Abstract:
X-ray polarimetry is a powerful tool to probe the geometry of the hot X-ray corona in active galactic
nuclei (AGN). Here, we present our results on the characterisation of the X-ray polarization of the radio-quiet
Seyfert-type AGN IC 4329A at a redshift of 𝑧 = 0.016. This is based on observations carried out by the Imaging
X-ray Polarimeter (IXPE). IXPE observed IC 4329A on January 5, 2023, for a total observing time of 458 ks. From
the model-independent analysis, we found a polarization degree (Π𝑋) of 3.7±1.5% and a polarization position
angle (Ψ𝑋) of 61◦±12◦
in the 2−8 keV energy range (at 1𝜎 confidence level). This is also in agreement with the
values of Π𝑋 and Ψ𝑋 of 4.7±2.2% and 71◦ ±14◦
respectively obtained from spectro-polarimetric analysis of the I,
Q and U Stokes spectra in the 2−8 keV energy band (at the 90% confidence). The value of Π𝑋 in the 2-8 keV band
obtained from the model-independent analysis is lower than the minimum detectable polarization (MDP) value
of 4.5%. However, Π𝑋 obtained from spectro-polarimetric analysis in the 2-8 keV band is larger than the MDP
value. In the 3-5 keV band, we found Π𝑋 of 6.5 ± 1.8, which is larger than the MDP value of 5.5%. The observed
moderate value of Π𝑋 obtained from the analysis of the IXPE data in the 3−5 keV band argues against a spherical
lamp−post geometry for the X-ray corona in IC 4329A; however, considering simulations, the observed polarization
measurements tend to favour a conical shape geometry for the corona. This is the first time measurement of X-ray
polarization in IC 4329A. Measurements of the X-ray polarization in many such radio-quiet AGN will help in
constraining the geometry of the X-ray corona in AGN.
