OISTER Optical and Near-Infrared Monitoring Observations of a Peculiar Radio-Loud Active Galactic Nucleus SDSS J110006.07+442144.3

TL;DR

This study presents optical and near-infrared monitoring of the peculiar radio-loud AGN SDSS J110006.07+442144.3, revealing stable spectral energy distribution despite rapid variability, supporting a jet-dominated emission mechanism.

Contribution

First detailed optical-NIR monitoring campaign of this peculiar AGN, demonstrating stable SED shape and jet-dominated emission over a year-long observation period.

Findings

Strong brightening observed in March 2015.

Stable optical-NIR SED shape despite rapid variability.

Evidence supports a low ν_peak jet-dominated AGN.

Abstract

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 $\sim5~\mu$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 $\nu_{\rm{peak}}$ 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.