NuSTAR discovery of a cyclotron line in the accreting X-ray pulsar IGR J16393-4643

Creators: Bodaghee, Arash; Tomsick, John A.; Fornasini, Francesca M.; Krivonos, Roman; Stern, Daniel; Mori, Kaya; Rahoui, Farid; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Zhang, William W.

Abstract

The high-mass X-ray binary and accreting X-ray pulsar IGR J16393-4643 was observed by the Nuclear Spectroscope Telescope Array in the 3–79 keV energy band for a net exposure time of 50 ks. We present the results of this observation which enabled the discovery of a cyclotron resonant scattering feature with a centroid energy of 29.3^(+1.3)_(-1.1) keV. This allowed us to measure the magnetic field strength of the neutron star for the first time: B = (2.5 ± 0.1) × 10^(12) G. The known pulsation period is now observed at 904.0 ± 0.1 s. Since 2006, the neutron star has undergone a long-term spin-up trend at a rate of P = -2 x 10^(-8) s s^(−1) (−0.6 s per year, or a frequency derivative of v = 3 x 10^(-14) Hz s^(−1)). In the power density spectrum, a break appears at the pulse frequency which separates the zero slope at low frequency from the steeper slope at high frequency. This addition of angular momentum to the neutron star could be due to the accretion of a quasi-spherical wind, or it could be caused by the transient appearance of a prograde accretion disk that is nearly in corotation with the neutron star whose magnetospheric radius is around 2 × 10^8 cm.

Additional Information

© 2016 The American Astronomical Society. Received 2015 July 7; accepted 2016 March 17; published 2016 June 1. The authors are grateful to the anonymous Referee for their constructive criticism that helped improve the quality of the manuscript. A.B. thanks Dr. Konstantin Postnov. FMF acknowledges support from the National Science Foundation Graduate Research Fellowship. R.K. acknowledges support from from Russian Science Foundation (grant 14-22-00271). The scientific results reported in this article are based on data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of: the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology; data obtained from the High Energy Astrophysics Science Archive Research Center (HEASARC) provided by NASA's Goddard Space Flight Center; NASA's Astrophysics Data System Bibliographic Services; and the SIMBAD database operated at CDS, Strasbourg, France. Facilities: NuSTAR, Swift.

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