756 research outputs found
Evaluation of scientific CMOS sensors for sky survey applications
Scientific CMOS image sensors are a modern alternative for a typical CCD
detectors, as they offer both low read-out noise, large sensitive area, and
high frame rates. All these makes them promising devices for a modern
wide-field sky surveys. However, the peculiarities of CMOS technology have to
be properly taken into account when analyzing the data. In order to
characterize these, we performed an extensive laboratory testing of Andor
Marana sCMOS camera. Here we report its results, especially on the temporal
stability and linearity, and compare it to the previous versions of Andor sCMOS
cameras. We also present the results of an on-sky testing of this sensor
connected to a wide-field lens, and discuss its applications for an
astronomical sky surveys.Comment: Accepted to Astronomische Nachrichte
All Sky Camera for the CTA Atmospheric Calibration work package
The All Sky Camera (ASC) is a passive non-invasive imaging system for rapid night sky atmosphere monitoring. By design, the operation of the ASC will not affect the measurement procedure of the CTA observatory, for which we discuss its application in this report. The data collected should enable improved productivity and increased measurement time for the CTA observatory. The goal of ASC is to identify cloud position, atmosphere attenuation and time evolution of the sky condition, working within the CTA Central Calibration Facilities (CCF) group. Clouds and atmosphere monitoring may allow near-future prediction of the night-sky quality, helping scheduling. Also, in the case of partly cloudy night sky the cameras will identify the uncovered regions of the sky during the operation time, and define potential observable sources that can be measured. By doing so, a higher productivity of the CTA observatory measurements may be possible
The bright optical flash from GRB 060117
We present a discovery and observation of an extraordinarily bright prompt
optical emission of the GRB 060117 obtained by a wide-field camera atop the
robotic telescope FRAM of the Pierre Auger Observatory from 2 to 10 minutes
after the GRB. We found rapid average temporal flux decay of alpha = -1.7 +-
0.1 and a peak brightness R = 10.1 mag. Later observations by other instruments
set a strong limit on the optical and radio transient fluxes, unveiling an
unexpectedly rapid further decay. We present an interpretation featuring a
relatively steep electron-distribution parameter p ~ 3.0 and providing a
straightforward solution for the overall fast decay of this optical transient
as a transition between reverse and forward shock.Comment: Accepted to A&A, 4 pages, corected few typos pointed out by X.F. W
Overview of Atmospheric Simulation Efforts in CTA
The Cherenkov Telescope Array (CTA) is an observatory for ground-based gamma-ray astronomy currently under construction, which will observe photons with very high energies (20 GeV – 300 TeV). One of the main contributions to the systematic uncertainties stems from the uncertainty on the atmospheric density profile, of molecules and aerosols. To minimize these systematics a full calibration of the atmospheric properties is important as well as a calibration of the detector response. In the paper we introduce the strategy for atmospheric simulations, use of Monte Carlo simulations and available CTA computing resources. We also describe in more detail realized and planned atmospheric simulations as well as the Czech contribution to this effort
The Galactic magnetic field and propagation of ultra-high energy cosmic rays
The puzzle of ultra-high energy cosmic rays (UHECRs) still remains
unresolved. With the progress in preparation of next generation experiments
(AUGER, EUSO, OWL) grows also the importance of directional analysis of
existing and future events. The Galactic magnetic field (GMF) plays the key
role in source identification even in this energy range. We first analyze
current status of our experimental and theoretical knowledge about GMF and
introduce complex up-to-date model of GMF. Then we present two examples of
simple applications of influence of GMF on UHECR propagation. Both examples are
based on Lorentz equation solution. The first one is basic directional analysis
of the incident directions of UHECRs and the second one is a simulation of a
change of chemical composition of CRs in the energy range 10^13 - 10^19 eV. The
results of these simple analyses are surprisingly rich - e.g. the rates of
particle escape from the Galaxy or the amplifications of particle flux in
specific directions.Comment: 10 pages, 7 figures, accepted for publication in A&
Measurement of Aerosols at the Pierre Auger Observatory
The air fluorescence detectors (FDs) of the Pierre Auger Observatory are
