We present a study of \thepulsar , 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 \sim 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 \pm 0.5 , corresponding to a companion mass range of 0.4 to 0.7 M _ { \odot } and an orbital inclination angle range of between 30 and 41 ^ { \circ } , assuming a pulsar mass range of 1.4 - 2.0 M _ { \odot } .
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 \thepulsar indicate that it is likely a ‘ ‘ redback ’ ’ system .
Unlike the five other Galactic redbacks discovered to date , \thepulsar 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 .