MAXI/GSC detects an X-ray spectral softening of the X-ray transient MAXI J1535-571

ATel #10729; S. Nakahira(RIKEN), H. Negoro (Nihon U.), T. Mihara, W. Iwakiri, M. Sugizaki, M. Shidatsu, M. Matsuoka (RIKEN), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, M. Serino, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki, H. Kawai (Chuo U.), M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.)
on 11 Sep 2017; 03:47 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 J1535-571 observed with MAXI/GSC.

Since the beginning of this outburst the X-ray brightness of MAXI J1535-571 is increasing linearly with time. The 2-20 keV X-ray flux is 2.2×10^-8 erg cm^-2 sec^-1 on September 6, 3.5×10^-8 erg cm^-2 sec^-1 on September 8 and reached 5.3×10^-8 erg cm^-2 sec^-1 on September 10.

On 2017 September 10 MAXI/GSC 10-20 keV X-ray count rate shows signs of leveling off. Meanwhile, 2-4 keV count rate is still increasing. The X-ray photon indices before September 9 changed gradually from ∼1.5 to 1.8 and then it changed to ∼2.0 at 17UT of September 10. This may indicate that the source is undergoing a hard-to-soft state transition.
Follow-up observations are encouraged.

The latest source flux can be checked at the following page;
http://maxi.riken.jp/top/index.php?cid=1&jname=J1535-572

MAXI J1535-572 monitor