The origin of the hump in the Cerenkov lateral distribution in gamma-ray showers and a possible means of separating them from proton showers

Rao, M. V. S.; Sinha, S.

doi:10.1088/0305-4616/14/6/022

Cited by 16 publications

(22 citation statements)

References 6 publications

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“…As a result, the lateral distribution ofČerenkov photons has been known to change with the altitude of the observation level. The core distance at which the hump appears as well as the prominence of the hump will be smaller with increasing altitude of observation [37,38]. Since theČerenkov front is being intercepted at different observation levels during its propagation in the atmosphere, the shower parameters like the average arrival angle, time etc also will be different at different observation levels.…”

Section: Altitude Dependence Of Quality Factorsmentioning

confidence: 99%

Possible discrimination between gamma rays and hadrons using Čerenkov photon timing measurements

Chitnis

Bhat

2001

Astroparticle Physics

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AtmosphericČerenkov Technique is an established methodology to study T eV energy gamma rays. However the challenging problem has always been the poor signal to noise ratio due to the presence of abundant cosmic rays. Several ingenious techniques have been employed to alleviate this problem, most of which are centred around theČerenkov image characteristics. However there are not many techniques available for improving the signal to noise ratio of the data from wavefront sampling observations. One such possible technique is to use theČerenkov photon arrival times and identify the species dependent characteristics in them. Here we carry out systematic monte carlo simulation studies of the timing information ofČerenkov photons at the observation level. We have parameterized the shape of theČerenkov shower front as well as the pulse shapes in terms of experimentally measurable quantities. We demonstrate the sensitivity of the curvature of the shower front, pulse shape parameters as well as the photon arrival time jitter to primary species and show their efficiency in improving the signal to noise ratio. The effect of limiting theČerenkov telescope opening angle by using a circular focal point mask, on the efficacy of the parameters has also been studied for each of the parameters. Radius of the shower front, pulse decay time and photon arrival time jitter have been found to be the most promising parameters which could be used to discriminate γ−ray events from the background. We also find that the efficiency of the first two parameters increases with zenith angle and efficiency of pulse decay time decreases with increasing altitude of observation.

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Section: Altitude Dependence Of Quality Factorsmentioning

confidence: 99%

Possible discrimination between gamma rays and hadrons using Čerenkov photon timing measurements

Chitnis

Bhat

2001

Astroparticle Physics

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“…Simulation studies in the past (Rao & Sinha, 1988;Hillas & Patterson, 1987;Zatsepin & Chudakov, 1962) have shown that the Čerenkov pool at the observation level has the signature of the primary. The lateral distribution of Čerenkov radiation seems to be distinctly different in γ− ray and proton initiated showers in the sense that in the former case it is flat upto about 140 m and characterized by an increased photon density (called the 'hump') at that distance while in the latter case it is steeper with practically no hump.…”

Section: Introductionmentioning

confidence: 99%

“…The lateral distribution of Čerenkov radiation seems to be distinctly different in γ− ray and proton initiated showers in the sense that in the former case it is flat upto about 140 m and characterized by an increased photon density (called the 'hump') at that distance while in the latter case it is steeper with practically no hump. It has been suggested (Rao & Sinha, 1988) that this characteristic difference could be measured in an observation and could be used for improving the signal to noise ratio. These arguments are based on the average properties of showers.…”

Section: Introductionmentioning

confidence: 99%

Čerenkov photon density fluctuations in extensive air showers

Chitnis

Bhat

1998

Astroparticle Physics

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“…The Cherenkov condition can be converted in a kinetic energy threshold for particles with rest mass m 0 : Note that in air n ≈ 1 can be expressed as n = 1 + η [Rao88] and thus the threshold scales with the mass of the particles. Since the lightest particles involved in EAS are electrons and positrons, they have by far the lowest Cherenkov threshold (at sea level: E min = 4.6 GeV, E p min = 40 GeV, and E e min = 22 MeV, respectively [Rao88]). The interplay of the electron Cherenkov threshold and the number of electrons in the shower (cf.…”

