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

TL;DR

This paper reports the discovery of extreme optical variability in SDSS J1100+4421, a peculiar radio-loud narrow-line Seyfert 1 galaxy with potential blazar-like jet activity and the largest radio structure observed in such galaxies.

Contribution

It presents the first detection of rapid, large-amplitude optical variability in this NLS1, suggesting the presence of relativistic jets and a unique large radio structure.

Findings

Optical brightness increased by a factor of three within half a day.

SDSS J1100+4421 is a highly radio-loud NLS1 with a linear radio structure of about 100 kpc.

The source exhibits variability similar to blazar-like cores in radio- and gamma-ray loud NLS1s.

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 Msun 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 x 10^2 - 3 x 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 gamma-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.