The MAXI new transient is likely MAXI J1543-564
ATel #17559; H. Negoro, M. Nakajima, K. Takagi, H. Nishio (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima, Y. Ishihara (Chuo U.), M. Shidatsu, C. Kang, T. Nakamoto, M. Uenishi, T. Usuki, S. Yatsuzuka (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), and S. Yamada (Tohoku U)
on 24 Dec 2025; 07:34 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Black Hole, Transient
MAXI discovered a new X-ray transient source on December 19, 2025 (ATel #17552). MAXI/GSC was unable to observe the source region from December 1 to December 18 due to the ISS polar axis direction and interference from the solar paddle and Cargo-Dragon. The sudden increase in X-ray flux observed in December 19 implies that the outburst began before December 19.
Swift/BAT data (https://swift.gsfc.nasa.gov/results/transients/) show that MAXI J1543-564 and XTE J1543-568 in the MAXI error region both exhibited a slight enhancement (~0.01 c/cm2/s ~ 50 mCrab) starting from around MJD 61010 (December 1). GSC 2-10 keV X-ray count rates have been slightly decreasing and the spectrum tends to soften since the discovery. An energy spectrum obtained with the GSC on December 22 and 23 can be represented by an absorbed disk-blackbody (diskbb) model with a temperature of approximately 0.7 keV with a fixed column density of Nh = 1.4e22. The unabsorbed 2-10 keV flux is about 8e-10 erg/s (40 mCrab). These nature is similar to that observed in the black hole X-ray binary MAXI J1543-564 in the intermediate state (Stiele et al. 2012, MNRAS 422, 679) rather than the (Be) X-ray pulsar XTE J1543-568 showing very hard spectra (in't Zand et al. 2001; Krimm et al. ATel #4008). Hardness ratios (HR) of GSC count rates in the 2-4 keV and 4-10 keV bands from December 19 (HR~0.5) to December 22 (HR~0.2) are also consistent with typical values in the intermediate state of the black hole X-ray binaries. MAXI J1543-564 is discovered in 2011 (ATel #3330), and this is the first renewed activity reported if the source is indeed MAXI J1543-564.
Of course, there is still a possibility that this outburst comes from a new black hole X-ray binary, MAXI J1544-565. It is, however, difficult to identify the source by soft X-ray observations until in the middle of January because the source is near the Sun direction. Then we requested ToO observations of NuSTAR, and also encourage in other wavelength observations.
MAXI data of MAXI J1543-564
