MAXI/GSC observations of the bursting pulsar GRO J1744-28 close to the Eddington luminosity
ATel #5963; H. Negoro (Nihon U.), T. Mihara (RIKEN), N. Kawai (Tokyo Tech), S. Ueno, H. Tomida, S. Nakahira, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA), M. Sugizaki, M. Serino, M. Morii, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN), R. Usui, T. Yoshii, Y. Tachibana (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Nakano, Y. Kawakubo, H. Ohtsuki (AGU), H. Tsunemi, M. Sasaki (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 (Chuo U.), M. Yamauchi, K. Yoshidome, Y. Ogawa, H. Yamada (Miyazaki U.), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team
on 10 Mar 2014; 07:41 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
Subjects: X-ray, Neutron Star, Transient
MAXI/GSC monitors the bursting accretion pulsar GRO J1744-28 currently in outburst (ATel #5790, #5810, #5845). The source is included in the region named as "Galactic Center Region" in the MAXI home page (see below).
Recent observations show that source count rates are still increasing, and that those of the persistent emission have reached 0.28 +/- 0.02 c/s/cm^2 (~160 mCrab) in the 2-4 keV band, 0.66 +/- 0.02 c/s/cm&2 (~560 mCrab) in the 4-10 keV band, and 0.35 +/- 0.02 c/s/cm2 (~1.0 Crab) in the 10-20 keV band, respectively, on average from 15:16 on March 7 to 05:11 on March 8. No burst was detected during this period. All the count rates are obtained by subtracting baseline count rates before the outburst (MJD 56530-56630), and by assuming that no other bright outburst is taking place in the source region (within 1.5 arc-degree radius from the Galactic center).
MAXI/GSC has also detected 7 bursts since the first detection at 09:46 on February 12, about 11 hours after the BAT detection (ATel #5883, also see #5895, #5910).
The 4-20 keV flux has become 3.5 times larger than that on January 21 (ATel #5790), and the 4-20 keV luminosity can be estimated to be ~2e38 erg/s, comparable to the Eddington luminosity for a neutron star with 1.4 solar mass. Here we assume the source distance to be 8.5 kpc. During the outburst in 1996, however, the WATCH/Granat detected persistent 8-20 keV emission reaching ~3.7 Crab (Sazonov et al. Atron Letters, 23, 326, 1997).
Further followup observations are encouraged to understand interesting nature of this peculiar bursting pulsar.
MAXI Galactic Center Region