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 \sim 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 \pm 0.03 ) \times 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 .