scholarly journals Modelling spin evolution of magnetars

2021 ◽  
Author(s):  
Jedrzej A Jawor ◽  
Thomas M Tauris
Keyword(s):  
Input Parameter ◽  
Time Derivative ◽  
Parameter Study ◽  
Physical Parameters ◽  
Spin Period ◽  
Spin Evolution ◽  
Synthetic Populations ◽  
Best Value ◽  
Field Decay ◽  
Radio Transients

Abstract The origin and fate of magnetars (young, extremely magnetized neutron stars, NSs) remains unsolved. Probing their evolution is therefore crucial for investigating possible links to other species of isolated NSs, such as the X-ray dim NSs (XDINSs) and rotating radio transients (RRATs). Here we investigate the spin evolution of magnetars. Two avenues of evolution are considered: one with exponentially decaying B-fields, the other with sub- and super-exponential decay. Using Monte Carlo methods, we synthesize magnetar populations using different input distributions and physical parameters, such as for the initial spin period, its time derivative and the B-field decay timescale. Additionally, we introduce a fade-away procedure that can account for the fading of old magnetars, and we briefly discuss the effect of alignment of the B-field and spin axes. Imposing the Galactic core-collapse supernova rate of ∼20 kyr−1 as a strict upper limit on the magnetar birthrate and comparing the synthetic populations to the observed one using both manual and automatic optimization algorithms for our input parameter study, we find that the B-field must decay exponentially or super-exponentially with a characteristic decay timescale of 0.5 − 10 kyr (with a best value of ∼4 kyr). In addition, the initial spin period must be less than 2 sec. If these constraints are kept, we conclude that there are multiple choices of input physics that can reproduce the observed magnetar population reasonably well. We also conclude that magnetars may well be evolutionary linked to the population of XDINSs, whereas they are in general unlikely to evolve into RRATs.

scholarly journals Thermal-timescale mass transfer and magnetic CVs

2004 ◽  
Vol 190 ◽  
pp. 8-14 ◽  
Author(s):  
Klaus Schenker ◽  
Graham A. Wynn ◽  
Roland Speith
Keyword(s):  
Mass Transfer ◽  
Numerical Simulations ◽  
Large Population ◽  
Spin Period ◽  
Spin Evolution ◽  
Unstable Phase ◽  
Definition Of

AbstractWe investigate the spin evolution of the unusual magnetic CV AE Aqr. As a prototype for a potentially large population of CVs subject to a thermally unstable phase of mass transfer, understanding its future is crucial. We present a new definition of the magnetospheric radius in terms of the white dwarf’s spin period, and use this along with numerical simulations to follow the spin evolution of AE Aqr. We also present preliminary SPH results suggesting the existence of a stable propeller state. These results highlight the complexity of MCVs and may provide an improved understanding of the evolution of all types of CVs.

scholarly journals Long-term observations of pulsars in the globular clusters 47 Tucanae and M15

2017 ◽  
Vol 13 (S337) ◽  
pp. 251-254
Author(s):  
A. Ridolfi ◽  
P. C. C. Freire ◽  
M. Kramer ◽  
C. G. Bassa ◽  
F. Camilo ◽  
...  
Keyword(s):  
Gravitational Potential ◽  
Globular Clusters ◽  
Higher Order ◽  
The Other ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Spin Period ◽  
Emission Beam ◽  
System Geometry

AbstractMulti-decade observing campaigns of the globular clusters 47 Tucanae and M15 have led to an outstanding number of discoveries. Here, we report on the latest results of the long-term observations of the pulsars in these two clusters. For most of the pulsars in 47 Tucanae we have measured, among other things, their higher-order spin period derivatives, which have in turn provided stringent constraints on the physical parameters of the cluster, such as its distance and gravitational potential. For M15, we have studied the relativistic spin precession effect in PSR B2127+11C. We have used full-Stokes observations to model the precession effect, and to constrain the system geometry. We find that the visible beam of the pulsar is swiftly moving away from our line of sight and may very soon become undetectable. On the other hand, we expect to see the opposite emission beam sometime between 2041 and 2053.

scholarly journals NGC 300 ULX1: A test case for accretion torque theory

2018 ◽  
Vol 620 ◽  
pp. L12 ◽  
Author(s):  
G. Vasilopoulos ◽  
F. Haberl ◽  
S. Carpano ◽  
C. Maitra
Keyword(s):  
Neutron Star ◽  
Test Case ◽  
X Ray ◽  
Spin Period ◽  
Spin Evolution ◽  
Spin Reversal ◽  
Eddington Limit

