Accretion-powered pulsations in an apparently quiescent neutron star binary

Accreting millisecond X-ray pulsars (AMXPs) are an important subset of low-mass X-ray binaries (LMXBs) in which coherent X-ray pulsations can be observed during occasional, bright outbursts (X-ray luminosity

{L}_{{\rm{X}}}\sim {10}^{36}\,\mathrm{erg}\,{{\rm{s}}}^{-1}

). These pulsations show that matter is being channeled onto the neutron star’s magnetic poles. However, such sources spend most of their time in a low-luminosity, quiescent state (

{L}_{{\rm{X}}}\lesssim {10}^{34}\,\mathrm{erg}\,{{\rm{s}}}^{-1}

), where the nature of the accretion flow onto the neutron star (if any) is not well understood. Here we report that the millisecond pulsar/LMXB transition object PSR J1023+0038 intermittently shows coherent X-ray pulsations at luminosities nearly 100 times fainter than observed in any other AMXP. We conclude that in spite of its low luminosity, PSR J1023+0038 experiences episodes of channeled accretion, a discovery that challenges existing models for accretion onto magnetized neutron stars.

Note:

9 pages, 7 figures, 1 table; accepted in ApJ

accretion, accretion disks
pulsars: individual
X-rays: binaries

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Figures(0)

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