GECAM detection of a bright thermonuclear burst from 4U 0614+091
ATel #14363; Y. P. Chen (IHEP), J. Li (USTC), S. L. Xiong (IHEP), L. Ji (SYSU), S. Zhang (IHEP), W. X. Peng (IHEP), R. Qiao, X. Y. Zhao, Y. Huang, F. J. Lu, S. N. Zhang, L. M. Song, S. Xiao, C. Cai, B. X. Zhang, Z. H. An, C. Chen, G. Chen, W. Chen, M. Gao, K. Gong, D. Y. Guo, J. J. He, B. Li, C. Li, C. Y. Li, J. H. Li, Q. X. Li, X. B. Li, X. Q. Li, Y. G. Li, X. H. Liang, J. Y. Liao, J. C. Liu, X. J. Liu, Y. Q. Liu, Q. Luo, X. Ma, G. Ou, D. L. Shi, J. Y. Shi, X. Y. Song, G. X. Sun, X. L. Sun, Y. L. Tuo, C. W. Wang, J. Z. Wang, P. Wang, X. Y. Wen, Y. B. Xu, Y. P. Xu, W. C. Xue, S. Yang, M. Yao, Q. B. Yi, C. Y. Zhang, D. L. Zhang, Fan Zhang, Fei Zhang, H. M. Zhang, K. Zhang, P. Zhang, Y. Q. Zhang, Z. Zhang, S. Y. Zhao, Y. Zhao, C. Zheng, S. J. Zheng, X. Zhou (IHEP), report on behalf of GECAM team:
on 1 Feb 2021; 05:06 UT
Credential Certification: Yu-Peng Chen (chenyp@ihep.ac.cn)
Subjects: X-ray, Binary, Neutron Star
During the commissioning phase, GECAM-B detected a very bright X-ray burst at 2021-01-24T11:50:03.600 UTC (denoted as T0, GCN 29350) from a direction centered on Ra: 94.9 degree, Dec: 6.6 degree with an error circle 2.7 degree (1-sigma, statistical only). The burst has a fast rise of 10 s, an exponential fashion decay and a duration of ~60 s. With 4 detectors out of 25, the peaks flux is ~700 cts/s above the pre-burst emission.
A pulsation at 413 Hz is detected with ~4 sigma. The 2-second time bin burst spectra are well represented by a blackbody, with a temperature peaking at 4.0+/-0.2 keV and a peak flux (3.3+/-0.2) x 10^-7 erg/cm2/s. The spectrum softens with the temperatures from ~4 keV to ~2 keV during the decay. Assuming the source at a distance 3 kpc, the unabsorbed bolometric peak luminosity is (3.6+/-0.2) x 10^38 erg/s, which is well consistent with the Eddington limit with a stellar mass of 1.4 solar mass for hydrogen-poor matter.
This analysis shows convincingly the burst is a genuine thermonuclear X-ray burst from 4U 0614+09, a faint and persistently accreting neutron star X-ray binary lying within the location error, from which the 415 Hz burst oscillation was first reported with data from Swift/BAT (Strohmayer et al. 2008). Since 4U 0614+091 has a burst recurrence time ~12 day (Linares et al. 2012), thanks to the very wide field of view (more than a half sky) of GECAM-B, more bursts should be detected during future observations of GECAM-B.
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission consists of two small satellites (GECAM-A and GECAM-B) in Low Earth Orbit (600 km, 29 deg), launched on Dec 10, 2020 (Beijing Time), which was funded by the Chinese Academy of Sciences (CAS).
