A Comprehensive Study of Type I (Thermonuclear) Bursts in the New Transient SRGA J144459.2–604207
Chen, Yupeng; Zhang, Shu; Li, Xiaobo; Galloway, Duncan K.; Ji, Long; Zhang, Shuang-Nan; Ge, Mingyu; Song, L. M.; Falanga, Maurizio; Kuiper, Lucien; Fu, Tao; Li, Zhaosheng; Pan, Yuanyue; Xu, Renxin
China, Netherlands, Australia, Sweden, Switzerland
Abstract
We report an analysis of Insight-HXMT observations of the newly discovered accreting millisecond pulsar SRGA J144459.2–604207. During the outburst, detected in 2024 February by SRG/ART-XC, the broadband persistent spectrum was well fitted by an absorbed Comptonization model. We detected 60 type I X-ray bursts in the Insight-HXMT medium energy (ME) data, and 37 were also detected with the low-energy (LE) telescope. By superimposing the Insight-HXMT/LE/ME/HE light curves of 37 bursts with similar profiles and intensities, we measured a deficit of X-rays in the 40–70 keV energy band. By analyzing the time-resolved X-ray burst spectra, we determine the mean ratio of persistent to burst flux ofα = 71 ± 7. We estimate the average hydrogen mass fraction in the fuel at ignition, as