One-zone SSC model for the core emission of Centaurus A revisited

Aims: We investigate the role of the second synchrotron self-Compton (SSC) photon generation to the multiwavelength emission from the compact regions of sources that are characterized as misaligned blazars. For this, we focus on the nearest high-energy emitting radio galaxy Centaurus A and we revisit the one-zone SSC model for its core emission. Methods: We have calculated analytically the peak luminosities of the first and second SSC components by, first, deriving the steady-state electron distribution in the presence of synchrotron and SSC cooling and, then, by using appropriate expressions for the positions of the spectral peaks. We have also tested our analytical results against those derived from a numerical code where the full emissivities and cross-sections were used. Results: We show that the one-zone SSC model cannot account for the core emission of Centaurus A above a few GeV, where the peak of the second SSC component appears. We, thus, propose an alternative explanation for the origin of the high energy ($\gtrsim 0.4$ GeV) and TeV emission, where these are attributed to the radiation emitted by a relativistic proton component through photohadronic interactions with the photons produced by the primary leptonic component. We show that the required proton luminosities are not extremely high, e.g. $\sim 10^{43}$ erg/s, provided that the injection spectra are modelled by a power-law with a high value of the lower energy cutoff. Finally, we find that the contribution of the core emitting region of Cen A to the observed neutrino and ultra-high energy cosmic-ray fluxes is negligible.Comment: 12 pages, 6 figures, 3 tables, accepted for publication in A&

On the spectral shape of radiation due to Inverse Compton Scattering close to the maximum cut-off

The spectral shape of radiation due to Inverse Compton Scattering is analyzed, in the Thomson and the Klein-Nishina regime, for electron distributions with exponential cut-off. We derive analytical, asymptotic expressions for the spectrum close to the maximum cut-off region. We consider monoenergetic, Planckian and Synchrotron photons as target photon fields. These approximations provide a direct link between the distribution of parent electrons and the up-scattered spectrum at the cut-off region.Comment: 27 pages, 15 figures, accepted for publication in Ap

Cold ultrarelativistic pulsar winds as potential sources of galactic gamma-ray lines above 100 GeV

The evidence of a line-like spectral feature at 130 GeV recently reported from some parts of the galactic plane poses serious challenges for any interpretation of this surprise discovery. It is generally believed that the unusually narrow profile of the spectral line cannot be explained by conventional processes in astrophysical objects, and, if real, is likely to be associated with Dark Matter. In this paper we argue that cold ultrarelativistic pulsar winds can be alternative sources of very narrow gamma-ray lines. We demonstrate that Comptonization of a cold ultrarelativistic electron-positron pulsar wind in the deep Klein-Nishina regime can readily provide very narrow distinct gamma-ray line features. To verify this prediction, we produced photon count maps based on the Fermi LAT data in the energy interval 100 to 140 GeV. We confirm earlier reports of the presence of marginal gamma-ray line-like signals from three regions of the galactic plane. Although the maps show some structure inside these regions, unfortunately the limited photon statistics do not allow any firm conclusion in this regard. The confirmation of 130 GeV line emission by low-energy threshold atmospheric Cherenkov telescope systems, in particular by the new 27 m diameter dish of the H.E.S.S. array, would be crucial for resolving the spatial structure of the reported hotspots, and thus for distinguishing between the Dark Matter and Pulsar origins of the `Fermi Lines'.Comment: 5 pages. 4 figure

Precarious workers, the casual workers' advice office and the 2014 labour relations act amendments

A research report submitted in partial fulfilment of the requirement for the degree of Master of Arts Industrial Sociology to the Faculty of Humanities, University of the Witwatersrand, 2017The contemporary precariousness of workers in South Africa can be understood from the historical development of South African labour regulations and policies. The acceleration of globalisation in the 1970s and the 1980s posed the labour movement with a challenge of flexible labour that rendered many workers precarious. Labour broking/Temporary Employment Services, part-time and contract work became the central strategy of capital rejuvenating itself and to avoid costs and legislation. This forced workers to engage in other forms of struggles to fight their precarious status as they found themselves on the periphery of the labour movement and legislative protection. In 2012 the government introduced the Labour Relations Bill that came to take effect in 2015 as the Labour Relations Act Amendment of 2014 to protect these groups of workers against the super-exploitative practices of flexible labour. This thesis explores the struggles of precarious workers at (and the role of) the Casual Workers’ Advice Office (CWAO) and self-organisation of workers in contemporary South Africa following the 2014 Labour Relations Amendments Act. The dissertation provides cases and notes struggles of workers at CWAO who sought to access their rights in terms of the LRA Amendments of 2014. It argues that the pursuit of legal struggles of various forms of precarious workers - TES, part-time and contract workers was important, but central to their victories was their own self-organisation, labour education and the role CWAO and David Cartwright Attorneys played in their struggles.MT 201

Non-variable TeV emission from the extended jet of a blazar in the stochastic acceleration scenario: the case of the hard TeV emission of 1ES 1101-232

