Very High Energy gamma-ray observations of Mrk 501 using TACTIC imaging gamma-ray telescope during 2005-06

Abstract

In this paper we report on the Markarian 501 results obtained during our TeV $\gamma$-ray observations from March 11 to May 12, 2005 and February 28 to May 7, 2006 for 112.5 hours with the TACTIC $\gamma$-ray telescope. During 2005 observations for 45.7 hours, the source was found to be in a low state and we have placed an upper limit of 4.62 $\times$ 10${}^{-12}$ photons cm${}^{-2}$ s${}^{-1}$ at 3$\sigma$ level on the integrated TeV $\gamma$-ray flux above 1 TeV from the source direction. However, during the 2006 observations for 66.8h, detailed data analysis revealed the presence of a TeV $\gamma$-ray signal from the source with a statistical significance of 7.5$\sigma$ above $E_{\gamma }\ge$ 1 TeV. The time averaged differential energy spectrum of the source in the energy range 1-11 TeV is found to match well with the power law function of the form ($d\Phi /dE=f_0{E}^{-\Gamma }$) with $f_0=(1.66\pm 0.52)\times 10^{-11}c{m}^{-2}{s}^{-1}Te{V}^{-1}$ and $\Gamma =2.80\pm 0.27$.

arXiv comment16 pages and 8 Figures Accepted for publication in the Journal of Physics G

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