268 research outputs found
Neural networks for gamma-hadron separation in MAGIC
Neural networks have proved to be versatile and robust for particle
separation in many experiments related to particle astrophysics. We apply these
techniques to separate gamma rays from hadrons for the MAGIC Cerenkov
Telescope. Two types of neural network architectures have been used for the
classi cation task: one is the MultiLayer Perceptron (MLP) based on supervised
learning, and the other is the Self-Organising Tree Algorithm (SOTA), which is
based on unsupervised learning. We propose a new architecture by combining
these two neural networks types to yield better and faster classi cation
results for our classi cation problem.Comment: 6 pages, 4 figures, to be published in the Proceedings of the 6th
International Symposium ''Frontiers of Fundamental and Computational
Physics'' (FFP6), Udine (Italy), Sep. 26-29, 200
The MAGIC Experiment and Its First Results
With its diameter of 17m, the MAGIC telescope is the largest Cherenkov
detector for gamma ray astrophysics. It is sensitive to photons above an energy
of 30 GeV. MAGIC started operations in October 2003 and is currently taking
data. This report summarizes its main characteristics, its rst results and its
potential for physics.Comment: 6 pages, 3 figures, to be published in the Proceedings of the 6th
International Symposium ''Frontiers of Fundamental and Computational
Physics'' (FFP6), Udine (Italy), Sep. 26-29, 200
The magnetar emission in the IR band: the role of magnetospheric currents
There is a general consensus about the fact that the magnetar scenario
provides a convincing explanation for several of the observed properties of the
Anomalous X-ray Pulsars and the Soft Gamma Repeaters. However, the origin of
the emission observed at low energies is still an open issue. We present a
quantitative model for the emission in the optical/infrared band produced by
curvature radiation from magnetospheric charges, and compare results with
current magnetars observations.Comment: 6 Pages, 2 Figures. Astrophysics and Space Science, in press.
Proceedings of the ICREA Workshop on The High-Energy Emission from Pulsars
and their Systems, Sant Cugat, April 12-16 201
A novel background reduction strategy for high level triggers and processing in gamma-ray Cherenkov detectors
Gamma ray astronomy is now at the leading edge for studies related both to
fundamental physics and astrophysics. The sensitivity of gamma detectors is
limited by the huge amount of background, constituted by hadronic cosmic rays
(typically two to three orders of magnitude more than the signal) and by the
accidental background in the detectors. By using the information on the
temporal evolution of the Cherenkov light, the background can be reduced. We
will present here the results obtained within the MAGIC experiment using a new
technique for the reduction of the background. Particle showers produced by
gamma rays show a different temporal distribution with respect to showers
produced by hadrons; the background due to accidental counts shows no
dependence on time. Such novel strategy can increase the sensitivity of present
instruments.Comment: 4 pages, 3 figures, Proc. of the 9th Int. Syposium "Frontiers of
Fundamental and Computational Physics" (FFP9), (AIP, Melville, New York,
2008, in press
Coherent Curvature Radiation and Proton Counterflow in the Pulsar Magnetosphere
In the proton counterflow model of a pulsar magnetosphere that we have
recently proposed, non-relativistic protons are supplied from the magnetosphere
to flow toward the pulsar surface and screen an electric field above the polar
cap region. In this Letter, we show that the proton counterflow is also
suitable for the bunching of pair plasma. The two-stream instability is easily
excited and can produce bunches of pairs with a relevant length scale to emit
coherent curvature radiation.Comment: 11pages, 1 figur
Observation of the moon shadow using a new reconstruction technique in the CLUE experiment
The CLUE experiment, located in La Palma island at 2200 m a.s.l., is an array of 3×3 telescope, detecting the UV
(190–230 nm) ˇCerenkov light produced by atmospheric showers. Due to the higher atmospheric absorption in the UV range than in the visible one, CLUE cannot apply existing algorithms normally used in IACT experiments to determine primary cosmic ray direction. In this paper we present a new method developed by CLUE. The algorithm performances were evaluated using simulated showers. CLUE experiment collected data in the last two years pointing to AGN sources and to Moon. The preliminary results obtained using the new technique on Crab Nebula and on Markarian 421 were presented in a previous paper. Here, we present the preliminary observation of Moon Shadow employing the new method. As described in the paper, we expect in a near future improvements on AGN sources and on Moon Shadow measurement
First bounds on the very high energy gamma-ray emission from Arp 220
Using the Major Atmospheric Gamma Imaging Cherenkov Telescope (MAGIC), we
have observed the nearest ultra-luminous infrared galaxy Arp 220 for about 15
hours. No significant signal was detected within the dedicated amount of
observation time. The first upper limits to the very high energy -ray
flux of Arp 220 are herein reported and compared with theoretical expectations.Comment: Accepted for publication in Ap
Observation of Pulsed Gamma-rays Above 25 GeV from the Crab Pulsar with MAGIC
One fundamental question about pulsars concerns the mechanism of their pulsed
electromagnetic emission. Measuring the high-end region of a pulsar's spectrum
would shed light on this question. By developing a new electronic trigger, we
lowered the threshold of the Major Atmospheric gamma-ray Imaging Cherenkov
(MAGIC) telescope to 25 GeV. In this configuration, we detected pulsed
gamma-rays from the Crab pulsar that were greater than 25 GeV, revealing a
relatively high cutoff energy in the phase-averaged spectrum. This indicates
that the emission occurs far out in the magnetosphere, hence excluding the
polar-cap scenario as a possible explanation of our measurement. The high
cutoff energy also challenges the slot-gap scenario.Comment: Slight modification of the analysis: Fitting a more general function
to the combined data set of COMPTEL, EGRET and MAGIC. Final result and
conclusion is unchange
First bounds on the high-energy emission from isolated Wolf-Rayet binary systems
High-energy gamma-ray emission is theoretically expected to arise in tight
binary star systems (with high mass loss and high velocity winds), although the
evidence of this relationship has proven to be elusive so far. Here we present
the first bounds on this putative emission from isolated Wolf-Rayet (WR) star
binaries, WR 147 and WR 146, obtained from observations with the MAGIC
telescope.Comment: (Authors are the MAGIC Collaboration.) Manuscript in press at The
Astrophysical Journal Letter
MAGIC observations of very high energy gamma-rays from HESS J1813-178
Recently, the HESS collaboration has reported the detection of gamma-ray
emission above a few hundred GeV from eight new sources located close to the
Galactic Plane. The source HESS J1813-178 has sparked particular interest, as
subsequent radio observations imply an association with SNR G12.82-0.02.
Triggered by the detection in VHE gamma-rays, a positionally coincident source
has also been found in INTEGRAL and ASCA data. In this Letter we present MAGIC
observations of HESS J1813-178, resulting in the detection of a differential
gamma-ray flux consistent with a hard-slope power law, described as dN/(dA dt
dE) = (3.3+/-0.5)*10^{-12} (E/TeV)^{-2.1+/-0.2} cm^(-2)s^(-1)TeV^(-1). We
briefly discuss the observational technique used, the procedure implemented for
the data analysis, and put this detection in the perspective of multifrequency
observations.Comment: Accepted by ApJ Letter
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