MAXI/GSC detection of possible X-ray periodicity from the X-ray transient MAXI J0655-013

ATel #15453; M. Nakajima (Nihon U.), J. Kohara (Chuo U.), M. Serino (AGU), H. Negoro (Nihon U.), W. Iwakiri (Chuo U.), K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri (Chuo U.), M. Shidatsu, M. Iwasaki (Ehime U.), N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Tominaga, T. Nagatsuka, T. Kurihara (JAXA), Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba (Kyoto U.), H. Tsunemi (Osaka U.), M. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), and M. Sugizaki (NAOC)
on 22 Jun 2022; 14:37 UT
Credential Certification: Motoki Nakajima (nakajima.motoki@nihon-u.ac.jp)

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MAXI J0655-013 is a newly discovered hard X-ray transient source on June 18, 2022 (Serino et al. 2022, ATel#15442; Kennea at al. 2022, ATel#15443). After the discovery, the day-averaged source flux steadily increased and reached 0.209 ± 0.016 photons/s/cm² in 2-20 keV band on June 19. In addition, the MAXI/GSC observation revealed that this source exhibits a possible flux modulation. The 2-20 keV light curve obtained from June 17-21 is represented by a sinusoidal curve with the periodicity of 0.982 ± 0.02 days. Unfortunately, MAXI stopped the operation due to the data processor hang up since June 21 06:07 UT. So, we can not confirm whether the periodic variation still continues or not. The spectrum extracted from a bright phase of ∼1 day periodicity can be roughly fitted by a power-law model without an absorption factor. The derived photon index is 0.89 ± 0.21, which is consistent with the typical value of X-ray pulsars.

We encourage multi-wavelength observations to reveal the nature of this source. The latest X-ray light-curve can be checked at the following page, http://maxi.riken.jp/pubdata/v7lrkn/J0655-015/index.html.