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MAXI/GSC detection of a possible superburst from SLX 1735-269

ATel #4622; H. Negoro, M. Asada (Nihon U.), M. Serino (RIKEN), S. Nakahira (JAXA), M. Morii (Tokyo Tech), Y. Ogawa (Miyazaki U.), S. Ueno, H. Tomida, M. Ishikawa, K. Yamaoka, M. Kimura (JAXA), T. Mihara, M. Sugizaki, K. Morihana, T. Yamamoto, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, R. Usui, K. Ishikawa (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, (Nihon U.), Y. Ueda, K. Hiroi, M. Shidatsu, R. Sato, T. Kawamuro (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.) M. Yamauchi, Y. Nishimura, T. Hanayama, K. Yoshidome (Miyazaki U.) on behalf of the MAXI team
on 6 Dec 2012; 12:37 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

Subjects: X-ray, Neutron Star, Transient

Referred to by ATel #: 10115

MAXI/GSC detected a possible superburst from the position consistent with SLX 1735-269. The burst was detected during scan transits at 03:40 on 2012 December 6 (UT) and 05:12, strongly suggesting the burst lasted more than 92 min. Furthermore, the collimator-response corrected light curve during the first scan transit shows that the source flux was almost constant, indicating that the burst had taken place between the previous scan transit at 02:07 on December 6 and the scan transit at 03:40. In the following scan transit at 06:45, the source flux was below the detection limit of GSC (~ 30 mCrab).

The 4-20 keV fluxes of the burst are approximately 1.7+-0.1 Crab during the scan transit at 03:40 and 0.19+/-0.05 Crab at 05:12. Preliminary analysis shows that the energy spectrum during the first scan transit is well described by an absorbed blackbody model with the temperature of 2.4 +/- 0.1 keV where the hydrogen column density is fixed to 1.47e22 (David et al. 1997, A&A, 322, 229).

The source position determined from the burst is (R.A., Dec) = (264.57 deg, -27.04 deg) = (17 38 17, -27 02 23) (J2000) with a 90% C.L. statistical error of 0.07 deg. There is additional systematic uncertainty of 0.1 deg (90% containment radius). Though the position is relatively close to the source-crowded galactic center region, SLX 1735-269 is the most likely because SLX 1735-269 previously exhibited long, and energetic bursts in 2003 (Molkov et al. 2005, A&A 434, 1069), in 2004 (Sguera et al. 2007, ATel #1340), and in 2005 (Suzuki and Kawai 2005, ATel #539).

This burst is possibly the longest (> 92 min) burst that ever confirmed for this source if the burst has really continued during the two scan transits. Before this event, MAXI has detected at least four long (> 30 min) X-ray bursts, which are from SAX J1747.0-2953 (Chenevez et al. 2011, ATel #3183), 4U 1820-30 (in 't Zand et al. 2011, ATel #3625), EXO 1745-248 in Terzan 5 (Serino et al. 2012, PASJ, 64, 91), and SAX J1828.5-1037 (Asada et al. 2011, ATel #3760).

Followup observations are also encouraged.

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