1,440 research outputs found
Modeling Flocks and Prices: Jumping Particles with an Attractive Interaction
We introduce and investigate a new model of a finite number of particles
jumping forward on the real line. The jump lengths are independent of
everything, but the jump rate of each particle depends on the relative position
of the particle compared to the center of mass of the system. The rates are
higher for those left behind, and lower for those ahead of the center of mass,
providing an attractive interaction keeping the particles together. We prove
that in the fluid limit, as the number of particles goes to infinity, the
evolution of the system is described by a mean field equation that exhibits
traveling wave solutions. A connection to extreme value statistics is also
provided.Comment: 35 pages, 9 figures. A shortened version appears as arXiv:1108.243
Comparing the observed properties of the GRBs detected by the Fermi and Swift satellites
We studied the distribution of the GRBs, observed by the Fermi satellite, in
the multidimensional parameter space consisting of the duration, Fluence, Peak
flux and Peak energy (if it was available). About 10% of the Fermi bursts was
observed also by the Swift satellite. We did not find significant differences
between the Peak flux and Peak energy of GRBs observed and not observed also by
the Swift satellite. In contrast, those GRBs detected also by the Swift
satellite had significantly greater Fluence and duration. We did a similar
study for the GRBs detected by the Swift satellite. About 30% percent of these
bursts was also measured by the Fermi satellite. We found a significant
difference in the Fluence, Peak flux and Photon index but none in duration.
These differences may be accounted for the different construction and observing
strategy of the Fermi and Swift satellites.Comment: 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 5 in eConf
Proceedings C130414
Discrete coherent states for higher Landau levels
We consider the quantum dynamics of a charged particle evolving under the
action of a constant homogeneous magnetic field, with emphasis on the discrete
subgroups of the Heisenberg group (in the Euclidean case) and of the SL(2, R)
group (in the Hyperbolic case). We investigate completeness properties of
discrete coherent states associated with higher order Euclidean and hyperbolic
Landau levels, partially extending classic results of Perelomov and of
Bargmann, Butera, Girardello and Klauder. In the Euclidean case, our results
follow from identifying the completeness problem with known results from the
theory of Gabor frames. The results for the hyperbolic setting follow by using
a combination of methods from coherent states, time-scale analysis and the
theory of Fuchsian groups and their associated automorphic forms.Comment: Revised for Annals of Physic
Survival analysis of the optical brightness of GRB host galaxies
We studied the unbiased optical brightness distribution which was calculated
from the survival analysis of host galaxies and its relationship with the Swift
GRB data of the host galaxies observed by the Keck telescopes. Based on the
sample obtained from merging the Swift GRB table and the Keck optical data we
also studied the dependence of this distribution on the data of the GRBs.
Finally, we compared the HGs distribution with standard galaxies distribution
which is in the DEEP2 galaxies catalog.Comment: Swift: 10 Years of Discovery. Conference paper. 2-5 December 2014. La
Sapienza University, Rome, Ital
Properties of the intermediate type of gamma-ray bursts
Gamma-ray bursts can be divided into three groups ("short", "intermediate",
"long") with respect to their durations. The third type of gamma-ray bursts -
as known - has the intermediate duration. We show that the intermediate group
is the softest one. An anticorrelation between the hardness and the duration is
found for this subclass in contrast to the short and long groups.Comment: In Sixteenth Maryland Astrophysics Conferenc
A Principal Component Analysis of the 3B Gamma-Ray Burst Data
We have carried out a principal component analysis for 625 gamma-ray bursts
in the BATSE 3B catalog for which non-zero values exist for the nine measured
variables. This shows that only two out of the three basic quantities of
duration, peak flux and fluence are independent, even if this relation is
strongly affected by instrumental effects, and these two account for 91.6% of
the total information content. The next most important variable is the fluence
in the fourth energy channel (at energies above 320 keV). This has a larger
variance and is less correlated with the fluences in the remaining three
channels than the latter correlate among themselves. Thus a separate
consideration of the fourth channel, and increased attention on the related
hardness ratio appears useful for future studies. The analysis gives the
weights for the individual measurements needed to define a single duration,
peak flux and fluence. It also shows that, in logarithmic variables, the
hardness ratio is significantly correlated with peak flux, while is
significantly anticorrelated with peak flux. The principal component analysis
provides a potentially useful tool for estimating the improvement in
information content to be achieved by considering alternative variables or
performing various corrections on available measurementsComment: Ap.J., accepted 12/9/97; revised version contains a new appendix,
somewhat expanded discussion; latex, aaspp4, 15 page
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