Velocity Dispersion of the GD-1 Stellar Stream
  Tidally dissolved globular clusters form thin stellar streams that preserve a
historical record of their past evolution. We report a radial velocity
dispersion of $2.3\pm0.3\,\textrm{km}\,\textrm{s}^{-1}$ in the GD-1 stellar
stream using a sample of 43 spectroscopically confirmed members. The GD-1
velocity dispersion is constant over the surveyed $\approx15^\circ$ span of the
stream. We also measured velocity dispersion in the spur adjacent to the main
GD-1 stream, and found a similar value at the tip of the spur. Surprisingly,
the region of the spur closer to the stream appears dynamically colder than the
main stream. An unperturbed model of the GD-1 stream has a velocity dispersion
of $\approx0.6\,\textrm{km}\,\textrm{s}^{-1}$, indicating that GD-1 has
undergone dynamical heating. Stellar streams arising from globular clusters,
which prior to their arrival in the Milky Way, orbited a dwarf galaxy with a
cored density profile are expected to have experienced the amount of heating
required to match the velocity dispersion observed in GD-1. This suggests that
GD-1 has been accreted and that imprints of its original host galaxy, including
the inner slope of its dark-matter halo, remain observable in the stream today.
