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Maxim V Barkov - One of the best experts on this subject based on the ideXlab platform.
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3d dynamics and morphology of Bow Shock pulsar wind nebulae
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Maxim V Barkov, Maxim Lyutikov, D KhangulyanAbstract:Bow-Shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute these variations to the intrinsic properties (relative orientation of the pulsar's spin, velocity, and magnetic inclination angle) - as well as the line of sight. We identify three basic types of Bow-Shock nebulae: (i) a "rifle bullet" (spin and velocity aligned); (ii) a "frisbee" (spin and velocity orthogonal, spin is in the plane of the sky) and (iii) a "cart-wheel" (like frisbee but the spin is perpendicular to the plane of the sky). Using 3D relativistic MHD simulations, as well as analytical calculations, we reproduce both the key morphological features of the BowShock PNEs, as well as variations are seen in different systems. Magnetic stresses within the pulsar wind strongly affect the overall structure, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, non-symmetric shapes etc. On the other hand, the ISM inhomogeneities, as well as the anisotropy of the wind luminosity, produce only mild variations of the PWN shape. In few cases we clearly identify the morphological structure - our results do not favor alignment of the pulsar spin and linear velocity. Our calculations of the underlying radiative process explain low synchrotron $X$-ray efficiency (in terms of the spin-down luminosity) and argue for energetically subdominant contribution of the IC processes.
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3d dynamics and morphology of Bow Shock pulsar wind nebulae
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Maxim V Barkov, Maxim Lyutikov, D KhangulyanAbstract:Bow-Shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute this diversity to the geometrical factors: relative orientations of the pulsar rotation axis, proper velocity, and the line of sight (magnetic inclination angle may also have a certain influence on the morphology). We identify three basic types of Bow-Shock nebulae: (i) a "Rifle Bullet" (pulsar spin axis and proper velocity are aligned); (ii) a "Frisbee" (pulsar spin axis and proper velocity are orthogonal with the spin axis lying in the plane of the sky), and (iii) a Cart Wheel" (like frisbee but the spin axis is perpendicular to the plane of the sky). Using 3D RMHD simulations, as well as analytical calculations, we reproduce the key morphological features of the Bow-Shock PWNe, as well as variations, are seen across different systems. magnetic stresses within the Shocked pulsar wind affect the overall structure strongly, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, as well as non-symmetric morphologies. On the other hand, the interstellar medium inhomogeneities and the anisotropy of the energy flux in the pulsar wind have only a mild impact of the PWN morphology. In a few cases, when we clearly identify specific morphological structures, our results do not favor alignment of the pulsar spin axis and proper velocity. Our calculations of the underlying emission processes explain the low synchrotron X-ray efficiency (in terms of the spin-down luminosity) and imply an energetical subdominant contribution of the inverse Compton process.
C T Russell - One of the best experts on this subject based on the ideXlab platform.
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Venusian Bow Shock as seen by the ASPERA-4 ion instrument on Venus Express
2020Co-Authors: I Whittaker, S Barabash, C. Mazelle, R Lundin, G Guymer, M Grande, B Pintér, A Federov, J A Sauvaud, C T RussellAbstract:[1] The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) instrument on Venus Express is used to determine Bow Shock position at Venus using ion data alone, using data recorded during a solar minimum from the Ion Mass Analyzer (IMA) which is part of the ASPERA-4 package. Previous models constructed from solar minimum data using Venus Express, Pioneer Venus Orbiter (PVO) and Venera 9 and 10 are also compared to the current fit. An important feature of this new fit is a statistical accuracy introduced in the form of a probability weighting function for the data points, based on the time spent in particular locations. The Bow Shock curve is then compared to two-dimensional ion maps. These verify the accuracy of this and previous solar minimum fit curves based on PVO and Venus Express magnetic data. Comparing all Bow Shock models to the 2D ion maps shows that a combination of models produces the best fit. Since all the fitted curves show differences in position they are investigated relative to the solar conditions pertaining at the times when the individual data sets were measured. The sub solar point and terminator distance were thus found to vary linearly with sunspot number and hence with solar activity. This relationship, which was already known to exist between solar maximum and solar minimum, is now shown to exist between different solar minima and even within the same minimum. This indicates a need for the mechanisms for Bow Shock maintenance and variance to be more closely modeled. Citation: Whittaker, I., et al. (2010), Venusian Bow Shock as seen by the ASPERA-4 ion instrument on Venus Express
