Intra-night optical variability characteristics of different classes of
  narrow line Seyfert 1 galaxies
  In a first systematic effort to characterize the intra-night optical
variability (INOV) of different classes of narrow line Seyfert 1 (NLSy1)
galaxies, we have carried out observations on a sample of radio-loud (RL) and
radio-quiet (RQ) NLSy1 galaxies. The RL-NLSy1 galaxies are further divided into
{\gamma}-ray loud (GL) and {\gamma}-ray quiet (GQ) NLSy1 galaxies. Our sample
consists of four sets, each set consisting of a RQ-NLSy1, a GQ-NLSy1 and a
GL-NLSy1 galaxy, closely matched in redshift and optical luminosity. Our
observations on both RQ and GQ-NLSy1 galaxies consist of a total of 19 nights,
whereas the data for GL-NLSy1 galaxies (18 nights) were taken from literature
published earlier by us. This enabled us to do a comparison of the duty cycle
(DC) of different classes of NLSy1 galaxies. Using power-enhanced F-test, with
a variability threshold of 1%, we find DCs of about 55%, 39% and 0% for GL, GQ
and RQ-NLSy1 galaxies respectively. The high DC and large amplitude of INOV
(24.0 +/- 13.7%) shown by GL-NLSy1 galaxies relative to the other two classes
might be due to their inner aligned relativistic jets having large bulk Lorentz
factors. The null DC of RQ-NLSy1 galaxies could mean the presence of low power
and/or largely misaligned jets in them. However, dividing RL-NLSy1 galaxies
into low and high optical polarization sources, we find that sources with large
polarization show somewhat higher DCs (69%) and amplitudes (29%) compared to
those with low polarization. This points to a possible link between INOV and
optical polarization.
