MAXI/GSC detection of large X-ray burst from 1A 1246-588

ATel #13305; W. Iwakiri (Chuo U.), K. Gendreau, Z. Arzoumanian (NASA/GSFC), John Pope (KBRwyle), H. Negoro, M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi, R. Takagi (Nihon U.), T. Mihara, C. Guo, Y. Zhou, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), N. Kawai, M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, R. Shimomukai, M. Tominaga (JAXA), Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake, T. Enoto (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC)
on 22 Nov 2019; 02:50 UT
Credential Certification: Wataru Iwakiri (wataru.iwakiri@riken.jp)

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The MAXI/GSC nova alert system detected a strong X-ray burst from LMXB 1A 1246-588 on Nov 21 00:13:31 UT. No significant decay is observed during this scan transit (about 40 sec). The spectrum is well represented by an absorbed blackbody model with a temperature 2.7(+0.2, -0.1) keV. The hydrogen column density was fixed at 4.3 x 10²¹ cm^-2 (ATel #875, Kong). The unabsorbed bolometric flux is 7.7(+0.6, -0.6) x 10^-8 erg/cm²/s. Assuming the flux reaches Eddington limit for a He type-I X-ray burst (3.8 x 10³⁸ erg/s, empirically derived by Kuulkers et al.2003), the distance to the source is 6.4 (+0.3, -0.2) kpc. There is no significant X-ray source at the next scan transit data of MAXI (92 minutes after). NICER observation started at 03:21:29 with 1 ksec exposure. The NICER lightcurve shows that there is no decay episode. The obtained spectrum by NICER is well fitted by an absorbed powerlaw model with a photon index of 2.8. The best-fit hydrogen column density is about 6 x 10²¹ cm^-2. The unabsorbed X-ray flux in the 2 - 10 keV is about 7 x 10^-11 erg/cm²/s. The flux is almost consistent with the persistent flux of this source (Jonker et al. 2007). Therefore, the burst had ended by the time the NICER observation began (3 hours later from the MAXI detection).
1A 1246-588 is a candidate of ultracompact X-ray binary (Bassa et al. 2006). Several intermediate duration bursts (in 't Zand et al. 2005; Cumming et al.2006) from this source have been reported (ATel #830, Levine et al.; ATel #837, Kuulkers & Levine; GCN #5436 Romano et al.; ATel #875, Kong; ATel #3482, Serino at al. ). Although we provide only upper limits of the duration of the burst (it is longer than 40 sec), this event is a possibly new intermediate duration burst from 1A 1246-588.