  We present a study of PSR J1723-2837, an eclipsing, 1.86 ms millisecond
binary radio pulsar discovered in the Parkes Multibeam survey. Radio timing
indicates that the pulsar has a circular orbit with a 15 hr orbital period, a
low-mass companion, and a measurable orbital period derivative. The eclipse
fraction of ~15% during the pulsar's orbit is twice the Roche lobe size
inferred for the companion. The timing behavior is significantly affected by
unmodeled systematics of astrophysical origin, and higher-order orbital period
derivatives are needed in the timing solution to account for these variations.
We have identified the pulsar's (non-degenerate) companion using archival
ultraviolet, optical, and infrared survey data and new optical photometry.
Doppler shifts from optical spectroscopy confirm the star's association with
the pulsar and indicate a pulsar-to-companion mass ratio of 3.3 +/- 0.5,
corresponding to a companion mass range of 0.4 to 0.7 Msun and an orbital
inclination angle range of between 30 and 41 degrees, assuming a pulsar mass
range of 1.4-2.0 Msun. Spectroscopy indicates a spectral type of G for the
companion and an inferred Roche-lobe-filling distance that is consistent with
the distance estimated from radio dispersion. The features of PSR J1723-2837
indicate that it is likely a "redback" system. Unlike the five other Galactic
redbacks discovered to date, PSR J1723-2837 has not been detected as a
gamma-ray source with Fermi. This may be due to an intrinsic spin-down
luminosity that is much smaller than the measured value if the unmeasured
contribution from proper motion is large.
