The Be/X-Ray Binary Swift J1626.6-5156 as a Variable Cyclotron Line Source
Abstract
Swift J1626.6-5156 is a Be/X-ray binary that was in outburst from 2005 December until 2008 November. We have examined Rossi X-ray Timing Explorer/Proportional Counter Array (PCA) and High Energy X-ray Timing Explorer spectra of three long observations of this source taken early in its outburst, when the PCA 2-20 keV count rate was >70 counts s-1 PCU-1, as well as several combined observations from different stages of the outburst. The spectra are best fit with an absorbed cutoff power law with a ~6.4 keV iron emission line and a Gaussian optical depth absorption line at ~10 keV. We present strong evidence that this absorption-like feature is a cyclotron resonance scattering feature, making Swift J1626.6-5156 a new candidate cyclotron line source. The redshifted energy of ~10 keV implies a magnetic field strength of ~8.6(1 + z) × 1011 G in the region of the accretion column close to the magnetic poles where the cyclotron line is produced. Analysis of phase-averaged spectra spanning the duration of the outburst suggests a possible positive correlation between the fundamental cyclotron energy and source luminosity. Phase-resolved spectroscopy from a long observation reveals a variable cyclotron line energy, with phase dependence similar to a variety of other pulsars, as well as the first harmonic of the fundamental cyclotron line.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2013
- DOI:
- 10.1088/0004-637X/762/1/61
- arXiv:
- arXiv:1211.3109
- Bibcode:
- 2013ApJ...762...61D
- Keywords:
-
- magnetic fields;
- stars: individual: Swift J1626.6–5156;
- stars: neutron;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 11 pages, 6 figures, to be published in the Astrophysical Journal