The Imaging X-ray Polarimetry Explorer (IXPE) measured with high significance the X-ray polarization of the brightest Z-source Scorpius X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0(0.2)% and a polarization angle of 8(6){\deg} at 90% of confidence level. This observation was strictly simultaneous with observations performed by NICER, NuSTAR, and Insight-HXMT, which allowed for a precise characterization of its broad-band spectrum from soft to hard X-rays. The source has been observed mainly in its soft state, with short periods of flaring. We also observed low-frequency quasi-periodic oscillations. From a spectro-polarimetric analysis, we associate a polarization to the accretion disk at <3.2% at 90% of confidence level, compatible with expectations for an electron-scattering dominated optically thick atmosphere at the Sco X-1 inclination of 44{\deg}; for the higher-energy Comptonized component, we obtain a polarization of 1.3(0.4)%, in agreement with expectations for a slab of Thomson optical depth of ~7 and an electron temperature of ~3 keV. A polarization rotation with respect to previous observations by OSO-8 and PolarLight, and also with respect to the radio-jet position angle, is observed. This result may indicate a variation of the polarization with the source state that can be related to relativistic precession or to a change in the corona geometry with the accretion flow.

Position angle

Thomson scattering

10.48550/arxiv.2311.06359

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RECENT RESULTS ON THE SEARCH FOR 2β DECAY PROCESSES WITH SCINTILLATORS AND PURE SAMPLES

R. Bernabei P. Belli S. d’Angelo Alessandro Di Marco F. Cappella

10.1142/9789814663618_0056

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Magnetic Structures and Turbulence in SN 1006 Revealed with Imaging X-Ray Polarimetry

The Astrophysical Journal (2023)

Ping Zhou Dmitry Prokhorov Riccardo Ferrazzoli Yi-Jung Yang Patrick Slane

Abstract Young supernova remnants strongly modify the surrounding magnetic fields, which in turn play an essential role in accelerating cosmic rays (CRs). The X-ray polarization measurements probe magnetic field morphology and turbulence at the immediate acceleration site. We report the X-ray polarization distribution in the northeastern shell of SN 1006 from a 1 Ms observation with the Imaging X-ray Polarimetry Explorer. We found an average polarization degree of 22.4% ± 3.5% and an average polarization angle of −45.°4 ± 4.°5 (measured on the plane of the sky from north to east). The X-ray polarization angle distribution reveals that the magnetic fields immediately behind the shock in the northeastern shell of SN 1006 are nearly parallel to the shock normal or radially distributed, similar to that in the radio observations, and consistent with the quasi-parallel CR acceleration scenario. The X-ray emission is marginally more polarized than that in the radio band. The X-ray polarization degree of SN 1006 is much larger than that in Cas A and Tycho, together with the relatively tenuous and smooth ambient medium of the remnant, favoring that CR-induced instabilities set the magnetic turbulence in SN 1006, and CR acceleration is environment-dependent.

Degree of polarization

10.3847/1538-4357/acf3e6

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Studying geometry of the ultraluminous X-ray pulsar Swift J0243.6+6124 using X-ray and optical polarimetry

Astronomy and Astrophysics (2024)

Juri Poutanen Sergey S. Tsygankov Victor Doroshenko Sofia V. Forsblom Peter Jenke

Discovery of pulsations from a number of ultra-luminous X-ray (ULX) sources proved that accretion onto neutron stars can produce luminosities exceeding the Eddington limit by several orders of magnitude. The conditions necessary to achieve such high luminosities as well as the exact geometry of the accretion flow in the neutron star vicinity are, however, a matter of debate. The pulse phase-resolved polarization measurements that became possible with the launch of the Imaging X-ray Polarimetry Explorer (IXPE) can be used to determine the pulsar geometry and its orientation relative to the orbital plane. They provide an avenue to test different theoretical models of ULX pulsars. In this paper we present the results of three IXPE observations of the first Galactic ULX pulsar Swift J0243.6+6124 during its 2023 outburst. We find strong variations in the polarization characteristics with the pulsar phase. The average polarization degree increases from about 5% to 15% as the flux dropped by a factor of three in the course of the outburst. The polarization angle (PA) as a function of the pulsar phase shows two peaks in the first two observations, but changes to a characteristic sawtooth pattern in the remaining data set. This is not consistent with a simple rotating vector model. Assuming the existence of an additional constant polarized component, we were able to fit the three observations with a common rotating vector model and obtain constraints on the pulsar geometry. In particular, we find the pulsar angular momentum inclination with respect to the line of sight of i p = 15°–40°, the magnetic obliquity of θ p = 60°–80°, and the pulsar spin position angle of χ p ≈ −50°, which significantly differs from the constant component PA of about 10°. Combining these X-ray measurements with the optical PA, we find evidence for at least a 30° misalignment between the pulsar angular momentum and the binary orbital axis.

Swift

10.1051/0004-6361/202450696

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A few final comments to arXiv:1210.7548[hep-ph]

arXiv (Cornell University) (2012)

R. Bernabei P. Belli F. Cappella V. Caracciolo R. Cerulli

A few final comments on arXiv:1210.7548 are given to confute incorrect arguments claimed there.

