MAXI/GSC detection of renewed X-ray activity in the black hole X-ray binary GRS 1739-278 or a new soft X-ray transient MAXI J1741-276

ATel #16097; 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, M. Serino, 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), and W. Iwakiri (Chiba U.)
on 27 Jun 2023; 16:27 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 detected a bright soft X-ray transient source at 04:48 UT on 2023 June 26. Assuming that the source flux was constant over five transits from 04:00 UT on June 27 to 11:45, we obtain the source position at
(R.A., Dec) = (265.499 deg, -27.615 deg) = (17 41 59, -27 36 53) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.22 deg and 0.18 deg, respectively. The roll angle of the long axis from the north direction is 45.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 124 +- 13 mCrab (2.0-4.0keV, 1 sigma error). We could not determine the position at 4-10 keV because of a small number of photons, indicating the source has a very soft X-ray spectrum.

The source region was hardly observed from June 24 to the detection time on June 26. Thus the outburst may started before the detection. The source position is consistent with that of the black hole X-ray binary GRS 1739-278 if the additional systematic uncertainty is taken into account. GRS 1739-278 exhibited a bright and long outburst in 2014 (ATel #5986, #5991). Continuous low (< 20 mCrab) activity in the hard state was also observed since 2016 (ATel #9517, #9541, #10137, #11869). On the other hand, such a soft X-ray spectrum likely in the soft state was not observed at the beginning of the outburst in 2014 (e.g., Yan and Yu 2017, MNRAS, 470, 4298; Wang et al. 2018, PASJ, 70, 67), suggesting this transient source is a new X-ray transient. We therefore tentatively name the source MAXI J1741-276.

Followup observations are strongly recommended. Swift/XRT followup observation will be requested.

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