A possible GeV-TeV connection in the direction of the Globular Cluster UKS 1

Abstract

Using public data collected by the Fermi Large Area Telescope (LAT) over 16 years, and the 1523 days of survey data (3HWC) from the High Altitude Water Cherenkov (HAWC) observatory, we searched for possible GeV-TeV connections in globular clusters (GCs). In addition to the confirmed $\gamma -$ray GCs in the 4FGL catalog, we report a GeV detection at the position of UKS 1 with a post-trial probability of $\sim 8\times 10^{-5}$ of it being a fluctuation. Its spectrum within this energy range is well described by a power-law model with $\Gamma \simeq 2.3\pm 0.5$. Furthermore, this GeV feature appears to extend southeast in a direction towards the Galactic plane. From the 3HWC survey data, we have also identified a TeV feature in the direction of UKS 1. It is well-resolved from any known Very High Energy (VHE) source. The post-trial probability that this feature is a fluctuation is $\sim 3\times 10^{-4}$. If confirmed, this would be the second detection of a TeV feature in the proximity of a GC. While the GeV emission mostly coincides with the center of UKS 1, the TeV peak is displaced from the cluster center by several tidal radii in the trailing direction of the GC's proper motion. Given the supersonic speed of UKS 1 at $\sim 270$ km s${}^{-1}$, our findings are consistent with a scenario where the VHE $\gamma -$rays are produced by inverse Compton scattering between relativistic particles and ambient soft photon fields during the course of their propagation away from the head of the bow shock.

arXiv comment6 pages, 4 figures, 1 table, A&A Letter in press

References in corpus (22)

• The H.E.S.S. Galactic plane survey
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W28 (G6.4-0.1) field
• 3HWC: The Third HAWC Catalog of Very-High-Energy Gamma-ray Sources
• A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope
• Fermi LAT Observation of Diffuse Gamma-Rays Produced Through Interactions between Local Interstellar Matter and High Energy Cosmic Rays
• Fermi Detection of a Luminous Gamma-ray Pulsar in a Globular Cluster
• Dynamical Formation of Millisecond Pulsars in Globular Clusters
• Fermi Discovery of Gamma-ray Emission from the Globular Cluster Terzan 5
• Gamma-ray emission from the globular clusters Liller 1, M80, NGC 6139, NGC 6541, NGC 6624, and NGC 6752
• Very-high-energy gamma-ray emission from the direction of the Galactic globular cluster Terzan 5
• Predictions of Gamma-ray Emission from Globular Cluster Millisecond Pulsars Above 100 MeV
• The Origin of Gamma-Rays from Globular Clusters
• The Fundamental Plane of Gamma-ray Globular Clusters
• The enigmatic globular cluster UKS~1 obscured by the bulge: \textit{H}-band discovery of nitrogen-enhanced stars
• Evidence for a high-energy tail in the gamma-ray spectra of globular clusters
• Search for pulsed gamma-ray emission from globular cluster M28
• Galactic globular clusters: a new catalog of masses, structural parameters, velocity dispersion profiles, proper motions and space orbits
• Constraining the cosmic ray spectrum in the vicinity of the supernova remnant W28: from sub-GeV to multi-TeV energies
• Misaligned TeV gamma-ray sources in the vicinity of globular clusters
• Discovery of gamma-ray pulsations of PSR J1835$-$3259B in the Globular Cluster NGC 6652
• Likely detection of gamma-ray pulsations of PSR~J1717+4308A in NGC~6341 and implication of the gamma-ray millisecond pulsars in globular clusters

Cited by in corpus (1)

• Search for TeV emission from spider millisecond pulsars with HAWC