Intra-night optical variability of $\gamma-$ray detected narrow-line
  Seyfert 1 galaxies
  We report the first attempt to systematically characterise intra-night
optical variability (INOV) of the rare and enigmatic subset of Narrow-Line
Seyfert1 galaxies (NLSy1s), which is marked by detection in the $\gamma$-ray
band and is therefore endowed with Doppler boosted relativistic jets, like
blazars. However, the central engines in these two types of AGN are thought to
operate in different regimes of accretion rate. Our INOV search in a fairly
large and unbiased sample of 15 $\gamma$-ray NLSy1s was conducted in 36
monitoring sessions, each lasting $\geq$ 3 hrs. In our analysis, special care
has been taken to address the possible effect on the differential light curves,
of any variation in the seeing disc during the session, since that might lead
to spurious claims of INOV from such AGN due to the possibility of a
significant contribution from the host galaxy to the total optical emission.
From our observations, a duty cycle (DC) of INOV detection in the $\gamma$-ray
NLSy1s is estimated to be around 25% - 30%, which is comparable to that known
for blazars. This estimate of DC will probably need an upward revision, once it
becomes possible to correct for the dilution of the AGN's nonthermal optical
emission by the (much steadier) optical emission contributed not only by the
host galaxy but also the nuclear accretion disc in these high Eddington rate
accretors. Finally, we also draw attention to the possibility that sharp
optical flux changes on sub-hour time scale are less rare for $\gamma$-ray
NLSy1s, in comparison to blazars.
