• X-ray polarimetry
• GRB
• Black hole binaries
• Data analysis

The Imaging X-ray Polarimetry Explorer (IXPE), launched on December 9, 2021, is the first mission with imaging capabilities completely dedicated to measuring the polarization of X-rays from a variety of cosmic sources, including pulsar wind nebulae, supernova remnants, X-ray binaries, active galactic nuclei, binaries, magnetars and pulsars. Part of the NASA Small Explorers mission program, it carries three identical telescopes on board (each one including a mirror-module assembly, focusing X-rays on a Gas Pixel Detector at the focal plane), sensitive in the 2-8 keV energy band. The main topic of this work is the analysis of two selected sources observed by IXPE, the black hole binary 4U-1630-47 and the gamma ray burst GRB221009A.
4U-1630-47 was observed from 2022 August 23 to 2022 September 2, for a total exposure of approximately 460 ks. The X-ray emission, believed
to be dominated by the thermal component from the accretion disc, revealed an unexpectedly high polarization degree, rising from 6% at
2 keV to 10% at 8 keV. These results are hard to reconcile with simple
models of thin accretion discs and suggest a geometrically thick disk, indicative of high accretion rate. An alternative interpretation is that the accretion disc may be still geometrically
thin, but with the addition of strong absorption effects and, possibly,
the presence of an outflow.
IXPE observed GRB221009A from October 11 to October 14 for an effective
exposure of 94 ks.
The instrument revealed the presence of a bright core emission, associated with the GRB afterglow and the extended emission of two expanding dust-scattering halo rings, associated with its prompt, allowing us to study the polarization features of both phases.
The polarization analysis of the afterglow emission revealed an upper limit of 13.8% on the polarization degree, favoring a jet opening angle wider than 1.5 degrees and a viewing angle wider than 2/3 of the jet opening angle. The temporal and spectral parameters of the afterglow at the time of
the IXPE observation were consistent with a forward shock propagating in a wind-like medium, with X-ray emission
arising from synchrotron processes. The polarization analysis of the dust-scattering rings revealed a non-significant polarization degree, which is in some tension with other extremely high polarization measurements of GRB in the prompt phase. This observation provided the first polarization measurement of a GRB in the soft X-rays band, opening new possibilities for the IXPE mission to include fast-transient events in its science portfolio.