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arXiv 2017年

作者： Evans, D.F. Southworth, J. Smalley, B. Jørgensen, U.G. Dominik, M. Andersen, M.I. Bozza, V. Bramich, D.M. Burgdorf, M.J. Ciceri, S. D’Ago, G. Jaimes, R. Figuera Gu, S.-H. Hinse, T.C. Henning, T.H. Hundertmark, M. Kains, N. Kerins, E. Korhonen, H. Kokotanekova, R. Kuffmeier, M. Longa-Peña, P. Mancini, L. MacKenzie, J. Popovas, A. Rabus, M. Rahvar, S. Sajadian, S. Snodgrass, C. Skottfelt, J. Surdej, J. Tronsgaard, R. Unda-Sanzana, E. von Essen, C. Wang, Yi-Bo Wertz, O. Astrophysics Group Keele University StaffordshireST5 5BG United Kingdom Niels Bohr Institute Centre for Star and Planet Formation University of Copenhagen Øster Voldgade 5 Copenhagen1350 - Denmark Centre for Exoplanet Science SUPA School of Physics & Astronomy University of St Andrews North Haugh St AndrewsKY16 9SS Dark Cosmology Centre Niels Bohr Institute University of Copenhagen Juliane Maries Vej 30 Copenhagen ØDK-2100 Dipartimento di Fisica "E.R. Caianiello" Università di Salerno Via Giovanni Paolo II 132 Fisciano84084 Italy Istituto Nazionale di Fisica Nucleare Sezione di Napoli Napoli Italy Universität Hamburg Faculty of Mathematics Informatics and Natural Sciences Department of Earth Sciences Meteorological Institute Bundesstraße 55 Hamburg20146 Germany Max Planck Institute for Astronomy Königstuhl 17 Heidelberg69117 Germany INAF-Osservatorio Astronomico di Capodimonte Salita Moiariello 16 Napoli80131 Italy European Southern Observatory Karl-Schwarzschild Straße 2 Garching bei München85748 Germany Yunnan Observatories Chinese Academy of Sciences Kunming650011 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Korea Astronomy & Space Science Institute 776 Daedukdae-ro Yuseong-gu Daejeon305-348 Astronomisches Rechen-Institut Zentrum für Astronomie der Universität Heidelberg Mönchhofstr. 12-14 Heidelberg69120 Germany Space Telescope Science Institute 3700 San Martin Drive BaltimoreMD21218 Jodrell Bank Centre for Astrophysics School of Physics and Astronomy University of Manchester Oxford Road ManchesterM13 9PL United Kingdom Väisäläntie 20 PiikkiöFI-21500 Finland Max Planck Institute for Solar System Research Justus-von-LiebigWeg 3 Göttingen37077 Germany School of Physical Sciences Faculty of Science Technology Engineering and Mathematics Open University Walton Hall Milton KeynesMK7 6AA United Kingdom Unidad de Astronomía Fac. de Ciencias Básicas

Context. The formation and dynamical history of hot Jupiters is currently debated, with wide stellar binaries having been suggested as a potential formation pathway. Additionally, contaminating light from both binary companions and unassociated stars can significantly bias the results of planet characterisation studies, but can be corrected for if the properties of the contaminating star are known. Aims. We search for binary companions to known transiting exoplanet host stars, in order to determine the multiplicity properties of hot Jupiter host stars. We also search for and characterise unassociated stars along the line of sight, allowing photometric and spectroscopic observations of the planetary system to be corrected for contaminating light. Methods. We analyse lucky imaging observations of 97 Southern hemisphere exoplanet host stars, using the Two Colour Instrument on the Danish 1.54m telescope. For each detected companion star, we determine flux ratios relative to the planet host star in two passbands, and measure the relative position of the companion. The probability of each companion being physically associated was determined using our two-colour photometry. Results. A catalogue of close companion stars is presented, including flux ratios, position measurements, and estimated companion star temperature. For companions that are potential binary companions, we review archival and catalogue data for further evidence. For WASP-77AB and WASP-85AB, we combine our data with historical measurements to determine the binary orbits, showing them to be moderately eccentric and inclined to the line of sight (and hence planetary orbital axis). Combining our survey with the similar Friends of Hot Jupiters survey, we conclude that known hot Jupiter host stars show a deficit of high mass stellar companions compared to the field star population;however, this may be a result of the biases in detection and target selection by ground-based surveys. Copyright © 2017, The Authors

