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MAXI/GSC detection of a possible new X-ray nova MAXI J1621-501 on the galactic plane

ATel #10869; T. Hashimoto (AGU), H. Negoro (Nihon U.), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Shidatsu, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, M. Serino, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki, H. Kawai (Chuo U.), M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), and K. Yamaoka (Nagoya U.)
on 19 Oct 2017; 12:49 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 #: 10874, 10876, 10969

The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray transient source at 05:45 UT on 2017 October 19. Using GSC camera GSC_5 data of 4 scan transits from 04:12 to 08:50, we obtain the source position at
(R.A., Dec) = (245.260 deg, -50.185 deg) = (16 21 02, -50 11 06) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.23 deg and 0.22 deg, respectively. The roll angle of long axis from the north direction is 64.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scans was 57 +- 9 mCrab (4.0-10.0keV, 1 sigma error).

Until the detection, the source region was invisible to GSC due to the direction of the ISS rotation axis. A few catalogued X-ray sources exist well within the error region, for instance, AX J1620.1-5002, and AX J1622.1-5005. We tentatively name the source MAXI J1621-501.

Swift/XRT Followup observations are requested.

Trigger Information of MAXI J1621-501