NGC 300 ULX1 is a newly identified ultra-luminous X-ray pulsar. The system is associated with the supernova impostor SN 2010da that was later classified as a possible supergiant Be X-ray binary. In this work we report on the spin period evolution of the neutron star based on all the currently available X-ray observations of the system. We argue that the X-ray luminosity of the system has remained almost constant since 2010, at a level above ten times the Eddington limit. Moreover, we find evidence that the spin period of the neutron star evolved from ∼126 s down to ∼18 s within a period of about 4 years. We explain this unprecedented spin evolution in terms of the standard accretion torque theory. An intriguing consequence for NGC 300 ULX1 is that a neutron star spin reversal should have occurred a few years after the SN 2010da event.

scholarly journals Dynamic response of a wedge through asymmetric free fall in 2 degrees of freedom

2017 ◽  
Vol 233 (1) ◽  
pp. 229-250 ◽  
Author(s):  
Parviz Ghadimi ◽  
Sasan Tavakoli ◽  
Abbas Dashtimanesh ◽  
Pouria Taghikhani
Keyword(s):  
Experimental Data ◽  
Dynamic Response ◽  
Degrees Of Freedom ◽  
Time Derivative ◽  
Free Fall ◽  
Added Mass ◽  
Roll Motion ◽  
Physical Parameters ◽  
Two Dimensional ◽  
Roll Speed

In this article, a mathematical model is presented for simulation of the coupled roll and heave motions of the asymmetric impact of a two-dimensional wedge body. This model is developed based on the added mass theory and momentum variation. To this end, new formulations are introduced which are related to the added mass caused by heave and roll motions of the wedge. These relations are developed by including the asymmetrical effects and roll speed. In addition, by considering the roll speed, a particular method is presented for the time derivative of half-wetted beam of an asymmetric wedge. Furthermore, two equations are derived for the roll and heave motions in which damping terms appear. Validity of the proposed method is verified by comparing the predicted results against available experimental data in two conditions of roll motion and no roll motion. Favorable agreement is observed between the predicted results and experimental data. The pressure and hydrodynamic load are computed, and the differences between the results associated with the considered conditions are explored. Subsequently, the effects of different physical parameters including deadrise angle, initial roll angle, and initial velocity on the dynamic response of a two-dimensional wedge section are investigated. Ultimately, time histories of hydrodynamic coefficients are determined in order to provide a better understanding of the derived equations.

scholarly journals Understanding the coexistence of spin-up and spin-down behaviours in long-period X-ray pulsars

2020 ◽  
Vol 492 (1) ◽  
pp. 762-769
Author(s):  
W Wang ◽  
H Tong
Keyword(s):  
Magnetic Field ◽  
Binary Systems ◽  
Accretion Rate ◽  
Constant Mass ◽  
X Ray ◽  
Spin Period ◽  
Long Period ◽  
Rotational Evolution ◽  
Order Of Magnitude ◽  
Field Decay

ABSTRACT Assuming wind-fed accretion magnetars in long-period X-ray pulsars, we calculated the rotational evolution of neutron stars. Our calculations considered the effects of magnetic field decay in magnetars. The results show that wind-fed accretion magnetars can evolve to long-period X-ray pulsars with a spin period much longer than 1000 s. The spin-down trend observed in 4U 2206+54-like sources is expected when young X-ray binary systems are on the way to their equilibrium period. Detailed calculations showed that the spin-down may be affected by accretion with outflows or accretion while spinning down. Due to magnetic field decay in magnetars, wind-fed accretion magnetars will have a decreasing equilibrium period for a constant mass accretion rate. For 2S 0114+65, the spin-up rate due to magnetic field decay is one order of magnitude smaller than observations. The spin-up rate of 2S 0114+65 may be attributed to the formation of a transient disc during wind accretion. The slowest X-ray pulsar AX J1910.7+0917 would be a link source between 4U 2206+54 and 2S 0114+65.

