D. F. Torres

Swings between rotation and accretion power in a binary millisecond pulsar

It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star’s rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.

Hadronic gamma-ray emission from windy microquasars

The jets of microquasars with high-mass stellar companions are exposed to the dense matter field of the stellar wind. We present estimates of the gamma-ray emission expected from the jet-wind hadronic interaction and we discuss the detectability of the phenomenon at high energies. The proposed mechanism could explain some of the unidentified gamma-ray sources detected by EGRET instrument on the galactic plane.

Quintessence, superquintessence, and observable quantities in Brans-Dicke and nonminimally coupled theories

The different definitions for the equation of state of a nonminimally coupled scalar field that have been introduced in the literature are analyzed. Particular emphasis is made upon those features that could yield an observable way of distinguishing nonminimally coupled theories from general relativity, with the same or with alternate potentials. It is found that some earlier claims that superquintessence, a stage of superaccelerated expansion of the universe, is possible within realistic nonminimally coupled theories are the result of an arguable definition of the equation of state. In particular, it is shown that these previous results do not import any observable consequence, i.e., that the theories are observationally identical to general relativity models and that superquintessence is not more than a mathematical outcome. Finally, in the case of nonminimally coupled theories with coupling

Astrophysical origins of ultrahigh energy cosmic rays

F=1+\ensuremath{\xi}{\ensuremath{\varphi}}^{2}

Supernova remnants and γ-ray sources

and tracking potentials, it is shown that no superquintessence is possible.

Early universe test of nonextensive statistics

In the first part of this review we discuss the basic observational features at the end of the cosmic ray (CR) energy spectrum. We also present there the main characteristics of each of the experiments involved in the detection of these particles. We then briefly discuss the status of the chemical composition and the distribution of arrival directions of CRs. After that, we examine the energy losses during propagation, introducing the Greisen–Zaptsepin–Kuzmin (GZK) cutoff, and discuss the level of confidence with which each experiment has detected particles beyond the GZK energy limit. In the second part of the review, we discuss the astrophysical environments that are able to accelerate particles up to such high energies, including active galactic nuclei, large scale galactic wind termination shocks, relativistic jets and hot-spots of Fanaroff–Riley radio galaxies, pulsars, magnetars, quasar remnants, starbursts, colliding galaxies, and gamma ray burst fireballs. In the third part of the review we provide a brief summary of scenarios which try to explain the super-GZK events with the help of new physics beyond the standard model. In the last section, we give an overview on neutrino telescopes and existing limits on the energy spectrum and discuss some of the prospects for a new (multi-particle) astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used to probe new physics beyond the electroweak scale.

X-ray coherent pulsations during a sub-luminous accretion disc state of the transitional millisecond pulsar XSS J12270−4859

Abstract A review of the possible relationship between γ -ray sources and supernova remnants (SNRs) is presented. Particular emphasis is given to the analysis of the observational status of the problem of cosmic ray acceleration at SNR shock fronts. All positional coincidences between SNRs and unidentified γ -ray sources listed in the Third EGRET Catalog at low Galactic latitudes are discussed on a case by case basis. For several coincidences of particular interest, new CO( J =1−0) and radio continuum maps are shown, and the mass content of the SNR surroundings is determined. The contribution to the γ -ray flux observed that might come from cosmic ray particles (particularly nuclei) locally accelerated at the SNR shock fronts is evaluated. We discuss the prospects for future research in this field and remark on the possibilities for observations with forthcoming γ -ray instruments.

A variability analysis of low-latitude unidentified gamma-ray sources

Within an early Universe scenario, nonextensive thermostatistics is investigated on the basis of data concerning primordial helium abundance. We obtain first order corrections to the energy densities and weak interaction rates, and use them to compute the deviation in the primordial helium abundance. After comparing with observational results, we get

A Strongly Magnetized Pulsar within the Grasp of the Milky Way's Supermassive Black Hole

|q\ensuremath{-}1|l2.08\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}

High energy gamma-ray emission from the starburst nucleus of NGC 253

as a bound for the nonextensive parameter.