A Fermi-LAT Study of Globular Cluster Dynamical Evolution in the Milky Way: Millisecond Pulsars as the Probe

Abstract

Using archival {\it Fermi}-LAT data with a time span of $\sim 12$ years, we study the population of Millisecond Pulsars (MSPs) in Globular Clusters (GlCs) and investigate their dependence on cluster dynamical evolution in the Milky Way Galaxy. We show that the $\gamma$-ray luminosity ($L_{\gamma }$) and emissivity (${\epsilon }_{\gamma }=L_{\gamma }/M$) are good indicators of the population and abundance of MSPs in GlCs, and they are highly dependent on the dynamical evolution history of the host clusters. Specifically speaking, the dynamically older GlCs with more compact structures are more likely to have larger $L_{\gamma }$ and ${\epsilon }_{\gamma }$, and these trends can be summarized as strong correlations with cluster stellar encounter rate $\Gamma$ and the specific encounter rate ($\Lambda =\Gamma /M$), with $L_{\gamma }\propto {\Gamma }^{0.70\pm 0.11}$ and ${\epsilon }_{\gamma }\propto {\Lambda }^{0.73\pm 0.13}$ for dynamically normal GlCs. However, as GlCs evolve into deep core collapse, these trends are found to be reversed, implying that strong encounters may have lead to the ejection of MSPs from core-collapsed Systems. Besides, the GlCs are found to exhibit larger ${\epsilon }_{\gamma }$ with increasing stellar mass function slope, decreasing tidal radius and distances from the Galactic Center (GC). These correlations indicate that, as GlCs losing kinetic energy and spiral in towards GC, tidal stripping and mass segregation have a preference in leading to the loss of normal stars from GlCs, while MSPs are more likely to concentrate to cluster center and be deposited into the GC. Moreover, we gauge ${\epsilon }_{\gamma }$ of GlCs is $\sim 10-1000$ times larger than the Galactic bulge, the latter is thought to reside thousands of unresolved MSPs and may responsible for the GC $\gamma$-ray excess, which support that GlCs are generous contributors to the population of MSPs in the GC.

23 pages, 9 figures, 3 tables, accepted for publication in RAA

References in corpus (32)

• Incremental Fermi Large Area Telescope Fourth Source Catalog
• MOCCA-SURVEY Database I: Coalescing Binary Black Holes Originating From Globular Clusters
• Formation and evolution of compact binaries in globular clusters: II. Binaries with neutron stars
• The Dynamical Evolution of Stellar Black Holes in Globular Clusters
• Dynamical age differences among coeval star clusters as revealed by blue stragglers
• Black holes and core expansion in massive star clusters
• On the Rate of Neutron Star Binary Mergers from Globular Clusters
• Formation and evolution of compact binaries in globular clusters: I.Binaries with white dwarfs
• Galactic Center gamma-ray "excess" from an active past of the Galactic Centre?
• Dynamical Formation of Close Binaries in Globular Clusters II: Cataclysmic Variables
• The characteristics of the Galactic center excess measured with 11 years of Fermi-LAT data
• The effect of stellar-mass black holes on the structural evolution of massive star clusters
• Millisecond Pulsars and Black Holes in Globular Clusters
• Millisecond pulsar interpretation of the Galactic center gamma-ray excess
• The global mass functions of 35 Galactic globular clusters: I. Observational data and correlations with cluster parameters
• The eye of Gaia on globular clusters structure: tidal tails
• Accreting black hole binaries in globular clusters
• The Gamma-Ray Pulsar Population of Globular Clusters: Implications for the GeV Excess
• White Dwarf Subsystems in Core-Collapsed Globular Clusters
• The Global Mass Functions of 35 Galactic globular clusters: II. Clues on the Initial Mass Function and Black Hole Retention Fraction
• Millisecond Pulsars from Accretion Induced Collapse as the Origin of the Galactic Centre Gamma-ray Excess Signal
• MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters -- I. cataclysmic variables -- present-day population
• Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars
• MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters -- III. Cataclysmic variables -- Implications of model assumptions
• The X-ray Emissivity of Low-Density Stellar Populations
• Exploring the Mass Segregation Effect of X-ray Sources in Globular Clusters: The Case of 47 Tucanae
• Orbits of globular clusters computed with dynamical friction in the Galactic anisotropic velocity dispersion field
• Dynamically Formed Black Hole Binaries: In-Cluster Versus Ejected Mergers
• Twenty Years of Searching for (and Finding) Globular Cluster Pulsars
• Exploring the Mass Segregation Effect of X-ray Sources in Globular Clusters. IV. Evidence of Black Hole Burning in $\omega$ Centauri
• Millisecond Pulsar Kicks Cause Difficulties in Explaining the Galactic Center Gamma-Ray Excess
• Millisecond Pulsars in Dense Star Clusters: Evolution, Scaling Relations, and the Galactic-Center Gamma-ray Excess

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• Characterizing the Gamma-ray Emission Properties of the Globular Cluster M5 with the Fermi-LAT
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