scholarly journals The impact of the environment of white dwarf mergers on fast radio bursts

2019 ◽  
Vol 492 (3) ◽  
pp. 3753-3762 ◽  
Author(s):  
Esha Kundu ◽  
Lilia Ferrario
Keyword(s):  
Radio Pulse ◽  
Outer Part ◽  
Dispersion Measure ◽  
Constant Density ◽  
Radio Bursts ◽  
Free Expansion ◽  
Expansion Phase ◽  
Rotation Measure ◽  
Power Law Index ◽  
The Impact

ABSTRACT Fast radio bursts (FRBs) are transient intense radio pulses with duration of milliseconds. Although, the first FRB was detected more than a decade ago, the progenitors of these energetic events are not yet known. The currently preferred formation channel involves the formation of a neutron star (NS)/magnetar. While these objects are often the end product of the core-collapse (CC) explosion of massive stars, they could also be the outcome of the merging of two massive white dwarfs. In the merger scenario the ejected material interacts with a constant-density circumbinary medium and creates supersonic shocks. We found that when a radio pulse passes through these shocks the dispersion measure (DM) increases with time during the free expansion phase. The rotation measure (RM) displays a similar trend if the power-law index, n, of the outer part of the ejecta is >6. For n = 6, the RM remains constant during this phase. Later, when the ejecta move into the Sedov–Taylor phase while the DM still increases, however, with a different rate, the RM reduces. This behaviour is somewhat similar to that of FRB 121102 for which a marginal increase of DM and a 10 per cent decrease of RM have been observed over time. These features are in contrast to the CC scenario, where the DM and RM contributions to the radio signal always diminish with time.

scholarly journals On the magnetoionic environments of fast radio bursts

2020 ◽  
Vol 499 (1) ◽  
pp. 355-361 ◽  
Author(s):  
Wei-Yang Wang ◽  
Bing Zhang ◽  
Xuelei Chen ◽  
Renxin Xu
Keyword(s):  
Magnetic Field ◽  
Mean Value ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
Host Galaxies ◽  
Surface Magnetic Field ◽  
Rotation Measure ◽  
The Mean

ABSTRACT Observations of the Faraday rotation measure, combined with the dispersion measure, can be used to infer the magnetoionic environment of a radio source. We investigate the magnetoionic environments of fast radio bursts (FRBs) by deriving their estimated average magnetic field strengths along the line of sight 〈B∥〉 in their host galaxies and comparing them with those of Galactic pulsars and magnetars. We find that for those FRBs with RM measurements, the mean 〈B∥〉 are $1.77^{+9.01}_{-1.48}\, \rm \mu G$ and $1.74^{+14.82}_{-1.55}\, \rm \mu G$ using two different methods, which is slightly larger but not inconsistent with the distribution of Galactic pulsars, $1.00^{+1.51}_{-0.60}\, \rm \mu G$. Only six Galactic magnetars have estimated 〈B∥〉. Excluding PSR J1745–2900 that has an anomalously high value due to its proximity with the Galactic Centre, the other five sources have a mean value of $1.70\, \rm \mu G$, which is statistically consistent with the 〈B∥〉 distributions of both Galactic pulsars and FRBs. There is no apparent trend of evolution of magnetar 〈B∥〉 as a function of age or surface magnetic field strength. Galactic pulsars and magnetars close to the Galactic Centre have relatively larger 〈B∥〉 values than other pulsars/magnetars. We discuss the implications of these results for the magnetoionic environments of FRB 121102 within the context of magnetar model and the model invoking a supermassive black hole, and for the origin of FRBs in general.

scholarly journals Investigation of the Earth Ionosphere Using the Radio Emission of Pulsars

2013 ◽  
Vol 22 (1) ◽  
Author(s):  
O. M. Ulyanov ◽  
A. I. Shevtsova ◽  
D. V. Mukha ◽  
A. A. Seredkina
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Dispersion Measure ◽  
Pulsar Radio ◽  
The Earth ◽  
Lack Of Information ◽  
Rotation Measure ◽  
System Data ◽  
Gps System ◽  
The Impact

AbstractThe investigation of the Earth ionosphere both in a quiet and a disturbed states is still desirable. Despite recent progress in its modeling and in estimating the electron concentration along the line of sight by GPS signals, the impact of the disturbed ionosphere and magnetic field on the wave propagation still remains not sufficiently understood. This is due to lack of information on the polarization of GPS signals, and due to poorly conditioned models of the ionosphere at high altitudes and strong perturbations. In this article we consider a possibility of using the data of pulsar radio emission, along with the traditional GPS system data, for the vertical and oblique sounding of the ionosphere. This approach also allows to monitor parameters of the propagation medium, such as the dispersion measure and the rotation measure using changes of the polarization between pulses. By using a selected pulsar constellation it is possible to increase the number of directions in which parameters of the ionosphere and the magnetic field can be estimated.

