924 research outputs found
Identification of high energy gamma-ray sources and source populations in the era of deep all-sky coverage
A large fraction of the anticipated source detections by the Gamma-ray Large
Area Space Telescope (GLAST-LAT) will initially be unidentified. We argue that
traditional approaches to identify individuals and/or populations of gamma ray
sources will encounter procedural limitations. Those limitations are discussed
on the background of source identifications from EGRET observations. Generally,
our ability to classify (faint) source populations in the anticipated GLAST
dataset with the required degree of statistical confidence will be hampered by
sheer source wealth. A new paradigm for achieving the classification of gamma
ray source populations is discussed.Comment: Comments: 6 pages, 2 figures, Accepted for publication in
Astrophysics and Space Science, Proc. of "The Multi-Messenger Approach to
High-Energy Gamma-ray Sources (Third Workshop on the Nature of Unidentified
High-Energy Sources)", Barcelona, July 4-7, 200
Possible new γ-ray pulsar detections by the AGILE and GLAST missions: An outer gap model look at the Parkes pulsar catalog
Fil:Torres, D.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Nuza, S.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
A Maple interface for computing variational symmetries in optimal control
A computer algebra package, for the automatic computation of variational symmetries in optimal control, was recently developed by the authors [2,3]. Now we present a graphical user interface which permit to interact, in a point-and-click environment, with all the previous symbolical tools
Computation of conservation laws in optimal control
Making use of a computer algebra system, we define computational tools to identify symmetries and conservation laws in optimal control
Status of the connection between unidentified EGRET sources and supernova remnants: The case of CTA 1
In this paper we briefly comment on the observational status of the possible
physical association between unidentified EGRET sources and supernova remnants
(SNRs) in our Galaxy. We draw upon recent results presented in the review by
Torres et al. (Physics Reports, 2003), concerning molecular gas in the vicinity
of all 19 SNRs found to be positionally coincident with EGRET sources at low
Galactic latitudes. In addition, we present new results regarding the supernova
remnant CTA~1. Our findings disfavor the possibility of a physical connection
with the nearby (in projection) EGRET source. There remains possible, however,
that the compact object produced in the supernova explosion be related with the
observed -ray flux.Comment: Presented for the proceedings of the II Workshop on Unidentified
Gamma-Ray Sources, Hong Kong, June 1-4, 2004. To appear in Astrophysics and
Space Science. Some changes to address referee's and readers' remarks.
References added. Results unchange
Collective effects of stellar winds and unidentified gamma-ray sources
We study collective wind configurations produced by a number of massive stars, and obtain densities and expansion velocities of the stellar wind gas that is to be target, in this model, of hadronic interactions. We study the expected -ray emission from these regions, considering in an approximate way the effect of cosmic ray modulation. We compute secondary particle production (electrons from knock-on interactions and electrons and positrons from charged pion decay), and solve the loss equation with ionization, synchrotron, bremsstrahlung, inverse Compton, and expansion losses. We provide examples where configurations can produce sources for GLAST satellite, and the MAGIC, HESS, or VERITAS telescopes in non-uniform ways, i.e., with or without the corresponding counterparts. We show that in all cases we studied no EGRET source is expected
Uma forma bidimensional que maximiza a resistência aerodinâmica newtoniana
In a previous work [18, 19] it is investigated, by means of computational
simulations, shapes of nonconvex bodies that maximize resistance to its motion on a
rare ed medium, considering that bodies are moving forward and at the same time slowly
rotating. Here the previous results are improved: we obtain a two-dimensional geometric
shape that confers to the body a resistance very close to the supremum value (R =
1:4965 < 1:5). Um corpo bidimensional, apresentando um ligeiro movimento rotacional, desloca-se num meio rarefeito de partículas que colidem com ele de uma forma perfeitamente elástica. Em investigações que os dois primeiros autores realizaram anteriormente [18, 19], procuraram-se formas de corpos que maximizassem a força de travagem do meio ao seu movimento. Dando continuidade a esse estudo, encetam-se agora novas investigações que