Advanced Design of Industrial Mixers for Fluid Foods Using Computational Fluid Dynamics

2013 ◽  
Vol 9 (3) ◽  
pp. 309-325 ◽  
Author(s):  
Gino Ferretti ◽  
Roberto Montanari ◽  
Federico Solari ◽  
Giuseppe Vignali
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Input Parameter ◽  
Solid Particles ◽  
Design Solution ◽  
Physical Parameters ◽  
Fluid Viscosity ◽  
Mixing Process ◽  
Dynamics Simulations ◽  
The Individual

AbstractThis work focuses on discontinuous (batch) vertical fluid mixing systems for food fluids with particles. A properly designed mixing process has to provide two main results: a satisfactory homogeneity of the product and the preservation of the integrity of the solid particles. The main problem in the design of a mixer for fluid–solid suspensions is to identify the operating levers which act in order to optimize the performance of the process, while preserving the integrity of the pieces. The purpose of this work is to identify some structural and physical parameters that have the strongest influence on the performance of the mixing process, in order to obtain useful indications for the design of mixing systems.Different mixer designs were thus analyzed thanks to computational fluid dynamics simulations, from which some key performance indicators (KPIs) related to the effectiveness of the mixing process were obtained. An analysis of variance and a residual analysis were then performed in order to assess the significance of the influence of each input parameter (position of the rotor, fluid viscosity, and aspect ratio), on the individual KPIs and on the global performance of the mixer. From these analyses, some conclusions useful to choose an appropriate design solution for fluid mixers were derived.

Seeing White: Qualia in the Context of Decoding Population Codes

1999 ◽  
Vol 11 (6) ◽  
pp. 1261-1280 ◽  
Author(s):  
Sidney R. Lehky ◽  
Terrence J. Sejnowski
Keyword(s):  
Nervous System ◽  
Input Parameter ◽  
Color Space ◽  
Neural Population ◽  
Physical Parameters ◽  
Representational Space ◽  
Population Codes ◽  
Single Input ◽  
High Level ◽  
Population Decoding

When the nervous system is presented with multiple simultaneous inputs of some variable, such as wavelength or disparity, they can be combined to give rise to qualitatively new percepts that cannot be produced by any single input value. For example, there is no single wavelength that appears white. Many models of decoding neural population codes have problems handling multiple inputs, either attempting to extract a single value of the input parameter or, in some cases, registering the presence of multiple inputs without synthesizing them into something new. These examples raise a more general issue regarding the interpretation of population codes. We propose that population decoding involves not the extraction of specific values of the physical inputs, but rather a transformation from the input space to some abstract representational space that is not simply related to physical parameters. As a specific example, a four-layer network is presented that implements a transformation from wavelength to a high-level hue-saturation color space.

scholarly journals Estimation of Physical Parameters Using a New Discrete-time Derivative Algorithm

2020 ◽  
Vol 53 (2) ◽  
pp. 2367-2372
Author(s):  
Davide Tebaldi ◽  
Riccardo Morselli ◽  
Roberto Zanasi
Keyword(s):  
Discrete Time ◽  
Time Derivative ◽  
Physical Parameters

scholarly journals The Green Bank Northern Celestial Cap Pulsar Survey. VI. Discovery and Timing of PSR J1759+5036: A Double Neutron Star Binary Pulsar

2021 ◽  
Vol 922 (1) ◽  
pp. 35
Author(s):  
G. Y. Agazie ◽  
M. G. Mingyar ◽  
M. A. McLaughlin ◽  
J. K. Swiggum ◽  
D. L. Kaplan ◽  
...  
Keyword(s):  
Neutron Star ◽  
Major Axis ◽  
Total System ◽  
Semi Major Axis ◽  
Binary Pulsar ◽  
Orbital Parameters ◽  
Spin Period ◽  
Timing Data ◽  
Star Binary ◽  
Radio Transients

Abstract The Green Bank North Celestial Cap survey is a 350 MHz all-sky survey for pulsars and fast radio transients using the Robert C. Byrd Green Bank Telescope. To date, the survey has discovered over 190 pulsars, including 33 millisecond pulsars and 24 rotating radio transients. Several exotic pulsars have been discovered in the survey, including PSR J1759+5036, a binary pulsar with a 176 ms spin period in an orbit with a period of 2.04 days, an eccentricity of 0.3, and a projected semi-major axis of 6.8 light seconds. Using seven years of timing data, we are able to measure one post–Keplerian parameter, advance of periastron, which has allowed us to constrain the total system mass to 2.62 ± 0.03 M ⊙. This constraint, along with the spin period and orbital parameters, suggests that this is a double neutron star system, although we cannot entirely rule out a pulsar-white dwarf binary. This pulsar is only detectable in roughly 45% of observations, most likely due to scintillation. However, additional observations are required to determine whether there may be other contributing effects.

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