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Khiali B.,University of Sao Paulo | De Gouveia Dal Pino E.M.,University of Sao Paulo | Del Valle M.V.,Instituto Argentino Of Radioastronomia Iar
Monthly Notices of the Royal Astronomical Society | Year: 2015

Recent studies have indicated that cosmic ray acceleration by a first-order Fermi process in magnetic reconnection current sheets can be efficient enough in the surrounds of compact sources. In this work, we discuss this acceleration mechanism operating in the core region of galactic black hole binaries (or microquasars) and show the conditions under which this can be more efficient than shock acceleration. In addition, we compare the corresponding acceleration rate with the relevant radiative loss rates obtaining the possible energy cut-off of the accelerated particles and also compute the expected spectral energy distribution (SED) for two sources of this class, namely Cygnus X-1 and Cygnus X-3, considering both leptonic and hadronic processes. The derived SEDs are comparable to the observed ones in the low- and high-energy ranges. Our results suggest that hadronic non-thermal emission due to photomeson production may produce the very high energy gamma-rays in these microquasars. © 2015 The Author. Source

Caiafa C.F.,Instituto Argentino Of Radioastronomia Iar | Cichocki A.,RIKEN | Cichocki A.,Polish Academy of Sciences
IEEE Transactions on Signal Processing | Year: 2015

In the framework of multidimensional Compressed Sensing (CS), we introduce an analytical reconstruction formula that allows one to recover an Nth-order data tensor bf XRI1× I2×× IN from a reduced set of multi-way compressive measurements by exploiting its low multilinear-rank structure. Moreover, we show that, an interesting property of multi-way measurements allows us to build the reconstruction based on compressive linear measurements taken only in two selected modes, independently of the tensor order N. In addition, it is proved that, in the matrix case and in a particular case with 3rd-order tensors where the same 2D sensor operator is applied to all mode-3 slices, the proposed reconstruction Xτ is stable in the sense that the approximation error is comparable to the one provided by the best low-multilinear-rank approximation, where τ is a threshold parameter that controls the approximation error. Through the analysis of the upper bound of the approximation error we show that, in the 2D case, an optimal value for the threshold parameter τ=τ-{0}>0 exists, which is confirmed by our simulation results. On the other hand, our experiments on 3D datasets show that very good reconstructions are obtained using τ=0, which means that this parameter does not need to be tuned. Our extensive simulation results demonstrate the stability and robustness of the method when it is applied to real-world 2D and 3D signals. A comparison with state-of-the-arts sparsity based CS methods specialized for multidimensional signals is also included. A very attractive characteristic of the proposed method is that it provides a direct computation, i.e., it is non-iterative in contrast to all existing sparsity based CS algorithms, thus providing super fast computations, even for large datasets. © 2014 IEEE. Source

Romero G.E.,Instituto Argentino Of Radioastronomia Iar | Romero G.E.,National University of La Plata | Romero G.E.,CONICET | Reynoso M.M.,CONICET | Christiansen H.R.,State University of Ceara
Astronomy and Astrophysics | Year: 2010

Context. We study the precession of accretion disks in the context of gamma-ray burst inner engines. Aims. Our aim is to quantitatively estimate the characteristics of gravitational waves produced by the precession of the transient accretion disk in gamma-ray bursts. Methods. We evaluate the possible periods of disk precession caused by the Lense-Thirring effect using an accretion disk model that allows for neutrino cooling. Assuming jet ejection perpendicular to the disk plane and a typical intrinsic time-dependence for the burst, we find gamma-ray light curves that have a temporal microstructure similar to that observed in some reported events. The parameters obtained for the precession are then used to evaluate the production of gravitational waves. Results. We find that the precession of accretion disks of outer radius smaller than 108 cm and accretion rates above 1 M⊙s-1could be detected by Advanced LIGO if they occur at distances of less than 100 Mpc. Conclusions. We conclude that the precession of a neutrino-cooled accretion disk in long gamma-ray bursts can be probed by gravitational wave astronomy. Precession of the disks in short gamma-ray events is undetectable with the current technology. © 2010 ESO. Source

Suad L.A.,Instituto Argentino Of Radioastronomia Iar | Caiafa C.F.,Instituto Argentino Of Radioastronomia Iar | Caiafa C.F.,University of Buenos Aires | Arnal E.M.,Instituto Argentino Of Radioastronomia Iar | And 2 more authors.
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2014

A New catalogue of H I supershell candidates (GSc) was developed in the outer part of the Galaxy. The search was carried out using a combination of two techniques: one based on a visual inspection plus an automatic algorithm. A statistical study of the main properties of the detected structure was also carried out. Source

Suad L.A.,Instituto Argentino Of Radioastronomia Iar | Caiafa C.F.,Instituto Argentino Of Radioastronomia Iar | Caiafa C.F.,University of Buenos Aires | Arnal E.M.,Instituto Argentino Of Radioastronomia Iar | And 2 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. The main goal of this work is to a have a new neutral hydrogen (H i) supershell candidate catalog to analyze their spatial distribution in the Galaxy and to carry out a statistical study of their main properties. Methods. This catalog was carried out making use of the Leiden-Argentine-Bonn (LAB) survey. The supershell candidates were identified using a combination of two techniques: a visual inspection plus an automatic searching algorithm. Our automatic algorithm is able to detect both closed and open structures. Results. A total of 566 supershell candidates were identified. Most of them (347) are located in the second Galactic quadrant, while 219 were found in the third one. About 98% of a subset of 190 structures (used to derive the statistical properties of the supershell candidates) are elliptical with a mean weighted eccentricity of 0.8 ± 0.1, and ~70% have their major axes parallel to the Galactic plane. The weighted mean value of the effective radius of the structures is ~160 pc. Owing to the ability of our automatic algorithm to detect open structures, we have also identified some "galactic chimney" candidates. We find an asymmetry between the second and third Galactic quadrants in the sense that in the second one we detect structures as far as 32 kpc, while for the 3rd one the farthest structure is detected at 17 kpc. The supershell surface density in the solar neighborhood is ~8 kpc-2, and decreases as we move farther away form the Galactic center. We have also compared our catalog with those by other authors. © ESO, 2014. Source

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