关键词： Extrasolar planets

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The top-scope survey of planck galactic cold clumps: survey overview and results of an exemplar source, pgcc g26.53+0.17

arXiv

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arXiv 2017年

作者： Liu, Tie Kim, Kee-Tae Juvela, Mika Wang, Ke Ken’ichi, Tatematsu Francesco, James Di Liu, Sheng-Yuan Wu, Yuefang Thompson, Mark Fuller, Gary Eden, David Li, Di Ristorcelli, I. Sung-ju, Kang Lin, Yuxin Johnstone, D. He, J.H. Koch, P.M. Sanhueza, Patricio Qin, Sheng-Li Zhang, Q. Hirano, N. Goldsmith, Paul F. Evans, Neal J. White, Glenn J. Choi, Minho Lee, Chang Won Toth, L.V. Mairs, Steve Yi, H.-W. Tang, Mengyao Soam, Archana Peretto, N. Samal, Manash R. Fich, Michel Parsons, Harriet Yuan, Jinghua Zhang, Chuan-Peng Malinen, Johanna Bendo, George J. Rivera-Ingraham, A. Liu, Hong-Li Wouterloot, Jan Li, Pak Shing Qian, Lei Rawlings, Jonathan Rawlings, Mark G. Feng, Siyi Aikawa, Yuri Akhter, S. Alina, Dana Bell, Graham Bernard, J.-P. Blain, Andrew Bogner, Rebeka Bronfman, L. Byun, D.-Y. Chapman, Scott Chen, Huei-Ru Chen, M. Chen, Wen-Ping Chen, X. Chen, Xuepeng Chrysostomou, A. Cosentino, Giuliana Cunningham, M.R. Demyk, K. Drabek-Maunder, Emily Doi, Yasuo Eswaraiah, C. Falgarone, Edith Fehér, O. Fraser, Helen Friberg, Per Garay, G. Ge, J.X. Gear, W.K. Greaves, Jane Guan, X. Harvey-Smith, Lisa Tetsuo, Hasegawa Hatchell, J. He, Yuxin Henkel, C. Hirota, T. Holland, W. Hughes, A. Jarken, E. Ji, Tae-Geun Jimenez-Serra, Izaskun Kang, Miju Kawabata, Koji S. Kim, Gwanjeong Kim, Jungha Kim, Jongsoo Kim, Shinyoung Koo, B.-C. Kwon, Woojin Kuan, Yi-Jehng Lacaille, K.M. Lai, S.-P. Lee, C.F. Lee, J.-E. Lee, Y.-U. Li, Dalei Hua-bai, Li Lo, N. Lopez, John A.P. Lu, Xing A-Ran, Lyo Mardones, D. Marston, A. McGehee, P. Meng, F. Montier, L. Montillaud, Julien Moore, T. Morata, O. Moriarty-Schieven, Gerald H. Ohashi, S. Pak, Soojong Park, Geumsook Paladini, R. Pattle, Kate M. Pech, Gerardo Pelkonen, V.-M. Qiu, K. Ren, Zhi-Yuan Richer, John Saito, M. Sakai, Takeshi Shang, H. Shinnaga, Hiroko Stamatellos, Dimitris Tang, Y.-W. Traficante, Alessio Vastel, Charlotte Viti, S. Walsh, Andrew Wang, Bingru Wang, Hongchi Wang, Junzhi Ward-Thompson, D. Whitworth, Anthony Xu, Ye Yang, J. Yang, Yao-Lun Yuan, Lixia Zavagno, A. Zhang, Guoyin Zhang, H.-W. Korea Astronomy and Space Science Institute 776 Daedeokdaero Yuseong-gu Daejeon34055 Korea Republic of East Asian Observatory 660 N. A’ohoku Place HiloHI96720 United States Department of Physics University of Helsinki P.O.Box 64 FI-00014 Finland European Southern Observatory Karl-Schwarzschild-Str.2 Garching bei MünchenD-85748 Germany National Astronomical Observatory of Japan National Institutes of Natural Sciences 2-21-1 Osawa Mitaka Tokyo181-8588 Japan NRC Herzberg Astronomy and Astrophysics 5071 West Saanich Rd VictoriaBCV9E 2E7 Canada Department of Physics and Astronomy University of Victoria VictoriaBCV8P 1A1 Canada Institute of Astronomy and Astrophysics Academia Sinica. 11F of Astronomy-Mathematics Building AS/NTU No.1 Sec. 4 Roosevelt Rd Taipei10617 Taiwan Department of Astronomy Peking University Beijing100871 China Centre for Astrophysics Research School of Physics Astronomy & Mathematics University of Hertfordshire College Lane HatfieldAL10 9AB United Kingdom UK ALMA Regional Centre Node Jodrell Bank Centre for Astrophysics School of Physics and Astronomy University of Manchester Oxford Road ManchesterM13 9PL United Kingdom Astrophysics Research Institute Liverpool John Moores University IC2 Liverpool Science Park 146 Brownlow Hill LiverpoolL3 5RF United Kingdom National Astronomical Observatories Chinese Academy of Sciences Beijing100012 China Key Laboratory of Radio Astronomy Chinese Academy of Science Nanjing210008 China IRAP Université de Toulouse CNRS UPS CNES Toulouse France Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 Bonn53121 Germany Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan observatories Chinese Academy of Sciences P.O. Box 110 KunmingYunnan Province650011 China Camino El Observatorio 1515 Las Condes Santiago Chile Departamento de Astronomía Universidad de Chile Las Condes Santiago Chile Department of Astronomy Yunnan University Key Laboratory o

