  The startling discovery of Prochter et al. (2006) that the frequency of very
strong (W_r(2796)>1 A) MgII absorbers along gamma-ray burst (GRB) lines of
sight ([dN/dz]_{GRB} = 0.90) is more than three times the frequency along
quasar lines of sight ([dN/dz]_{QSO} = 0.24), over similar redshift ranges, has
yet to be understood. We reconsider the possibility that the excess of very
strong MgII absorbers toward GRBs is intrinsic either to the GRBs themselves or
to their immediate environment, and associated with bulk outflows with
velocities as large as v_{max} ~ 0.3c. In order to examine this hypothesis, we
accumulate a sample of 27 W_r(2796) > 1 A absorption systems found toward 81
quasars, and compare their properties to those of 9 W_r(2796)>1 A absorption
systems found toward 6 GRBs; all systems have been observed at high spectral
resolution (R = 45,000) using the Ultraviolet and Visual Echelle Spectrograph
on the Very Large Telescope. We make multiple comparisons of the absorber
properties across the two populations, testing for differences in metallicity,
ionization state, abundance patterns, dust abundance, kinematics, and phase
structure. We find no significant differences between the two absorber
populations using any of these metrics, implying that, if the excess absorbers
toward GRB lines of sight are indeed intrinsic, they must be produced in a
process which has strong similarities to the processes yielding strong MgII
systems in association with intervening galaxies. Although this may seem a
priori unlikely, given the high outflow velocities required for any intrinsic
model, we note that the same conclusion was reached, recently, with respect to
the narrow absorption line systems seen in some quasars.

Astrophysics