首页|A Fermi-LAT Study of Globular Cluster Dynamical Evolution in the Milky Way:Millisecond Pulsars as the Probe
A Fermi-LAT Study of Globular Cluster Dynamical Evolution in the Milky Way:Millisecond Pulsars as the Probe
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Using archival Fermi-LAT data with a time span of～12 yr,we study the population of Millisecond Pulsars(MSPs)in Globular Clusters(GlCs)and investigate their dependence on cluster dynamical evolution in the Milky Way.We show that the γ-ray luminosity(Lγ)and emissivity(i.e.,εγ=Lγ/M,with M the cluster mass)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 Lγ and εγ,and these trends can be summarized as strong correlations with cluster stellar encounter rate T and the specific encounter rate(Λ=Γ/M),with Lγ ∝ Γ0.70±011 and εγ∝ Λ0.73±013 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 disruption of Low-Mass X-ray Binaries and ejection of MSPs from core-collapsed systems.Besides,the GlCs are found to exhibit larger εγ with increasing stellar mass function slope(εγ∝ i0(0.57±01)α),decreasing tidal radius(εγ ∝ R-10±0.22)and distances from the Galactic Center(GC,εγ ∝ Rgc-113±0.21).These correlations indicate that,as GlCs losing kinetic energy and spiral in toward the 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 εγ of GlCs is～10-1000 times larger than the Galactic bulge,the latter is thought to reside thousands of unresolved MSPs and may be responsible for the GC γ-ray excess,which supports that GlCs are generous contributors to the population of MSPs in the GC.
(Galaxy:)globular clusters:general(stars:)pulsars:generalGalaxy:kinematics and dynamicsGalaxy:centerGalaxy:bulgegamma-rays:starsgamma-rays:diffuse backgroundgamma-rays:galaxies
Li Feng、Zhongqun Cheng、Wei Wang、Zhiyuan Li、Yang Chen
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School of Astronomy and Space Science,Nanjing University,Nanjing 210023,China
Department of Astronomy,School of Physics and Technology,Wuhan University,Wuhan 430072,China
WHU-NAOC Joint Center for Astronomy,Wuhan University,Wuhan 430072,China
Key Laboratory of Modem Astronomy and Astrophysics,Nanjing University,Nanjing 210023,China
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