Testing the homogeneous synchrotron self Compton model for gamma ray production in Mrk 421

Based on the detected variability time scales of X-ray and TeV gamma-ray emission, and the observed multiwavelength photon spectrum, of Mrk 421 we place constraints on the allowed parameter space (magnetic field and Doppler factor of the emission region) for the homogeneous synchrotron self-Compton model. The spectra calculated for the allowed parameters are marginally consistent with the available spectral information above $\sim 1$ TeV reported by the Whipple Observatory in the case of a 1 day flare time scale. However, for the recently reported very short duration flares varying on a time scale of 15 min, the calculated spectra are significantly steeper, suggesting that the homogeneous synchrotron self Compton model has problems in describing the relatively flat observed spectra extending above a few TeV. We determine the maximum ratio of TeV gamma-ray luminosity to X-ray luminosity during flaring which is allowed by the homogeneous synchrotron self-Compton model for the case of no significant photon-photon absorption in the source.Comment: 5 pages, 2 figures, LaTeX uses mn.sty, submitted to MNRA

Gamma rays from interactions of stars with AGN jets

We have developed a model for gamma ray emission in jets of active galactic nuclei in which particle acceleration takes place at a shock in the relativistic jet plasma due to a massive star in the central region of the host galaxy moving through the jet. The gamma rays are produced in a pair-Compton cascade in the radiation field of the star initiated by accelerated electrons. Our model may account for the observed GeV to TeV gamma ray spectrum and variability of Markarian 421 and other blazars detected by the EGRET instrument on the Compton Gamma Ray Observatory.Comment: 5 pages, 3 figures, latex (uses mn.sty), submitted to MNRA

The physical parameters of Markarian 501 during flaring activity

We determine the physical parameters (magnetic field and Doppler factor) of the homogeneous synchrotron self-Compton model allowed by the observed X-ray to gamma-ray spectra and variability of Markarian~501 during the 15-16 April 1997 flaring activity. We find that magnetic fields between 0.07 G and 0.6 G and Doppler factors between 12 and 36 could fit (depending on observed variability time scale) these observations. We take account of photon-photon pair production interactions of gamma-ray photons occurring both inside the emission region and during propagation to Earth and find these to be extremely important in correctly determining the allowed model parameters. Previous estimates of the allowed parameter space have neglected this effect. Future multi-wavelength campaigns during strong flaring activity, including observations from optical to TeV gamma-rays, should enable the physical parameters to be further constrained.Comment: 18 pages, 5 figures, minor changes, additional reference, accepted for publication in MNRA

The quark strange star in the enlarged Nambu-Jona-Lasinio model

The strange quark star is investigated within the enlarged SU(3) Nambu-Jona-Lasinio (NJL). The stable quark star exists till maximal configutation with rho_m=3.1, 10^15, g/cm^3 with M_m=1.61, M_Sun and R_m=8.74, km is reached. Strange quarks appear for density above rho_c=9.84 g/cm^3 for the quark star with radius R_c=8.003 km and M_c=0.77, M_Sun. The comparison of a quark star properties obtained in the Quark Mean Field (QMF) approach to a neutron star model constructed within the Relativistic Mean Field (RMF) theory is presented.Comment: 23 pages, iop latex2e + hyperref, 11 figures, to appear in NJ

Structure and properties of neutron stars in the Relativistic Mean - Field Theory

Properties of rotating neutron stars with the use of relativistic mean-field theory are considered. The performed analysis of neutron star matter is based on the nonlinear Lgrangian density. The presence of nonlinear interaction of vector mesons modifies the density dependence of the rho field and influences bulk parameters of neutron stars. The observed quasi-periodic X-ray oscillations of low mass X-ray binaries can be used in order to constrain the equation of state of neutron star matter. Having assumed that the maximum frequency of the quasi periodic oscillations originates at the circular orbit it is possible to estimate masses and radii of neutron stars.Comment: 18 pages, latex2e, 10 colour eps figures, submitted to International Journal of Modern Physic

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

Review: \u27Flights of Imagination: Aviation, Landscape, Design\u27

The advent of powered flight in the early part of the twentieth century brought profound changes to society and culture globally. In her work Flights of Imagination: Aviation, Landscape, Design, Sonja Dümpelmann explores how it influenced the perspective and work of architects, landscape architects, and urban planners and designers, primarily in the United States and Europe. Specifically, the book “deals with those moments during the twentieth- and early twenty-first centuries when these professionals developed an aerial imagination and an epistemology based upon aerial vision, and when they realized the opportunities that the new technology offered them in shaping the land” (1). In addition to airport design, Dümpelmann examines such topics as the impact of aerial photography on both urban and landscape design, the development of the art and science of camouflage, and the relationship between aerial views and environmental thought