| 1. |
- Godambe, S. V., et al.
(författare)
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Very high energy γ-ray and near infrared observations of 1ES2344+514 during 2004 05
- 2007
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 34, s. 1683-1695
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Godambe, S. V., et al.
(författare)
-
Very High Energy Gamma-ray and Near Infrared observations of 1ES2344+514 with TACTIC and MIRO Telescopes
- 2005
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Ingår i: 29th International Cosmic Ray Conference Pune (2005).
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Konferensbidrag (refereegranskat)abstract
- 1ES2344+514 (z = 0.04) is one of the rst BL Lac objects to be reported as an extreme synchrotron blazar withsynchotron peak energy reaching up to 100keV and was discovered as a source of Very High Energy (VHE)gamma- rays by the Whipple group in 1995. Subsequently, it was observed by the HEGRA group in 1997/98and 2002. We have recently (Oct.- Dec. 2004) observed the 1ES2344+514 using the imaging element of theTACTIC array and have collected data for 53 hours in on/off mode. The source was also observed in nearinfrared bands J, H and K, for some nights using NICMOS-3 array mounted on 1.2m MIRO infrared telescope.Such a study is expected to provide clues to the dominance or otherwise of the Compton component. Afterdetailed analysis of the TACTIC data we have placed an upper limit of photons cmsata 3condence level on the gamma-ray ux from the source. In the near infrared band the source shows lowlevel variations without any aring activity.
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| 3. |
- Koul, R., et al.
(författare)
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The TACTIC atmospheric Cherenkov imaging telescope
- 2007
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 578:3, s. 548-564
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Tidskriftsartikel (refereegranskat)abstract
- The TACTIC (TeV Atomospheric Cherenkov Telescope with Imaging Camera) γγ-ray telescope, equipped with a light collector of area ∼9.5m2 and a medium resolution imaging camera of 349 pixels, has been in operation at Mt. Abu, India, since 2001. This paper describes the main features of its various subsystems and its overall performance with regard to (a) tracking accuracy of its two-axes drive system, (b) spot size of the light collector, (c) back-end signal processing electronics and topological trigger generation scheme, (d) data acquisition and control system and (e) relative and absolute gain calibration methodology. Using a trigger field-of-view of 11×1111×11 pixels (∼3.4∘×3.4∘)(∼3.4∘×3.4∘), the telescope records a cosmic ray event rate of ∼2.5Hz at a typical zenith angle of 15∘15∘. Monte Carlo simulation results are also presented in the paper for comparing the expected performance of the telescope with actual observational results. The consistent detection of a steady signal from the Crab Nebula above ∼1.2TeV energy, at a sensitivity level of ∼5.0σ∼5.0σ in ∼25h, alongwith excellent matching of its energy spectrum with that obtained by other groups, reassures that the performance of the TACTIC telescope is quite stable and reliable. Furthermore, encouraged by the detection of strong γγ-ray signals from Mrk 501 (during 1997 and 2006 observations) and Mrk 421 (during 2001 and 2005–2006 observations), we believe that there is considerable scope for the TACTIC telescope to monitor similar TeV γγ-ray emission activity from other active galactic nuclei on a long-term basis.
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| 4. |
- Godambe, S. V., et al.
(författare)
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Very high energy γ-ray observations of Mrk 501 using the TACTIC imaging γ-ray telescope during 2005 06
- 2008
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 35:6
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Rannot, R. C., et al.
(författare)
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TeV gamma-ray Observations of the Blazar Markarian 421 from January to April 2004 with TACTIC Imaging Element
- 2005
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Ingår i: 29th International Cosmic Ray Conference Pune (2005). ; , s. 355-358
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Konferensbidrag (refereegranskat)abstract
- We have observed the blazar Markarian 421 (z=0.031 ) with the TACTIC gamma- ray telescope having thresholdenergy of 1.5TeV at Mt. Abu Rajasthan India from January to April 2004. Observations were made intracking mode for a total of 84(on) /16 (off-source) hours with its imaging element equipped with a 349- pixelPMTs camera. During this period, we nd an evidence of a TeV gamma-ray signal with a statistical signi-cance of 6.8. The differential energy spectrum derived in the energy range 2 - 9 TeV is well represented bya simple power law, with a differential spectral index of 2.800.20.
