Time filter

Source Type

Martin J.,Institute of Space science IEEC CSIC | Torres D.F.,Institute of Space science IEEC CSIC | Torres D.F.,Catalan Institution for Research and Advanced Studies | Cillis A.,Institute Astronomia y Fisica del Espacio | de Ona Wilhelmi E.,Institute of Space science IEEC CSIC
Monthly Notices of the Royal Astronomical Society | Year: 2014

We make a time-dependent characterization of pulsar wind nebulae (PWNe) surrounding some of the highest spin-down pulsars that have not yet been detected at TeV. Our aim is assessing their possible level of magnetization. We analyse the nebulae driven by J2022+3842 in G76.9+1.0, J0540-6919 in N158A (the Crab twin), J1400-6325 in G310.6-1.6, and J1124-5916 in G292.0+0.18, none of which have been found at TeV energies. For comparison, we refer to published models of G54.1+0.3, the Crab nebula, and develop a model for N157B in the Large Magellanic Cloud (LMC). We conclude that further observations of N158A could lead to its detection at VHE. According to our model, a far-infrared energy density of 5 eV cm-3 could already lead to a detection in H.E.S.S. (assuming no other IC target field) within 50 h of exposure, and just the cosmic microwave background inverse Compton contribution would produce VHE photons at the CTA sensitivity. We also propose models for G76.9+1.0, G310.6-1.6 and G292.0+1.8 which suggest their TeV detection in a moderate exposure for the latter two with the current generation of Cherenkov telescopes. We analyse the possibility that these PWNe are highly magnetized, where the low number of particles explains the residual detection in X-rays and their lack of detection at TeV energies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Torres D.F.,Institute of Space science IEEC CSIC | Torres D.F.,Catalan Institution for Research and Advanced Studies | Cillis A.N.,Institute Astronomia y Fisica Del Espacio | Martin Rodriguez J.,Institute of Space science IEEC CSIC
Astrophysical Journal Letters | Year: 2013

We present a time-dependent spectral model of the nebula 3C 58 and compare it with available data. The model is for a leptonic nebula in which particles are subject to synchrotron, inverse Compton, self-synchrotron Compton, adiabatic, and bremsstrahlung processes. We find that 3C 58 is compatible with being a particle-dominated nebula, with a magnetic field of 35 μG. A broken power-law injection fits well the multi-frequency data, with a break energy at about 40 GeV. We find that 3C 58 is not expected to appear in VERITAS or MAGIC II, unless the local IR background is a factor of ∼20 off Galactic models' averages. For cases in which the cosmic microwave background dominates the inverse Compton contribution, we find that 3C 58 will not be visible either for the Cherenkov Telescope Array. © 2013. The American Astronomical Society. All rights reserved.

Torres D.F.,Institute of Space science IEEC CSIC | Torres D.F.,Catalan Institution for Research and Advanced Studies | Cillis A.,Institute Astronomia y Fisica del Espacio | Martin J.,Institute of Space science IEEC CSIC | de Ona Wilhelmi E.,Institute of Space science IEEC CSIC
Journal of High Energy Astrophysics | Year: 2014

The increasing sensitivity of instruments at X-ray and TeV energies has revealed a large number of nebulae associated with bright pulsars. Despite this large data set, the observed pulsar wind nebulae (PWNe) do not show a uniform behavior and the main parameters driving features like luminosity, magnetization, and others are still not fully understood. To evaluate the possible existence of common evolutive trends and to link the characteristics of the nebula emission with those of the powering pulsar, we selected a sub-set of 10 TeV detections which are likely ascribed to young PWNe and model the spectral energy distribution with a time-dependent description of the nebulae's electron population. In 9 of these cases, a detailed PWNe model, using up-to-date multiwavelength information, is presented. The best-fit parameters of these nebulae are discussed, together with the pulsar characteristics. We conclude that TeV PWNe are particle-dominated objects with large multiplicities, in general far from magnetic equipartition, and that relatively large photon field enhancements are required to explain the high level of Comptonized photons observed. We do not find significant correlations between the efficiencies of emission at different frequencies and the magnetization. The injection parameters do not appear to be particularly correlated with the pulsar properties either. We find that a normalized comparison of the SEDs (e.g., with the corresponding spin-down flux) at the same age significantly reduces the spectral distributions dispersion. © 2014 Elsevier B.V.

