MAXI/GSC detection of a possible X-ray burst from 4U 1702-429 or a new X-ray source

ATel #16081; W. Iwakiri (Chiba U.) , M. Serino (AGU),H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto (Chuo U.), M. Shidatsu (Ehime U.), I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, T. Kurihara (JAXA), Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani (Kyoto U.), M. Yamauchi, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC)
on 12 Jun 2023; 09:35 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)

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The MAXI/GSC nova alert system triggered an X-ray enhancement at 14:32 on June 11, 2023. The X-ray flux averaged over the scan was 194 +- 31 mCrab (4.0-10.0keV, 1 sigma error). There was no significant excess flux in the previous and next transits at 12:59 UT and 16:05 UT with an upper limit of 20 mCrab.
Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (255.692 deg, -43.098 deg) = (17 02 46, -43 05 51) (J2000) with a 90% C.L. statistical error of 0.32 deg and an additional systematic uncertainty of 0.1 deg (90% containment radius). There are no known X-ray sources in the error region as determined under this assumption.
Without the assumption of the source constancy, we obtain a rectangular error box for the transient source with the following corners. (254.734, -42.737) deg = (16 58 56, -42 44 13) (J2000) (254.615, -43.354) deg = (16 58 27, -43 21 14) (J2000) (256.771, -43.556) deg = (17 07 05, -43 33 21) (J2000) (256.869, -42.936) deg = (17 07 28, -42 56 09) (J2000) There is an additional systematic uncertainty of 0.1 deg (90% containment radius). In this case, the estimated error region includes the known NS-LMXB 4U 1702-429 (Ara X-1) location.
The absorbed blackbody model fitting the spectrum of the scan transits in the 2-20 keV band gives the blackbody temperature of 1.5 (+0.5, -0.3) keV, which is consistent with a typical value of type-I X-ray bursts. Here, the hydrogen column density was fixed at 2.44 × 10²² cm^-2 (Mazzola et al., 2019).
Thus, we conclude that the observed X-ray enhancement was probably caused by the type-I X-ray burst from NS-LMXB 4U 1702-429 (Ara X-1) or a new source (we tentatively name the source MAXI J1702-430).