47,957 research outputs found
A propeller scenario for the gamma-ray emission of low-mass X-ray binaries: The case of XSS J12270-4859
XSS J12270-4859 is the only low mass X-ray binary (LMXB) with a proposed
persistent gamma-ray counterpart in the Fermi-LAT 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 in-fall, such as that recently
observed from the transitional pulsar PSR J1023+0038. While the surface
magnetic field of a typical NS in a 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 in-flow is truncated in a
NS-LMXB system is much lower. 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.Comment: 12 pages, 3 figures, accepted for publication in MNRAS. References
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A 3D Printed Toolbox for Opto-Mechanical Components
Nowadays is very common to find headlines in the media where it is stated
that 3D printing is a technology called to change our lives in the near future.
For many authors, we are living in times of a third industrial revolution.
Howerver, we are currently in a stage of development where the use of 3D
printing is advantageous over other manufacturing technologies only in rare
scenarios. Fortunately, scientific research is one of them. Here we present the
development of a set of opto-mechanical components that can be built easily
using a 3D printer based on Fused Filament Fabrication (FFF) and parts that can
be found on any hardware store. The components of the set presented here are
highly customizable, low-cost, require a short time to be fabricated and offer
a performance that compares favorably with respect to low-end commercial
alternatives.Comment: 9 pages, 9 figure
Precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying baryon and the emitted charged lepton
We calculate the radiative corrections to the angular correlation between the
polarization of the decaying baryon and the direction of the emitted charged
lepton in the semileptonic decays of spin one-half baryons to order
(\alpha/\pi)(q/M_1). The final results are presented, first, with the triple
integration of the bremsstrahlung photon ready to be performed numerically and,
second, in an analytical form. A third presentation of our results in the form
of numerical arrays of coefficients to be multiplied on the quadratic products
of form factors is discussed. This latter may be the most practical one to use
in Monte Carlo simulations. A series of crosschecks is performed. The results
are useful in the analysis of the Dalitz plot of precision experiments
involving light and heavy quarks and is not compromised to fixing the form
factors at predetermined values. It is assumed that the real photons are
kinematically discriminated. Otherwise, our results have a general
model-independent applicability.Comment: 8 pages, RevTex4, 5 tables, no figures. Shortened version; results
and conclusions remain unchange
How does breakup influence the total fusion of Li at the Coulomb barrier?
Total (complete + incomplete) fusion excitation functions of Li on
Co and Bi targets around the Coulomb barrier are obtained using
a new continuum discretized coupled channel (CDCC) method of calculating
fusion. The relative importance of breakup and bound-state structure effects on
total fusion is particularly investigated. The effect of breakup on fusion can
be observed in the total fusion excitation function. The breakup enhances the
total fusion at energies just around the barrier, whereas it hardly affects the
total fusion at energies well above the barrier. The difference between the
experimental total fusion cross sections for Li on Co is notably
caused by breakup, but this is not the case for the Bi target.Comment: 9 pages, 9 figures, Submitted to Phys. Rev.
Precision radiative corrections to the semileptonic Dalitz plot with angular correlation between polarized decaying and emitted baryons: Effects of the four-body region
Analytical radiative corrections of order (\alpha/\pi)(q/M_1) are calculated
for the four-body region of the Dalitz plot of baryon semileptonic decays when
the s_1 \cdot p_2 correlation is present. Once the final result is available,
it is possible to exhibit it in terms of the corresponding final result of the
three-body region following a set of simple changes in the latter. We cover two
cases, a charged and a neutral polarized decaying baryon.Comment: Revtex4, 7 pages, no figure
Integration of statistics and food process engineering: Assessing the uncertainty of thermal processing and shelf-life estimations
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