Publication:
Observations of M31 and M33 with the Fermi Large Area Telescope: A Galactic Center Excess in Andromeda?

Issued Date

2017-02-20

Resource Type

Article

ISSN

15384357
0004637X

DOI

10.3847/1538-4357/aa5c3d

Other identifier(s)

2-s2.0-85014315519

Rights

Mahidol University

Rights Holder(s)

SCOPUS

Bibliographic Citation

Astrophysical Journal. Vol.836, No.2 (2017)

Suggested Citation

M. Ackermann, M. Ajello, A. Albert, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, R. Bellazzini, E. Bissaldi, E. D. Bloom, R. Bonino, E. Bottacini, T. J. Brandt, J. Bregeon, P. Bruel, R. Buehler, R. A. Cameron, R. Caputo, M. Caragiulo, P. A. Caraveo, E. Cavazzuti, C. Cecchi, E. Charles, A. Chekhtman, G. Chiaro, S. Ciprini, F. Costanza, S. Cutini, F. D'Ammando, F. De Palma, R. Desiante, S. W. Digel, N. Di Lalla, M. Di Mauro, L. Di Venere, C. Favuzzi, S. Funk, P. Fusco, F. Gargano, N. Giglietto, F. Giordano, M. Giroletti, T. Glanzman, D. Green, I. A. Grenier, L. Guillemot, S. Guiriec, K. Hayashi, X. Hou, G. Jóhannesson, T. Kamae, J. Knödlseder, A. K.H. Kong, M. Kuss, G. La Mura, S. Larsson, L. Latronico, J. Li, F. Longo, F. Loparco, P. Lubrano, S. Maldera, D. Malyshev, A. Manfreda, P. Martin, M. N. Mazziotta, P. F. Michelson, N. Mirabal, W. Mitthumsiri, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, M. Negro Observations of M31 and M33 with the Fermi Large Area Telescope: A Galactic Center Excess in Andromeda?. Astrophysical Journal. Vol.836, No.2 (2017). doi:10.3847/1538-4357/aa5c3d Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/42454

Research Projects

Organizational Units

Authors

Journal Issue

Thesis

Title

Observations of M31 and M33 with the Fermi Large Area Telescope: A Galactic Center Excess in Andromeda?

Author(s)

M. Ackermann
 M. Ajello
 A. Albert
 L. Baldini
 J. Ballet
 G. Barbiellini
 D. Bastieri
 R. Bellazzini
 E. Bissaldi
 E. D. Bloom
 R. Bonino
 E. Bottacini
 T. J. Brandt
 J. Bregeon
 P. Bruel
 R. Buehler
 R. A. Cameron
 R. Caputo
 M. Caragiulo
 P. A. Caraveo
 E. Cavazzuti
 C. Cecchi
 E. Charles
 A. Chekhtman
 G. Chiaro
 S. Ciprini
 F. Costanza
 S. Cutini
 F. D'Ammando
 F. De Palma
 R. Desiante
 S. W. Digel
 N. Di Lalla
 M. Di Mauro
 L. Di Venere
 C. Favuzzi
 S. Funk
 P. Fusco
 F. Gargano
 N. Giglietto
 F. Giordano
 M. Giroletti
 T. Glanzman
 D. Green
 I. A. Grenier
 L. Guillemot
 S. Guiriec
 K. Hayashi
 X. Hou
 G. Jóhannesson
 T. Kamae
 J. Knödlseder
 A. K.H. Kong
 M. Kuss
 G. La Mura
 S. Larsson
 L. Latronico
 J. Li
 F. Longo
 F. Loparco
 P. Lubrano
 S. Maldera
 D. Malyshev
 A. Manfreda
 P. Martin
 M. N. Mazziotta
 P. F. Michelson
 N. Mirabal
 W. Mitthumsiri
 T. Mizuno
 M. E. Monzani
 A. Morselli
 I. V. Moskalenko
 M. Negro

Other Contributor(s)

Deutsche Elektronen-Synchrotron
 Clemson University
 Los Alamos National Laboratory
 Università di Pisa
 Institut de Recherche sur les Lois Fondamentales de l'Univers
 Istituto Nazionale di Fisica Nucleare, Roma
 Università degli Studi di Trieste
 Istituto Nazionale Di Fisica Nucleare, Sezione di Padova
 Università degli Studi di Padova
 Istituto Nazionale Di Fisica Nucleare, Sezione di Pisa
 Kavli Institute for Particle Astrophysics and Cosmology
 Università degli Studi di Torino
 NASA Goddard Space Flight Center
 Laboratoire Univers et Particules de Montpellier
 Laboratoire Leprince-Ringuet
 Santa Cruz Institute for Particle Physics
 Università degli Studi di Bari
 INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
 Agenzia Spaziale Italiana
 Università degli Studi di Perugia
 George Mason University, Fairfax Campus
 Istituto Di Radioastronomia, Bologna
 Alma Mater Studiorum Università di Bologna
 Università degli Studi di Napoli Federico II
 Università degli Studi di Udine
 Erlangen Centre for Astroparticle Physics
 University of Maryland
 Universite d'Orleans
 Institut National des Sciences de l'Univers
 Nagoya University
 Chinese Academy of Sciences
 National Tsing Hua University
 University Science Institute Reykjavik
 University of Tokyo
 CNRS Centre National de la Recherche Scientifique
 Université de Toulouse
 The Royal Institute of Technology (KTH)
 Oskar Klein Centre for Cosmoparticle Physics
 Universitat Autònoma de Barcelona
 Mahidol University
 Hiroshima University
 University of Denver
 Max Planck Institut für Physik (Werner-Heisenberg-Institut)
 Osservatorio Astronomico di Trieste
 Medizinische Universitat Innsbruck
 Stockholms universitet
 NYCB Realtime Computing Inc.
 Max Planck Institut für Kernphysik
 Institucio Catalana de Recerca I Estudis Avancats
 Naval Research Laboratory

Abstract

© 2017. The American Astronomical Society. All rights reserved. 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 , 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) × 10-12erg cm-2s-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 the decay or annihilation of dark matter particles, similar to what has been proposed to account for the so-called Galactic center excess found in Fermi-LAT observations of the MW.

Keyword(s)

Earth and Planetary Sciences

Availability

URI

https://repository.li.mahidol.ac.th/handle/20.500.14594/42454

Collections

Scopus 2016-2017