Gamma-ray emission from globular clusters

Abstract

Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as Millisecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gamma-ray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed gamma-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that gamma-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.

11 pages, 7 figures, 2 tables, J. Astron. Space Sci., in press

References in corpus (15)

• The ATNF Pulsar Catalogue
• Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT
• A state change in the missing link binary pulsar system PSR J1023+0038
• The First Fermi-LAT Catalog of Sources Above 10 GeV
• HST Proper Motions and Stellar Dynamics in the Core of the Globular Cluster 47 Tucanae
• Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae
• Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
• Distances of the bulge globular clusters Terzan 5, Liller 1, UKS 1 and Terzan 4 based on HST NICMOS photometry
• Broadband Pulsations from PSR B1821-24: Implications for Emission Models and the Pulsar Population of M28
• CANGAROO-III Search for Gamma Rays from Centaurus A and the $\omega$ Centauri Region
• Search for pulsed gamma-ray emission from globular cluster M28
• Search for Very-high-energy γ-ray emission from Galactic globular clusters with H.E.S.S
• Gamma-ray emission from globular clusters
• Misaligned TeV gamma-ray sources in the vicinity of globular clusters
• Remnants of compact binary mergers

Cited by in corpus (10)

• Evidence for a high-energy tail in the gamma-ray spectra of globular clusters
• Milky Way globular clusters in gamma-rays: analyzing the dynamical formation of millisecond pulsars
• Gamma-ray emission from globular clusters
• Deep observations of the globular cluster M15 with the MAGIC telescopes
• Galactic Observatory Science with the ASTRI Mini-Array at the Observatorio del Teide
• Likely detection of gamma-ray pulsations of PSR~J1717+4308A in NGC~6341 and implication of the gamma-ray millisecond pulsars in globular clusters
• Identifying the brightest Galactic globular clusters for future observations by H.E.S.S. and CTA
• Probing the pulsar population of Terzan 5 via spectral modeling
• A Fermi-LAT Study of Globular Cluster Dynamical Evolution in the Milky Way: Millisecond Pulsars as the Probe
• Characterizing the Gamma-ray Emission Properties of the Globular Cluster M5 with the Fermi-LAT