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

The GeV-TeV Connection in Galactic gamma-ray sources

Recent observations with atmospheric Cherenkov telescope systems such as H.E.S.S. and MAGIC have revealed a large number of new sources of very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated along the Galactic plane. At lower energies (100 MeV - 10 GeV) the satellite-based instrument EGRET revealed a population of sources clustering along the Galactic Plane. Given their adjacent energy bands a systematic correlation study between the two source catalogues seems appropriate. Here, the populations of Galactic sources in both energy domains are characterised on observational as well as on phenomenological grounds. Surprisingly few common sources are found in terms of positional coincidence and spectral consistency. These common sources and their potential counterparts and emission mechanisms will be discussed in detail. In cases of detection only in one energy band, for the first time consistent upper limits in the other energy band have been derived. The EGRET upper limits are rather unconstraining due to the sensitivity mismatch to current VHE instruments. The VHE upper limits put strong constraints on simple power-law extrapolation of several of the EGRET spectra and thus strongly suggest cutoffs in the unexplored energy range from 10 GeV - 100 GeV. Physical reasons for the existence of cutoffs and for differences in the source population at GeV and TeV energies will be discussed. Finally, predictions will be derived for common GeV - TeV sources for the upcoming GLAST mission bridging for the first time the energy gap between current GeV and TeV instruments.Comment: (1) Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford, USA (2) Stanford University, W.W. Hansen Experimental Physics Lab (HEPL) and KIPAC, Stanford, USA (3) ICREA & Institut de Ciencies de l'Espai (IEEC-CSIC) Campus UAB, Fac. de Ciencies, Barcelona, Spain. (4) School of Physics and Astronomy, University of Leeds, UK. Paper Submitted to Ap

On the edges: Mennonite peacemakers on Christian peacemaker teams

This study explores how Christian Peacemaker Teams (CPT) members’ self-conceptions change throughout the course of their involvement with the CPT. To address this issue, I produce an ethnographic life history account of two members of CPT, Keith Rempel and Lena Siegers. This thesis offers both a descriptive survey of CPT and a record of the life histories collected through fieldwork with the organization. The thesis devotes special attention to how these CPT members understand their religious identities; specifically, their sense of being similar to or different from their families, friends and religious tradition—in this case, the Mennonite faith. Charles Taylor’s theories of identity formation form the basis of this investigation of Keith’s and Lena’s self-conceptions. Their understanding of their faith and how it motivates the work that they do in situations characterized by violence is also examined. There are two primary conclusions. First, while CPT connects with Keith’s and Lena’s identities, especially as Mennonites, involvement with CPT accentuates their actual and perceived difference from their families, friends and religious tradition. Second, work with CPT also strengthens Keith’s and Lena’s commitments to their faith, while at the same time making it more political

On hadronic beam models for quasars and microquasars

Most of the hadronic jet models for quasars (QSOs) and microquasars (MQs) found in literature represent beams of particles (e.g. protons). These particles interact with the matter in the stellar wind of the companion star in the system or with crossing clouds, generating gamma-rays via proton-proton processes. Our aim is to derive the particle distribution in the jet as seen by the observer, so that proper computation of the $\gamma$-ray and neutrino yields can be done. We use relativistic invariants to obtain the transformed expressions in the case of a power-law and power-law with a cutoff particle distribution in the beam. We compare with previous expressions used earlier in the literature. We show that formerly used expressions for the particle distributions in the beam as seen by the observer are in error, differences being strongly dependent on the viewing angle. For example, for $\Gamma =10$ ($\Gamma$ is the Lorentz factor of the blob) and angles larger than $\sim 20^o$, the earlier-used calculation entails an over-prediction (order of magnitude or more) of the proton spectra for $E>\Gamma mc^2$, whereas it always over-predicts (two orders of magnitude) the proton spectrum at lower energies, disregarding the viewing angle. All the results for photon and neutrino fluxes in hadronic models in beams that have made use of the earlier calculation are affected. Given that correct gamma-ray fluxes will be in almost any case significantly diminished in comparison with published results, and that the time of observations in Cherenkov facilities grows with the square of the flux-reduction factor in a statistically limited result, the possibility of observing hadronic beams is undermined.Comment: Accepted for publication in A&A Letter

Monte Carlo Calculations of Electron Emission at Surface Edges

A Monte Carlo method using Mott cross-sections for elastic scattering and a modification of the Bethe continuous-slowing-down by inelastic scattering at inner- shell electrons has been used to calculate linescans across surface edges and steps using a two-detector system for SE and BSE with exit momenta to the right (detector A) and to the left (detector B). The step height h=10R, R, R/2, R/5 and R/10 (R = electron range) and the inclination angles =30°- 80° of edges and steps have been varied to get information about the influence of these quantities on the linescans. The signals contain contributions by surface tilt contrast, electron diffusion contrast, self-shadowing of the specimen and \u27mutual illumination\u27 caused by backscattered electrons re-entering the specimen. The latter results in a larger increase of the signal for an extended step relative to a surface edge with the same angle The difference signals A-B contain information about the surface profile. The SE A-B signal is in first order proportional to tan and the BSE A-B signal is proportional to sin where denotes the local surface tilt angle. Reconstructions of the surface profile using the calculated signals show the errors caused by signal contributions different to pure surface tilt contrast