On the Correlation of Torque and Luminosity in GX 1+4
Abstract
Over 5 years of daily hard X-ray (>20 keV) monitoring of the 2 minute 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 day 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 that 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1997
- DOI:
- 10.1086/310666
- arXiv:
- arXiv:astro-ph/9703047
- Bibcode:
- 1997ApJ...481L.101C
- Keywords:
-
- ACCRETION;
- ACCRETION DISKS;
- STARS: NEUTRON;
- STARS: PULSARS: INDIVIDUAL ALPHANUMERIC: GX 1+4;
- X-RAYS: STARS;
- Accretion;
- Accretion Disks;
- Stars: Pulsars: Individual: Alphanumeric: GX 1+4;
- Stars: Neutron;
- X-Rays: Stars;
- Astrophysics
- E-Print:
- 10 pages including 3 PS figures. To appear in ApJ Letters