OISTER optical and near-infrared monitoring observations of peculiar radio-loud active galactic nucleus SDSS J110006.07+442144.3
Authors: Morokuma Tomoki , Tanaka Masaomi , Tanaka Yasuyuki T. , Itoh Ryosuke , Tominaga Nozomu , Gandhi Poshak , Pian Elena , Mazzali Paolo , Ohta Kouji , Matsumoto Emiko , Shibata Takumi , Akimoto Hinako , Akitaya Hiroshi , Ali Gamal B. , Aoki Tsutomu , Doi Mamoru , Ebisuda Nana , Essam Ahmed , Fujisawa Kenta , Fukushima Hideo , Goda Shuhei , Gouda Yuya , Hanayama Hidekazu , Hashiba Yasuhito , Hashimoto Osamu , Hayashida Kenzo , Hiratsuka Yuichiro , Honda Satoshi , Imai Masataka , Inoue Kanichiro , Ishibashi Michiko , Iwata Ikuru , Izumiura Hideyuki , Kanda Yuka , Kawabata Miho , Kawaguchi Kenji , Kawai Nobuyuki , Kokubo Mitsuru , Kuroda Daisuke , Maehara Hiroyuki , Mito Hiroyuki , Mitsuda Kazuma , Miyagawa Ryota , Miyaji Takeshi , Miyamoto Yusuke , Morihana Kumiko , Moritani Yuki , Morokuma-Matsui Kana , Murakami Kotone , Murata Katsuhiro L. , Nagayama Takahiro , Nakamura Kazuki , Nakaoka Tatsuya , Niinuma Kotaro , Nishimori Takafumi , Nogami Daisaku , Oasa Yumiko , Oda Tatsunori , Ohshima Tomohito , Saito Yoshihiko , Sakata Shuichiro , Sako Shigeyuki , Sarugaku Yuki , Sawada-Satoh Satoko , Seino Genta , Sorai Kazuo , Soyano Takao , Taddia Francesco , Takahashi Jun , Takagi Yuhei , Takaki Katsutoshi , Takata Koji , Tarusawa Ken’ichi , Uemura Makoto , Ui Takahiro , Urago Riku , Ushioda Kazutoshi , Watanabe Jun-ichi , Watanabe Makoto , Yamashita Satoshi , Yanagisawa Kenshi , Yonekura Yoshinori , Yoshida Michitoshi 
Published: August 2017

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 2014 February. The campaigns consist of three intensive observing runs from the discovery to 2015 March, 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 2015 March. 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 ∼5 μm in the observed frame using the archival WISE data. Given the lack of absorption lines and the steep power-law spectrum of αν ∼ −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 νpeak jet-dominated AGN. In addition, sub-arcsecond 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.