Phlebotomine sand fly survey in the focus of leishmaniasis in Madrid, Spain (2012-2014): seasonal dynamics, Leishmania infantum infection rates and blood meal preferences

BACKGROUND: An unusual increase of human leishmaniasis cases due to Leishmania infantum is occurring in an urban area of southwestern Madrid, Spain, since 2010. Entomological surveys have shown that Phlebotomus perniciosus is the only potential vector. Direct xenodiagnosis in hares (Lepus granatensis) and rabbits (Oryctolagus cuniculus) collected in the focus area proved that they can transmit parasites to colonized P. perniciosus. Isolates were characterized as L. infantum. The aim of the present work was to conduct a comprehensive study of sand flies in the outbreak area, with special emphasis on P. perniciosus. METHODS: Entomological surveys were done from June to October 2012-2014 in 4 stations located close to the affected area. Twenty sticky traps (ST) and two CDC light traps (LT) were monthly placed during two consecutive days in every station. LT were replaced every morning. Sand fly infection rates were determined by dissecting females collected with LT. Molecular procedures applied to study blood meal preferences and to detect L. infantum were performed for a better understanding of the epidemiology of the outbreak. RESULTS: A total of 45,127 specimens belonging to 4 sand fly species were collected: P. perniciosus (75.34%), Sergentomyia minuta (24.65%), Phlebotomus sergenti (0.005%) and Phlebotomus papatasi (0.005%). No Phlebotomus ariasi were captured. From 3203 P. perniciosus female dissected, 117 were infected with flagellates (3.7%). Furthermore, 13.31% and 7.78% of blood-fed and unfed female sand flies, respectively, were found infected with L. infantum by PCR. The highest rates of infected P. perniciosus were detected at the end of the transmission periods. Regarding to blood meal preferences, hares and rabbits were preferred, although human, cat and dog blood were also found. CONCLUSIONS: This entomological study highlights the exceptional nature of the Leishmania outbreak occurring in southwestern Madrid, Spain. It is confirmed that P. perniciosus is the only vector in the affected area, with high densities and infection rates. Rabbits and hares were the main blood meal sources of this species. These results reinforce the need for an extensive and permanent surveillance in this region, and others of similar characteristics, in order to control the vector and regulate the populations of wild reservoirs.This study was partially sponsored and funded by: Dirección General de Salud Pública, Consejería de Sanidad, Comunidad de Madrid; Colegio de Veterinarios de Madrid; Colegio de Biólogos de Madrid and EU grant FP7-261504 EDENext (http://www.edenext.eu).S

Complex variations in X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431

We report on Imaging X-ray polarimetry explorer (IXPE) observations of the Be-transient X-ray pulsar LS V +44 17/RX J0440.9+4431 made at two luminosity levels during the giant outburst in January- February 2023. Considering the observed spectral variability and changes in the pulse profiles, the source was likely caught in supercritical and subcritical states with significantly different emission-region geometry, associated with the presence of accretion columns and hot spots, respectively. We focus here on the pulse-phase-resolved polarimetric analysis and find that the observed dependencies of the polarization degree and polarization angle (PA) on the pulse phase are indeed drastically different for the two observations. The observed differences, if interpreted within the framework of the rotating vector model (RVM), imply dramatic variations in the spin axis inclination, the position angle, and the magnetic colatitude by tens of degrees within the space of just a few days. We suggest that the apparent changes in the observed PA phase dependence are predominantly related to the presence of an unpulsed polarized component in addition to the polarized radiation associated with the pulsar itself. We then show that the observed PA phase dependence in both observations can be explained with a single set of RVM parameters defining the pulsar s geometry. We also suggest that the additional polarized component is likely produced by scattering of the pulsar radiation in the equatorial disk wind

A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375

Accreting X-ray pulsars (XRPs) are presumed to be ideal targets for polarization measurements, as their high magnetic field strength is expected to polarize the emission up to a polarization degree of 80%. However, such expectations are being challenged by recent observations of XRPs with the Imaging X-ray Polarimeter Explorer (IXPE). Here, we report on the results of yet another XRP, namely, EXO 2030+375, observed with IXPE and contemporarily monitored with Insight-HXMT and SRG/ART-XC. In line with recent results obtained with IXPE for similar sources, an analysis of the EXO 2030+375 data returns a low polarization degree of 0%- 3% in the phase-averaged study and a variation in the range of 2%- 7% in the phase-resolved study. Using the rotating vector model, we constrained the geometry of the system and obtained a value of 60 for the magnetic obliquity. When considering the estimated pulsar inclination of 130, this also indicates that the magnetic axis swings close to the observera's line of sight. Our joint polarimetric, spectral, and timing analyses hint toward a complex accreting geometry, whereby magnetic multipoles with an asymmetric topology and gravitational light bending significantly affect the behavior of the observed source

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 broadband 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

Discovery of strongly variable X-ray polarization in the neutron star low-mass X-ray binary transient XTE J1701-462

