119 research outputs found
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
Black hole entropy in 3D gravity with torsion
The role of torsion in quantum three-dimensional gravity is investigated by
studying the partition function of the Euclidean theory in Riemann-Cartan
spacetime. The entropy of the black hole with torsion is found to differ from
the standard Bekenstein-Hawking result, but its form is in complete agreement
with the first law of black hole thermodynamics.Comment: 17 pages, RevTeX, minor revision
Does hypoglycemia following a glucose challenge test identify a high risk pregnancy?
<p>Abstract</p> <p>Objective</p> <p>An association between maternal hypoglycemia during pregnancy with fetal growth restriction and overall perinatal mortality has been reported. In a retrospective pilot study we found that hypoglycemia was linked with a greater number of special care/neonatal intensive care unit admissions and approached significance in the number of women who developed preeclampsia. That study was limited by its retrospective design, a narrow patient population and the inability to perform multivariate analysis because of the limitations in the data points collected. This study was undertaken to compare the perinatal outcome in pregnancies with hyoglycemia following a glucose challenge test (GCT) to pregnancies with a normal GCT.</p> <p>Methods</p> <p>Obstetric patients (not pre-gestational diabetics or gestational diabetes before 24 weeks were eligible. Women with a 1 hour glucose ≤ 88 mg/dL (4.8 m/mol) following a 50-gram oral GCT were matched with the next patient with a 1 hour glucose of 89–139 mg/dL. Pregnancy outcomes were evaluated.</p> <p>Results</p> <p>Over 22 months, 436 hypoglycemic patients and 434 normal subjects were identified. Hypoglycemia was increased in women < 25 (p = 0.003) and with pre-existing medical conditions (p < 0.001). Hypoglycemia was decreased if pre-pregnancy BMI ≥ 30 (p = 0.008).</p> <p>Preeclampsia/eclampsia was more common in hypoglycemic women. (OR = 3.13, 95% CI 1.51 – 6.51, p = 0.002) but not other intrapartum and perinatal outcomes.</p> <p>Conclusion</p> <p>Hypoglycemic patients are younger, have reduced pre-pregnancy weight, lower BMIs, and are more likely to develop preeclampsia than normoglycemic women.</p
MAGIC Upper Limits for two Milagro-detected, Bright Fermi Sources in the Region of SNR G65.1+0.6
We report on the observation of the region around supernova remnant G65.1+0.6
with the stand-alone MAGIC-I telescope. This region hosts the two bright GeV
gamma-ray sources 1FGL J1954.3+2836 and 1FGL J1958.6+2845. They are identified
as GeV pulsars and both have a possible counterpart detected at about 35 TeV by
the Milagro observatory. MAGIC collected 25.5 hours of good quality data, and
found no significant emission in the range around 1 TeV. We therefore report
differential flux upper limits, assuming the emission to be point-like (<0.1
deg) or within a radius of 0.3 deg. In the point-like scenario, the flux limits
around 1 TeV are at the level of 3 % and 2 % of the Crab Nebula flux, for the
two sources respectively. This implies that the Milagro emission is either
extended over a much larger area than our point spread function, or it must be
peaked at energies beyond 1 TeV, resulting in a photon index harder than 2.2 in
the TeV band.Comment: 8 pages, 3 figures, 1 tabl
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
Upper limit for gamma-ray emission above 140 GeV from the dwarf spheroidal galaxy Draco
The nearby dwarf spheroidal galaxy Draco with its high mass to light ratio is
one of the most auspicious targets for indirect dark matter searches.
Annihilation of hypothetical DM particles can result in high-energy gamma-rays,
e.g. from neutralino annihilation in the supersymmetric framework. With the
MAGIC telescope a search for a possible DM signal originating from Draco was
performed during 2007. The analysis of the data results in a flux upper limit
of 1.1x10^-11 photons cm^-2 sec^-1 for photon energies above 140 GeV, assuming
a point like source. Furthermore, a comparison with predictions from
supersymmetric models is given. While our results do not constrain the mSUGRA
phase parameter space, a very high flux enhancement can be ruled out.Comment: Accepted for publication by Astrophysical Journa
Neutrinos in a gravitational background: a test for the universality of the gravitational interaction
In this work we propose an extended formulation for the interaction between
neutrinos and gravitational fields. It is based on the parametrized
post-Newtonian aproach, and includes a violation of the universality of the
gravitational interaction which is non diagonal in the weak flavor space. We
find new effects that are not considered in the standard scenario for violation
of the equivalence principle. They are of the same order as the effects
produced by the Newtonian potential, but they are highly directional dependent
and could provide a very clean test of that violation. Phenomenological
consequences are briefly discussed.Comment: 18 pages, revtex, no figure
Simultaneous multi-frequency observation of the unknown redshift blazar PG 1553+113 in March-April 2008
The blazar PG 1553+113 is a well known TeV gamma-ray emitter. In this paper,
we determine its spectral energy distribution using simultaneous
multi-frequency data in order to study its emission processes. An extensive
campaign was carried out between March and April 2008, where optical, X-ray,
high-energy (HE) gamma-ray, and very-high-energy (VHE) gamma-ray data were
obtained with the KVA, Abastumani, REM, RossiXTE/ASM, AGILE and MAGIC
telescopes, respectively. This is the first simultaneous broad-band (i.e.,
HE+VHE) gamma-ray observation, though AGILE did not detect the source. We
combine data to derive source's spectral energy distribution and interpret its
double peaked shape within the framework of a synchrotron self compton modelComment: 5 pages, 2 figures, publishe
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