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The paper presents the analysis of optically selected GAMA groups and clusters in the SRG/eROSITA X-ray map of eROSITA Final Equatorial Depth Survey, in the halo mass range 1013−5 × 1014 M⊙ and at z < 0.2. All X-ray detections have a clear GAMA counterpart, but most of the GAMA groups in the halo mass range 1013−1014 M⊙ remain undetected. We compare the X-ray surface brightness profiles of the eROSITA detected groups with the mean stacked profile of the undetected low-mass haloes at fixed halo mass. Overall, we find that the undetected groups exhibit less concentrated X-ray surface brightness, dark matter, and galaxy distributions with respect to the X-ray-detected haloes. The mean gas mass fraction profiles are consistent in the two samples within 1.5σ, indicating that the gas follows the dark matter profile. The low-mass concentration and the magnitude gap indicate that these systems are young. They reside with a higher probability in filaments while X-ray-detected groups favour the nodes of the Cosmic Web. Because of the lower central emission, the undetected systems tend to be X-ray underluminous at fixed halo mass and to lie below the LX − M halo relation. Interestingly, the X-ray-detected systems inhabiting the nodes scatter the less around the relation, while those in filaments tend to lie below it. We do not observe any strong relationship between the system X-ray appearance and the active galactic nucleus (AGN) activity. We cannot exclude the role of the past AGN feedback in affecting the gas distribution over the halo lifetime. However, the data suggests that the observed differences might be related to the halo assembly bias. [ABSTRACT FROM AUTHOR]

We present a study of optically selected dual Active Galactic Nuclei (AGN) with projected separations of 3–97 kpc. Using multiwavelength (MWL) information (optical, X-ray, mid-IR), we characterized the intrinsic nuclear properties of this sample and compared them with those of isolated systems. Among the 124 X-ray-detected AGN candidates, 52 appear in pairs and 72 as single X-ray sources. Through MWL analysis, we confirmed the presence of the AGN in >80 per cent of the detected targets in pairs (42 out of 52). X-ray spectral analysis confirms the trend of increasing AGN luminosity with decreasing separation, suggesting that mergers may have contributed to triggering more luminous AGN. Through X-ray/mid-IR ratio versus X-ray colours, we estimated a fraction of Compton-thin AGN (with 1022 cm−2 < N H < 1024 cm−2) of about 80 per cent, while about 16 per cent are Compton-thick sources (with N H > 1024 cm−2). These fractions of obscured sources are larger than those found in samples of isolated AGN, confirming that pairs of AGN show higher obscuration. This trend is further confirmed by comparing the de-reddened [O  iii ] emission with the observed X-ray luminosity. However, the derived fraction of Compton-thick sources in this sample at the early stages of merging is lower than that reported for late-merging dual-AGN samples. Comparing N H from X-rays with that derived from E (B − V) from narrow-line regions, we found that the absorbing material is likely to be associated with the torus or broad-line regions. We also explored the X-ray detection efficiency of dual-AGN candidates, finding that, when observed properly (at on-axis positions and with long exposures), X-ray data represent a powerful way to confirm and investigate dual-AGN systems. [ABSTRACT FROM AUTHOR]

We present multiwavelength observations of supernova (SN) 2017hcc with the Chandra X-ray telescope and the X-ray telescope onboard Swift (Swift-XRT) in X-ray bands, with the Spitzer and the TripleSpec spectrometer in near-infrared (IR) and mid-IR bands and with the Karl G. Jansky Very Large Array (VLA) for radio bands. The X-ray observations cover a period of 29 to 1310 d, with the first X-ray detection on day 727 with the Chandra. The SN was subsequently detected in the VLA radio bands from day 1000 onwards. While the radio data are sparse, synchrotron-self absorption is clearly ruled out as the radio absorption mechanism. The near- and the mid-IR observations showed that late time IR emission dominates the spectral energy distribution. The early properties of SN 2017hcc are consistent with shock breakout into a dense mass-loss region, with |$\dot{M} \sim 0.1$| M⊙ yr−1 for a decade. At few 100 d, the mass-loss rate declined to ∼0.02 M⊙ yr−1, as determined from the dominant IR luminosity. In addition, radio data also allowed us to calculate a mass-loss rate at around day 1000, which is two orders of magnitude smaller than the mass-loss rate estimates around the bolometric peak. These values indicate that the SN progenitor underwent an enhanced mass-loss event a decade before the explosion. The high ratio of IR to X-ray luminosity is not expected in simple models and is possible evidence for an asymmetric circumstellar region. [ABSTRACT FROM AUTHOR]

