Phase-Resolved Spectroscopy of the Magnetar SGR J1745–2900 Based on Data from the NuSTAR Observatory

The magnetar SGR J1745–2900 located in the vicinity of the supermassive black hole Sgr A${}^{\star}$ was detected during its X-ray outburst with the Swift/XRT telescope in April 2013. For several months after its detection the source was observed with the NuSTAR observatory, which allowed pulsations with a period ${\sim}3.76$ s to be recorded. Using these observations, we have studied in detail the dependence of the pulse profile and the pulsed fraction on the energy and intensity of the magnetar. The pulsed fraction in the 3–5 and 5–10 keV energy bands is shown to be 40–50$\%$, slightly increasing with decreasing flux. We have performed phase-resolved spectroscopy for the source in the energy range from 3 to ${\sim}40$ keV and show that the temperature of the emitting regions remains fairly stable during the pulse, while their apparent size changes significantly with phase.