MAXI/GSC detection of an X-ray flare from the dMe star FT Psc
ATel #12016; R. Sasaki (Chuo U.), S. Nakahira (RIKEN), Y. Tsuboi, W. Iwakiri, H. Kawai, T. Sato (Chuo U.), H. Negoro, M. Nakajima, A. Sakamaki, W. Maruyama (Nihon U.), T. Mihara, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU), N. Kawai, M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.)
on 7 Sep 2018; 02:36 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)
Subjects: X-ray, Star, Transient, Variables
We report an X-ray flare from the dMe star FT Psc on 2018 September 1 detected with the MAXI/GSC.
The flare event was detected during a scan transit at 14:31 UT on 2018 September 1. Assuming the source flux was constant over the transit, we obtained the source position of (R.A., Dec) = (12.409 deg, 24.843 deg) = (00 49 38, +24 50 34) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.31 deg and 0.26 deg, respectively. The roll angle of long axis from the north direction was 43.0 deg counterclockwise. There was an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 162 +/- 35 mCrab (4.0-10.0 keV, 1 sigma error). There was no significant excess flux in the previous transit at 12:58 UT and in the next transit at 16:04 UT with an upper limit of 20 mCrab for each. We conclude that this is the X-ray flare from the dMe star FT Psc, since no other source in the ROSAT Bright Source Catalog is located in the elliptical error region.
FT Psc is a single dMe star with a spectral type of M4 V (Gaidos et al. 2014). The rotation period and the distance are derived as 1.6968 day and 11.845 pc by Newton et al. (2017) and McDonald et al. (2017), respectively. If we assume the distance of 11.845 pc, the above flux is corresponding to 5e+31 erg/s in luminosity.
We should note that the flare from FT Psc was also detected with the MAXI/GSC during a scan transit at 23:44 UT on 2017 May 3, with no significant detection in the previous and the next transit. With the same procedure and assumption, we obtained the source position of (R.A., Dec) = (12.714 deg, 24.742 deg) = (00 50 51, +24 44 31) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.41 deg and 0.34 deg, respectively. The roll angle of long axis from the north direction was 14.0 deg counterclockwise. There was also an additional systematic uncertainty of 0.1 deg (90% containment radius). With no other source in the ROSAT Bright Source Catalog in this error region, we conclude that this flare was also from the dMe star FT Psc. The X-ray flux averaged over the scan was 160 +/- 35 mCrab (4.0-10.0 keV, 1 sigma error), which is comparable to the newly detected flare on 2018 September 1.