Short rise times of fast blue optical transients (FBOTs) require very light ejected envelopes, |$M_{\rm ej} \le 10^{-1} \, \mathrm{M}_\odot$|⁠ , much smaller than of a typical supernova. The detection by Chandra of X-ray emission in AT2020mrf of L X ∼ 1042 erg s−1 after 328 d implies total, overall dominant, X-ray energetics at the gamma-ray burst level of ∼6 × 1049 erg. We further develop a model of Lyutikov and Toonen, whereby FBOTs are the results of a late accretion-induced collapse of the product of double white dwarf (WD) merger between ONeMg WD and another WD. Small ejecta mass, and the rarity of FBOTs, results from the competition between mass-loss from the merger product to the wind, and ashes added to the core, on a time-scale of ∼103–104 yr. FBOTs proper come from central engine-powered radiation-dominated forward shock as it propagates through ejecta. All the photons produced by the central source deep inside the ejecta escape almost simultaneously, producing a short bright event. The high-energy emission is generated at the highly relativistic and highly magnetized termination shock, qualitatively similar to pulsar wind nebulae. The X-ray bump observed in AT2020mrf by SRG /eROSITA, predicted by Lyutikov and Toonen, is coming from the breakout of the engine-powered shock from the ejecta into the preceding wind. The model requires total energetics of just few × 1050 erg, slightly above the observed X-rays. We predict that the system is hydrogen poor. [ABSTRACT FROM AUTHOR]

X-ray emission detection in a galaxy is one of the efficient tools for selecting active galactic nuclei (AGNs). However, many X-ray-selected AGNs are not easily selected as AGNs by their optical emission. These galaxies, so-called optically dull (OD) AGNs, are fascinating since their X-ray emission is bright even though the AGN signature in the optical regime is absent. In a deep multiwavelength survey over 2 deg2 of the Cosmic Evolution Survey (COSMOS) field, we have looked for the OD AGNs using photometric, spectroscopic, and X-ray data. We identified 310 non-broad line sources with optical spectra as AGNs using X-ray selection up to redshift z ∼ 1.5. We inspected the spectra to check for any AGN signature in their optical emission lines: [Ne  v ] forbidden emission line, Mass Excitation diagram (MEx), color excitation diagram (TBT), and excess in [O  ii ] emission line. Finally, we found 48 AGNs that show AGN signatures in the optical spectrum, classified as narrow-line AGN, and 180 AGNs that did not show any AGN signature as the OD AGN sample. Simple explanations of the nature of OD AGNe are a bright host galaxy that dilutes the AGN light or dust materials obscuring the AGN light. We found that the bright host galaxy dilution explains nearly |$70\%$| of our OD AGN sample. At the same time, the dust material obscuration is unlikely to be the main reason. By estimating the Eddington ratio, we also found that 95 out of 180 of our OD AGNs have a lower accretion rate, (λEdd) ≲ 10−2, than the typical AGN value. We expected the lower accretion rate sources that suffer from neither host galaxy dilution nor obscuration to have radiatively inefficient flow (RIAF) in their accretion disk. Finally, nine sources have been identified to be most likely hosts of the RIAF disk. [ABSTRACT FROM AUTHOR]

