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

Journal Article · · Astronomy and Astrophysics
 [1]
  1. Naval Research Lab. (NRL), Washington, DC (United States); et al.
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.
Research Organization:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Organization:
USDOE
Contributing Organization:
Fermi LAT Collaboration
Grant/Contract Number:
AC02-76SF00515
OSTI ID:
1357510
Journal Information:
Astronomy and Astrophysics, Journal Name: Astronomy and Astrophysics Vol. 524; ISSN 0004-6361
Publisher:
EDP SciencesCopyright Statement
Country of Publication:
United States
Language:
English

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Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess journal March 2018
X-ray follow-up observations of the two γ -ray pulsars PSR J1459–6053 and PSR J1614–2230 journal August 2012
Stellar Encounter rate in Galactic Globular Clusters journal March 2013
Disrupted Globular Clusters can Explain the Galactic Center Gamma-Ray Excess journal October 2015
FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG journal March 2012
THE SECOND FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS journal September 2013
Globular cluster interstellar media: ionized and ejected by white dwarfs journal November 2014
Gamma-ray and X-ray emission from the Galactic centre: hints on the nuclear star cluster formation history journal June 2018
A Deep X-ray Survey of the globular cluster Omega Centauri journal March 2018
Search for multiwavelength emission from the binary millisecond pulsar PSR J1836-2354A in the globular cluster M22 journal April 2019
Milky Way globular clusters in γ-rays: analysing the dynamical formation of millisecond pulsars journal March 2019
Comment on “Understanding the γ -ray emission from the globular cluster 47 Tuc: Evidence for dark matter?” journal September 2019
Detection of a gamma-ray source in the Galactic Center consistent with extended emission from dark matter annihilation and concentrated astrophysical emission journal October 2012
Pulsar-black hole binaries in the Galactic Centre: PSR-BH binaries in the Galactic Centre journal June 2011
Luminosities of recycled radio pulsars in globular clusters: Recycled radio pulsars in globular clusters journal September 2011
Fermi Large Area Telescope Fourth Source Catalog collection January 2020
The Second Fermi Large area Telescope Catalog of Gamma-Ray Pulsars text January 2013
Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess text January 2018
Fermi Large Area Telescope Fourth Source Catalog text January 2020
Radio Detection Prospects for a Bulge Population of Millisecond Pulsars as Suggested by Fermi-Lat Observations of the Inner Galaxy journal August 2016
Millisecond Pulsar Origin of the Galactic Center Excess and Extended Gamma-Ray Emission from Andromeda: A Closer Look journal July 2018
The MAVERIC Survey: Still No Evidence for Accreting Intermediate-mass Black Holes in Globular Clusters journal July 2018
Population Syntheses of Millisecond Pulsars from the Galactic Disk and Bulge journal August 2018
Evidence for Cosmic-Ray Escape in the Small Magellanic Cloud Using Fermi Gamma Rays journal October 2018
Probing the Pulsar Population of Terzan 5 via Spectral Modeling journal July 2019
Fermi Large Area Telescope Fourth Source Catalog journal March 2020
ESTIMATING THE GeV EMISSION OF MILLISECOND PULSARS IN DWARF SPHEROIDAL GALAXIES journal November 2016
Second Repeating FRB 180814.J0422+73: Ten-year Fermi -LAT Upper Limits and Implications journal April 2019
Discovery of Millisecond Pulsars in the Globular Cluster Omega Centauri journal January 2020
Detection of a Gamma-Ray Source in the Galactic Center Consistent with Extended Emission from Dark Matter Annihilation and Concentrated Astrophysical Emission text January 2012
Stellar Encounter Rate in Galactic Globular Clusters text January 2013
Disrupted Globular Clusters Can Explain the Galactic Center Gamma Ray Excess text January 2015
Radio detection prospects for a bulge population of millisecond pulsars as suggested by Fermi LAT observations of the inner Galaxy text January 2015
Galactic Bulge Preferred Over Dark Matter for the Galactic Center Gamma-Ray Excess text January 2016
The MAVERIC Survey: Still No Evidence for Accreting Intermediate-mass Black Holes in Globular Clusters text January 2018
Population syntheses of millisecond pulsars from the Galactic Disk and Bulge text January 2018
Evidence for Cosmic-Ray Escape in the Small Magellanic Cloud using Fermi Gamma-rays text January 2018
Comment on "Understanding the $γ$-ray emission from the globular cluster 47 Tuc: evidence for dark matter?" text January 2018
Search for multiwavelength emission from the binary millisecond pulsar PSR J1836-2354A in the globular cluster M22 text January 2019
Probing the pulsar population of Terzan 5 via spectral modeling text January 2019
Gamma-Ray And X-Ray Emission From The Galactic Centre: Hints On The Nuclear Star Cluster Formation History text January 2018
Gamma-Ray And X-Ray Emission From The Galactic Centre: Hints On The Nuclear Star Cluster Formation History text January 2018

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