KITP: how neutron stars get their kicks

intense and dense afternoon as we get the current state of the art about neutron star natal kicks, theory and observational constraints

Chevy supernova!

Vicky - on NS-NS constraints (video and podcast)

need >~ 2.1-2.3 solar mass He cores to get to iron and classic type II SNe
stable mass transfer may lower this limit
electron capture supernovae, in binaries, may limit on core masses right before SNe town to ~ 1.45 solar masses or more

evidence other than presence in globulars for subpopulation of neutron stars having low kick speeds: high mass x-ray binaries with e < 0.2 and orbital periods > 30 days
- unlikely to have had strong tidal evolution, so the NS in these systems look like they have low SNe kicks, of maybe < 50 km/sec - also infer maybe broad underlying progenitor mass range of 8-14 solar mass

there are other ways to get formation channels with low kicks - Fe core collapse but maybe with rapidly rotating cores, or low mass cores with stripped envelopes, or, what the heck, maybe it is the dratted magnetic field...

use the known NS-NS systems in the Milky Way, for which there is enough information - masses, spin orientation and system velocity
to constrain kicks on the second neutron star formed in these systems.

oh boy, biases when marginalizing 5-D probability distribution functions
there is a reason why these are not often discussed... read the paper!
bottom line, integrating PDFs by eye is not a robust process for typical astronomers...

so PSR0737-3039 may have had second NS through electron capture supernova with associated low velocity natal kick
1534 and 1913 are consistent with high kick Fe core collapse from higher mass core

Philip - wraps up from this morning on Electron Capture Supernovae and Black Hole kicks (video and podcast) and Natasha - binary population synthesis on globulars (video and podcast)

summarises why NS with natal kicks are retained is a problem, very nicely

get ~ 10% retention fraction with electron capture supernovae, for suitable range of binaries and mass ranges, at low Z, that go to ECS channel

cf Ivanova et al 2008

NB: ECS formed NS have lower gravitational mass, so expect 80-90% of NS in globulars to be relatively low mass (< 1.3 solar masses - but to see them spun up some mass may of course have been accreted)