MAXI/GSC detection of a long-term soft X-ray flaring event MAXI J1807+132

ATel #10208; H. Negoro (Nihon U.), T. Kawamuro, Y. Ueda (Kyoto U.), S. Nakahira, S. Ueno, H. Tomida, , M. Ishikawa, Y. Sugawara (JAXA), T. Mihara, M. Sugizaki, M. Serino, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura, T. Yoneyama (Osaka U.), M. Nakajima, K. Tanaka, T. Masumitsu, T. Kawase, A. Sakamaki (Nihon U.), T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), Y. E. Nakagawa (JAMSTEC), K. Yamaoka (Nagoya U.)
on 25 Mar 2017; 08:16 UT
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Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

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We report the MAXI/GSC detection of an on-going, long-term soft X-ray flaring event, MAXI J1807+132. The X-ray enhancement has been recognized in the 2-4 keV band since 2017 March 13, and the 2-4 keV and 4-10 keV X-ray fluxes averaged over 5 days from March 15 to March 19 are 0.0104 +/- 0.0012 counts/s/cm2 (approximately 10.4+/-1.2 mCrab) and 0.0105 +/0 0.0016 counts/s/cm2 (9.0+/-1.6 mCrab), respectively.

Using GSC 4-10 keV data from 18:39 UT on March 18 to 19:14 on March 20, we obtain the source position at
(R.A., Dec) = (271.851 deg, 13.235 deg) = (18 07 24, +13 14 05) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.41 deg and 0.3 deg, respectively. The roll angle of the long axis from the north direction is 151.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). We also obtain the following position using 2-4 keV data on the same period at
(R.A., Dec) = (271.881 deg, 13.227 deg) = (18 07 31, +13 13 37) (J2000)
with long and short radii of 0.52 deg and 0.33 deg, respectively. The two positions are almost perfectly consistent, indicating that the error region is smaller than the above values.

Interestingly, the source position is consistent with that of a longterm flaring event 2MAXIt J1807+132 detected in 2011 May (Kawamuro et al. 2016, PASJ, 68, 58), and the best positions are 3.3 arc-min apart. Although Kawamuro et al. (2016) did not firmly identify 2MAXIt J1807+132 as a tidal disruption event, we do not rule out the possibility. There is no other known X-ray source in the source error region.

We requested Swift/XRT ToO observations to obtain the precise source position and reveal the nature of the source.

Flash Report for MAXI J1807+132