Pointing of HAGAR telescope mirrors

Gothe, K. S.; Prabhu, T. P.; Vishwanath, P. R.; Acharya, B. S.; Srinivasan, R.; Chitnis, V. R.; Kamath, Pritish; Srinivasulu, G. Naga; Saleem, Farrukh; Kemkar, P. M. M.; Pathakoti, Mahesh; Gabriel, F.; Manoharan, J.; Dorji, N.; Dorjai, Tsewang; Angchuk, Dorje; D'Souza, Arvind I.; Duhan, S. K.; Nagesh, B. K.; Rao, S. K.; Sharma, Shubham; Singh, B. B.; Sudersanan, P. V.; Thsering, M. Tashi; Upadhya, S. S.; Anupama, G. C.; Britto, R. J.; Cowsik, R.; Saha, L.; Shukla, Amit

doi:10.1007/s10686-012-9319-9

Cited by 7 publications

(4 citation statements)

References 2 publications

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“…1. The telescope structures are based on alt-azimuth design (details given in Gothe et al 2013) and the separation between two nearest telescopes is 50 m. Each of the seven telescopes has seven para-axially mounted front coated parabolic mirrors of diameter 0.9 m with a UV-sensitive photo-multiplier tube (PMT) at the focus of individual mirrors. The opening angle (field of view) of the HAGAR telescopes is 3…”

Section: Hagarmentioning

confidence: 99%

Long-term study of Mkn 421 with the HAGAR Array of Telescopes

Sinha

Shukla

Saha

et al. 2016

A&A

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Context. The HAGAR Telescope Array at Hanle, Ladakh has been regularly monitoring the nearby blazar Mkn 421 for the past seven years. Aims. Blazars show flux variability in all timescales across the electromagnetic spectrum. While there is abundant literature characterizing the short-term flares from different blazars, comparatively little work has been carried out to study the long-term variability. We aim to study the long-term temporal and spectral variability in the radiation from Mkn 421 during 2009−2015. Methods. We quantify the variability and lognormality from the radio to very high-energy (VHE) bands, and compute the correlations between various wavebands using the z-transformed discrete correlation function. We construct the spectral energy distribution (SED) contemporaneous with HAGAR observation seasons and fit this SED with a one-zone synchrotron self-Compton model to study the spectral variability. Results. The flux is found to be highly variable across all timescales. The variability is energy dependant and is maximum in the X-ray and VHE bands. A strong correlation is found between the Fermi-LAT (gamma) and radio bands and between Fermi-LAT and optical, but no correlation is found between Fermi-LAT and X-ray. Lognormality in the flux distribution is clearly detected. This is the third blazar, following BL Lac and PKS 2155+304 to show this behaviour. The SED can be well fit by a one-zone SSC model, and variations in the flux states can be attributed mainly to changes in the particle distribution. A strong correlation is seen between the break energy γ b of the particle spectrum and the total bolometric luminosity.

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Section: Hagarmentioning

confidence: 99%

Long-term study of Mkn 421 with the HAGAR Array of Telescopes

Sinha

Shukla

Saha

et al. 2016

A&A

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“…Each telescope is separated by 50 m distance from its neighboring telescope. These telescopes use alt-azimuth mounting system (Gothe et al 2013). All seven telescopes have seven para-axially mounted front coated parabolic mirrors of diameter 0.9 m in each, with a UV-sensitive photo-tube at the focus of individual mirrors.…”

Section: Hagarmentioning

confidence: 99%

MULTI-FREQUENCY, MULTI-EPOCH STUDY OF Mrk 501: HINTS FOR A TWO-COMPONENT NATURE OF THE EMISSION

Shukla

Chitnis

Singh

et al. 2014

ApJ

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Since the detection of very high energy (VHE) γ-rays from Mrk 501, its broad band emission of radiation was mostly and quite effectively modeled using one zone emission scenario. However, broadband spectral and flux variability studies enabled by the multiwavelength campaigns carried out during the recent years have revealed rather complex behavior of Mrk 501. The observed emission from Mrk 501 could be due to a complex superposition of multiple emission zones.Moreover new evidences of detection of very hard intrinsic γ-ray spectra obtained from Fermi-LAT observations have challenged the theories about origin of VHE γ-rays. Our studies based on Fermi-LAT data indicate the existence of two separate components in the spectrum, one for low energy γ-rays and the other for high energy γ-rays. Using multiwaveband data from several ground and space based instruments, in addition to HAGAR data, the spectral energy distribution of Mrk 501 is obtained for various flux states observed during 2011. In the present work, this observed broadband spectral energy distribution is reproduced with a leptonic, multi-zone Synchrotron Self-Compton model.

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“…The over-all accuracy in pointing of the mirrorsis about 12 arc minutes. Details of the telescope control and the pointing model of HAGAR array have been extensively discussed [Gothe et al 2013]. The high voltages to PMTs are controlled and monitored through CAEN universal multi-channel power supply system.…”

Section: Hagarmentioning

confidence: 99%

“…The over-all accuracy in pointing of the mirrorsis about 12 arc minutes. Details of the telescope control and the pointing model of HAGAR array have been extensively discussed [Gothe et al 2013]. The high voltages to PMTs are controlled and A DAQ consisting of eight channel Flash ADC (fast waveform digitizer, Acqiris make) system has been used to digitize 7-telescope pulses.…”

Section: Hagarmentioning

confidence: 99%

VHE gamma-ray observation of Crab Nebula with HAGAR telescope array

et al. 2019

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HAGAR is a system of seven Non-imaging Atmospheric Cherenkov Telescopes located at Hanle in the Ladakh region of the Indian Himalayas at an altitude of 4270 meters amsl. Since 2008, we have observed the Crab Nebula to assess the performance of the HAGAR telescopes. We describe the analysis technique for the estimation of γ-ray signal amidst cosmic ray background. The consolidated results spanning nine years of the Crab nebula observations show long term performance of the HAGAR telescopes. Based on about 219 hours of data, we report the detection of γ-rays from the Crab Nebula at a significance level of about 20σ, corresponding to a time averaged flux of (1.64±0.09) ×10 −10 photons cm −2 sec −1 above 230 GeV. Also, we perform a -75013 2 B.B. Singh et al.detailed study of possible systematic effects in our analysis method on data taken with the HAGAR telescopes.

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Pointing of HAGAR telescope mirrors

Cited by 7 publications

References 2 publications

Long-term study of Mkn 421 with the HAGAR Array of Telescopes

Long-term study of Mkn 421 with the HAGAR Array of Telescopes

MULTI-FREQUENCY, MULTI-EPOCH STUDY OF Mrk 501: HINTS FOR A TWO-COMPONENT NATURE OF THE EMISSION

VHE gamma-ray observation of Crab Nebula with HAGAR telescope array

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