A Double Outburst from IGR J00291+5934: Implications for Accretion Disk Instability Theory
Abstract
The accretion-powered millisecond pulsar IGR J00291+5934 underwent two ~10 day long outbursts during 2008, separated by 30 days in quiescence. Such a short quiescent period between outbursts has never been seen before from a neutron star X-ray transient. X-ray pulsations at the 599 Hz spin frequency are detected throughout both outbursts. For the first time, we derive a pulse phase model that connects two outbursts, providing a long baseline for spin frequency measurement. Comparison with the frequency measured during the 2004 outburst of this source gives a spin-down during quiescence of -(4 ± 1) × 10-15 Hz s-1, approximately an order of magnitude larger than the long-term spin-down observed in the 401 Hz accretion-powered pulsar SAX J1808.4-3658. If this spin-down is due to magnetic dipole radiation, it requires a 2 × 108 G field strength, and its high spin-down luminosity may be detectable with the Fermi Large Area Telescope. Alternatively, this large spin-down could be produced by gravitational wave emission from a fractional mass quadrupole moment of Q/I = 1 × 10-9. The rapid succession of the outbursts also provides a unique test of models for accretion in low-mass X-ray binaries. Disk instability models generally predict that an outburst will leave the accretion disk too depleted to fuel a second outburst after such a brief quiescence. We suggest a modification in which the outburst is shut off by the onset of a propeller effect before the disk is depleted. This model can explain the short quiescence and the unusually slow rise of the light curve of the second 2008 outburst.
- Publication:
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The Astrophysical Journal
- Pub Date:
- January 2011
- DOI:
- 10.1088/0004-637X/726/1/26
- arXiv:
- arXiv:1006.1908
- Bibcode:
- 2011ApJ...726...26H
- Keywords:
-
- binaries: general;
- stars: individual: IGR J00291+5934;
- stars: neutron;
- stars: rotation;
- X-rays: binaries;
- X-rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 17 pages, 8 figures