After about 18 years of steadily spinning down, the accretion-powered pulsar 4U 1626-67, experienced a new torque reversal at the beginning of 2008. For the present study we have used all available Fermi/GBM data since its launch in 2008 June 11 and over 5 yr of hard X-ray Swift/BAT observations (starting from 2004 October up to the present time). From 2004 up to the end of 2007 the spin-down rate averaged at a mean rate of ∼ν = −4.8 × 10 −13 Hz s −1 until the torque reversal reported here. This second detected torque reversal was centered near MJD 54500 (2008 Feb 4) and it lasted approximately 150 days.During the reversal the source also underwent an increase in flux by a fraction of ∼2.5. Since then it has been following a steady spin-up at a mean rate of ∼ν = 4 × 10 −13 Hz s −1 . We present a detailed long-term timing analysis of this source and a long term spectral hardness ratio study in order to see whether there are spectral changes around this new observed torque reversal.

4U 2206+54 is a high mass X-ray binary which has been suspected to contain a neutron star accreting from the wind of its companion BD +53 • 2790. Reig et al. (2009) have recently detected 5560 s period pulsations in both RXTE and INTEGRAL observations which they conclude are due to the spin of the neutron star. We present observations made with Suzaku which are contemporaneous with their RXTE observation of this source. We find strong pulsations at a period of 5554 ± 9 s in agreement with their results. We also present a reanalysis of BeppoSAX observations of 4U 2206+54 made in 1998, in which we find strong pulsations at a period of 5420 ± 28 seconds, revealing a spin-down trend in this long-period accreting pulsar. Analysis of these data suggests that the neutron star in this system is an accretion-powered magnetar.

Several relatively bright, persistent X-ray sources display regular pulses, with periods in the range of 700-10000 s. These sources are identified with massive close binaries in which a neutron star accretes material onto its surface. The observed pulsations in all of them, but one, are unambiguously associated with the spin period of the neutron star. Analyzing possible history of these pulsars I conclude that the neutron stars in these systems undergo spherical accretion and their evolutionary tracks in a previous epoch contained three instead of two states, namely, ejector, supersonic propeller, and subsonic propeller. An assumption about a supercritical value of the initial magnetic field of the neutron stars within this scenario is not necessary. Furthermore, I show that the scenario in which the neutron star in 2S 0114+650 is assumed to be a magnetar descendant encounters major difficulties in explaining the evolution of the massive companion. An alternative interpretation of the spin evolution of the neutron star in this system is presented and the problem raised by association of the 10000 s pulsations with the spin period of the neutron star is briefly discussed.Comment: 7 pages, 2 tables, accepted for publication in MNRA

We explore a possibility to explain the phenomenon of the Anomalous X-ray Pulsars (AXP) and Soft Gamma-ray Repeaters (SGR) within the scenario of fall-back magnetic accretion onto a young isolated neutron star. The X-ray emission of the pulsar in this case is originated due to accretion of matter onto the surface of the neutron star from the magnetic slab surrounding its magnetosphere. The expected spin-down rate of the neutron star within this approach is close to the observed value. We show that these neutron stars are relatively young and are going through a transition from the propeller state to the accretor state. The pulsars activity in the gamma-rays is connected with their relative youth and is provided by the energy stored in the non-equilibrium layer located in the crust of low-mass neutron stars. This energy can be released due to mixing of matter in the neutron star crust with super heavy nuclei approaching its surface and getting unstable. The nuclei fission in the low-density region initiates chain reactions leading to the nuclear explosion. The outbursts are likely to be triggered by an instability developing in the region where the matter accreted by the neutron star is accumulated at the magnetic pole regions.

Abstract. The observed properties of the close binary AE Aqr indicate that the mass transfer in this system operates via the Roche lobe overflow mechanism, but the material transferred from the normal companion is neither accreted onto the surface of the white dwarf nor stored in a disk around its magnetosphere. As previously shown, such a situation can be realized if the white dwarf operates as a propeller. At the same time, the efficiency of the propeller action by the white dwarf is insufficient to explain the rapid braking of the white dwarf, which implies that the spin-down power is in excess of the bolometric luminosity of the system. To avoid this problem we have simulated the mass-transfer process in AE Aqr assuming that the observed braking of the white dwarf is governed by a pulsar-like spin-down mechanism. We show that the expected Hα Doppler tomogram in this case resembles the tomogram observed from the system. We find that the agreement between the simulated and the observed tomograms is rather good provided the mean value of the mass-transfer rate Ṁ ∼ 5 × 10 16 g s −1 . Three spatially separated sources of Hα emission can be distinguished within this approach. The structure of the tomogram depends on the relative contributions of these sources to the Hα emission and is expected to vary from night to night.

Aims. The accretion-powered pulsar 4U 1626-67 experienced a new torque reversal at the beginning of 2008, after about 18 years of steadily spinning down. The main goal of the present work is to study this recent torque reversal that occurred in February 2008. Methods. We present a spectral analysis of this source using two pointed observations performed by Suzaku in March 2006 and in September 2010. Results. We confirm with Suzaku the presence of a strong emission-line complex centered on 1 keV, with the strongest line being the hydrogen-like Ne Lyα at 1.025(3) keV. We were able to resolve this complex with up to seven emission lines. A dramatic increase in the intensity of the Ne Lyα line after the 2008 torque reversal occurred, with the equivalent width of this line reaching almost the same value measured by ASCA in 1993. We also report on the detection of a cyclotron line feature centered at ∼37 keV. In spite of the increase in the X-ray luminosity (0.5−100 keV) of a factor of ∼2.8 that occurred between these two observations, no significant change in the energy of the cyclotron line feature was observed. However, the intensity of the ∼1 keV line complex increased by an overall factor of ∼8. Conclusions. Our results favor a scenario in which the neutron star in 4U 1626-67 accretes material from a geometrically thin disk during both the spin-up and spin-down phases.

Abstract. We present the results of bispectrum speckle interferometry of the B[e] star MWC 349A obtained with the SAO 6 m telescope. Our diffraction-limited J-, H-, and K-band images (resolutions 43-74 mas) suggest the star is surrounded by a circumstellar disk seen almost edge-on. The observed visibility shape is consistent with a two-component elliptical disk model, probably corresponding to the gaseous and dusty components of the disk. We show that the classification of the object as a pre-main-sequence star or a young planetary nebula is problematic. An analysis of the uncertainties in the basic parameter determination leads us to the conclusion that MWC 349A is probably either a B[e] supergiant or a binary system, in which the B[e]-companion dominates the observed properties.

Abstract. The condition for the subsonic propeller → accretor state transition of neutron stars in wind-fed massexchange binary systems is discussed. I show that the value of the break period, at which the neutron star change its state to accretor, presented by Davies & Pringle (1981) is underestimated by a factor of 7.5. The correct value is P br 450 µ 16/21 30Ṁ−5/7 15 (M/M ) −4/21 s. This result forced us to reconsider some basic conclusions on the efficiency of the propeller spindown mechanism.