1,424 research outputs found
FlashCam: A fully digital camera for CTA telescopes
The future Cherenkov Telescope Array (CTA) will consist of several tens of
telescopes of different mirror sizes. CTA will provide next generation
sensitivity to very high energy photons from few tens of GeV to >100 TeV.
Several focal plane instrumentation options are currently being evaluated
inside the CTA consortium. In this paper, the current status of the FlashCam
prototyping project is described. FlashCam is based on a fully digital camera
readout concept and features a clean separation between photon detector plane
and signal digitization/triggering electronics.Comment: In Proceedings of the 2012 Heidelberg Symposium on High Energy
Gamma-Ray Astronomy. All CTA contributions at arXiv:1211.184
Mirror Position Determination for the Alignment of Cherenkov Telescopes
Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with
large apertures to map the faint Cherenkov light emitted in extensive air
showers onto their image sensors. Segmented reflectors fulfill these needs
using mass produced and light weight mirror facets. However, as the overall
image is the sum of the individual mirror facet images, alignment is important.
Here we present a method to determine the mirror facet positions on a segmented
reflector in a very direct way. Our method reconstructs the mirror facet
positions from photographs and a laser distance meter measurement which goes
from the center of the image sensor plane to the center of each mirror facet.
We use our method to both align the mirror facet positions and to feed the
measured positions into our IACT simulation. We demonstrate our implementation
on the 4 m First Geiger-mode Avalanche Cherenkov Telescope (FACT).Comment: 11 figures, small ray tracing performance simulation, and
implementation demonstratio
Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope
The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of
the performance of silicon photo detectors in Cherenkov Astronomy. For more
than two years it is operated on La Palma, Canary Islands (Spain), for the
purpose of long-term monitoring of astrophysical sources. For this, the
performance of the photo detectors is crucial and therefore has been studied in
great detail. Special care has been taken for their temperature and voltage
dependence implementing a correction method to keep their properties stable.
Several measurements have been carried out to monitor the performance. The
measurements and their results are shown, demonstrating the stability of the
gain below the percent level. The resulting stability of the whole system is
discussed, nicely demonstrating that silicon photo detectors are perfectly
suited for the usage in Cherenkov telescopes, especially for long-term
monitoring purpose
FACT - Monitoring Blazars at Very High Energies
The First G-APD Cherenkov Telescope (FACT) was built on the Canary Island of
La Palma in October 2011 as a proof of principle for silicon based photosensors
in Cherenkov Astronomy. The scientific goal of the project is to study the
variability of active galatic nuclei (AGN) at TeV energies. Observing a small
sample of TeV blazars whenever possible, an unbiased data sample is collected.
This allows to study the variability of the selected objects on timescales from
hours to years. Results from the first three years of monitoring will be
presented. To provide quick flare alerts to the community and trigger
multi-wavelength observations, a quick look analysis has been installed on-site
providing results publicly online within the same night. In summer 2014,
several flare alerts were issued. Results of the quick look analysis are
summarized.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Data compression for the First G-APD Cherenkov Telescope
The First Geiger-mode Avalanche photodiode (G-APD) Cherenkov Telescope (FACT)
has been operating on the Canary island of La Palma since October 2011.
Operations were automated so that the system can be operated remotely. Manual
interaction is required only when the observation schedule is modified due to
weather conditions or in case of unexpected events such as a mechanical
failure. Automatic operations enabled high data taking efficiency, which
resulted in up to two terabytes of FITS files being recorded nightly and
transferred from La Palma to the FACT archive at ISDC in Switzerland. Since
long term storage of hundreds of terabytes of observations data is costly, data
compression is mandatory. This paper discusses the design choices that were
made to increase the compression ratio and speed of writing of the data with
respect to existing compression algorithms.
