MAXI/GSC detects a new outburst of MAXI J1807+132

ATel #13097; . Shidatsu (Ehime U.),H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), N. Kawai, M. Sugizaki, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, N. Isobe, R. Shimomukai, M. Tominaga (JAXA), Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
on 11 Sep 2019; 08:39 UT
Credential Certification: Megumi Shidatsu (shidatsu@kusastro.kyoto-u.ac.jp)

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On September 10, the MAXI/GSC nova-alert system detected the X-ray transient MAXI J1807+132, discovered in 2017 (Negoro et al. 2017, ATel #10208), after a ~2-year quiescence. The 4-10 keV flux, averaged for September 8-10, was estimated to be 19 +/- 6 mCrab. An optical brightening, detected with Gaia on September 6, was also reported via Variable Star Network (Denisenko et al. 2019, VSNET-alert 23544). We note that the source was in the FoV of a low-sensitivity GSC camera until September 7 and has become observable with normal cameras since September 8. To monitor the outburst and investigate the nature of the compact object, which is still unclear (Shidatsu et al. 2017, Jim'enez-Ibarra et al. 2018), follow-up observations are highly encouraged.