1,878 research outputs found
Novel technique for monitoring the performance of the LAT instrument on board the GLAST satellite
The Gamma-ray Large Area Space Telescope (GLAST) is an observatory designed
to perform gamma-ray astronomy in the energy range 20 MeV to 300 GeV, with
supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. GLAST will
be launched at the end of 2007, opening a new and important window on a wide
variety of high energy astrophysical phenomena . The main instrument of GLAST
is the Large Area Telescope (LAT), which provides break-through high-energy
measurements using techniques typically used in particle detectors for collider
experiments. The LAT consists of 16 identical towers in a four-by-four grid,
each one containing a pair conversion tracker and a hodoscopic crystal
calorimeter, all covered by a segmented plastic scintillator anti-coincidence
shield. The scientific return of the instrument depends very much on how
accurately we know its performance, and how well we can monitor it and correct
potential problems promptly. We report on a novel technique that we are
developing to help in the characterization and monitoring of LAT by using the
power of classification trees to pinpoint in a short time potential problems in
the recorded data. The same technique could also be used to evaluate the effect
on the overall LAT performance produced by potential instrumental problems.Comment: 2 pages, 1 figure, manuscript submitted on behalf of the GLAST/LAT
collaboration to First GLAST symposium proceeding
Recommended from our members
The GLAST Large Area Telescope Detector Performance Monitoring
The Large Area Telescope (LAT) is one of two instruments on board the Gamma-ray Large Area Telescope (GLAST), the next generation high energy gamma-ray space telescope. The LAT contains sixteen identical towers in a four-by-four grid. Each tower contains a silicon-strip tracker and a CsI calorimeter that together will give the incident direction and energy of the pair-converting photon in the energy range 20 MeV - 300 GeV. In addition, the instrument is covered by a finely segmented Anti-Coincidence Detector (ACD) to reject charged particle background. Altogether, the LAT contains more than 864k channels in the trackers, 1536 CsI crystals and 97 ACD plastic scintillator tiles and ribbons. Here we detail some of the strategies and methods for how we are planning to monitor the instrument performance on orbit. It builds on the extensive experience gained from Integration & Test and Commissioning of the instrument on ground
Snowmass CF1 Summary: WIMP Dark Matter Direct Detection
As part of the Snowmass process, the Cosmic Frontier WIMP Direct Detection
subgroup (CF1) has drawn on input from the Cosmic Frontier and the broader
Particle Physics community to produce this document. The charge to CF1 was (a)
to summarize the current status and projected sensitivity of WIMP direct
detection experiments worldwide, (b) motivate WIMP dark matter searches over a
broad parameter space by examining a spectrum of WIMP models, (c) establish a
community consensus on the type of experimental program required to explore
that parameter space, and (d) identify the common infrastructure required to
practically meet those goals.Comment: Snowmass CF1 Final Summary Report: 47 pages and 28 figures with a 5
page appendix on instrumentation R&
CDMSlite: A Search for Low-Mass WIMPs using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment
SuperCDMS is an experiment designed to directly detect Weakly Interacting
Massive Particles (WIMPs), a favored candidate for dark matter ubiquitous in
the Universe. In this paper, we present WIMP-search results using a
calorimetric technique we call CDMSlite, which relies on voltage- assisted
Luke-Neganov amplification of the ionization energy deposited by particle
interactions. The data were collected with a single 0.6 kg germanium detector
running for 10 live days at the Soudan Underground Laboratory. A low energy
threshold of 170 eVee (electron equivalent) was obtained, which allows us to
constrain new WIMP-nucleon spin-independent parameter space for WIMP masses
below 6 GeV/c2.Comment: 7 pages, 4 figure
ASCR/HEP Exascale Requirements Review Report
This draft report summarizes and details the findings, results, and
recommendations derived from the ASCR/HEP Exascale Requirements Review meeting
held in June, 2015. The main conclusions are as follows. 1) Larger, more
capable computing and data facilities are needed to support HEP science goals
in all three frontiers: Energy, Intensity, and Cosmic. The expected scale of
the demand at the 2025 timescale is at least two orders of magnitude -- and in
some cases greater -- than that available currently. 2) The growth rate of data
produced by simulations is overwhelming the current ability, of both facilities
and researchers, to store and analyze it. Additional resources and new
techniques for data analysis are urgently needed. 3) Data rates and volumes
from HEP experimental facilities are also straining the ability to store and
analyze large and complex data volumes. Appropriately configured
leadership-class facilities can play a transformational role in enabling
scientific discovery from these datasets. 4) A close integration of HPC
simulation and data analysis will aid greatly in interpreting results from HEP
experiments. Such an integration will minimize data movement and facilitate
interdependent workflows. 5) Long-range planning between HEP and ASCR will be
required to meet HEP's research needs. To best use ASCR HPC resources the
experimental HEP program needs a) an established long-term plan for access to
ASCR computational and data resources, b) an ability to map workflows onto HPC
resources, c) the ability for ASCR facilities to accommodate workflows run by
collaborations that can have thousands of individual members, d) to transition
codes to the next-generation HPC platforms that will be available at ASCR
facilities, e) to build up and train a workforce capable of developing and
using simulations and analysis to support HEP scientific research on
next-generation systems.Comment: 77 pages, 13 Figures; draft report, subject to further revisio
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of
SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a
significance of 38 sigma is found to coincide with SNR W49B. The energy
spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The
luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy
range. There is no indication that the gamma-ray emission comes from a pulsar.