scholarly journals Redshift estimates for fast radio bursts and implications on intergalactic magnetic fields

2020 ◽  
Vol 498 (4) ◽  
pp. 4811-4829
Author(s):  
S Hackstein ◽  
M Brüggen ◽  
F Vazza ◽  
L F S Rodrigues
Keyword(s):  
Magnetic Fields ◽  
Dispersion Measure ◽  
Radio Bursts ◽  
Probability Estimates ◽  
Rotation Measure ◽  
Upper Limits ◽  
Fast Radio Burst ◽  
Stellar Sources ◽  
Lower Limits ◽  
Temporal Broadening

ABSTRACT Fast radio bursts are transient radio pulses from presumably compact stellar sources of extragalactic origin. With new telescopes detecting multiple events per day, statistical methods are required in order to interpret observations and make inferences regarding astrophysical and cosmological questions. We present a method that uses probability estimates of fast radio burst observables to obtain likelihood estimates for the underlying models. Considering models for all regions along the line of sight, including intervening galaxies, we perform Monte Carlo simulations to estimate the distribution of the dispersion measure (DM), rotation measure (RM), and temporal broadening. Using Bayesian statistics, we compare these predictions to observations of fast radio bursts. By applying Bayes theorem, we obtain lower limits on the redshift of fast radio bursts with extragalactic DM ≳ 400 pc cm−3. We find that intervening galaxies cannot account for all highly scattered fast radio bursts in FRBcat, thus requiring a denser and more turbulent environment than an SGR 1935+2154-like magnetar. We show that a sample of ≳103 unlocalized fast radio bursts with associated extragalactic RM ≥ 1 rad m−2 can improve current upper limits on the strength of intergalactic magnetic fields.

scholarly journals A comparison of Galactic electron density models using PyGEDM

2021 ◽  
Vol 38 ◽  
Author(s):  
D. C. Price ◽  
C. Flynn ◽  
A. Deller
Keyword(s):  
Electron Density ◽  
Large Scale ◽  
Galactic Halo ◽  
Application Programming Interface ◽  
Dispersion Measure ◽  
Radio Pulsars ◽  
Distribution Models ◽  
Distance Measurements ◽  
Application Programming ◽  
The Impact

Abstract Galactic electron density distribution models are crucial tools for estimating the impact of the ionised interstellar medium on the impulsive signals from radio pulsars and fast radio bursts. The two prevailing Galactic electron density models (GEDMs) are YMW16 (Yao et al. 2017, ApJ, 835, 29) and NE2001 (Cordes & Lazio 2002, arXiv e-prints, pp astro–ph/0207156). Here, we introduce a software package PyGEDM which provides a unified application programming interface for these models and the YT20 (Yamasaki & Totani 2020, ApJ, 888, 105) model of the Galactic halo. We use PyGEDM to compute all-sky maps of Galactic dispersion measure (DM) for YMW16 and NE2001 and compare the large-scale differences between the two. In general, YMW16 predicts higher DM values towards the Galactic anticentre. YMW16 predicts higher DMs at low Galactic latitudes, but NE2001 predicts higher DMs in most other directions. We identify lines of sight for which the models are most discrepant, using pulsars with independent distance measurements. YMW16 performs better on average than NE2001, but both models show significant outliers. We suggest that future campaigns to determine pulsar distances should focus on targets where the models show large discrepancies, so future models can use those measurements to better estimate distances along those line of sight. We also suggest that the Galactic halo should be considered as a component in future GEDMs, to avoid overestimating the Galactic DM contribution for extragalactic sources such as FRBs.

scholarly journals On the linear stability of anisotropic pressure equilibria with field-aligned incompressible flow

2020 ◽  
Vol 86 (3) ◽  
Author(s):  
A. Evangelias ◽  
G. N. Throumoulopoulos
Keyword(s):  
Linear Stability ◽  
Incompressible Flow ◽  
Mass Density ◽  
Anisotropic Pressure ◽  
Constant Density ◽  
Specific Class ◽  
Pressure Anisotropy ◽  
Symmetry Transformations ◽  
Tensor Element ◽  
The Impact

