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# A schematic layout of the PACT. Each telescope consists of seven mirrors and each sector consist of six telescopes and their data acquisition centers.

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We present the results of observation of the Geminga pulsar carried out in the TeV energy band during the 6 year period spanning 2000–2006 using the Pachmarhi Array of Cherenkov Telescopes (PACT). A long stretch of data, new computer codes and the “Tempo” package have been used in the present analysis. We have searched for evidence of pulsed emissi...

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... The PACT experiment in India was of a similar design to THEMISTOCLE, but with higher sensitivity due to the larger size of both the mirror area of individual stations and the cluster of distributed stations [20]. ...
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In the past three decades, the ground-based technique of imaging atmospheric Cherenkov telescopes has established itself as a powerful discipline in science. Approximately 250 sources of very high gamma rays of both galactic and extra-galactic origin have been discovered largely due to this technique. The study of these sources is providing clues to many basic questions in astrophysics, astro-particle physics, physics of cosmic rays and cosmology. The currently operational generation of telescopes offer a solid performance. Further improvements of this technique led to the next-generation large instrument known as the Cherenkov Telescope Array. In its final configuration, the sensitivity of CTA will be several times higher than that of the currently best instruments VERITAS, H.E.S.S., and MAGIC. This article is devoted to outlining the technological developments that shaped this technique and led to today’s success.
... It was discovered in γ-rays with the SAS-2 experiment [3] before being observed in other wavelengths. Pulsations were first observed in X-rays [4] with ROSAT and later EGRET [5] but have not been observed in the TeV range [6,7,8]. X-ray Multimirror Mission-Newton observations show a pulsar wind around Geminga with an extent of a few arc minutes [9]. ...
... The Tibet Air shower array reported an excess of 2.2σ at the location of the pulsar but did not report extended emission [18]. Imaging Atmospheric Cherenkov Telescopes (IACTs) have observed Geminga without significant detection [6,19,7] for over two decades. An extended, hard TeV source is extremely difficult to observe with the IACT technique. ...
... It was discovered in γ-rays with the SAS-2 experiment [3] before being observed in other wavelengths. Pulsations were first observed in X-rays [4] with ROSAT and later EGRET [5] but have not been observed in the TeV range [6,7,8]. X-ray Multimirror Mission-Newton observations show a pulsar wind around Geminga with an extent of a few arc minutes [9]. ...
... The Tibet Air shower array reported an excess of 2.2σ at the location of the pulsar but did not report extended emission [18]. Imaging Atmospheric Cherenkov Telescopes (IACTs) have observed Geminga without significant detection [6,19,7] for over two decades. An extended, hard TeV source is extremely difficult to observe with the IACT technique. ...
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Geminga is a radio-quiet pulsar ~250 parsecs from Earth that was first discovered as a GeV gamma-ray source and then identified as a pulsar. Milagro observed an extended TeV source spatially consistent with Geminga. HAWC observes a similarly extended source. Observations of Geminga's flux and extension will be presented.
... The Geminga pulsar has been a target for groundbased very-high-energy gamma-ray detectors for over two decades. Limits on the pulsed gamma-ray flux in the TeV regime at the ∼10% Crab Nebula level have been reported by the Whipple, HEGRA and PACT collaborations (Akerlof et al. 1993;Aharonian et al. 1999;Singh et al. 2009), while the Ootacamund, Durham and Crimean groups have reported weak evidence (∼3σ level) for pulsed emission at the ∼50-100% Crab Nebula level (Vishwanath et al. 1993;Bowden et al. 1993;Neshpor et al. 2001). Given the far higher sensitivity of current ground-based gamma-ray arrays, it seems likely that these reported excesses are due to statistical fluctuations. ...
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... Observations on AGNs like Mrk 421, Mrk 501, 1ES 1426+428, ON 231 etc. were carried out using PACT [28,29]. The PACT result on daily average γ-ray rate per minute is shown for Mrk 421 in Fig. 5 along with daily average X-ray photon rate per second obtained by the All Sky Monitor (ASM) on board RXTE satellite for circa 2000 to 2005. ...
... Search for TeV γ-rays from Geminga Pulsar was carried out during the six year period spanning 2000- 2006 using the PACT [29]. No evidence for pulsed emission of γ-rays was seen in the long stretch of data at a threshold energy of 825 GeV. ...
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A short historical account of TeV γ-ray astronomy in India is presented. Special attention is given to the development of experimental techniques vis-a-vis world-wide development of the field.
... tudes is PACT(Pachmarhi Array of Cherenkov Telescopes)( [21][22][23]) in INDIA. It is installed at Pachmarhi, on the hills of Satpura moun- tain range, in the state of Madhya Pradesh (Central India). ...
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We present results of Monte Carlo simulations for the High Altitude Gamma Ray (HAGAR) telescope array which detects very high energy gamma rays from astronomical sources. This telescope array, located at Hanle at an altitude of 4270 m in the Ladakh region of the Himalayas in India, is the highest altitude atmospheric Cherenkov experiment in the world. Taking advantage of the high altitude, this experiment could achieve relatively low energy threshold with a modest mirror area coverage. To understand the performance parameters of this telescope system, we have simulated large samples of extensive air showers initiated by gamma rays and various species of cosmic rays, using the CORSIKA package. Cherenkov photons produced in the atmosphere are sampled at ground level. These photons are then passed through the detector simulation program, which takes into account various design details and the data acquisition system of HAGAR. Night sky photons are also considered in the detector simulation program as performance of the telescope depends strongly on the level of night sky background (NSB) at the observation site. We have estimated various performance parameters like energy threshold and effective area for vertically incident showers as well as inclined showers. Details of these parameters, results obtained from simulations and comparison with the observed data are presented. It is shown that the energy threshold of the HAGAR telescope system is about 208 GeV, a factor of ∼4 less than for a similar set up at about 1000 m altitude, and it is able to detect Crab like sources at 5σ5σ significance in 17 h of observation without imposing additional criteria, like gamma-hadron separation, for further rejection of cosmic rays.
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