We examine Chandra observations of the powerful Fanaroff–Riley class II (FR II) radio galaxy Cygnus A for an X-ray counterpart to the radio transient Cygnus A-2 that was first detected in 2011. Observations are performed using the High-Resolution Camera (HRC) instrument in order to spatially resolve Cygnus A-2 and the central active galactic nucleus (AGN) at a separation of  0.′′42. Simulated images are generated of the emission region, and radial profiles for the region of interest are extracted. A comparison between the simulations and observations reveals no X-ray detection of Cygnus A-2 to a 0.5–7.0 keV flux upper limit of |$1.04 \times 10^{-12}\rm \, erg\, cm^{-2}\, s^{-1}$|⁠ , or a rest-frame 2–10 keV luminosity of |$8.6\times 10^{42}\rm \, erg\, s^{-1}$|⁠. We estimate the black hole mass of Cygnus A-2 based on our X-ray flux limit and find it to be consistent with a flaring black hole rather than a steadily accreting source. The HRC observations are additionally compared with archival Advanced CCD Imaging Spectrometer (ACIS) data from 2016 to 2017, and both the overall morphology and the flux limits of the AGN complex agree between the two data sets. This consistency is despite the pile-up effect in ACIS which was previously considered to bias the observed morphology of the AGN. The agreement between the data sets demonstrates the viability of utilizing the archival Chandra data of Cygnus A to analyse its AGN at an unprecedented level of precision. [ABSTRACT FROM AUTHOR]

Neutron stars in low mass X-ray binaries (LMXBs) are hypothesised to emit continuous gravitational waves that may be detectable by ground-based observatories. The torque balance model predicts that a higher accretion rate produces larger-amplitude gravitational waves, hence LMXBs with high X-ray flux are promising targets for gravitational wave searches. The detection of X-ray pulsations would identify the spin frequency of these neutron stars, and thereby improve the sensitivity of continuous gravitational-wave searches by reducing the volume of the search parameter space. We perform a semi-coherent search for pulsations in the two LMXBs Scorpius X-1 (Sco X-1) and Cygnus X-2 (Cyg X-2) using X-ray data from the Rossi X-ray Timing Explorer Proportional Counter Array. We find no clear evidence for pulsations, and obtain upper limits (at 90 per cent confidence) on the fractional pulse amplitude, with the most stringent being 0.034 per cent for Sco X-1 and 0.23 per cent for Cyg X-2. These upper limits improve upon those in previous work by factors of ∼8.2 and ∼1.6, respectively. [ABSTRACT FROM AUTHOR]

Galaxy mergers are predicted to trigger accretion on to the central supermassive black holes, with the highest rates occurring during final coalescence. Previously, we have shown elevated rates of both optical and mid-IR selected active galactic nuclei (AGNs) in post-mergers, but to date the prevalence of X-ray AGNs has not been examined in the same systematic way. We present XMM–Newton data of 43 post-merger galaxies selected from the Sloan Digital Sky Survey along with 430 non-interacting control galaxies matched in stellar mass, redshift, and environment in order to test for an excess of hard X-ray (2–10 keV) emission in post-mergers attributable to triggered AGNs. We find two X-ray detections in the post-mergers (⁠|$4.7^{+9.3}_{-3.8}{{\ \rm per\ cent}}$|⁠) and nine in the controls (⁠|$2.1^{+1.5}_{-1.0}{{\ \rm per\ cent}}$|⁠), an excess of |$2.22^{+4.44}_{-2.22}$|⁠ , where the confidence intervals are 90 per cent. While, we therefore do not find statistically significant evidence for an X-ray AGN excess in post-mergers (p  = 0.26), we find a factor of ∼17 excess of mid-IR AGNs in our sample, consistent with the past work and inconsistent with the observed X-ray excess (p  = 2.7 × 10−4). Dominant, luminous AGNs are therefore more frequent in post-mergers, and the lack of a comparable excess of 2–10 keV X-ray AGNs suggests that AGNs in post-mergers are more likely to be heavily obscured. Our results are consistent with the post-merger stage being characterized by enhanced AGN fueling, heavy AGN obscuration, and more intrinsically luminous AGN, in line with theoretical predictions. [ABSTRACT FROM AUTHOR]

