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Magnetically gated accretion in an accreting ‘non-magnetic’ white dwarf
Nature ( IF 64.8 ) Pub Date : 2017-12-01 , DOI: 10.1038/nature24653
S. Scaringi , T. J. Maccarone , C. D’Angelo , C. Knigge , P. J. Groot

White dwarfs are often found in binary systems with orbital periods ranging from tens of minutes to hours in which they can accrete gas from their companion stars. In about 15 per cent of these binaries, the magnetic field of the white dwarf is strong enough (at 106 gauss or more) to channel the accreted matter along field lines onto the magnetic poles. The remaining systems are referred to as ‘non-magnetic’, because until now there has been no evidence that they have a magnetic field that is strong enough to affect the accretion dynamics. Here we report an analysis of archival optical observations of the ‘non-magnetic’ accreting white dwarf in the binary system MV Lyrae, whose light curve displays quasi-periodic bursts of about 30 minutes duration roughly every 2 hours. The timescale and amplitude of these bursts indicate the presence of an unstable, magnetically regulated accretion mode, which in turn implies the existence of magnetically gated accretion, in which disk material builds up around the magnetospheric boundary (at the co-rotation radius) and then accretes onto the white dwarf, producing bursts powered by the release of gravitational potential energy. We infer a surface magnetic field strength for the white dwarf in MV Lyrae of between 2 × 104 gauss and 1 × 105 gauss, too low to be detectable by other current methods. Our discovery provides a new way of studying the strength and evolution of magnetic fields in accreting white dwarfs and extends the connections between accretion onto white dwarfs, young stellar objects and neutron stars, for which similar magnetically gated accretion cycles have been identified.

中文翻译:

吸积的“非磁性”白矮星中的磁门吸积

白矮星通常存在于双星系统中,其轨道周期从几十分钟到几小时不等,在此期间它们可以从伴星中吸积气体。在这些双星中,大约有 15% 的白矮星磁场足够强(106 高斯或更高),可以将吸积物质沿磁力线引导到磁极上。其余的系统被称为“非磁性”系统,因为直到现在还没有证据表明它们具有足以影响吸积动力学的磁场。在这里,我们报告了对双星系统 MV Lyrae 中“非磁性”吸积白矮星的档案光学观测的分析,其光变曲线显示大约每 2 小时持续约 30 分钟的准周期性爆发。这些爆发的时间尺度和幅度表明存在不稳定的磁调节吸积模式,这反过来意味着存在磁选通吸积,其中盘材料围绕磁层边界(在同转半径处)积聚,然后吸积到白矮星上,产生由释放引力势能驱动的爆发。我们推断 MV Lyrae 中白矮星的表面磁场强度介于 2 × 104 高斯和 1 × 105 高斯之间,太低而无法通过其他当前方法检测到。我们的发现提供了一种研究吸积白矮星中磁场强度和演化的新方法,并将吸积与白矮星、年轻恒星物体和中子星之间的联系扩展,
更新日期:2017-12-01
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