The swansong in context: long-timescale X-ray variability of NGC 4051

On 9-11 May 1998, the highly-variable, low luminosity Seyfert 1 galaxy NGC4051 was observed in an unusual low flux state by BeppoSAX (Guainazzi et al. 1998) RXTE and EUVE. We present fits of the 4-15 keV RXTE spectrum and BeppoSAX MECS spectrum obtained during this observation, which are consistent with the interpretation that the source had switched off, leaving only the spectrum of pure reflection from distant cold matter. We place this result in context by showing the X-ray lightcurve of NGC4051 obtained by our RXTE monitoring campaign over the past two and a half years, which shows that the low state lasted for ~150 days before the May observations (implying that the reflecting material is > 10^17 cm from the continuum source) and forms part of a lightcurve showing distinct variations in long-term average flux over timescales > months. We show that the long-timescale component to X-ray variability is intrinsic to the primary continuum and is probably distinct from the variability at shorter timescales, possibly associated with variations in the accretion flow of matter onto the central black hole. As the source approaches the low state, the variability process becomes non-linear. NGC4051 may represent a microcosm of all X-ray variability in radio quiet active galactic nuclei (AGNs), displaying in a few years a variety of flux states and variability properties which more luminous AGNs may pass through on timescales of decades to thousands of years.Comment: 5 pages, accepted for publication in MNRA

Short Timescale AGN X-ray Variability with EXOSAT: Black hole mass and Normalised Variability Amplitude

The old EXOSAT medium energy measurements of high frequency (HF) AGN power spectral normalisation are re-examined in the light of accurate black hole mass determinations which were not available when these data were first published (Green et al 1993). It is found that the normalised variability amplitude (NVA), measured directly from the power spectrum, is proportional to M^{beta} where beta ~ -0.54 +/- 0.08. As NVA is the square root of the power, these observations show that the normalisation of the HF power spectrum for this sample of AGN varies very close to inversely with black hole mass. Almost the same value of $\beta$ is obtained whether the quasar 3C273 is included in the sample or not, suggesting that the same process that drives X-ray variability in Seyfert galaxies applies also to 3C273. These observations support the work of Gierlinski et al (2008) who show that an almost exactly linear anticorrelation is required if the normalisations of the HF power spectra of AGN and X-ray binary systems are to scale similarly. These observations are also consistent with a number of studies showing that the short timescale variance of AGN X-ray lightcurves varies approximately inversely with mass.Comment: 6 pages, 2 figures, accepted for publication in Monthly Notices as a lette

Adult reading teachers’ beliefs about how less-skilled adult readers can be taught to read.

Despite large-scale interventions, significant numbers of adults worldwide continue to have problems with basic literacy, in particular in the area of reading. To be effective, adult reading teachers need expert knowledge at practitioner level. However, practices in adult reading education vary widely, often reflecting the individual beliefs of each teacher about how an adult can learn to read. In this study, phenomenographic analysis was used to identify categories of approaches to teaching adult reading, used by a group of 60 teachers in Western Australia and New Zealand. Four approaches were identified: reassurance, task-based, theory-based and responsive. It is argued that for teachers to become effective and consistent in responding to learner needs, they must understand their own beliefs and the consequences of these. The identification of different approaches in adult reading education is an important step in this process

An Elasticity Measure Of Welfare Loss In Symmetric Oligopoly

We derive a measure of welfare loss as a proportion of the value of sales under quantity-setting symmetric oligopoly in terms of the equilibrium industry price elasticity of demand, the number of firms in the industry and a conjectural variation term in the context of the standard linear model. This generalises the monopoly measure in James and McHardy (1997)

Airport Deregulation and Airline Competition

Liberalisation has affected all parts of the air travel industry, with airports as well as airlines increasingly run on commercial lines. This paper models interactions between airports and airlines to show that, for example, the potential benefits to passengers of increased competition between airlines may be (more than) absorbed by the unregulated airports through which they travel, and that effecting airport competition in one country may lead to the majority of the gains going abroad. The policy conclusion is that the (de)regulation of airlines and associated services should be fully co-ordinated and internationally coherent. Keywords: Airports, airlines, competition, deregulation

Measuring the Balance of Intra-Regional Trade

We introduce an original method of measuring the extent of the overall balance of migration among countries within a region which allows comparisons of the balance over time as well as between regions and various possible sub-regions

Airport Deregulation and Airline Competition

Liberalisation has affected all parts of the air travel industry, with airports as well as airlines increasingly run on commercial lines. This paper models interactions between airports and airlines to show that, for example, the potential benefits to passengers of increased competition between airlines may be (more than) absorbed by the unregulated airports through which they travel, and that effecting airport competition in one country may lead to the majority of the gains going abroad. The policy conclusion is that the (de)regulation of airlines and associated services should be fully co-ordinated and internationally coherent. Keywords: Airports, airlines, competition, deregulation

Secrecy versus patents: process innovations and the role of uncertainty

Whilst firms often prefer secrecy to patents and process innovations particu- larly lend themselves to secrecy, we establish a rationale for process innovators who patent. Using a simple two-period model, we show that under myopic op- timisation, the incentive to patent rather than pursue secrecy increases as the probability that the rival firm attaches to it being low-cost falls and as the pro- portion of the cost reduction due to the innovation, secured by the rival firm in the period after the patent has expired, falls. However, the gain to the innovating firm from patenting rather than secrecy strictly increases if the cost reduction due to the innovation is sufficiently small that the high-cost firm could profitably bluff that it is low-cost. Finally, allowing the low-cost firm the option of using an output signal in such cases, may make the patent strategy more or less attractive relative to the case of myopic optimisation

A Slower Superluminal Velocity for the Quasar 1156+295

As part of an ongoing effort to observe high energy gamma-ray blazars with VLBI, we have produced 8 and 2 GHz VLBI images, at ten epochs spanning the years 1988 to 1996, of the quasar 1156+295. The VLBI data have been taken from the Washington VLBI correlator's geodetic database. We have detected detected four components and have measured their apparent speeds to be 8.8 +/- 2.3, 5.3 +/- 1.1, 5.5 +/- 0.9, and 3.5 +/- 1.2 h^{-1}c from the outermost component inwards. (H_{0}=100h km/(s Mpc), q_{0}=0.5 throughout paper). These velocities contradict a previously published very high superluminal velocity of 26 h^{-1}c for this source.Comment: 8 pages, 2 figures, accepted to ApJ Letter

On the problem of network monopoly

We introduce a new regulatory concept: the independent profit-maximising agent, as a model for regulating a network monopoly. The agent sets prices on cross-network goods taking either a complete, or arbitrarily small, share of the associated profit. We examine welfare and profits with and without each agent type under both network monopoly and network duopoly. We show that splitting up the network monopoly (creating network duopoly) may be inferior for both firm(s) and society compared with a network monopoly "regulated" by an agent and that society always prefers any of the four agent regimes over network monopoly and network duopoly