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| 6. |
- Yadav, K. K., et al.
(författare)
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Observations of TeV γ-rays from Mrk 421 during December 2005 to April 2006 with the TACTIC telescope
- 2007
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 27:5, s. 447-454
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Tidskriftsartikel (refereegranskat)abstract
- The TACTIC γ-ray telescope has observed Mrk 421 on 66 clear nights from December 07, 2005 to April 30, 2006, totalling ∼202 h of on-source observations. Here, we report the detection of flaring activity from the source at ⩾1 TeV energy and the time-averaged differential γ-ray spectrum in the energy range 1–11 TeV for the data taken between December 27, 2005 and February 07, 2006 when the source was in a relatively higher state as compared to the rest of the observation period. Analysis of this data spell, comprising ∼97 h reveals the presence of a ∼12.0σ γ-ray signal with daily flux of >1 Crab unit on several days. A pure power law spectrum with exponent −3.11 ± 0.11 as well as a power law spectrum with an exponential cutoff (Γ = −2.51 ± 0.26 and E0 = (4.7 ± 2.1) TeV) are found to provide reasonable fits to the inferred differential spectrum within statistical uncertainties. We believe that the TeV light curve presented here, for nearly 5 months of extensive coverage, as well as the spectral information at γ-ray energies of >5 TeV provide a useful input for other groups working in the field of γ-ray astronomy.
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| 7. |
- Yadav, K. K., et al.
(författare)
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Search for TeV γ-rays from H1426+428 during 2004-2007 with the TACTIC telescope
- 2009
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 36:8
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Dhar, V. K., et al.
(författare)
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ANN based energy estimation procedure and energy spectrum of the Crab Nebula as measured by the TACTIC gamma-ray telescope
- 2005
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Ingår i: 29th International Cosmic Ray Conference Pune (2005). ; , s. 179-182
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Konferensbidrag (refereegranskat)abstract
- A novel energy reconstruction procedure based on the utilization of Articial Neural Network has been developedfor the TACTIC atmospheric Cerenkov imaging telescope to estimate the energy of the primary gammaraysin the TeV energy range. The procedure uses a 3:20:1 conguration of the ANN with resilient backpropagationtraining algorithm to estimate the energy of a-ray like event on the basis of its image SIZE,DISTANCE and zenith angle. The results obtained by using the CORSIKA code simulated data suggest theenergy resolution of the telescope is40for retaining90of the-ray events in a particular energybin which is comparable to the energy resolution of other single element imaging telescopes. Details of theenergy estimation procedure along with results obtained by determining the Crab Nebula energy spectrum inthe energy range 1-16 TeV as measured by the TACTIC telescope are presented in the paper.
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| 9. |
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| 10. |
- Tickoo, A. K., et al.
(författare)
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A generalized ray-tracing procedure for an atmospheric Cherenkov imaging telescope and optical characteristics of the TACTIC light collector
- 2005
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 539:1-2, s. 177-190
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Tidskriftsartikel (refereegranskat)abstract
- A generalized ray-tracing procedure has been developed, which facilitates the design of a multimirror-based light collector used in atmospheric Cherenkov telescopes. This procedure has been employed to study the optical characteristics of the 3.5 m diameter light collector of the TACTIC Imaging telescope. Comparison of the measured point-spread function of the light collector with the simulated performance of ideal Davies–Cotton and paraboloid designs has been made to determine an optimum arrangement of the 34 spherical mirror facets used in the telescope to obtain the best possible point-spread function. A description of the ray-tracing subroutine used for processing CORSIKA-generated Cherenkov data, required for carrying out Monte-Carlo simulation studies, is also discussed in the paper.
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