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The Fermi source 2FGL~J0523.3$-$2530 has recently been identified as acandidate millisecond pulsar binary with an orbital period of 16.5 hrs. We havecarried out detailed studies of the source's emission properties by analyzingdata taken with the Fermi Large Area Telescope in the 0.2--300 GeV energyrange. Long-term, yearly variability from the source has been found, with afactor of 4 flux variations in 1--300 GeV. From spectral analysis, we find anextra spectral component at 2--3 GeV that causes the source brightening. Whileno orbital modulations have been found from the Fermi data over the wholeperiod of 2008--2014, orbital modulation in the source's $>$2 GeV emission isdetected during the last 1.5 yrs of the Fermi observation. Our results supportthe millisecond pulsar binary nature of 2FGL~J0523.3$-$2530. Multi-wavelengthobservations of the source are warranted in order to find any correlated fluxvariations and thus help determine the origin of the long-term variability,which currently is not understood.

Fermi Variability Study of the Candidate Pulsar Binary 2FGL~J0523.3-2530