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MAXI/GSC detects a softening of the X-ray transient GRO J1716-249

ATel #10595; S. Nakahira, M. Shidatsu T. Mihara, M. Sugizaki, M. Serino, W. Iwakiri, M. Matsuoka (RIKEN), T. Kawamuro (NAOJ), 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, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), H. Negoro, 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.), K. Yamaoka (Nagoya U.)
on 25 Jul 2017; 06:55 UT
Credential Certification: Satoshi NAKAHIRA (nakahira@crab.riken.jp)

Subjects: X-ray, Binary, Black Hole, Neutron Star

We report on a spectral softening of the X-ray transient, GRO J1716-249. The source has been in the X-ray outburst starting in 2016 December (#9876), and now it is in the declining phase. Since the first detection by MAXI/GSC on 2016 December 18, the hardness ratio of the 6-20 keV to the 2-6 keV flux had been stable at around 0.4-0.6, indicating the hard state, throughoutly.

Recently, MAXI/GSC detected that the soft X-ray began to increase again; the 2-6 keV flux increased from 0.27 +-0.01 photons s^-1 cm^-2 on July 18 and 19, to 0.40 +- 0.02 photon s^-1 cm^-2 on July 23 and 24. Contrary, the 6-20 keV flux keeps decreasing steadily. Hence, the hardness ratio changed down to 0.22+-0.03. This suggests that the source undergoes 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=J1719-250