Speaker
Description
Microquasars are known to produce strong hard X-ray emission during their outbursts, which is thought to be either inverse Compton emission, synchrotron emission or a mix of both. Although challenging to measure properly, polarization is a critical tool to distinguish between them. For this task, the IBIS telescope onboard the INTEGRAL satellite can be used to probe the polarization of bright sources above 200 keV, thanks to the Compton scattering of photons between its two detectors: ISGRI (30 – 500 keV) and PICsIT (170 keV – 10 MeV). The transient nature of most microquasars makes MAXI continuous monitoring of the sky an essential instrument: once a bright enough Microquasars is detected, the outburst evolution (flux and hardness-ratio) can be tracked by MAXI and polarization measurement can be made through the different states by the INTEGRAL/IBIS Compton mode. We will give a review of the previous polarization results, where some sources were found to be highly polarized (>50%) during their Hard State while some showed weaker or no polarization. We will also present recent results from the very bright outburst of the Microquasar Swift J1727.8-1613, which allowed us to measure polarization in both the Hard and Soft Intermediate states (SIMS). Interestingly the polarization angle was found to be aligned with the jet axis in the SIMS, and the same jet alignment was found after reanalyzing data of the source MAXI J1348-630. We therefore argue that this behavior may be more generic than first thought. Finally, we interpret the possible orientation of the polarization angle and magnetic field compared to the gamma-ray emitting jet during the outburst, and we suggest a way to constrain the inclination of the jet using the polarization fraction and photon index.
