Timing and Flux Evolution of the Galactic Center Magnetar SGR J1745-2900

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We present the X-ray timing and spectral evolution of the Galactic Center magnetar SGR J1745-2900 for the first ~4 months post-discovery using data obtained with the Nuclear Spectroscopic Telescope Array (NuSTAR)} and Swift observatories.

• Our timing analysis reveals a large increase in the magnetar spin-down rate by a factor of 2.60 +/- 0.07 over our data span.
• We further show that the change in spin evolution was likely coincident with a bright X-ray burst observed in 2013 June by Swift, and if so, there was no accompanying discontinuity in the frequency.
• We find that the source 3-10 keV flux has declined monotonically by a factor of ~2 over an 80-day period post-outburst accompanied by a ~20% decrease in the source's blackbody temperature, although there is evidence for both flux and kT having levelled off.