Serenelli A.M.,Institute of Space science IEEC CSIC | Serenelli A.M.,Max Planck Institute for Astrophysics | Bergemann M.,Max Planck Institute for Astrophysics | Ruchti G.,Max Planck Institute for Astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

For studies of Galactic evolution, the accurate characterization of stars in terms of their evolutionary stage and population membership is of fundamental importance. A standard approach relies on extracting this information from stellar evolution models but requires the effective temperature, surface gravity and metallicity of a star obtained by independent means. In previous work, we determined accurate effective temperatures and non-local thermodynamic equilibrium log g and [Fe/H] (NLTE-Opt) for a large sample of metal-poor stars, -3 < [Fe/H] < -0.5, selected from the Radial Velocity Experiment (RAVE) survey. As a continuation of that work, we derive here their masses, ages and distances using a Bayesian scheme and GARSTEC stellar tracks. For comparison, we also use stellar parameters determined from the widely used 1D LTE excitation-ionization balance of Fe (LTE-Fe).We find that the latter leads to systematically underestimated stellar ages, by 10-30 per cent, but overestimated masses and distances. Metal-poor giants suffer from the largest fractional distance biases of 70 per cent. Furthermore, we compare our results with those released by the RAVE collaboration (DR3) for the stars in common. This reveals -400 to +400K offsets in effective temperature, -0.5 to 1 dex offsets in surface gravity and 10 to 70 per cent in distances. The systematic trends strongly resemble the correlation we find between the NLTE-Opt and LTE-Fe parameters, indicating that the RAVE DR3 data may be affected by the physical limitations of the 1D LTE synthetic spectra. Our results bear on any study, where spectrophotometric distances underlie stellar kinematics. In particular, they shed new light on the debated controversy about the Galactic halo origin raised by the SDSS/SEGUE observations. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Anchordoqui L.A.,Lehman College, CUNY | Anchordoqui L.A.,University of Wisconsin - Milwaukee | Paul T.C.,University of Wisconsin - Milwaukee | Paul T.C.,Northeastern University | And 4 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Very recently, the IceCube Collaboration reported a flux of neutrinos in the energy range 50TeVEν2PeV, which departs from expectations from atmospheric background at the 5.7σ level. This flux is in remarkable agreement with the expected diffuse flux of neutrinos from starburst galaxies, and the three highest energy events have uncertainty contours encompassing some of such systems. These events, all of which have well-measured energies above 1 PeV, exhibit shower topologies, for which the angular resolution is about 15°. Due to this angular uncertainty and the a posteriori nature of cuts used in our study, it is not possible to assign a robust statistical significance to this association. Using muon tracks, which have angular resolution <1°, we compute the number of observations required to make a statistically significant statement and show that in a few years of operation the upgraded IceCube detector should be able to confirm or refute this hypothesis. We also note that double bang topology rates constitute a possible discriminator among various astrophysical sources. © 2014 American Physical Society.

Gil-Marin H.,Institute of Space science IEEC CSIC | Jimenez R.,University of Barcelona | Verde L.,University of Barcelona
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present a modification of the standard halo model with the goal of providing an improved description of galaxy clustering. Recent surveys, like the Sloan Digital Sky Survey (SDSS) and the Anglo-Australian two-degree survey (2dF), have shown that there seems to be a correlation between the clustering of galaxies and their properties such as metallicity and star formation rate, which are believed to be environment-dependent. This environmental dependence is not included in the standard halo model where the host halo mass is the only variable specifying galaxy properties. In our approach, the halo properties, i.e. the concentration, and the halo occupation distribution (HOD) prescription, will not only depend on the halo mass (like in the standard halo model) but also on the halo environment. We examine how different environmental dependence of halo concentration and HOD prescription affects the correlation function. We see that at the level of dark matter, the concentration of haloes moderately affects the dark matter correlation function only at small scales. However, the galaxy correlation function is extremely sensitive to the HOD details, even when only the HOD of a small fraction of haloes is modified. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Ji L.,CAS Institute of High Energy Physics | Zhang S.,CAS Institute of High Energy Physics | Chen Y.,CAS Institute of High Energy Physics | Zhang S.-N.,CAS Institute of High Energy Physics | And 4 more authors.
Astrophysical Journal | Year: 2014

We report on a study of GS 1826-238 using all available Rossi X-Ray Timing Explorer observations, concentrating on the behavior of the hard X-rays during type-I bursts. We find a hard X-ray shortage at 30-50 keV prompted by the shower of soft X-rays coming from type-I bursts. This shortage happens with a time delay after the peak of the soft flux of 3.6 ± 1.2 s. The behavior of hard X-rays during bursts indicates cooling and reheating of the corona, during which a large amount of energy is required. We speculate that this energy originates from the feedback of the type-I bursts to the accretion process, resulting in a rapid temporary increase of the accretion rate. © 2014. The American Astronomical Society. All rights reserved..

