X-Ray Monitoring of the Magnetar CXOU J171405.7-381031 in Supernova Remnant CTB 37B

We present the results of our 8 yr X-ray monitoring campaign on CXOU J171405.7-381031, the magnetar associated with the faint supernova remnant (SNR) CTB 37B. It is among the youngest by inferred spin-down age, and most energetic in spin-down power of magnetars, and may contribute, at least partially, to the GeV and TeV emission coincident with the SNR. We use a series of Chandra, XMM-Newton, and NuSTAR observations to characterize the timing and spectral properties of the magnetar. The spin-down rate of the pulsar almost doubled in <1 yr and then decreased slowly to a more stable value. Its X-ray flux varied by ≈50%, possibly correlated with the spin-down rate. The 1-79 keV spectrum is well-characterized by an absorbed blackbody plus power-law model with an average temperature of kT = 0.62 ± 0.04 keV and photon index Γ = 0.92 ± 0.16, or by a Comptonized blackbody with kT = 0.55 ± 0.04 keV and an additional hard power law with Γ = 0.70 ± 0.20. In contrast with most magnetars, the pulsed signal is found to decrease with energy up to 6 keV, which is apparently caused by mixing with the hard spectral component that is pulse-phase shifted by ≈0.43 cycles from the soft X-rays. We also analyze the spectrum of the nearby, diffuse nonthermal source XMMU J171410.8-381442, whose relation to the SNR is uncertain.