We present an analysis of the time-averaged spectrum of the Seyfert-2 active galaxy NGC 4388, obtained by NICER. The intrinsic strength of the reflection spectrum in NGC 4388, the large collecting ...area and favorable passband of NICER, and a net exposure of 105.6 ks yielded an exceptionally sensitive spectrum. Using two independent families of models, the intrinsic spectrum from the central engine is found to be highly obscured but not Compton-thick. Enforcing physical self-consistency within each model, the independent treatments give formally consistent results: or . Past measurements made with Suzaku and XMM-Newton are in broad agreement with these column density values. A more recent measurement with NuSTAR (in late 2013) recorded a column density about twice as large; the robustness of this variability is reinforced by the use of consistent models and procedures. The neutral Fe K line in the NICER spectrum is nominally resolved and consistent with an origin in the optical broad-line region). The data also require ionized absorption in the Fe K band, similar to the "warm absorbers" detected in Seyfert-1 active galactic nuclei. The low-energy spectrum is consistent with a set of ionized plasma components. We discuss these findings and note that the geometric inferences that derive from this analysis can be tested with XRISM and Athena.
Type-1 radio-quiet active galactic nuclei (AGN) are seen from the polar direction and offer a direct view of their central X-ray engine. If most of X-ray photons have traveled from the primary source ...to the observer with minimum light-matter interaction, a fraction of radiation is emitted at different directions and is reprocessed by the parsec-scale equatorial circumnuclear region or the polar outflows. It is still unclear how much the polarization expected from type-1 AGN is affected by radiation that have scattered on the distant AGN components. In this paper, we examine the contribution of remote material onto the polarized X-ray spectrum of type-1 Seyfert galaxies using radiative transfer Monte Carlo codes. We find that the observed X-ray polarization strongly depends on the initial polarization emerging from the disk-corona system. For unpolarized and parallelly polarized photons (parallel to the disk), the contribution is negligible below 3 keV and tends to increase the polarization degree by up to one percentage points at higher energies, smoothing out the energy-dependent variations of the polarization angle. For perpendicularly polarized corona photons, the addition of the circumnuclear scattered (parallel) component adds to the polarization above 10 keV, decreases polarization below 10 keV and shifts the expected 90 deg rotation of the polarization angle to lower energies. In conclusion, we found that simulations of Seyfert-1s that do not account for reprocessing on the parsec-scale equatorial and polar material are under- or over-estimating the X-ray polarization by 0.1 - 1 percentage points.
SMSS\,J114447.77-430859.3 (\(z=0.83\)) has been identified in the SkyMapper Southern Survey as the most luminous quasar in the last \(\sim 9\,\rm Gyr\). In this paper, we report on the ...eROSITA/Spectrum-Roentgen-Gamma (SRG) observations of the source from the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and NuSTAR. The source shows a clear variability by factors of \(\sim 10\) and \(\sim 2.7\) over timescales of a year and of a few days, respectively. When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a \(\Gamma=2.2 \pm 0.2\) and \(E_{\rm cut}=23^{+26}_{-5}\,\rm keV\). Assuming Comptonisation, we estimate a coronal optical depth and electron temperature of \(\tau=2.5-5.3\, (5.2-8)\) and \(kT=8-18\, (7.5-14)\,\rm keV\), respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile. The former model results in a black hole mass estimate of the order of \(10^{10}\,M_\odot\), slightly higher than prior optical estimates; meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning black hole, and a compact (\(\sim 10\,r_{\rm g}\)) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of magnitude over the period of \(\sim 900\,\rm days\).
X-ray reflection is a very powerful method to assess the spin of supermassive black holes (SMBHs) in active galactic nuclei (AGN), yet this technique is not universally accepted. Indeed, complex ...reprocessing (absorption, scattering) of the intrinsic spectra along the line of sight can mimic the relativistic effects on which the spin measure is based. In this work, we test the reliability of SMBH spin measurements that can currently be achieved through the simulations of high-quality XMM-Newton and NuSTAR spectra. Each member of our group simulated ten spectra with multiple components that are typically seen in AGN, such as warm and (partial-covering) neutral absorbers, relativistic and distant reflection, and thermal emission. The resulting spectra were blindly analysed by the other two members. Out of the 60 fits, 42 turn out to be physically accurate when compared to the input model. The SMBH spin is retrieved with success in 31 cases, some of which (9) are even found among formally inaccurate fits (although with looser constraints). We show that, at the high signal-to-noise ratio assumed in our simulations, neither the complexity of the multi-layer, partial-covering absorber nor the input value of the spin are the major drivers of our results. The height of the X-ray source (in a lamp-post geometry) instead plays a crucial role in recovering the spin. In particular, a success rate of 16 out of 16 is found among the accurate fits for a dimensionless spin parameter larger than 0.8 and a lamp-post height lower than five gravitational radii.