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initial venus express magnetic field observations of the venus Bow Shock location at solar minimum
Planetary and Space Science, 2008Co-Authors: C T Russell, T L Zhang, M Delva, W Baumjohann, M Volwerk, S Barabash, M A Balikhin, S A Pope, K H GlassmeierAbstract:Abstract In this study, magnetic field measurements obtained by the Venus Express spacecraft are used to determine the Bow Shock position at solar minimum. The best fit of Bow Shock location from solar zenith angle 20–120° gives a terminator Bow Shock location of 2.14 R V (1 R V =6052 km) which is 1600 km closer to Venus than the 2.40 R V determined during solar maximum conditions, a clear indication of the solar cycle variation of the Venus Bow Shock location. The best fit to the subsolar Bow Shock is 1.32 R V , with the Bow Shock completely detached. Finally, a global Bow Shock model at solar minimum is constructed based on our best-fit empirical Bow Shock in the sunlit hemisphere and an asymptotic limit of the distant Bow Shock which is a Mach cone under typical Mach number of 5.5 at solar minimum. We also describe our approach to making the measurements and processing the data in a challenging magnetic cleanliness environment. An initial evaluation of the accuracy of measurements shows that the data are of a quality comparable to magnetic field measurements made onboard magnetically clean spacecraft.
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orientation location and velocity of saturn s Bow Shock initial results from the cassini spacecraft
Journal of Geophysical Research, 2006Co-Authors: Nick Achilleos, C T Russell, M K Dougherty, C Bertucci, G B Hospodarsky, A M Rymer, C S Arridge, M E Burton, Stefan Hendricks, E J SmithAbstract:[1] The Cassini spacecraft commenced its tour of the planet Saturn on 1 July 2004 (GMT). During the insertion orbit, the Cassini magnetometer (MAG), radio/plasma wave experiment (RPWS), and plasma spectrometer (CAPS) obtained in situ measurements of the magnetic field and plasma conditions associated with Saturn's environment. Analysis of the magnetic field data indicate that Cassini repeatedly crossed a mainly quasi-perpendicular Bow Shock boundary on both the inbound (post-dawn) and outbound (predawn) legs. Modeling of the Bow Shock and magnetopause crossing positions shows evidence for a magnetospheric compression during Cassini's immersion in the magnetosphere. The magnetic signatures of the Bow Shock crossings show the clearly defined “overshoot” and “foot” regions associated with the quasi-perpendicular geometry. The duration of the Shock foot, considered in combination with the RPWS and CAPS solar wind electron parameters upstream of the Bow Shock crossings, indicates that the length scale for the Bow Shock ramp at Saturn is about an ion inertial length. This is consistent with multispacecraft observations of the spatial scale of the Earth's Shock foot region. The data are generally consistent with Saturn Bow Shock velocities up to ∼400 km s−1 and Shock structures governed by ion dynamics.
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Bow Shock and upstream waves at jupiter and saturn cassini magnetometer observations
THE PHYSICS OF COLLISIONLESS SHOCKS: 4th Annual IGPP International Astrophysics Conference, 2005Co-Authors: C Bertucci, C T Russell, M K Dougherty, M E Burton, E J Smith, N Achilleos, B T Tsurutani, C. MazelleAbstract:The measurements obtained by the Cassini magnetometer investigation (MAG) during the first orbits of its mission around Saturn yielded a rich set of observations of the Bow Shock and the upstream region at that planet. In this work we comment on the properties of the Kronian Bow Shock as implied by MAG data. We also study the properties of non‐linear, low frequency waves observed in the foreShock of Saturn and we discuss their origin and their role in the formation of the quasi parallel Shock. Finally, we compare these recent results with similar observations at Jupiter obtained by Cassini MAG during the 2000–2001 Jupiter flyby.
