Nodal and periastron precession of inclined orbits in the field of a rapidly rotating neutron star

We derive a formula for the nodal precession frequency and the Keplerian period of a particle at an arbitrary orbital inclination (with a minimum latitudinal angle reached at the orbit) in the post-Newtonian approximation in the external field of an oblate rotating neutron star (NS). We also derive formulas for the nodal precession and periastron rotation frequencies of slightly inclined low-eccentricity orbits in the field of a rapidly rotating NS in the form of asymptotic expansions whose first terms are given by the Okazaki-Kato formulas. The NS gravitational field is described by the exact solution of the Einstein equation that includes the NS quadrupole moment induced by rapid rotation. Convenient asymptotic formulas are given for the metric coefficients of the corresponding space-time in the form of Kerr metric perturbations in Boyer-Lindquist coordinates.     

Solar Flare Activity and Variability of Electric Current Helicity

1 INTRODUCTIONRecently Bao, Zhang, Ai, and Zhang (1999), using Huairou vector magnetograph data,have shown that the average current helicity (h.) or the curreflt helicity imbalance ph of activeregions change rapidly after so1ar flares. Up'an the onset of flares it tends to decrease for a fewhours and then to increase again, whereas ifQ some cases the flare promotes an increase in thecurrent helicity The observations led to tbe fol1owing conclusions: (1) raPid and substantialchanges of c…     

The formation of X-ray radiation in a boundary layer during disk accretion onto a neutron star

We present computed radiation spectra for the boundary layer (BL) of the accretion disk that is formed near the surface of a neutron star. Both free-free processes and Comptonization were taken into account. Our computations are based on the hydrodynamic solution obtained by Popham and Sunyaev (2001) for the BL structure. The computed spectra are highly diluted compared to the Planck spectra of the same surface temperature. They are complex in shape; in particular, an intense Wien emission component is formed in their high-energy region at high accretion rates. In general, the computed spectra are harder than those observed in actual X-ray sources. This is the result of a very high temperature found by Popham and Sunyaev (2001) for the BL. We show that such temperatures could result from an oversimplified treatment of radiative transfer in their paper, which completely ignored the frequency dependence of the matter opacity and radiation intensity. Our computations indicate that at moderate accretion rates, a proper treatment of radiative transfer with allowance for Comptonization leads to appreciably lower plasma temperatures and to softer radiation spectra.     

Thermal X-ray emission from hot polar cap in drifting subpulse pulsars

Within the framework of the partially screened inner acceleration region the relationship between the X-ray luminosity and the circulational periodicity of drifting subpulses is derived. This relationship is quite well satisfied in pulsars for which an appropriate radio and X-ray measurements exist. A special case of PSR B0943+10 is presented and discussed. The problem of formation of a partially screened inner acceleration region for all pulsars with drifting subpulses is also considered. It is argued that an efficient inner acceleration region just above the polar cap can be formed in a very strong and curved non-dipolar surface magnetic field. We acknowledge the support of the Polish State Committee for scientific research under Grant P03D 029 26. G.M. was partially supported by Georgian NSF grant ST06/4-096.     

High-mass X-ray binaries and the spiral structure of the host galaxy

We investigate the manifestation of the spiral structure in the distribution of high-mass X-ray binaries (HMXBs) over the host galaxy. We construct the simplest kinematic model. It shows that the HMXBs should be displaced relative to the spiral structure observed in such traditional star formation rate indicators as the Hα and far-infrared emissions because of their finite lifetimes. Using Chandra observations of M51, we have studied the distribution of X-ray sources relative to the spiral arms of this galaxy observed in Hα. Based on K-band data and background source number counts, we have separated the contributions from high-mass and low-mass X-ray binaries and active galactic nuclei. In agreement with model predictions, the distribution of HMXBs is wider than that of bright H II regions concentrated in the region of ongoing star formation. However, the statistical significance of this result is low, as is the significance of the concentration of the total population of X-ray sources to the spiral arms. We also predict the distribution of HMXBs in our Galaxy in Galactic longitude. The distribution depends on the mean HMXB age and can differ significantly from the distributions of such young objects as ultracompact H II regions.     

