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Register a new userDiscovery of Dramatic Optical Variability in SDSS J1100+4421: A Peculiar Radio-Loud Narrow-Line Seyfert 1 Galaxy?
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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.
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Narrow-line Seyfert 1 galaxies (NLS1) are an intriguing subclass of active galactic nuclei. Their observed properties indicate low central black hole mass and high accretion rate. The extremely radio-loud NLS1 sources often show relativistic beaming and are usually regarded as younger counterparts of blazars. Recently, the object SDSS J110006.07+442144.3 was reported as a candidate NLS1 source. The characteristics of its dramatic optical flare indicated its jet-related origin. The spectral energy distribution of the object was similar to that of the gamma-ray detected radio-loud NLS1, PMN J0948+0022. Our high-resolution European Very Long Baseline Interferometry Network observations at 1.7 and 5 GHz revealed a compact core feature with a brightness temperature of >~ 10^(10) K. Using the lowest brightness temperature value and assuming a moderate Lorentz factor of ~9 the jet viewing angle is <~ 26 deg. Archival Very Large Array data show a large-scale radio structure with a projected linear size of ~150 kpc reminiscent of double-sided morphology.
SDSS J094857.3+002225 is a very radio-loud narrow-line Seyfert 1 (NLS1) galaxy. Here, we report our discovery of the intranight optical variability (INOV) of this galaxy through the optical monitoring in the B and R bands that covered seven nights in 2009. Violent rapid variability in the optical bands was identified in this RL-NLS1 for the first time, and the amplitudes of the INOV reaches 0.5 mag in both the B and R bands on the timescale of several hours. The detection of the INOV provides a piece of strong evidence supporting the fact that the object carries a relativistic jet with a small viewing angle, which confirms the conclusion drawn from the previous multi-wavelength studies.
Most of the radio-loud narrow-line Seyfert 1 (NLS1) galaxies resemble compact steep-spectrum sources. However, the extremely radio-loud ones show blazar-like characteristics, like flat radio spectra, compact radio cores, substantial variability and high brightness temperatures. These objects are thought to be similar to blazars as they possess relativistic jets seen at small angle to the line of sight. This claim has been further supported by the Fermi satellite discovery of gamma-ray emission from a handful of these sources. Using the Wide-Field Infrared Survey Explorer (WISE) data, we analyzed the mid-infrared variability characteristics of $42$ radio-loud NLS1 at $3.4$ and $4.6,mu$m. We found that $27$ out of the studied $42$ sources showed variability in at least one of the two infrared bands. In some cases, significant changes in the infrared colors can alter the location of the source in the WISE color-color diagram which might lead to different classification. More than $60$% of the variable sources also showed variability within a $1-1.5$ day interval. Such short time scales argue for a compact emission region like those associated with the jets. This connection is further strengthened by the fact that the brightest $gamma$-ray emitters of the sample ($6$ sources), all showed short time scale infrared variability.
As hybrids of narrow-line Seyfert 1 (NLS1) galaxies and blazars, {gamma}-ray emitting NLS1s are important probes of jet physics in the high Eddington-ratio regime. Only very few of them are known to date; the majority of them below redshift z = 0.5. Here we present the identification of the {gamma}-ray emitting AGN TXS 0943+105 (SDSS J094635.06+101706.1) as a high-redshift NLS1 galaxy. It turns out to be one of the radio-loudest NLS1s known, highly variable at all wavelengths, and shows widely extended radio emission at a (projected) > 100 kpc scale. It is a known strong {gamma}-ray emitter with a luminous flare reported previously. At redshift z=1.004, this is the most distant {gamma}-NLS1 known to date.
Recently, Rakshit et al. (2018) reported the discovery of SDSS J103024.95$+$551622.7, a radio-loud narrow-line Seyfert 1 galaxy having a $sim 100$ kpc scale double-lobed radio structure. Here we analyse archival radio interferometric imaging data taken with the Very Large Array (VLA) at 5 GHz, and with the Very Long Baseline Array (VLBA) at 4.3 and 7.6 GHz. Two hotspots and a compact core are detected with the VLA at arcsec scale, while a single milliarcsec-scale compact radio core is seen with the highest resolution VLBA observations. The Fermi Large Area Telescope did not detect $gamma$-ray emission at the position of this source. In the mid-infrared, the Wide-field Infrared Survey Explorer satellite light curve, covering more than 7 years and including the most recent data points, hints on flux density variability at 3.4 $mu$m. Our findings support the notion that this source is a young version of Fanaroff-Riley type II radio galaxies.
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