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probabilistic models of the jovian magnetopause and Bow Shock locations
Journal of Geophysical Research, 2002Co-Authors: M G Kivelson, C T Russell, Raymond J Walker, K K Khurana, Tatsuki OginoAbstract:[1] New three-dimensional models of the Jovian magnetopause and Bow Shock were derived by combining spacecraft observations with boundary characteristics inferred from a magnetohydrodynamic (MHD) simulation. The MHD simulation provides polynomial forms parameterized by solar wind dynamic pressure. Observations from Pioneer 10 and 11, Voyager 1 and 2, Ulysses, and Galileo were used to establish the probability that regions surrounding Jupiter fall inside or outside these boundary surfaces. The magnetopause location was found to have a bimodal probability distribution with the two most probable standoff distances at 63 RJ (σ = 4 RJ) and 92 RJ (σ = 6 RJ). The Bow Shock location distribution appears bimodal, but a single distribution function description cannot be ruled out at the 95% confidence level. The mean Bow Shock standoff distance is 84 RJ (σ = 16 RJ). Analysis of solar wind measurements near 5.2 AU (interplanetary magnetic field, dynamic pressure, and Alfven Mach number) suggests that the bimodal distribution of boundary positions results at least in part from the bimodal distribution of solar wind parameters in the vicinity of Jupiter. The probability density distributions of these parameters within and between regions of disturbed solar wind, caused by corotating interaction regions and coronal mass ejections, are statistically distinct. Smaller variations were also observed in these parameters over the solar cycle.
D Khangulyan - One of the best experts on this subject based on the ideXlab platform.
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3d dynamics and morphology of Bow Shock pulsar wind nebulae
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Maxim V Barkov, Maxim Lyutikov, D KhangulyanAbstract:Bow-Shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute these variations to the intrinsic properties (relative orientation of the pulsar's spin, velocity, and magnetic inclination angle) - as well as the line of sight. We identify three basic types of Bow-Shock nebulae: (i) a "rifle bullet" (spin and velocity aligned); (ii) a "frisbee" (spin and velocity orthogonal, spin is in the plane of the sky) and (iii) a "cart-wheel" (like frisbee but the spin is perpendicular to the plane of the sky). Using 3D relativistic MHD simulations, as well as analytical calculations, we reproduce both the key morphological features of the BowShock PNEs, as well as variations are seen in different systems. Magnetic stresses within the pulsar wind strongly affect the overall structure, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, non-symmetric shapes etc. On the other hand, the ISM inhomogeneities, as well as the anisotropy of the wind luminosity, produce only mild variations of the PWN shape. In few cases we clearly identify the morphological structure - our results do not favor alignment of the pulsar spin and linear velocity. Our calculations of the underlying radiative process explain low synchrotron $X$-ray efficiency (in terms of the spin-down luminosity) and argue for energetically subdominant contribution of the IC processes.
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3d dynamics and morphology of Bow Shock pulsar wind nebulae
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Maxim V Barkov, Maxim Lyutikov, D KhangulyanAbstract:Bow-Shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute this diversity to the geometrical factors: relative orientations of the pulsar rotation axis, proper velocity, and the line of sight (magnetic inclination angle may also have a certain influence on the morphology). We identify three basic types of Bow-Shock nebulae: (i) a "Rifle Bullet" (pulsar spin axis and proper velocity are aligned); (ii) a "Frisbee" (pulsar spin axis and proper velocity are orthogonal with the spin axis lying in the plane of the sky), and (iii) a Cart Wheel" (like frisbee but the spin axis is perpendicular to the plane of the sky). Using 3D RMHD simulations, as well as analytical calculations, we reproduce the key morphological features of the Bow-Shock PWNe, as well as variations, are seen across different systems. magnetic stresses within the Shocked pulsar wind affect the overall structure strongly, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, as well as non-symmetric morphologies. On the other hand, the interstellar medium inhomogeneities and the anisotropy of the energy flux in the pulsar wind have only a mild impact of the PWN morphology. In a few cases, when we clearly identify specific morphological structures, our results do not favor alignment of the pulsar spin axis and proper velocity. Our calculations of the underlying emission processes explain the low synchrotron X-ray efficiency (in terms of the spin-down luminosity) and imply an energetical subdominant contribution of the inverse Compton process.
M K Dougherty - One of the best experts on this subject based on the ideXlab platform.
