MAXI/GSC detection of a new X-ray outburst and a burst from the direction of Terzan 1

ATel #15955; H. Negoro, M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, J. Kohara, S. Urabe, S. Nawa, N. Nemoto (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, T. Kurihara (JAXA), Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba, Y. Nakatani (Kyoto U.), M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC), and W. Iwakiri (Chiba U.)
on 21 Mar 2023; 15:34 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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The MAXI/GSC nova alert system triggered on a bright X-ray transient source at 16:50 UT on March 20, 2023. We also found that the 2-20 keV X-ray flux in the globular cluster Terzan 1 region gradually increased since March 16, 2023 (http://maxi.riken.jp/pubdata/v7l/J1735-304/). Assuming that the source flux was constant over eight scan transits from 12:09 on March 16 to 3:38 on March 17, we obtain the source position at
(R.A., Dec) = (263.649 deg, -30.404 deg) = (17 34 35, -30 24 14) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.52 deg and 0.41 deg, respectively. The roll angle of the long axis from the north direction is 51.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scans was 32 +- 7 mCrab (4.0-10.0 keV, 1 sigma error).

The GSC also detected an X-ray burst from the same region at 19:33 on March 18. Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (264.619 deg, -30.229 deg) = (17 38 28, -30 13 44) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.58 deg and 0.35 deg, respectively. The roll angle of the long axis from the north direction is 62.0 deg counterclockwise.
Without the assumption on the source constancy, we obtain a rectangular error box for the burst source with the following corners.
(263.319, -28.302) deg = (17 33 16, -28 18 07) (J2000)
(262.432, -29.109) deg = (17 29 43, -29 06 32) (J2000)
(264.941, -31.173) deg = (17 39 45, -31 10 22) (J2000)
(265.826, -30.348) deg = (17 43 18, -30 20 52) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 163 +- 33 mCrab (4.0-10.0keV, 1 sigma error).

Curiously, the above error regions obtained on March 16-17 and for the burst are overlapped only in a small part of the regions. The former region contains Terzan 1 (XB 1732-304) and the X-ray transient MAXI J1735-304 (or Swift J1734.5-3027, see Negoro et al. 2016, PASJ, 68, S1) which exhibited an outburst in 2013. The latter two regions for the burst, however, contain neither source unless the systematic uncertainty is taken into account. Thus, two X-ray transients may appear. Tentatively, we name the sources, MAXI J1734-304 and MAXI J1738-302, respectively.

Followup observations are encouraged.

MAXI trigger information