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. CaliandroR. 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, Jun 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

    Research output: Contribution to journalArticle

    103 Citations (Scopus)

    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.

    Original languageEnglish
    Article number75
    JournalAstronomy and Astrophysics
    Volume524
    Issue number3
    DOIs
    Publication statusPublished - 2010 Nov 24

    Fingerprint

    globular clusters
    pulsars
    gamma rays
    telescopes
    estimates
    energy
    encounter rate
    cut-off
    Fermi Gamma-ray Space Telescope
    radio
    encounters
    emitters
    luminosity
    signatures

    Keywords

    • gamma rays: general
    • globular clusters: general
    • pulsars: general

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    Abdo, A. A., Ackermann, M., Ajello, M., Baldini, L., Ballet, J., Barbiellini, G., ... Ziegler, M. (2010). A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope. Astronomy and Astrophysics, 524(3), [75]. https://doi.org/10.1051/0004-6361/201014458

    A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope. / 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.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Charles, E.; Chaty, S.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Decesar, M. E.; Dermer, C. D.; De Palma, F.; Digel, S. W.; Do Couto E Silva, E.; Drell, P. S.; 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, M. H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Hays, E.; Jean, P.; Jóhannesson, G.; Johnson, T. J.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, Jun; Kerr, M.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S. H.; Lemoine-Goumard, M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Makeev, A.; Mazziotta, M. N.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Pancrazi, B.; Parent, D.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Reimer, A.; Reimer, O.; Reposeur, T.; Ripken, J.; Romani, R. W.; Roth, M.; Sadrozinski, H. F W; Saz Parkinson, P. M.; Sgrò, C.; Siskind, E. J.; Smith, D. A.; Spinelli, P.; Strickman, M. S.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vasileiou, V.; Venter, C.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Webb, N.; Winer, B. L.; Yang, Z.; Ylinen, T.; Ziegler, M.

    In: Astronomy and Astrophysics, Vol. 524, No. 3, 75, 24.11.2010.

    Research output: Contribution to journalArticle

    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, no. 3, 75. https://doi.org/10.1051/0004-6361/201014458
    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. ; Caliandro, G. A. ; Cameron, R. A. ; Caraveo, P. A. ; Carrigan, S. ; Casandjian, J. M. ; Charles, E. ; Chaty, S. ; Chekhtman, A. ; Cheung, C. C. ; Chiang, J. ; Ciprini, S. ; Claus, R. ; Cohen-Tanugi, J. ; Conrad, J. ; Decesar, M. E. ; Dermer, C. D. ; De Palma, F. ; Digel, S. W. ; Do Couto E Silva, E. ; Drell, P. S. ; 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, M. H. ; Grove, J. E. ; Guillemot, L. ; Guiriec, S. ; Hadasch, D. ; Harding, A. K. ; Hays, E. ; Jean, P. ; Jóhannesson, G. ; Johnson, T. J. ; Johnson, W. N. ; Kamae, T. ; Katagiri, H. ; Kataoka, Jun ; Kerr, M. ; Knödlseder, J. ; Kuss, M. ; Lande, J. ; Latronico, L. ; Lee, S. H. ; Lemoine-Goumard, M. ; Llena Garde, M. ; Longo, F. ; Loparco, F. ; Lovellette, M. N. ; Lubrano, P. ; Makeev, A. ; Mazziotta, M. N. ; Michelson, P. F. ; Mitthumsiri, W. ; Mizuno, T. ; Monte, C. ; Monzani, M. E. ; Morselli, A. ; Moskalenko, I. V. ; Murgia, S. ; Naumann-Godo, M. ; Nolan, P. L. ; Norris, J. P. ; Nuss, E. ; Ohsugi, T. ; Omodei, N. ; Orlando, E. ; Ormes, J. F. ; Pancrazi, B. ; Parent, D. ; Pepe, M. ; Pesce-Rollins, M. ; Piron, F. ; Porter, T. A. ; Rainò, S. ; Rando, R. ; Reimer, A. ; Reimer, O. ; Reposeur, T. ; Ripken, J. ; Romani, R. W. ; Roth, M. ; Sadrozinski, H. F W ; Saz Parkinson, P. M. ; Sgrò, C. ; Siskind, E. J. ; Smith, D. A. ; Spinelli, P. ; Strickman, M. S. ; Suson, D. J. ; Takahashi, H. ; Takahashi, T. ; Tanaka, T. ; Thayer, J. B. ; Thayer, J. G. ; Tibaldo, L. ; Torres, D. F. ; Tosti, G. ; Tramacere, A. ; Uchiyama, Y. ; Usher, T. L. ; Vasileiou, V. ; Venter, C. ; Vilchez, N. ; Vitale, V. ; Waite, A. P. ; Wang, P. ; Webb, N. ; Winer, B. L. ; Yang, Z. ; Ylinen, T. ; Ziegler, M. / A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope. In: Astronomy and Astrophysics. 2010 ; Vol. 524, No. 3.
    @article{f18501ddc8304d0499951a344c413726,
    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 Jun 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 = "11",
    day = "24",
    doi = "10.1051/0004-6361/201014458",
    language = "English",
    volume = "524",
    journal = "Astronomy and Astrophysics",
    issn = "0004-6361",
    publisher = "EDP Sciences",
    number = "3",

    }

    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, Jun

    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

    UR - http://www.scopus.com/inward/record.url?scp=78649512351&partnerID=8YFLogxK

    UR - http://www.scopus.com/inward/citedby.url?scp=78649512351&partnerID=8YFLogxK

    U2 - 10.1051/0004-6361/201014458

    DO - 10.1051/0004-6361/201014458

    M3 - Article

    AN - SCOPUS:78649512351

    VL - 524

    JO - Astronomy and Astrophysics

    JF - Astronomy and Astrophysics

    SN - 0004-6361

    IS - 3

    M1 - 75

    ER -