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suprathermal electrons at saturn s Bow Shock
The Astrophysical Journal, 2016Co-Authors: A Masters, A J Coates, A H Sulaiman, N Sergis, L Stawarz, M Fujimoto, M K DoughertyAbstract:The leading explanation for the origin of galactic cosmic rays is particle acceleration at the Shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma Shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR Shocks. However, the Cassini spacecraft has shown that the Shock standing in the solar wind sunward of Saturn (Saturn's Bow Shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's Bow Shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (<100 keV) were above background. We show that these results are consistent with the theory in which the "injection" of thermal electrons into an acceleration process involves interaction with whistler waves at the Shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong Shocks around young SNRs. A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ∼1 MeV).
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suprathermal electrons at saturn s Bow Shock
arXiv: High Energy Astrophysical Phenomena, 2016Co-Authors: A Masters, A J Coates, A H Sulaiman, N Sergis, L Stawarz, M Fujimoto, M K DoughertyAbstract:The leading explanation for the origin of galactic cosmic rays is particle acceleration at the Shocks surrounding young supernova remnants (SNRs), although crucial aspects of the acceleration process are unclear. The similar collisionless plasma Shocks frequently encountered by spacecraft in the solar wind are generally far weaker (lower Mach number) than these SNR Shocks. However, the Cassini spacecraft has shown that the Shock standing in the solar wind sunward of Saturn (Saturn's Bow Shock) can occasionally reach this high-Mach number astrophysical regime. In this regime Cassini has provided the first in situ evidence for electron acceleration under quasi-parallel upstream magnetic conditions. Here we present the full picture of suprathermal electrons at Saturn's Bow Shock revealed by Cassini. The downstream thermal electron distribution is resolved in all data taken by the low-energy electron detector (CAPS-ELS, 18 keV) measured a suprathermal electron signature at 31 of 508 crossings, where typically only the lowest energy channels (<100 keV) were above background. We show that these results are consistent with theory in which the "injection" of thermal electrons into an acceleration process involves interaction with whistler waves at the Shock front, and becomes possible for all upstream magnetic field orientations at high Mach numbers like those of the strong Shocks around young SNRs. A future dedicated study will analyze the rare crossings with evidence for relativistic electrons (up to ~1 MeV).
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characterization of saturn s Bow Shock magnetic field observations of quasi perpendicular Shocks
arXiv: Space Physics, 2016Co-Authors: A Masters, A H Sulaiman, M K DoughertyAbstract:Collisionless Shocks vary drastically from terrestrial to astrophysical regimes resulting in radically different characteristics. This poses two complexities. Firstly, separating the influences of these parameters on physical mechanisms such as energy dissipation. Secondly, correlating observations of Shock waves over a wide range of each parameter, enough to span across different regimes. Investigating the latter has been restricted since the majority of studies on Shocks at exotic regimes (such as supernova remnants) have been achieved either remotely or via simulations, but rarely by means of in-situ observations. Here we present the parameter space of MA Bow Shock crossings from 2004-2014 as observed by the Cassini spacecraft. We find that Saturn's Bow Shock exhibits characteristics akin to both terrestrial and astrophysical regimes (MA of order 100), which is principally controlled by the upstream magnetic field strength. Moreover, we determined the {\theta}Bn of each crossing to show that Saturn's (dayside) Bow Shock is predominantly quasi-perpendicular by virtue of the Parker spiral at 10 AU. Our results suggest a strong dependence on MA in controlling the onset of physical mechanisms in collisionless Shocks, particularly non-time stationarity and variability. We anticipate our comprehensive assessment will yield deeper insight into high MA collisionless Shocks and provide a broader scope for understanding the structures and mechanisms of collisionless Shocks.
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characterization of saturn s Bow Shock magnetic field observations of quasi perpendicular Shocks
Journal of Geophysical Research, 2016Co-Authors: A Masters, A H Sulaiman, M K DoughertyAbstract:Collisionless Shocks vary drastically from terrestrial to astrophysical regimes resulting in radically different characteristics. This poses two complexities. First, separating the influences of these parameters on physical mechanisms such as energy dissipation. Second, correlating observations of Shock waves over a wide range of each parameter, enough to span across different regimes. Investigating the latter has been restricted since the majority of studies on Shocks at exotic regimes (such as supernova remnants) have been achieved either remotely or via simulations, but rarely by means of in situ observations. Here we present the parameter space of MA Bow Shock crossings from 2004 to 2014 as observed by the Cassini spacecraft. We find that Saturn's Bow Shock exhibits characteristics akin to both terrestrial and astrophysical regimes (MA of order 100), which is principally controlled by the upstream magnetic field strength. Moreover, we determined the θBn of each crossing to show that Saturn's (dayside) Bow Shock is predominantly quasi-perpendicular by virtue of the Parker spiral at 10 AU. Our results suggest a strong dependence on MA in controlling the onset of physical mechanisms in collisionless Shocks, particularly nontime stationarity and variability. We anticipate that our comprehensive assessment will yield deeper insight into high MA collisionless Shocks and provide a broader scope for understanding the structures and mechanisms of collisionless Shocks.
