NuSTAR Detection Of A Cyclotron Line In The Supergiant Fast X-ray   Transient IGR J17544-2619
  We present NuSTAR spectral and timing studies of the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619. The spectrum is well-described by a ~1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a cyclotron line at 17 keV, confirming that the compact object in IGR J17544-2619 is indeed a neutron star. This is the first measurement of the magnetic field in a SFXT. The inferred magnetic field strength, B = (1.45 +/- 0.03) * 10^12 G * (1+z) is typical of neutron stars in X-ray binaries, and rules out a magnetar nature for the compact object. We do not find any significant pulsations in the source on time scales of 1-2000 s. 
Varun Bhalerao (1), Patrizia Romano (2), John Tomsick (3), Lorenzo   Natalucci (4), David M. Smith (5), Eric Bellm (6), Stev...
astro-ph.HE