Cut-offs and pile-ups in shock acceleration spectra

We have examined cutoffs and pile-ups due to various processes in the spectra of particles produced by shock acceleration, and found that, even in the absence of energy losses, the shape of the spectrum of accelerated particles at energies well below the nominal maximum energy depends strongly on the energy dependence of the diffusion coefficient. This has implications in many areas, for example, in fitting the observed cosmic ray spectrum with models based on power-law source spectra and rigidity dependent diffusive escape from the galaxy. With continuous energy losses, prominent pile-ups may arise, and these should be included when modelling synchrotron X-ray and inverse Compton gamma-ray spectra from a shock-accelerated electron population. We have developed a Monte Carlo/numerical technique to model the shape of the spectrum for the case of non-continuous energy losses such as inverse Compton scattering in the Klein-Nishina regime. We find that the shapes of the resulting cut-offs differ substantially from those arising from continuous processes, and we suggest that such differences could be observable through their effect on the spectrum of radiation emitted by a population of recently accelerated electrons as, for example, may exist in young supernova remnants.Comment: 23 pages, 8 figures, submitted to Astroparticle Physic

Cosmic ray antiprotons in closed galaxy model

The flux of secondary antiprotons expected for the leaky-box model was calculated as well as that for the closed galaxy model of Peters and Westergard (1977). The antiproton/proton ratio observed at several GeV is a factor of 4 higher than the prediction for the leaky-box model but is consistent with that predicted for the closed galaxy model. New low energy data is not consistent with either model. The possibility of a primary antiproton component is discussed

The brightness temperature problem in extreme IDV quasars: a model for PKS 0405-385

I re-examine the brightness temperature problem in PKS 0405-385 which is an extreme intra-day variable radio quasar with an inferred brightness temperature of $\sim 5 \times 10^{14}$ K at 5 GHz, well above the Compton catastrophe limit of $\sim 10^{11}$ K reached when the synchrotron photon energy density exceeds the energy density of the magnetic field. If one takes into account the uncertainty in the distance to the ionized clouds responsible for interstellar scintillation causing rapid intra-day variability in PKS 0405-385 it is possible that the brightness temperature could be as low as $\sim 10^{13}$ K at 5 GHz, or even lower. The radio spectrum can be fitted by optically thin emission from mono-energetic electrons, or an electron spectrum with a low-energy cut-off such that the critical frequency of the lowest energy electrons is above the radio frequencies of interest. If one observes optically thin emission along a long narrow emission region, the average energy density in the emission region can be many orders of magnitude lower than calculated from the observed intensity if one assumed a spherical emission region. I discuss the physical conditions in the emission region and find that the Compton catastrophe can then be avoided using a reasonable Doppler factor. I also show that MeV to 100 GeV gamma-ray emission at observable flux levels should be expected from extreme intra-day variable sources such as PKS 0405-385.Comment: 10 pages, 6 figures. Accepted for publication in MNRA

Integration of digital video sequences and supportive interactive animations into the Level 1 module Introductory Microbiology, to enhance the delivery and effectiveness of experimental microbiology.

Report of a CELT project on supporting students through innovation and researchFrom a previous innovations project during 2002/2003, the feasibility of producing and editing digital video of experimental microbiological procedures was established. The digital video was produced for eventual use on the Level 1 Introductory Microbiology within the University of Wolverhampton virtual learning environment (WOLF), to improve an understanding of the principles and practice of experimental procedures encountered on the module. In addition to the video sequences, supportive animations of the practical exercises were produced, to be viewed eventually by students in association with the video also via WOLF. The end of the previous project had produced several video and animation sequences, although these had not, at that time, been added to the WOLF topic. To provide an effective package of video and animation sequences to fully support the practical component of the module, more sequences were required, together with refinement of existing material. In addition, following integration into the WOLF topic, an analysis of the effectiveness of the sequences, in supporting an understanding of the theory and practice of the experimental exercises, was considered to be of value

Energy spectrum of extragalactic gamma-ray sources

The result of Monte Carlo electron photon cascade calculations for propagation of gamma rays through regions of extragalactic space containing no magnetic field are given. These calculations then provide upper limits to the expected flux from extragalactic sources. Since gamma rays in the 10 to the 14th power eV to 10 to the 17th power eV energy range are of interest, interactions of electrons and photons with the 3 K microwave background radiation are considered. To obtain an upper limit to the expected gamma ray flux from sources, the intergalactic field is assumed to be so low that it can be ignored. Interactions with photons of the near-infrared background radiation are not considered here although these will have important implications for gamma rays below 10 to the 14th power eV if the near infrared background radiation is universal. Interaction lengths of electrons and photons in the microwave background radiation at a temperature of 2.96 K were calculated and are given

A Proton Synchrotron Blazar Model for Flaring in Markarian~501

(abr.) The spectral energy distribution (SED) of blazars typically has a double-humped appearance usually interpreted in terms of synchrotron self-Compton models. In proton blazar models, the SED is instead explained in terms of acceleration of protons and subsequent cascading. We discuss a variation of the Synchrotron Proton Blazar model, first proposed by M\"ucke & Protheroe (1999), in which the low energy part of the SED is mainly synchrotron radiation by electrons co-accelerated with protons which produce the high energy part of the SED mainly asproton synchrotron radiation. Using a Monte Carlo/numerical technique to simulate the interactions and subsequent cascading of the accelerated protons, we are able to fit the observed SED of Markarian 501 during the April 1997 flare. We find that the emerging cascade spectra initiated by gamma-rays from $\pi^0$ decay and by $e^\pm$ from $\mu^\pm$ decay turn out to be relatively featureless. Synchrotron radiation produced by $\mu^\pm$ from $\pi^\pm$ decay, and even more importantly by protons, and subsequent synchrotron-pair cascading, is able to reproduce well the high energy part of the SED. For this fit we find that synchrotron radiation by protons dominates the TeV emission, pion photoproduction being less important with the consequence that we predict a lower neutrino flux than in other proton blazar models.Comment: 28 pages, 8 Figures, accepted for publication in Astropart.Phy