In 2003, the magnetar XTE J1810-197 started an outburst that lasteduntil early 2007. In the following 11 yr, the source stayed in aquiescent/low-activity phase. XTE J1810-197 is one of the closestmagnetars, hence its X-ray properties can be studied in detail even inquiescence and an extended monitoring has been carried out to study itslong-term timing and spectral evolution. Here, we report the results ofnew X-ray observations, taken between 2017 September and 2018 April,with XMM-Newton, Chandra, and NICER. We derived a phase-connected timingsolution yielding a frequency derivative of -9.26(6) \times10$^-14$ Hz s$^-1$. This value is consistent with thatmeasured between 2009 and 2011, indicating that the pulsar spin-downrate remained quite stable during the long quiescent period. A spectralanalysis of all the X-ray observations taken between 2009 and 2018 doesnot reveal significant spectral and/or flux variability. The spectrum ofXTE J1810-197 can be described by the sum of two thermal components withtemperatures of 0.15 and 0.3 keV, plus a power-law component with photonindex 0.6. We also found evidence for an absorption line at \tilde1.2keV and width of 0.1 keV. Due to the long exposure time of the summedXMM-Newton observations, we could also carry out a phase-resolvedspectral analysis for this source in quiescence. This showed that theflux modulation can be mainly ascribed to the warmer of the two thermalcomponents, whose flux varies by \tilde45 per cent along the pulsephase.
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