Assuming that the SNR shell is the site of gamma-ray production, the observed
spectrum can be explained either by the decay of neutral pi mesons produced
through the proton-proton collisions or by electron bremsstrahlung. The
calculated energy density of relativistic particles responsible for the LAT
flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either
gamma-ray production mechanism.Comment: 9 pages, 10 figure
Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope
routinely detects the highly dust-absorbed, reddened, and MeV-peaked flat
spectrum radio quasar PKS 1830-211 (z=2.507). Its apparent isotropic gamma-ray
luminosity (E>100 MeV) averaged over 3 years of observations and peaking
on 2010 October 14/15 at 2.9 X 10^{50} erg s^{-1}, makes it among the brightest
high-redshift Fermi blazars. No published model with a single lens can account
for all of the observed characteristics of this complex system. Based on radio
observations, one expects time delayed variability to follow about 25 days
after a primary flare, with flux about a factor 1.5 less. Two large gamma-ray
flares of PKS 1830-211 have been detected by the LAT in the considered period
and no substantial evidence for such a delayed activity was found. This allows
us to place a lower limit of about 6 on the gamma rays flux ratio between the
two lensed images. Swift XRT observations from a dedicated Target of
Opportunity program indicate a hard spectrum and with no significant
correlation of X-ray flux with the gamma-ray variability. The spectral energy
distribution can be modeled with inverse Compton scattering of thermal photons
from the dusty torus. The implications of the LAT data in terms of variability,
the lack of evident delayed flare events, and different radio and gamma-ray
flux ratios are discussed. Microlensing effects, absorption, size and location
of the emitting regions, the complex mass distribution of the system, an
energy-dependent inner structure of the source, and flux suppression by the
lens galaxy for one image path may be considered as hypotheses for
understanding our results.Comment: 14 pages, 6 figures, 2 tables. Accepted by the The Astrophysical
Journal. Corresponding authors: S. Ciprini (ASI ASDC & INAF OAR, Rome,
Italy), S. Buson (INAF Padova & Univ. of Padova, Padova, Italy), J. Finke
(NRL, Washington, DC, USA), F. D'Ammando (INAF IRA, Bologna, Italy
Fermi-LAT observations of the exceptional gamma-ray outbursts of 3C 273 in September 2009
We present the light curves and spectral data of two exceptionally luminous
gamma-ray outburts observed by the Large Area Telescope (LAT) experiment on
board Fermi Gamma-ray Space Telescope from 3C 273 in September 2009. During
these flares, having a duration of a few days, the source reached its highest
gamma-ray flux ever measured. This allowed us to study in some details their
spectral and temporal structures. The rise and decay are asymmetric on
timescales of 6 hours, and the spectral index was significantly harder during
the flares than during the preceding 11 months. We also found that short, very
intense flares put out the same time-integrated energy as long, less intense
flares like that observed in August 2009.Comment: Corresponding authors: E. Massaro, [email protected]; G.
Tosti, [email protected]. 15 pages, 4 figures, published in The
Astrophysical Journal Letters, Volume 714, Issue 1, pp. L73-L78 (2010
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