MAXI/GSC detection of X-ray rebrightening of the X-ray transient MAXI J1810-222
ATel #12496; H. Negoro, W. Maruyama, M. Nakajima, A. Sakamaki, M. Aoki, K. Kobayashi (Nihon U.), T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, T. Hashimoto, A. Yoshida (AGU), N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita, M. 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 (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.)
on 12 Feb 2019; 08:11 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Request for Observations, Black Hole, Neutron Star, Transient
The soft X-ray transient MAXI J1810-222 discovered on 2018 December 1 (MJD 58453, ATel #12254, #12264, #12283, #12398) had been once below the 1-d MAXI/GSC detection-limit, 10-15 mCrab, since around MJD 58465. The recent Swift/XRT observation on February 9, however, detected the source at almost the same flux level as the NuSTAR observation on December 9 (Kennea & Negoro #ATel #12487). The (extrapolated) 2-4 keV fluxes on both observations are about 1e-10 erg/s/cm2, which is comparable to 15-20 mCrab in the count rate of MAXI/GSC, implying the X-ray flux increased again. Recent MAXI/GSC data indeed show that the source has been brightening again since February 7 or before. The energy spectrum is still quite soft, and the current 2-4 keV flux on February 11 is about 40 mCrab, which is the brightest so far.
The source showed peculiar energy spectra consisting of a soft thermal spectrum well described with a diskbb model with a temperature Tin of 0.4-0.5 keV and a steep power-law with a photon index of more than 3 (see ATel #12398, #12487). The nature of the source is still unknown, but the distance may be only about 730 pc (ATel #12487). We encourage multi-wavelength followup observations to reveal the nature of this unique source.
MAXI light curves of MAXI J1810-222