MAXI/GSC detection of an X-ray burst probably from SAX J1748.9-2021

ATel #10827; S. Harita, S. Sugita (Tokyo Tech), A. Sakamaki, 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, T. Yoshii, Y. Tachibana, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, M. Serino, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), M. Nakajima, T. Kawasei (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda, T. Morita, S. Yamada (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 6 Oct 2017; 10:19 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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The MAXI/GSC nova alert system detected a bright X-ray burst lasting 10 s in the scan transit at 06:44 UT on 2017 October 6. The source position is consistent with that of the globular cluster NGC 6440.

This X-ray burst is likely to originate from the source, which was recently detected with MAXI/GSC (ATel #10821) and confirmed with Swift/XRT to be the cluster member, SAX J1748.9(8)-2021 (CX1) or CX3 in NGC 6440 (ATel #10826). The millisecond X-ray pulsar SAX J1748.9-2021 peculiarly showed X-ray bursts previously (e.g., Kaaret et al. 2003, ApJ, 598, 481; Pintore et al. 2016, MNRAS, 457, 2988). The peak flux of this burst is roughly 2-3e-8 erg/s/cm2, which is comparable to those of the bursts that RXTE detected (Kaaret et al. 2003). The burst duration is also similar to those of the previous bursts. These properties strengthen the possibility that this burster is SAX J1748.9-2021. Finally, we also note that Swift detected a possible type I X-ray burst (#10826).

Detected X-ray burst from NGC 6440