culminam num resultado que representa um grande avanço qualitativo relativamente aos então alcançados. Esse resultado, que agora se apresenta, consiste numa forma bidimensional que confere ao corpo uma resistência muito próxima do seu limite teórico. Mas o seu interesse não se fica pela maximização da resistência newtoniana; atendendo às suas características, apontam-se ainda outros domínios de aplicação onde se pensa poder vir
a revelar-se de grande utilidade. Tendo a forma óptima encontrada resultado de estudos numéricos, é objecto de um estudo adicional de natureza analítica, onde se demonstram algumas propriedades importantes que explicam em grande parte o seu virtuosismo
Uma forma bidimensional que maximiza a resistência aerodinâmica newtoniana
In a previous work [18, 19] it is investigated, by means of computational
simulations, shapes of nonconvex bodies that maximize resistance to its motion on a
rare ed medium, considering that bodies are moving forward and at the same time slowly
rotating. Here the previous results are improved: we obtain a two-dimensional geometric
shape that confers to the body a resistance very close to the supremum value (R =
1:4965 < 1:5). Um corpo bidimensional, apresentando um ligeiro movimento rotacional, desloca-se num meio rarefeito de partículas que colidem com ele de uma forma perfeitamente elástica. Em investigações que os dois primeiros autores realizaram anteriormente [18, 19], procuraram-se formas de corpos que maximizassem a força de travagem do meio ao seu movimento. Dando continuidade a esse estudo, encetam-se agora novas investigações que
culminam num resultado que representa um grande avanço qualitativo relativamente aos então alcançados. Esse resultado, que agora se apresenta, consiste numa forma bidimensional que confere ao corpo uma resistência muito próxima do seu limite teórico. Mas o seu interesse não se fica pela maximização da resistência newtoniana; atendendo às suas características, apontam-se ainda outros domínios de aplicação onde se pensa poder vir
a revelar-se de grande utilidade. Tendo a forma óptima encontrada resultado de estudos numéricos, é objecto de um estudo adicional de natureza analítica, onde se demonstram algumas propriedades importantes que explicam em grande parte o seu virtuosismo
INTEGRAL/XMM views on the MeV source GRO J1411-64
The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and
XMM-Newton in 2005. The Circinus Galaxy is the only source detected within the
4 location error of GRO J1411-64, but in here excluded as the possible
counterpart. At soft X-rays, 22 reliable and statistically significant sources
(likelihood ) were extracted and analyzed from XMM-Newton data. Only one
of these sources, XMMU J141255.6 -635932, is spectrally compatible with GRO
J1411-64 although the fact the soft X-ray observations do not cover the full
extent of the COMPTEL source position uncertainty make an association hard to
quantify and thus risky. At the best location of the source, detections at hard
X-rays show only upper limits, which, together with MeV results obtained by
COMPTEL suggest the existence of a peak in power output located somewhere
between 300-700 keV for the so-called low state. Such a spectrum resembles
those in blazars or microquasars, and might suggest at work by a similar
scenario.
However, an analysis using a microquasar model consisting on a magnetized
conical jet filled with relativistic electrons, shows that it is hard to comply
with all observational constrains. This fact and the non-detection at hard
X-rays introduce an a-posteriori question mark upon the physical reality of
this source, what is discussed here.Comment: Accepted for publication in Astrophysics and Space Science, as
proceedings of "The Multi-Messenger Approach to High-Energy Gamma-Ray
Sources", Barcelona, July 4-7, 2006, J. M. Paredes, O. Reimer, and D. F.
Torres, editor
Computing ODE Symmetries as Abnormal Variational Symmetries
We give a new computational method to obtain symmetries of ordinary
differential equations. The proposed approach appears as an extension of a
recent algorithm to compute variational symmetries of optimal control problems
[Comput. Methods Appl. Math. 5 (2005), no. 4, pp. 387-409], and is based on the
resolution of a first order linear PDE that arises as a necessary and
sufficient condition of invariance for abnormal optimal control problems. A
computer algebra procedure is developed, which permits to obtain ODE symmetries
by the proposed method. Examples are given, and results compared with those
obtained by previous available methods
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