2024MNRAS.529.3103S

Using the MESA (Modules for Experiments in Stellar Astrophysics) code, we have carried out a detailed survey of the available parameter space for the double-peaked type I X-ray bursts. We find that the double-peaked structure appears at mass accretion rate $\dot{M}$ in the range of $\sim (4-8)\times 10^{-10}\, {\rm M}_{\odot }\,{\rm yr}^{-1}$ when metallicity Z = 0.01, while in the range of $\sim (4-8)\times 10^{-9}\, {\rm M}_{\odot }\,\rm {yr}^{-1}$ when Z = 0.05. Calculations of the metallicity impact suggest that the double peaks will disappear when Z ≲ 0.005 for $\dot{M}=5\times 10^{-10}\, {\rm M}_{\odot }\,\rm {yr}^{-1}$ and Z ≲ 0.04 for $\dot{M}=5\times 10^{-9}\, {\rm M}_{\odot }\,\rm {yr}^{-1}$. Besides, the impacts of base heating Q_b, as well as nuclear reaction waiting points: $^{22}\rm {Mg}$, $^{26}\rm {Si}$, $^{30}\rm {S}$, $^{34}\rm {Ar}$, ⁵⁶Ni, $^{60}\rm Zn$, $^{64}\rm {Ge}$, $^{68}\rm {Se}$, and $^{72}\rm {Kr}$ have been explored. The luminosity of the two peaks decreases as Q_b increases. ⁶⁸Se(p, γ)⁶⁹Br is the most sensitive reaction, the double peaks disappear assuming that ⁵⁶Ni(p, γ)⁵⁷Cu, and ⁶⁴Ge(p, γ)⁶⁵As reaction rates have been underestimated by a factor of 100 and the ²²Mg(α, p)²⁵Al reaction rate has been overestimated by a factor of 100, which indicates that ²²Mg, ⁵⁶Ni, ⁶⁴Ge, and ⁶⁸Se are possibly the most important nuclear waiting points impedance in the thermonuclear reaction flow to explain the double-peaked bursts. Comparisons to the double-peaked bursts from 4U 1636-53 and 4U 1730-22 suggest that the nuclear origins of double-peaked type I X-ray bursts are difficult to explain the observed larger peak times ($t_{\rm p,1}\gtrsim 4\, {\rm s}$, $t_{\rm p,2}\gtrsim 8\, {\rm s}$) and smaller peak ratio (r_1, 2_ ≲ 0.5). The composition of ashes from double-peaked bursts is very different from the single-peaked bursts especially for the heavier p-nuclei.