Discovery of a New 89 Second X-ray Pulsar XTE J1906+09

We report on the discovery of a new pulsating X-ray source during Rossi X-ray Timing Explorer observations of a low galactic latitude field centered at RA (J2000) = 19 hr 05 m 43 s and Dec (J2000) = +08 deg 58 arcmin 48 arcsec. Significant pulsations were detected by both the PCA and HEXTE instruments aboard RXTE at a fundamental period of 89.17 +/- 0.02 seconds, with higher harmonics also visible in the 2-10 keV power spectrum. The folded lightcurve from the source is multiply peaked at lower energies, and changes to single peaked morphology above ~20 keV. The phase averaged spectrum from the source is well fit by strongly absorbed power law or thermal bremsstrahlung spectral models of photon index 1.9 +/- 0.1 or temperature 19.5 +/- 4.6 keV, respectively. The mean neutral hydrogen column density is approximately 10^23 cm^-2, suggesting a distance of >10 kpc to the source and a minimum 2-10 keV X-ray luminosity of 2*10^{35} ergs s^{-1}. By comparison with other pulsars with similar periods and luminosities, we suggest that XTE J1906+09 has a supergiant companion with an underfilled Roche lobe. We speculate further that one of the M stars in a peculiar M star binary system may be the companion.Comment: 14 pages, 2 figures. Accepted by ApJ Letter

Disappearing Pulses in Vela X-1

We present results from a 20 h RXTE observation of Vela X-1, ncluding a peculiar low state of a few hours duration, during which the pulsation of the X-ray emission ceased, while significant non-pulsed emission remained. This ``quiescent state'' was preceded by a ``normal state'' without any unusual signs and followed by a ``high state'' of several hours of increased activity with strong, flaring pulsations. while there is clear spectral evolution from the normal state to the low state, the spectra of the following high state are surprisingly similar to those of the low state.Comment: 5 pages, 5 figures, Proceedings of the 5th Compton Symposium, AIP, in pres

Spectrum of the gamma-ray diffuse component observed from HEAO-1

The spectrum of the diffuse X and gamma ray background was measured between 15 keV and 4 MeV with the scintillation detectors aboard the HEAO 1 satellite. The apertures of the detectors were modulated on time scales of hours and the difference in counting rates measured the diffuse component flux. The observed spectrum is presented and compared with other measurements. At least two components are indicated, one below -100 keV and the other above. Possible origins are discussed

The flux phase problem on the ring

We give a simple proof to derive the optimal flux which minimizes the ground state energy in one dimensional Hubbard model, provided the number of particles is even.Comment: 8 pages, to appear in J. Phys. A: Math. Ge

A discrete methodology for controlling the sign of curvature and torsion for NURBS

This paper develops a discrete methodology for approximating the so-called convex domain of a NURBS curve, namely the domain in the ambient space, where a user-specified control point is free to move so that the curvature and torsion retains its sign along the NURBS parametric domain of definition. The methodology provides a monotonic sequence of convex polyhedra, converging from the interior to the convex domain. If the latter is non-empty, a simple algorithm is proposed, that yields a sequence of polytopes converging uniformly to the restriction of the convex domain to any user-specified bounding box. The algorithm is illustrated for a pair of planar and a spatial Bézier configuration

2-10 keV luminosity of high-mass binaries as a gauge of ongoing star-formation rate

Based on recent work on spectral decomposition of the emission of star-forming galaxies, we assess whether the integrated 2-10 keV emission from high-mass X-ray binaries (HMXBs), L_{2-10}^{HMXB}, can be used as a reliable estimator of ongoing star formation rate (SFR). Using a sample of 46 local (z < 0.1) star forming galaxies, and spectral modeling of ASCA, BeppoSAX, and XMM-Newton data, we demonstrate the existence of a linear SFR-L_{2-10}^{HMXB} relation which holds over ~5 decades in X-ray luminosity and SFR. The total 2-10 keV luminosity is not a precise SFR indicator because at low SFR (i.e., in normal and moderately-starbursting galaxies) it is substantially affected by the emission of low-mass X-ray binaries, which do not trace the current SFR due to their long evolution lifetimes, while at very high SFR (i.e., for very luminous FIR-selected galaxies) it is frequently affected by the presence of strongly obscured AGNs. The availability of purely SB-powered galaxies - whose 2-10 keV emission is mainly due to HMXBs - allows us to properly calibrate the SFR-L_{2-10}^{HMXB} relation. The SFR-L_{2-10}^{HMXB} relation holds also for distant (z ~ 1) galaxies in the Hubble Deep Field North sample, for which we lack spectral information, but whose SFR can be estimated from deep radio data. If confirmed by more detailed observations, it may be possible to use the deduced relation to identify distant galaxies that are X-ray overluminous for their (independently estimated) SFR, and are therefore likely to hide strongly absorbed AGNs.Comment: Astronomy & Astrophysics, in press (15 pages, 7 figures, 4 tables

Induced Gamma-band Activity Elicited by Visual Representation of Unattended Objects

Peer reviewedPostprin

On the Second Law of thermodynamics and the piston problem

The piston problem is investigated in the case where the length of the cylinder is infinite (on both sides) and the ratio $m/M$ is a very small parameter, where $m$ is the mass of one particle of the gaz and $M$ is the mass of the piston. Introducing initial conditions such that the stochastic motion of the piston remains in the average at the origin (no drift), it is shown that the time evolution of the fluids, analytically derived from Liouville equation, agrees with the Second Law of thermodynamics. We thus have a non equilibrium microscopical model whose evolution can be explicitly shown to obey the two laws of thermodynamics.Comment: 29 pages, 9 figures submitted to Journal of Statistical Physics (2003