BeppoSAX-WFC monitoring of the Galactic Center region

We review the results obtained with the Galactic center campaigns of the BeppoSAX Wide Field X-ray Cameras (WFCs). This pertains to the study of luminous low-mass X-ray binaries (LMXBs). When pointed at the Galactic center, the WFC field of view contains more than half of the Galactic LMXB population. The results exemplify the excellent WFC capability to detect brief X-ray transients. Firstly, the WFCs expanded the known population of Galactic thermonuclear X-ray bursters by 50%. At least half of all LMXBs are now established to burst and, thus, to contain a neutron star as compact accretor rather than a black hole candidate. We provide a complete list of all 76 currently known bursters, including the new case 1RXS J170854.4-321857. Secondly, the WFCs have uncovered a population of weak transients with peak luminosities up to ~10^37 erg/s and durations from days to weeks. One is the first accretion-powered millisecond pulsar SAX J1808.4-3658. Thirdly, the WFCs contributed considerably towards establishing that nearly all (12 out of 13) luminous low-mass X-ray binaries in Galactic globular clusters contain neutron stars rather than black holes. Thus, the neutron star to black hole ratio in clusters differs from that in the Galactic disk at a marginal confidence level of 97%.Comment: 10 pages 6 figures, to appear in Proc. "The Restless High-Energy Universe" (2nd BeppoSAX Symposium), eds. E.P.J. van den Heuvel, J.J.M. in 't Zand & R.A.M.J. Wijers, Nucl. Instrum. Meth. B Suppl. Se

Discovery of SAX J1753.5-2349 and SAX J1806.5-2215: two X-ray bursters without detectable steady emission

We report the discovery with BeppoSAX-WFC of two new X-ray sources that were only seen during bursts: SAX J1753.5-2349 and SAX J1806.5-2215. For both sources, no steady emission was detected above an upper limit of 5 mCrab (2 to 8 keV) for 3 10**5 s around the burst events. The single burst detected from SAX J1753.5-2349 shows spectral softening and a black body color temperature of 2.0 keV. Following the analogy with bursts in other sources the burst very likely originates in a thermonuclear flash on a neutron star. The first of two burst detected from SAX J1806.5-2215 does not show spectral softening and cannot be confirmed as a thermonuclear flash.Comment: 4 pages, 4 figures, to be published in Proceedings of the Symposium "The Active X-Ray Sky: Results from BeppoSAX and Rossi-XTE", Rome, Italy, 21-24 October, 1997, Nuclear Physics B Proceedings Supplements. Eds. L. Scarsi, H. Bradt, P. Giommi, and F. Fior

Bright X-ray bursts from 1E 1724-3045 in Terzan 2

During about 3 years wide field monitoring of the Galactic Center region by the WFC telescopes on board the BeppoSAX satellite, a total of 14 type-I X-ray bursts were detected from the burster 1E 1724-3045 located in the globular cluster Terzan 2. All the observed events showed evidence for photospheric radius expansion due to Eddington-limit burst luminosity, thus leading to an estimate of the source distance (~7.2 kpc). Preliminary results of the analysis of the bursts are presented.Comment: 5 pages, 2 figures, Proc. 5th Compton Symp., Portsmouth 199

The use of artificial neural networks to study fatty acids in neuropsychiatric disorders

<p>Abstract</p> <p>Background</p> <p>The range of the fatty acids has been largely investigated in the plasma and erythrocytes of patients suffering from neuropsychiatric disorders. In this paper we investigate, for the first time, whether the study of the platelet fatty acids from such patients may be facilitated by means of artificial neural networks.</p> <p>Methods</p> <p>Venous blood samples were taken from 84 patients with a DSM-IV-TR diagnosis of major depressive disorder and from 60 normal control subjects without a history of clinical depression. Platelet levels of the following 11 fatty acids were analyzed using one-way analysis of variance: C14:0, C16:0, C16:1, C18:0, C18:1 <it>n</it>-9, C18:1 <it>n</it>-7, C18:2 <it>n</it>-6, C18:3 <it>n</it>-3, C20:3 <it>n</it>-3, C20:4 <it>n</it>-6 and C22:6 <it>n</it>-3. The results were then entered into a wide variety of different artificial neural networks.</p> <p>Results</p> <p>All the artificial neural networks tested gave essentially the same result. However, one type of artificial neural network, the self-organizing map, gave superior information by allowing the results to be described in a two-dimensional plane with potentially informative border areas. A series of repeated and independent self-organizing map simulations, with the input parameters being changed each time, led to the finding that the best discriminant map was that obtained by inclusion of just three fatty acids.</p> <p>Conclusion</p> <p>Our results confirm that artificial neural networks may be used to analyze platelet fatty acids in neuropsychiatric disorder. Furthermore, they show that the self-organizing map, an unsupervised competitive-learning network algorithm which forms a nonlinear projection of a high-dimensional data manifold on a regular, low-dimensional grid, is an optimal type of artificial neural network to use for this task.</p