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electron heating at saturn s Bow Shock
Journal of Geophysical Research, 2011Co-Authors: A Masters, S J Schwartz, E M Henley, M F Thomsen, B Zieger, A J Coates, Nick Achilleos, J W Mitchell, Kirk C Hansen, M K DoughertyAbstract:Collisionless Shock waves are a widespread phenomenon in both solar system and astrophysical contexts. The nature of energy dissipation at such Shocks is of particular interest, especially at high Mach numbers. We use data taken by the Cassini spacecraft to investigate electron heating at Saturn's Bow Shock, one of the strongest collisionless Shocks encountered by spacecraft to date. Measurements of the upstream solar wind ion parameters are scarce due to spacecraft pointing constraints and the absence of an upstream monitor. To address this, we use solar wind speed predictions from the Michigan Solar Wind Model. Since these model predictions are based on near-Earth solar wind measurements, we restrict our analysis to Bow Shock crossings made by Cassini within ±75 days of apparent opposition of Earth and Saturn. An analysis of the resulting set of 94 crossings made in 2005 and 2007 reveals a positive correlation between the electron temperature increase across the Shock and the kinetic energy of an incident proton, where electron heating accounts for between ∼3% and ∼7% of this incident ram energy. This percentage decreases with increasing Alfven Mach number, a trend that we confirm continues into the hitherto poorly explored high–Mach number regime, up to an Alfven Mach number of ∼150. This work reveals that further studies of the Saturnian Bow Shock will bridge the gap between the more modest Mach numbers encountered in near-Earth space and more exotic astrophysical regimes where Shock processes play central roles.
Roger W Romani - One of the best experts on this subject based on the ideXlab platform.
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psr j2030 4415 s remarkable Bow Shock pwn and filament
arXiv: High Energy Astrophysical Phenomena, 2020Co-Authors: Martijn De Vries, Roger W RomaniAbstract:We report on new X-ray and optical observations of PSR J2030+4415, a Gamma-ray Pulsar with an H$\alpha$ Bow Shock. These data reveal the velocity structure of the Bow Shock apex and resolve unusual X-ray structure in its interior. In addition the system displays a very long, thin filament, extending at least $5^\prime$ at $\sim 130^\circ$ to the pulsar motion vector. Careful astrometry, compared with a short archival exposure, detects the pulsar proper motion at 85 mas yr$^{-1}$. With the H$\alpha$ velocity structure this allows us to estimate the distance as $0.75$ kpc.
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the asymmetric Bow Shock pulsar wind nebula of psr j2124 3358
The Astrophysical Journal, 2017Co-Authors: Roger W Romani, Patrick Slane, Andrew W GreenAbstract:We describe new measurements of the remarkable Hα/UV/X-ray Bow Shock and pulsar wind nebula (PWN) of the isolated millisecond pulsar (MSP) PSR J2124−3358. Chandra X-ray Observatory imaging shows a one-sided jet structure with a softer equatorial outflow. KOALA integral field unit spectroscopy shows that non-radiative emission dominates the Bow Shock and that the Hα nebula is asymmetric about the pulsar velocity with an elongation into the plane of the sky. We extend analytic models of the contact discontinuity to accommodate such shapes and compare these to the data. Using Hubble Space Telescope UV detections of the pulsar and Bow Shock, radio timing distance, proper motion measurements, and the CXO-detected projected spin axis, we model the 3D PWN momentum flux distribution. The integrated momentum flux depends on the ionization of the ambient ISM, but for an expected ambient warm neutral medium, we infer . This implies , depending on the equation of state, which in turn suggests that the MSP gained significant mass during recycling and then lost its companion. However, this conclusion is at present tentative, since lower ionization allows lower masses, and uncertainty in the parallax allows up to 50% error.