vital for the determination of the air shower energy scale. To compensate for
variations in atmospheric conditions that affect the energy measurement, the
Observatory operates an array of monitoring instruments to record hourly
atmospheric conditions across the detector site, an area exceeding 3,000 square
km. This paper presents results from four instruments used to characterize the
aerosol component of the atmosphere: the Central Laser Facility (CLF), which
provides the FDs with calibrated laser shots; the scanning backscatter lidars,
which operate at three FD sites; the Aerosol Phase Function monitors (APFs),
which measure the aerosol scattering cross section at two FD locations; and the
Horizontal Attenuation Monitor (HAM), which measures the wavelength dependence
of aerosol attenuation.Comment: Contribution to the 30th International Cosmic Ray Conference, Merida
Mexico, July 2007; 4 pages, 4 figure
Ultra-high energy cosmic rays from a finite number of point sources
We have calculated the probability that the clustering of arrival directions
of ultra-high energy cosmic rays (UHECRs) is consistent with a finite number of
uniformly distributed proton sources. The case of a continuous source
distribution is reached only for an unrealisticly high source density, . Even for densities as large as , less than
half of the observed cluster are on average by chance. For the best-fit value
derived from the AGASA data, the probability
that at least one observed cluster is from a true point source is larger than
99.97%, while on average almost all observed clusters are true. The best-fit
value found is comparable to the density of AGNs and consistent with the recent
HiRes stereo data. In this scenario, the Pierre Auger Observatory will not only
establish the clustering of UHECRs but also determine the density of UHECR
sources within a factor of a few after one year of data taking.Comment: 12 pages, 4 figures; v2 matches version to appea
Ultra-High Energy Cosmic Rays Detected by Auger and AGASA:Corrections for Galactic Magnetic Field Deflections, Source Populations, and Arguments for Multiple-Components
The origin and composition of Ultra-High Energy Cosmic Ray Events (UHECRs)
are under debate. Here we improve constraints on the source population(s) and
compositions of UHECRs by accounting for UHECR deflections within existing
Galactic magnetic field models (GMFs). We used Monte Carlo simulations for
UHECRs detected by the Pierre Auger Observatory and AGASA in order to determine
their outside-the-Galaxy arrival directions, and compared these with Galactic
and extragalactic sources. The simulations, which used UHECR compositions from
protons to Iron and seven models of the ordered GMF, include uncertainties in
the GMF and a turbulent magnetic field. The correlation between UHECRs and
nearby extended radiogalaxies (Nagar & Matulich 2008) remains valid, even
strengthened, within several GMF models. Both the nearest radiogalaxy CenA, and
the nearest radio-extended BL Lac, CGCG 413-019, are likely sources of multiple
UHECRs. The correlation appears to be linked to the presence of the extended
radio source rather than a tracer of an underlying population. It is possible,
but unlikely, that all UHECRs originate in the nearby radiogalaxy CenA. For
light UHECRs about a third of UHECRs can be "matched" to nearby galaxies with
extended radio jets. The remaining UHECRs could also be explained as
originating in extended radiogalaxies if one has at least one of: a large UHECR
mean free path, a high cluster and/or intergalactic magnetic field, a heavy
composition for two-thirds of the detected UHECRs. Several UHECRs have
trajectories which pass close to Galactic magnetars and/or microquasars.
If extended radiogalaxies are, or trace, UHECR sources, the most consistent
models for the ordered GMF are the BS-S and BS-A models; the GMF models of Sun
et al. 2008 are acceptable if a dipole component is added.Comment: to appear in A&
Ultrahigh Energy Nuclei in the Turbulent Galactic Magnetic Field
In this work we study how the turbulent component of the Galactic magnetic
field (GMF) affects the propagation of ultrahigh energy heavy nuclei. We
investigate first how the images of individual sources and of the supergalactic
plane depend on the properties of the turbulent GMF. Then we present a
quantitative study of the impact of the turbulent field on (de-) magnification
of source fluxes, due to magnetic lensing effects. We also show that it is
impossible to explain the Pierre Auger data assuming that all ultrahigh energy
nuclei are coming from Cen A, even in the most favorable case of a strong,
extended turbulent field in the Galactic halo.Comment: 10 pages (2 columns), 8 figures. Published in Astroparticle Physic
- …