Gravitational microlensing of gamma-ray blazars

We present a detailed study of the effects of gravitational microlensing on compact and distant $\gamma$-ray blazars. These objects have $\gamma$-ray emitting regions which are small enough as to be affected by microlensing effects produced by stars lying in intermediate galaxies. We analyze the temporal evolution of the gamma-ray magnification for sources moving in a caustic pattern field, where the combined effects of thousands of stars are taken into account using a numerical technique. We propose that some of the unidentified $\gamma$-ray sources (particularly some of those lying at high galactic latitude whose gamma-ray statistical properties are very similar to detected $\gamma$-ray blazars) are indeed the result of gravitational lensing magnification of background undetected Active Galactic Nuclei (AGNs).Comment: 30 pages, 27 figures. Four figures are being submitted only as .gif files, and should be printed separately. The abstract below has been shortened from the actual version appearing in the pape

Discovery of a new radio galaxy within the error box of the unidentified gamma-ray source 3EG J1735-1500

We report the discovery of a new radio galaxy within the location error box of the gamma-ray source 3EG J1735-1500. The galaxy is a double-sided jet source forming a large angle with the line of sight. Optical observations reveal a V ~ 18 magnitude galaxy at the position of the radio core. Although the association with the EGRET source is not confirmed at the present stage, because there is a competing, alternative gamma-ray candidate within the location error contours which is also studied here, the case deserves further attention. The new radio galaxy can be used to test the recently proposed possibility of gamma-ray emitting radio galaxies beyond the already known case of Centaurus A.Comment: 12 pages, 3 figures. Accepted for publication in Ap

Permanent-magnet atom chips for the study of long, thin atom clouds

Atom-chip technology can be used to confine atoms tightly using permanently magnetised videotape along with external magnetic fields. The one-dimensional (1D) gas regime can be realised and studied by trapping the atoms in high-aspect-ratio traps in which the radial motion of the system is confined to zero-point oscillation

Cooling, Gravity and Geometry: Flow-driven Massive Core Formation

We study numerically the formation of molecular clouds in large-scale colliding flows including self-gravity. The models emphasize the competition between the effects of gravity on global and local scales in an isolated cloud. Global gravity builds up large-scale filaments, while local gravity -- triggered by a combination of strong thermal and dynamical instabilities -- causes cores to form. The dynamical instabilities give rise to a local focusing of the colliding flows, facilitating the rapid formation of massive protostellar cores of a few 100 M$_\odot$. The forming clouds do not reach an equilibrium state, though the motions within the clouds appear comparable to ``virial''. The self-similar core mass distributions derived from models with and without self-gravity indicate that the core mass distribution is set very early on during the cloud formation process, predominantly by a combination of thermal and dynamical instabilities rather than by self-gravity.Comment: 13 pages, 12 figures, accepted by Ap

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.

Microquasar models for 3EG J1828+0142 and 3EG J1735-1500

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.Comment: (1)Universitat de Barcelona, (2)Instituto Argentino de Radioastronomia (3) Facultad de Ciencias Astronomicas y Geofisicas (4)Lawrence Livermore National Laboratory 6 pages, 2 figures. Presented as a poster at the V Microquasar Workshop, Beijing, June 2004. Accepted for publication in the Chinese Journal of Astronomy & Astrophysic

Gamma-ray variability from wind clumping in HMXBs with jets

In the subclass of high-mass X-ray binaries known as "microquasars", relativistic hadrons in the jets launched by the compact object can interact with cold protons from the star's radiatively driven wind, producing pions that then quickly decay into gamma rays. Since the resulting gamma-ray emissivity depends on the target density, the detection of rapid variability in microquasars with GLAST and the new generation of Cherenkov imaging arrays could be used to probe the clumped structure of the stellar wind. We show here that the fluctuation in gamma rays can be modeled using a "porosity length" formalism, usually applied to characterize clumping effects. In particular, for a porosity length defined by h=l/f, i.e. as the ratio of the characteristic size l of clumps to their volume filling factor f, we find that the relative fluctuation in gamma-ray emission in a binary with orbital separation a scales as sqrt(h/pi a) in the "thin-jet" limit, and is reduced by a factor 1/sqrt(1 + phi a/(2 l)) for a jet with a finite opening angle phi. For a thin jet and quite moderate porosity length h ~ 0.03 a, this implies a ca. 10 % variation in the gamma-ray emission. Moreover, the illumination of individual large clumps might result in isolated flares, as has been recently observed in some massive gamma-ray binaries.Comment: Accepted for publication in ApJ; 5 pages, 1 figur

Interaction of the Electromagnetic p-Waves with Thin Metal Films

For the first time it is shown that for thin metallic films thickness of which not exceed thickness of skin-layer, the problem allows analytical solution for arbitrary boundary value problems. The analysis of dependence of coefficients of transmission, reflection and absorbtion on angle incidence, thickness of films and coefficient of specular reflection is carried out.Comment: 15 pages, 9 figure

A Holistic Scenario of Turbulent Molecular Cloud Evolution and Control of the Star Formation Efficiency. First Tests

We compile a holistic scenario for molecular cloud (MC) evolution and control of the star formation efficiency (SFE), and present a first set of numerical tests of it. A {\it lossy} compressible cascade can generate density fluctuations and further turbulence at small scales from large-scale motions, implying that the turbulence in MCs may originate from the compressions that form them. Below a {\it sonic} scale \ls, turbulence cannot induce any further subfragmentation, nor be a dominant support agent against gravity. Since progressively smaller density peaks contain progressively smaller fractions of the mass, we expect the SFE to decrease with decreasing \ls, at least when the cloud is globally supported by turbulence. Our numerical experiments confirm this prediction. We also find that the collapsed mass fraction in the simulations always saturates below 100% efficiency. This may be due to the decreased mean density of the leftover interclump medium, which in real clouds (not confined to a box) should then be more easily dispersed, marking the ``death'' of the cloud. We identify two different functional dependences (``modes'') of the SFE on \ls, which roughly correspond to globally supported and unsupported cases. Globally supported runs with most of the turbulent energy at the largest scales have similar SFEs to those of unsupported runs, providing numerical evidence of the dual role of turbulence, whereby large-scale turbulent modes induce collapse at smaller scales. We tentatively suggest that these modes may correspond to the clustered and isolated modes of star formation, although here they are seen to form part of a continuum rather than being separate modes. Finally, we compare with previous proposals that the relevant parameter is the energy injection scale.Comment: 6 pages, 3 figures. Uses emulateapj. Accepted in ApJ Letter