The low dust temperatures (−1, respectively. Ten massive clumps including eight starless ones are found along the filament. The most massive Clump as a whole may be still in global collapse while its denser part seems to be undergoing expansion due to outflow feedback. The fragmentation in G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, non-magnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (β) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed due to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud. Copyright © 2017, The Authors. All rights reserved.

关键词： Surveys

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The New Photometric Observations for Transiting Exoplanet HAT-P-24b

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Proceedings of the International Astronomical Union 2014年第S293期8卷 122-124页

作者： Xiao-Bin Wang Andrew Collier Cameron Sheng-Hong Gu National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China email: wangxb@*** Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming 650011 China School of Physics and Astronomy University of St Andrews North Haugh St Andrews Fife KY16 9SS UK

The transiting exoplanetary system HAT-P-24 was observed by using CCD cameras at Yunnan Observatory and Hokoon Astronomical Centre, China in 2010 and 2012. Three new transit light curves are analyzed by means of MCMC technique, and the new physical parameters of the system are derived, which are compatible with the old ones in the discovery paper. The orbital period of HAT-P-24b is refined and no obvious TTV signal can be found from five transit events during 2010-2012.

关键词： exoplanetary system transit individual:HAT-P-24

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Diffuse emission of TeV neutrinos and gamma-rays from young pulsars by photomeson interaction in the Galaxy

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Research in Astronomy and Astrophysics 2013年第9期13卷 1097-1106页

作者： Zhi-Xiong Li Gui-Fang Lin Wei-Wei Na Department of Physics Yunnan University Yunnan Astronomical Observatory National Astronomical Observatories Chinese Academy of Sciences Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Department of Physics Yuxi Normal University

It is generally believed that young, rapidly rotating pulsars are important sites of particle acceleration, in which protons can be accelerated to relativistic energy above the polar cap region if the magnetic moment is antiparallel to the spin axis （μ·Ω 〈 0）. To obtain diffuse neutrinos and gamma-rays at TeV that originate in our Galaxy, we use the Monte Carlo method to generate a sample of young pulsars with ages less than 106 yr in our galaxy; the neutrinos and high-energy gamma-rays can be produced through a photomeson process with the interaction of energetic protons and soft X-ray photons （p ＋γ→△＋→n＋π＋/p＋π0） for a single pulsar, and these X-ray photons come from the surface of the neutron star. The results suggest that the flux of diffuse neutrinos at TeV energies is lower than the background flux, indicating they are difficult to detect using current neutrino telescopes.

