115 research outputs found
Constraining Lorentz invariance violations using the Crab pulsar TeV emission
Fast variations of gamma-ray flux from Active Galactic Nuclei and Gamma-Ray
Bursts can constrain Lorentz Invariance Violation (LIV) because of the delayed
(or advanced) arrival of photons with higher energies: this approach has lead
to the current world-best limits on the energy scale of Quantum Gravity. Here
we report on constraints on LIV studying the gamma-ray emission up to TeV
energies from the Galactic Crab pulsar, recently discovered by the MAGIC
collaboration. A likelihood analysis of the pulsar events reconstructed for
energies above 400 GeV finds no significant variation of energy-dependent
arrival time, and 95% CL limits are then obtained on the effective LIV energy
scale after taking into account systematic uncertainties. Only a factor of
about two less constraining than the current world-best limit on a quadratic
LIV scenario, pulsars are now well established as a third and independent class
of astrophysical objects suitable to constrain the characteristic energy scale
of LIV.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Analysis techniques and performance of the Domino Ring Sampler version 4 based readout for the MAGIC telescopes
Recently the readout of the MAGIC telescopes has been upgraded to a new
system based on the Domino Ring Sampler version 4 chip. We present the analysis
techniques and the signal extraction performance studies of this system. We
study the behaviour of the baseline, the noise, the cross-talk, the linearity
and the time resolution. We investigate also the optimal signal extraction. In
addition we show some of the analysis techniques specific to the readout based
on the Domino Ring Sampler version 2 chip, previously used in the MAGIC II
telescope.Comment: 13 pages, 20 figures, 1 table, Accepted for publication in NIM
Strategy Implementation for the CTA Atmospheric Monitoring Program
The Cherenkov Telescope Array (CTA) is the next generation facility of
Imaging Atmospheric Cherenkov Telescopes. It will reach unprecedented
sensitivity and energy resolution in very-high-energy gamma-ray astronomy. CTA
will detect Cherenkov light emitted within an atmospheric shower of particles
initiated by cosmic-gamma rays or cosmic rays entering the Earth's atmosphere.
From the combination of images the Cherenkov light produces in the telescopes,
one is able to infer the primary particle energy and direction. A correct
energy estimation can be thus performed only if the local atmosphere is well
characterized. The atmosphere not only affects the shower development itself,
but also the Cherenkov photon transmission from the emission point in the
particle shower, at about 10-20 km above the ground, to the detector. Cherenkov
light on the ground is peaked in the UV-blue region, and therefore molecular
and aerosol extinction phenomena are important. The goal of CTA is to control
systematics in energy reconstruction to better than 10%. For this reason, a
careful and continuous monitoring and characterization of the atmosphere is
required. In addition, CTA will be operated as an observatory, with data made
public along with appropriate analysis tools. High-level data quality can only
be ensured if the atmospheric properties are consistently and continuously
taken into account. In this contribution, we concentrate on discussing the
implementation strategy for the various atmospheric monitoring instruments
currently under discussion in CTA. These includes Raman lidars and ceilometers,
stellar photometers and others available both from commercial providers and
public research centres.Comment: (6 pages, 2 figures, Proceedings of the 2nd AtmoHEAD Conference,
Padova, Italy May 19-21, 2014
Tools and Procedures for the CTA Array Calibration
The Cherenkov Telescope Array (CTA) is an international initiative to build
the next generation ground-based very-high-energy gamma-ray observatory. Full
sky coverage will be assured by two arrays, one located on each of the northern
and southern hemispheres. Three different sizes of telescopes will cover a wide
energy range from tens of GeV up to hundreds of TeV. These telescopes, of which
prototypes are currently under construction or completion, will have different
mirror sizes and fields-of-view designed to access different energy regimes.
Additionally, there will be groups of telescopes with different optics system,
camera and electronics design. Given this diversity of instruments, an overall
coherent calibration of the full array is a challenging task. Moreover, the CTA
requirements on calibration accuracy are much more stringent than those
achieved with current Imaging Atmospheric Cherenkov Telescopes, like for
instance: the systematic errors in the energy scale must not exceed 10%.In this
contribution we present both the methods that, applied directly to the acquired
observational CTA data, will ensure that the calibration is correctly performed
to the stringent required precision, and the calibration equipment that,
external to the telescopes, is currently under development and testing.
Moreover, some notes about the operative procedure to be followed with both
methods and instruments, will be described. The methods applied to the
observational CTA data include the analysis of muon ring images, of carefully
selected cosmic-ray air shower images, of the reconstructed electron spectrum
and that of known gamma-ray sources and the possible use of stereo techniques
hardware-independent. These methods will be complemented with the use of
calibrated light sources located on ground or on board unmanned aerial
vehicles.Comment: All CTA contributions at arXiv:1709.0348
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