547 research outputs found
Is there a left-handed magnetic field in the solar neighborhood?:Exploring helical magnetic fields in the interstellar medium through dust polarization power spectra
The full-sky Planck polarization data at 850um revealed unexpected properties
of the E and B mode power spectra of dust emission in the interstellar medium
(ISM). The positive cross-correlation between the total dust intensity, T, with
the B modes has raised new questions about the physical mechanisms that affect
dust polarization, such as the Galactic magnetic-field structure. This is key
both to better understanding ISM dynamics and to accurately describing Galactic
foregrounds to the polarization of the Cosmic Microwave Background (CMB). In
this theoretical paper we investigate the possibility that the observed
cross-correlations in the dust polarization power spectra, and specifically
between T and B, can be related to a parity-odd quantity in the ISM such as the
magnetic helicity. We produce synthetic dust polarization data, derived from 3D
analytical toy models of density structures and helical magnetic fields, to
compare with the E and B modes of observations. Focusing on the observed T-B
correlation, we propose a new line of interpretation of the Planck observations
based on a large-scale helical component of the Galactic magnetic field in the
solar neighborhood. Our analysis shows that: I) the sign of magnetic helicity
does not affect E and B modes for isotropic magnetic-field configurations; II)
helical magnetic fields threading interstellar filaments cannot reproduce the
Planck results; III) a weak helical left-handed magnetic field structure in the
solar neighborhood may explain the T-B correlation seen in the Planck data.
This work suggests a new perspective for the interpretation of the dust
polarization power spectra, which strongly supports the imprint of a
large-scale structure of the Galactic magnetic field in the solar neighborhood.Comment: Accepted by Astronomy & Astrophysics on November 24, 201
BeppoSAX observation of the X-ray binary pulsar Vela X-1
We report on the spectral (pulse averaged) and timing analysis of the ~ 20
ksec observation of the X-ray binary pulsar Vela X-1 performed during the
BeppoSAX Science Verification Phase. The source was observed in two different
intensity states: the low state is probably due to an erratic intensity dip and
shows a decrease of a factor ~ 2 in intensity, and a factor 10 in Nh. We have
not been able to fit the 2-100 keV continuum spectrum with the standard (for an
X--ray pulsar) power law modified by a high energy cutoff because of the
flattening of the spectrum in ~ 10-30 keV. The timing analysis confirms
previous results: the pulse profile changes from a five-peak structure for
energies less than 15 keV, to a simpler two-peak shape at higher energies. The
Fourier analysis shows a very complex harmonic component: up to 23 harmonics
are clearly visible in the power spectrum, with a dominant first harmonic for
low energy data, and a second one as the more prominent for energies greater
than 15 keV. The aperiodic component in the Vela X-1 power spectrum presents a
knee at about 1 Hz. The pulse period, corrected for binary motion, is 283.206
+/- 0.001 sec.Comment: 5 pages, 4 PostScript figure, uses aipproc.sty, to appear in
Proceedings of Fourth Compton Symposiu
Medical decision making and risky choices : psychological and medicolegal consequences of HIV and HCV contamination of blood products
Aims: The overall goal of this article is to make a scientific comment about the psycho-social consequences of hemophilia patients affected by human immunodeficiency virus (HIV) and/or hepatitis C virus (HCV) and to point out the related medicolegal issues.
Methods: This commentary takes into account some published evidences about the current scenario of hemophilia patients infected by HIV and/or HCV who received contaminated blood products in the late 1970s through 1985.
Results: Several psychological and medicolegal consequences are related with HIV and HCV contamination of blood products. A multidisciplinary approach is needed to treat all the difficulties experienced by these patients and to ensure good clinical decisions in medical practice.
Conclusion: The literature on the psychosocial functioning of hemophilia patients with human HIV and HCV infection offers a number of implications, including medicolegal issues, that can be discussed for guaranteeing a good level of care and safeguard of this group of patients
ASCA and BeppoSAX observations of the peculiar X-ray source 4U1700+24/HD154791
The X-ray source 4U1700+24/HD154791 is one of the few galactic sources whose
counterpart is an evolved M star. In X-rays the source shows extreme erratic
variability and a complex and variable spectrum. While this strongly suggests
accretion onto a compact object, no clear diagnosis of binarity was done up to
now. We report on ASCA and BeppoSAX X-ray broad band observations of this
source and on ground optical observations from the Loiano 1.5 m telescope.Comment: 5 pages, 4 figures, uses aipproc.sty, to appear in Proceedings of the
Fifth Compton Symposiu
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