Kavli Affiliate: Herman L. Marshall
| First 5 Authors: Swati Ravi, Swati Ravi, , ,
| Summary:
Observations from the Imaging X-ray Polarimetry Explorer (IXPE) have revealed
electric vector position angle (EVPA) rotation in several neutron star low-mass
X-ray binaries, including the galactic X-ray burster GX 13+1. We developed a
novel Bayesian nested sampling framework-"Q-U Event-by-Event Nested sampling
for Bayesian EVPA Evolution" (QUEEN-BEE)-to model unbinned Stokes parameters
and infer optimal EVPA rotation rates in IXPE data. We then applied this
framework to three previous IXPE observations of GX 13+1. In the first
observation, QUEEN-BEE recovers a rotation rate of 42+/-4 degrees/day,
consistent with prior binned analysis. Energy-binned QUEEN-BEE analysis of this
first observation suggests a slab-like coronal geometry, providing the first
constraints between slab and shell coronae for this source. We also explore
alternative EVPA rotation scenarios in GX 13+1 including variable disk wind
behavior. The second observation of this source shows no evidence of rotation,
and the third observation shows transient rotating behavior with an EVPA
rotation rate when exiting a light curve dip of 170 +20/-40 degrees/day. The
results show marginal but consistent increases in the overall measured
polarization degree (PD) for epochs where the EVPA rotation is identified.
These results demonstrate that QUEEN-BEE can identify evolving polarization
signatures in both time- and energy-resolved regimes, even where binned methods
fall below detection thresholds. Our findings highlight the diagnostic
potential of QUEEN-BEE as a tool for discriminating between competing physical
models of coronal geometry and probing disk-wind-related polarization behavior,
highlighting the promising potential for application of this framework in a
variety of other IXPE observations.
| Search Query: ArXiv Query: search_query=au:”Herman L. Marshall”&id_list=&start=0&max_results=3