  Localizing sources on the sky is crucial for realizing the full potential of
gravitational waves for astronomy, astrophysics, and cosmology. We show that
the mid-frequency band, roughly 0.03 to 10 Hz, has significant potential for
angular localization. The angular location is measured through the changing
Doppler shift as the detector orbits the Sun. This band maximizes the effect
since these are the highest frequencies in which sources live several months.
Atom interferometer detectors can observe in the mid-frequency band, and even
with just a single baseline can exploit this effect for sensitive angular
localization. The single baseline orbits around the Earth and the Sun, causing
it to reorient and change position significantly during the lifetime of the
source, and making it similar to having multiple baselines/detectors. For
example, atomic detectors could predict the location of upcoming black hole or
neutron star merger events with sufficient accuracy to allow optical and other
electromagnetic telescopes to observe these events simultaneously. Thus,
mid-band atomic detectors are complementary to other gravitational wave
detectors and will help complete the observation of a broad range of the
gravitational spectrum.