10.48550/arxiv.1211.6346

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Investigating Earth shadowing effect with DAMA/LIBRA-phase1

The European Physical Journal C (2015)

R. Bernabei P. Belli S. d’Angelo Alessandro Di Marco F. Montecchia

In the present paper the results obtained in the investigation of possible diurnal effects for low-energy single-hit scintillation events of DAMA/LIBRA-phase1 (1.04 ton $$\times $$ year exposure) have been analysed in terms of an effect expected in case of dark matter (DM) candidates inducing nuclear recoils and having high cross-section with ordinary matter, which implies low DM local density in order to fulfill the DAMA/LIBRA DM annual modulation results. This effect is due to the different Earth depths crossed by those DM candidates during the sidereal day.

Sidereal time

10.1140/epjc/s10052-015-3473-y

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X-Ray Polarization of BL Lacertae in Outburst

The Astrophysical Journal Letters (2023)

Abel L. Peirson Michela Negro Ioannis Liodakis R. Middei Dawoon E. Kim

Abstract We report the first >99% confidence detection of X-ray polarization in BL Lacertae. During a recent X-ray/ γ -ray outburst, a 287 ks observation (2022 November 27–30) was taken using the Imaging X-ray Polarimetry Explorer (IXPE), together with contemporaneous multiwavelength observations from the Neil Gehrels Swift observatory and XMM-Newton in soft X-rays (0.3–10 keV), NuSTAR in hard X-rays (3–70 keV), and optical polarization from the Calar Alto and Perkins Telescope observatories. Our contemporaneous X-ray data suggest that the IXPE energy band is at the crossover between the low- and high-frequency blazar emission humps. The source displays significant variability during the observation, and we measure polarization in three separate time bins. Contemporaneous X-ray spectra allow us to determine the relative contribution from each emission hump. We find >99% confidence X-ray polarization Π 2 – 4 keV = 21.7 − 7.9 + 5.6 % and electric vector polarization angle ψ 2–4keV = −28.°7 ± 8.°7 in the time bin with highest estimated synchrotron flux contribution. We discuss possible implications of our observations, including previous IXPE BL Lacertae pointings, tentatively concluding that synchrotron self-Compton emission dominates over hadronic emission processes during the observed epochs.

10.3847/2041-8213/acd242

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X-ray Polarization Observations of BL Lacertae

arXiv (Cornell University) (2022)

R. Middei Ioannis Liodakis M. Perri Simonetta Puccetti E. Cavazzuti

Blazars are a class of jet-dominated active galactic nuclei with a typical double-humped spectral energy distribution. It is of common consensus the Synchrotron emission to be responsible for the low frequency peak, while the origin of the high frequency hump is still debated. The analysis of X-rays and their polarization can provide a valuable tool to understand the physical mechanisms responsible for the origin of high-energy emission of blazars. We report the first observations of BL Lacertae performed with the Imaging X-ray Polarimetry Explorer ({IXPE}), from which an upper limit to the polarization degree $Π_X<$12.6\% was found in the 2-8 keV band. We contemporaneously measured the polarization in radio, infrared, and optical wavelengths. Our multiwavelength polarization analysis disfavors a significant contribution of proton synchrotron radiation to the X-ray emission at these epochs. Instead, it supports a leptonic origin for the X-ray emission in BL Lac.

BL Lac object

Spectral energy distribution

Degree of polarization

10.48550/arxiv.2211.13764

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Discovery of polarized X-ray emission from the accreting millisecond pulsar SRGA J144459.2-604207

Astronomy and Astrophysics (2025)

Alessandro Papitto Alessandro Di Marco Juri Poutanen Tuomo Salmi Giulia Illiano

We report the discovery of polarized X-ray emission from an accreting millisecond pulsar. During a 10-day-long coverage of the February 2024 outburst of srga the Imaging X-ray Polarimetry Explorer ( detected an average polarization degree of the 2--8 keV emission of $2.3% ± 0.4%$ at an angle of $59 (east of north; the uncertainties quoted are at the 1σ confidence level). The polarized signal shows a significant energy dependence with a degree of $4.0%±0.5%$ between 3 and 6 keV and $ <1.5%$ (90% c.l.) in the 2--3 keV range. We used and observations to obtain an accurate pulse-timing solution and to perform a phase-resolved polarimetric analysis of ixpe data. We did not detect any significant variability in the Stokes parameters Q and U with the spin and orbital phases. We used the relativistic rotating-vector model to show that a moderately fan-beam emission from two point-like spots at low magnetic obliquity (≃ 10 is compatible with the observed pulse profile and polarization properties. ixpe also detected 52 type I X-ray bursts whose recurrence time Δ t_ rec increased from 2 to 8 h as a function of the observed count rate C as Δ t_ rec ∝ C^ . We stacked the emission observed during all the bursts and obtained an upper limit on the polarization degree of $8.5$% (90% c.l.).

Millisecond

Degree of polarization

Stokes parameters

10.1051/0004-6361/202451775

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

The Astrophysical Journal (2024)

Adam Ingram Niek Bollemeijer Alexandra Veledina Michal Dovčiak Juri Poutanen

Abstract We report on an observational campaign on the bright black hole (BH) X-ray binary Swift J1727.8–1613 centered around five observations by the Imaging X-ray Polarimetry Explorer. These observations track for the first time the evolution of the X-ray polarization of a BH X-ray binary across a hard to soft state transition. The 2–8 keV polarization degree decreased from ∼4% to ∼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, 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 (≳10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR 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 undersampled subpopulation.

Black hole (networking)

10.3847/1538-4357/ad3faf

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Citations (17)