.5 × 1014 Hz and 3.7 × 1014 Hz, which might originate in the synchrotron self-absorption. [ABSTRACT FROM AUTHOR]

Published
2017
Full Text
View/download PDF

11. The Low-luminosity Type IIP Supernova 2016bkv with Early-phase Circumstellar Interaction.

Author

Tatsuya Nakaoka, Koji S. Kawabata, Keiichi Maeda, Masaomi Tanaka, Masayuki Yamanaka, Takashi J. Moriya, Nozomu Tominaga, Tomoki Morokuma, Katsutoshi Takaki, Miho Kawabata, Naoki Kawahara, Ryosuke Itoh, Kensei Shiki, Hiroki Mori, Jun Hirochi, Taisei Abe, Makoto Uemura, Michitoshi Yoshida, Hiroshi Akitaya, and Yuki Moritani

Subjects
SUPERNOVAE, STELLAR activity, MASS loss (Astrophysics), LUMINOSITY, LIGHT curves, OPTICAL spectra
Abstract

We present optical and near-infrared observations of a low-luminosity (LL) Type IIP supernova (SN) 2016bkv from the initial rising phase to the plateau phase. Our observations show that the end of the plateau is extended to ≳140 days since the explosion, indicating that this SN takes one of the longest times to finish the plateau phase among Type IIP SNe (SNe IIP), including LL SNe IIP. The line velocities of various ions at the middle of the plateau phase are as low as 1000–1500 km s−1, which is the lowest even among LL SNe IIP. These measurements imply that the ejecta mass in SN 2016bkv is larger than that of the well-studied LL IIP SN 2003Z. In the early phase, SN 2016bkv shows a strong bump in the light curve. In addition, the optical spectra in this bump phase exhibit a blue continuum accompanied by a narrow Hα emission line. These features indicate an interaction between the SN ejecta and the circumstellar matter (CSM) as in SNe IIn. Assuming the ejecta–CSM interaction scenario, the mass loss rate is estimated to be yr−1 within a few years before the SN explosion. This is comparable to or even larger than the largest mass loss rate observed for the Galactic red supergiants ( yr−1 for VY CMa). We suggest that the progenitor star of SN 2016bkv experienced a violent mass loss just before the SN explosion. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

12. X-Ray and GeV Gamma-Ray Variability of the Radio Galaxy NGC 1275.

Author

Yasushi Fukazawa, Kensei Shiki, Yasuyuki Tanaka, Ryosuke Itoh, Hiromitsu Takahashi, Fumiya Imazato, Filippo D’Ammando, Roopesh Ojha, and and Hiroshi Nagai

Subjects
*PROTON-induced gamma ray emission, *ENERGY bands, *RADIO galaxies, *ACTIVE galactic nuclei, *SPECTRAL energy distribution
Abstract

We analyzed Suzaku/XIS data (2006–2015) and Fermi/LAT data (2008–2015) of the gamma-ray emitting radio galaxy NGC 1275. Correlated brightening of the nucleus in both the X-ray and GeV gamma-ray energy bands was found for the period 2013–2015. This is the first evidence of correlated variability between these two energy bands for NGC 1275. We also analyzed Swift/XRT data and found that the X-ray flux increased over several days in 2010, coincidentally with the GeV gamma-ray flare. During the flare, the X-ray spectra were softer, with a photon index of ∼2 compared with 1.5–2.1 of the other periods, suggesting the brightening of a synchrotron component. The GeV gamma-ray band also showed a higher flux with a harder spectrum during the 2010 flare. Simultaneous X-ray and GeV gamma-ray flux increase in the flare could be explained by the shock-in-jet scenario. On the other hand, a long-term gradual brightening of radio, X-ray, and GeV gamma-ray flux with a larger gamma-ray amplitude could have an origin other than internal shocks, and some of these possibilities are discussed. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

