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Magnetically Accreting Isolated Old Neutron Stars

Rutledge, Robert E. (2001) Magnetically Accreting Isolated Old Neutron Stars. Astrophysical Journal, 553 (2). pp. 796-800. ISSN 0004-637X.

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Previous work on the emission from isolated old neutron stars (IONSs) accreting from the interstellar medium (ISM) has focused on gravitational capture—i.e., Bondi accretion. We propose a new class of sources that accrete via magnetic interaction with the ISM. While for the Bondi mechanism the accretion rate M_Bondi decreases with increasing neutron star velocity, in magnetic accretors (MAGACs) M_MAGAC increases with increasing neutron star velocity (M_(Bondi) α v^(-3) vs. M_(MAGAC) α v^(1/3)). MAGACs will be produced among high-velocity (≳ 100 km s^(-1)), high magnetic field (B > 10^(14) G) radio pulsars—the "magnetars"—after they have evolved first through magnetic dipole spin-down, followed by a "propeller" phase (during which the object sheds angular momentum on a timescale ≾ 10^(10) yr). The properties of MAGACs may be summarized thus: dipole magnetic fields of B ≳ 10^(14) G; minimum velocities relative to the ISM of 25-100 km s^(-1) or higher, depending on B, well below the median in the observed radio pulsar population; spin periods of greater than days to years; accretion luminosities of 10^(28)-10^(31) ergs s^(-1); and effective temperatures kT_(eff) = 0.3-2.5 keV if they accrete onto the magnetic polar cap. We find no examples of MAGACs among previously observed source classes (anomalous X-ray pulsars, soft gamma-ray repeaters, or known IONs). However, MAGACs may be more prevalent in flux-limited X-ray catalogs than their gravitationally accreting counterparts.

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Additional Information:© 2001. The American Astronomical Society. Received 2000 December 13; accepted 2001 February 2. I thank Lars Bildsten, Omer Blaes, David Chernoff, and Chris Thompson for useful discussions. I thank Lars Bildsten and Omer Blaes for comments on the draft of this paper, which improved the manuscript. I am grateful to the participants in the ITP Workshop, "Spin and Magnetism in Young Neutron Stars," for stimulating discussions which brought about this work. This research was supported in part by National Science Foundation grant PHY 99-07949.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
NSFPHY 99-07949
Subject Keywords:pulsars: general; stars: magnetic fields; stars: neutron; X-rays: stars
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2001-02
Issue or Number:2
Record Number:CaltechAUTHORS:20150226-092646998
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55240
Deposited By: Deborah Miles
Deposited On:26 Feb 2015 19:48
Last Modified:03 Oct 2019 08:04

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