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MAXI/GSC detection of an X-ray burst probably from IGR J17254-3257

ATel #10132; H. Negoro, (Nihon U.), M. Serino (RIKEN), S. Ueno, H. Tomida, S. Nakahira, M. Ishikawa, Y. Sugawara (JAXA), T. Mihara, M. Sugizaki, W. Iwakiri, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN), N. Kawai, N. Isobe, S. Sugita, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki (Tokyo Tech), M. Nakajima, T. Masumitsu, K. Tanaka, T. Kawase, A. Sakamaki (Nihon U.), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka (AGU), H. Tsunemi, R. Shomura (Osaka U.), Y. Ueda, T. Kawamuro, T. Hori, S. Oda, A. Tanimoto (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, K. Furuya (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI Team
on 27 Feb 2017; 00:20 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)

Subjects: X-ray, Neutron Star

MAXI/GSC detected a bright X-ray burst at the scan transit at 22:08 UT on 2017 February 23. Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (261.420 deg, -33.181 deg) = (17 25 40, -33 10 51) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.23 deg and 0.21 deg, respectively. The roll angle of the long axis from the north direction is 78.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 158 +/- 27 mCrab (0.20 +/- 0.03 counts/s/cm2) (4.0-10.0keV, 1 sigma error). The position is marginally consistent with that of the X-ray burster IGR J17254-3257, 0.23 arc-deg apart. The burst duration is unclear, but last at least 40 sec.

The burst spectrum obtained with GSC shows a thermal spectrum, represented by an absorbed blackbody model with a temperature of 2.1 (+0.7, -0.5) keV (90% confidence level). The column density n_H was fixed at 1.79e22 because it could not be determined from the spectrum and was referred from that of IGR J17254-3257/1RXS J172525.5-325717 (Chenevez et al. 2007, A&A, 469, L27). The radius of a spherical emission region is 3.7 (+1.9, -1.4) km, assuming the distance of 8 kpc. The small radius is similar to that obtained during the long burst observed by INTEGRAL in 2006 (Chenevez et al. 2007).

These results are consistent with a hypothesis that the burst came from IGR J17254-3257. X-ray bursts from IGR J17254-3257 seem be rare, and only one short burst in 2004 (Brandt et al. ATel, 778), and one short and one long bursts in 2006 (Chenevez et al. 2007) were reported. From MAXI archival data, however, at least four burst-like events from the region were found at the scan transits, 17:14 UT on 2010 Feb. 02, 12:28 on 2011 Aug. 18, 18:27 on 2013 Feb. 03, and 11:08 on 2014 Nov. 11. 4-10 keV count fluxes of these bursts were 0.17 +/- 0.03 c/s/cm2, 0.10 +/- 0.02 c/s/cm2, 0.19 +/- 0.04 c/s/cm2, and 0.18 +/- 0.03 c/s/cm2, respectively. Some of these bursts may come from any sources other than IGR J17254-3257, but all the burst spectra were highly absorbed, and the column densities were consistent with the above fixed value.