  We present results on a systematic study of flux variability on hourly
time-scales in a large sample of active galactic nuclei (AGN) in the 3-79 keV
band using data from Nuclear Spectroscopic Telescope Array. Our sample consists
of 4 BL Lac objects (BL Lacs), 3 flat spectrum radio quasars (FSRQs) 24 Seyfert
1, 42 Seyfert 2 and 8 narrow line Seyfert 1 (NLSy1) galaxies. We find that in
the 3-79 keV band, about 65% of the sources in our sample show significant
variations on hourly time scales. Using Mann-Whitney U-test and
Kolmogorov-Smirnov test, we find no difference in the variability behaviour
between Seyfert 1 and 2 galaxies. The blazar sources (FSRQs and BL Lacs) in our
sample, are more variable than Seyfert galaxies that include Seyfert 1 and
Seyfert 2 in the soft (3-10 keV), hard (10-79 keV) and total (3-79 keV) bands.
NLSy1 galaxies show the highest duty cycle of variability (87%), followed by BL
Lacs (82%), Seyfert galaxies (56%) and FSRQs (23%). We obtained flux
doubling/halving time in the hard X-ray band less than 10 min in 11 sources.
The flux variations between the hard and soft bands in all the sources in our
sample are consistent with zero lag.

Astrophysics of Galaxies;High Energy Astrophysical Phenomena