Persistent time lags in light curves of Sagittarius A*: evidence of
  outflow
  The compact radio source at the center of our Galaxy, Sagittarius A* (Sgr
A*), is the subject of intensive study as it provides a close-up view of an
accreting supermassive black hole. Sgr A* provides us with a prototype of a
low-luminosity active galactic nucleus (LLAGN), but interstellar scattering and
the resolution limits of our instruments have limited our understanding of the
emission sites in its inner accretion flow. The temporal variability of Sgr A*
can help us understand whether we see a plasma outflow or inflow in the region
close to the black hole. In this work, we look at a comprehensive set of
multi-epoch data recorded with the Karl G. Jansky Very Large Array (VLA) to
understand the persistence of the time lag relations that have been found in
previous radio observations of Sgr A*. We analyse 8 epochs of data, observed in
Spring 2015, each of which has a frequency coverage from 18 to 48 GHz. We
cross-correlate the calibrated light curves across twelve frequency subbands.
We also generate synthetic data with the appropriate variability
characteristics and use it to study the detectability of time lag relations in
data with this sampling structure. We find that the variability amplitude
increases with frequency. We see positive time lag slopes across all subbands
in five out of eight epochs, with the largest slopes in the cases where a clear
extremum in flux density is present. Three epochs show lag slopes close to
zero. With the synthetic data analysis we show that these results are explained
by a persistent lag relation of $\sim$40 min/cm that covers the bulk of the
variability, with at most 2 percent of the total flux density in an
uncorrelated variability component. Together with the size-frequency relation
and inclination constraints this indicates an outflow velocity with $\gamma
\beta$ = 1.5, consistent with predictions of jet models for Sgr A*.
