Misaligned TeV gamma-ray sources in the vicinity of globular clusters

TL;DR

This paper explains the observed misalignment of TeV gamma-ray sources near globular clusters by modeling the interaction of pulsar wind nebulae with the surrounding medium, showing that environmental density influences gamma-ray source morphology.

Contribution

It introduces a model linking the morphology of TeV gamma-ray sources to the density of the surrounding medium around globular clusters, explaining observed misalignments.

Findings

Misaligned gamma-ray sources are explained by nebula interactions with dense medium.

Numerical simulations match observed gamma-ray source positions.

Environmental density determines gamma-ray source shape and alignment.

Abstract

Globular clusters (GCs) contain huge number of low mass stars and also large number of millisecond pulsars (MSPs). Due to the number of stars, the stellar and MSP winds mix efficiently within the GC. Such mixture of winds leaves GC and interacts with the galactic medium creating a bow shock nebula around GC. The bow shock nebula is filled with relativistic leptons accelerated in the pulsar magnetospheres and/or wind regions. We argue that nebulae around globular clusters, immersed in relatively dense medium close to the galactic plane, should have complicated morphology due to interaction with the surrounding gas. Therefore, TeV $\gamma$-ray sources, related to these nebulae, are expected to be misaligned in respect to GC cores, as observed in the case of GC Ter 5. On the other hand, GCs in low density medium, i.e. far away from the galactic disk, should produce bow shocks at large distances from the GC cores. The TeV $\gamma$-ray sources around such nebulae are expected to be almost spherical and centred on the GC cores. We perform numerical calculations of the TeV $\gamma$-ray emission produced by leptons escaping from the GC Ter 5. It is shown that TeV $\gamma$-ray source related to Ter 5 should be misaligned in respect to the core of GC as observed by the HESS Collaboration.