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Journal Articles The Astrophysical Journal Year : 2017

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

M. Ackermann (1) , M. Ajello (2) , A. Albert (3) , L. Baldini (4) , Jean Ballet (5) , Guido Barbiellini (6) , D. Bastieri (7) , R Bellazzini (8) , E Bissaldi (4) , E. Bottacini (9) , E.D. Bloom (10) , Johan Bregeon (11) , R D Bonino (12) , T.J. Brandt (13) , Pascal Bruel (14) , R D Buehler (15) , R A Cameron (9) , R. Caputo (16) , M. Caragiulo (8) , P. A. Caraveo (17) , E. Cavazzuti (18) , C. Cecchi (19) , E. Charles (9) , A. Chekhtman (20) , G. Chiaro (21) , S. Ciprini (18) , F. Costanza (4) , S. Cutini (18) , F. d'Ammando (22) , F. de Palma (4) , R. Desiante (12) , S. W. Digel (9) , N. Di Lalla (4) , M. Di Mauro (10) , L. Di Venere (8) , C. Favuzzi (8) , S. Funk (23) , P. Fusco (8) , F. Gargano (4) , N. Giglietto (8) , F. Giordano (8) , M. Giroletti (24) , T. Glanzmann (10) , D. Green (13) , I.A. Grenier (5) , Lucas Guillemot (25) , S. Guiriec (13) , K Hayashi (26) , X. Hou (27) , G. Jóhannesson (28) , T. Kamae (29) , Jürgen Knödlseder (30) , A.K.H. Kong (31) , M. Kuss (4) , G. La Mura (32) , S. Larsson (33) , L. Latronico (12) , J. Li (34) , F. Longo (8) , F. Loparco , P. Lubrano (19) , S. Maldera (12) , D. Malyshev, (23) , A. Manfreda (4) , Pierrick Martin (30) , M. N. Mazziotta (8) , P.F. Michelson (9) , N Mirabal (13) , W. Mitthumsiri (35) , T. Mizuno (36) , M.E. Monzani (9) , A. Morselli (37) , I. V. Moskalenko (10) , M. Negro (12) , E. Nuss (11) , T. Ohsugi (36) , N. Omodei (10) , E. Orlando (9) , J. F. Ormes (38) , D. Paneque (39) , M. Persic (40) , M. Pesce-Rollins (4) , F. Piron (11) , T.A. Porter (9) , G. Principe (23) , S. Rainò (8) , R. Rando (21) , M. Razzano (41) , O. Reimer (42) , M. Sánchez Conde (43) , C. Sgró , D. Simone (8) , E. J. Siskind (44) , F S Spada (4) , G. Spandre (4) , P. Spinelli (8) , K Tanaka (36) , L. Tibaldo (45) , D.F Torres (46) , E. Troja (13) , Y Uchiyama (47) , J.C. Wang (31) , K.S. Wood (48) , M. Wood (9) , G. Zaharijas (6) , M. Zhou (27)
1 DESY - Deutsches Elektronen-Synchrotron [Hamburg]
2 Department of Physics and Astronomy [Clemson]
3 LANL - Los Alamos National Laboratory
4 INFN - Istituto Nazionale di Fisica Nucleare [Pisa]
5 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
6 INFN, Sezione di Trieste - Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
7 INFN, Sezione di Padova - Istituto Nazionale di Fisica Nucleare, Sezione di Padova
8 INFN, sezione di Bari - Istituto Nazionale di Fisica Nucleare, sezione di Bari
9 KIPAC - Kavli Institute for Particle Astrophysics and Cosmology
10 Stanford University
11 LUPM - Laboratoire Univers et Particules de Montpellier
12 INFN, Sezione di Torino - Istituto Nazionale di Fisica Nucleare, Sezione di Torino
13 GSFC - NASA Goddard Space Flight Center
14 LLR - Laboratoire Leprince-Ringuet
15 DESY - Deutsches Elektronen-Synchrotron [Zeuthen]
16 SCIPP - Santa Cruz Institute for Particle Physics
17 IASF-MI - Istituto di Astrofisica Spaziale e Fisica Cosmica - Milano
18 Agenzia Spaziale Italiana (ASI) Science Data Center
19 INFN, Sezione di Perugia - Istituto Nazionale di Fisica Nucleare, Sezione di Perugia
20 George Mason University [Fairfax]
21 Unipd - Università degli Studi di Padova = University of Padua
22 IRA - Istituto di Radioastronomia [Bologna]
23 ECAP - Erlangen Centre for Astroparticle Physics
24 INAF - Istituto Nazionale di Astrofisica
25 USN - Unité Scientifique de la Station de Nançay
26 Department of Astrophysics [Nagoya]
27 Yunnan Observatories, Chinese Academy of Sciences
28 University of Iceland [Reykjavik]
29 Tokyo University of Science [Tokyo]
30 IRAP - Institut de recherche en astrophysique et planétologie
31 NTHU - National Tsing Hua University [Hsinchu]
32 DIEE
33 KTH - KTH Royal Institute of Technology [Stockholm]
34 IEEC-CSIC - Institut d'Estudis Espacials de Catalunya
35 Mahidol University [Bangkok]
36 Hiroshima University
37 INFN, Sezione di Roma Tor Vergata - Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tor Vergata
38 Department of Physics and Astronomy [Denver]
39 MPI-P - Max-Planck-Institut für Physik (Werner-Heisenberg-Institut)
40 OAT - INAF - Osservatorio Astronomico di Trieste
41 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
42 Universität Innsbruck [Innsbruck]
43 Stockholm University
44 NYCB Real-Time Computing Inc., Lattingtown
45 MPIK - Max-Planck-Institut für Kernphysik
46 ICE-CSIC - Institut de Ciencies de l'Espai [Barcelona]
47 Rikkyo University [Tokyo]
48 Università degli Studi di Udine - University of Udine [Italie]
A. Albert
E.D. Bloom
  • Function : Author
M. Di Mauro
  • Function : Author
T. Glanzmann
  • Function : Author
D. Green
Lucas Guillemot
  • Function : Author
  • PersonId : 1027087
G. La Mura
  • Function : Author
F. Loparco
  • Function : Author
T. Mizuno
  • Function : Author
T. Ohsugi
  • Function : Author
N. Omodei
  • Function : Author
M. Persic
C. Sgró
  • Function : Author
K Tanaka
  • Function : Author

Abstract

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´-of´of´-2.0 10 erg cm s 12 2 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 s 10. Its spectrum is consistent with a power law with photon index G =  + 2.4 0.1 stat syst and a – 0.1 100 GeV energy flux of ()  ´ +-5.6 0.6 10 erg cm s stat syst 12 2 1. M31 is detected to be extended with a s 4 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.
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Dates and versions

insu-01522758 , version 1 (18-05-2017)

Identifiers

Cite

M. Ackermann, M. Ajello, A. Albert, L. Baldini, Jean Ballet, et al.. Observations of M31 and M33 with the Fermi Large Area Telescope: A Galactic Center Excess in Andromeda?. The Astrophysical Journal, 2017, 836, pp.208. ⟨10.3847/1538-4357/aa5c3d⟩. ⟨insu-01522758⟩
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