13. SYSTEMATIC STUDY OF GAMMA-RAY-BRIGHT BLAZARS WITH OPTICAL POLARIZATION AND GAMMA-RAY VARIABILITY.

Author

Ryosuke Itoh, Krzysztof Nalewajko, Yasushi Fukazawa, Makoto Uemura, Yasuyuki T. Tanaka, Koji S. Kawabata, Greg M. Madejski, Frank. K. Schinzel, Yuka Kanda, Kensei Shiki, Hiroshi Akitaya, Miho Kawabata, Yuki Moritani, Tatsuya Nakaoka, Takashi Ohsugi, Mahito Sasada, Katsutoshi Takaki, Koji Takata, Takahiro Ui, and Masayuki Yamanaka

Subjects
OPTICAL polarization, BL Lacertae objects, GAMMA-ray scattering, GALACTIC nuclei, ACTIVE galaxies, ELECTROMAGNETIC waves
Abstract

Blazars are highly variable active galactic nuclei that emit radiation at all wavelengths from radio to gamma rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies, and it also varies dramatically. The polarization of blazars is of interest for understanding the origin, confinement, and propagation of jets. However, even though numerous measurements have been performed, the mechanisms behind jet creation, composition, and variability are still debated. We performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars between 2008 July and 2014 December to investigate the mechanisms of variability and search for a basic relation between the several subclasses of blazars. We identify a correlation between the maximum degree of optical linear polarization and the gamma-ray luminosity or the ratio of gamma-ray to optical fluxes. Since the maximum polarization degree depends on the condition of the magnetic field (chaotic or ordered), this result implies a systematic difference in the intrinsic alignment of magnetic fields in parsec-scale relativistic jets between different types of blazars (flat-spectrum radio quasars vs. BL Lacs) and consequently between different types of radio galaxies (FR I versus FR II). [ABSTRACT FROM AUTHOR]

Published
2016
Full Text
View/download PDF

14. Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar.

Author

Clark CJ, Pletsch HJ, Wu J, Guillemot L, Kerr M, Johnson TJ, Camilo F, Salvetti D, Allen B, Anderson D, Aulbert C, Beer C, Bock O, Cuéllar A, Eggenstein HB, Fehrmann H, Kramer M, Kwang SA, Machenschalk B, Nieder L, Ackermann M, Ajello M, Baldini L, Ballet J, Barbiellini G, Bastieri D, Bellazzini R, Bissaldi E, Blandford RD, Bloom ED, Bonino R, Bottacini E, Brandt TJ, Bregeon J, Bruel P, Buehler R, Burnett TH, Buson S, Cameron RA, Caputo R, Caraveo PA, Cavazzuti E, Cecchi C, Charles E, Chekhtman A, Ciprini S, Cominsky LR, Costantin D, Cutini S, D'Ammando F, De Luca A, Desiante R, Di Venere L, Di Mauro M, Di Lalla N, Digel SW, Favuzzi C, Ferrara EC, Franckowiak A, Fukazawa Y, Funk S, Fusco P, Gargano F, Gasparrini D, Giglietto N, Giordano F, Giroletti M, Gomez-Vargas GA, Green D, Grenier IA, Guiriec S, Harding AK, Hewitt JW, Horan D, Jóhannesson G, Kensei S, Kuss M, La Mura G, Larsson S, Latronico L, Li J, Longo F, Loparco F, Lovellette MN, Lubrano P, Magill JD, Maldera S, Manfreda A, Mazziotta MN, McEnery JE, Michelson PF, Mirabal N, Mitthumsiri W, Mizuno T, Monzani ME, Morselli A, Moskalenko IV, Nuss E, Ohsugi T, Omodei N, Orienti M, Orlando E, Palatiello M, Paliya VS, de Palma F, Paneque D, Perkins JS, Persic M, Pesce-Rollins M, Porter TA, Principe G, Rainò S, Rando R, Ray PS, Razzano M, Reimer A, Reimer O, Romani RW, Saz Parkinson PM, Sgrò C, Siskind EJ, Smith DA, Spada F, Spandre G, Spinelli P, Thayer JB, Thompson DJ, Torres DF, Troja E, Vianello G, Wood K, and Wood M

Abstract

Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date, radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs, we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs, one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations, raising hopes for detecting MSPs from a predicted Galactic bulge population.

Published
2018
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results