MAXI/GSC and Swift/BAT detection of enhanced hard X-ray emission from the Galactic center region, renewed activity of GRO J1744-28 ?
ATel #5790; H. Negoro (Nihon U.), M. Sugizaki (RIKEN), H. A. Krimm (CRESST/GSFC/USRA), J. A. Kennea (PSU), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), T. Mihara, M. Serino, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), N. Kawai, R. Usui, K. Ishikawa, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, M. Sasaki, D. Uchida (Osaka U.), M. Nakajima, H. Sakakibara, K. Fukushima, T. Onodera, K. Suzuki (Nihon U.), Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.), Y. Tsuboi, M. Higa, A. Kawagoe (Chuo U.), M. Yamauchi, K. Yoshidome, Y. Ogawa, H. Yamada, Y. Morooka (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 23 Jan 2014; 06:22 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Black Hole, Neutron Star, Transient
Referred to by ATel #: 5810, 5845, 5858, 5883, 5895, 5901, 5904, 5910, 5963, 5997, 5999, 10073
MAXI/GSC has detected enhanced hard X-ray emission from the Galactic center region. 4-10 keV and 10-20 keV count rates have gradually increased since 2014 January 18, and reached 0.19 +/- 0.02 ct/s/cm^2 (~160 mCrab) and 0.10 +/- 0.02 ct/s/cm^2 (~280 mCrab), respectively, on January 21. 2-4 keV count rates have not been increased significantly (0.06 +/- 0.02 ct/s/cm^2 ~32 mCrab), implying that the source spectrum is heavily absorbed. If the source is near the Galactic center (8.5 kpc), the luminosity in the 4-10 keV band is 3e37 erg/s (no absorption correction).
We have attempted to identify the MAXI galactic center source using the Swift/BAT hard X-ray transient monitor. Although the transient X-ray pulsar GRO J1744-28 was not in the BAT monitor catalog, examination of archival data shows that this source currently has an enhancement in the hard X-ray rate, reaching a peak level of 0.06 +/- 0.002 ct/s/cm^2 (~270 mCrab) in the 15-50 keV band on 2014 January 21 and 22. This source also triggered BAT onboard on 2014 January 18 (trigger 584284). We note, however, that there also appears to be a flux increase in the BAT monitor from the nearby (12.2 arcmin) source Granat J1741.9-2853. Although a 12 arcmin separation is normally large enough to prevent source confusion in the BAT, the strong correlation between light curves of GRO J1744-28 and Granat J1741.9-2853 suggests that the same astrophysical source is causing the rate increase in both BAT light curves. However, since the signal is stronger for GRO J1744-28, we tentatively identify this transient as the source of the hard X-ray emission seen by MAXI and Swift/BAT.
The bursting pulsar GRO 1744-28 (Fishman et al. 1995, IAUC 6272 ) exhibited outbursts in 1995 and 1996 (Woods et al. 1999, ApJ, 517, 431). The latest outburst from Granat (GRS) J1741.9-2853 was in 2009 October (Chenevez et al. ATel #2235, Kennea ATel #2236).
We note that, due to the Sun constraint, Swift/XRT can not observe the region till Feb 2nd.
MAXI public data products for the Galactic center region