MAXI/GSC detection of a new X-ray nova MAXI J1834-021

ATel #15929; 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 (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC), and W. Iwakiri (Chiba U.)
on 6 Mar 2023; 02:43 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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The MAXI/GSC detects a faint uncatalogued X-ray transient source which started an outburst on around MJD 59980, 2023 February 05. Assuming that the source flux was constant over nine transits from 22:48 UT on 2023 February 28 (MJD 60003.950) to 12:44 UT on 2023 March 1 (MJD 60004.531), we obtain the source position at
(R.A., Dec) = (278.634 deg, -2.130 deg) = (18 34 32, -02 07 47) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.62 deg and 0.28 deg, respectively. The roll angle of the long axis from the north direction is 131.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 18 +- 4 mCrab (4.0-10.0keV, 1 sigma error).

The 2-10 keV X-ray flux has gradually increased since MJD 59980 and reached about 10 mCrab in MJD 59990-60000. After that, the flux is gradually decreasing, and currently expected to be 5 mCrab or less. The 4-10 keV/2-4 keV count ratio is 0.6-1 and does not change significantly during the outburst. The ratio and the source position on the Galactic plain, (l, b) = (29.1 deg, 2.8 deg), suggest the source is a low-mass X-ray binary hosting a neutron star (Negoro et al. 2016, PASJ, 68, S1).

Since there is no known bright X-ray source around the error region, we tentatively name the source MAXI J1834-021. XRT followup observations were requested. Followup observations are encouraged.

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