# Fastest neutron star, 1100 km/second

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## Main Question or Discussion Point

press release from NRAO
http://www.nrao.edu/pr/2005/fastpulsar/
The fastest-moving neutron star ever seen, clocked at 1100 kilometers per second, a speed that will take it out of the Milky Way galaxy, was given its initial "kick-off" by the supernova that formed it.

journal article
http://arxiv.org/abs/astro-ph/0509031
Getting Its Kicks: A VLBA Parallax for the Hyperfast Pulsar B1508+55
S. Chatterjee et al.
5 pages, including 2 figures
Astrophys.J. 630 (2005) L61-L64
"The highest velocity neutron stars establish stringent constraints on natal kicks, asymmetries in supernova core collapse, and the evolution of close binary systems. Here we present the first results of a long-term pulsar astrometry program using the VLBA. We measure a proper motion and parallax for the pulsar B1508+55, leading to model-independent estimates of its distance (2.37+0.23-0.20 kpc) and transverse velocity (1083+103-90 km/s), the highest velocity directly measured for a neutron star. We trace the pulsar back from its present Galactic latitude of 52.3 degrees to a birth site in the Galactic plane near the Cyg OB associations, and find that it will inevitably escape the Galaxy. Binary disruption alone is insufficient to impart the required birth velocity, and a natal kick is indicated. A composite scenario including a large kick along with binary disruption can plausibly account for the high velocity.

popular magazine account:
http://www.astronomy.com/asy/default.aspx?c=a&id=3471

a discussion of various "kick" mechanisms that might give neutron stars high speeds is in this paper, see bottom of page 7
http://arxiv.org/abs/astro-ph/0106159

Related Astronomy and Astrophysics News on Phys.org
SpaceTiger
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...and that doesn't even include the unknown radial component -- though, considering selection biases, it's likely small. Good find.

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Dearly Missed
SpaceTiger said:
...and that doesn't even include the unknown radial component -- though, considering selection biases, it's likely small. Good find.
Tiger could you please summarize the prevailing idea(s) of how a supernova delivers such a kick to the neutronstar remnant?

why is the SN collapse not symmetric?

I can see orbit disruption of a binary system contributing a part, but these papers indicate that would not be enough

Labguy
marcus said:
Tiger could you please summarize the prevailing idea(s) of how a supernova delivers such a kick to the neutronstar remnant?

why is the SN collapse not symmetric?

I can see orbit disruption of a binary system contributing a part, but these papers indicate that would not be enough
Hello, Marcus, long time no-type. I'm not Tiger, but there are many supernovae models, and observations, that show evidence for non-symmetric SN explosions. S.E. Woosley is probably considered the foremost astrophysicist today working on supernovae properties. His paper at: http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v475n2/33428/33428.html [Broken] is one of the best and discusses Type Ia carbon deflagration/detonation asymmetries.

There is a lot more information on SN explosion asymmetries, including type Ic and Type II, that has agreed with observations for quite some time. Take a look at these for lots of info:
http://newton.ex.ac.uk/aip/glimpse.txt/physnews.181.1.html [Broken]
ASYMMETRIC SUPERNOVA EXPLOSIONS can impart a "kick" to the neutron star remnants born during the explosions. After a new reassessment, the proper motions (the motions across the sky) of 86 pulsars were found to have a mean velocity of 450 km/sec, which exceeds the escape velocities for a number of celestial systems, such as binary stars, globular clusters, and even for our galaxy. The University of Manchester (UK) astronomers who performed the study conclude that more than half of all pulsars will escape from the Milky Way and that those that stay will assume a larger and more spherical distribution than was previously thought. Therefore, the astronomers assert, this population of old, high-velocity pulsars might be responsible for more of the gamma bursts seen by the Gamma Ray Observatory than previously expected. (A.G. Lyne and D.R. Lorimer, Nature, 12 May 1994.)
And;
http://arxiv.org/abs/astro-ph/9605186
http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/308773 [Broken]
http://xxx.sf.nchc.gov.tw/abs/astro-ph/0505199 [Broken]
Some of the condensed quotes from these sites are:
For the binary pulsars PSR 1534 + 12 and PSR 1913 + 16, the presupernova evolution models of helium stars provide important constraints on the parameters of the binary system. If the progenitor helium star is more massive than about 5 solar masses, its radius would not exceed the Roche lobe so that its explosion should be highly asymmetric, imparting a large kick velocity to the newly born neutron star. If the helium star is less massive than about 5 solar masses, it undergoes spiral-in of the companion neutron star to become a C + O star. The explosion of the C + O star might be a type Ic supernova or a peculiar type Ia supernova such as SN 1991 bg. The resultant double neutron star system would probably be smaller than those observed. However, such an evolutionary route would enhance the current estimate of the frequency of neutron star merging that could give rise to a gamma-ray burst and emission of gravitational radiation.
We present an analytical method for studying the changes of the orbital characteristics of binary systems with circular orbits due to a kick velocity imparted to the newborn neutron star during a supernova explosion (SN). Assuming a Maxwellian distribution of kick velocities we derive analytical expressions for the distribution functions of orbital separations and eccentricities immediately after the explosion, of orbital separations after circularization of the post-SN orbits, and of systemic velocities of binaries that remain bound after the explosion. These distributions of binary characteristics can be used to perform analytical population synthesis calculations of various types of binaries, the formation of which involves a supernova explosion. We study in detail the dependence of the derived distributions on the kick velocity and the pre-SN characteristics, we identify all the limits imposed on the post-SN orbital characteristics, and we discuss their implications for the population of X-ray binaries and double neutron star systems. We show that large kick velocities do not necessarily result in large systemic velocities; for typical X-ray binary progenitors the maximum post-SN systemic velocity is comparable to the relative orbital velocity prior to the explosion. We also find that, unless accretion-induced collapse is a viable formation channel, X-ray binaries in globular clusters have most probably been formed by stellar dynamical interactions only, and not directly from primordial binaries.
and much more.

