THE Be/X-RAY BINARY SWIFT J1626.6−5156 AS A VARIABLE CYCLOTRON LINE SOURCE
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DeCesar, Megan E., Patricia T. Boyd, Katja Pottschmidt, Jörn Wilms, Slawomir Suchy, and M. Coleman Miller. “THE Be/X-RAY BINARY SWIFT J1626.6−5156 AS A VARIABLE CYCLOTRON LINE SOURCE.” The Astrophysical Journal 762, no. 1 (December 2012): 61. https://doi.org/10.1088/0004-637X/762/1/61.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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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.