2,720 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
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A model for delayed emission in a very-high energy gamma-ray flare in Markarian 501
Recently, the MAGIC collaboration reported evidence for a delay in the
arrival times of photons of different energies during a gamma-ray flare from
the blazar Markarian 501 on 2005 July 9. We apply a homogeneous synchrotron
self-Compton (SSC) model under the assumption that the blob containing
relativistic electrons was observed in its acceleration phase. This modified
SSC model predicts the appearance of a gamma-ray flare first at lower energies
and subsequently at higher energies. Based on the reported time delay of
approx. 240 s between the flare observed at 190 GeV and 2.7 TeV, we predict a
delay on the order of 1 h if observed between 10 GeV and 100 GeV. Such delay
timescales can be tested in the future by simultaneous flare observations with
the Gamma Ray Large Area Space Telescope (GLAST) and Cherenkov telescopes.Comment: 4 pages, no figures, Astronomy & Astrophysics in pres
Magnetic-field asymmetry of electron wave packet transmission in bent channels capacitively coupled to a metal gate
We study the electron wave packet moving through a bent channel. We
demonstrate that the packet transmission probability becomes an uneven function
of the magnetic field when the electron packet is capacitively coupled to a
metal plate. The coupling occurs through a non-linear potential which
translates a different kinetics of the transport for opposite magnetic field
orientations into a different potential felt by the scattered electron
Magnetic-field-induced binding of few-electron systems in shallow quantum dots
Binding of few-electron systems in two-dimensional potential cavities in the
presence of an external magnetic field is studied with the exact
diagonalization approach. We demonstrate that for shallow cavities the
few-electron system becomes bound only under the application of a strong
magnetic field. The critical value of the depth of the cavity allowing the
formation of a bound state decreases with magnetic field in a non-smooth
fashion, due to the increasing angular momentum of the first bound state. In
the high magnetic field limit the binding energies and the critical values for
the depth of the potential cavity allowing the formation of a bound system tend
to the classical values
Accuracy of the Hartree-Fock method for Wigner molecules at high magnetic fields
Few-electron systems confined in two-dimensional parabolic quantum dots at
high magnetic fields are studied by the Hartree-Fock (HF) and exact
diagonalization methods. A generalized multicenter Gaussian basis is proposed
in the HF method. A comparison of the HF and exact results allows us to discuss
the relevance of the symmetry of the charge density distribution for the
accuracy of the HF method. It is shown that the energy estimates obtained with
the broken-symmetry HF wave functions become exact in the infinite
magnetic-field limit. In this limit the charge density of the broken-symmetry
solution can be identified with the classical charge distribution.Comment: to appear in EPJ
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