arXiv subjects

Vittoria Elvezia Gianolli

Publications and source records attributed to Vittoria Elvezia Gianolli.

5 recordsLinked to original sources

arXiv2026

X-ray polarization of the Compton-thin Seyfert galaxy NGC 5506 with IXPE

We report on the observation of the Compton-thin Seyfert galaxy NGC~5506 performed with the Imaging X-ray Polarimetry Explorer (IXPE). The observation, with a net observing time of 975~ks, was partly simultaneous with \textit{NuSTAR} (52~ks) and \textit{XMM-Newton} (37~ks). Using a simple baseline model with IXPE data only, we find an upper limit on the 2--8~keV polarization fraction at the $99\%$ confidence level: $Π<3.1\%$. We then performed a spectropolarimetric analysis combining data from the three X-ray observatories. While pure spectral modeling confirms the presence of both relativistic and cold distant reflection, in addition to the primary continuum power law, their contributions lead to somewhat different constraints on the coronal $Π$, depending on the specific assumptions. We also performed Monte Carlo simulations with the radiative transfer code \texttt{MONK}, exploring various coronal geometries. Comparing these results with the IXPE data, and assuming a radially extended corona, as suggested by previous observations of similar sources, the corresponding polarization upper limits require inclination angles below 40°.

astro-ph.HE↗

arXiv2026

EXPO: a quantum leap in fast, wide-band X-ray polarimetry for astrophysics

The Enhanced X-ray Polarimetry Observatory (EXPO) is a mission concept proposed to ESA as an M8 candidate, with a prospective launch in 2041. Building on the scientific success of IXPE, EXPO is designed to overcome its two main limitations, the narrow 2-8 keV energy band and the very slow repointing time, and to enable new scientific capabilities. A wide energy band and fast repointing are essential for investigating the hard X-ray emission of magnetars and black-hole binaries, particle acceleration in supernova remnants and pulsar-wind nebulae, radiative transfer in highly magnetized plasmas, X-ray reflection in accretion flows and active galactic nuclei, and the prompt and afterglow emission of gamma-ray bursts and magnetar flares. EXPO comprises five focusing X-ray telescopes and gas photoelectric polarimeters based on the Timepix ASIC family with InGrid amplification, enabling three-dimensional track imaging and operation in the 2-35 keV band through optimized low- and medium-energy detector configurations. The mirror modules use proven electroformed nickel technology with Au-C coatings and an XMM-like focal length of 7.5 m. The polarimeters are complemented by a coded-mask Wide Field Instrument (WFI), derived from SVOM/ECLAIRs for continuous monitoring of a 2 sr field of view; a Spectral Imaging Camera (SIC), based on stacked CMOS and CdTe detectors for broadband imaging spectroscopy and accurate spectro-polarimetric decomposition; and an Instrument Control Unit (ICU) for payload management, onboard WFI image reconstruction, transient identification, and autonomous spacecraft repointing requests. These capabilities extend X-ray polarimetry into the hard X-ray domain and open a new observational window on fast transients, time-domain astrophysics, and multi-messenger astronomy.

astro-ph.IM↗

arXiv2026

The hidden variability of the torus in local Active Galactic Nuclei: 20 years of Chandra, XMM-Newton, and NuSTAR observations

X-ray absorption variability in active galactic nuclei (AGN) provides key constraints on the structure and dynamics of the circumnuclear obscuring medium, the so-called torus. A fraction of nearby AGN, however, have been classified as non-variable in line-of-sight (LoS) column density based on limited temporal coverage. We present the first systematic study of a sample of 11 local (z $\leq$ 0.1) obscured (N$_{\rm H} \geq 10^{22}$ cm$^{-2}$) AGN, initially classified as non-variable. The sample is selected from the Swift-BAT 100-month catalog, and comprises 60 observations from Chandra, XMM-Newton, and NuSTAR, spanning timescales from days to nearly two decades. We simultaneously model all available spectra for each source adopting physically motivated torus models: X-skirtor, RXTorusD, and UXCLUMPY. This approach allows us to derive the global properties of the obscurer while tracking possible epoch-to-epoch variations in the LoS column density and intrinsic X-ray emission. We find that the original non-variable classification (based on only two X-ray observations) is frequently not robust: clear N$_{\rm H,LoS}$ variability is detected in half of the sample, whereas 7 out of 10 AGN require intrinsic flux variability, with the rest showing flux-N$_{\rm H,LoS}$ degeneracies. We also find that the probability of identifying absorption variability increases with the number of observations, and the largest column density changes preferentially occur on long timescales, consistent with absorption by extended, structured clouds on torus scales. These findings support a clumpy and dynamic obscuring medium as a common feature of nearby AGN and highlight the importance of long-term X-ray monitoring for accurately characterizing AGN obscuration.

astro-ph.GA↗

arXiv2026

XPE and VLT /FORS2 polarimetry challenge the Seyfert-1.9 classification of MCG-05-23-16

We report the third observation of the Seyfert-1.9 active galactic nucleus (AGN) MCG-05-23-16 with the Imaging X-ray Polarimetry Explorer (\textit{IXPE}), together with optical spectro-polarimetry obtained at the Very Large Telescope (VLT), and combined with archival near-ultraviolet, optical and near-infrared polarimetric data. No X-ray polarization was detected in the 2-8 keV band, with a 99\% confidence upper limit of $\leq$2.9\%, further reduced to $\leq$2.5\% when combined with the two past IXPE observations of the same target. Monte Carlo simulations suggest that equatorial coronal models are disfavored if the AGN is indeed a type-1.9/2 AGN, but coronae coplanar to the accretion disk remain consistent if the source is less inclined than previously assumed. \textit{VLT}/FORS2 data reveal a typical type-2 spectrum in total flux, a broad H$α$ line in polarized flux, and strongly wavelength dependent polarization degree and angle, rotating by nearly 70$^\circ$ across the optical band. Comparison with historical measurements confirms long-term stability of the polarization spectrum and a $\sim$90$^\circ$ rotation in the near-ultraviolet. Interpreting the multi-wavelength polarization relative to the AGN ionization axis indicates that the main obscurer is not a compact circumnuclear torus, but a distant kpc-scale dust lane crossing the galaxy. This result implies that MCG-05-23-16 is in fact a type-1 AGN seen through foreground dust. The low X-ray column density becomes consistent with the absence of polarization, provided that the nuclear inclination is low.

astro-ph.HE↗

arXiv2025

Exploring MAXI J1744-294: IXPE insights into a Newly Discovered X-ray Transient

We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744$-$294, a transient X-ray source discovered during a bright 2025 outburst in the Galactic center region. During the $\sim$150 ks observation, the source was found in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. No significant polarization was detected, and we derived a 3$σ$ upper limit on the polarization degree of $1.3\%$ in the 2--8 keV energy band. This result is consistent with previous findings for soft-state black hole binaries observed at low to intermediate inclination angles. By comparing the polarization degree upper limit with theoretical predictions for standard accretion disk emission, we constrain the disk inclination to $i \lesssim 38^\circ$--$71^\circ$, depending on the black hole spin and the disk atmosphere albedo.

astro-ph.HE↗