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MAXI/GSC detection of a bright X-ray outburst from KS 1741-293 or a new hard X-ray transient MAXI J1744-294 near the galactic center

ATel #16975; Y. Kudo, H. Negoro, M. Nakajima, H. Shibui, K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, H. Nishikawa, Y. Kondo, S. Sasao, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.), M. Shidatsu, Y. Niida (Ehime U.), I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, Y. Okada, K. Fujiwara (Kyoto U.), M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), and W. Iwakiri (Chiba U.)
on 13 Jan 2025; 04:30 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

Subjects: X-ray, Black Hole, Neutron Star, Transient

Referred to by ATel #: 16983, 17009, 17010

MAXI/GSC detects a hard X-ray transient from the galactic center region (http://maxi.riken.jp/v7l3h/J1745-290/index.html). The hard X-ray enhancement has been recognized in 10-20 keV X-ray images at least since the January 2, 2025 (MJD 60677). Assuming that the source flux was constant over 25 scan transits from 09:56 UT on January 7 to 08:21 on January 9, we obtain the source position at
(R.A., Dec) = (266.116 deg, -29.433 deg) = (17 44 27, -29 25 58) (J2000),
with a statistical 90% C.L. elliptical error region with long and short radii of 0.14 deg and 0.11 deg, respectively. The roll angle of the long axis from the north direction is 22.0 deg counterclockwise. The X-ray flux averaged over the scans was 103 +- 8 mCrab (4.0-10.0keV, 1 sigma error). There is an additional systematic uncertainty of 0.1 deg (90% containment radius). Using following 11 scan transit data from 09:54 on January 9 to 09:07 on January 10, we also obtain a source flux of 133 +- 13 mCrab (4.0-10.0keV, 1 sigma error) from the position consistent with the above region.

The source position is close to the galactic center, (l, b) = (359.44 deg, -0.04 deg), and marginally consistent with that of the transient neutron star X-ray binary KS 1741-293. Currently, Swift/BAT data of KS 1741-293/AX J1744.8-2921 do not provide sufficient data (https://swift.gsfc.nasa.gov/results/transients/weak/AXJ1744.8-2921/) because of the sun-angle constraint. Instead, using an experimental image-fit analysis at 10-20 keV, we obtain 10-20 keV X-ray fluxes at the source position of about 100 mCrab from January 1, which is near the highest level in MAXI 15 years observations. On the other hand, KS 1741-293 exhibited frequent outbursts reaching 20-30 mCrab or less (see Degenaar and Wijnands, 2012, Proc. IAU Symposium No.290; Kuulkers et al. 2013, ATel #4840; Chenevez et al. 2016, ATel #9387; Heinke et al. 2019, ATel #12843). Therefore it is possible that this transient source is not KS 1741-293. Then we tentatively name the source MAXI J1744-294.

The 4-10 keV and 10-20 keV fluxes imply that the source has a power-law spectrum with a photon index of about 2, suggesting the source is a black hole or neutron star X-ray binary in a hard or a steep power-law state. Followup observations are encouraged.

MAXI data for the Galactic Center Region