We derive a sufficient condition for the linear stability of plasma equilibria with incompressible flow parallel to the magnetic field, $\boldsymbol{B}$ , constant mass density and anisotropic pressure such that the quantity $\unicode[STIX]{x1D70E}_{d}=\unicode[STIX]{x1D707}_{0}(P_{\Vert }-P_{\bot })/B^{2}$ , where $P_{\Vert }$ ( $P_{\bot }$ ) is the pressure tensor element parallel (perpendicular) to $\boldsymbol{B}$ , remains constant. This condition is applicable to any steady state without geometrical restriction. The condition, generalising the respective condition for magnetohydrodynamic equilibria with isotropic pressure and constant density derived in Throumoulopoulos & Tasso (Phys. Plasmas, vol. 14, 2007, 122104), involves physically interpretable terms related to the magnetic shear, the flow shear and the variation of total pressure perpendicular to the magnetic surfaces. On the basis of this condition we prove that, if a given equilibrium is linearly stable, then the ones resulting from the application of Bogoyavlenskij symmetry transformations are linearly stable too, provided that a parameter involved in those transformations is positive. In addition, we examine the impact of pressure anisotropy, flow and torsion of a helical magnetic axis, for a specific class of analytic equilibria. In this case, we find that the pressure anisotropy and the flow may have either stabilising or destabilising effects. Also, helical configurations with small torsion and large pitch seem to have more favourable stability properties.

Abundance and size of European lobsters (Homarus gammarus) and brown crabs (Cancer pagurus) inside and outside the Kåvra lobster reserve (west coast of Sweden)

Crustaceana ◽  
2020 ◽  
Vol 93 (2) ◽  
pp. 157-169
Author(s):  
Vidar Øresland ◽  
Gert Oxby ◽  
Fredrik Oxby
Keyword(s):  
Size Distribution ◽  
Relative Abundance ◽  
West Coast ◽  
Outer Part ◽  
Swedish West Coast ◽  
Offshore Area ◽  
Homarus Gammarus ◽  
Cancer Pagurus ◽  
And Migration ◽  
The Impact

Abstract The common method of using lobster-pot catch data for investigating relative abundance, sex and size distribution has serious disadvantages. This study estimates relative abundance and size of the European lobster Homarus gammarus and the brown crab Cancer pagurus using scuba diving techniques. The study areas were the Kåvra lobster reserve (Kåvra) on the Swedish west coast and three very different nearby areas where fishing for crustaceans is allowed: Gullmarsfjorden; the archipelago; and the offshore area. A total of 167 lobsters and 337 brown crabs were observed during 33 scuba dives (each 30 minutes long) in 2018-2019. The estimated mean abundance of lobsters was three to fifteen times as high at Kåvra in comparison with the other three areas (all exact showing that the statistical populations were distinct in comparison with Kåvra; Wilcoxon-Mann-Whitney Test). Dive sites in the outer part of the offshore area had the lowest abundance of lobsters although they had seemingly good lobster habitats and low fishing intensity. Large lobsters with a carapace length of ⩾15 cm were found only at Kåvra where they made up 24% of the lobsters. The proportion of large lobsters inside Kåvra continues to increase after 30 years of protection. Together, this emphasizes the impact of fishing on lobster abundance and size distribution, and indicates that limited recruitment and migration might possibly affect offshore lobster “sub populations”. Kåvra was the only area where the abundance of lobsters exceeded the abundance of brown crabs (). However, the abundance of brown crabs at Kåvra was as low as in Gullmarsfjorden () where fishing for crabs is allowed. Possible complex lobster/brown crab interactions together with other factors that might explain the low abundance of the protected brown crab at Kåvra, need to be investigated further.

Heat Transfer Enhancement in Annular Shear-Thinning Flows Over a Sudden Pipe Expansion

2017 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Power Law ◽  
Shear Thinning ◽  
Diameter Ratio ◽  
Transfer Enhancement ◽  
Heat Transfer Augmentation ◽  
Prandtl Numbers ◽  
Power Law Index ◽  
The Impact

Heat transfer enhancement in suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid is studied within the steady laminar flow regime. Conservation of mass, momentum, and energy equations, along with the power-law constitutive model are numerically solved. The impact of inflow inertia, annular-nozzle-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported for: Re = {50, 100}, k = {0, 0.5, 0.7}; n = {1, 0.8, 0.6}; and Pr = {1, 10, 100}. Heat transfer enhancement downstream of the expansion plane, i.e., Nusselt numbers, Nu, higher than the fully developed value, in the downstream pipe, is observed only for Pr = 10 and 100. Higher Prandtl numbers, power-law index values, and annular diameter ratios, in general, reflect a more dramatic heat transfer augmentation downstream of the expansion plane. Heat transfer augmentation for Pr = 10 and 100, is more dramatic for suddenly expanding annular flows, in comparison with suddenly expanding pipe flow. For a given annular diameter ratio and Reynolds numbers, increasing the Prandtl number from Pr = 10 to Pr = 100, always results in higher peak Nu values, for both Newtonian and shear-thinning non-Newtonian flows.

