arXiv subjects

Romana Mikusincova

Publications and source records attributed to Romana Mikusincova.

10 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

Discovery of Strong Energy-Dependent X-ray Polarization in the Intermediate State of GS 1354-64

We report the discovery of significant X-ray polarization from the dynamically confirmed black hole X-ray binary (BHXB) GS 1354-64 during its 2025-2026 outburst, obtained with the Imaging X-ray Polarimetry Explorer (IXPE). The observation, obtained shortly after a bright X-ray flare, captures the source in an intermediate state following a stalled (failed) state transition. We discover significant 2-8 keV polarization at the ~4% level with high statistical support--14-sigma significance from frequentist analysis and log Bayes Factor 283+/-1 in a Bayesian framework--measuring PD 4.0+/-0.2% and PA-1+/-2 degrees (90% credible interval). The PD exhibits a statistically significant increasing trend with energy--the strongest such increase yet observed by IXPE in a BHXB--going from 2.1+/-0.3% in the 2-3 keV band to 11+/-3% in the 6.5-7 keV band, while the PA appears stable across both energy and time to within statistical uncertainties. Timing analysis of the IXPE data reveals a ~5 Hz Type-C quasi-periodic oscillation. IXPE + NuSTAR spectropolarimetric modeling suggests that the data can be described by polarized thermal disk and Comptonized components with PAs differing by ~90 degrees, or by a dominant Comptonized polarized component whose effective PD increases across the IXPE bandpass--the inferred component-level polarization levels are therefore model-dependent. In either picture, GS 1354-64 retains a strong coronal component during the transitional period observed by IXPE. These results illustrate how X-ray polarimetry can provide a sensitive diagnostic of the accretion state and geometry in black hole X-ray binary accretion flows, exploring a liminal phase at the cusp of state transition.

astro-ph.HE↗

arXiv2025

X-ray linear polarization prediction in Black-Hole binaries and Active Galactic Nuclei and its measurements by IXPE

We present a theoretical framework for the formation of X-ray linear polarization in black hole (BH) source. The X-ray linear polarization originates from up-scatterings of initially soft photons within a hot, optically thick Compton cloud (CC) characterized by a flat geometry. The IXPE observations of several BHs X-ray binaries and of one Seyfert-1 galaxy confirm our theoretical prediction regarding values of the linear polarization P. The goal of this paper is to demonstrate that the main physical parameters of these Galactic and extragalactic sources can be derived without any free parameter using the polarization and X-ray spectral measurements. We estimate the CC optical depth, τ0 for all BHs observed by IXPE, using the plot of P vs μ = cos i, where i is an observer inclination with respect to the normal, and considering the values P for a given source. Using X ray spectral analysis, we obtain the photon index Γ and, analytically determined the CC plasma temperature kBTe. Different BHs (Cyg X 1, 4U 1630 47, LMC X 1, 4U 1957+115, Swift J1727.8 1613, GX 339 4) and the Seyfert 1 NGC 4151 exhibited polarization between 1 and 8 percent level nearly independently of energy. kBTe is in the range between 5 and 90 keV with a smaller value in High/Soft State with respect to Low/Hard State. We find a similarity between the physical parameter and the IXPE findings and we provide evidence suggesting that the CC exhibits a flat geometry.

astro-ph.HE↗

arXiv2024

Tracking the X-ray Polarization of the Black Hole Transient Swift J1727.8-1613 during a State Transition

We report on an observational campaign on the bright black hole X-ray binary Swift J1727.8$-$1613 centered around five observations by the Imaging X-ray Polarimetry Explorer (IXPE). These observations track for the first time the evolution of the X-ray polarization of a black hole X-ray binary across a hard to soft state transition. The 2--8 keV polarization degree decreased from $\sim$4\% to $\sim$3\% across the five observations, but the polarization angle remained oriented in the North-South direction throughout. Based on observations with the Australia Telescope Compact Array (ATCA), we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher spatial resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long ($\gtrsim$10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR (NICER) are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8$-$1613 is a member of a hitherto under-sampled sub-population.

astro-ph.HE↗

arXiv2023

X-ray Polarization of the Eastern Lobe of SS 433

How astrophysical systems translate the kinetic energy of bulk motion into the acceleration of particles to very high energies is a pressing question. SS 433 is a microquasar that emits TeV gamma-rays indicating the presence of high-energy particles. A region of hard X-ray emission in the eastern lobe of SS 433 was recently identified as an acceleration site. We observed this region with the Imaging X-ray Polarimetry Explorer and measured a polarization degree in the range 38% to 77%. The high polarization degree indicates the magnetic field has a well ordered component if the X-rays are due to synchrotron emission. The polarization angle is in the range -12 to +10 degrees (east of north) which indicates that the magnetic field is parallel to the jet. Magnetic fields parallel to the bulk flow have also been found in supernova remnants and the jets of powerful radio galaxies. This may be caused by interaction of the flow with the ambient medium.

