WISEview of narrow-line Seyfert 1 galaxies: mid-infrared colour and variability

Abstract

We present the color and flux variability analysis at 3.4 µm (W 1-band) and 4.6 µm (W 2-band) of 492 narrow-line Seyfert 1 (NLSy1) galaxies using archival data from the Wide-field Infrared Survey Explorer (WISE). In the WISE color-color, (W 1 − W 2) versus (W 2 − W 3) diagram, ∼ 58% of the NLSy1 galaxies of our sample lie in the region occupied by the blazar category of active galactic nuclei (AGN). The mean W 1 − W 2 color of candidate variable NLSy1 galaxies is 0.99 ± 0.18 mag. The average amplitude of variability is 0.11 ± 0.07 mag in long-term (multi-year) with no difference in variability between W 1 and W 2-bands. The W 1 − W 2 color of NLSy1 galaxies is anti-correlated with the relative strength of [O III] to Hβ, strongly correlated with continuum luminosity, black hole mass, and Eddington ratio. The long-term amplitude of variability shows weak anti-correlation with the Fe II strength, continuum luminosity and Eddington ratio. A positive correlation between color as well as the amplitude of variability with the radio power at 1.4 GHz was found for the radio-detected NLSy1 galaxies. This suggests non-thermal synchrotron contribution to the mid-infrared color and flux variability in radio-detected NLSy1 galaxies.

A Low Incidence of Mid-Infrared Variability in Dwarf Galaxies

“…To robustly estimate the standard deviation, we used the median absolute deviation (e.g., Huber 1981), and the calculation of the median is weighted by the inverse variance of the data to account for differing measurement uncertainties. The total number of single measurements per epoch and the length of time between the first and last measurement depend on ecliptic latitude, but for our dwarf and control samples these are on average 11 measurements over 2 days, 6 We note that since the midinfrared emission arises from spatial scales much larger than the optical and UV accretion disk emission, short term variability is expected to be "smoothed out" in the reprocessed mid-infrared emission from the dust, a result that is confirmed in previous mid-infrared variability studies (Koz lowski et al 2016(Koz lowski et al , 2010Rakshit et al 2019).…”

“…We explored several non-parametric variability metrics commonly employed in the literature. We calculate the variances, covariances, and Pearson r as in Koz lowski et al ( 2016), equations 1-3, the amplitude of variability following Sesar et al (2007), equation 4 (see also Rakshit et al 2019), and the combined significance of variances in W 1 and W 2 following Koz lowski et al (2016, Equation 4). To account for additional systematic uncertainty in the WISE magnitudes, we add 0.024 mag and 0.028 mag in quadrature to the formal W 1 and W 2 band uncertainties (Jarrett et al 2011).…”

SDSS J094635.06+101706.1: a redshift one, very radio-loud, γ-ray emitting narrow-line Seyfert 1 galaxy

“…Intra-day variability of w1 flux is detected with p-values of P < 0.5 per cent using the χ 2 -test against the null hypothesis of no variation in 2015 November. The rapid variability restricts the size of the emitting region to be much smaller than the scale of the torus, implying a jet origin (see also Jiang et al 2012;Gabanyi et al 2018a;Rakshit et al 2019). On timescale of years, the NIR flux varied by nearly 0.4 dex from May 2014 to November 2015.…”

The Variability of the Narrow-line Seyfert 1 Galaxies from the PanSTARRS's View

“…By means of the variance of observed magnitudes, we obtain the variability amplitude which is revised the contribution from the measurement errors in the data sets (Sesar et al 2007;Rakshit et al 2019). The expression is as follows,…”