A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

A. A. Abdo; M. Ackermann; M. Ajello; L. Baldini; J. Ballet; G. Barbiellini; D. Bastieri; R. Bellazzini; R. D. Blandford; E. D. Bloom; E. Bonamente; A. W. Borgland; A. Bouvier; T. J. Brandt; J. Bregeon; M. Brigida; P. Bruel; R. Buehler; S. Buson; G. A. Caliandro; R. A. Cameron; P. A. Caraveo; S. Carrigan; J. M. Casandjian; E. Charles; S. Chaty; A. Chekhtman; C. C. Cheung; J. Chiang; S. Ciprini; R. Claus; J. Cohen-Tanugi; J. Conrad; M. E. Decesar; C. D. Dermer; F. De Palma; S. W. Digel; E. Do Couto E Silva; P. S. Drell; R. Dubois; D. Dumora; C. Favuzzi; P. Fortin; M. Frailis; Y. Fukazawa; P. Fusco; F. Gargano; D. Gasparrini; N. Gehrels; S. Germani; N. Giglietto; F. Giordano; T. Glanzman; G. Godfrey; I. Grenier; M. H. Grondin; J. E. Grove; L. Guillemot; S. Guiriec; D. Hadasch; A. K. Harding; E. Hays; P. Jean; G. Jóhannesson; T. J. Johnson; W. N. Johnson; T. Kamae; H. Katagiri; J. Kataoka; M. Kerr; J. Knödlseder; M. Kuss; J. Lande; L. Latronico; S. H. Lee; M. Lemoine-Goumard; M. Llena Garde; F. Longo; F. Loparco; M. N. Lovellette; P. Lubrano; A. Makeev; M. N. Mazziotta; P. F. Michelson; W. Mitthumsiri; T. Mizuno; C. Monte; M. E. Monzani; A. Morselli; I. V. Moskalenko; S. Murgia; M. Naumann-Godo; P. L. Nolan; J. P. Norris; E. Nuss; T. Ohsugi; N. Omodei; E. Orlando; J. F. Ormes; B. Pancrazi; D. Parent; M. Pepe; M. Pesce-Rollins; F. Piron; T. A. Porter; S. Rainò; R. Rando; A. Reimer; O. Reimer; T. Reposeur; J. Ripken; R. W. Romani; M. Roth; H. F.W. Sadrozinski; P. M. Saz Parkinson; C. Sgrò; E. J. Siskind; D. A. Smith; P. Spinelli; M. S. Strickman; D. J. Suson; H. Takahashi; T. Takahashi; T. Tanaka; J. B. Thayer; J. G. Thayer; L. Tibaldo; D. F. Torres; G. Tosti; A. Tramacere; Y. Uchiyama; T. L. Usher; V. Vasileiou; C. Venter; N. Vilchez; V. Vitale; A. P. Waite; P. Wang; N. Webb; B. L. Winer; Z. Yang; T. Ylinen; M. Ziegler

doi:10.1051/0004-6361/201014458

A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

A. A. Abdo
, M. Ackermann
, M. Ajello
, L. Baldini
, J. Ballet
, G. Barbiellini
, D. Bastieri
, R. Bellazzini
, R. D. Blandford
, E. D. Bloom
, E. Bonamente
, A. W. Borgland
, A. Bouvier
, T. J. Brandt
, J. Bregeon
, M. Brigida
, P. Bruel
, R. Buehler
, S. Buson
, G. A. Caliandro

