Nature of the Comptonizing emitting region in GX 349+2
Determine whether the hard X-ray Comptonized emission in GX 349+2 originates in a classical neutron-star boundary layer, a spreading layer, or another specific region of the immediate neutron-star environment.
References
Although the present work does not include polarimetric modelling and therefore cannot distinguish between a spreading layer and a boundary layer, our broadband spectral results are qualitatively consistent with the same overall physical picture. We find that the relative contribution of the accretion disk decreases systematically along the Z-track, while the thermal surface emission and the associated Comptonized component become increasingly dominant. At the same time, the inferred inner disk radius remains large and shows no evidence for systematic inward motion, indicating that the additional accretion power released toward the flaring branch is dissipated primarily in the neutron-star surface region rather than through a substantial restructuring of the disk. Although our adopted continuum model partitions the soft thermal emission differently from that used by , both studies consistently indicate that the hard X-ray emission originates in the immediate vicinity of the NS surface. The IXPE spectro-polarimetric results therefore provide complementary, independent support for the spectroscopic interpretation presented here, while the exact nature of the Comptonizing emitting region remains an open question.