Following a more detailed motivation, the FACT compression algorithm along
with the associated I/O layer is discussed. Eventually, the performances of the
algorithm is compared to other approaches.Comment: 17 pages, accepted to Astronomy and Computing special issue on
astronomical file format
FACT -- Operation of the First G-APD Cherenkov Telescope
Since more than two years, the First G-APD Cherenkov Telescope (FACT) is
operating successfully at the Canary Island of La Palma. Apart from its purpose
to serve as a monitoring facility for the brightest TeV blazars, it was built
as a major step to establish solid state photon counters as detectors in
Cherenkov astronomy.
The camera of the First G-APD Cherenkov Telesope comprises 1440 Geiger-mode
avalanche photo diodes (G-APD aka. MPPC or SiPM) for photon detection. Since
properties as the gain of G-APDs depend on temperature and the applied voltage,
a real-time feedback system has been developed and implemented. To correct for
the change introduced by temperature, several sensors have been placed close to
the photon detectors. Their read out is used to calculate a corresponding
voltage offset. In addition to temperature changes, changing current introduces
a voltage drop in the supporting resistor network. To correct changes in the
voltage drop introduced by varying photon flux from the night-sky background,
the current is measured and the voltage drop calculated. To check the stability
of the G-APD properties, dark count spectra with high statistics have been
taken under different environmental conditions and been evaluated.
The maximum data rate delivered by the camera is about 240 MB/s. The recorded
data, which can exceed 1 TB in a moonless night, is compressed in real-time
with a proprietary loss-less algorithm. The performance is better than gzip by
almost a factor of two in compression ratio and speed. In total, two to three
CPU cores are needed for data taking. In parallel, a quick-look analysis of the
recently recorded data is executed on a second machine. Its result is publicly
available within a few minutes after the data were taken.
[...]Comment: 19th IEEE Real-Time Conference, Nara, Japan (2014
FACT -- The G-APD revolution in Cherenkov astronomy
Since two years, the FACT telescope is operating on the Canary Island of La
Palma. Apart from its purpose to serve as a monitoring facility for the
brightest TeV blazars, it was built as a major step to establish solid state
photon counters as detectors in Cherenkov astronomy. The camera of the First
G-APD Cherenkov Telesope comprises 1440 Geiger-mode avalanche photo diodes
(G-APD), equipped with solid light guides to increase the effective light
collection area of each sensor. Since no sense-line is available, a special
challenge is to keep the applied voltage stable although the current drawn by
the G-APD depends on the flux of night-sky background photons significantly
varying with ambient light conditions. Methods have been developed to keep the
temperature and voltage dependent response of the G-APDs stable during
operation. As a cross-check, dark count spectra with high statistics have been
taken under different environmental conditions. In this presentation, the
project, the developed methods and the experience from two years of operation
of the first G-APD based camera in Cherenkov astronomy under changing
environmental conditions will be presented.Comment: Proceedings of the Nuclear Science Symposium and Medical Imaging
Conference (IEEE-NSS/MIC), 201
Cherenkov Telescopes as Optical Telescopes for Bright Sources: Today's Specialised Thirty Metre Telescopes?
Imaging Atmospheric Cherenkov Telescopes (IACTs) use large-aperture (~ 10 -
30 m) optical telescopes with arcminute angular resolution to detect TeV
gamma-rays in the atmosphere. I show that IACTs are well-suited for optical
observations of bright sources (V <= 8 - 10), because these sources are
brighter than the sky background. Their advantages are especially great on
rapid time-scales. Thus, IACTs are ideal for studying many phenomena optically,
including transiting exoplanets and the brightest gamma-ray bursts. In
principle, an IACT could achieve millimagnitude photometry of these objects
with second-long exposures. I also consider the potential for optical
spectroscopy with IACTs, finding that their poor angular resolution limits
their usefulness for high spectral resolutions, unless complex instruments are
developed. The high photon collection rate of IACTs is potentially useful for
precise polarimetry. Finally, I briefly discuss the broader possibilities of
extremely large, low resolution telescopes, including a 10" resolution
telescope and spaceborne telescopes.Comment: 10 pages, 3 figures, accepted by MNRA
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