We report on a 10 ks simultaneous Chandra /HETG - NuSTAR observation of the Bursting Pulsar , GRO J1744 - 28 , during its third detected outburst since discovery and after nearly 18 years of quiescence .
The source is detected up to 60 keV with an Eddington persistent flux level .
Seven bursts , followed by dips , are seen with Chandra , three of which are also detected with NuSTAR .
Timing analysis reveals a slight increase in the persistent emission pulsed fraction with energy ( from 10 % to 15 % ) up to 10 keV , above which it remains constant .
The 0.5 - 70 keV spectra of the persistent and dip emission are the same within errors , and well described by a blackbody ( BB ) , a power-law with an exponential rolloff , a 10 keV feature , and a 6.7 keV emission feature , all modified by neutral absorption .
Assuming that the BB emission originates in an accretion disc , we estimate its inner ( magnetospheric ) radius to be about 4 \times 10 ^ { 7 } cm , which translates to a surface dipole field B \approx 9 \times 10 ^ { 10 } G. The Chandra /HETG spectrum resolves the 6.7 keV feature into ( quasi- ) neutral and highly ionized Fe XXV and Fe XXVI emission lines .
XSTAR modeling shows these lines to also emanate from a truncated accretion disk .
The burst spectra , with a peak flux more than an order of magnitude higher than Eddington , are well fit with a power-law with an exponential rolloff and a 10 keV feature , with similar fit values compared to the persistent and dip spectra .
The burst spectra lack a thermal component and any Fe features .
Anisotropic ( beamed ) burst emission would explain both the lack of the BB and any Fe components .