Submillimeter Pulsations from the Magnetar XTE J1810-197

We present the first detection of pulsations from a neutron star in submillimeter range. The source is magnetar XTE J1810-197, observed with James Clerk Maxwell Telescope (JCMT) on 2020 February 27, July 9 and 2021 May 15. J1810-197 detected at 353 GHz ($\lambda=0.85\,$mm) three epochs, but not simultaneously-observed band 666 ($\lambda=0.45\,$mm). measure an averaged flux density 6.7$\pm$1.0, 4.0$\pm$0.6, 1.3$\pm$0.3 mJy set 3$\sigma$ upper limits 11.3, 4.7 4.3 mJy, each observing respectively. Combining close-in-time observations Effelsberg 100m IRAM 30m telescopes covering non-contiguously 6 to 225 (5.0 cm$>\lambda>$1.33 mm), we investigate spectral shape frequency range potential turn-up predicted by some pulsar radio emission models. results demonstrate that beamed stars can extend into regime, are inconclusive existence location within covered properties resemble those longer wavelengths, support coherent mechanism for production GHz.