Speaker
Description
We present the results of a comprehensive spectro-polarimetric analysis of nine black hole X-ray binaries namely Cyg X$-1$, 4U 1630$-47$, 4U 1957$+115$, Cyg X$-3$, LMC X$-1$, LMC X$-3$, Swift J1727.8$-1613$, Swift J151857.0$-572147$ and GX 339$-4$ using quasi-simultaneous IXPE, NICER and NuSTAR observations. Polarimetric measurements with IXPE confirm the detection of a significant degree of polarization varying in the range of $1.44-21.41\%$ ($2-8$ keV) for all the sources in different spectral states (LHS, HIMS, SIMS, HSS) except LMC X$-1$. The energy-dependent polarization study imparts a significant ($> 4\sigma$) increase of polarization degree with energy up to $\sim 11\%$ ($25\%$) for 4U 1630$-47$ (Cyg X$-3$) whereas marginal ($<2\sigma$) variation is observed for rest of the sources. A detailed spectro-polarimetric study ($2-8$ keV) and broad-band spectral analysis ($0.7-60$ keV) using the high quality IXPE, NICER and NuSTAR observations further corroborates the detection of polarization from model-dependent approach and reveals the morphologies of distinct spectral states, respectively. In addition, we find a significant correlation between the spectro-polarimetric parameters, tightly connected to the spectral states of the sources. Based on the obtained results, we infer the disc-jet-corona geometry of the sources in different spectral states and the possible origin of the polarized emissions. Finally, we discuss the prospects of India's first X-ray polarimetric mission, XPoSat in the context of IXPE results.
