68 research outputs found
Prototyping Hexagonal Light Concentrators Using High-Reflectance Specular Films for the Large-Sized Telescopes of the Cherenkov Telescope Array
We have developed a prototype hexagonal light concentrator for the
Large-Sized Telescopes of the Cherenkov Telescope Array. To maximize the
photodetection efficiency of the focal-plane camera pixels for atmospheric
Cherenkov photons and to lower the energy threshold, a specular film with a
very high reflectance of 92-99% has been developed to cover the inner surfaces
of the light concentrators. The prototype has a relative anode sensitivity
(which can be roughly regarded as collection efficiency) of about 95 to 105% at
the most important angles of incidence. The design, simulation, production
procedure, and performance measurements of the light-concentrator prototype are
reported.Comment: 21 pages, 14 figures, accepted for publication in JINS
Development of the photomultiplier tube readout system for the first Large-Sized Telescope of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the next generation ground-based very
high energy gamma-ray observatory. The Large-Sized Telescope (LST) of CTA
targets 20 GeV -- 1 TeV gamma rays and has 1855 photomultiplier tubes (PMTs)
installed in the focal plane camera. With the 23 m mirror dish, the night sky
background (NSB) rate amounts to several hundreds MHz per pixel. In order to
record clean images of gamma-ray showers with minimal NSB contamination, a fast
sampling of the signal waveform is required so that the signal integration time
can be as short as the Cherenkov light flash duration (a few ns). We have
developed a readout board which samples waveforms of seven PMTs per board at a
GHz rate. Since a GHz FADC has a high power consumption, leading to large heat
dissipation, we adopted the analog memory ASIC "DRS4". The sampler has 1024
capacitors per channel and can sample the waveform at a GHz rate. Four channels
of a chip are cascaded to obtain deeper sampling depth with 4096 capacitors.
After a trigger is generated in a mezzanine on the board, the waveform stored
in the capacitor array is subsequently digitized with a low speed (33 MHz) ADC
and transferred via the FPGA-based Gigabit Ethernet to a data acquisition
system. Both a low power consumption (2.64 W per channel) and high speed
sampling with a bandwidth of 300 MHz have been achieved. In addition, in
order to increase the dynamic range of the readout we adopted a two gain system
achieving from 0.2 up to 2000 photoelectrons in total. We finalized the board
design for the first LST and proceeded to mass production. Performance of
produced boards are being checked with a series of quality control (QC) tests.
We report the readout board specifications and QC results.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Propagation of Ultra-High-Energy Cosmic Ray Nuclei in Cosmic Magnetic Fields and Implications for Anisotropy Measurements
(Abridged) Recent results from the Pierre Auger Observatory (PAO) indicate
that the composition of ultra-high-energy cosmic rays (UHECRs) with energies
above eV may be dominated by heavy nuclei. An important question is
whether the distribution of arrival directions for such UHECR nuclei can
exhibit observable anisotropy or positional correlations with their
astrophysical source objects despite the expected strong deflections by
intervening magnetic fields. For this purpose, we have simulated the
propagation of UHECR nuclei including models for both the extragalactic
magnetic field and the Galactic magnetic field. Assuming that only iron nuclei
are injected steadily from sources with equal luminosity and spatially
distributed according to the observed large scale structure in the local
Universe, at the number of events published by the PAO so far, the arrival
distribution of UHECRs would be consistent with no auto-correlation at 95%
confidence if the mean number density of UHECR sources
Mpc, and consistent with no cross-correlation with sources within 95%
errors for Mpc. On the other hand, with 1000 events
above eV in the whole sky, next generation experiments can
reveal auto-correlation with more than 99% probability even for Mpc, and cross-correlation with sources with more than 99%
probability for Mpc. In addition, we find that the
contribution of Centaurus A is required to reproduce the currently observed
UHECR excess in the Centaurus region. Secondary protons generated by
photodisintegration of primary heavy nuclei during propagation play a crucial
role in all cases, and the resulting anisotropy at small angular scales should
provide a strong hint of the source location if the maximum energies of the
heavy nuclei are sufficiently high.Comment: 17 pages, 15 figure
MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study
https://pos.sissa.it/395/815/pdfPublished versio
Signal Fluctuations in the Auger Surface Detector
Abstract We measured theČerenkov signal fluctuations in the water tanks of the Pierre Auger Observatory (PAO). Two stations located near the center of the 32-tank Engineering Array (EA) separated by 11 m were used for the purpose. At this separation the stations sample nearly the same region of the air shower. Sources of the signal fluctuations are discussed
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