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.

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

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• Two decades of X-ray observations of the isolated neutron star RX J1856.5-3754: detection of thermal and non-thermal hard X-rays and refined spin-down measurement
• Multi-frequency radio observations of the radio-loud magnetar XTE J1810-197
• High-cadence monitoring of the emission properties of magnetar XTE J1810-197 with the Stockert radio telescope
• Magnetar Outburst Models with Cooling Simulations
• An alternative interpretation of magnetars' traits deduced from the observational data on their outburst fluxes and spectra
• 4XMM J175136.8-275858: A New Magnetar Candidate?
• Giant radio pulses in the magnetar XTE J1810-197 detected with the IAR's telescopes
• A magnetar outburst with atypical evolution: the case of Swift J1555.2-5402
• A month of monitoring the new magnetar Swift J1555.2-5402 during an X-ray outburst