Study of the Cir X--1 Broad Band Spectrum at Orbital Phases Close to the Apoastron

We report on the results of a BeppoSAX (1.8--200 keV) observation of the peculiar X-ray binary source Circinus X--1 (Cir X--1) at the orbital phases between 0.61 and 0.63. We find that three components are needed to fit the broad band spectrum: a blackbody component, at a temperature of $\sim 0.6$ keV, a Comptonized component, with a seed-photon temperature of $\sim 1.2$ keV, electron temperature of $\sim 6$ keV and optical depth of $\sim 1.7$, and a power-law component dominating the spectrum at energies higher than 20 keV. We interpret the blackbody as the emission from the accretion disk, while the Comptonized component probably comes from a corona surrounding the inner part of the system. This spectrum is different from that observed at the periastron (Iaria et al. 2001a) because of the presence of the blackbody component. We discuss the implications of this difference and the presence of the power-law component.Comment: 15 pages, 6 figures, accepted by Ap

Planning Your Journey in Audio: Design and Evaluation of Auditory Route Overviews

Auditory overviews of routes can provide routing and map information to blind users enabling them to preview route maps before embarking on a journey. This paper investigates the usefulness of a system designed to do this through a Preliminary Survey, followed by a Design Study to gather the design requirements, development of a prototype and evaluation through a Usability Study. The design is drawn in 2-stages with 8 audio designers and 8 potential blind users. The auditory route overview is sequential and automatically generated as integrated audio. It comprises auditory icons to represent points of interest, earcons for auditory brackets encapsulating repeating points of interest, and speech for directions. A prototype based on this design is developed and evaluated with 22 sighted and 8 blind participants. The software architecture of the prototype including the route information retrieval and mapping onto audio has been included. The findings show that both groups perform well in route reconstruction and recognition tasks. Moreover, the functional route information and auditory icons are effectively designed and useful in forming a mental model of the route, which improves over time. However, the design of auditory brackets needs further improvement and testing. At all stages of the system development, input has been acquired from the end-user population and the design is adapted accordingly

Evidence for a parsec scale X-ray jet from the accreting neutron star Circinus X-1

We analyzed the zero-order image of a 50 ks Chandra gratings observation of Circinus X-1, taken in 2005 during the source's low-flux state. Circinus X-1 is an accreting neutron star that exhibits ultra-relativistic arcsecond-scale radio jets and diffuse arcminute-scale radio jets and lobes. The image shows a clear excess along the general direction of the north-western counter-jet, coincident with the radio emission, suggesting that it originates either in the jet itself or in the shock the jet is driving into its environment. This makes Circinus X-1 the first neutron star for which an extended X-ray jet has been detected. The kinetic jet power we infer is significantly larger than the minimum power required for the jet to inflate the large scale radio nebula.Comment: Added journal reference, corrected on reference and typo in labels for Fig. 1; 5 pages, 3 figures, ApJ Letter, in pres

EDIN design study alternate space shuttle booster replacement concepts. Volume 2: Design simulation results

Historical weight estimating relationships were developed for the liquid rocket booster (LRB) using Saturn technology, and modified as required to support the EDIN05 study. Mission performance was computed using February 1975 shuttle configuration groundrules to allow reasonable comparison of the existing shuttle with the EDIN05 designs. The launch trajectory was constrained to pass through both the RTLS/AOA and main engine cut-off points. Performance analysis was based on a point design trajectory model which optimized initial tilt rate and exo-atmospheric pitch profile. A gravity turn was employed during the boost phase in place of the shuttle angle-of-attack profile. Engine throttling add/or shutdown was used to constrain dynamic pressure and/or longitudinal acceleration where necessary

