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arXiv · 2412.05779

A comprehensive study of type I (thermonuclear) bursts in the new transient SRGA J144459.2$-$604207

Tao Fu·Zhaosheng Li·Yuanyue Pan·Long Ji·Yupeng Chen·Lucien Kuiper·Duncan K. Galloway·Maurizio Falanga·Renxin Xu·Xiaobo Li·Mingyu Ge·L. M. Song·Shu Zhang·Shuang-Nan Zhang
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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 of $\alpha=71\pm7$. We estimate the average hydrogen mass fraction in the fuel at ignition, as $\bar{X} =0.342\pm0.033$, and constrain the burst fuel composition as $X_0\leq0.4$. We found that 14 out of 60 X-ray bursts exhibited photospheric expansion, and thus we estimated the distance to the source as $10.0\pm0.71$ kpc. Combined with IXPE observations, the burst recurrence time increased from 1.55 to 8 hr as the local mass accretion rate decreased, which can be described as $\Delta T_{\rm rec}\sim \dot{m}^{-0.91\pm0.02}$.

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Tao Fu, Zhaosheng Li, Yuanyue Pan, Long Ji, Yupeng Chen, Lucien Kuiper, Duncan K. Galloway, Maurizio Falanga, Renxin Xu, Xiaobo Li, Mingyu Ge, L. M. Song, Shu Zhang, Shuang-Nan Zhang. 2024-12-08. A comprehensive study of type I (thermonuclear) bursts in the new transient SRGA J144459.2$-$604207. https://doi.org/10.3847/1538-4357/adadee

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