We have analyzed 866 RXTE observations of the 2006-2007 outburst of the accreting neutron star XTE J1701-462, during which the source evolves from super-Eddington luminosities to quiescence. The X-ray color evolution first resembles the Cyg X-2 subgroup of Z sources, with frequent excursions on the horizontal and normal branches (HB/NB). The source then decays and evolves to the Sco X-1 subgroup, with increasing focus on the flaring branch (FB) and the lower vertex of the "Z". Finally, the FB subsides, and the source transforms into an atoll source, with the lower vertex evolving to the atoll soft state. Spectral analyses suggest that the atoll stage is characterized by a constant inner disk radius, while the Z stages exhibit a luminosity-dependent expansion of the inner disk, which we interpret as effects related to the local Eddington limit. Contrary to the view that the mass accretion rate ($\dot{m}$) changes along the Z, we find that changes in $\dot{m}$ are instead responsible for the secular evolution of the Z and the subclasses. Motion along the Z branches appears to be caused by three different mechanisms that may operate at roughly constant $\dot{m}$. For the Sco X-1-like Z stage, we find that the FB is an instability track that proceeds off the lower vertex when the inner disk radius shrinks from the value set by the X-ray luminosity toward the value measured for the atoll soft state. Excursions up the NB occur when the apparent size of the boundary layer increases while the disk exhibits little change. The HB is associated with Comptonization of the disk emission. The Z branches for the Cyg X-2-like stage are more complicated, and their origin is unclear. Finally, our spectral results lead us to hypothesize that the lower and upper Z vertices correspond to a standard thin disk and a slim disk, respectively.
The magnetic fields of our Milky Way galaxy are the main agent for cosmic rays to transport. In the last decade, much new knowledge has been gained from measurements of the Galactic magnetic fields. In the Galactic disk, from the RMs of a large number of newly discovered pulsars, the large-scale magnetic fields along the spiral arms have been delineated in a much larger region than ever before, with alternating directions in the arm and interarm regions. The toroidal fields in the Galactic halo were revealed to have opposite directions below and above the Galactic plane, which is an indication of an A0 mode dynamo operating in the halo. The strength of large-scale fields obtained from pulsar RM data has been found to increase exponentially towards the Galactic center. Compared to the steep Kolmogorov spectrum of magnetic energy at small scales, the large-scale magnetic fields show a shallow broken spatial magnetic energy spectrum.
The traditional celestial navigation system(CNS) is used the moon, stars, and planets as celestial guides. Then the star tracker(i.e. track one star or planet or angle between it) and star sensor(i.e. sense many star simultaneous) be used to determine the attitude of the spacecraft. Pulsar navigation also be introduced to CNS. Maser is another interested celestial in radio astronomy which has strong flux density as spectral line. Now I analysis the principle of maser navigation which base measure Doppler shift frequency spectra and the feasibility that use the exist instrument, and discuss the integrated navigation use maser, then give the perspective in the Milk Way and the intergalatic. Maser navigation can give the continuous position in deep space, that means we can freedom fly successfully in the Milk Way use celestial navigation that include maser, pulsar and traditional star sensor. Maser as nature beacon in the universe will make human freely fly in the space of the Milk Way, even outer of it. That is extraordinary in the human evolution to type III of Karadashev civilizations.
An outburst of the accreting X-ray millisecond pulsar SAX J1808.4-3658 in October-November 2002 was followed by the RXTE for more than a month. For the first time, we demonstrate that the area covered by the hotspot at the neutron star surface as well as the reflection amplitude decrease during the outburst. This is in agreement with the scenario, where the disc inner edge is receding from the neutron star as the mass accretion rate drops. This is further supported by the variations of the pulse profiles, showing the presence of the secondary maximum at the late stages of the outburst after October 29, when the disc has moved sufficiently far from the neutron star to open the view of the lower magnetic pole. We estimate the disc inner radius, the inclination at i=60^o+-5^o and to put constraints on the stellar magnetic moment mu=(7+-3)x10^{25} G cm^3, which corresponds to the surface field of about 10^8 G, and is in agreement with the value obtained recently from the observed pulsar spin-down rate. The timing noise and sharp changes in the phase of the fundamental are intimately related to the variations of the pulse profile, which are associated with the varying obscuration of the antipodal spot. We also demonstrate that the strong dependence of the pulse profiles on photon energy and the observed soft time lags result from the different phase dependence of the two spectral components, the blackbody and the Comptonized tail. The pulse profile amplitude allows us to estimate the colatitude of the hotspot centroid to be 4^o-10^o.
Links to: arXiv, form interface, find, astro-ph, recent, 0901, contact, help (Access key information)