The TeV atmospheric Cherenkov telescope with imaging camera (TACTIC)
γ
-ray telescope has been in operation at Mt. Abu, India since 2001 to study TeV
γ
-ray emission from celestial sources. During ...the last 10 years, apart from consistently detecting a steady signal from the Crab Nebula above ∼1.2 TeV energy, at a sensitivity level of ∼5.0
σ
in ∼25 h, the telescope has also detected flaring activity from Mrk 421 and Mrk 501 on several occasions. Although we used Crab Nebula data partially, in some of the reported results, primarily for testing the validity of the full data analysis chain, the main aim of this work is to study the long term performance of the TACTIC telescope by using consolidated data collected between 2003 and 2010. The total on-source data, comprising ∼402 h, yields an excess of ∼(3742±192)
γ
-ray events with a statistical significance of ∼19.9
σ
. The off-source data, comprising ∼107 h of observation, is found to be consistent with a no-emission hypothesis, as expected. The resulting
γ
-ray rate for the on-source data is determined to be ∼(9.31±0.48) h
−1
. A power law fit (d
Φ
/d
E
=
f
0
E
−
Γ
) with
f
0
∼ (2.66±0.29) × 10
−11
cm
−2
s
−1
TeV
−1
and Γ ∼ 2.56±0.10 is found to provide reasonable fit to the inferred differential spectrum within statistical uncertainties. The spectrum matches reasonably well with that obtained by other groups. A brief summary of the improvements in the various subsystems of the telescope carried out recently, which has resulted in a substantial improvement in its detection sensitivity (viz., ∼5
σ
in an observation period of ∼13 h as compared to ∼25 h earlier) are also presented in this paper. Encouraged by the detection of strong
γ
-ray signals from Mrk 501 and Mrk 421 on several occasions, there is considerable scope for the TACTIC telescope to monitor similar TeV
γ
-ray emission activity from other active galactic nuclei on a long-term basis.
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 (\(d\Phi/dE=f_0 E^{-\Gamma}\)) with \(f_0=(1.66\pm0.52)\times 10^{-11}cm^{-2}s^{-1}TeV^{-1}\) and \(\Gamma=2.80\pm0.27\).
J.Phys.G36:085201,2009 The BL Lac object H1426+428 ($z\equiv 0.129$) is an established source of TeV
$\gamma$-rays and detections of these photons from this object also have
important implications ...for estimating the Extragalactic Background Light (EBL)
in addition to the understanding of the particle acceleration and $\gamma$-ray
production mechanisms in the AGN jets. We have observed this source for about
244h in 2004, 2006 and 2007 with the TACTIC $\gamma$-ray telescope located at
Mt. Abu, India. Detailed analysis of these data do not indicate the presence of
any statistically significant TeV $\gamma$-ray signal from the source
direction. Accordingly, we have placed an upper limit of
$\leq1.18\times10^{-12}$ $photons$ $cm^{-2}$ $s^{-1}$ on the integrated
$\gamma$-ray flux at 3$\sigma$ significance level.
J.Phys.G34:1683-1696,2007 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.
The BL Lac object H1426+428 (\(z\equiv 0.129\)) is an established source of TeV \(\gamma\)-rays and detections of these photons from this object also have important implications for estimating the ...Extragalactic Background Light (EBL) in addition to the understanding of the particle acceleration and \(\gamma\)-ray production mechanisms in the AGN jets. We have observed this source for about 244h in 2004, 2006 and 2007 with the TACTIC \(\gamma\)-ray telescope located at Mt. Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV \(\gamma\)-ray signal from the source direction. Accordingly, we have placed an upper limit of \(\leq1.18\times10^{-12}\) \(photons\) \(cm^{-2}\) \(s^{-1}\) on the integrated \(\gamma\)-ray flux at 3\(\sigma\) significance level.
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.
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