Neutron Stars - Nonthermal

X-rays from rotation-powered pulsars provide important information on the physical processes operating in these objects. Figure 1 shows a high resolution ROSAT HRI observation of the Crab Nebula superimposed on an optical image (upper panel). The bright compact emission in the center is a neutron star, the Crab pulsar (the lower panel shows the pulse-off and pulse-on states). It is the power source for high relativistic electrons, which lose their energy by producing synchrotron radiation in the magnetic field of the pulsar nebula. The diagram (Fig. 2) shows the relation between the X-ray luminosity (0.1 - 2.4 keV) and the spin-down energy for the 26 rotation-powered pulsars detected by ROSAT. The suprisingly close correlation between the X-ray luminosity LX and spin down energy dE/dt strongly suggests that the bulk of the observed X-rays is emitted at the expense of the neutron star's rotational energy, i.e. by nonthermal emission.

[ROSAT HRI image of the crab nebula superimposed on an optical image]
Figure 1

[X-ray luminosities of nonthermal NSs as a function of spin-down energy]
Figure 2

Becker, W. and J. Trümper, The X-ray luminosity of rotation-powered neutron stars, Astron. & Astrophys. 326, 682-691 (1997)

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