Abstract
X-ray pulsars1,2 are magnetized, spinning neutron stars accreting matter from their binary companions. Their pulse periods P, ranging over four orders of magnitude, increase and decrease in complex ways1,3,4. The more luminous ones tend to show faster spin-up1,5. A puzzle is that the spin-up timescales of many X-ray pulsars are much shorter than their binary-evolution timescales, thus apparently violating the steady-state condition. It has there-fore been suspected6 that there exist many 'turned-off X-ray pulsars currently spinning down undetected. An excellent test for this hypothesis became available using the X-ray pulsar GX1 +4, which used to show the fastest spin-up over a decade1,7–10and then faded away11. Using the X-ray satellite Ginga12, we detected GX1+4 at ∼1/40 the previous intensity, and found that it now has an average spin-down trend. This discovery apparently supports the above hypothesis.
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Makishima, K., Ohashi, T., Sakao, T. et al. Spin-down of the X-ray pulsar GX1 +4 during an extended low state. Nature 333, 746–748 (1988). https://doi.org/10.1038/333746a0
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DOI: https://doi.org/10.1038/333746a0
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