Evidence of jet-induced optical microvariability in radio-loud narrow-line Seyfert 1 galaxies

To quantify the role of radio jets for Intra-Night Optical Variability (INOV) in radio-loud narrow-line Seyfert 1 (RLNLSy1) galaxies, we report the first systematic comparative INOV study of 23 RLNLSy1 galaxies, with 15 RLNLSy1s having confirmed detection of jets (jetted) and the remaining 8 RLNLSy1s having no detection of jets (non-jetted) based on their Very Long Baseline Array observations. We have monitored these two samples, respectively, in 37 and 16 sessions of a minimum 3-h duration each. Based upon F-eta-test at 99 per cent confidence level with a typical INOV amplitude (psi) detection threshold of >3 per cent, we find the INOV duty cycles (DC) of 12 per cent for the sample of jetted RLNLSy1s, however, none of the sources showed INOV in the sample of non-jetted RLNLSy1s. Among the jetted RLNLSy1s, we find that the DC for jetted gamma-ray detected (gamma-ray) RLNLSy1s is found to be 34 per cent in contrast to null INOV detection in the case of non-gamma-ray RLNLSy1s. It suggests that instead of the mere presence of a jet, relativistic beaming plays a significant role for INOV in the case of low-luminous high accreting AGNs, such as NLSy1s, in which dilution of the AGN's non-thermal optical emission by the (much steadier) optical emission contributed by the nuclear accretion disc is quite likely. Our study of jetted gamma-ray RLNLSy1s shows more frequent INOV detection for sources with higher apparent jet speed. Further, our results also suggest that among the NLSy1s, only jetted gamma-ray RNLSy1 galaxies DC approach blazar-like DC.