Multi-band optical variability of three TeV Blazars on Diverse
  Timescales
  We present our optical photometric observations of three TeV blazars, PKS
1510-089, PG 1553+113 and Mrk 501 taken using two telescopes in India, one in
Bulgaria, one in Greece and one in Serbia during 2012 - 2014. These
observations covered a total of 95 nights with a total of 202 B filter frames,
247 images in V band, 817 in R band while 229 images were taken in the I
filter. This work is focused on multi-band flux and colour variability studies
of these blazars on diverse timescales which are useful in understanding the
emission mechanisms. We studied the variability characteristics of above three
blazars and found all to be active over our entire observational campaigns. We
also searched for any correlation between the brightness of the sources and
their colour indices. During the times of variability, no significant evidence
for the sources to display spectral changes correlated with magnitude was found
on timescales of a few months. We briefly discuss the possible physical
mechanisms most likely responsible for the observed flux variability.
