MAXI/GSC detects an X-ray spectral softening of the X-ray transient MAXI J1348-630

ATel #12469; S. Nakahira (RIKEN), N. Kawai (Tokyo Tech), H. Negoro, M. Nakajima, A. Sakamaki, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), T. Mihara, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN),T. Sakamoto, M. Serino, S. Sugita, T. Hashimoto, A. Yoshida (AGU), M. Sugizaki, Y. Tachibana, K. Morita (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.), Y. Kawakubo (LSU)
on 4 Feb 2019; 10:10 UT
Credential Certification: Satoshi NAKAHIRA (nakahira@crab.riken.jp)

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We report on the X-ray spectral softening of the X-ray transient MAXI J1348-630 observed with MAXI/GSC.

Since the beginning of this outburst the X-ray flux of MAXI J1348-630 has been increasing with time. The 2-20 keV X-ray flux was 1.2×10^-8 erg cm^-2 sec^-1 at January 27.0, 6.2×10^-8 erg cm^-2 sec^-1 at January 31.0 and reached 7.3×10^-8 erg cm^-2 sec^-1 at February 4.35
The X-ray photon indices before February 3 changed gradually from ∼1.5 to 1.8. After February 3.5, it is showing rather rapid softening and it reached Γ=2.0 at February 4.35. This may indicate that the source is undergoing a hard-to-soft state transition.
Follow-up observations are encouraged.

The latest source flux, hardness-intensity diagram and energy spectrum can be checked at the following page;
http://maxi.riken.jp/nakahira/1348monitor/