关键词： pulsars： general -- stars： neutron -- neutrinos and gamma-rays： stars --elementary： neutrinos

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Discovery of four W UMa type eclipsing binaries in the field of open cluster ASCC 5

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Research in Astronomy and Astrophysics 2013年第9期13卷 1052-1062页

作者： Xiang-Song Fang Sheng-Hong Gu Li-Yun Zhang Qing-Feng Pi National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences University of Chinese Academy of Sciences College of Science/Department of Physics & NAOC-GZU-Sponsored Center for Astronomy Research Guizhou University

We carried out time-series photometric observations in the Re-band of the young, poorly studied open cluster ASCC 5 during November and December, 2012, to search for magnetically active stars, and discovered four eclipsing binary stars in this field. In order to characterize these four newly discovered binaries, we derived their orbital periods by their times of light minimum, estimated their effective tem- peratures based on their （J - H） colors and analyzed their light curves using the Wilson-Devinney light curve modeling technique. Our analyses reveal that all of them are contact binaries with short orbital periods of less than 0.5 d, with spectral types from late-F to mid-K. Among them, one is a typical A subtype contact binary with a mass ratio around 0.5 and a period of 0.44 d, and one is an H subtype contact binary with a high mass ratio around 0.9 and a short period of about 0.27 d. The other two systems show low amplitudes of light variation （Ant 〈0.11m）; their actual photomet- ric mass ratios could not be determined by the light curve modelings, probably due to their attributes of being partially eclipsing stars. A preliminary analysis for these two systems indicates that both of them are likely to be W subtype contact binaries with low orbital inclinations. In addition, both of these two low amplitude variables show asymmetric distorted light curves （e.g., O＇Connell effect of ARc --~0.02m） during the observing runs, suggesting the presence of starspots on these two systems. More inter- estingly, the one showing a large case of the O＇Connell effect presented a remarkable variation in the shape of the light curve on a time scale of one day, indicating that this star is in a very active state. Therefore, these two stars need spectroscopic observations to precisely determine their parameters, as well as further photometric observations to understand the properties of their magnetic activity, e.g., the evolution of starspots.

关键词： stars：binaries： close -- stars：binaries： eclipsing -- stars： spots

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Search for extended sources in the galactic plane using 6 years of Fermi-Large area telescope pass 8 data above 10 GeV

