Multiwavelength Modelling of the Globular Cluster Terzan 5

TL;DR

This paper models the multiwavelength emission from the globular cluster Terzan 5, aiming to understand the population of millisecond pulsars and the cluster's magnetic and radiation environment through combined X-ray, HE, and VHE data.

Contribution

It introduces a comprehensive multiwavelength modeling approach to constrain the properties of MSPs and the cluster environment in Terzan 5, integrating spatially-resolved fluxes across different energy bands.

Findings

Constraints on the number of MSPs in Terzan 5.

Estimates of the cluster's magnetic field and photon energy densities.

Insights into particle acceleration and diffusion processes within the cluster.

Abstract

Diffuse X-ray emission has recently been detected from the globular cluster (GC) Terzan 5, extending out to ~2.5' from the cluster centre. This emission may arise from synchrotron radiation (SR) by energetic leptons being injected into the cluster by the resident millisecond pulsar (MSP) population that interact with the cluster field. These leptons may also be reaccelerated in shocks created by collisions of pulsar winds, and may interact with bright starlight and cosmic microwave background (CMB) photons, yielding gamma rays at very high energies (VHE) through the inverse Compton (IC) process. In the GeV range, Fermi Large Area Telescope (LAT) has detected a population of GCs, very plausibly including Terzan 5, their spectral properties and energetics being consistent with cumulative magnetospheric emission from a population of MSPs. H.E.S.S. has furthermore detected a VHE excess in the direction of Terzan 5. One may derive constraints on the number of MSPs, N_tot, and the radial profiles of the GC B-field, stellar energy density, as well as the diffusion coefficient using the spatially-resolved X-ray, high-energy (HE), and VHE fluxes. If the Fermi LAT flux is due to magnetospheric processes, it will scale with the number of visible gamma-ray MSPs, N_vis. The HE spectrum therefore provides an independent way of constraining the number of MSPs (since N_tot >= N_vis). Consequently, the synthesis of available multiwavelength data presents a unique opportunity to constrain several parameters of the GC Terzan 5.