astro-ph.HE↗

arXiv2023

The first X-ray polarimetric observation of the black hole binary LMC X-1

We report on an X-ray polarimetric observation of the high-mass X-ray binary LMC X-1 in the high/soft state, obtained by the Imaging X-ray Polarimetry Explorer (IXPE) in October 2022. The measured polarization is below the minimum detectable polarization of 1.1 per cent (at the 99 per cent confidence level). Simultaneously, the source was observed with the NICER, NuSTAR and SRG/ART-XC instruments, which enabled spectral decomposition into a dominant thermal component and a Comptonized one. The low 2-8 keV polarization of the source did not allow for strong constraints on the black-hole spin and inclination of the accretion disc. However, if the orbital inclination of about 36 degrees is assumed, then the upper limit is consistent with predictions for pure thermal emission from geometrically thin and optically thick discs. Assuming the polarization degree of the Comptonization component to be 0, 4, or 10 per cent, and oriented perpendicular to the polarization of the disc emission (in turn assumed to be perpendicular to the large scale ionization cone orientation detected in the optical band), an upper limit to the polarization of the disc emission of 1.0, 0.9 or 0.9 per cent, respectively, is found (at the 99 per cent confidence level).

astro-ph.HE↗

arXiv2023

Discovery of X-ray Polarization from the Black Hole Transient Swift J1727.8-1613

We report the first detection of the X-ray polarization of the bright transient Swift J1727.8-1613 with the Imaging X-ray Polarimetry Explorer. The observation was performed at the beginning of the 2023 discovery outburst, when the source resided in the bright hard state. We find a time- and energy-averaged polarization degree of 4.1%+/-0.2% and a polarization angle of 2.2+/-1.3 degrees (errors at 68% confidence level; this translates to about 20-sigma significance of the polarization detection). This finding suggests that the hot corona emitting the bulk of the detected X-rays is elongated, rather than spherical. The X-ray polarization angle is consistent with that found in sub-mm wavelengths. Since the sub-mm polarization was found to be aligned with the jet direction in other X-ray binaries, this indicates that the corona is elongated orthogonal to the jet.

astro-ph.HE↗

arXiv2023

X-ray Polarimetry as a Tool to Measure the Black Hole Spin in Microquasars: Simulations of IXPE Capabilities

Measurements of the angular momentum (spin) of astrophysical black holes are extremely important, as they provide information on the black hole formation and evolution. We present simulated observations of a X-ray binary system with the Imaging X-ray Polarimetry Explorer (IXPE), with the aim to study the robustness of black hole spin and geometry measurements using X-ray polarimetry. As a representative example, we used the parameters of GRS 1915+105 in its former unobscured, soft state. In order to simulate the polarization properties, we modeled the source emission with a multicolor blackbody accounting for thermal radiation from the accretion disk, including returning radiation. Our analysis shows that the polarimetric observations in the X-ray waveband will be able to estimate both spin and inclination of the system with a good precision (without returning radiation we obtained for the lowest spin $Δa \leq 0.4$ (0.4/0.998 $\sim$ 40%) for spin and $Δi \leq 30^\circ$ (30$^\circ$/70$^\circ$ $\sim$ 43%) for inclination, while for the higher spin values we obtained $Δa \leq 0.12$ ($\sim$ 12%) for spin and $Δi \leq 20^\circ$ ($ \sim $ 29%) for inclination, within 1$ σ$ errors). When focusing on the case of returning radiation and treating inclination as a known parameter, we were able to successfully reconstruct spin and disk albedo in $Δa \leq 0.15$ ($\sim$ 15%) interval and $Δ$ albedo $\leq 0.45$ (45%) intervals within 1$ σ$ errors. We conclude that X-ray polarimetry will be a useful tool to constrain black hole spins, in addition to timing and spectral-fitting methods.

astro-ph.HE↗

arXiv2022

Polarization properties of the weakly magnetized neutron star X-ray binary GS 1826-238 in the high soft state

The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826-238, performed on 2022 March 29-31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2-8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broad-band spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826-238.

astro-ph.HE↗

arXiv2018

Physics and astrophysics of strong magnetic field systems with eXTP

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies of strongly magnetized objects. We will focus on the physics and astrophysics of strongly magnetized objects, namely magnetars, accreting X-ray pulsars, and rotation powered pulsars. We also discuss the science potential of eXTP for QED studies. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.

astro-ph.HE↗