Photoionization modelling of planetary nebulae with realistic density distribution using detailed method for diffuse radiation calculation and Outward Only approximation

2018 ◽  
Vol 8 (1) ◽  
pp. 3-8
Author(s):  
O. Buhajenko ◽  
B. Melekh
Keyword(s):  
Density Distribution ◽  
Outer Part ◽  
Planetary Nebulae ◽  
Diffuse Radiation ◽  
Constant Density ◽  
Approximate Methods ◽  
Detailed Method ◽  
Spatially Extended ◽  
Calculation Algorithms ◽  
Density Radius

The approximate methods to calculate the diffuse ionizing radiation (DIR) during the photoionization modelling (PhM) of the nebular environments are frequently used with purpose to increase the calculation speed of modern photoionization codes as well as for simplification of their calculation algorithms. The most popular Outward Only method in many cases gives the satisfactory calculation precision and speed. However, in our previous studies it was shown that even for nebular environments with constant density the calculation errors, related to usage of approximate method of DIR, are significant for spatially extended or optically thin objects. However, constant density is a bit rough assumption. In present work to compare the detailed method of DIR calculation with Outward Only one we used more realistic density distribution for planetary nebulae proposed by Golovatyy & Mal’kov. Using optimal photoionization models for IC 5117 and NGC 7293, obtained by Melekh et al. and calculated in Outward Only approximation, we recalculated them using detailed method of DIR calculation. While IC 5117 is the most compact (young) and dense planetary nebula from sample used by Golovatyy & Mal’kov, NGC 7293 is the most extended (old) with lowest density one from the same sample. We compared PhM results for these PNe obtained using Outward Only approximation and detailed method of DIR treatment. It was concluded that largest differences in ionization structure of nebula caused by differences in DIR calculation methods are in outer part of PN - at radii larger than maximal density radius. Therefore, [N II], [O II] and [S II] and other emission lines, that achieve the maximal emissivities in outer part of PNe, are the most sensitive to DIR calculation method.

Flow Inertia and Heat Transfer in Suddenly Expanding Annular Shear-Thinning Flows

2017 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Heat Transfer ◽  
Power Law ◽  
Shear Thinning ◽  
Heat Transfer Augmentation ◽  
Flow And Heat Transfer ◽  
Prandtl Numbers ◽  
Power Law Index ◽  
Annular Pipe ◽  
Flow Inertia ◽  
The Impact

The impact of flow inertia on flow and heat transfer in suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid is studied within the steady laminar flow regime. The equations governing conservation of mass, momentum, and energy, along with the power-law constitutive model are numerically solved using a finite-difference numerical scheme. The influence of inflow inertia, annular-nozzle-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported for: Re = {50, 100}, k = {0, 0.5}; n = {1, 0.6}; and Pr = {1, 10, 100}. Heat transfer augmentation, downstream the plane of expansion, is only observed for Pr = 10 and 100. The extent and intensity of recirculation in the corner region, increases with inflow inertia. Higher Reynolds and Prandtl numbers, power-law index values, and annular diameter ratios, in general, reflect a more dramatic heat transfer augmentation downstream of the expansion plane.

The Combined Effects of Heat Loss and Reversibility on the Propagation of Planar Premixed Counterflow Flames

2018 ◽  
Vol 10 (6) ◽  
Author(s):  
Faisal Al-Malki
Keyword(s):  
Activation Energy ◽  
Finite Elements ◽  
Strain Rate ◽  
Heat Loss ◽  
Constant Density ◽  
Combined Effects ◽  
Stability Of Solutions ◽  
Counterflow Flames ◽  
The Stability ◽  
The Impact

Abstract We study in this paper the combined effect of heat loss and reversibility on the propagation of planar flames formed within the counterflow configuration. The problem has been formulated first using the thermodiffusive model with constant density and then solved numerically using finite elements. The impact of four main parameters, namely the reversibility r, the heat loss κ, the strain rate ε, and the activation energy β, on the propagation of planar flames has been discussed in details. The study has shown that planar flames under reversible conditions behave qualitatively similar to those observed for irreversible reactions, which agree with the asymptotic findings. In the presence of heat loss, the problem exhibits multiplicity of solutions whose number and stability were found to vary according to the strain rate ε. In addition, the study has predicted the existence of a certain value of the reversibility parameter r beyond which the impact of reversibility becomes negligible. Finally, we have examined the stability of the solutions and determined the domain of stability of solutions and their multiplicity for this problem.

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