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MAXI/GSC detected two X-ray bursts from IGR J18245-2452 in M28

ATel #4961; M. Serino, T. Takagi (RIKEN), H. Negoro (Nihon U.), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa (JAXA), T. Mihara, M. Sugizaki, M. Morii, T. Yamamoto, J. Sugimoto, M. Matsuoka (RIKEN), N. Kawai, R. Usui, K. Ishikawa, T. Yoshii (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano (AGU), H. Tsunemi, M. Sasaki (Osaka U.), M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro (Kyoto U.), Y. Tsuboi, M. Higa (Chuo U.), M. Yamauchi, K. Yoshidome, Y. Ogawa, H. Yamada (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 8 Apr 2013; 16:13 UT
Credential Certification: Motoko Suzuki (motoko@crab.riken.jp)

Subjects: X-ray, Binary, Neutron Star, Transient

Referred to by ATel #: 4964, 4981, 5031, 5069, 5086

At 2013-04-07T22:15:57 (UT), MAXI/GSC detected a bright X-ray burst-like event from the position consistent with the currently active hard X-ray transient IGR J18245-2452 (Eckert et al. ATel #4925, also see #4927, #4929 #4934, #4959, and #4960).

The 4-10 keV X-ray flux averaged during the scan transit was about 350+-40 mCrab. GSC spectral fitting with a blackbody model gives the temperature of 1.4+-0.2 keV and the luminosity of 3.0+0.4e37 erg/s assuming the source distance to be 5.5 kpc. Poor statistics do not allow us to put a limitation on the absorption column density.

A collimator-response corrected light curve assuming the source position to be that of IGR J18245-2452 shows an exponential decay profile with a time constant of about 18 sec. These characteristics strongly suggest that MAXI/GSC detected an X-ray burst from a neutron star low-mass X-ray binary, probably IGR J18245-2452.

We note that this event (MAXI alert ID=6390849999, MAXI X-ray-star ML No. 216) is identical with the event reported by Papitto et al. (ATel #4959) and Linares (ATel #4960), while MAXI transit started 14 sec after the burst peak.

MAXI/GSC also detected a burst-like event during the scan transit at 2013-04-03T10:02(MAXI alert ID=6385727013, MAXI X-ray-star ML No. 214). At that time, the averaged 4-10 X-ray flux was roughly 80 mCrab, which might be a part of a similar X-ray burst event. X-ray fluxes during scan transits before and after these two events were both below the detection limit of about 20 mCrab.