Cyclotron Line Measurements and a Torque Reversal in 4U 1538-522 as Seen by INTEGRAL
Abstract
We present an analysis of all public INTEGRAL observations of the high-mass X-ray binary 4U 1538-522. Pulse period measurements strongly suggest that the source underwent a torque reversal in early 2009, departing from its spin-up trend of the past 20 years. We perform a detailed spectral analysis of the INTEGRAL data from either side of this torque reversal, and find few significant changes in the X-ray spectral parameters, both with respect to date (before or after the reversal) and source luminosity. Perhaps most notably, no correlation is found between the centroid energy of the cyclotron line (detected at ~22 keV) and luminosity, a result which is in line with the predictions of Becker et al. (2012)'s work on luminosity regimes in the accretion column. We also make significant detections of the harmonic CRSF at ~50 keV, supporting the results of Rodes-Roca et al. (2009).
- Publication:
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AAS/High Energy Astrophysics Division #13
- Pub Date:
- April 2013
- Bibcode:
- 2013HEAD...1312635H