Ocean g-modes on transient neutron stars

Journal Article · Sun Nov 20 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/832/1/44· OSTI ID:22868455

Deibel, Alex ^[1]

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1. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

The neutron star ocean is a plasma of ions and electrons that extends from the base of the neutron star’s envelope to a depth where the plasma crystallizes into a solid crust. During an accretion outburst in an X-ray transient, material accumulates in the envelope of the neutron star primary. This accumulation compresses the neutron star’s outer layers and induces nuclear reactions in the ocean and crust. Accretion-driven heating raises the ocean’s temperature and increases the frequencies of g-modes in the ocean; when accretion halts, the ocean cools and ocean g-mode frequencies decrease. If the observed low-frequency quasi-periodic oscillations on accreting neutron stars are g-modes in the ocean, the observed quasi-periodic oscillation frequencies will increase during the outburst—reaching a maximum when the ocean temperature reaches steady state—and subsequently decrease during quiescence. For time-averaged accretion rates during outbursts between 〈 M-dot 〉=0.1--1.0 M-dot {sub Edd} the predicted g-mode fundamental n = 1 l = 2 frequency is between ≈3–7 Hz for slowly rotating neutron stars. Accreting neutron stars that require extra shallow heating, such as the Z-sources MAXI J0556-332, MXB 1659-29, and XTE J1701-462, have predicted g-mode fundamental frequencies between ≈3–16 HZ. Therefore, observations of low-frequency quasi-periodic oscillations between ≈8--16 Hz in these sources, or in other transients that require shallow heating, will support a g-mode origin for the observed quasi-periodic oscillations.

• OSTI ID: 22868455
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 832; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELECTRONS
NEUTRON STARS
NUCLEAR REACTIONS
OSCILLATIONS
PERIODICITY
PLASMA
STEADY-STATE CONDITIONS
X RADIATION