TIMING AND FLUX EVOLUTION OF THE GALACTIC CENTER MAGNETAR SGR J1745–2900

Abstract

We present the X-ray timing and spectral evolution of the Galactic Center\nmagnetar SGR J1745-2900 for the first ~4 months post-discovery using data\nobtained with the Nuclear Spectroscopic Telescope Array (NuSTAR)} and Swift\nobservatories. Our timing analysis reveals a large increase in the magnetar\nspin-down rate by a factor of 2.60 +/- 0.07 over our data span. We further show\nthat the change in spin evolution was likely coincident with a bright X-ray\nburst observed in 2013 June by Swift, and if so, there was no accompanying\ndiscontinuity in the frequency. We find that the source 3-10 keV flux has\ndeclined monotonically by a factor of ~2 over an 80-day period post-outburst\naccompanied by a ~20% decrease in the source's blackbody temperature, although\nthere is evidence for both flux and kT having levelled off. We argue that the\ntorque variations are likely to be magnetospheric in nature and will dominate\nover any dynamical signatures of orbital motion around Sgr A*.\n