Discovery of Dramatic Optical Variability in SDSS J1100+4421: A Peculiar Radio-Loud Narrow-Line Seyfert 1 Galaxy?

Abstract

We present our discovery of dramatic variability in SDSS J1100+4421 by the high-cadence transient survey Kiso Supernova Survey (KISS). The source brightened in the optical by at least a factor of three within about half a day. Spectroscopic observations suggest that this object is likely a narrow-line Seyfert 1 galaxy (NLS1) at z = 0.840, however with unusually strong narrow emission lines. The estimated black hole mass of ∼ 10 7 M ⊙ implies bolometric nuclear luminosity close to the Eddington limit. SDSS J1100+4421 is also extremely radio-loud, with a radio loudness parameter of R ≃ 4 × 10 2 − 3 × 10 3 , which implies the presence of relativistic jets. Rapid and large-amplitude optical variability of the target, reminiscent of that found in a few radio-and γ-ray loud NLS1s, is therefore produced most likely in a blazar-like core. The 1.4 GHz radio image of the source shows an extended structure with a linear size of about 100 kpc. If SDSS J1100+4421 is a genuine NLS1, as suggested here, this radio structure would then be the largest ever discovered in this type of active galaxies.

OISTER optical and near-infrared monitoring observations of peculiar radio-loud active galactic nucleus SDSS J110006.07+442144.3

“…In addition to fitting the photometric SEDs, the FOCAS and GMOS optical spectra were also fitted with a single power-law. We note that the fitting results for the FOCAS spectra (αν = −1.40 ± 0.01) were presented in Tanaka et al (2014). The obtained power-law index of the GMOS spectrum is αν = −1.48±0.10 but the spectrum is not corrected for the differential slit loss due to atmospheric differential refraction.…”

“…First, we briefly summarize the discovery with Kiso KWFC and 1-month follow-up observations after the discovery, which were described in detail in Tanaka et al (2014). The object showed a rapid increase in brightness from non-detection (g > 20 − 21 mag) to 19.73 ± 0.13 mag on February 23, 2014.…”

“…The observing epochs fall into three intensive campaigns: from February, 2014 to March, 2014, right after the discovery described in Tanaka et al (2014), from October, 2014 to November, 2014, and in March 2015. In the second observing campaign, from Oct 2014 to Nov 2014, we obtained data at least once in multiple bands almost every night if the weather permitted.…”

“…Bias subtraction, overscan subtraction (if necessary), flat-fielding, sky subtraction, and astrometry procedures are done with a data reduction pipeline for each instrument. We combined all images taken within a night to create one stacked image per day, except for the discovery and quick follow-up data shown in Tanaka et al (2014) and the OAO KOOLS optical data in March 2015. The HSC data was reduced using hscPipe version 3.8.5, which was developed based on the LSST pipeline (Ivezic et al 2008;Axelrod et al 2010).…”

“…Quick imaging and spectroscopic follow-up observations with the Faint Object Camera and Spectrograph (FOCAS; Kashikawa et al 2002) on the Subaru 8.2-m telescope right after the flare detection indicated that the object was a narrow-line AGN at z = 0.840 with a small BH mass of MBH = 1.0 − 1.5 × 10 7 M⊙ and a sub-Eddington ratio of L bol /L Edd ∼ 0.3 . By combining these optical data with archival radio, infrared (WISE), γ-ray (Fermi) data and X-ray data taken via a ToO observation with X-ray Telescope (XRT) on board the Swift satellite, Tanaka et al (2014) revealed the similarity of this object's SED to those of the radio/γ-ray-loud NLS1s, although the large [O III]/Hβ flux ratio does not satisfy the general criteria for NLS1s. Flux ratio between the [O III] emission lines and radio emission is also consistent with those of radio-loud NLS1s (Berton et al 2016).…”