Study of microflares through soxs mission

We present a study of 10 microflares observed in 4–30 keV by SOXS mission simultaneously with Hα observations made at NAOJ, Japan during the interval between February and August 2004. The X-ray and Hα light curves showed that the lifetime of microflares varies between 4 and 25 min. We found that the X-ray emission in all microflares under study in the dynamic energy range of 4–30 keV can be fitted by thermal plus non-thermal components. The thermal spectrum appeared to start from almost 4 keV, low level discriminator (LLD) of both Si and CZT detectors, however it ends below 8 keV. We also observed the Fe line complex features at 6.7 keV in some microflares and attempted to fit this line by isothermal temperature assumption. The temperature of isothermal plasma of microflares varies in the range between 8.6 and 10.1 MK while emission measure between 0.5 and 2x10⁴9 cm^-3. Non-thermal (NT) emission appeared in the energy range 7–15 keV with exponent -6.8 ≤γ≤-4.8. Our study of microflares that had occurred on 25 February 2004 showed that sometimes a given active region produces recurrent microflare activity of a similar nature. We concluded from X-ray and simultaneous Hα observations that the microflares are perhaps the result of the interaction of low lying loops. It appears that the electrons that accelerated during reconnection heat the ambient coronal plasma as well as interact with material while moving down along the loops and thereby produce Hα bright kernels.     

Eb Light Curve Models – What’s Next?

Enhanced unity in binary system observables models is discussed, including development strategy and connections between morphology and solutions. Distance estimation can be made direct (one step) via simultaneous light/velocity solutions that incorporate a simple flux-scaling procedure. Potential importance of time-variable polarization work is emphasized, especially for Algols, with mention of needed improvements in polarimetric analysis and reporting of data. Recent developments in general all-data (light, velocity, etc.) ephemerides are reviewed, with projections for further generalization, and ideas and formalisms for analysis of period change events (perhaps discontinuous) are introduced. Advantages and practical problems of unified [light, velocity, pulse arrival time] analyses for X-ray binaries, possibly constrained by measured X-ray eclipse durations, are discussed.     

Optical properties of Laue lenses for hard X-rays (>60 keV)

We report on preliminary results obtained with a Monte Carlo (MC) code developed to study the optical properties of Laue lenses for astro-physical observations. The MC code is written in the Python programming language and uses open source libraries. Among the physical quantities which can be investigated with the MC code, we paid our attention mainly to the estimation of the effective area, field of view (FOV) and point spread function (PSF) of the lens for observation of sources on-axis and off-axis.     

The soft X-ray novae, black-hole candidates XTE J2012+381 and XTE J 1550-564

In 1998–1999, the X-ray transients XTE J2012+381 and XTE J1550-564 were observed with the TTM X-ray telescope onboard the Mir-Kvant astrophysical module. Spectral properties of these sources on the descent of the light curve after the secondary maxima of their outbursts are studied. Upper limits on the off-state flux are given. Comparison with other X-ray novae observed with the TTM telescope leads us to conclude that XTE J2012+381 and XTE J 1550-564 are soft X-ray novae. XTE J2012+381 probably belongs to the subclass of long-period X-ray transients.     

Quasi-periodic X-ray oscillations in the source Scorpius X-1

The RXTE observations of Scorpius X-1 in 1996–1999 are presented. The properties of its quasi-periodic X-ray oscillations are studied in detail. The results obtained are used for analysis in terms of the transition-layer model (TLM) and the relativistic-precession model (RPM) for a slowly rotating neutron star. Theoretical predictions of the two models are compared and their self-consistency is verified. The tilt of the magnetosphere to the accretion-disk plane, the neutron-star mass, and its angular momentum are determined in terms of the models.