Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4-3114

Sharp dips observed in the pulse profiles of three X-ray pulsars (GX 1+4, RX J0812.4-3114 and A 0535+26) have previously been suggested to arise from partial eclipses of the emission region by the accretion column occurring once each rotation period. We present pulse-phase spectroscopy from Rossi X-ray Timing Explorer satellite observations of GX 1+4 and RX J0812.4-3114 which for the first time confirms this interpretation. The dip phase corresponds to the closest approach of the column axis to the line of sight, and the additional optical depth for photons escaping from the column in this direction gives rise to both the decrease in flux and increase in the fitted optical depth measured at this phase. Analysis of the arrival time of individual dips in GX~1+4 provides the first measurement of azimuthal wandering of a neutron star accretion column. The column longitude varies stochastically with standard deviation 2-6 degrees depending on the source luminosity. Measurements of the phase width of the dip both from mean pulse profiles and individual eclipses demonstrates that the dip width is proportional to the flux. The variation is consistent with that expected if the azimuthal extent of the accretion column depends only upon the Keplerian velocity at the inner disc radius, which varies as a consequence of the accretion rate Mdot.Comment: 7 pages, 5 figures, accepted by MNRAS. Included reference

Producing poultry meat for profit - Part 2

Because the profit per bird is usually small, large numbers must be reared and marketed to give a worthwhile income from poultry meat production. Factors such as feed and labour costs, the degree of cheapness or availability of other meats— and similar influences over which the poultry meat producer has little or no control— are liable to bring about unpredictable variations in returns over a period

Seven factors in profitable poultry farming

Profitable poultry farming depends upon getting the greatest number of eggs from the birds by good breeding and management, and carrying enough birds to give a reasonable income

Planning boosts poultry profits

Amazing as it may seem, the time and labour expended in the ordinary everyday chores on a poultry farm carrying 1,000 birds can be reduced five times by adopting modern efficiency methods. This will appeal to poultry farmers in this State who know that low labour costs are closely linked to high profits

Spectral variation in the X-ray pulsar GX 1+4 during a low-flux episode

The X-ray pulsar GX 1+4 was observed with the RXTE satellite for a total of 51ks between 1996 July 19 - 21. During this period the flux decreased smoothly from an initial mean level of ~ 6 X 10^36 erg/s to a minimum of ~ 4 X 10^35 erg/s (2-60 keV, assuming a source distance of 10 kpc) before partially recovering towards the initial level at the end of the observation. BATSE pulse timing measurements indicate that a torque reversal took place approximately 10 d after this observation. Both the mean pulse profile and the photon spectrum varied significantly. The observed variation in the source may provide important clues as to the mechanism of torque reversals. The single best-fitting spectral model was based on a component originating from thermal photons with kT ~ 1 keV Comptonised by a plasma of temperature kT \~ 7 keV. Both the flux modulation with phase during the brightest interval and the evolution of the mean spectra over the course of the observation are consistent with variations in this model component; with, in addition, a doubling of the column density nH contributing to the mean spectral change. A strong flare of duration 50 s was observed during the interval of minimum flux, with the peak flux ~ 20 times the mean level. Although beaming effects are likely to mask the true variation in Mdot thought to give rise to the flare, the timing of a modest increase in flux prior to the flare is consistent with dual episodes of accretion resulting from successive orbits of a locally dense patch of matter in the accretion disc.Comment: 8 pages, 3 figures, submitted to MNRA

Caponising cockerels

Because of its tenderness, succulence and delicate flavour, the flesh of the capon has long been held in high regard by epicures in many lands. Over three centuries have passed since Shakespeare wrote of the portly justice whose fair round belly was with fat capon lined, but throughout the years capons have usually commanded high prices from discriminating consumers of table poultry

Christmas Island rock phosphate in poultry feeding trials

In Western Australia, increasing quantities of ground rock phosphate from Christmas Island are being incorporated in stock foods to increase the calcium and phosphorus content. In a previous article (Snook 1958) experiments are reported which indicate that this particular rock phosphate can be incorporated in the rations of laying hens without any apparent effect on the health or productivity of the birds