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

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 $\alpha =71\pm 7$. We estimate the average hydrogen mass fraction in the fuel at ignition, as $\bar{X}=0.342\pm 0.033$, and constrain the burst fuel composition as $X_0\le 0.4$. We found that 14 out of 60 X-ray bursts exhibited photospheric expansion, and thus we estimated the distance to the source as $10.0\pm 0.71$ 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 $\Delta T_{\mathrm{rec}}\sim {\dot{m}}^{-0.91\pm 0.02}$.

arXiv commentPublished in ApJ

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Cited by in corpus (5)

• Dense Matter in Neutron Stars with eXTP
• NinjaSat monitoring of Type-I X-ray bursts from the clocked burster SRGA J144459.2$-$604207
• Quenching and recovery of persistent X-ray emission during a superburst in 4U 1820$-$30
• Timing and spectral studies of SRGA J144459.2$-$604207 with NICER, Einstein Probe, IXPE, NuSTAR, Insight-HXMT and INTEGRAL during its 2024 outburst
• Long thermonuclear burst driven thermal-viscous instability of accretion disk: triggering an outburst-like X-ray flare