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  • 1.
    Godambe, S. V.
    et al.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Baliyan, K. S.
    Physical Research Laboratory, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Chanchalani, K.
    Bhabha Atomic Research Centre, India.
    Ganesh, S.
    Physical Research Laboratory, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Joshi, U. C.
    Physical Research Laboratory, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Sahaynathan, S.
    Bhabha Atomic Research Centre, India.
    Shah, C.
    Physical Research Laboratory, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Very high energy γ-ray and near infrared observations of 1ES2344+514 during 2004 052007In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 34, p. 1683-1695Article in journal (Refereed)
    Abstract [en]

    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 the 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(≥1.5 TeV) ≤ 3.84 × 10−12 photons cm−2 s−1 at a 3σ confidence level on the integrated γ-ray flux. In addition, we have also compared TACTIC TeV light curves with those of the RXTE ASM (2–12 keV) 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 and H bands. However, during the 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 and H, bands simultaneously. The light travel time arguments suggest that the emission region size is of the order of 1017 cm.

  • 2.
    Godambe, S. V.
    et al.
    Bhabha Atomic Research Centre, India.
    Rannot, R. C.
    Bhabha Atomic Research Centre, India.
    Chandra, P.
    Bhabha Atomic Research Centre, India.
    Yadav, K. K.
    Bhabha Atomic Research Centre, India.
    Tickoo, A. K.
    Bhabha Atomic Research Centre, India.
    Venugopal, K.
    Bhabha Atomic Research Centre, India.
    Bhatt, N.
    Bhabha Atomic Research Centre, India.
    Bhattacharyya, S.
    Bhabha Atomic Research Centre, India.
    Chanchalani, K.
    Bhabha Atomic Research Centre, India.
    Dhar, V. K.
    Bhabha Atomic Research Centre, India.
    Goyal, H. C.
    Bhabha Atomic Research Centre, India.
    Kaul, R. K.
    Bhabha Atomic Research Centre, India.
    Kothari, M.
    Bhabha Atomic Research Centre, India.
    Kotwal, S.
    Bhabha Atomic Research Centre, India.
    Koul, M. K.
    Bhabha Atomic Research Centre, India.
    Koul, R.
    Bhabha Atomic Research Centre, India.
    Sahaynathan, B. S.
    Bhabha Atomic Research Centre, India.
    Sharma, M.
    Bhabha Atomic Research Centre, India.
    Thoudam, Satyendra
    Bhabha Atomic Research Centre, India.
    Very high energy γ-ray observations of Mrk 501 using the TACTIC imaging γ-ray telescope during 2005 062008In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 35, no 6, article id 065202Article in journal (Refereed)
    Abstract [en]

    In this paper we report on the Markarian 501 results obtained during our TeV γ-ray observations from 11 March to 12 May 2005 and 28 February to 7 May 2006 for 112.5 h with the TACTIC γ-ray telescope. During 2005 observations for 45.7 h, the source was found to be in a low state and we have placed an upper limit of 4.62 × 10−12 photons cm−2 s−1 at 3σ level on the integrated TeV γ-ray flux above 1 TeV from the source direction. However, during 2006 observations for 66.8 h, detailed data analysis revealed the presence of a TeV γ-ray signal from the source with a statistical significance of 7.5σ above Eγ≥ 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 (dΦ/dE = f0E−Γ) with f0 = (1.66 ± 0.52) × 10−11 cm−2 s−1 TeV−1 and Γ = 2.80 ± 0.27.

  • 3. Yadav, K. K.
    et al.
    Rannot, R. C.
    Chandra, P.
    Tickoo, A. K.
    Thoudam, Satyendra
    Venugopal, K.
    Bhatt, N.
    Bhattacharyya, S.
    Chanchalani, K.
    Dhar, V. K.
    Godambe, S. V.
    Goyal, H. C.
    Kothari, M.
    Kotwal, S.
    Koul, M. K.
    Koul, R.
    Sahaynathan, S.
    Sharma, M.
    Search for TeV γ-rays from H1426+428 during 2004-2007 with the TACTIC telescope2009In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 36, no 8Article in journal (Refereed)
    Abstract [en]

    The BL Lac object H1426+428 (z ≡ 0.129) is an established source of TeV γ-rays and detections of these photons from this object also have important implications for estimating the extragalactic background light in addition to the understanding of the particle acceleration and γ-ray production mechanisms in the AGN jets. We have observed this source for about 244 h in 2004, 2006 and 2007 with the TACTIC γ-ray telescope located at Mt Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV γ-ray signal from the source direction. Accordingly, we have placed an upper limit of ≤1.18 × 10−12 photons cm−2 s−1 on the integrated γ-ray flux at 3σ significance level.

1 - 3 of 3
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