TeV Gamma-ray Observations of Markarian 421 using TACTIC during 2009-10
  We have observed the blazar Markarian 421 with the TACTIC $\gamma$-ray
telescope at Mt. Abu, India, from 22 November 2009 to 16 May 2010 for 265
hours. Detailed analysis of the data so recorded revealed presence of a TeV
$\gamma$-ray signal with a statistical significance of 12.12$\sigma$ at
$E_{\gamma}\geq$ 1 TeV. We have estimated the time averaged differential energy
spectrum of the source in the energy range 1.0 - 16.44 TeV. The spectrum fits
well with the power law function of the form ($dF/dE=f_0 E^{-\Gamma}$) with
$f_0=(1.39\pm0.239)\times 10^{-11}cm^{-2}s^{-1}TeV^{-1}$ and
$\Gamma=2.31\pm0.14$.
