Civil religion and political theology

Reviewed Book: Rouner, Leroy S. Civil religion and political theology. Notre Dame, Ind: University of Notre Dame Press, 1986. Boston University studies in philosophy and religio

High-energy particle transport in 3D hydrodynamic models of colliding-wind binaries

Massive stars in binary systems (as WR140, WR147 or $\eta$ Carinae) have long been regarded as potential sources of high-energy $\gamma$-rays. The emission is thought to arise in the region where the stellar winds collide and produce relativistic particles which subsequently might be able to emit $\gamma$-rays. Detailed numerical hydrodynamic simulations have already offered insight in the complex dynamics of the wind collision region (WCR), while independent analytical studies, albeit with simplified descriptions of the WCR, have shed light on the spectra of charged particles. In this paper, we describe a combination of these two approaches. We present a 3D-hydrodynamical model for colliding stellar winds and compute spectral energy distributions of relativistic particles for the resulting structure of the WCR. The hydrodynamic part of our model incorporates the line-driven acceleration of the winds, gravity, orbital motion and the radiative cooling of the shocked plasma. In our treatment of charged particles we consider diffusive shock acceleration in the WCR and the subsequent cooling via inverse Compton losses (including Klein-Nishina effects), bremsstrahlung, collisions and other energy loss mechanisms.Comment: 28 pages, 9 figures / accepted for publication in The Astrophysical Journa

The new surprising behaviour of the two "prototype" blazars PKS 2155-304 and 3C 279

Recent VHE observations have unveiled a surprising behaviour in two well-known blazars at opposite sides of the blazar sequence. PKS 2155-304 have shown for the first time in an HBL a large Compton dominance, high gamma-ray luminosities and a cubic relation between X-ray and VHE fluxes. 3C 279 is the first FSRQ detected at VHE. The high luminosity required to overcome the significant absorption caused by the BLR emission cannot be easily reconciled with the historical and quasi-simultaneous SED properties. Both cases shed a new light on the structure and ambient fields of blazars. Contrary to previous claims, it is also shown that 3C 279 --as any FSRQ-- cannot in general provide robust constraints on the EBL.Comment: Proceedings of "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008" (Gamma 2008), July 7-11, 2008. Slightly refined text with updated reference

Optimal trading strategies - a time series approach

Motivated by recent advances in the spectral theory of auto-covariance matrices, we are led to revisit a reformulation of Markowitz' mean-variance portfolio optimization approach in the time domain. In its simplest incarnation it applies to a single traded asset and allows to find an optimal trading strategy which - for a given return - is minimally exposed to market price fluctuations. The model is initially investigated for a range of synthetic price processes, taken to be either second order stationary, or to exhibit second order stationary increments. Attention is paid to consequences of estimating auto-covariance matrices from small finite samples, and auto-covariance matrix cleaning strategies to mitigate against these are investigated. Finally we apply our framework to real world data

Parameter constraints for high-energy models of colliding winds of massive stars: the case WR 147

We explore the ability of high energy observations to constrain orbital parameters of long period massive binary systems by means of an inverse Compton model acting in colliding wind environments. This is particular relevant for (very) long period binaries where orbital parameters are often poorly known from conventional methods, as is the case e.g. for the Wolf-Rayet (WR) star binary system WR 147 where INTEGRAL and MAGIC upper limits on the high-energy emission have recently been presented. We conduct a parameter study of the set of free quantities describing the yet vaguely constrained geometry and respective effects on the non-thermal high-energy radiation from WR 147. The results are confronted with the recently obtained high-energy observations and with sensitivities of contemporaneous high-energy instruments like Fermi-LAT. For binaries with sufficient long periods, like WR 147, gamma-ray attenuation is unlikely to cause any distinctive features in the high-energy spectrum. This leaves the anisotropic inverse Compton scattering as the only process that reacts sensitively on the line-of-sight angle with respect to the orbital plane, and therefore allows the deduction of system parameters even from observations not covering a substantial part of the orbit. Provided that particle acceleration acts sufficiently effectively to allow the production of GeV photons through inverse Compton scattering, our analysis indicates a preference for WR 147 to possess a large inclination angle. Otherwise, for low inclination angles, electron acceleration is constrained to be less efficient as anticipated here.Comment: 33 pages, 9 figures; accepted by Ap

TeV gamma rays and cosmic rays from the nucleus of M87, a mis-aligned BL Lac object

The unresolved nuclear region of M87 emits strong non-thermal emission from radio to X-rays. Assuming this emission to originate in the pc scale jet aligned at $\theta \sim 30^\circ$ to the line of sight, we interpret this emission in the context of the Synchrotron Proton Blazar (SPB) model. We find the observed nuclear jet emission to be consistent with M87 being a mis-aligned BL Lac Object and predict gamma-ray emission extending up to at least 100 GeV at a level easily detectable by GLAST and MAGIC, and possibly by VERITAS depending on whether it is high-frequency or low-frequency peaked. Predicted neutrino emission is below the sensitivity of existing and planned neutrino telescopes. Ultra-high energy neutrons produced in pion photoproduction interactions decay into protons after escaping from the host galaxy. Because energetic protons are deflected by the intergalactic magnetic field, the protons from the decay of neutrons emitted in all directions, including along the jet axis where the Doppler factor and hence emitted neutron energies are higher, can contribute to the observed ultra-high energy cosmic rays. We consider the propagation of these cosmic ray protons to Earth and conclude that M87 could account for the observed flux if the extragalactic magnetic field topology were favourable.Comment: 17 pages, 6 figures. 3 additional references plus minor changes, acctepted for publication in Astroparticle Physic