•Nine Citrus sinensis leaves cultivars in Egypt were analyzed via GC–MS.•47 metabolites were identified by GC–MS.•Monoterpenes hydrocarbons represented the main class in the essential oils.•PCA and ...HCA displayed successful discrimination between different cultivars.•All essential oils showed promising cytotoxic activity by MTT assay.
Citrus sinensis L. Osbeck, (family Rutaceae), known as sweet orange, is a fruit-bearing shrub that widely cultivated all over the world due to its nutritive value, nutraceutical attributes and economic importance. In the present study, a comparative metabolic profile study of the essential oils of the leaves of nine cultivars of Citrus sinensis cultivated in Egypt was carried out based on GC–MS analysis coupled to chemometrics. A total of 47 compounds were identified, where monoterpenes hydrocarbons (61.39 %–78.26 %) represented the main recognized class in the essential oils. Sabinene (8.25 %–28.81 %), 2-carene (11.25 %–16.72 %) and cis-β-ocimene (10.22 %–13.93 %) were the major components identified in different cultivars. Chemometric analyses comprising Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were experienced for their ability to discriminate between closely related cultivars. Both PCA score plot and HCA dendrogram could successfully segregate different cultivars based on their metabolic profiles. The MTT assay was used to evaluate the cytotoxicity of essential oils of Citrus sinensis leaves cultivars on different cell lines; MCF-7, HepG-2, HeLa, were all essential oils showed moderate cytotoxic activity. The MCF-7 cell lines were the most resistant cells with IC50 range from 243 to 343 μg/mL, while HeLa cells were the most sensitive cell lines IC50 range from 203 to 283 μg/mL. This may be attributed to the synergistic effects of different chemical components.
The UV/optical variations in many AGN are very well correlated, showing delays which increase with increasing wavelength. It is thought that this is due to thermal reprocessing of the X-ray emission ...by the accretion disk. In this scenario, the variable X-ray flux from the corona illuminates the accretion disk where it is partially reflected, and partially absorbed and thermalized in the disk producing a UV/optical reverberation signal. This will lead to a time lag increasing with wavelength. However, although the shape of the observed time-lags as a function of wavelength is consistent with the model predictions, their amplitude suggested a disk which is significantly hotter than expected. In this work, we estimate the response functions and the corresponding time lags assuming a standard Novikov-Thorne accretion disk illuminated by a point-like X-ray source. We take into account all relativistic effects in the light propagation from the X-ray source to the disk then to the observer. We also compute the disk reflection, accounting for its ionization profile. Our results show that thermal reverberation effects are stronger in sources with large X-ray source height and low accretion rate. We also found that the time lags increase with height and accretion rate. We apply our model to NGC 5548 and we show that the observed lags in this source can be explained by the model, for a source height of \(\sim 60 ~\rm r_g\) and an accretion rate of a few percent of the Eddington limit for a maximally-spinning black hole.
Active galactic nuclei (AGNs) are known to be variable across all wavelengths. Significant observational efforts have been invested in the last decade in studying their ultraviolet (UV) and optical ...variability. Long and densely sampled, multi-wavelength monitoring campaigns of numerous Seyfert galaxies have been conducted with the aim of determining the X-ray/UV/optical continuum time lags. Time-lag studies can be used to constrain theoretical models. The observed time lags can be explained by thermal reprocessing of the X-rays illuminating the accretion disc (known as the X-ray reverberation model). However, the observed light curves contain more information that can be used to further constrain physical models. Our primary objective is to investigate whether, in addition to time lags, the X-ray reverberation model can also explain the UV/optical variability amplitude of nearby Seyferts. We measured the excess variance of four sources (namely Mrk\,509, NGC\,4151, NGC\,2617, and Mrk\,142) as a function of wavelength using data from archival long, multi-wavelength campaigns with and ground-based telescopes. We also computed the model excess variance in the case of the X-ray reverberation model by determining the disc's transfer function and assuming a bending power law for the X-ray power spectrum. We tested the validity of the model by comparing the measured and model variances for a range of accretion rates and X-ray source heights. Our main result is that the X-ray thermal reverberation model can fit both the continuum, UV/optical time lags, as well as the variance (i.e. the variability amplitude) in these AGNs, for the same physical parameters. Our results suggest that the accretion disc is constant and that all the observed UV/optical variations, on timescales of days and up to a few weeks, can be fully explained by the variable X-rays as they illuminate the accretion disc.
The assessment of nitrate pollution origin using stable isotope techniques is a fundamental prerequisite for the application of sustainable groundwater management plans. Although nitrate pollution is ...a worldwide groundwater quality problem, existing knowledge on the origin of nitrate pollution in arid and semi-arid regions is still scarce. Using the example of the Grombalia aquifer (NE Tunisia), this work summarizes the main strengths and constraints of multi-isotope techniques targeting at nitrate source identification and apportionment The results highlighted that, even in the case of well-established methodologies, like those of isotope hydrogeochemistry (δ15NNO3, δ 18ONO3 and δ 11B) and mixing modelling for source apportionment, it is fundamental to take into account regional and local end-members to avoid biased data interpretation and to fully exploit the potential of such accurate tools.
