A software toolbox for robotics

A method for programming cooperating manipulators, which is guided by a geometric description of the task to be performed, is given. For this a suitable language must be used and a method for describing the workplace and the objects in it in geometric terms. A task level command language and its implementation for concurrently driven multiple robot arm is described. The language is suitable for driving a cell in which manipulators, end effectors, and sensors are controlled by their own dedicated processors. These processors can communicate with each other through a communication network. A mechanism for keeping track of the history of the commands already executed allows the command language for the manipulators to be event driven. A frame based world modeling system is utilized to describe the objects in the work environment and any relationships that hold between these objects. This system provides a versatile tool for managing information about the world model. Default actions normally needed are invoked when the data base is updated or accessed. Most of the first level error recovery is also invoked by the database by utilizing the concepts of demons. The package can be utilized to generate task level commands in a problem solver or a planner

The pulsar wind nebula of the Geminga pulsar

The superb spatial resolution of Chandra has allowed us to detect a 20''-long tail behind the Geminga pulsar, with a hard spectrum (photon index 1.0+/-0.2) and a luminosity (1.3+/-0.2) 10^{29} ergs/s in the 0.5 - 8 keV band, for an assumed distance of 200 pc. The tail could be either a pulsar jet, confined by a toroidal magnetic field of about 100 microGauss, or it can be associated with the shocked relativistic wind behind the supersonically moving pulsar confined by the ram pressure of the oncoming interstellar medium. We also detected an arc-like structure 5'' - 7'' ahead of the pulsar, extended perpendicular to the tail, with a factor of 3 lower luminosity. We see a 3-sigma enhancement in the Chandra image apparently connecting the arc with the southern outer tail that has been possibly detected with XMM-Newton. The observed structures imply that the Geminga's pulsar wind is intrinsically anisotropic.Comment: Revised version: data analysis described in more detail, Figure 2 replaced; 6 pages, 2 color figures; accepted for publication in ApJ (v.643, 2006 June 1

Fading of the Transient Anomalous X-ray Pulsar XTE J1810-197

Three observations of the 5.54 s Transient Anomalous X-ray Pulsar XTE J1810-197 obtained over 6 months with the Newton X-Ray Multi-Mirror Mission (XMM-Newton) are used to study its spectrum and pulsed light curve as the source fades from outburst. The decay is consistent with an exponential of time constant 300 days, but not a power law as predicted in some models of sudden deep crustal heating events. All spectra are well fitted by a blackbody plus a steep power law, a problematic model that is commonly fitted to anomalous X-ray pulsars (AXPs). A two-temperature blackbody fit is also acceptable, and better motivated physically in view of the faint optical/IR fluxes, the X-ray pulse shapes that weakly depend on energy in XTE J1810-197, and the inferred emitting areas that are less than or equal to the surface area of a neutron star. The fitted temperatures remained the same while the flux declined by 46%, which can be interpreted as a decrease in area of the emitting regions. The pulsar continues to spin down, albeit at a reduced rate of (5.1+/-1.6)x10^{-12} s s^{-1}. The inferred characteristic age Tau_c = P/2Pdot ~17,000 yr, magnetic field strength B_s ~1.7x10^{14} G, and outburst properties are consistent with both the outburst and quiescent X-ray luminosities being powered by magnetic field decay, i.e., XTE J1810-197 is a magnetar.Comment: 10 pages, 5 figures, accepted by Ap.

Phase Structure of Compact Star in Modified Quark-Meson Coupling Model

The K$^-$ condensation and quark deconfinement phase transitions are investigated in the modified quark-meson coupling model. It is shown that K$^-$ condensation is suppressed because of the quark deconfinement when $B^{1/4}<$202.2MeV, where $B$ is the bag constant for unpaired quark matter. With the equation of state (EOS) solved self-consistently, we discuss the properties of compact stars. We find that the EOS of pure hadron matter with condensed K$^-$ phase should be ruled out by the redshift for star EXO0748-676, while EOS containing unpaired quark matter phase with $B^{1/4}$ being about 180MeV could be consistent with this observation and the best measured mass of star PSR 1913+16. We then probe into the change of the phase structures in possible compact stars with deconfinment phase as the central densities increase. But if the recent inferred massive star among Terzan 5 with M$>$1.68M$_{\odot}$ is confirmed, all the present EOSes with condensed phase and deconfined phase would be ruled out and therefore these exotic phases are unlikely to appear within neutron stars.Comment: 11 pages, 5 figure

X-ray observations of the compact central object in supernova remnant G347.3-0.5

We present Chandra, XMM-Newton and RXTE observations of 1WGA J1713.4-3949, a compact source at the center of the galactic supernova remnant (SNR) G347.3-0.5. The X-ray spectrum of the source is well-fitted by the sum of a blackbody component with a temperature of about 0.4 keV plus a power law component with photon index about 4. We found no pulsations down to 4% in the 0.01-0.16 Hz range and down to 25% in the 0.01-128 Hz range. This source resembles other compact central objects (CCOs) in SNRs, and we suggest that 1WGA J1713.4-3949 is the associated neutron star for G347.3--0.5. We also measured the properties of the adjacent radio pulsar PSR J1713-3945 with a 392 ms period and show that it is not associated with 1WGA J1713.4-3949 nor, most probably, with SNR G347.3-0.5 as well.Comment: 8 pages, 2 figures, accepted for publication in ApJ Letter

Phase-resolved Crab Studies with a Cryogenic TES Spectrophotometer

We are developing time- and energy-resolved near-IR/optical/UV photon detectors based on sharp superconducting-normal transition edges in thin films. We report observations of the Crab pulsar made during prototype testing at the McDonald 2.7m telescope with a fiber-coupled transition-edge sensor (TES) system. These data show substantial (d[alpha]~0.3), rapid variations in the spectral index through the pulse profile, with a strong phase-varying IR break across our energy band. These variations correlate with X-ray spectral variations, but no single synchrotron population can account for the full Spectral Energy Distribution (SED). We also describe test spectrophotopolarimetry observations probing the energy dependence of the polarization sweep; this may provide a new key to understanding the radiating particle population.Comment: 12 pages, 10 figures -- to appear in ApJ V56

Spot-like Structures of Neutron Star Surface Magnetic Fields

There is growing evidence, based on both X-ray and radio observations of isolated neutron stars, that besides the large--scale (dipolar) magnetic field, which determines the pulsar spin--down behaviour, small--scale poloidal field components are present, which have surface strengths one to two orders of magnitude larger than the dipolar component. We argue in this paper that the Hall--effect can be an efficient process in producing such small--scale field structures just above the neutron star surface. It is shown that due to a Hall--drift induced instability, poloidal magnetic field structures can be generated from strong subsurface toroidal fields, which are the result of either a dynamo or a thermoelectric instability acting at early times of a neutron star's life. The geometrical structure of these small--scale surface anomalies of the magnetic field resembles that of some types of ``star--spots''. The magnetic field strength and the length--scales are comparable with values that can be derived from various observations.Comment: 4 pages, 2 figures, accepted by Astronomy & Astrophysics Letters; language improved, 2nd para of Sect. 3 change