MAXI/GSC detection of an X-ray short transient event MAXI J0709-159

ATel #15178; M. Serino (AGU), H. Negoro, M. Nakajima, K. Kobayashi, K. Asakura, K. Seino (Nihon U.), T. Mihara, T. Tamagawa, J. Li, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, K. Komachi, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, H. Kawai, Y. Okamoto, S. Kitakoga, J. Kohara (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, M. Kurihara (JAXA), Y. Ueda, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, Y. Goto, R. Uematsu, K. Inaba (Kyoto U.), H. Tsunemi (Osaka U.), M. Yamauchi, Y. Nonaka, T. Sato, R. Hatsuda, R. Fukuoka (Miyazaki U.), T. Kawamuro (UDP/NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC)
on 25 Jan 2022; 12:47 UT
Credential Certification: Motoko Suzuki (motoko@crab.riken.jp)

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The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 10:42:28 UT on 2022 January 25. Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (107.280 deg, -15.923 deg) = (07 09 07, -15 55 22) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.16 deg and 0.14 deg, respectively. The roll angle of long axis from the north direction is 161.0 deg counterclockwise. Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners:
(R.A., Dec) = (106.814, -15.283) deg = (07 07 15, -15 16 58) (J2000)
(R.A., Dec) = (106.608, -15.459) deg = (07 06 25, -15 27 32) (J2000)
(R.A., Dec) = (107.823, -16.775) deg = (07 11 17, -16 46 29) (J2000)
(R.A., Dec) = (108.029, -16.598) deg = (07 12 06, -16 35 52) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 266 +- 32 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous transit at 09:09 UT and in the next transit at 12:15 UT with an upper limit of 20 mCrab for each.

Since the source showed a soft X-ray spectrum and the source is located at low galactic latitude at (l, b) ~ (229.1 deg, -3.4 deg), it is possible that the source is a galactic transient source. We tentatively name the source MAXI J0709-159.