296 research outputs found
Monte Carlo studies on the sensitivity of the HEGRA imaging atmospheric Cerenkov telescope system in observations of extended gamma-ray sources
In this paper, we present the results of Monte Carlo simulations of
atmospheric showers induced by diffuse gamma rays as detected by the
high-energy gamma ray astronomy (HEGRA) system of five imaging atmospheric
Cerenkov telescopes (IACTs). We have investigated the sensitivity of
observations on extended gamma ray emission over the entire field of view of
the instrument. We discuss a technique to search for extended gamma ray sources
within the field of view of the instrument. We give estimates for HEGRA
sensitivity of observations on extended TeV gamma ray sources.Comment: 21 pages, 7 figures, accepted for publication in "Journal of Physics
G: Nuclear and Particle Physics
Comparison of techniques to reconstruct VHE gamma-ray showers from multiple stereoscopic Cherenkov images
For air showers observed simultaneously by more than two imaging atmospheric
Cherenkov telescopes, the shower geometry is overconstrained by the images and
image information should be combined taking into account the quality of the
images. Different algorithms are discussed and tested experimentally using data
obtained from observations of Mkn 501 with the HEGRA IACT system. Most of these
algorithms provide an estimate of the accuracy of the reconstruction of shower
geometry on an event-by-event basis, allowing, e.g., to select higher-quality
subsamples for precision measurements.Comment: 14 Pages, 6 figures, Late
Untersuchung der ausgedehnten galaktischen Region im Laengenbereich zwischen 37 Grad und 43 Grad auf diffuse Gamma-Strahlung und Punktquellen im Energiebereich oberhalb 1 TeV mit dem HEGRA-Tscherenkov-Teleskopsystem
Mit dem von der HEGRA-Kollaboration betriebenem stereoskopischen Tscherenkov-Teleskop-System auf der Kanarischen Insel La Palma wurde im Sommer 1999 eine Durchmusterung der galaktischen Region zwischen und bei einer Energieschwelle von 1 TeV durchgef'uhrt. Ziel war hierbei die Suche nach diffuser Emission von -Strahlung aus der galaktischen Scheibe, und die Suche nach -Emission von Punktquellen. Dargestellt werden die Beobachtungskampagne, die Methoden der Analyse und detaillierte Monte-Carlo-Simulationen zum Verst'andnis der Akzeptanz f'ur elektromagnetische Schauer 'uber das Gesichtsfeld des Teleskopsystems. Es wurde keine Emission aus der galaktischen Scheibe nachgewiesen und keine Punktquelle in der beobachteten Region entdeckt. Die abgeleiteten oberen Grenzen f'ur die Punktquellen sind in der Gr'o'senordnung 1/10 des Flu'ses vom Krebsnebel. Die obere Grenze mit einem Vertrauensintervall von > auf die diffuse Emission aus der galaktischen Scheibe wird zu TeV ph cm s sr abgeleitet
Improved energy resolution for VHE gamma-ray astronomy with systems of Cherenkov telescopes
We present analysis techniques to improve the energy resolution of
stereoscopic systems of imaging atmospheric Cherenkov telescopes, using the
HEGRA telescope system as an example. The techniques include (i) the
determination of the height of the shower maximum, which is then taken into
account in the energy determination, and (ii) the determination of the location
of the shower core with the additional constraint that the direction of the
gamma rays is known a priori. This constraint can be applied for gamma-ray
point sources, and results in a significant improvement in the localization of
the shower core, which translates into better energy resolution. Combining both
techniques, the HEGRA telescopes reach an energy resolution between 9% and 12%,
over the entire energy range from 1 TeV to almost 100 TeV. Options for further
improvements of the energy resolution are discussed.Comment: 13 Pages, 7 figures, Latex. Astroparticle Physics, in pres
Statistical Classification Techniques for Photometric Supernova Typing
Future photometric supernova surveys will produce vastly more candidates than
can be followed up spectroscopically, highlighting the need for effective
classification methods based on lightcurves alone. Here we introduce boosting
and kernel density estimation techniques which have minimal astrophysical
input, and compare their performance on 20,000 simulated Dark Energy Survey
lightcurves. We demonstrate that these methods are comparable to the best
template fitting methods currently used, and in particular do not require the
redshift of the host galaxy or candidate. However both methods require a
training sample that is representative of the full population, so typical
spectroscopic supernova subsamples will lead to poor performance. To enable the
full potential of such blind methods, we recommend that representative training
samples should be used and so specific attention should be given to their
creation in the design phase of future photometric surveys.Comment: 19 pages, 41 figures. No changes. Additional material and summary
video available at
http://cosmoaims.wordpress.com/2010/09/30/boosting-for-supernova-classification
Search for point sources and diffuse emission from the Galactic plane with the HEGRA-IACT-system
