2,022 research outputs found
Photon-Photon Absorption of Very High Energy Gamma-Rays from Microquasars: Application to LS 5039
Very high energy (VHE) gamma-rays have recently been detected from the
Galactic black-hole candidate and microquasar LS 5039. A plausible site for the
production of these VHE gamma-rays is the region close to the mildly
relativistic outflow. However, at distances comparable to the binary
separation, the intense photon field of the stellar companion will lead to
substantial gamma-gamma absorption of VHE gamma-rays. If the system is viewed
at a substantial inclination (i > 0), this absorption feature will be modulated
on the orbital period of the binary as a result of a phase-dependent
stellar-radiation intensity and pair-production threshold. We apply our results
to LS 5039 and find that (1) gamma-gamma absorption effects will be substantial
if the photon production site is located at a distance from the central compact
object of the order of the binary separation (~ 2.5e12 cm) or less; (2) the
gamma-gamma absorption depth will be largest at a few hundred GeV, leading to a
characteristic absorption trough; (3) the gamma-gamma absorption feature will
be strongly modulated on the orbital period of the binary, characterized by a
spectral hardening accompanying periodic dips of the VHE gamma-ray flux; and
(4) gamma rays can escape virtually unabsorbed, even from within ~ 10^{12} cm,
when the star is located behind the production site as seen by the observer.Comment: Submitted to ApJ Letters. AASTeX, 12 ms pages, including 4 eps
figure
Geomagnetic field and altitude effects on the performance of future IACT arrays
The performance of IACT's arrays is sensitive to the altitude and geomagnetic
field (GF) of the observatory site. Both effects play important role in the
region of the sub-TeV gamma-ray measurements. We investigate the influence of
GF on detection rates and the energy thresholds for five possible locations of
the future CTA observatory using the Monte Carlo simulations. We conclude that
the detection rates of gamma rays and the energy thresholds of the arrays can
be fitted with linear functions of the altitude and the component of the GF
perpendicular to the shower axis core. These results can be directly
extrapolated for any possible localization of the CTA. In this paper we also
show the influence of both geophysical effects on the images of shower and
gamma/hadron separation.Comment: 4 pages, 6 figures, two-column. Contribution to ICRC 2013 proceeding
Stability of negative and positive trions in quantum wires
Binding energies of negative () and positive trions () in quantum
wires are studied for strong quantum confinement of carriers which results in a
numerical exactly solvable model. The relative electron and hole localization
has a strong effect on the stability of trions. For equal hole and electron
confinement, is more stable but a small imbalance of the particle
localization towards a stronger hole localization e.g. due to its larger
effective mass, leads to the interchange of and recombination lines
in the photoluminescent spectrum as was recently observed experimentally. In
case of larger stability, a magnetic field oriented parallel to the wire
axis leads to a stronger increase of the binding energy resulting in a
crossing of the and lines
Gamma-rays from binary system with energetic pulsar and Be star with aspherical wind: PSR B1259-63/SS2883
At least one massive binary system containing an energetic pulsar, PSR
B1259-63/SS2883, has been recently detected in the TeV gamma-rays by the HESS
telescopes. These gamma-rays are likely produced by particles accelerated in
the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization
of soft radiation from the massive star. However, the process of gamma-ray
production in such systems can be quite complicated due to the anisotropy of
the radiation field, complex structure of the pulsar wind termination shock and
possible absorption of produced gamma-rays which might initiate leptonic
cascades. In this paper we consider in detail all these effects. We calculate
the gamma-ray light curves and spectra for different geometries of the binary
system PSR B1259-63/SS2883 and compare them with the TeV gamma-ray
observations. We conclude that the leptonic IC model, which takes into account
the complex structure of the pulsar wind shock due to the aspherical wind of
the massive star, can explain the details of the observed gamma-ray light
curve.Comment: 12 pages, 11 figures, accepted for publication in MNRA
The influence of strength of hyperon-hyperon interactions on neutron star properties
An equation of state of neutron star matter with strange baryons has been
obtained. The effects of the strength of hyperon-hyperon interactions on the
equations of state constructed for the chosen parameter sets have been
analyzed. Numerous neutron star models show that the appearance of hyperons is
connected with the increasing density in neutron star interiors. The performed
calculations have indicated that the change of the hyperon-hyperon coupling
constants affects the chemical composition of a neutron star. The obtained
numerical hyperon star models exclude large population of strange baryons in
the star interior.Comment: 18 pages, 22 figures, accepted to be published in Journal of Physics
G: Nuclear and Particle Physic
Vitellogenins in the spider Parasteatoda tepidariorum â expression profile and putative hormonal regulation of vitellogenesis
Background: Knowledge about vitellogenesis in spiders is rudimentary. Therefore, the aim of study was to check
the vitellogenin (Vg) presence in various tissues of the female spider Parasteatoda tepidariorum, determine when
and where vitellogenesis starts and takes place, and the putative role of selected hormones in the vitellogenesis.
Results: Here we show two genes encoding Vg (PtVg4 and PtVg6) in the genome of the spider P. tepidariorum.
One gene PtVg4 and three subunits of Vg (250 kDa, 47 kDa and 30 kDa) are expressed in the midgut glands, ovaries
and hemolymph. Heterosynthesis of the Vg in the midgut glands and autosynthesis in the ovaries were observed.
Vitellogenesis begins in the last nymphal stage in the midgut glands (heterosynthesis). However, after sexual
maturity is reached, Vg is also synthesized in the ovaries (autosynthesis). Changes in the PtVg4 expression level and
in the Vg concentration after treatment with 20-hydroxyecdysone, a juvenile hormone analog (fenoxycarb) and an
antijuvenoid compound (precocene I) were observed. Therefore, we propose a hypothetical model for the hormonal
regulation of vitellogenesis in P. tepidariorum.
Conclusions: Our results are the first comprehensive study on spider vitellogenesis. In our opinion, this work will open
discussion on the evolutionary context of possible similarities in the hormonal control of vitellogenesis between
P. tepidariorum and other arthropods as well as their consequences
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