R. A. Cameron, P. A. Caraveo, S. Carrigan, J. M. Casandjian, E. Charles, S. Chaty, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, M. E. Decesar, C. D. Dermer, F. De Palma, S. W. Digel, E. Do Couto E Silva, P. S. Drell, R. Dubois, D. Dumora, C. Favuzzi, P. Fortin, M. Frailis, Y. Fukazawa, P. Fusco, F. Gargano, D. Gasparrini, N. Gehrels, S. Germani, N. Giglietto, F. Giordano, T. Glanzman, G. Godfrey, I. Grenier, M. H. Grondin, J. E. Grove, L. Guillemot, S. Guiriec, D. Hadasch, A. K. Harding, E. Hays, P. Jean, G. Jóhannesson, T. J. Johnson, W. N. Johnson, T. Kamae, H. Katagiri, J. Kataoka, M. Kerr, J. Knödlseder, M. Kuss, J. Lande, L. Latronico, S. H. Lee, M. Lemoine-Goumard, M. Llena Garde, F. Longo, F. Loparco, M. N. Lovellette, P. Lubrano, A. Makeev, M. N. Mazziotta, P. F. Michelson, W. Mitthumsiri, T. Mizuno, C. Monte, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, M. Naumann-Godo, P. L. Nolan, J. P. Norris, E. Nuss, T. Ohsugi, N. Omodei, E. Orlando, J. F. Ormes, B. Pancrazi, D. Parent, M. Pepe, M. Pesce-Rollins, F. Piron, T. A. Porter, S. Rainò, R. Rando, A. Reimer, O. Reimer, T. Reposeur, J. Ripken, R. W. Romani, M. Roth, H. F.W. Sadrozinski, P. M. Saz Parkinson, C. Sgrò, E. J. Siskind, D. A. Smith, P. Spinelli, M. S. Strickman, D. J. Suson, H. Takahashi, T. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, L. Tibaldo, D. F. Torres, G. Tosti, A. Tramacere, Y. Uchiyama, T. L. Usher, V. Vasileiou, C. Venter, N. Vilchez, V. Vitale, A. P. Waite, P. Wang, N. Webb, B. L. Winer, Z. Yang, T. Ylinen, M. Ziegler

Naval Research Laboratory
National Research Council
Kavli Institute for Particle Astrophysics and Cosmology
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
Universite Paris-Saclay
INFN Sezione di Trieste
University of Trieste
INFN
University of Padova
INFN Sezione di Perugia
University of Perugia
CNRS
The Ohio State University
Politecnico di Bari
INFN Sezione di Bari
INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
George Mason University
Laboratoire Univers et Particules de Montpellier
Stockholm University
Oskar Klein Centre
Royal Swedish Academy of Sciences
NASA Goddard Space Flight Center
University of Maryland
UMR 5797
Univ. Bordeaux
and Physics University of Udine
INAF-Trieste
Hiroshima University
Science and Research Directorate
Max-Planck-Institut für Radioastronomie
Center for Space Plasma and Aeronomic Research
Pompeu Fabra University (UPF)
Waseda University
University of Washington
INFN Roma Tor Vergata
University of Denver
Max Planck Institut für Extraterrestrische Physik
Medical University of Innsbruck
University of California at Santa Cruz
NYCB Real-Time Computing Inc.
Purdue University Northwest
ISAS/JAXA
International Doctorate on Astroparticle Physics (IDAPP) Program
Campus UAB
Consorzio Interuniversitario per la Fisica Spaziale (CIFS)
University of Geneva
Biochemical and Environmental Engineering
North-West University
University of Rome “Tor Vergata”
KTH Royal Institute of Technology
University of Kalmar

Résultats de recherche: Contribution à un journal › Article › Revue par des pairs

Résumé

Context. Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. The observation of this emission provides a powerful tool to assess the millisecond pulsar population of a cluster, is essential for understanding the importance of binary systems for the evolution of globular clusters, and provides complementary insights into magnetospheric emission processes. Aims. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. Methods. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Results. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices (0.7 < Γ <1.4) and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices (1.0 < Γ < 1.7), however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. Conclusions. The observation of high-energy gamma-ray emission from globular clusters thus provides a reliable independent method to assess their millisecond pulsar populations.

langue originale	Anglais
Numéro d'article	A75
journal	Astronomy and Astrophysics
Volume	524
Numéro de publication	3
Les DOIs	https://doi.org/10.1051/0004-6361/201014458
état	Publié - 24 nov. 2010

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10.1051/0004-6361/201014458

Contient cette citation

Abdo, A. A., Ackermann, M., Ajello, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Borgland, A. W., Bouvier, A., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., ... Ziegler, M. (2010). A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope. Astronomy and Astrophysics, 524(3), Article A75. https://doi.org/10.1051/0004-6361/201014458