X-ray transients, such as accreting neutron stars, periodically undergo outbursts, thought to be caused by a thermal-viscous instability in the accretion disc. Usually outbursts of accreting neutron stars are identified when the accretion disc has undergone an instability, and the persistent X-ray flux has risen to a threshold detectable by all sky monitors on X-ray space observatories. Here, we present the earliest known combined optical, UV, and X-ray monitoring observations of the outburst onset of an accreting neutron star low-mass X-ray binary (LMXB) system. We observed a significant, continuing increase in the optical i ′-band magnitude starting on July 25, 12 d before the first X-ray detection with Swift /XRT and NICER (August 6), during the onset of the 2019 outburst of SAX J1808.4−3658. We also observed a 4 d optical to X-ray rise delay, and a 2 d UV to X-ray delay, at the onset of the outburst. We present the multiwavelength observations that were obtained, discussing the theory of outbursts in X-ray transients, including the disc instability model, and the implications of the delay. This work is an important confirmation of the delay in optical to X-ray emission during the onset of outbursts in LMXBs, which has only previously been measured with less sensitive all sky monitors. We find observational evidence that the outburst is triggered by ionization of hydrogen in the disc. [ABSTRACT FROM AUTHOR]

We present new X-ray observations of luminous heavily dust-reddened quasars (HRQs) selected from infrared (IR) sky surveys. HRQs appear to be a dominant population at high redshifts and the highest luminosities, and may be associated with a transitional 'blowout' phase of black hole and galaxy co-evolution models. Despite this, their high-energy properties have been poorly known. We use the overall sample of 10 objects with XMM–Newton coverage to study the high-energy properties of HRQs at $\langle$ Lbol $\rangle$  =1047.5 erg s−1 and $\langle$ z $\rangle$  =2.5. For seven sources with strong X-ray detections, we perform spectral analyses. These find a median X-ray luminosity of $\left\langle L_{\rm 2\!-\!10\, keV} \right\rangle = 10^{45.1}$  erg s−1, comparable to the most powerful X-ray quasars known. The gas column densities are NH = (1–8) × 1022 cm−2, in agreement with the amount of dust extinction observed. The dust-to-gas ratios are sub-Galactic, but are higher than found in local AGN. The intrinsic X-ray luminosities of HRQs are weak compared to the mid-IR ($L_{\rm 6\, \mu m}$) and bolometric luminosities (Lbol), in agreement with findings for other luminous quasar samples. For instance, the X-ray to bolometric corrections range from κbol ≈ 50 to 3000. The moderate absorption levels and accretion rates close to the Eddington limit ($\langle$ λEdd $\rangle$  =1.06) are in agreement with a quasar blowout phase. Indeed, we find that the HRQs lie in the forbidden region of the NH–λEdd plane, and therefore that radiation pressure feedback on the dusty interstellar medium may be driving a phase of blowout that has been ongoing for a few 105 yr. The wider properties, including [O iii] narrow-line region kinematics, broadly agree with this interpretation. [ABSTRACT FROM AUTHOR]

