13,583 research outputs found
Quasi-Periodic Oscillations and energy spectra from the two brightest Ultra-Luminous X-ray sources in M82
Ultra-Luminous X-ray sources are thought to be accreting black holes that
might host Intermediate Mass Black Holes (IMBH), proposed to exist by
theoretical studies, even though a firm detection (as a class) is still
missing. The brightest ULX in M82 (M82 X-1) is probably one of the best
candidates to host an IMBH. In this work we analyzed the data of the recent
release of observations obtained from M82 X-1 taken by XMM-Newton. We performed
a study of the timing and spectral properties of the source. We report on the
detection of (46+-2) mHz Quasi-Periodic Oscillations (QPOs) in the power
density spectra of two observations. A comparison of the frequency of these
high-frequency QPOs with previous detections supports the 1:2:3 frequency
distribution as suggested in other studies. We discuss the implications if the
(46+-2) mHz QPO detected in M82 X-1 is the fundamental harmonic, in analogy
with the High-Frequency QPOs observed in black hole binaries. For one of the
observations we have detected for the first time a QPO at 8 mHz (albeit at a
low significance), that coincides with a hardening of the spectrum. We suggest
that the QPO is a milli-hertz QPO originating from the close-by transient ULX
M82 X-2, with analogies to the Low-Frequency QPOs observed in black hole
binaries.Comment: 9 pages (with 4 figures and 4 tables). Accepted for publication in
MNRAS (26/09/13
Parity violation in quasielastic electron-nucleus scattering within the relativistic impulse approximation
We study parity violation in quasielastic (QE) electron-nucleus scattering
using the relativistic impulse approximation. Different fully relativistic
approaches have been considered to estimate the effects associated with the
final-state interactions. We have computed the parity-violating quasielastic
(PVQE) asymmetry and have analyzed its sensitivity to the different ingredients
that enter in the description of the reaction mechanism: final-state
interactions, nucleon off-shellness effects, current gauge ambiguities.
Particular attention has been paid to the description of the weak neutral
current form factors. The PVQE asymmetry is proven to be an excellent
observable when the goal is to get precise information on the axial-vector
sector of the weak neutral current. Specifically, from measurements of the
asymmetry at backward scattering angles good knowledge of the radiative
corrections entering in the isovector axial-vector sector can be gained.
Finally, scaling properties shown by the interference nuclear
responses are also analyzed.Comment: 15 pages, 11 figure
Parity violation and dynamical relativistic effects in reactions
It is well known that coincidence quasielastic reactions are
not appropriate to analyze effects linked to parity violation due the presence
of the fifth electromagnetic (EM) response . Nevertheless, in this
work we develop a fully relativistic approach to be applied to parity-violating
(PV) quasielastic processes. This is of importance as a
preliminary step in the subsequent study of inclusive quasielastic PV
reactions. Moreover, our present analysis allows us to
disentangle effects associated with the off-shell character of nucleons in
nuclei, gauge ambiguities and the role played by the lower components in the
nucleon wave functions, i.e., dynamical relativistic effects. This study can
help in getting clear information on PV effects. Particular attention is paid
to the relativistic plane-wave impulse approximation where the explicit
expressions for the PV single-nucleon responses are shown for the first time.Comment: 39 pages, 9 figure
Global analysis of parity-violating asymmetry data for elastic electron scattering
We perform a statistical analysis of the full set of parity-violating
asymmetry data for elastic electron scattering including the most recent high
precision measurement from -weak. Given the basis of the present analysis,
our estimates appear to favor non-zero vector strangeness, specifically,
positive (negative) values for the electric (magnetic) strange form factors. We
also provide an accurate estimate of the axial-vector nucleon form factor at
zero momentum transfer, . Our study shows to be
importantly reduced with respect to the currently accepted value. We also find
our analysis of data to be compatible with the Standard Model values for the
weak charges of the proton and neutron.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PR
Developing the Next Generation of Physics Assessments
Science education at all levels is currently undergoing dramatic changes to
its curricula and developing assessments for these new curricula is paramount.
We have used the basis of many of these new changes (scientific practices,
crosscutting concepts, and core ideas) to develop sets of criteria that can be
used to guide assessment development for this new curriculum. We present a case
study that uses the criteria we have developed to revise a traditional physics
assessment item into an assessment item that is much more aligned with the
goals of current transformation efforts. Assessment items developed using this
criteria can be used to assess student learning of both the concepts and
process of science.Comment: Revised version for PERC 2015 Conference Proceeding
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