@article{93c0b2b5c9ad49d18f15ba37839454a9,

title = "A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope",

abstract = "Context. Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. The observation of this emission provides a powerful tool to assess the millisecond pulsar population of a cluster, is essential for understanding the importance of binary systems for the evolution of globular clusters, and provides complementary insights into magnetospheric emission processes. Aims. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. Methods. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Results. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices (0.7 < Γ <1.4) and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices (1.0 < Γ < 1.7), however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. Conclusions. The observation of high-energy gamma-ray emission from globular clusters thus provides a reliable independent method to assess their millisecond pulsar populations.",

keywords = "gamma rays: general, globular clusters: general, pulsars: general",

author = "Abdo, \{A. A.\} and M. Ackermann and M. Ajello and L. Baldini and J. Ballet and G. Barbiellini and D. Bastieri and R. Bellazzini and Blandford, \{R. D.\} and Bloom, \{E. D.\} and E. Bonamente and Borgland, \{A. W.\} and A. Bouvier and Brandt, \{T. J.\} and J. Bregeon and M. Brigida and P. Bruel and R. Buehler and S. Buson and Caliandro, \{G. A.\} and Cameron, \{R. A.\} and Caraveo, \{P. A.\} and S. Carrigan and Casandjian, \{J. M.\} and E. Charles and S. Chaty and A. Chekhtman and Cheung, \{C. C.\} and J. Chiang and S. Ciprini and R. Claus and J. Cohen-Tanugi and J. Conrad and Decesar, \{M. E.\} and Dermer, \{C. D.\} and \{De Palma\}, F. and Digel, \{S. W.\} and \{Do Couto E Silva\}, E. and Drell, \{P. S.\} and R. Dubois and D. Dumora and C. Favuzzi and P. Fortin and M. Frailis and Y. Fukazawa and P. Fusco and F. Gargano and D. Gasparrini and N. Gehrels and S. Germani and N. Giglietto and F. Giordano and T. Glanzman and G. Godfrey and I. Grenier and Grondin, \{M. H.\} and Grove, \{J. E.\} and L. Guillemot and S. Guiriec and D. Hadasch and Harding, \{A. K.\} and E. Hays and P. Jean and G. J{\'o}hannesson and Johnson, \{T. J.\} and Johnson, \{W. N.\} and T. Kamae and H. Katagiri and J. Kataoka and M. Kerr and J. Kn{\"o}dlseder and M. Kuss and J. Lande and L. Latronico and Lee, \{S. H.\} and M. Lemoine-Goumard and \{Llena Garde\}, M. and F. Longo and F. Loparco and Lovellette, \{M. N.\} and P. Lubrano and A. Makeev and Mazziotta, \{M. N.\} and Michelson, \{P. F.\} and W. Mitthumsiri and T. Mizuno and C. Monte and Monzani, \{M. E.\} and A. Morselli and Moskalenko, \{I. V.\} and S. Murgia and M. Naumann-Godo and Nolan, \{P. L.\} and Norris, \{J. P.\} and E. Nuss and T. Ohsugi and N. Omodei and E. Orlando and Ormes, \{J. F.\} and B. Pancrazi and D. Parent and M. Pepe and M. Pesce-Rollins and F. Piron and Porter, \{T. A.\} and S. Rain{\`o} and R. Rando and A. Reimer and O. Reimer and T. Reposeur and J. Ripken and Romani, \{R. W.\} and M. Roth and Sadrozinski, \{H. F.W.\} and \{Saz Parkinson\}, \{P. M.\} and C. Sgr{\`o} and Siskind, \{E. J.\} and Smith, \{D. A.\} and P. Spinelli and Strickman, \{M. S.\} and Suson, \{D. J.\} and H. Takahashi and T. Takahashi and T. Tanaka and Thayer, \{J. B.\} and Thayer, \{J. G.\} and L. Tibaldo and Torres, \{D. F.\} and G. Tosti and A. Tramacere and Y. Uchiyama and Usher, \{T. L.\} and V. Vasileiou and C. Venter and N. Vilchez and V. Vitale and Waite, \{A. P.\} and P. Wang and N. Webb and Winer, \{B. L.\} and Z. Yang and T. Ylinen and M. Ziegler",