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•Current knowledge of nitrate pollution origin in (semi)arid regions is still scarce.•New frontiers for nitrate source apportionment in (semi)arid regions are discussed.•δ15N/δ11B systematics: not effective for groundwater with high B natural background.•SIAR outcomes are highly dependent on the values attributed to the sources.•Unbiased source apportionment is fundamental to support groundwater management.
Sameh Msaad,1 Nouha Ketata,2 Nesrine Kammoun,3 Rahma Gargouri,1 Rim Khemekhem,1 Sourour Abid,1 Saeb Bader,1 Sabrine Efidha,4 Narjes Abid,5 Jamel EL Ghoul,6 Imen Sahnoun,4 Hazem Altalaa,1 Jihene ...Jdidi,2 Mohamed Jlidi,7 Nadia Keskes Boudaouara,8 Imen Gargouri,9 Najla Bahloul,1 Samy Kammoun1 1Department of Respiratory and Sleep Medicine, Hedi Chaker University Hospital of Sfax, Faculty of Medicine of Sfax, University of Sfax, Sfax, Tunisia; 2Department of Preventive Medicine, Hedi Chaker University Hospital of Sfax, Faculty of Medicine of Sfax, University of Sfax, Sfax, Tunisia; 3Tunisian Occupational Health and Safety Institute, Faculty of Medicine of Tunis, University of Tunis El Manar, Tunis, Tunisia; 4Department of Pneumology, Abderrahman Mami University Hospital of Ariana, Faculty of Medicine of Tunis, University of Tunis El Manar, Tunis, Tunisia; 5Department of Pneumology, Mohamed Taher Maamouri University Hospital of Nabeul, Faculty of Medicine of Tunis, University of Tunis El Manar, Tunis, Tunisia; 6Department of Pneumology, Habib Bourguiba University Hospital of Mednine, Faculty of Medicine of Sfax, University of Sfax, Sfax, Tunisia; 7Orthopedics and Traumatology Department, Mohamed Taher Maâmouri University Hospital of Nabeul, Faculty of Medicine of Tunis, University of Tunis EL Manar, Tunis, Tunisia; 8Department of Pneumology, Taher Sfar University Hospital of Mahdia, Faculty of Medicine of Monastir, University of Monastir, Monastir, Tunisia; 9Department of Pneumology, Farhat Hached University Hospital of Sousse, Faculty of Medicine of Sousse, University of Sousse, Sousse, TunisiaCorrespondence: Sameh Msaad, Email pneumo1972@gmail.com
Context. Over recent decades, astronomy has entered the era of massive data and real-time surveys. This is improving the study of transient objects – although they still contain some of the most ...poorly understood phenomena in astrophysics, as it is inherently more difficult to obtain data to constrain the proposed models. Aims. In order to help detect these objects in their brightest state and build synergies with multi-wavelength real-time surveys, we have built a quasi-real time automatic transient detection system for the XMM-Newton pipeline: the Search for Transient Objects in New detections using Known Sources (STONKS) pipeline. Methods. STONKS detects long-term X-ray transient events by automatically comparing new XMM-Newton detections to any available archival X-ray data at this position, sending out an alert if the variability between observations (defined as the ratio between the maximum flux and the minimum flux or upper limit) is over 5. This required an initial careful cross-correlation and flux calibration of various X-ray catalogs from different observatories ( XMM-Newton, Chandra, Swift , ROSAT, and eROSITA). A Bayesian framework was put into place to solve any ambiguous associations. We also systematically computed the XMM-Newton upper limits at the position of any X-ray source covered by the XMM-Newton observational footprint, even without any XMM-Newton counterpart. The behavior of STONKS was then tested on all 483 observations performed with imaging mode in 2021. Results. Over the 2021 testing run, STONKS provided a daily alert rate of 0.7 −0.5 +0.7 alerts per day, about 80% of them corresponding to serendipitous sources. Among the detected variable serendipitous sources, there are: several highly variable active galactic nuclei (AGNs) and flaring stars, as well as new X-ray binary and ultra-luminous X-ray source candidates, some of which are present here. STONKS also detected targeted tidal disruption events, ensuring its ability to detect other serendipitous events. As a byproduct of our method, the archival multi-instrument catalog contains about one million X-ray sources, with 15% of them involving several catalogs and 60% of them having XMM-Newton (pointed or slew) upper limits. Conclusions. STONKS demonstrates a great potential for revealing future serendipitous transient X-ray sources, providing the community with the ability to follow-up on these objects a few days after their detection with the goal of obtaining a better understanding of their nature. The underlying multi-instrument archival X-ray catalog will be made available to the community and kept up to date with future X-ray data releases.
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