MAXI J1535-571 currently shows softest spectrum
ATel #11020; M. Shidatsu, S. Nakahira (RIKEN), H. Negoro (Nihon U.), N. Kawai (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), T. Mihara, M. Sugizaki, W. Iwakiri, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), 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, T. Morita, S. Yamada (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 28 Nov 2017; 03:10 UT
Credential Certification: Megumi Shidatsu (email@example.com)
Subjects: X-ray, Black Hole, Transient
We report the recent MAXI/GSC monitoring of the black hole candidate MAXI J1535-571
discovered on 2017 September 2 (GCN #21788, ATels #10699, #10700, #10702, #10704,
#10708, #10711, #10714, #10716, #10734, #10745, #10761, #10768, #10816, #10899).
The source showed rapid X-ray spectral softening in September 18-22
when its flux was at around the maximum, and exhibited hardening from
around October 13 as it decreased its flux. However, MAXI J1535-571
started to exhibit steady spectral softening since October 25.
The hardness ratio of the MAXI/GSC fluxes (6-20 keV/2-6 keV) in the last
10 days until November 27 reached ~0.03, the lowest value in the current outburst,
and significantly lower than the value of ~0.1 at the previous
minimum near the flux peak before the temporary hardening occurred.
The time-averaged GSC spectrum obtained in November 23-25 was well
reproduced by a multi-color disk model with an inner temperature
of ~0.8 keV, convolved with a power-law component with a fixed photon
index of 2.4, both absorbed by interstellar matter with a fixed hydrogen
column density of 2.6e22 /cm2. The inner disk radius was estimated as ~110 km
(i=30 deg and D=10 kpc were assumed), consistent with the values obtained
in the first softening. However, the fraction of the power-law component (<~0.02),
was much smaller compared with that in the previous softening (~0.1).
These results indicate that the source is now in the high/soft state, and
this would be a good timing of soft X-ray observations to determine the disk
Further multi-wavelength observations are encouraged, as the source would make
the soft-to-hard transition soon. The MAXI/GSC data of MAXI J1535-571 are available at http://maxi.riken.jp/nakahira/1535monitor/ .