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Labguy said:
Hello, Marcus, long time no-type...
Same here! Long time no, Labguy. I havent been around Astronomy forum as much lately.

Interesting looking bunch of links. keep me busy trying to understand supernovas in my spare time.

it never occurred to me that an explosion like that could be lopsided

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http://arxiv.org/abs/astro-ph/0007272
Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins
Dong Lai, David F. Chernoff, James M. Cordes (Cornell)
ApJ, Vol.549 (March 10, 2001)
We study implications for the apparent alignment of the spin axes, proper-motions, and polarization vectors of the Crab and Vela pulsars. The spin axes are deduced from recent Chandra X-ray Observatory images that reveal jets and nebular structure having definite symmetry axes. The alignments indicate these pulsars were born either in isolation or with negligible velocity contributions from binary motions. We examine the effects of rotation and the conditions under which spin-kick alignment is produced for various models of neutron star kicks. If the kick is generated when the neutron star first forms by asymmetric mass ejection or/and neutrino emission, then the alignment requires that the protoneutron star possesses an original spin with period $P_s$ much less than the kick timescale, thus spin-averaging the kick forces. The kick timescale ranges from 100 ms to 10 s depending on whether the kick is hydrodynamically driven or neutrino-magnetic field driven. For hydrodynamical models, spin-kick alignment further requires the rotation period of an asymmetry pattern at the radius near shock breakout (>100 km) to be much less than ~100 ms; this is difficult to satisfy unless rotation plays a dynamically important role in the core collapse and explosion ($P_s\lo 1$ ms). Aligned kick and spin vectors are inherent to the slow process of asymmetric electromagnetic radiation from an off-centered magnetic dipole. We reassess the viability of this effect, correcting a factor of 4 error in Harrison and Tademaru's calculation that increases the size of the effect. To produce a kick velocity of order a few hundred km/s requires that the neutron star be born with an initial spin close to 1 ms and that spindown due to r-mode driven gravitational radiation be inefficient compared to standard magnetic braking."

Labguy
Thanks, Marcus. I hadn't seen that one.

Chronos
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I'm less inclined to think the explosion was that unbalanced. More like a gravitational sling shot event.

SpaceTiger
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And a brand new one:

Wang, Lai, & Han 2005

Neutron Star Kicks in Isolated and Binary Pulsars: Observational Constraints and Implications for Kick Mechanisms
Authors: Chen Wang, Dong Lai, JinLin Han
Comments: 30 pages, 2 figures, submitted to ApJ

We study observational constraints on neutron star (NS) kicks for isolated pulsars and for neutron stars in binary systems. We are particularly interested in the evidence of kick-spin alignment/misalignment and its dependence on the neutron star initial spin period. For several young pulsars, X-ray observations of compact nebulae showed that pulsar proper motion is aligned with the spin direction as defined by the symmetry axis of the nebula. We also critically examine the measurements of the proper motion and the projected spin axis from a large sample of pulsars with well-calibrated polarization data. We find that among the two dozen pulsars for which reliable measurements are available, there is a significant correlation between the spin axis and the proper motion. For various NS binaries, including double NS systems, binaries with massive main-sequence star companion and binaries with massive white-dwarf companion, we obtain constraints on the kick magnitudes and directions from the observed orbital characteristics of the system. The kick velocity is generally misaligned with the NS spin axis, particularly when the initial spin period (when available) is long. These constraints, together with spin-kick alignment observed in many isolated pulsars, suggest that the kick time scale is about 1 s, so that spin-kick alignment or misalignment can be obtained depending on the initial spin period of the NS. We discuss the implication of our result for various NS kick mechanisms.