3,069 research outputs found
Effects of Compton scattering on the neutron star radius constraints in rotation-powered millisecond pulsars
The aim of this work is to study the possible effects and biases on the
radius constraints for rotation-powered millisecond pulsars when using Thomson
approximation to describe electron scattering in the atmosphere models, instead
of using exact formulation for Compton scattering. We compare the differences
between the two models in the energy spectrum and angular distribution of the
emitted radiation. We also analyse a self-generated synthetic phase-resolved
energy spectrum, based on Compton atmosphere and the most X-ray luminous
rotation-powered millisecond pulsars observed by the Neutron star Interior
Composition ExploreR (NICER). We derive constraints for the neutron star
parameters using both the Compton and Thomson models. The results show that the
method works by reproducing the correct parameters with the Compton model.
However, biases are found in size and the temperature of the emitting hot spot,
when using the Thomson model. The constraints on the radius are still not
significantly changed, and therefore the Thomson model seems to be adequate if
we are interested only in the radius measurements using NICER.Comment: 6 pages, 9 figures, published in A&
Experimental Investigation of Drag of Afterbodies with Exiting Jet at High Subsonic Mach Numbers
Effects of leading-edge devices and trailing-edge flaps on longitudinal characteristics of two 47.7 degree sweptback wings of aspect ratios 5.1 and 6.0 at a Reynolds number of 6.0 x 10(exp 6)
Low-speed Longitudinal Aerodynamic Characteristics of a Twisted and Cambered Wing of 45 Degree Sweepback and Aspect Ratio 8 with and Without High-lift and Stall-control Devices and a Fuselage at Reynolds Numbers from 1.5 x 10(exp 6) to 4.8 x 10(exp 6
Pressure-distribution Measurements over an Extensible Leading-edge Flap on Two Wings Having Leading-edge Sweep of 42 Degrees and 52 Degrees
Yaw Characteristics of a 52 Degree Sweptback Wing of NACA 64(sub 1)-112 Section with a Fuselage and with Leading-edge and Split Flaps at Reynolds Numbers from 1.93 x 10(exp 6) to 6.00 x 10(exp 6)
Preliminary Investigation of Methods to Increase Base Pressure of Plug Nozzles at Mach 0.9
The effects of various afterbody changes on the base pressure of a nacelle-type isentropic plug nozzle installation operating at lower-than-design jet pressure ratios were investigated at a Mach number of 0.9. Although the estimates of the net propulsive force contain some uncertainties, the results indicate that both a plain-ring base shroud and a circular-arc boattail fairing reduced the loss in net propulsive force experienced with a cylindrical nacelle installation of the plug nozzle
A Three-Dimensional Flow Expander as a Device to Increase the Mach Number in a Supersonic Wind Tunnel
A preliminary investigation of a simple 5 deg conical-flow expander was made to determine the feasibility of using this type of device to increase the Mach number in the test section of a supersonic wind tunnel. The inlet-to-exit area ratio of the nozzle was that required to increase one-dimensional flow from a Mach number of 3.88 to 5.5. The Mach numbers obtained at the expander exit varied from about 5.1 at the centerline to about 5.4 near the walls. No difficulty in operation of the main wind tunnel was experienced
Bayesian parameter constraints for neutron star masses and radii using X-ray timing observations of accretion-powered millisecond pulsars
We present a Bayesian method to constrain the masses and radii of neutron
stars (NSs) using the information encoded in the X-ray pulse profiles of
accreting millisecond pulsars. We model the shape of the pulses using "oblate
Schwarzschild" approximation, which takes into account the deformed shape of
the star together with the special and general relativistic corrections to the
photon trajectories and angles. The spectrum of the radiation is obtained from
an empirical model of Comptonization in a hot slab in which a fraction of seed
blackbody photons is scattered into a power-law component. By using an
affine-invariant Markov chain Monte Carlo ensemble sampling method, we obtain
posterior probability distributions for the different model parameters,
especially for the mass and the radius. To test the robustness of our method,
we first analyzed self-generated synthetic data with known model parameters.
Similar analysis was then applied for the observations of SAX J1808.4-3658 by
the Rossi X-ray Timing Explorer (RXTE). The results show that our method can
reproduce the model parameters of the synthetic data, and that accurate
constraints for the radius can be obtained using the RXTE pulse profile
observations if the mass is a priori known. For a mass in the range 1.5-1.8
Msun, the radius of the NS in SAX J1808.4-3658 is constrained between 9 and 13
km. If the mass is accurately known, the radius can be determined with an
accuracy of 5% (68% credibility). For example, for the mass of 1.7 Msun the
equatorial radius is Req = 11.9+0.5 -0.4 km. Finally, we show that further
improvements can be obtained when the X-ray polarization data from the Imaging
X-ray Polarimeter Explorer will become available.Comment: 16 pages, 9 figures, published in A&
Longitudinal Characteristics of Two 47.7 Degree Sweptback Wings with Aspect Ratios of 5.1 and 6.0 at Reynolds Numbers up to 10 x 10(exp 6)
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