531 research outputs found
Gamma-ray absorption in the microquasar SS433
We discuss the gamma-ray absorption in the inner region of the microquasar
SS433. Our investigation includes several contributions to the opacity of this
system. They result from the ambient fields generated by the primary star,
possibly an A-type supergiant, and a very extended disk around the black hole.
Besides the sharp and dramatic absorption effect that occurs every time the
star crosses the emission zone, we find in the UV photon field from the
extended disk an important source of absorption for very high energy
gamma-rays. This results in periodic gamma-ray observational signatures.Comment: 8 pages, 9 figures, to appear in Astropart.Phy
An MHD study of SN 1006 and determination of the ambient magnetic field direction
In this work we employ an MHD numerical code to reproduce the morphology
observed for SN 1006 in radio synchrotron and thermal X-ray emission. We
introduce a density discontinuity, in the form of a flat cloud parallel to the
Galactic Plane, in order to explain the NW filament observed in optical
wavelengths and in thermal X-rays. We compare our models with observations. We
also perform a test that contrasts the radio emitting bright limbs of the SNR
against the central region, finding additional support to our results. Our main
conclusion is that the most probable direction of the ambient magnetic field is
on average perpendicular to the Galactic Plane.Comment: 7 pages, 5 figures, accepted by MNRA
3D MHD simulation of polarized emission in SN 1006
We use three dimensional magnetohydrodynamic (MHD) simulations to model the
supernova remnant SN 1006. From our numerical results, we have carried out a
polarization study, obtaining synthetic maps of the polarized intensity, the
Stokes parameter , and the polar-referenced angle, which can be compared
with observational results. Synthetic maps were computed considering two
possible particle acceleration mechanisms: quasi-parallel and
quasi-perpendicular. The comparison of synthetic maps of the Stokes parameter
maps with observations proves to be a valuable tool to discern
unambiguously which mechanism is taking place in the remnant of SN 1006, giving
strong support to the quasi-parallel model.Comment: 6 pages, 4 figures, accepted by MNRA
The neutral gas in the environs of the Geminga gamma-ray pulsar
We present a high-resolution (24 arcsec) study of the HI interstellar gas
distribution around the radio-quiet neutron star Geminga. Based on Very Large
Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field
around Geminga. These observations have revealed the presence of a neutral gas
shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which
surrounds Geminga at a radial velocity compatible with the kinematical distance
of the neutron star. In addition, morphological agreement is observed between
the internal face of the HI shell and the brightest structure of Geminga's tail
observed in X-rays.We explore the possibility that this morphological agreement
is the result of a physical association.Comment: One tarfile including a Latex file (7 pages) and two figures. Paper
accepted for publication in Advances in Space Research; typos corrected;
changes in section Results and Discussion after referee's suggestions. S.
Johnston's affilation correcte
G332.5-5.6, a new Galactic supernova remnant
We present radio observations of the source G332.5-5.6, a candidate supernova
remnant (SNR). Observations have been performed with the Australia Telescope
Compact Array (ATCA) at two frequencies, at 1.4 and 2.4 GHz. Our results
confirm that G332.5-5.6 is an SNR, with a spectral index equal to -0.7 +/- 0.2
for the whole source and an average fractional polarization of ~35% at 2.4 GHz.
The central component is coincident with extended X-ray emission and the
distance to the SNR is estimated to be ~3.4 kpc. Based on its radio and X-ray
morphology, this SNR should be classified as a composite, and we suggest that
it belongs to a trident-shaped subclass like G291.0-0.1.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
A molecular shell with star formation toward the supernova remnant G349.7+0.2
A field of ~38'x38' around the supernova remnant (SNR) G349.7+0.2 has been
surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO,
using the On-The-Fly technique. The resolution of the observations is 54". We
have found that this remnant is interacting with a small CO cloud which, in
turn, is part of a much larger molecular complex, which we call the ``Large CO
Shell''. The Large CO Shell has a diameter of about 100 pc, an H_2 mass of
930,000 solar masses, and a density of 35 cm-3. We investigate the origin of
this structure and suggest that an old supernova explosion ocurred about 4
million years ago, as a suitable hypothesis. Analyzing the interaction between
G349.7+0.2 and the Large CO Shell, it is possible to determine that the shock
front currently driven into the molecular gas is a non-dissociative shock
(C-type), in agreement with the presence of OH 1720 MHz masers. The positional
and kinematical coincidence among one of the CO clouds that constitute the
Large CO Shell, an IRAS point-like source and an ultracompact H II region,
indicate the presence of a recently formed star. We suggest that the formation
of this star was triggered during the expansion of the Large CO Shell, and
suggest the possibility that the same expansion also created the progenitor
star of G349.7+0.2. The Large CO Shell would then be one of the few
observational examples of supernova-induced star formation.Comment: accepted in Astronomical Journal, corrected typo in the abstract (in
first line, 38' instead of 38"
Magnetic field effects on neutrino production in microquasars
We investigate the effects of magnetic fields on neutrino production in
microquasars. We calculate the steady particle distributions for the pions and
muons generated in p-gamma and p-p interactions in the jet taking the effects
of all energy losses into account. The obtained neutrino emission is
significantly modified due to the synchrotron losses suffered by secondary
pions and muons. The estimates made for neutrino fluxes arriving on the Earth
imply that detection of high-energy neutrinos from the vicinity of the compact
object can be difficult. However, in the case of windy microquasars, the
interaction of energetic protons in the jet with matter of dense clumps of the
wind could produce detectable neutrinos. This is because the pions and muons at
larger distances from the compact object will not be affected by synchrotron
losses.Comment: 12 pages, 11 figures, accepted for publication in A&
Cyclotron motion and magnetic focusing in semiconductor quantum wells with spin-orbit coupling
We investigate the ballistic motion of electrons in III-V semiconductor
quantum wells with Rashba spin-orbit coupling in a perpendicular magnetic
field. Taking into account the full quantum dynamics of the problem, we explore
the modifications of classical cyclotron orbits due to spin-orbit interaction.
As a result, for electron energies comparable with the cyclotron energy the
dynamics are particularly rich and not adequately described by semiclassical
approximations. Our study is complementary to previous semiclassical approaches
concentrating on the regime of weaker fields.Comment: 14 pages, 8 figures included, version to appear in Phys. Rev.
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