CONTEXT: After about 16 years since its first outburst, the transient neutron star low-mass X-ray binary XTE J1701−462 turned on again in September 2022, allowing for the first study of its X-ray polarimetric characteristics by a dedicated observing program with the Imaging X-ray Polarimeter Explorer (IXPE). AIMS: Polarimetric studies of XTE J1701−462 have been expected to improve our understanding of accreting weakly magnetized neutron stars, in particular, the physics and the geometry of the hot inner regions close to the compact object. METHOD: The IXPE data of two triggered observations were analyzed using time-resolved spectroscopic and polarimetric techniques, following the source along its Z-track of the color–color diagram. RESULTS: During the first pointing on 2022 September 29, an average 2–8 keV polarization degree of (4.6 ± 0.4)% was measured, the highest value found up to now for this class of sources. Conversely, only a ∼0.6% average degree was obtained during the second pointing ten days later. CONCLUSIONS: The polarimetric signal appears to be strictly related to the higher energy blackbody component associated with the boundary layer (BL) emission and its reflection from the inner accretion disk, and it is as strong as 6.1% and 1.2% (> 95% significant) above 3–4 keV for the two measurements, respectively. The variable polarimetric signal is apparently related to the spectral characteristics of XTE J1701−462, which is the strongest when the source was in the horizontal branch of its Z-track and the weakest in the normal branch. These IXPE results provide new important observational constraints on the physical models and geometry of the Z-sources. Here, we discuss the possible reasons for the presence of strong and variable polarization among these sources

Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC 4151 with IXPE

We present an X-ray spectropolarimetric 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 per cent and angle Ψ = 86° ± 7° east of north (68 per cent confidence level) are measured in the 2–8 keV energy range. The spectropolarimetric 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 per cent) polarization degree. Assuming more reasonable values, a polarization degree of the hot corona ranging from ∼4 to ∼8 per cent 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 active galactic nucleus with an X-ray polarization measure for the corona, illustrating the capabilities of X-ray polarimetry and IXPE in unveiling its geometry

The X-ray polarization of the Seyfert 1 galaxy IC 4329A

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 polarization in the 2–8 keV band with 2.97σ confidence. We report a polarization degree of 3.3 ± 1.1 per cent and a polarization angle of 78° ± 10° (errors are 1σ confidence). The X-ray polarization 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 spectropolarimetric modelling indicates that the 2–8 keV polarization is consistent with being dominated by emission directly observed from the X-ray corona, but the polarization of the reflection component is completely unconstrained. Our constraints on viewer inclination and polarization degree tentatively favour more asymmetric, possibly out-flowing, coronal geometries that produce more highly polarized emission, but the coronal geometry is unconstrained at the 3σ level

The geometry of the hot corona in MCG-05-23-16 constrained by X-ray polarimetry

We report on the second observation of the radio-quiet active galactic nucleus MCG-05-23-16 performed with the Imaging X-ray Polarimetry Explorer (IXPE). The observation started on 2022 November 6 for a net observing time of 640 ks, and was partly simultaneous with NuSTAR (86 ks). After combining these data with those obtained in the first IXPE pointing on 2022 May (simultaneous with XMM–Newton and NuSTAR) we find a 2–8 keV polarization degree Π = 1.6 ± 0.7 (at 68 per cent confidence level), which corresponds to an upper limit Π = 3.2 per cent (at 99 per cent confidence level). We then compare the polarization results with Monte Carlo simulations obtained with the monk code, with which different coronal geometries have been explored (spherical lamppost, conical, slab, and wedge). Furthermore, the allowed range of inclination angles is found for each geometry. If the best-fitting inclination value from a spectroscopic analysis is considered, a cone-shaped corona along the disc axis is disfavoured

X-ray polarimetry of X-ray pulsar X Persei: another orthogonal rotator?

X Persei is a persistent low-luminosity X-ray pulsar of period of ≈ 835 s in a Be binary system. The field strength at the neutron star surface is not known precisely, but indirect signs indicate a magnetic field above 1013 G, which makes the object one of the most magnetized known X-ray pulsars. Here we present the results of observations X Persei performed with the Imaging X-ray Polarimetry Explorer (IXPE). The X-ray polarization signal was found to be strongly dependent on the spin phase of the pulsar. The energy-averaged polarization degree in 3–8 keV band varied from several to ∼20 per cent over the pulse with a phase dependence resembling the pulse profile. The polarization angle shows significant variation and makes two complete revolutions during the pulse period, resulting in nearly nil pulse-phase averaged polarization. Applying the rotating vector model to the IXPE data we obtain the estimates for the rotation axis inclination and its position angle on the sky, as well as for the magnetic obliquity. The derived inclination is close to the orbital inclination, reported earlier for X Persei. The polarimetric data imply a large angle between the rotation and magnetic dipole axes, which is similar to the result reported recently for the X-ray pulsar GRO J1008−57. After eliminating the effect of polarization angle rotation over the pulsar phase using the best-fitting rotating vector model, the strong dependence of the polarization degree with energy was discovered, with its value increasing from 0 at ∼2 keV to 30per cent at 8 keV