Papitto A.,Institute of Space science IEEC CSIC | Torres D.F.,Institute of Space science IEEC CSIC | Torres D.F.,Catalan Institution for Research and Advanced Studies | Li J.,Institute of Space science IEEC CSIC
Monthly Notices of the Royal Astronomical Society | Year: 2014

XSS J12270-4859 is the only low-mass X-ray binary (LMXB) with a proposed persistent gamma-ray counterpart in the Fermi-Large Area Telescope domain, 2FGL 1227.7-4853. Here, we present the results of the analysis of recent INTEGRAL observations, aimed at assessing the long-term variability of the hard X-ray emission, and thus the stability of the accretion state.We confirm that the source behaves as a persistent hard X-ray emitter between 2003 and 2012. We propose that XSS J12270-4859 hosts a neutron star in a propeller state, a state we investigate in detail, developing a theoretical model to reproduce the associated X-ray and gamma-ray properties. This model can be understood as being of a more general nature, representing a viable alternative by which LMXBs can appear as gamma-ray sources. In particular, this may apply to the case of millisecond pulsars performing a transition from a state powered by the rotation of their magnetic field to a state powered by matter infall, such as that recently observed from the transitional pulsar PSR J1023+0038. While the surface magnetic field of a typical neutron star (NS) in an LMXB is lower by more than four orders of magnitude than the much more intense fields of neutron stars accompanying high-mass binaries, the radius at which the matter inflow is truncated in an NS-LMXB system is much smaller. The magnetic field at the magnetospheric interface is then orders of magnitude larger at this interface, and as consequence, so is the power to accelerate electrons. We demonstrate that the cooling of the accelerated electron population takes place mainly through synchrotron interaction with the magnetic field permeating the interface, and through inverse Compton losses due to the interaction between the electrons and the synchrotron photons they emit.We found that self-synchrotron Compton processes can explain the high-energy phenomenology of XSS J12270-4859. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Torres D.F.,Institute of Space science IEEC CSIC | Torres D.F.,Catalan Institution for Research and Advanced Studies | Martln J.,Institute of Space science IEEC CSIC | de Ona Wilhelmi E.,Institute of Space science IEEC CSIC | Cillis A.,Institute Astronomla y Flsica del Espacio
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate the time-dependent behaviour of Crab-like pulsar wind nebulae (PWNe) generating a set of models using four different initial spin-down luminosities (L0 = {1, 0.1, 0.01, 0.001} × L0,Crab), eight values of magnetic fraction (η = 0.001, 0.01, 0.03, 0.1, 0.5, 0.9, 0.99 and 0.999, i.e. from fully particle dominated to fully magnetically dominated nebulae) and three distinctive ages: 940, 3000 and 9000 years. We find that the self-synchrotron Compton (SSC) contribution is irrelevant for LSD = 0.1, 1 and 10 per cent of the Crab power, disregarding the age and the magnetic fraction. SSC only becomes relevant for highly energetic (̃70 per cent of the Crab), particle dominated nebulae at low ages (of less than a few kyr), located in a far-infrared (FIR) background with relatively low energy density. Since no pulsar other than Crab is known to have these features, these results clarify why the Crab nebula, and only it, is SSC dominated. No young PWN would be detectable at TeV energies if the pulsar's spin-down power is 0.1 per cent Crab or lower. For 1 per cent of the Crab spin-down, only particle-dominated nebulae can be detected by HESS-like telescopes when young enough (with details depending on the precise injection and environmental parameters). Above 10 per cent of the Crab's power, all PWNe are detectable by HESS-like telescopes if they are particle dominated, no matter the age. The impact of the magnetic fraction on the final spectral energy distribution is varied and important, generating order of magnitude variations in the luminosity output for systems that are otherwise the same (equal P, Ṗ,injection and environment). © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Odintsov S.D.,Institute of Space science IEEC CSIC | Odintsov S.D.,Catalan Institution for Research and Advanced Studies | Odintsov S.D.,Kazan Federal University | Oikonomou V.K.,Tomsk State University of Control Systems and Radioelectronics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

In this letter we study some variant forms of gravitational baryogenesis by using higher order terms containing the partial derivative of the Gauss–Bonnet scalar coupled to the baryonic current. This scenario extends the well known theory that uses a similar coupling between the Ricci scalar and the baryonic current. One appealing feature of the scenario we study is that the predicted baryon asymmetry during a radiation domination era is non-zero. We calculate the baryon to entropy ratio for the Gauss–Bonnet term and by using the observational constraints we investigate which are the allowed forms of the R+F(G) gravity controlling the evolution. Also we briefly discuss some alternative higher order terms that can generate a non-zero baryon asymmetry, even in the conformal invariance limit. © 2016 The Author(s)

Loading Institute of Space science IEEC CSIC collaborators
Loading Institute of Space science IEEC CSIC collaborators