year = "2010",

month = nov,

day = "24",

doi = "10.1051/0004-6361/201014458",

language = "English",

volume = "524",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

number = "3",

}

Abdo, AA, Ackermann, M, Ajello, M, Baldini, L, Ballet, J, Barbiellini, G, Bastieri, D, Bellazzini, R, Blandford, RD, Bloom, ED, Bonamente, E, Borgland, AW, Bouvier, A, Brandt, TJ, Bregeon, J, Brigida, M, Bruel, P, Buehler, R, Buson, S, Caliandro, GA, Cameron, RA, Caraveo, PA, Carrigan, S, Casandjian, JM, Charles, E, Chaty, S, Chekhtman, A, Cheung, CC, Chiang, J, Ciprini, S, Claus, R, Cohen-Tanugi, J, Conrad, J, Decesar, ME, Dermer, CD, De Palma, F, Digel, SW, Do Couto E Silva, E, Drell, PS, Dubois, R, Dumora, D, Favuzzi, C, Fortin, P, Frailis, M, Fukazawa, Y, Fusco, P, Gargano, F, Gasparrini, D, Gehrels, N, Germani, S, Giglietto, N, Giordano, F, Glanzman, T, Godfrey, G, Grenier, I, Grondin, MH, Grove, JE, Guillemot, L, Guiriec, S, Hadasch, D, Harding, AK, Hays, E, Jean, P, Jóhannesson, G, Johnson, TJ, Johnson, WN, Kamae, T, Katagiri, H, Kataoka, J, Kerr, M, Knödlseder, J, Kuss, M, Lande, J, Latronico, L, Lee, SH, Lemoine-Goumard, M, Llena Garde, M, Longo, F, Loparco, F, Lovellette, MN, Lubrano, P, Makeev, A, Mazziotta, MN, Michelson, PF, Mitthumsiri, W, Mizuno, T, Monte, C, Monzani, ME, Morselli, A, Moskalenko, IV, Murgia, S, Naumann-Godo, M, Nolan, PL, Norris, JP, Nuss, E, Ohsugi, T, Omodei, N, Orlando, E, Ormes, JF, Pancrazi, B, Parent, D, Pepe, M, Pesce-Rollins, M, Piron, F, Porter, TA, Rainò, S, Rando, R, Reimer, A, Reimer, O, Reposeur, T, Ripken, J, Romani, RW, Roth, M, Sadrozinski, HFW, Saz Parkinson, PM, Sgrò, C, Siskind, EJ, Smith, DA, Spinelli, P, Strickman, MS, Suson, DJ, Takahashi, H, Takahashi, T, Tanaka, T, Thayer, JB, Thayer, JG, Tibaldo, L, Torres, DF, Tosti, G, Tramacere, A, Uchiyama, Y, Usher, TL, Vasileiou, V, Venter, C, Vilchez, N, Vitale, V, Waite, AP, Wang, P, Webb, N, Winer, BL, Yang, Z, Ylinen, T & Ziegler, M 2010, 'A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope', Astronomy and Astrophysics, VOL. 524, Numéro 3, A75. https://doi.org/10.1051/0004-6361/201014458

TY - JOUR

T1 - A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

AU - Abdo, A. A.

AU - Ackermann, M.

AU - Ajello, M.

AU - Baldini, L.

AU - Ballet, J.

AU - Barbiellini, G.

AU - Bastieri, D.

AU - Bellazzini, R.

AU - Blandford, R. D.

AU - Bloom, E. D.

AU - Bonamente, E.

AU - Borgland, A. W.

AU - Bouvier, A.

AU - Brandt, T. J.

AU - Bregeon, J.

AU - Brigida, M.

AU - Bruel, P.

AU - Buehler, R.

AU - Buson, S.

AU - Caliandro, G. A.

AU - Cameron, R. A.

AU - Caraveo, P. A.

AU - Carrigan, S.

AU - Casandjian, J. M.

AU - Charles, E.

AU - Chaty, S.

AU - Chekhtman, A.

AU - Cheung, C. C.

AU - Chiang, J.

AU - Ciprini, S.

AU - Claus, R.

AU - Cohen-Tanugi, J.

AU - Conrad, J.

AU - Decesar, M. E.

AU - Dermer, C. D.

AU - De Palma, F.

AU - Digel, S. W.

AU - Do Couto E Silva, E.

AU - Drell, P. S.

AU - Dubois, R.

AU - Dumora, D.

AU - Favuzzi, C.

AU - Fortin, P.

AU - Frailis, M.

AU - Fukazawa, Y.

AU - Fusco, P.

AU - Gargano, F.

AU - Gasparrini, D.

