55995908
A magnetic reconnection model for quasi-periodic oscillations in black hole systems
The quasi-periodic oscillations (QPOs) in black hole (BH) systems with different scales are interpreted based on the magnetic reconnection of large-scale magnetic fields generated by toroidal electric currents flowing in the inner region of the accretion disk, where the current density is assumed to be proportional to the mass density of the accreting plasma. The magnetic connection (MC) is taken into account in resolving dynamic equations describing the accretion disk, in which the MC between the inner and outer disk regions, between the plunging region and the disk, and between the BH horizon and the disk are involved. It turns out that a single QPO frequency associated with several BH systems with different scales can be fitted by invoking the magnetic reconnection due to the MC between the inner and outer regions of the disk, including the BH binaries XTE J1859+226, XTE J1650 i 500 and GRS 1915+105 and the massive BHs in NGC 5408 X-1 and RE J1034+396. In addition, the X-ray spectra corresponding to the QPOs for these sources are fitted based on the typical disk-corona model.
119219570
A model of low-frequency quasi-periodic oscillations in black hole X-ray binaries
A model of low-frequency quasi-periodic oscillations (LFQPOs) of black hole X-ray binaries (BHXBs) is proposed based on the perturbed magnetohydrodynamic equations of an accretion disk. It turns out that the LFQPO frequencies of some BHXBs can be fitted by the frequencies of the toroidal Alfven wave oscillation corresponding to the maximal radiation flux. In addition, the positive correlation of the LFQPO frequencies with the radiation flux from an accretion disk is well interpreted.
6241544
Wind Accretion and State Transitions in Cygnus X-1
We present the results of a spectroscopic monitoring program (from 1998 to 2002) of the Hα emission strength in HDE 226868, the optical counterpart of the black hole binary Cyg X-1. The feature provides an important probe of the mass-loss rate in the base of the stellar wind of the supergiant star. We derive an updated ephemeris for the orbit based on radial velocities measured from He I λ6678. We list net equivalent widths for the entire Hα emission/absorption complex, and we find that there are large variations in emission strength over both long (years) and short (hours to days) time spans. There are coherent orbital phase-related variations in the profiles when the spectra are grouped by Hα equivalent width. The profiles consist of (1) a P Cygni component associated with the wind of the supergiant, (2) emission components that attain high velocity at the conjunctions and that probably form in enhanced outflows both toward and away from the black hole, and (3) an emission component that moves in antiphase with the supergiant's motion. We argue that the third component forms in accreted gas near the black hole and that the radial velocity curve of the emission is consistent with a mass ratio of MX/Mopt ≈ 0.36 ± 0.05. We find that there is a general anticorrelation between the Hα emission strength and X-ray flux (from the Rossi X-Ray Timing Explorer All Sky Monitor) in the sense that when the Hα emission is strong (Wλ < -0.5 A) the X-ray flux is weaker and the spectrum harder. On the other hand, there is no correlation between Hα emission strength and X-ray flux when Hα is weak. We argue that this relationship is not caused by wind X-ray absorption nor by the reduction in Hα emissivity by X-ray heating. Instead, we suggest that the Hα variations track changes in wind density and strength near the photosphere. The density of the wind determines the size of X-ray ionization zones surrounding the black hole, and these in turn control the acceleration of the wind in the direction of the black hole. During the low/hard X-ray state, the strong wind is fast and the accretion rate is relatively low, while during the high/soft state, the weaker, highly ionized wind attains only a moderate velocity and the accretion rate increases. We argue that the X-ray transitions from the normal low/hard to the rare high/soft state are triggered by episodes of decreased mass-loss rate in the supergiant donor star.
38889804
Experimental demonstration of plasma-drag acceleration of a dust cloud to hypervelocities.
Simultaneous acceleration of hundreds of dust particles to hypervelocities by collimated plasma flows ejected from a coaxial gun is demonstrated. Graphite and diamond grains with radii between 5 and 30 microm, and flying at speeds up to 3.7 km/s, have been recorded with a high-speed camera. The observations agree well with a model for plasma-drag acceleration of microparticles much larger than the plasma screening length.
117063918
Recent physics results at BES
¢ 2 S£ and 33 pb¤ 1 ψ ¥¥ events collected at BES-II detector, some charm physics results are obtained. In J ¡ ψ decay, we observed an unknown resonance X(1835) and study the controversial particle σ and κ. In ψ ¢ 2 S£ decay, we test the " 12% rule " via many decay modes and find many new χ cJ decay channels. In ψ ¥¥ decay, we observed the non-D ¯ D decay via ψ ¥¥ § ¦ π ¨ π ¤ J ¡ ψ and study the semi-leptonic decay of D meson. In addition, we give the preliminary ψ ¥¥ resonance parameters with higher precision. c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
14342177
Disk Accretion onto Magnetized Neutron Stars: The Inner Disk Radius and Fastness Parameter
It is well known that the accretion disk around a magnetized compact star can penetrate inside the magnetospheric boundary, so that the magnetospheric radius R0 does not represent the true inner edge Rin of the disk, but controversies exist in the literature concerning the relation between R0 and Rin. In the model of Ghosh & Lamb, the width of the boundary layer is given by δ=R0-RinR0, or RinR0, while Li & Wickramasinghe recently argued that Rin could be significantly smaller than R0 in the case of a slow rotator. Here we show that if the star is able to absorb the angular momentum of the disk plasma at R0, appropriate for binary X-ray pulsars, the inner disk radius can be constrained by 0.8Rin/R01, and the star reaches spin equilibrium with a relatively large value of the fastness parameter (~0.7-0.95). For accreting neutron stars in low-mass X-ray binaries (LMXBs), R0 is generally close to the stellar radius, Rs, so that the toroidal field cannot transfer the spin-up torque efficiently to the star. In this case, the critical fastness parameter becomes smaller, but Rin is still near R0.
108637108
The construction and space qualification of the control electronics for the tracker detector cooling system of the AMS-02 experiment
Abstract This article describes the control electronics for the silicon tracker cooling system in the AMS-02 apparatus. It also contains a brief description of the cooling system itself necessary for the description of the electronics. The tracker cooling system includes a set of various sensors and actuators which are necessary for bringing the tracker detector to a uniform temperature at which it can operate correctly. In order to test the system performing the various qualification activities we have built also an Electronic Ground support equipment (EGSE). The EGSE should simulate the behaviour of all sensors and actuators previously mentioned.