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MAXI/GSC detection of the magnetar XTE J1810-197

ATel #12291; T. Mihara (RIKEN), H. Negoro (Nihon U.), N. Kawai (Tokyo Tech), M. Nakajima, W. Maruyama, A. Sakamaki, M. Aoki, K. Kobayashi (Nihon U.), S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), M. Sugizaki, Y. Tachibana, K. Morita, T. Oeda, K. Shiraishi (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai, T. Midooka (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada, S. Ogawa (Kyoto U.), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, K. Hidaka, S. Iwahori, Y. Kurihara (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.) report on behalf of the MAXI team
on 13 Dec 2018; 11:11 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Tatehiro Mihara (mihara@crab.riken.jp)

Subjects: X-ray, Neutron Star, Magnetar

Referred to by ATel #: 12297, 12312, 12484, 12600, 12689

MAXI team noticed an X-ray enhancement at around (272.6, -19.6) on December 8, 2018. According to ATel #12284, #12285, and #12288, the agreement of the position and the start days of activity suggests that the X-ray would come from XTE J1810-197. The MAXI light curve of XTE J1810-197 is shown in http://maxi.riken.jp/plot/XTEJ1810-197.png Positive X-ray from this region has been detected since 58450 MJD (Nov.28), while the last non-detection was on 58439 MJD (Nov.17) before the observation gap.
The flux in 58450 (Nov.28) - 58458 (Dec.6) MJD was almost flat with 0.016 c/s/cm2 in 2-4 keV. No burst was observed. The spectrum was well fit by a blackbody with kT = 0.90 +- 0.13 keV without inter-stellar absorption. The flux was (2.9 +- 0.3) x 10^-10 erg/s/cm2 (2-10 keV). The powerlaw model fits a little worse with the photon index = 2.7 +- 0.4. Although MAXI coverage in 58459 (Dec.7) - 58465 (Dec.13) were not complete, the light curves looks constant in MAXI HP : http://maxi.riken.jp/star_data/J1809-197/J1809-197.html
Although XTE J1810-197 is close to the sun now, detailed observation with Nu-STAR would be encouraged.