Kilohertz QPOs in Neutron Star Binaries modeled as Keplerian Oscillations in a Rotating Frame of Reference

Since the discovery of kHz quasi-periodic oscillations (QPO) in neutron star binaries, the difference between peak frequencies of two modes in the upper part of the spectrum, i.e. Delta (omega)=omega_h-omega_K has been studied extensively. The idea that the difference Delta(omega) is constant and (as a beat frequency) is related to the rotational frequency of the neutron star has been tested previously. The observed decrease of Delta(omega) when omega_h and omega_k increase has weakened the beat frequency interpretation. We put forward a different paradigm: a Keplerian oscillator under the influence of the Coriolis force. For such an oscillator, omega_h and the assumed Keplerian frequency omega_k hold an upper hybrid frequency relation: omega^2_h-omega^2_K=4*Omega^2, where Omega is the rotational frequency of the star's magnetosphere near the equatorial plane. For three sources (Sco X-1, 4U 1608-52 and 4U 1702-429), we demonstrate that the solid body rotation Omega=Omega_0=const. is a good first order approximation. Within the second order approximation, the slow variation of Omega as a function of omega_K reveals the structure of the magnetospheric differential rotation. For Sco X-1, the QPO have frequencies approximately 45 and 90 Hz which we interpret as the 1st and 2nd harmonics of the lower branch of the Keplerian oscillations for the rotator with vector Omega not aligned with the normal of the disk: omega_L/2 pi=(Omega/pi)(omega_K/omega_h)sin(delta) where delta is the angle between vector Omega and the vector normal to the disk.Comment: 13 pages, 3 figures, accepted for publications in ApJ Letter

The non-linear evolution of magnetic flux ropes: 3. effects of dissipation

International audienceWe study the evolution (expansion or oscillation) of cylindrically symmetric magnetic flux ropes when the energy dissipation is due to a drag force proportional to the product of the plasma density and the radial speed of expansion. The problem is reduced to a single, second-order, ordinary differential equation for a damped, non-linear oscillator. Motivated by recent work on the interplanetary medium and the solar corona, we consider polytropes whose index, ?, may be less than unity. Numerical analysis shows that, in contrast to the small-amplitude case, large-amplitude oscillations are quasi-periodic with frequencies substantially higher than those of undamped oscillators. The asymptotic behaviour described by the momentum equation is determined by a balance between the drag force and the gradient of the gas pressure, leading to a velocity of expansion of the flux rope which may be expressed as (1/2?)r/t, where r is the radial coordinate and t is the time. In the absence of a drag force, we found in earlier work that the evolution depends both on the polytropic index and on a dimensionless parameter, ?. Parameter ? was found to have a critical value above which oscillations are impossible, and below which they can exist only for energies less than a certain energy threshold. In the presence of a drag force, the concept of a critical ? remains valid, and when ? is above critical, the oscillatory mode disappears altogether. Furthermore, critical ? remains dependent only on ? and is, in particular, independent of the normalized drag coefficient, ?*. Below critical ?, however, the energy required for the flux rope to escape to infinity depends not only on ? (as in the conservative force case) but also on ?*. This work indicates how under certain conditions a small change in the viscous drag coefficient or the initial energy may alter the evolution drastically. It is thus important to determine ?* and ? from observations

Combined Multipoint Remote and In Situ Observations of the Asymmetric Evolution of a Fast Solar Coronal Mass Ejection

