Intranight optical variability of  -ray-loud narrow-line Seyfert 1 galaxies

Abstract

The Large Area Telescope (LAT) onboard the Fermi Gamma Ray Space Telescope has detected γ-ray emission in about half-a-dozen Narrow Line Seyfert 1 (NLSy1) galaxies. This indicates the presence of relativistic jets in these sources similar to blazars and radio galaxies. In an attempt to have an idea of the intranight optical variability (INOV) characteristics of these γ-ray loud NLSy1 galaxies, we have carried out optical flux monitoring observations of three NLSy1 galaxies detected by Fermi/LAT: 1H 0323+342, PMN J0948+0022 and PKS 1502+036. These optical monitoring observations in R C band carried out during January − May 2012, showed the presence of rapid optical flux variations in these sources. The intranight differential light curves of these sources have revealed flux variations on time scales of hours with amplitudes of variability > 3 percent for most of the time. However, for one source, PMN J0948+0022 we observed amplitude of variability as large as 52 percent. On using the F-statistics to classify the variability nature of these sources, we obtained a duty cycle (DC) of INOV of ∼85 percent. Alternatively, the more commonly used C-statistics gave a DC of INOV of ∼57 percent. Such high DC of INOV are characteristics of the BL Lac class of AGN. The results of our monitoring observations thus indicate that there is similarity in the INOV nature of γ-ray loud NLSy1 galaxies and BL Lac objects, arguing strongly for the presence of relativistic jets aligned closely to the observers line of sight in γ-ray loud NLSy1s. Moreover, our dense monitoring observations on some of the nights have led to the clear detection of some mini-flares superimposed on the flux variations during the night over timescales as short as 12 minutes. The detection of short timescale flux variability in the sources studied here is clearly due to stronger time compression leading to the jets in these sources having large doppler factors, similar to that of the inner jets of TeV blazars.

The disc-like host galaxies of radio-loud narrow-line Seyfert 1s

“…Previous studies, conducted to RL-NLSy1s, had already supported the idea that, when compared with blazars, RL-NLSy1s are particularly similar to FSRQs (e.g. Paliya et al 2013;Foschini et al 2015;Paliya & Stalin 2016). Provided that RL-NLsy1s are hosted by spiral galaxies, what our findings suggest, might be a substantive contribution since blazars are known to be hosted by elliptical galaxies and powered by massive black holes.…”

Optical and Gamma-Ray Variability of the vRL NLSy1 Galaxy, 1H 0323+342

“…This demonstrates, for the first time, the reality of very low-amplitude (∆MR ≤ 0.05) microvariability events for 1H 0323+342. Previously, Paliya et al [4] and Paliya et al [5] reported detecting the presence of intranight optical variability (INOV) for 1H 0323+342. These results report the presence of low-level linear trends occurring during a single night, but not microvariations.…”

On the Reliability of Microvariability Tests in Quasars

“…The F -test does not require additional efforts in comparison, for example, to the C-test, and thus Paper I has contributed to popularize its use (e.g. Joshi et al 2011;Joshi & Chand 2013;Paliya et al 2013;Goyal et al 2013). Nevertheless, interest for developing new test procedures has not decayed, and a number of test adjustments have been considered.…”