We present a multi-wavelength study of the unassociated Fermi -LAT source , 3FGL J0954.8 - 3948 , which is likely the \gamma -ray counterpart of a 9.3-hour binary in the field .
With more than 9 years of Pass 8 LAT data , we updated the \gamma -ray spectral properties and the LAT localization of the \gamma -ray source .
While the binary lies outside the cataloged 95 % error ellipse , the optimized LAT ellipse is 0.1 degrees closer and encloses the binary .
The system is likely spectrally hard in X-rays ( photon index \Gamma _ { X } = 1.4 ^ { +1.2 } _ { -1.0 } ) with orbital modulations detected in optical , UV , and possibly X-rays .
A steep spectrum radio counterpart ( spectral index \alpha \approx - 1.6 ) is also found in the TIFR GMRT Sky Survey ( TGSS ) , implying that it is a pulsar system .
We obtained a series of SOAR and Gemini spectroscopic observations in 2017/2018 , which show a low-mass secondary orbiting in a close circular orbit with K _ { 2 } = 272 \pm 4 km s ^ { -1 } under strong irradiation by the primary compact object .
All the observations as well as the modelling of the X/ \gamma -ray high-energy emission suggest that 3FGL J0954.8 - 3948 is a redback millisecond pulsar in a rotation-powered state .