Open in new tab Download slide Open in new tab Download slide OBJECTIVES Thoracic ultrasound is superior to chest X-ray for the detection of a pneumothorax in trauma and intensive care medicine. Data regarding its use in non-cardiac thoracic surgery are scarce and contradictory. Previous studies are heterogeneous regarding sonographic methodology and patient selection. This study aimed to evaluate the accuracy of thoracic ultrasound for pneumothorax assessment after lung resecting surgery in unselected patients. METHODS SONOR (SONO graphy vs x- R ay) is a prospective observational trial (registry-ID DRKS00014557). A total of 123 consecutive patients with lung resecting surgery received a standardized thoracic ultrasound the same day and in addition to routine chest X-rays in erect position after removal of the chest tube. The sonographer was blinded to radiological findings and vice versa. RESULTS Sensitivity, specificity, positive and negative predictive values of ultrasound after removing the chest tube were 0.32, 0.85, 0.54, 0.69 for any pneumothorax and 1.0, 0.82, 0.19, 1.0 for pneumothorax ≥3 cm. No clinically relevant pneumothorax was missed. The agreement between sonography- and routine-based therapeutic decisions was 97%. Lung pulse was the most frequently detected sign to sonographically rule out a pneumothorax. CONCLUSIONS Postoperative thoracic ultrasound in unselected patients has a low overall sensitivity to detect a residual pneumothorax; however, its sensitivity and negative predictive values regarding clinically relevant pneumothorax are high. Test quality depends on the distinct sonographic methodology and patient selection. Anatomic differences in postsurgical and medical patients may be responsible for the contradictory results of previous trials. Studies with a larger population size are required to validate the accuracy of relevant pneumothoraces and identify appropriate selection criteria. Clinical trial registration number DRKS—German Clinical Trials Register, www.drks.de, registry-ID DRKS00014557. [ABSTRACT FROM AUTHOR]

We model the X-ray surface brightness distribution of emission associated with Fanaroff & Riley type-II radio galaxies. Our approach builds on the RAiSE dynamical model which describes broad-band radio frequency synchrotron evolution of jet-inflated lobes in a wide range of environments. The X-ray version of the model presented here includes: (1) inverse-Compton upscattering of cosmic microwave background radiation; (2) the dynamics of the shocked gas shell and associated bremsstrahlung radiation; and (3) emission from the surrounding ambient medium. We construct X-ray surface brightness maps for a mock catalogue of extended FR-IIs based on the technical characteristics of the eRosita telescope. The integrated X-ray luminosity function at low redshifts (z ≤ 1) is found to strongly correlate with the density of the ambient medium in all but the most energetic sources, whilst at high-redshift (z > 1) the majority of objects are dominated by inverse-Compton lobe emission due to the stronger cosmic microwave background radiation. By inspecting our mock spatial brightness distributions, we conclude that any extended X-ray detection can be attributed to AGN activity at redshifts z ≥ 1. We compare the expected detection rates of active and remnant high-redshift radio AGNs for eRosita and LOFAR , and future more sensitive surveys. We find that a factor of ten more remnants can be detected using X-ray wavelengths over radio frequencies at z > 2.2, increasing to a factor of 100 for redshifts z > 3.1. [ABSTRACT FROM AUTHOR]

Background: A CT scanner makes many measurements, from different rotational angles, of X-ray attenuation (weakening in force or intensity) through the cross-sectional plane of the thorax. It then uses these data to reconstruct a digital representation of the cross-section with each pixel of the image representing a measurement of the mean attenuation through the thickness of the predetermined segment. This measurement quantifies the fraction of radiation removed in passing through a given amount of material of a certain thickness. Objective: To compare the chest CT scan and chest x-ray for early detection of pulmonary complications for adults hospitalized in intensive care unit. Patients and Methods: In the present prospective study, we included 40 adults' patients, who were hospitalized in Intensive Care Unit (ICU), in order to compare the diagnostic accuracy of chest X-ray and CT scan for early detection of pulmonary complications. Patients were recruited from the ICUs of Ain Shams University and Misr University for Science and Technology Hospitals. They were included whether they had primary respiratory manifestations or started to develop respiratory manifestations during ICU stay. Results: In the present study, we included 10 patients who were diagnosed with pulmonary embolism. The mean age of the included patients was 59.7 ± 16.3 years old. Five patients were correctly identified by the chest X-ray. Thus, the chest X-ray sensitivity for the detection of pneumonia was 50% and the positive predictive value was 100%. Conclusion: In our cohort of patients with a wide variety of chest disorders, routine chest X-ray was not useful to clinicians in the diagnosis of lung disease, compared to chest CT. In addition, chest X-ray had a very low sensitivity in specific conditions like pulmonary embolism and pneumothorax. [ABSTRACT FROM AUTHOR]