Modeling quasar accretion disc temperature profiles

Microlensing observations indicate that quasar accretion discs have half-light radii larger than expected from standard theoretical predictions based on quasar fluxes or black hole masses. Blackburne and colleagues have also found a very weak wavelength dependence of these half-light radii. We consider disc temperature profile models that might match these observations. Nixon and colleagues have suggested that misaligned accretion discs around spinning black holes will be disrupted at radii small enough for the Lense-Thirring torque to overcome the disc's viscous torque. Gas in precessing annuli torn off a disc will spread radially and intersect with the remaining disc, heating the disc at potentially large radii. However, if the intersection occurs at an angle of more than a degree or so, highly supersonic collisions will shock-heat the gas to a Compton temperature of T~10^7 K, and the spectral energy distributions (SEDs) of discs with such shock-heated regions are poor fits to observations of quasar SEDs. Torn discs where heating occurs in intermittent weak shocks that occur whenever the intersection angle reaches a tenth of a degree pose less of a conflict with observations, but do not have significantly larger half-light radii than standard discs. We also study two phenomenological disc temperature profile models. We find that discs with a temperature spike at relatively large radii and lowered temperatures at radii inside the spike yield improved and acceptable fits to microlensing sizes in most cases. Such temperature profiles could in principle occur in sub-Keplerian discs partially supported by magnetic pressure. However, such discs overpredict the fluxes from quasars studied with microlensing except in the limit of negligible continuum emission from radii inside the temperature spike.Comment: Submitted to MNRAS. Comments welcome. 20 pages, 5 figure

Organizational and corporate identity revisited: Towards a comprehensive understanding of identity in business

ABSTRACT: Purpose – This paper provides a comprehensive and integrative review of academic literature analyzing identity in business. The literature review proposed by the authors helps clearing up theoretical and practical understanding of this concept. Design/methodology/approach – A review of existing literature in organizational behavior and marketing fields is proposed to clarify the meaning of organizational and corporate identity. On the basis of this review, the authors also identify an integrative perspective proposed for managers to identify and effectively manage all dimensions of their business identities. Findings – Literature on the identity of businesses is extensive and blurred, failing to provide useful guidance for practitioners to manage this concept. A new approach proposes understanding this kind of identity as a global concept that integrates proposals from diverse research fields in order to take advantage of cross-fertilization. Practical implications – This research allows identity and communication managers to understand dimensions of business identity for a more effective management of this concept in their organizations. Originality/value – The line of research that proposes an integrative multidisciplinary approach to the study of identity in business is quite new and, as so, it still needs further contributions to clarify this nascent domain. In this paper, the authors also classify previous studies on business identity according to the theoretical approach they assume just as no other research has done before. Borra