arXiv

引用

arXiv 2017年

作者： Ackermann, M. Ajello, M. Baldini, L. Ballet, J. Barbiellini, G. Bastieri, D. Bellazzini, R. Bissaldi, E. Bloom, E.D. Bonino, R. Bottacini, E. Brandt, T.J. Bregeon, J. Bruel, P. Buehler, R. Cameron, R.A. Caragiulo, M. Caraveo, P.A. Castro, D. Cavazzuti, E. Cecchi, C. Charles, E. Chekhtman, A. Cheung, C.C. Chiaro, G. Ciprini, S. Cohen, J.M. Costantin, D. Costanza, F. Cutini, S. D’Ammando, F. de Palma, F. Desiante, R. Digel, S.W. Di Lalla, N. Di Mauro, M. Di Venere, L. Favuzzi, C. Fegan, S.J. Ferrara, E.C. Franckowiak, A. Fukazawa, Y. Funk, S. Fusco, P. Gargano, F. Gasparrini, D. Giglietto, N. Giordano, F. Giroletti, M. Green, D. Grenier, I.A. Grondin, M.-H. Guillemot, L. Guiriec, S. Harding, A.K. Hays, E. Hewitt, J.W. Horan, D. Hou, X. Jóhannesson, G. Kamae, T. Kuss, M. la Mura, G. Larsson, S. Lemoine-Goumard, M. Li, J. Longo, F. Loparco, F. Lubrano, P. Magill, J.D. Maldera, S. Malyshev, D. Manfreda, A. Mazziotta, M.N. Michelson, P.F. Mitthumsiri, W. Mizuno, T. Monzani, M.E. Morselli, A. Moskalenko, I.V. Negro, M. Nuss, E. Ohsugi, T. Omodei, N. Orienti, M. Orlando, E. Ormes, J.F. Paliya, V.S. Paneque, D. Perkins, J.S. Persic, M. Pesce-Rollins, M. Petrosian, V. Piron, F. Porter, T.A. Principe, G. Rainò, S. Rando, R. Razzano, M. Razzaque, S. Reimer, A. Reimer, O. Reposeur, T. Sgrò, C. Simone, D. Siskind, E.J. Spada, F. Spandre, G. Spinelli, P. Suson, D.J. Tak, D. Thayer, J.B. Thompson, D.J. Torres, D.F. Tosti, G. Troja, E. Vianello, G. Wood, K.S. Wood, M. Deutsches Elektronen Synchrotron DESY ZeuthenD-15738 Germany Department of Physics and Astronomy Clemson University Kinard Lab of Physics ClemsonSC29634-0978 United States Università di Pisa Istituto Nazionale di Fisica Nucleare Sezione di Pisa PisaI-56127 Italy Laboratoire AIM CEA-IRFU CNRS Université Paris Diderot Service d’Astrophysique CEA Saclay Gif sur YvetteF-91191 France Istituto Nazionale di Fisica Nucleare Sezione di Trieste TriesteI-34127 Italy Dipartimento di Fisica Università di Trieste TriesteI-34127 Italy Istituto Nazionale di Fisica Nucleare Sezione di Padova PadovaI-35131 Italy Dipartimento di Fisica e Astronomia "G. Galilei" Università di Padova PadovaI-35131 Italy Istituto Nazionale di Fisica Nucleare Sezione di Pisa PisaI-56127 Italy Istituto Nazionale di Fisica Nucleare Sezione di Bari BariI-70126 Italy W. W. Hansen Experimental Physics Laboratory Kavli Institute for Particle Astrophysics and Cosmology Department of Physics SLAC National Accelerator Laboratory Stanford University StanfordCA94305 United States Istituto Nazionale di Fisica Nucleare Sezione di Torino TorinoI-10125 Italy Dipartimento di Fisica Università degli Studi di Torino TorinoI-10125 Italy NASA Goddard Space Flight Center GreenbeltMD20771 United States Laboratoire Univers et Particules de Montpellier Université Montpellier CNRS/IN2P3 MontpellierF-34095 France Laboratoire Leprince-Ringuet École polytechnique CNRS/IN2P3 PalaiseauF-91128 France Dipartimento di Fisica "M. Merlin" dell’Università e del Politecnico di Bari BariI-70126 Italy INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica Milano via E. Bassini 15 MilanoI-20133 Italy Science Data Center RomaI-00133 Italy Istituto Nazionale di Fisica Nucleare Sezione di Perugia PerugiaI-06123 Italy Dipartimento di Fisica Università degli Studi di Perugia PerugiaI-06123 Italy College of Science George Mason University Fairfax VA22030 United States Naval Research Laboratory Washi

The spatial extension of a γ-ray source is an essential ingredient to determine its spectral properties as well as its potential multi-wavelength counterpart. The capability to spatially resolve γ-ray sources is greatly improved by the newly delivered Fermi-Large Area Telescope (LAT) Pass 8 event-level analysis which provides a greater acceptance and an improved point spread function, two crucial factors for the detection of extended sources. Here, we present a complete search for extended sources located within 7◦ from the Galactic plane, using 6 years of Fermi-LAT data above 10 GeV. We find 46 extended sources and provide their morphological and spectral characteristics. This constitutes the first catalog of hard Fermi-LAT extended sources, named the Fermi Galactic Extended Source Catalog, which allows a thorough study of the properties of the Galactic plane in the sub-TeV domain. Copyright © 2017, The Authors. All rights reserved.

