We present monitoring campaign observations at optical and near-infrared ( NIR ) wavelengths for a radio-loud active galactic nucleus ( AGN ) at z = 0.840 , SDSS J110006.07+442144.3 ( hereafter , J1100+4421 ) , which was identified during a flare phase in late February , 2014 .
The campaigns consist of three intensive observing runs from the discovery to March , 2015 , mostly within the scheme of the OISTER collaboration .
Optical-NIR light curves and simultaneous spectral energy distributions ( SEDs ) are obtained .
Our measurements show the strongest brightening in March , 2015 .
We found that the optical-NIR SEDs of J1100+4421 show an almost steady shape despite the large and rapid intranight variability .
This constant SED shape is confirmed to extend to \sim 5 ~ { } \mu m in the observed frame using the archival WISE data .
Given the lack of absorption lines and the steep power-law spectrum of \alpha _ { \nu } \sim - 1.4 , where f _ { \nu } \propto \nu ^ { \alpha _ { \nu } } , synchrotron radiation by a relativistic jet with no or small contributions from the host galaxy and the accretion disk seems most plausible as an optical-NIR emission mechanism .
The steep optical-NIR spectral shape and the large amplitude of variability are consistent with this object being a low \nu _ { peak } jet-dominated AGN .
In addition , sub-arcsec resolution optical imaging data taken with Subaru Hyper Suprime-Cam does not show a clear extended component and the spatial scales are significantly smaller than the large extensions detected at radio wavelengths .
The optical spectrum of a possible faint companion galaxy does not show any emission lines at the same redshift and hence a merging hypothesis for this AGN-related activity is not supported by our observations .