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

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 $E_{gamma}geq$ 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 ($dPhi/dE=f_0 E^{-Gamma}$) with $f_0=(1.66pm0.52)times 10^{-11}cm^{-2}s^{-1}TeV^{-1}$ and $Gamma=2.80pm0.27$.

Very High Energy $gamma$-ray and Near Infrared observations of 1ES2344+514 during 2004-05

We have observed the BL Lac object 1ES2344+514 (z = 0.044) in Very High Energy (VHE) gamma-ray and near-infrared wavelength bands with TACTIC and MIRO telescopes respectively. The observations were made from 18th October to 9th December 2004 and 27th October 2005 to 1st January 2006. Detailed analysis of the TACTIC data indicates absence of a statistically significant gamma-ray signal both in overall data and on a nightly basis from the source direction. We estimate an upper limit of I($geq$1.5 TeV)$leq 3.84 times 10^{-12}$ photons cm$^{-2}$ s$^{-1}$ at a 3$sigma$ confidence level on the integrated $gamma$-ray flux. In addition, we have also compared TACTIC TeV light curves with those of the RXTE ASM (2-12keV) for the contemporary period and find that there are no statistically significant increases in the signal strengths from the source in both these energy regions. During 2004 IR observations, 1ES2344+514 shows low level (~0.06 magnitude) day-to-day variation in both, J & H bands. However, during 2005 observation epoch, the source brightens up by about 0.41 magnitude from its October 2005 level J magnitude= 12.64 to J = 12.23 on December 6, 2005. It then fades by about 0.2 magnitude during 6 to 10 December, 2005. The variation is seen in both, J & H, bands simultaneously. The light travel time arguments suggest that the emission region size is of the order of $10^{17}$ cms.