An X-ray Pulsar with a Superstrong Magnetic Field in
the Soft Gamma-Ray Repeater SGR 1806-20
Kouveliotou, C., Dieters, S., Strohmayer, T., Van Paradijs, J.,
Fishman, G. J., Meegan, C. A., Hurley, K., Kommers, J., Smith, I.,
Frail, D., & Murakami, T.
Soft gamma-ray repeaters (SGRs) emit multiple, brief (0.1 s), intense
outbursts of low-energy gamma-rays.
They are extremely rare - three are known in our Galaxy and one in the
Large Magellanic Cloud.
Two SGRs are associated with young supernova remnants (SNRs), and therefore
most probably with neutron stars, but it remains a puzzle why SGRs are so
different from `normal' radio pulsars.
Here we report the discovery of pulsations in the persistent X-ray flux
of SGR 1806-20, with a period of 7.47 s and a spindown rate of
2.6 x 10^-3 s yr^-1.
We argue that the spindown is due to magnetic dipole emission and find
that the pulsar age and (dipolar) magnetic field strength are 1,500
years and 8 x 10^14 gauss, respectively.
Our observations demonstrate the existence of `magnetars', neutron stars
with magnetic fields about 100 times stronger than those of radio pulsars,
and support earlier suggestions that SGR bursts are caused by neutron-star
`crustquakes' produced by magnetic stresses.
The `magnetar' birth rate is about one per millennium - a substantial
fraction of that of radio pulsars.
Thus our results may explain why some SNRs have no radio pulsars.
Status:
1998, Nature, 393, 235.
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