We present an analysis of the fast coronal mass ejection (CME) of 2012 March 7, which was imaged by both STEREO spacecraft and observed in situ by MESSENGER, Venus Express, Wind and Mars Express. Based on detected arrivals at four different positions in interplanetary space, it was possible to strongly constrain the kinematics and the shape of the ejection. Using the white-light heliospheric imagery from STEREO-A and B, we derived two different kinematical profiles for the CME by applying the novel constrained self-similar expansion method. In addition, we used a drag-based model to investigate the influence of the ambient solar wind on the CME's propagation. We found that two preceding CMEs heading in different directions disturbed the overall shape of the CME and influenced its propagation behavior. While the Venus-directed segment underwent a gradual deceleration (from ~2700 km/s at 15 R_sun to ~1500 km/s at 154 R_sun), the Earth-directed part showed an abrupt retardation below 35 R_sun (from ~1700 to ~900 km/s). After that, it was propagating with a quasi-constant speed in the wake of a preceding event. Our results highlight the importance of studies concerning the unequal evolution of CMEs. Forecasting can only be improved if conditions in the solar wind are properly taken into account and if attention is also paid to large events preceding the one being studied

Low-temperature study of a new nevirapine pseudopolymorph

The title compound (systematic name: 11-cyclo­propyl-4-methyl-5,11-dihydro-6H-dipyrido[3,2-b:2′,3′-e][1,4]diazepin-6-one butanol 0.3-solvate), C15H14N4O·0.3C4H9OH, was crystallized in a new triclinic pseudopolymorphic form, a butanol solvate, and the crystal structure determined at 150 K. The mol­ecular conformation of this new form differs from that reported previously, although the main inter­molecular hydrogen-bond pattern remains the same. N—H⋯O hydrogen bonds [N⋯O = 2.957 (3) Å] form centrosymmetric dimers and the crystal packing of this new pseudopolymorph generates infinite channels along the b axis

(1-Bromo­naphthalen-2-yl)acetonitrile

The title compound, C12H8BrN, was prepared as a starting material for a Suzuki cross-coupling reaction with a pinacol ester. The torsion angle about the ring–methylene C—C bond is 30.7 (3)°, such that the N atom is displaced by 1.174 (4) Å from the plane of the naphthalene ring system

Bis(triphenyl­phospho­ranyl­idene)ammonium iodide

The title compound, C36H30NP2 +·I−, was obtained accidently from crystallization of a reaction mixture containing [(Ph3P)2N]OH and B(OH)3, which was contaminated with MeI. There are two independent [(Ph3P)2N]+ cations and two I− anions within the asymmetric unit. The central PNP angles are non-linear [137.6 (2) and 134.4 (2)°] and the phenyl substituents on P centres adopt different conformations within these two cations

In situ observations from STEREO/PLASTIC: a test for L5 space weather monitors

Stream interaction regions (SIRs) that corotate with the Sun (corotating interaction regions, or CIRs) are known to cause recurrent geomagnetic storms. The Earth's L5 Lagrange point, separated from the Earth by 60 degrees in heliographic longitude, is a logical location for a solar wind monitor – nearly all SIRs/CIRs will be observed at L5 several days prior to their arrival at Earth. Because the Sun's heliographic equator is tilted about 7 degrees with respect to the ecliptic plane, the separation in heliographic latitude between L5 and Earth can be more than 5 degrees. In July 2008, during the period of minimal solar activity at the end of solar cycle 23, the two STEREO observatories were separated by about 60 degrees in longitude and more than 4 degrees in heliographic latitude. This time period affords a timely test for the practical application of a solar wind monitor at L5. We compare in situ observations from PLASTIC/AHEAD and PLASTIC/BEHIND, and report on how well the BEHIND data can be used as a forecasting tool for in situ conditions at the AHEAD spacecraft with the assumptions of ideal corotation and minimal source evolution. Preliminary results show the bulk proton parameters (density and bulk speed) are not in quantitative agreement from one observatory to the next, but the qualitative profiles are similar

Diaqua­tetra­chloridotin(IV)–diglyme (1/2)

In the title 1:2 adduct, [SnCl4(H2O)2]·2C6H14O3, the SnIV atom (site symmetry 2) adopts a cis-SnO2Cl4 octa­hedral geometry. In the crystal structure, O—H⋯O hydrogen bonds lead to associations of one metal complex and two diglyme mol­ecules