The detections of X-ray emission from the kiloparsec-scale jets of blazars and radio galaxies may imply the existence of high energy electrons in these extended jets, and these electrons could produce high energy emission through inverse Compton (IC) process. In this paper we study the non-variable hard TeV emission from a blazar. The multi-band emission consists of two components: one is the traditional synchrotron self-Compton (SSC) emission from the inner jet, and the other is the emission produced via SSC and IC scattering of cosmic microwave background (CMB) photons (IC/CMB) and extragalactic background light (EBL) photons (IC/EBL) by relativistic electrons in the extended jet under the stochastic acceleration scenario. Such a model is applied to 1ES 1101-232. The results indicate that (1) the non-variable hard TeV emission of 1ES 1101-232 can be reproduced well, which is dominated by IC/CMB emission from the extended jet, using three characteristic values of Doppler factor ($\delta_{\rm D}=5,10,15$) for the TeV emitting region in the extended jet; and (2) in the cases of $\delta_{\rm D}=15$ and 10, the physical parameters can achieve the equipartition (or quasi-equipartition) between the relativistic electrons and the magnetic field; In contrast, the physical parameters largely deviate from the equipartition for the case of $\delta_{\rm D}=5$. It is therefore concluded that the TeV emission region of 1ES 1101-232 in the extended jet should be moderately or highly beamed.Comment: 8 pages, 4 figures, 2 tables, accepted for publication in MNRA

Maximising energy recovery from the brewery wastewater treatment system: a study evaluating the anaerobic digestion wastewater treatment plant at SAB's newlands brewery

Includes bibliography.This study has been encouraged by the successful recovery of useful energy from brewery wastewater using anaerobic digestion technology. It aims to evaluate the environmental benefits or burden of improving energy production by using organic brewery by-products as additional feedstock into the SABWTP. An environmental impact assessment on the SABWTP and its associated process was carried out using life cycle assessment (LCA) tools. Anaerobic digestibility of the two major organic brewery by-products, brewer’s spent grain and brewer’s spent yeast, was evaluated experimentally using laboratory bench scale reactors. The results were used to postulate the feasibility of adding these feedstocks into the SABWTP. Based on these findings, three viable processing scenarios were synthesised and assessed in terms of environmental impact analysis. In the environmental impact analysis, the three scenarios were compared using average process conditions and the main contributing factors to environmental burdens associated with each scenario were identified

Limits on the extragalactic background light in the Fermi era

Very high energy (VHE, energy $E \gtrsim 100$\,GeV) \gamma-rays from cosmological sources are attenuated due to the interaction with photons of the extragalactic background light (EBL) in the ultraviolet to infrared wavelength band. The EBL, thus, leaves an imprint on the observed energy spectra of these objects. In the last four years, the number of extragalactic VHE sources discovered with imaging atmospheric Cherenkov telescopes (IACTs), such as MAGIC, H.E.S.S., and VERITAS, has doubled. Furthermore, the measurements of the \emph{Fermi} satellite brought new insights into the intrinsic spectra of the sources at GeV energies. In this paper, upper limits on the EBL intensity are derived by considering the most extensive VHE source sample ever used in this context. This is accomplished by constructing a large number of generic EBL shapes and combining spectral informations from \emph{Fermi} and IACTs together with minimal assumptions about the source physics at high and very high \gamma-ray energies. The evolution of the EBL with redshift is accounted for and the possibility of the formation of an electromagnetic cascade and the implications on the upper limits are explored. The EBL density at $z=0$ is constrained over a broad wavelength range between 0.4 and 100\,\mu m. At optical wavelengths, the EBL density is constrained below 24\,nW\,m$^{-2}$\,sr$^{-1}$ and below 5\,nW\,m$^{-2}$\,sr$^{-1}$ between 8\,\mu m and 31\,\mu m.Comment: 14 pages, 10 figures; accepted for publication in Astronomy & Astrophysic

Effects of competition on consumer decision making : matching advertising to culture

The dual mediation model suggests that in addition to a direct effect, ad attitude (Aad) also has an indirect influence on brand attitude (Ab) through brand cognition (Cb). As well, brand attitude (Ab) influences purchase intention (PI). However, the model fails to take ad affect (AFFad) and confidence in evaluating a brand (CONb) into account, and it does not include competition. The competitive vulnerability model includes competition, but it lacks the fundamental constructs such as ad cognition (Cad), AFFad, and Aad. By integrating the dual mediation model and the competitive vulnerability model, this research offers a more comprehensive understanding of the effects of advertising on consumer brand choice behavior. This study also fills the void in the literature by extending the framework into a multicultural setting and examining whether the proposed consumer brand choice model is invariant across North American and Chinese cultures. Furthermore, the interaction effects of culture-laden advertising appeals, ad arguments, and culture-laden pictures on consumers' attitudes and purchase behavior are examined and compared between North American and Chinese consumers. Specifically, this comparison is examined in the multiple-ad and multiple-brand environment. A total of ten testable hypotheses are proposed. In order to test these hypotheses, two separate experiments are developed. Experiment 1 is designed to study the interaction effects of ad contents (i.e., weak and strong arguments) and advertising appeals (i.e., individualistic-laden and collectivistic-laden advertising appeals) on consumers' Cad, AFFad, Aad, Cb, Ab, CONb and PI in a competitive environment. Experiment 2 is designed to study the interaction effects of culture-laden pictures (i.e., individualistic-laden and collectivistic-laden pictures) and culture-laden advertising appeals on these measures in a competitive situation. Both experiments test the extended competitive vulnerability model and the interaction effects on consumer brand choice behavior across two cultures. In order to put the data for this dissertation to its most effective use, both experiments are undertaken with consumers, or "real people," and not from a student sample in North America and China. Such verification increases confidence in the findings. The data are analyzed using MANOVA and structural equation modeling. The results from this research contribute to the understanding of how the multiple-ads and multiple-brands influence consumer attitudes and purchase behavior in multicultural environments