81 research outputs found
FACT - Threshold prediction for higher duty cycle and improved scheduling
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise
a higher photon detection efficiency, more robustness and higher precision than
photo-multiplier tubes. Being operated during different light-conditions, the
threshold settings of a Cherenkov telescope have to be adapted to feature the
lowest possible threshold but also an efficient suppression of triggers from
night-sky background photons. Usually this threshold is set either by
experience or a mini-ratescan. Since the measured current through the sensors
is directly correlated with the noise level, the current can be used to set the
best threshold at any time. Due to the correlation between the physical
threshold and the final energy threshold, the current can also be used as a
measure for the energy threshold of any observation. This presentation
introduces a method which uses the properties of the moon and the source
position to predict the currents and the corresponding energy threshold for
every upcoming observation allowing to adapt the observation schedule
accordingly
FACT - Long-term stability and observations during strong Moon light
The First G-APD Cherenkov Telescope (FACT) is the first Cherenkov telescope
equipped with a camera made of silicon photon detectors (G-APD aka. SiPM).
Since October 2011, it is regularly taking data on the Canary Island of La
Palma. G-APDs are ideal detectors for Cherenkov telescopes as they are robust
and stable. Furthermore, the insensitivity of G-APDs towards strong ambient
light allows to conduct observations during bright Moon and twilight. This gain
in observation time is essential for the long-term monitoring of bright TeV
blazars. During the commissioning phase, hundreds of hours of data (including
data from the the Crab Nebula) were taken in order to understand the
performance and sensitivity of the instrument. The data cover a wide range of
observation conditions including different weather conditions, different zenith
angles and different light conditions (ranging from dark night to direct full
Moon). We use a new parmetrisation of the Moon light background to enhance our
scheduling and to monitor the atmosphere. With the data from 1.5 years, the
long-term stability and the performance of the camera during Moon light is
studied and compared to that achieved with photomultiplier tubes so far.Comment: 3 pages, 3 figures, FACT Contribution to the 33rd International
Cosmic Ray Conference (ICRC), Rio de Janeir
FACT - How stable are the silicon photon detectors?
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise
a higher photon detection efficiency, more robustness and higher precision than
photo-multiplier tubes. Since the properties of G-APDs depend on auxiliary
parameters like temperature, a feedback system adapting the applied voltage
accordingly is mandatory.
In this presentation, the feedback system, developed and in operation for
FACT, is presented. Using the extraction of a single photon-equivalent (pe)
spectrum as a reference, it can be proven that the sensors can be operated with
very high precision. The extraction of the single-pe, its spectrum up to
10\,pe, its properties and their precision, as well as their long-term behavior
during operation are discussed. As a by product a single pulse template is
obtained. It is shown that with the presented method, an additional external
calibration device can be omitted. The presented method is essential for the
application of G-APDs in future projects in Cherenkov astronomy and is supposed
to result in a more stable and precise operation than possible with
photo-multiplier tubes
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 -- 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
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
Der diskrete Charme der Bourgeoisie - Ein Beitrag zur Soziologie des modernen WirtschaftsbĂĽrgertums
Entgegen der These der Auflösungserscheinungen des Bürgertums stellt der Autor die Annahme auf den Prüfstand, dass wir es nach wie vor mit gesellschaftlichen Fraktionierungen bürgerlicher Lebensweisen zu tun haben. Am Beispiel autobiographischer Schriften von deutschen Topmanagern stellt der Text ein modernes Verständnis des Wirtschaftsbürgertums vor, das organisational (durch die Karrieremechanismen der Organisation) und institutionell (im Feld der Wirtschaft) verankert ist. Die moderne Sozialformation des Wirtschaftsbürgertums ist nur noch auf der Grundlage von Organisationen denkbar. Sie lässt sich, jenseits von Klasse und Stand, als Positionselite beschreiben. Anhand der Autobiographien lässt sich die Reproduktion dieser Elite auf Basis einer engen Verknüpfung zwischen familialer Herkunft, an organisationale Karrieren gebundene Leistungsbereitschaft und hoher formaler Bildung nachzeichnen. Die Abgrenzung in der Statusreproduktion zwischen Bildungs- und Wirtschaftsbürgertum weist der Autor am jeweiligen Verhältnis zur Bildung nach; zwar können beide einen hohen Bildungsgrad in Form von Bildungspatenten nachweisen, doch im Falle des Wirtschaftsbürgertums herrscht ein instrumentelles Verhältnis zur Bildung vor. Der hohe Bildungsgrad folgt hier dem Bedürfnis, den Status mittels formaler Bildung abzusichern und damit die Gefahr der eigenen Austauschbarkeit - als Personal der Organisation - zu kompensieren. Der Text macht außerdem generationale Effekte sichtbar; insbesondere indem er darlegt, inwieweit der "moderne Manager" einerseits in der Betonung seines Status seinen Vorgängern gleicht und sich doch gleichzeitig in der Art der Unternehmensführung abgrenzt - indem er bspw. die Managementkonzepte seiner Zeit aufgreift
Design and Operation of FACT -- The First G-APD Cherenkov Telescope
The First G-APD Cherenkov Telescope (FACT) is designed to detect cosmic
gamma-rays with energies from several hundred GeV up to about 10 TeV using the
Imaging Atmospheric Cherenkov Technique. In contrast to former or existing
telescopes, the camera of the FACT telescope is comprised of solid-state
Geiger-mode Avalanche Photodiodes (G-APD) instead of photomultiplier tubes for
photo detection. It is the first full-scale device of its kind employing this
new technology. The telescope is operated at the Observatorio del Roque de los
Muchachos (La Palma, Canary Islands, Spain) since fall 2011. This paper
describes in detail the design, construction and operation of the system,
including hardware and software aspects. Technical experiences gained after one
year of operation are discussed and conclusions with regard to future projects
are drawn.Comment: Corresponding authors: T. Bretz and Q. Weitze
Altered localisation of the copper efflux transporters ATP7A and ATP7B associated with cisplatin resistance in human ovarian carcinoma cells
Metals in Catalysis, Biomimetics & Inorganic Material
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