Pintore, FabioFabioPintore0000-0002-3869-2925MEREGHETTI, SandroSandroMEREGHETTI0000-0003-3259-7801ESPOSITO, PAOLOPAOLOESPOSITO0000-0003-4849-5092Turolla, RobertoRobertoTurollaTIENGO, ANDREAANDREATIENGO0000-0002-6038-1090Rea, NandaNandaReaBERNARDINI, FedericoFedericoBERNARDINI0000-0001-5326-2010ISRAEL, Gian LucaGian LucaISRAEL0000-0001-5480-64382020-12-142020-12-1420190035-8711http://hdl.handle.net/20.500.12386/28821In 2003, the magnetar XTE J1810-197 started an outburst that lasted until early 2007. In the following 11 yr, the source stayed in a quiescent/low-activity phase. XTE J1810-197 is one of the closest magnetars, hence its X-ray properties can be studied in detail even in quiescence and an extended monitoring has been carried out to study its long-term timing and spectral evolution. Here, we report the results of new X-ray observations, taken between 2017 September and 2018 April, with XMM-Newton, Chandra, and NICER. We derived a phase-connected timing solution yielding a frequency derivative of -9.26(6) × 10<SUP>-14</SUP> Hz s<SUP>-1</SUP>. This value is consistent with that measured between 2009 and 2011, indicating that the pulsar spin-down rate remained quite stable during the long quiescent period. A spectral analysis of all the X-ray observations taken between 2009 and 2018 does not reveal significant spectral and/or flux variability. The spectrum of XTE J1810-197 can be described by the sum of two thermal components with temperatures of 0.15 and 0.3 keV, plus a power-law component with photon index 0.6. We also found evidence for an absorption line at ∼1.2 keV and width of 0.1 keV. Due to the long exposure time of the summed XMM-Newton observations, we could also carry out a phase-resolved spectral analysis for this source in quiescence. This showed that the flux modulation can be mainly ascribed to the warmer of the two thermal components, whose flux varies by ∼45 per cent along the pulse phase.STAMPAenArticle10.1093/mnras/sty33782-s2.0-85064454928000462280000066https://academic.oup.com/mnras/article/483/3/3832/52387412019MNRAS.483.3832PFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation::PE9_6 Stars and stellar systems