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MAXI/GSC detection of a weak X-ray outburst from RX J1709.5-2639 (XTE J1709-267)

ATel #10671; H. Negoro (Nihon U.), S. Harita, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai (JAXA), T. Mihara, M. Sugizaki, M. Serino, S. Nakahira, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN), N. Kawai, S. Sugita, T. Yoshii, Y. Tachibana, Y. Muraki (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.)
on 26 Aug 2017; 11:35 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

Subjects: X-ray, Neutron Star, Transient

A gradual increase in X-ray intensity from the recurrent soft X-ray transient RX J1709.5-2639 (XTE J1709-267) triggered the MAXI Nova-Alert system at 09:30 on 2017 August 23. The alert system also triggered on the eclipsing low-mass X-ray binary XTE J1710-281 (1RXS J171012.3-280754) at 04:26 on 2017 August 18. The angular distance of these two sources is ~1.5 deg, which is comparable to the FWHM of the MAXI/GSC, so that we performed the image fitting analysis (Morii et al. 2016, PASJ, 68, S11) to confirm the position and obtain the fluxes from these sources.

We found that the X-ray flux of RX J1709.5-2639 had increased since around 2017 August 17, and the 2-4 keV X-ray flux rapidly increased on August 22. The average 2-4 keV and 4-10 keV X-ray fluxes on August 22-24 were (25+/-4)e-3 photons/s/cm2 (~23 mCrab) and (16+/-4)e-3 photons/s/cm2 (~14 mCrab), respectively.

The X-ray flux from XTE J1710-281 do not vary significantly on August 17-24 and the 2-4 keV and 4-10 keV fluxes in that period are (5.8+/-1.2)e-3 photons/s/cm2 (~5.4 mCrab) and (6.2+/-1.5)e-3 photon/s/cm2 (~5.3 mCrab), respectively. The flux level is not so high compared with the previous activity observed in the previous MAXI observations and the RXTE PCA Monitoring Observations (see https://asd.gsfc.nasa.gov/Craig.Markwardt/galscan/html/XTE_J1710-281.html).

This is the 5th outburst of RX J1709.5-2639 that MAXI detected since 2009: 2010 (ATel. #2729), 2012 (ATel. #4304), 2013 (ATel. #5319, #5332), and 2016 (ATel. #9108, #9181). The current flux is still the lowest in five, but is comparable to those of four outbursts in 2004, 2005, 2008, 2009 (see https://asd.gsfc.nasa.gov/Craig.Markwardt/galscan/html/RXJ1709.5-263.html).

MAXI data for RX J1709.5-2639 and XTE J1710-281 (not used here):
http://maxi.riken.jp/pubdata/v3.rkn/J1709-266/
http://maxi.riken.jp/pubdata/v3.rkn/J1710-281/