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 $\Gamma=2.31\pm0.14$. 
P. Chandra, R.C. Rannot, K.K. Yadav, A.K. Tickoo, K. K. Singh, K.   Chanchalani, M. Kothari, N.K. Agarwal, A. Goyal, H.C. Go...
astro-ph.HE astro-ph.CO