The X-ray evolution and geometry of the 2018 outburst of XTE J1810-197

Abstract

After 15 years, in late 2018, the magnetar XTE J1810-197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM-Newton, NuSTAR, and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of two change in its spin-down rate from $\sim 7.2\times 10^{-12}$ s s${}^{-1}$ to $\sim 1.5\times 10^{-11}$ s s${}^{-1}$ after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810-197 is well-modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810-197 has likely evolved relative to that found for the 2003 event.

arXiv comment14 pages, 12 figures, 4 tables. Accepted for publications in MNRAS

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• The first 7 months of the 2020 X-ray outburst of the magnetar SGR J1935+2154
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