2025ApJ...980..161F

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 $\overline{X}=0.342\pm 0.033$, and constrain the burst fuel composition as X₀ ≲ 0.4. We found that 14 out of 60 X-ray bursts exhibited photospheric expansion, and thus we estimated the distance to the source as 10.03 ± 0.71 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 ${\rm{\Delta }}{T}_{{\rm{rec}}}\sim {\dot{m}}^{-0.91\pm 0.02}$.