Spectro-Polarimetric Study of Weakly Magnetized Neutron Star X-ray binary GX 349+2

We report the first spectro-polarimetric investigation of the bright Z-type source GX 349+2 using simultaneous observations of $\mathit{\text{IXPE}}$, $\mathit{\text{NuSTAR}}$ and $\mathit{\text{Swift/XRT}}$. The source exhibited significant polarization in the 2-8 keV energy range during the flaring branch (FB) and normal branch (NB). The estimated polarization degree (PD) and polarization angle (PA) for FB are $1.74\pm 0.52\mathrm{\%}$ ($3.3\sigma$) and $19.4\pm {8.9}^{\circ }$, respectively; while for NB, PD and PA are $0.8\pm 0.22\mathrm{\%}$ ($3.6\sigma$) and $35.4\pm {7.9}^{\circ }$, respectively. The energy-resolved polarization for NB revealed an increase in PD from $0.78\pm 0.2\mathrm{\%}$ ($3.6\sigma$) to $1.32\pm 0.40\mathrm{\%}$ ($3.3\sigma$) and a change in PA from $17.9\pm {8.1}^{\circ }$, and $53.2\pm {8.6}^{\circ }$, in the energy range of 2-4 and 4-8 keV, respectively. Using the simultaneous observations of $\mathit{\text{Swift/XRT}}$ and $\mathit{\text{NuSTAR}}$, we investigated the spectral properties of the source during NB, and the Western model well explained it. The spectra also depicted a strong and broad Fe K$\alpha$ line. However, spectro-polarimetric analyses carried out by $\mathit{\text{IXPE}}$ align closely with model-independent polarimetric results. We discuss results obtained from the polarimetric studies in the context of various coronal geometries, and we confirm the slab-like geometry in the NB for GX 349+2.