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MAXI/GSC detection of an increase in X-ray intensity from LS I +61 303

ATel #10803; S. Sugita (Tokyo Tech), H. Negoro (Nihon U.), M. Serino (AGU), 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, S. Harita, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki, H. Kawai (Chuo U.), M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team:
on 30 Sep 2017; 15:18 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

Subjects: X-ray, Transient

Referred to by ATel #: 10809, 10813, 10815

At 09:40:16 UT on 2017 September 29, the MAXI/GSC nova alert system triggered an increase in X-ray intensity at the position which was consistent with the position of the high mass X-ray binary LS I +61 303.

The position of the triggered event was determined at 10 scan orbits from 2017-09-29 09:37:15 to 09-30 04:13:44, as
(R.A., Dec) = (40.837 deg, 61.341 deg) = (02 43 20,+61 20 27) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.54 deg and 0.31 deg, respectively. The roll angle of long axis from the north direction was 61.0 deg. There was an additional systematic uncertainty of 0.1 deg (90% containment radius). This position was consistent with that of LS I +61 303. No other source was listed in the ROSAT Bright Source Catalog in this error region.

We found that the X-ray flux of LS I +61 303 had been increasing at 2-4 keV since around 2017 September 19, and at 4-10 keV since around September 24. The averaged 2-4 keV and 4-10 keV X-ray fluxes on September 29 were (15.4+/-4)e-3 photons/s/cm2 (~14 mCrab) and (25.8+/-5)e-3 photons/s/cm2 (~22 mCrab), respectively.

The source was also detected with the nova alert system on 2013 September 21 with the flux of ~5 mCrab at 4-10 keV.

MAXI data for LS I +61 303