Section: Cherenkov Light Productionmentioning

confidence: 99%

“…After crossing the so-called Cherenkov hump, the distribution levels off at larger distances, because light produced in the shower halo is predominantly sampled there. The hump itself is a geometrical feature that comes about by the changing refractive index of the atmosphere and the changing Cherenkov light emission angle [Rao88], leading to a focusing effect. The photon density inside the Cherenkov light pool as a function of the energy of the primary particle is given for different particle types in fig.…”

Section: Production and Attenuation Of Cherenkov Light In The Atmospherementioning

confidence: 99%

Measurement of Very High Energy Gamma‐Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study

Wagner¹

2007

PUBL ASTRON SOC PAC

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SummaryThe thesis reports on the measurement of very high energy (VHE) gamma-rays from four Active Galactic Nuclei (AGN) with the Major Atmospheric Gamma-ray Imaging Cherenkov telescope (MAGIC). When taking into account -ray absorption by the extragalactic background light (EBL), a hint for an inverse Compton peak is found with the peak energy moving from (0.3 ± 0.1) TeV to (1.4 ± 0.7) TeV with increasing flux level. This evidence is strengthened by the observation of a moving structure also in the measured spectra, which are free of uncertainties of the EBL model used.Unprecedented rapid flux variability with doubling times of ≤ 5 minutes was found during some of the observation nights. These fast flares are used to infer significant limits on the size of the acceleration region of R · δ −1 ≤ 10 12 cm for homogeneous one-zone SelfSynchrotron Compton models. Significant spectral hardening of ∆α = 0.4 within less than 20 minutes could be observed. The well-defined fast flares were also used to infer a lower limit on the quantum gravity energy scale of 1.5 × 10 17 GeV.For the BL Lac object 1ES 2344+514 for the first time a differential energy spectrum during a state of low -ray activity is inferred, which between 140 GeV and 5 TeV can be vii described by a power law of the form dF dE = (1.18 ± 0.13) × 10The study of the 24-day VHE -ray light curve of 1ES 2344+514 yields a low flux level of 0.04 ≤ F E>350 GeV ≤ 0.11 times the Crab nebula flux. In combination with the all-time (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)) light curve a low emission level of about ≈4% of the Crab nebula flux is found.Within the thesis, predictions for the detectability of BL Lac candidate objects in VHE -rays with the MAGIC telescope are presented. These predictions led to the discovery of two new objects in this energy domain, PG 1553+113 and BL Lacertae. PG 1553+113 was detected at a high significance level of 8.8σ . The softest gamma ray spectrum observed so far in VHE -rays was found for this source. It can be described by a pure power law between 95 GeV and 500 GeV:The spectrum is used to infer an upper limit of z < 0.78 on the yet undetermined redshift of PG 1553+113 by imposing a maximum hardness of the intrinsic spectrum. While the light curve does not show apparent short-term variability, simultaneously recorded optical data feature a substantial flare, which leaves room for interpretation of the non-existing correlations.BL Lacertae, the prototype of the BL Lac objects, was detected at a significance level of 5.6σ . This object is the first low-frequency peaked BL Lac object seen in VHE -rays. A preliminary spectrum hints at a steep slope of ≈ −3.7 between 100 GeV and 1 TeV.For the first time a synoptic study of all high-frequency peaked BL Lac-type objects detected as VHE gamma-ray emitters is performed. The intrinsic properties of the observed emission are compared and correlated among each other and with the individual estimated black hole masses. Key findings are (1) that all currently known VHE -r...

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The origin of the hump in the Cerenkov lateral distribution in gamma-ray showers and a possible means of separating them from proton showers

Cited by 16 publications

References 6 publications

Possible discrimination between gamma rays and hadrons using Čerenkov photon timing measurements

Possible discrimination between gamma rays and hadrons using Čerenkov photon timing measurements

Čerenkov photon density fluctuations in extensive air showers

Measurement of Very High Energy Gamma‐Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study

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