2011/09/09 by Kuldeep Yadav, Yadav, Kuldeep
Physics and Astronomy · #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #astro-ph.CO
paper · pdf · doi:10.48550/arxiv.1109.1967
221 pages, 68 figures, PhD Thesis, University of Mumbai, India
arxiv created 2011/09/09 · arxiv updated 2011/09/12
We have observed extragalactic sources Mrk421 (z=0.30) and H1426+428 (z=0.129) in very high energy gamma region using TACTIC telescope at Mount Abu, Rajasthan, India. Mrk421 was observed during 07 December 2005 to 18 April 2007 for a total of ~331hours while H1426+428 was observed for ~244 hours between 22 March 2004 and 11 June 2007. Detailed analysis of Mrk421 data revealed the presence of a gamma signal with the excess of (~951± 82) gamma like events corresponding to a statistical significance of ~12.0 σin ~97 hours during 27 December 2005 to 07 February 2006. The combined average flux was measured to be ~(1.04±0.14) Crab units. Observed time averaged differential energy spectrum was found to be consistent with both a pure power law dΦ/dE=(4.66±0.46)× 10-11 E(-3.11±0.11) cm-2 s-1 TeV-1 and power law with an exponential cutoff functions dΦ/dE=f0E-Γexp(-E/E0) with f0=(4.88±0.38)×10-11 cm-2 s-1 TeV-1, Γ=2.51±0.26 and E0=(4.7±2.1)TeV. The later function fits the observed spectrum well with lower value of reduced χ2. However, during the observation period from 18 December 2006 to 18 April 2007, the source was found to be in a low emission state and we have placed an upper limit of 1.44× 10-12 photons cm-2 s-1 at 3σ level on the integrated \gam flux above 1 TeV. Detailed analysis of H1426+428 data does not indicate the presence of any statistically significant TeV \gam signal. Accordingly we have placed an upper limit of ≤1.18×10-12 photons cm-2 s-1 on the integrated γ-ray flux above 1 TeV at 3σ significance level.