NuSTAR Discovery of a cyclotron line in KS 1947+300
Abstract
We present a spectral analysis of three simultaneous NuSTAR and Swift/XRT observations of the transient Be-neutron star binary KS 1947+300 taken during its outburst in 2013/2014. These broad-band observations were supported by Swift/XRT monitoring snap-shots every 3 days, which we use to study the evolution of the spectrum over the outburst. We find strong changes of the power-law photon index, which shows a weak trend of softening with increasing X-ray flux. The neutron star shows very strong pulsations with a period of P ~ 18.8 s. The 0.8-79 keV broad-band spectrum can be described by a power-law with an exponential cutoff and a black-body component at low energies. During the second observation we detect a cyclotron resonant scattering feature at 12.5 keV, which is absent in the phase-averaged spectra of observations 1 and 3. Pulse phase-resolved spectroscopy reveals that the strength of the feature changes strongly with pulse phase and is most prominent during the broad minimum of the pulse profile. At the same phases the line also becomes visible in the first and third observation at the same energy. This discovery implies that KS 1947+300 has a magnetic field strength of B ~ 1.1e12 (1+z)G, which is at the lower end of known cyclotron line sources.
Keywords
Cite
@article{arxiv.1403.1901,
title = {NuSTAR Discovery of a cyclotron line in KS 1947+300},
author = {Felix Fuerst and Katja Pottschmidt and Joern Wilms and Jamie Kennea and Matteo Bachetti and Eric Bellm and Steven E. Boggs and Deepto Chakrabarty and Finn E. Christensen and William W. Craig and Charles J. Hailey and Fiona Harrison and Daniel Stern1 and John A. Tomsick and Dominic J. Walton and William Zhang and Cahill Center and Caltech and USA and CSST and UMBC and USA and CRESST and GSFC and USA and Remeis-Observatory and ECAP and Germany and Penn State University and USA and Universite de Toulouse and France and CNRS and IRAP and France and SSL and UCB and USA and Kavli Institute for Astrophysics and MIT and USA and DTU Space and TU Denmark and Denmark and Columbia Astrophysics Lab and Columbia University and USA and JPL and USA and GSFC and ASD and USA},
journal= {arXiv preprint arXiv:1403.1901},
year = {2019}
}
Comments
6 pages, 3 figures, accepted for publication in ApJ Letters