2,583 research outputs found
The Blackholic energy and the canonical Gamma-Ray Burst IV: the "long", "genuine short" and "fake - disguised short" GRBs
(Shortened) [...] After recalling the basic features of the "fireshell
model", we emphasize the following novel results: 1) the interpretation of the
X-ray flares in GRB afterglows as due to the interaction of the optically thin
fireshell with isolated clouds in the CircumBurst Medium (CBM); 2) an
interpretation as "fake - disguised" short GRBs of the GRBs belonging to the
class identified by Norris & Bonnell [...] consistent with an origin from the
final coalescence of a binary system in the halo of their host galaxies with
particularly low CBM density [...]; 3) the first attempt to study a genuine
short GRB with the analysis of GRB 050509B, that reveals indeed still an open
question; 4) the interpretation of the GRB-SN association in the case of GRB
060218 via the "induced gravitational collapse" process; 5) a first attempt to
understand the nature of the "Amati relation", a phenomenological correlation
between the isotropic-equivalent radiated energy of the prompt emission E_{iso}
with the cosmological rest-frame \nu F_{\nu} spectrum peak energy E_{p,i}. In
addition, recent progress on the thermalization of the electron-positron plasma
close to their formation phase, as well as the structure of the electrodynamics
of Kerr-Newman Black Holes are presented. An outlook for possible explanation
of high-energy phenomena in GRBs to be expected from the AGILE and the Fermi
satellites are discussed. As an example of high energy process, the work by
Enrico Fermi dealing with ultrarelativistic collisions is examined. It is clear
that all the GRB physics points to the existence of overcritical
electrodynamical fields. In this sense we present some progresses on a unified
approach to heavy nuclei and neutron stars cores, which leads to the existence
of overcritical fields under the neutron star crust.Comment: 68 pages, 50 figures, in the Proceedings of the XIII Brazilian School
on Cosmology and Gravitation, M. Novello, S.E. Perez-Bergliaffa, editor
The canonical GRB scenario
The canonical GRB scenario implied by the fireshell model is briefly summarized
Theory of photospheric emission from relativistic outflows
In this paper we reexamine the optical depth of ultrarelativistic spherically
symmetric outflows and reevaluate the photospheric radius for each model during
both the acceleration and coasting phases. It is shown that for both the wind
and the shell models there are two asymptotic solutions for the optical depth
during the coasting phase of the outflow. In particular we show that quite
counterintuitively a geometrically thin shell may appear as a thick wind for
photons propagating inside it. For this reason we introduce notions of photon
thick and photon thin outflows, which appear more general and better physically
motivated with respect to winds and shells. Photosphere of relativistic outflow
is a dynamic surface. We study its geometry and find that the photosphere of
photon thin outflow has always a convex shape, while in the photon thick one it
is initially convex (there is always a photon thin layer in any outflow) and
then it becomes concave asymptotically approaching the photosphere of an
infinitely long wind. We find that both instantaneous and time integrated
observed spectra are very close to the thermal one for photon thick outflows,
in line with existing studies. It is our main finding that the photospheric
emission from the photon thin outflow produces non thermal time integrated
spectra, which may be described by the Band function well known in the GRB
literature. We find that energetic GRBs should produce photon thin outflows
with photospheric emission lasting less than one second for the total energy
erg and baryonic loading parameter . It means
that only time integrated spectra may be observed from such GRBs.Comment: Revision of the previous version, new effect is discussed.
Conclusions remain unchange
Ageing test of the ATLAS RPCs at X5-GIF
An ageing test of three ATLAS production RPC stations is in course at X5-GIF,
the CERN irradiation facility. The chamber efficiencies are monitored using
cosmic rays triggered by a scintillator hodoscope. Higher statistics
measurements are made when the X5 muon beam is available. We report here the
measurements of the efficiency versus operating voltage at different source
intensities, up to a maximum counting rate of about 700Hz/cm^2. We describe the
performance of the chambers during the test up to an overall ageing of 4 ATLAS
equivalent years corresponding to an integrated charge of 0.12C/cm^2, including
a safety factor of 5.Comment: 4 pages. Presented at the VII Workshop on Resistive Plate Chambers
and Related Detectors; Clermont-Ferrand October 20th-22nd, 200
The Study of TeV Variability and Duty Cycle of Mrk 421 from 3 Years of Observations with the Milagro Observatory
TeV flaring activity with time scales as short as tens of minutes and an
orphan TeV flare have been observed from the blazar Markarian 421 (Mrk 421).
