MAXI/GSC detection of the newly discovered X-ray transient Swift J1728.9-3613 (= MAXI J1728-360)
ATel #12437; H. Negoro (Nihon U.), S. Nakahira (RIKEN), 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), N. Kawai, 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.), and Y. Kawakubo (LSU)
on 28 Jan 2019; 05:03 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Black Hole, Neutron Star, Transient
The MAXI/GSC nova alert system triggered on an uncatalogued X-ray transient source at 18:49 UT on 2019 January 26. Assuming that the source flux was constant over eight transits from 2:33 to 18:00 on January 27, we obtain the source position at
(R.A., Dec) = (262.033 deg, -36.058 deg) = (17 28 07, -36 03 28) (J2000)
The source position is consistent with that of the newly discovered X-ray transient Swift J1728.9-3613 (Barthelmy et al. GCN #23800/ATel. #12436) if the systematic uncertainty of the localization is taken into account.
The 4-10 keV flux has been gradually increasing since January 25-26, and reaches 150+/-30 mCrab at 18:00 on January 27. The nature of the source is unclear from these MAXI observations, but the timescale of the increase in intensity and the spectral hardness suggest that the source is an accreting X-ray pulsar or a hard-state black hole binary.
We first misidentified this source as EXO 1722-363 on January 26 [MAXI X-ray-star ML: 669] , and circulated again as a new X-ray transient MAXI J1728-360 [X-ray-star ML: 670, New-transient: 268] at almost the same time as (just one-minute after!) the Swift/BAT report to GCN. We apologize for any confusion these may have caused.
MAXI trigger info for Swift J1728.9-3613
