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MAXI/GSC detection of a possible X-ray flare from HR1099 (V711 Tau)

ATel #10753; H. Kawai (Chuo U.), Y. Takao (RIKEN), Y. Tsuboi, R. Sasaki, Y. Nakamura (Chuo U.), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN), N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, M. Serino, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), H. Negoro, M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.)
on 15 Sep 2017; 15:21 UT
Credential Certification: Yohko Tsuboi (tsuboi@phys.chuo-u.ac.jp)

Subjects: X-ray, Binary, Star, Transient, Variables

Referred to by ATel #: 10786

At 06:08 UT on September 15th 2017, the MAXI/GSC nova alert system triggered on a bright source at a position consistent with that of an RS CVn star HR1099.

The position was determined from the data at the triggered scan, as (R.A., Dec) = (54.368 deg, 0.625 deg) = (03 37 28, +00 37 30) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.25 deg and 0.18 deg, respectively. The roll angle of long axis from the north direction is 11.0 deg. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). This position is consistent with that of an RS CVn star HR1099. No other source is listed in the ROSAT Bright Source Catalog in this error region.

The flux was 280 +/- 39 mCrab (4-10 keV) at the triggered scan, corresponding to a luminosity of 6e+32 ergs/s for an assumed distance of 29 pc. The flux is the largest among the previously detected flares with MAXI/GSC from this source. At the next scan transit at 07:42 UT on September 15th, on the other hand, the flux decreased down to 72 +/- 27 mCrab (90% error) in the same energy band.