The TeV emission from Mrk 421 is believed to be produced by leptonic
synchrotron self-Compton (SSC) emission. In this scenario, correlations between
the X-ray and the TeV fluxes are expected, TeV orphan flares are hardly
explained and the activity (measured as duty cycle) of the source at TeV
energies is expected to be equal or less than that observed in X-rays if only
SSC is considered. To estimate the TeV duty cycle of Mrk 421 and to establish
limits on its variability at different time scales, we continuously observed
Mrk 421 with the Milagro observatory. Mrk 421 was detected by Milagro with a
statistical significance of 7.1 standard deviations between 2005 September 21
and 2008 March 15. The observed spectrum is consistent with previous
observations by VERITAS. We estimate the duty cycle of Mrk 421 for energies
above 1 TeV for different hypothesis of the baseline flux and for different
flare selections and we compare our results with the X-ray duty cycle estimated
by Resconi et al. 2009. The robustness of the results is discussed.Comment: 27 pages, 6 figures, ApJ accepte
TRPV4 related skeletal dysplasias: a phenotypic spectrum highlighted byclinical, radiographic, and molecular studies in 21 new families
Extent: 8p.Background: The TRPV4 gene encodes a calcium-permeable ion-channel that is widely expressed, responds to many different stimuli and participates in an extraordinarily wide range of physiologic processes. Autosomal dominant brachyolmia, spondylometaphyseal dysplasia Kozlowski type (SMDK) and metatropic dysplasia (MD) are currently considered three distinct skeletal dysplasias with some shared clinical features, including short stature, platyspondyly, and progressive scoliosis. Recently, TRPV4 mutations have been found in patients diagnosed with these skeletal phenotypes. Methods and Results: We critically analysed the clinical and radiographic data on 26 subjects from 21 families, all of whom had a clinical diagnosis of one of the conditions described above: 15 with MD; 9 with SMDK; and 2 with brachyolmia. We sequenced TRPV4 and identified 9 different mutations in 22 patients, 4 previously described, and 5 novel. There were 4 mutation-negative cases: one with MD and one with SMDK, both displaying atypical clinical and radiographic features for these diagnoses; and two with brachyolmia, who had isolated spine changes and no metaphyseal involvement. Conclusions: Our data suggest the TRPV4 skeletal dysplasias represent a continuum of severity with areas of phenotypic overlap, even within the same family. We propose that AD brachyolmia lies at the mildest end of this spectrum and, since all cases described with this diagnosis and TRPV4 mutations display metaphyseal changes, we suggest that it is not a distinct entity but represents the mildest phenotypic expression of SMDK.Elena Andreucci, Salim Aftimos, Melanie Alcausin, Eric Haan, Warwick Hunter, Peter Kannu, Bronwyn Kerr, George McGillivray, RJ McKinlay Gardner, Maria G Patricelli, David Sillence, Elizabeth Thompson, Margaret Zacharin, Andreas Zankl, Shireen R Lamandé and Ravi Savariraya
Search for Branons at LEP
We search, in the context of extra-dimension scenarios, for the possible
existence of brane fluctuations, called branons. Events with a single photon or
a single Z-boson and missing energy and momentum collected with the L3 detector
in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are
analysed. No excess over the Standard Model expectations is found and a lower
limit at 95% confidence level of 103 GeV is derived for the mass of branons,
for a scenario with small brane tensions. Alternatively, under the assumption
of a light branon, brane tensions below 180 GeV are excluded
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