MAXI observation of a long X-ray burst from SAX J1712.6-3739
W. Iwakiri (Chuo U.), H. Negoro(Nihon U.), M. Serino (AGU), J. in 't Zand (SRON), N. Kawai (Tokyo Tech), M. Nakajima, A. Sakamaki, W. Maruyama (Nihon U.), T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, T. Hashimoto, A. Yoshida (AGU),   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.),  Y. Tsuboi,  R. Sasaki, H. Kawai, T. Sato (Chuo U.), H. Tsunemi, T. Yoneyama (Osaka U.),  M. Yamauchi, K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime U.)
We analyzed the MAXI observation of the long type-I X-ray burst from SAX J1712.6-3739 reported by Lin & Yu (ATel #11623, 2018). MAXI observed the region of SAX J1712.6-3739 during 09:25:38 to 09:26:58 UT May 8th 2018 which is about 8 minutes after the peak observed with Swift/BAT (at 09:18:12 UT according to Lin & Yu 2018). We found that the 4 - 10 keV flux of this region reached 1.6 +/- 0.2 Crab. The spectrum of this scan transit is well fitted by an absorbed blackbody model with a temperature of kT = 1.9 (+0.3, -0.2) keV. The hydrogen column density was fixed at 1.3 x 1022 cm-2 (Fiocchi et al. 2008, A&A 477, 239). Assuming a distance of 7 kpc which is based on the peak flux of previous type-I X-ray burst (Cocchi et al. 2001, MmSAI 72, 757), the unabsorbed bolometric luminosity reached 2.0 (+/- 0.3) x 1038 erg/s. Therefore, the X-ray luminosity remained close to the theoretical Eddington luminosity of a typical 1.4 solar mass neutron star with a hydrogen-dominated atmosphere (2.5 x 1038 erg/s) for 8 minutes between the peak of the burst observed by Swift/BAT (Lin & Yu 2018) and the MAXI observation. Since the X-ray flux decreased to about 70 mCrab (which is almost the detection limit of one MAXI scan transit) at the next scan transit of MAXI (92 minutes after), the upper limit of the e-folding decay time is less than 2000 sec. The estimated duration is shorter than all but perhaps one previously observed superbursts (e.g., in 't Zand 2017, Proc. '7 years of MAXI: Monitoring X-ray Transients', eds. M. Serino et al., RIKEN, 121), but consistent with many intermediate duration bursts (e.g., Serino et al. 2016, PASJ 68, 95). On the basis of these results, we suggest that this is an intermediate-duration burst defined in Cumming et al. (2006, ApJ 646, 429) and Falanga et al. (2008, A&A 48, 43).
x-ray,binary,neutron star,star,transient