AU - Gehrels, N.

AU - Germani, S.

AU - Giglietto, N.

AU - Giordano, F.

AU - Glanzman, T.

AU - Godfrey, G.

AU - Grenier, I.

AU - Grondin, M. H.

AU - Grove, J. E.

AU - Guillemot, L.

AU - Guiriec, S.

AU - Hadasch, D.

AU - Harding, A. K.

AU - Hays, E.

AU - Jean, P.

AU - Jóhannesson, G.

AU - Johnson, T. J.

AU - Johnson, W. N.

AU - Kamae, T.

AU - Katagiri, H.

AU - Kataoka, J.

AU - Kerr, M.

AU - Knödlseder, J.

AU - Kuss, M.

AU - Lande, J.

AU - Latronico, L.

AU - Lee, S. H.

AU - Lemoine-Goumard, M.

AU - Llena Garde, M.

AU - Longo, F.

AU - Loparco, F.

AU - Lovellette, M. N.

AU - Lubrano, P.

AU - Makeev, A.

AU - Mazziotta, M. N.

AU - Michelson, P. F.

AU - Mitthumsiri, W.

AU - Mizuno, T.

AU - Monte, C.

AU - Monzani, M. E.

AU - Morselli, A.

AU - Moskalenko, I. V.

AU - Murgia, S.

AU - Naumann-Godo, M.

AU - Nolan, P. L.

AU - Norris, J. P.

AU - Nuss, E.

AU - Ohsugi, T.

AU - Omodei, N.

AU - Orlando, E.

AU - Ormes, J. F.

AU - Pancrazi, B.

AU - Parent, D.

AU - Pepe, M.

AU - Pesce-Rollins, M.

AU - Piron, F.

AU - Porter, T. A.

AU - Rainò, S.

AU - Rando, R.

AU - Reimer, A.

AU - Reimer, O.

AU - Reposeur, T.

AU - Ripken, J.

AU - Romani, R. W.

AU - Roth, M.

AU - Sadrozinski, H. F.W.

AU - Saz Parkinson, P. M.

AU - Sgrò, C.

AU - Siskind, E. J.

AU - Smith, D. A.

AU - Spinelli, P.

AU - Strickman, M. S.

AU - Suson, D. J.

AU - Takahashi, H.

AU - Takahashi, T.

AU - Tanaka, T.

AU - Thayer, J. B.

AU - Thayer, J. G.

AU - Tibaldo, L.

AU - Torres, D. F.

AU - Tosti, G.

AU - Tramacere, A.

AU - Uchiyama, Y.

AU - Usher, T. L.

AU - Vasileiou, V.

AU - Venter, C.

AU - Vilchez, N.

AU - Vitale, V.

AU - Waite, A. P.

AU - Wang, P.

AU - Webb, N.

AU - Winer, B. L.

AU - Yang, Z.

AU - Ylinen, T.

AU - Ziegler, M.

PY - 2010/11/24

Y1 - 2010/11/24

N2 - Context. Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. The observation of this emission provides a powerful tool to assess the millisecond pulsar population of a cluster, is essential for understanding the importance of binary systems for the evolution of globular clusters, and provides complementary insights into magnetospheric emission processes. Aims. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. Methods. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Results. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices (0.7 < Γ <1.4) and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices (1.0 < Γ < 1.7), however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. Conclusions. The observation of high-energy gamma-ray emission from globular clusters thus provides a reliable independent method to assess their millisecond pulsar populations.

AB - Context. Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. The observation of this emission provides a powerful tool to assess the millisecond pulsar population of a cluster, is essential for understanding the importance of binary systems for the evolution of globular clusters, and provides complementary insights into magnetospheric emission processes. Aims. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. Methods. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Results. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices (0.7 < Γ <1.4) and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices (1.0 < Γ < 1.7), however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. Conclusions. The observation of high-energy gamma-ray emission from globular clusters thus provides a reliable independent method to assess their millisecond pulsar populations.

KW - gamma rays: general

KW - globular clusters: general

KW - pulsars: general

U2 - 10.1051/0004-6361/201014458

DO - 10.1051/0004-6361/201014458

M3 - Article

AN - SCOPUS:78649512351

SN - 0004-6361

VL - 524

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

IS - 3

M1 - A75

ER -

A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

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