Journal Article

SGR 0418+5729 as an evolved Quark-Nova compact remnant

R. Ouyed, D. Leahy and B. Niebergal

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 2, pages 1590-1596
Published in print August 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18804.x
SGR 0418+5729 as an evolved Quark-Nova compact remnant

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Soft γ-ray repeaters (SGRs) and anomalous X-ray pulsars are believed to be magnetars, i.e. neutron stars powered by extreme magnetic fields, B∼ 1014–1015 G. The recent discovery of an SGR with low magnetic field (<7.5 × 1012 G), SGR 0418+5729, which shows bursts similar to those of SGRs, implies that a high surface dipolar magnetic field might not be necessary for magnetar-like activity. We show that the quiescent and bursting properties of SGR 0418+5729 find natural explanations in the context of low magnetic field Quark-Nova (detonative transition from a neutron star to a quark star) remnants, i.e. an old quark star surrounded by degenerate (iron-rich) Keplerian ring/debris ejected during the Quark-Nova explosion. We find that a 16 Myr old quark star surrounded by an ∼10−10 M ring, extending in radius from ∼30 to 60 km, reproduces many observed properties of SGR 0418+5729. The SGR-like burst is caused by magnetic penetration of the inner part of the ring and subsequent accretion. Radiation feedback results in months long accretion from the ring’s non-degenerate atmosphere which matches well the observed decay phase. We make specific predictions (such as an accretion glitch of ΔP/P∼−2 × 10−11 during burst and a sub-keV proton cyclotron line from the ring) that can be tested by sensitive observations.

Keywords: stars: neutron; stars: magnetic fields

Journal Article.  4875 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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