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

Gated combo nanodevice for sequential operations on single electron spin

An idea for a nanodevice in which an arbitrary sequence of three basic quantum single qubit gates - negation, Hadamard and phase shift - can be performed on a single electron spin. The spin state is manipulated using the spin-orbit coupling and the electron trajectory is controlled by the electron wave function self-focusing mechanism due to the electron interaction with the charge induced on metal gates. We present results of simulations based on iterative solution of the time dependent Schr\"odinger equation in which the subsequent operations on the electron spin can be followed and controlled. Description of the moving electron wave packet requires evaluation of the electric field within the entire nanodevice in each time step

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

Simulation of Ultra-High Energy Photon Propagation in the Geomagnetic Field

The identification of primary photons or specifying stringent limits on the photon flux is of major importance for understanding the origin of ultra-high energy (UHE) cosmic rays. We present a new Monte Carlo program allowing detailed studies of conversion and cascading of UHE photons in the geomagnetic field. The program named PRESHOWER can be used both as an independent tool or together with a shower simulation code. With the stand-alone version of the code it is possible to investigate various properties of the particle cascade induced by UHE photons interacting in the Earth's magnetic field before entering the Earth's atmosphere. Combining this program with an extensive air shower simulation code such as CORSIKA offers the possibility of investigating signatures of photon-initiated showers. In particular, features can be studied that help to discern such showers from the ones induced by hadrons. As an illustration, calculations for the conditions of the southern part of the Pierre Auger Observatory are presented.Comment: 41 pages, 9 figures, added references in introduction, corrected energy in row 1 of Table 3, extended caption of Table

Gamma Rays from Compton Scattering in the Jets of Microquasars: Application to LS 5039

Recent HESS observations show that microquasars in high-mass systems are sources of VHE gamma-rays. A leptonic jet model for microquasar gamma-ray emission is developed. Using the head-on approximation for the Compton cross section and taking into account angular effects from the star's orbital motion, we derive expressions to calculate the spectrum of gamma rays when nonthermal jet electrons Compton-scatter photons of the stellar radiation field. Calculations are presented for power-law distributions of nonthermal electrons that are assumed to be isotropically distributed in the comoving jet frame, and applied to $\gamma$-ray observations of LS 5039. We conclude that (1) the TeV emission measured with HESS cannot result only from Compton-scattered stellar radiation (CSSR), but could be synchrotron self-Compton (SSC) emission or a combination of CSSR and SSC; (2) fitting both the HESS data and the EGRET data associated with LS 5039 requires a very improbable leptonic model with a very hard electron spectrum. Because the gamma rays would be variable in a leptonic jet model, the data sets are unlikely to be representative of a simultaneously measured gamma-ray spectrum. We therefore attribute EGRET gamma rays primarily to CSSR emission, and HESS gamma rays to SSC emission. Detection of periodic modulation of the TeV emission from LS 5039 would favor a leptonic SSC or cascade hadron origin of the emission in the inner jet, whereas stochastic variability alone would support a more extended leptonic model. The puzzle of the EGRET gamma rays from LS 5039 will be quickly solved with GLAST. (Abridged)Comment: 17 pages, 11 figures, ApJ, in press, June 1, 2006, corrected eq.

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

Time-Dependent Synchrotron and Compton Spectra from Jets of Microquasars

Jet models for the high-energy emission of Galactic X-ray binary sources have regained significant interest with detailed spectral and timing studies of the X-ray emission from microquasars, the recent detection by the HESS collaboration of very-high-energy gamma-rays from the microquasar LS~5039, and the earlier suggestion of jet models for ultraluminous X-ray sources observed in many nearby galaxies. Here we study the synchrotron and Compton signatures of time-dependent electron injection and acceleration, adiabatic and radiative cooling, and different jet geometries in the jets of Galactic microquasars. Synchrotron, synchrotron-self-Compton, and external-Compton radiation processes with soft photons provided by the companion star and the accretion disk are treated. An analytical solution is presented to the electron kinetic equation for general power-law geometries of the jets for Compton scattering in the Thomson regime. We pay particular attention to predictions concerning the rapid flux and spectral variability signatures expected in a variety of scenarios, making specific predictions concerning possible spectral hysteresis, similar to what has been observed in several TeV blazars. Such predictions should be testable with dedicated monitoring observations of Galactic microquasars and ultraluminous X-ray sources using Chandra and/or XMM-Newton.Comment: Accepted for publication in ApJ; 37 manuscript pages, including 10 eps figures; uses AASTeX macro