beans III: ensemble mode application to SRGA J144459.2–604207
The remarkable X-ray transient SRGA J144459.2–604207 was discovered by
ART-XC/SRG when
it went into outburst in 2024, and quickly distinguished itself as a
447.9 Hz accretion-powered pulsar in a 5.2 hr binary, with polarisation
detected from the persistent emission with IXPE, and a
frequent, consistent series of bursts observed with IXPE and
Insight-HXMT. Almost 100 thermonuclear (type-I) bursts were detected from the source,
with recurrence times as short as 1.6 hr.
To analyse such datasets we added an "ensemble" mode to the beans(p) code, written by Adelle Goodwin and myself, which works in a much more efficient way by matching the average properties of samples of regular, consistent ("clocked") bursts like in SRGA J144459.2–604207 and a few other sources. We applied the new code to daily epochs of data and derive a slightly sub-solar fuel composition, with X=0.54 and ZCNO=0.01. While the code mostly matches the observations, we suspect the simple ignition model we use doesn't quite include sufficient physics to be very confident in the constraints. Even so, the analysis (and the related simulations) are an important proof-of-concept for the code.
The paper has been submitted to PASA and is also available at arXiv:2608.21196.