关键词： Gamma rays

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Helium double-detonation explosions for the progenitors of type Ia supernovae

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Proceedings of the International Astronomical Union 2014年第S298期9卷 442-442页

作者： B. Wang D. Liu S. Jia Z. Han Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Astronomical Observatory CAS Kunming 650011 China (email: wangbo@***)

Thermonuclear explosions from helium double-detonation sub-Chandrasekhar mass model have been considered as an alternative way for the production of type Ia supernovae (SNe Ia). In this work, we systematically studied the helium double-detonation model, in which a carbon–oxygen white dwarf (CO WD) accumulates a helium layer from a non-degenerate helium star.

关键词： binaries: close – supernovae: general – white dwarfs

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High velocity and hypervelocity stars from the companions of type Ia supernovae

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Proceedings of the International Astronomical Union 2014年第S298期9卷 443-443页

作者： B. Wang D. Liu S. Jia Z. Han Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Astronomical Observatory CAS Kunming 650011 China (email: wangbo@***)

The single-degenerate (SD) model is currently a favourable progenitor scenario for the production of type Ia supernovae (SNe Ia). The companion in the SD model would survive after the SN explosion. In this work, we obtained the velocity distribution of the surviving companion stars from different SD scenarios in the Galaxy, which can be verified by future observations.

关键词： binaries: close – supernovae: general – white dwarfs

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Velocity distributions of surviving companion stars of type Ia supernovae in the Milky Way

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Proceedings of the International Astronomical Union 2014年第S298期9卷 413-413页

作者： S. Jia B. Wang Z. Han Key Laboratory for the Structure and Evolution of Celestial Objects Yunnan Astronomical Observatory CAS Kunming 650011 China (email: jiashi@***)

The companion stars of type Ia supernovae (SNe Ia) would survive the explosions and show peculiar properties in the single-degenerate (SD) scenario. Whit different SD SN Ia channels, we obtained the velocity distributions of the surviving companion stars in the Milky Way. All properties presented may be verified by future observations.

关键词： binaries: close – supernovae: general – Galaxy: kinematics and dynamics

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OBSERVATIONS OF M31 AND M33 WITH THE FERMI LARGE AREA TELESCOPE: A GALACTIC CENTER EXCESS IN ANDROMEDA?

