We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy NGC 4151. The source has been observed with the Imaging X-ray Polarimetry Explorer (IXPE) for 700 ks, complemented with simultaneous XMM-Newton (50 ks) and NuSTAR (100 ks) pointings. A polarization degree Π = 4.9 ± 1.1% and angle Ψ = 86^○ ± 7^○ east of north (68% confidence level) are measured in the 2–8 keV energy range. The spectro-polarimetric analysis shows that the polarization could be entirely due to reflection. Given the low reflection flux in the IXPE band, this requires however a reflection with a very large (>38%) polarization degree. Assuming more reasonable values, a polarization degree of the hot corona ranging from ∼4 to ∼8% is found. The observed polarization degree excludes a ‘spherical’ lamppost geometry for the corona, suggesting instead a slab-like geometry, possibly a wedge, as determined via Monte Carlo simulations. This is further confirmed by the X-ray polarization angle, which coincides with the direction of the extended radio emission in this source, supposed to match the disc axis. NGC 4151 is the first AGN with an X-ray polarization measure for the corona, illustrating the capabilities of X-ray polarimetry and IXPE in unveiling its geometry.

We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy IC 4329A. The Imaging X-ray Polarimetry Explorer (IXPE) observed the source for ∼500 ks, supported by XMM-Newton (∼60 ks) and NuSTAR (∼80 ks) exposures. We detect polarisation in the 2–8 keV band with 2.97σ confidence. We report a polarisation degree of 3.3 ± 1.1 per cent and a polarisation angle of 78^○ ± 10^○ (errors are 1σ confidence). The X-ray polarisation is consistent with being aligned with the radio jet, albeit partially due to large uncertainties on the radio position angle. We jointly fit the spectra from the three observatories to constrain the presence of a relativistic reflection component. From this, we obtain constraints on the inclination angle to the inner disc (<39^○ at 99 per cent confidence) and the disc inner radius (<11 gravitational radii at 99 per cent confidence), although we note that modelling systematics in practice add to the quoted statistical error. Our spectro-polarimetric modelling indicates that the 2–8 keV polarisation is consistent with being dominated by emission directly observed from the X-ray corona, but the polarisation of the reflection component is completely unconstrained. Our constraints on viewer inclination and polarisation degree tentatively favour more asymmetric, possibly out-flowing, coronal geometries that produce more highly polarised emission, but the coronal geometry is unconstrained at the 3σ level.

The elusive supermassive black hole binaries (SMBHBs) are thought to be the penultimate stage of galaxy mergers, preceding a final coalescence phase. SMBHBs are sources of continuous gravitational waves, possibly detectable by pulsar timing arrays; the identification of candidates could help in performing targeted gravitational wave searches. Due to SMBHBs’ origin in the innermost parts of active galactic nuclei (AGN), X-rays are a promising tool for unveiling their presence, by means of either double Fe Kα emission lines or periodicity in their light curve. Here we report on a new method for selecting SMBHBs by means of the presence of a periodic signal in their Swift Burst Alert Telescope (BAT) 105 month light curves. Our technique is based on Fisher’s exact g-test and takes into account the possible presence of colored noise. Among the 553 AGN selected for our investigation, only the Seyfert 1.5 galaxy Mrk 915 emerges as a candidate SMBHB; from subsequent analysis of its light curve we find a period P ₀ = 35 ± 2 months, and the null hypothesis is rejected at the 3.7σ confidence level. We also present a detailed analysis of the BAT light curve of the only previously X-ray-selected binary candidate source in the literature, the Seyfert 2 galaxy MCG+11-11-032. We find P ₀ = 26.3 ± 0.6 months, consistent with the one inferred from previously reported double Fe Kα emission lines.

