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Polarization and Variation of Near-IR Light from Fermi/LAT gamma-ray Sources

We present the results of our follow-up observation program of gamma-ray sources detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. 26 blazars and 39 sources unidentified at other wavelengths were targeted at IRSF 1.4 m telescope equipped with the SIRIUS/SIRPOL imager and polarimeter. H-band magnitudes of the blazars at the epoch of 2010 Dec -- 2011 Feb are presented, which reveal clear flux variation since the Two Micron All Sky Survey observations and can be useful data for variation analyses of these objects in longer periods. We also find that nearly half of the gamma-ray blazars are highly (>10 %) polarized in near-infrared wavelengths. Combining the polarization and variation properties, most (~90 %) of the blazars are clearly distinguished from all other types of objects at high Galactic latitudes. On the other hand, we find only one highly polarized and/or variable object in the fields of unidentified sources. This object is a counterpart of the optical variable source PQV1 J131553.00-073302.0 and the radio source NVSS J131552-073301, and is a promising candidate of new gamma-ray blazars. From the measured polarization and variation statistics, we conclude that most of the Fermi/LAT unidentified sources are not likely similar types of objects to the known gamma-ray blazars.