arXiv

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arXiv 2017年

作者： Ackermann, M. Ajello, M. Albert, A. Baldini, L. Ballet, J. Barbiellini, G. Bastieri, D. Bellazzini, R. Bissaldi, E. Bloom, E.D. Bonino, R. Bottacini, E. Brandt, T.J. Bregeon, J. Bruel, P. Buehler, R. Cameron, R.A. Caputo, R. Caragiulo, M. Caraveo, P.A. Cavazzuti, E. Cecchi, C. Charles, E. Chekhtman, A. Chiaro, G. Ciprini, S. Costanza, F. Cutini, S. D’Ammando, F. de Palma, F. Desiante, R. Digel, S.W. Di Lalla, N. Di Mauro, M. Di Venere, L. Favuzzi, C. Funk, S. Fusco, P. Gargano, F. Giglietto, N. Giordano, F. Giroletti, M. Glanzman, T. Green, D. Grenier, I.A. Guillemot, L. Guiriec, S. Hayashi, K. Hou, X. Jóhannesson, G. Kamae, T. Knödlseder, J. Kong, A.K.H. Kuss, M. la Mura, G. Larsson, S. Latronico, L. Li, J. Longo, F. Loparco, F. Lubrano, P. Maldera, S. Malyshev, D. Manfreda, A. Martin, P. Mazziotta, M.N. Michelson, P.F. Mirabal, N. Mitthumsiri, W. Mizuno, T. Monzani, M.E. Morselli, A. Moskalenko, I.V. Negro, M. Nuss, E. Ohsugi, T. Omodei, N. Orlando, E. Ormes, J.F. Paneque, D. Persic, M. Pesce-Rollins, M. Piron, F. Porter, T.A. Principe, G. Rainò, S. Rando, R. Razzano, M. Reimer, O. Sánchez-Conde, M. Sgrò, C. Simone, D. Siskind, E.J. Spada, F. Spandre, G. Spinelli, P. Tanaka, K. Tibaldo, L. Torres, D.F. Troja, E. Uchiyama, Y. Wang, J.C. Wood, K.S. Wood, M. Zaharijas, G. Zhou, M. Deutsches Elektronen Synchrotron DESY ZeuthenD-15738 Germany Department of Physics and Astronomy Clemson University Kinard Lab of Physics ClemsonSC29634-0978 United States Los Alamos National Laboratory Los AlamosNM87545 United States Università di Pisa Istituto Nazionale di Fisica Nucleare Sezione di Pisa PisaI-56127 Italy Laboratoire AIM CEA-IRFU CNRS Université Paris Diderot Service d’Astrophysique CEA Saclay Gif sur YvetteF-91191 France Istituto Nazionale di Fisica Nucleare Sezione di Trieste TriesteI-34127 Italy Dipartimento di Fisica Università di Trieste TriesteI-34127 Italy Istituto Nazionale di Fisica Nucleare Sezione di Padova PadovaI-35131 Italy Dipartimento di Fisica e Astronomia "G. Galilei" Università di Padova PadovaI-35131 Italy Istituto Nazionale di Fisica Nucleare Sezione di Pisa PisaI-56127 Italy Istituto Nazionale di Fisica Nucleare Sezione di Bari BariI-70126 Italy W. W. Hansen Experimental Physics Laboratory Kavli Institute for Particle Astrophysics and Cosmology Department of Physics SLAC National Accelerator Laboratory Stanford University StanfordCA94305 United States Istituto Nazionale di Fisica Nucleare Sezione di Torino TorinoI-10125 Italy Dipartimento di Fisica Università degli Studi di Torino TorinoI-10125 Italy NASA Goddard Space Flight Center GreenbeltMD20771 United States Laboratoire Univers et Particules de Montpellier Université Montpellier CNRS/IN2P3 MontpellierF-34095 France Laboratoire Leprince-Ringuet École polytechnique CNRS/IN2P3 PalaiseauF-91128 France Santa Cruz Institute for Particle Physics Department of Physics Department of Astronomy and Astrophysics University of California at Santa Cruz Santa CruzCA95064 United States Dipartimento di Fisica "M. Merlin" dell’Università e del Politecnico di Bari BariI-70126 Italy INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica Milano via E. Bassini 15 MilanoI-20133 Italy Science Data Center RomaI-00133 Italy Istituto Nazionale di Fi

The Fermi Large Area Telescope (LAT) has opened the way for comparative studies of cosmic rays (CRs) and high-energy objects in the Milky Way (MW) and in other, external, star-forming galaxies. Using 2 yr of observations with the Fermi LAT, Local Group galaxy M31 was detected as a marginally extended gamma-ray source, while only an upper limit has been derived for the other nearby galaxy M33. We revisited the gamma-ray emission in the direction of M31 and M33 using more than 7 yr of LAT Pass 8 data in the energy range 0.1−100 GeV, presenting detailed morphological and spectral analyses. M33 remains undetected, and we computed an upper limit of 2.0×10−12 erg cm−2 s−1 on the 0.1−100 GeV energy flux (95% confidence level). This revised upper limit remains consistent with the observed correlation between gamma-ray luminosity and star-formation rate tracers and implies an average CR density in M33 that is at most half of that of the MW. M31 is detected with a significance of nearly 10σ. Its spectrum is consistent with a power law with photon index Γ = 2.4±0.1stat+syst and a 0.1−100 GeV energy flux of (5.6±0.6stat+syst)×10−12 erg cm−2 s−1. M31 is detected to be extended with a 4σ significance. The spatial distribution of the emission is consistent with a uniform-brightness disk with a radius of 0◦.4 and no offset from the center of the galaxy, but nonuniform intensity distributions cannot be excluded. The flux from M31 appears confined to the inner regions of the galaxy and does not fill the disk of the galaxy or extend far from it. The gamma-ray signal is not correlated with regions rich in gas or star-formation activity, which suggests that the emission is not interstellar in origin, unless the energetic particles radiating in gamma rays do not originate in recent star formation. Alternative and nonexclusive interpretations are that the emission results from a population of millisecond pulsars dispersed in the bulge and disk of M31 by disrupted globular clusters or from

关键词： Galaxies

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