2025ApJ...995...70C

The thermonuclear X-ray burster, 4U 0614+09, which is located at a distance of ∼3 kpc, serves as a valuable laboratory for studying the interaction between thermonuclear X-ray bursts and the surrounding accretion environment. By analyzing the archived data from NICER and Insight-HXMT, we found that two bursts were identified by NICER, while none were detected by Insight-HXMT. Time-resolved spectroscopy of the bright burst revealed interaction-related characteristics, with the burst tail exhibiting an exceptionally prolonged duration exceeding 400 s-distinct from intermediate or superburst classifications-a feature discernible due to the source's relative proximity and enhanced instrumental sensitivity. There was a notable deviation from the expected canonical blackbody model near the burst peak, which could be attributed to either an enhanced preburst/persistent emission or the Comptonization of the burst and enhanced disk emission by the corona. The burst-induced flux enhancement of the accretion flow was observed to be proportional to the square root of the burst flux, i.e., ${L}_{{\rm{PR}}}\propto {L}_{{\rm{bb}}}^{1/2}$, which also suggests the retreat of the disk away from the neutron star. During the tail end of the X-ray burst cooling phase, the burst temperature stabilized at around 0.47 keV, with an inferred neutron star surface temperature of 0.33 keV. This temperature was used and fixed during the spectral fitting of the persistent/outburst emission.