Variability of the X-ray P Cygni Line Profiles from Circinus X-1 Near Zero Phase

The luminous X-ray binary Circinus X-1 has been observed twice near zero orbital phase using the High-Energy Transmission Grating Spectrometer (HETGS) onboard Chandra. The source was in a high-flux state during a flare for the first observation, and it was in a low-flux state during a dip for the second. Spectra from both flux states show clear P Cygni lines, predominantly from H-like and He-like ion species. These indicate the presence of a high-velocity outflow from the Cir X-1 system which we interpret as an equatorial accretion-disk wind, and from the blueshifted resonance absorption lines we determine outflow velocities of 200 - 1900 km/s with no clear velocity differences between the two flux states. The line strengths and profiles, however, are strongly variable both between the two observations as well as within the individual observations. We characterize this variability and suggest that it is due to both changes in the amount of absorbing material along the line of sight as well as changes in the ionization level of the wind. We also refine constraints on the accretion-disk wind model using improved plasma diagnostics such as the He-like Mg XI triplet, and we consider the possibility that the X-ray absorption features seen from superluminal jet sources can generally be explained via high-velocity outflows.Comment: 12 pages, 8 figures, accepted by ApJ (Main

The Discovery of Broad P Cygni X-ray Lines from Circinus X-1 with the Chandra High Energy Transmission Grating Spectrometer

We present the first grating-resolution X-ray spectra of the X-ray binary Cir X-1, obtained with the High Energy Transmission Grating Spectrometer on Chandra. These reveal a rich set of lines from H-like and/or He-like Ne, Mg, Si, S and Fe detected with a high signal-to-noise ratio. The lines are broad (+/- 2000 km/s) and show P Cygni profiles. The absorption components of the lines extend to low velocity, and they have about the same widths and strengths as the corresponding emission components. The widths of the X-ray P Cygni lines are comparable to that of the broad component of the strong, asymmetric H-alpha line from Cir X-1, suggesting that the two phenomena may be related. We discuss outflow models and propose that the P Cygni profiles may arise in the moderate temperature (5 x 10^6 K) region of the wind from an X-ray heated accretion disk. This basic picture strengthens the idea that the accretion disk in Cir X-1 is viewed in a relatively edge-on manner, and it suggests that Cir X-1 is the X-ray binary analog of a Broad Absorption Line quasar.Comment: 17 pages, ApJL, in press; minor improvements made to address referee's suggestion

Spectral Evolution of Circinus X-1 Along its Orbit

We report on the spectral analysis of Circinus X-1 observed by the ASCA satellite in March 1998 along one orbital period. The luminosity of the source (in the 0.1-100 keV band) ranges from $2.5 \times 10^{38}$ erg s$^{-1}$ at the periastron (orbital phase 0.01) to $1.5 \times 10^{38}$ erg s$^{-1}$ at orbital phase 0.3. From the spectral analysis and the lightcurve we argue that Cir X-1 shows three states along the orbital evolution. The first state is at the orbital phase interval 0.97-0.3: the luminosity becames super-Eddington and a strong flaring activity is present. In this state a shock could form in the inner region of the system due to the super-Eddington accretion rate, producing an outflow of ionized matter whose observational signature could be the prominent absorption edge at $\sim 8.7$ keV observed in the energy spectrum at these phases. In the second state, corresponding to the orbital phase interval between 0.3 and 0.7, the accretion rate is sub-Eddington and we observe a weaker outflow, with smaller hydrogen column: the absorption edge is now at $\sim 8.3$ keV with an optical depth a factor of 2.5 to 6 smaller. The third state corresponds to the orbital phase interval 0.78-0.97. In this state the best fit model to the spectrum requires the presence of a partial covering component, indicating that the emission from the compact object is partially absorbed by neutral matter, probably the atmosphere of the companion star and/or the accreting matter from the companion.Comment: 18 pages, 3 figures. Accepted by Ap

Differential decay rate for B→πlνB \to \pi l \nu semileptonic decays

We present our study on $B \to \pi l \nu$ semileptonic decay form factors with NRQCD action for heavy quark from a quenched lattice QCD simulation at $\beta$=5.9 on a $16^3\times 48$ lattice. We obtain form factors defined in the context of heavy quark effective theory by Burdman et al. and find that their $1/m_B$ correction is small. The limit of physical heavy and light quark masses can be performed without introducing any model function, and we obtain a prediction for the differential decay rate $d\Gamma/dq^2$. We also discuss the soft pion limit of the form factors.Comment: Lattice 2000, 4 pages, 4 figures, Late