The HEGRA-IACT-system with a FoV of ~1.5 deg radius has been used for
surveying one quater of the Galactic disc in respect to point sources,
moderately extended sources and for diffuse emission in the energy range above
1 TeV. In total 140 h of good observation time were accumulated.
No new source has been discoverd. Limits on the level of 20% or lower of the
Crab flux on about 87 potential sources like SNR, Pulsars and EGRET sources are
derived. A limit on the diffuse emission is given on the level of dPhi/dE(E=1
TeV) = 6.1 10^-15 ph cm-2 s-1 sr-1 Mev-1 resulting in a lower limit of 2.5 on
the spectral index for the extrapolation of the meassured EGRET flux for the
diffuse emission.Comment: 4 pages, 5 figures, 1 table, Submitted to ICRC, Hambur
Photometric Supernova Cosmology with BEAMS and SDSS-II
Supernova cosmology without spectroscopic confirmation is an exciting new
frontier which we address here with the Bayesian Estimation Applied to Multiple
Species (BEAMS) algorithm and the full three years of data from the Sloan
Digital Sky Survey II Supernova Survey (SDSS-II SN). BEAMS is a Bayesian
framework for using data from multiple species in statistical inference when
one has the probability that each data point belongs to a given species,
corresponding in this context to different types of supernovae with their
probabilities derived from their multi-band lightcurves. We run the BEAMS
algorithm on both Gaussian and more realistic SNANA simulations with of order
10^4 supernovae, testing the algorithm against various pitfalls one might
expect in the new and somewhat uncharted territory of photometric supernova
cosmology. We compare the performance of BEAMS to that of both mock
spectroscopic surveys and photometric samples which have been cut using typical
selection criteria. The latter typically are either biased due to contamination
or have significantly larger contours in the cosmological parameters due to
small data-sets. We then apply BEAMS to the 792 SDSS-II photometric supernovae
with host spectroscopic redshifts. In this case, BEAMS reduces the area of the
(\Omega_m,\Omega_\Lambda) contours by a factor of three relative to the case
where only spectroscopically confirmed data are used (297 supernovae). In the
case of flatness, the constraints obtained on the matter density applying BEAMS
to the photometric SDSS-II data are \Omega_m(BEAMS)=0.194\pm0.07. This
illustrates the potential power of BEAMS for future large photometric supernova
surveys such as LSST.Comment: 25 pages, 15 figures, submitted to Ap
Dark matter scaling relations in intermediate z haloes
We investigate scaling relations between the dark matter (DM) halo model
parameters for a sample of intermediate redshift early - type galaxies (ETGs)
resorting to a combined analysis of Einstein radii and aperture velocity
dispersions. Modeling the dark halo with a Navarro - Frenk - White profile and
assuming a Salpeter initial mass function (IMF) to estimate stellar masses, we
find that the column density and the Newtonian acceleration within
the halo characteristic radius and effective radius are not
universal quantities, but correlate with the luminosity , the stellar mass
and the halo mass , contrary to recent claims in the
literature. We finally discuss a tight correlation among the DM mass
within the effective radius , the stellar mass
and itself. The slopes of the scaling relations
discussed here strongly depend, however, on the DM halo model and the IMF
adopted so that these ingredients have to be better constrained in order to
draw definitive conclusions on the DM scaling relations for ETGs.Comment: 8 pages, 1 figure, 4 tables, MNRAS submitted version (including
corrections after the referee report
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