The presence of blueshifted absorption lines in the X-ray spectra of black hole low-mass X-ray binaries is the telltale mark of massive outflows called winds. These signatures are found almost exclusively in soft states of high-inclined systems, hinting at equatorial ejections originating from the accretion disk and deeply intertwined with the evolution of the outburst patterns displayed by these systems. In the wake of the launch of the new generation of X-ray spectrometers, studies of wind signatures remain mostly restricted to single sources and outbursts, with some of the recent detections departing from the commonly expected behaviors. We thus give an update to the current state of iron band absorption line detections through the analysis of all publicly available XMM-Newton-pn and Chandra-HETG exposures of known black hole low-mass X-ray binary candidates. Our results agree with previous studies, as our wind detections are exclusively found in dipping, high-inclined sources and almost exclusively in bright (L_X > 0.01L_Edd) soft (HR < 0.8) states with blueshift values generally restricted to a few 100 km s⁻¹. The line parameters indicate similar properties between objects and outbursts of single sources, and despite more than 20 yr of data, very few sources have the HID sampling necessary to properly study the evolution of the wind during a single outburst. We provide an online tool with details of the wind signatures and outburst evolution data for all sources in our sample.

The detection of blueshifted absorption lines likely associated with ionized iron K-shell transitions in the X-ray spectra of many active galactic nuclei (AGNs) suggests the presence of a highly ionized gas outflowing with mildly relativistic velocities (0.03c–0.6c) named ultra-fast outflow (UFO). Within the SUBWAYS project, we characterized these winds starting from a sample of 22 radio-quiet quasars at an intermediate redshift (0.1 ≤ z ≤ 0.4) and compared the results with similar studies in the literature on samples of local Seyfert galaxies (i.e., 42 radio-quiet AGNs observed with XMM-Newton at z ≤ 0.1) and high redshift radio-quiet quasars (i.e., 14 AGNs observed with XMM-Newton and Chandra at z ≥ 1.4). The scope of our work is a statistical study of UFO parameters and incidence considering the key physical properties of the sources, such as supermassive black hole (SMBH) mass, bolometric luminosity, accretion rates, and spectral energy distribution (SED) with the aim of gaining new insights into the UFO launching mechanisms. We find indications that highly luminous AGNs with a steeper X-ray/UV ratio, α_ox, are more likely to host UFOs. The presence of UFOs is not significantly related to any other AGN property in our sample. These findings suggest that the UFO phenomenon may be transient. Focusing on AGNs with UFOs, other important findings from this work include: (1) faster UFOs have larger ionization parameters and column densities; (2) X-ray radiation plays a more crucial role in driving highly ionized winds compared to UV; (3) the correlation between outflow velocity and luminosity is significantly flatter than what is expected for radiatively driven winds; (4) more massive black holes experience higher wind mass losses, suppressing the accretion of matter onto the black hole; (5) the UFO launching radius is positively correlated with the Eddington ratio. Furthermore, our analysis suggests the involvement of multiple launching mechanisms, including radiation pressure and magneto-hydrodynamic processes, rather than pointing to a single, universally applicable mechanism.

We report on the second observing program of the active galactic nucleus NGC 4151 with simultaneous Imaging X-ray Polarimetry Explorer (IXPE; 750 ks), NuSTAR (∼60 ks), XMM-Newton (∼75 ks), and NICER (∼65 ks) pointings. NGC 4151 is the first Type-1 radio-quiet Seyfert galaxy with constrained polarization properties for the X-ray corona. Despite the lower flux state in which the source was re-observed and the resulting higher contribution of the constant reflection component in the IXPE energy band, our results are in agreement with the first detection. From polarimetric analysis, a polarization degree Π = 4.7 ± 1.3% and polarization angle Ψ = 77° ± 8° east of north (68% c.l.) were derived in the 2.0–8.0 keV energy range. Combining the two observations leads to polarization properties that are more constrained than those of the individual detections, showing Π = 4.5 ± 0.9% and Ψ = 81° ± 6° (with a detection significance of ∼4.6 σ ). The observed polarization angle aligns very well with the radio emission in this source, supporting, together with the significant polarization degree, a slab or wedge geometry for the X-ray corona. However, a switch in the polarization angle at low energies (37° ±7° in the 2–3.5 keV bin) suggests the presence of another component. When it is included in the spectro-polarimetric fit, a high polarization degree disfavors an interpretation in terms of a leakage through the absorbers, instead pointing to scattering from some kind of mirror.