RXTE observations of the dipping low-mass X-ray binary 4U 1624-49

We analyse ~ 360 ks of archival data from the Rossi X-Ray Timing Explorer (RXTE) of the 21 hr orbital period dipping low-mass X-ray binary 4U 1624-49. We find that outside the dips the tracks in the colour-colour and hardness-intensity diagrams (CDs and HIDs) are reminiscent of those of atoll sources in the middle and upper parts of the banana branch. The tracks show secular shifts up to ~ 10%. We study the power spectrum of 4U 1624-49 as a function of the position in the CD. This is the first time power spectra of this source are presented. No quasi-periodic oscillations (QPOs) are found. The power spectra are dominated by very low frequency noise (VLFN), characteristic for atoll sources in the banana state, and band limited noise (BLN) which is not reliably detected but may, uncharacteristically, strengthen and increase in frequency with spectral hardness. The VLFN fits to a power law, which becomes steeper when the source moves to the harder part of the CD. We conclude that 4U 1624-49 is an atoll source which in our observations is in the upper banana branch. Combining this with the high (0.5-0.7 L_Edd) luminosity, the long-term flux stability of the source as seen with the RXTE All-Sky Monitor (ASM), and with the fact that it is an X-ray dip source, we conclude that 4U 1624-49 is most likely a GX atoll source such as GX 3+1 and GX 9+9, but seen edge on.Comment: 8 pages, 5 figures, 2 tables, accepted for publication in A&A. This version: a few typos correcte

Improving green manure quality with phosphate rocks in Ontario Canada

Phosphate rock (PR) was applied to one conventional and two organic dairy fields and planted with buckwheat (Fagopyrum esculentum) as a green manure crop. In total, five types of PR were applied at three application rates in order to determine the yield, concentration of P in the aboveground tissue and the P uptake of buckwheat. It was found that PR of relatively high carbonate substitution and small particle diameter could increase buckwheat tissue concentrations to a quality such that mineralization of the buckwheat mulch could occur. Buckwheat mulch and residual PR increased soil P flux as determined by anion exchange membranes in situ in the following spring. This provides evidence that buckwheat of high P quality has the potential to supply P to a subsequent crop

X-ray spectral and timing properties of the 2001 superburst of 4U 1636-536

Preliminary results are reported on the spectral and timing properties of the spectacular 2001 superburst of 4U 1636-536 as seen by the RXTE/PCA. The (broad-band) power-spectral and hardness properties during the superburst are compared to those just before and after the superburst. Not all of the superburst emission can be fitted by pure black-body radiation. We also gathered BeppoSAX/WFC and RXTE/ASM data, as well as other RXTE/PCA data, obtained days to months before and after the superburst to investigate the normal X-ray burst behavior around the time of the superburst. The first normal X-ray burst after the 2001 superburst was detected 23 days later. During inspection of all the RXTE/ASM data we found a third superburst. This superburst took place on June 26, 1999, which is ~2.9 yrs after the 1996 superburst and ~1.75 yrs before the 2001 superburst. The above findings are the strongest constraints observed so far on the duration of the cessation of normal X-ray bursts after a superburst and the superburst recurrence times.Comment: 4 pages, 4 figures,to appear in the proceedings of "X-Ray Timing 2003: Rossi and Beyond", eds. P. Kaaret, F.K. Lamb, & J.H. Swank (Melville, NY: AIP

Polar decompositions of quaternion matrices in indefinite inner product spaces

Polar decompositions of quaternion matrices with respect to a given indefinite inner product are studied. Necessary and sufficient conditions for the existence of an $H$-polar decomposition are found. In the process an equivalent to Witt's theorem on extending $H$-isometries to $H$-unitary matrices is given for quaternion matrices