Kavli Affiliate: Renxin Xu
| First 5 Authors: Liyu Song, Helei Liu, Chunhua Zhu, Guoqing Zhen, Guoliang Lv
| Summary:
Using the MESA 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 $sim(4-8)times10^{-10},M_{odot}/{rm yr}$ when metallicity $Z=0.01$,
while in the range of $sim(4-8)times10^{-9},M_{odot}/rm{yr}$ when
$Z=0.05$. Calculations of the metallicity impact suggest that the double peaks
will disappear when $Zlesssim0.005$ for
$dot{M}=5times10^{-10},M_{odot}/rm{yr}$ and $Zlesssim0.04$ for
$dot{M}=5times10^{-9},M_{odot}/rm{yr}$. Besides, the impacts of base
heating $Q_{rm b}$, as well as nuclear reaction waiting points:
$^{22}rm{Mg}$, $^{26}rm{Si}$, $^{30}rm{S}$, $^{34}rm{Ar}$, $^{56}{rm Ni}$,
$^{60}rm Zn$, $^{64}rm{Ge}$, $^{68}rm{Se}$, $^{72}rm{Kr}$ have been
explored. The luminosity of the two peaks decreases as $Q_{rm b}$ increases.
$^{68}{rm Se}(p,gamma){^{69}{rm Br}}$ is the most sensitive reaction, the
double peaks disappear assuming that $^{56}{rm Ni}(p,gamma)^{57}{rm Cu}$ and
$^{64}{rm Ge}(p,gamma)^{65}{rm As}$ reaction rates have been underestimated
by a factor of 100 and the $^{22}{rm Mg}(alpha,p)^{25}{rm Al}$ reaction rate
has been overestimated by a factor of 100, which indicates that $^{22}{rm
Mg}$, $^{56}{rm Ni}$, $^{64}{rm Ge}$, $^{68}{rm Se}$ are possibly the most
important nuclear waiting points impedance. 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 ($t_{rm p,1}gtrsim4,{rm s}$, $t_{rm p,2}gtrsim8,{rm s}$) and
smaller peak ratio($r_{1,2}lesssim0.5$). The composition of ashes from
double-peaked bursts is very different from the single-peaked bursts especially
for the heavier p-nuclei.
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