Extended Data Fig. 1: Geometry of Terzan 5 relative to the Sun and the Milky Way.

We show Terzan 5’s position (blue circle) and velocity (blue arrow) in a coordinate system where the Galactic Centre (black cross) lies at the origin and the Sun lies at (X, Y, Z) = ( − 8.22, 0, 0.208) kpc, in the direction indicated by the orange arrow. The top panel shows a top-down view of the Galactic Plane, and the bottom panel shows a side-on view. In both panels the dashed blue line shows the distance from the Galactic Centre to Terzan 5. The shaded green band in the top panel indicates the rough position of the Galactic Bar; we take the Bar thickness to be ≈ 1 kpc and the orientation to be 30^∘ from the Sun-Galactic Centre line in the direction of Galactic rotation⁵². The black arrow indicates our 50th percentile value for the direction of Terzan 5’s magnetotail as inferred from our 50th percentile value for μ_obs together with the observed sky position of the TeV emission centroid⁷; shaded grey arcs around this arrow show the 1σ and 2σ uncertainty intervals. We take the position, proper motion, and radial velocity of Terzan 5 from ref. ¹² and we transform all quantities from sky coordinates to Galactocentric coordinates using the astropy Galactocentric coordinate package version 4.0 (refs. ^53,54,55).