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On the Correlation of Torque and Luminosity in GX 1+4

Deepto Chakrabarty·Lars Bildsten·Mark H. Finger·John M. Grunsfeld·Danny T. Koh·Robert W. Nelson·Thomas A. Prince·Brian A. Vaughan·Robert B. Wilson
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Abstract

Over five years of daily hard X-ray (>20 keV) monitoring of the 2-min accretion-powered pulsar GX 1+4 with the Compton Gamma Ray Observatory/BATSE large-area detectors has found nearly continuous rapid spin-down, interrupted by a bright 200-d spin-up episode. During spin-down, the torque becomes more negative as the luminosity increases (assuming that the 20-60 keV pulsed flux traces bolometric luminosity), the opposite of what is predicted by standard accretion torque theory. No changes in the shape of the 20-100 keV pulsed energy spectrum were detected, so that a very drastic change in the spectrum below 20 keV or the pulsed fraction would be required to make the 20-60 keV pulsed flux a poor luminosity tracer. These are the first observations which flatly contradict standard magnetic disk accretion theory, and they may have important implications for understanding the spin evolution of X-ray binaries, cataclysmic variables, and protostars. We briefly discuss the possibility that GX 1+4 may be accreting from a retrograde disk during spin-down, as previously suggested.

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Deepto Chakrabarty, Lars Bildsten, Mark H. Finger, John M. Grunsfeld, Danny T. Koh, Robert W. Nelson, Thomas A. Prince, Brian A. Vaughan, Robert B. Wilson. 1997-03-07. On the Correlation of Torque and Luminosity in GX 1+4. https://doi.org/10.1086/310666

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