Search

In this work, we present the results of the survey carried out on one of the deepest X-ray fields observed by the XMM-Newton satellite. The 1.75 Ms Ultra Narrow Deep Field (XMM175UNDF) survey is made by 13 observations taken over 2 yr with a total exposure time of 1.75 Ms (1.372 Ms after flare-filtered) in a field of 30′ × 30′ centered around the blazar 1ES 1553+113. We stacked the 13 observations reaching flux limits of 4.03 × 10−16, 1.3 × 10−15, and 9.8 × 10−16 erg s−1 cm−2 in the soft (0.2–2 keV), hard (2–12 keV), and full (0.2–12 keV) bands, respectively. Using a conservative threshold of Maximum Likelihood significance of ML ≥ 6, corresponding to 3σ, we detected 301 point-sources for which we derived positions, fluxes in different bands, and hardness ratios. Thanks to an optical follow-up that was carried out using the 10.4m the Gran Telescopio Canarias on the same field in the u′g′r′i′z′ bands, combined with WISE/2MASS IR data, we identified 244 optical/IR counterpart candidates for our X-ray sources and estimated their X-ray luminosities, redshift distribution, X-ray/optical–X-ray/IR flux ratios, and absolute magnitudes. Finally, we divided this subsample into 40 non-active sources and 204 active galactic nuclei, of which 139 are classified as Seyfert galaxies and 41 as Quasars. [ABSTRACT FROM AUTHOR]

We present a comprehensive multifrequency study of the high-frequency-peaked BL Lac object 1ES 1959+650 using data from various facilities during the period 2016–2017, including X-ray data from AstroSat and Swift during the historically high X-ray flux state of the source observed until 2021 February. The unprecedented quality of X-ray data from high-cadence monitoring with AstroSat during 2016–2017 enables us to establish a detailed description of X-ray flares in 1ES 1959+650. The synchrotron peak shifts significantly between different flux states, in a manner consistent with a geometric (changing Doppler factor) interpretation. A time-dependent leptonic diffusive shock acceleration and radiation transfer model is used to reproduce the spectral energy distributions and X-ray light curves, to provide insight into the particle acceleration during the major activity periods observed in 2016 and 2017. The extensive data of Swift-XRT from 2015 December to 2021 February (exp. = 411.3 ks) reveals a positive correlation between flux and peak position. [ABSTRACT FROM AUTHOR]

Although ultraluminous X-ray sources (ULX) are important for astrophysics because of their extreme apparent super-Eddington luminosities, their nature is still poorly known. Theoretical and observational studies suggest that ULXs could be a diversified group of objects that are composed of low-mass X-ray binaries, high-mass X-ray binaries and marginally also systems containing intermediate-mass black holes. Observational data on the ULX donors could significantly boost our understanding of these systems, but only a few have been detected. There are several candidates, mostly red supergiants (RSGs), but surveys are typically biased toward luminous near-infrared objects. In ULXs harbouring RSGs matter accreted onto the compact body would have to be provided by the stellar wind of the companion because a Roche-lobe overflow could be unstable for relevant mass-ratios. We present a comprehensive study of the evolution and population of wind-fed ULXs, and we provide a theoretical support for the link between RSGs and ULXs. Assuming a minimal model of stellar-wind emission, our estimated upper limit on contribution of wind-fed ULX to the overall ULX population is ∼75%–96% for young (<100 Myr) star-forming environments, ∼49%–87% for prolonged constant star formation (e.g., disk of Milky Way), and ≲1% for environments in which star formation ceased long time (>2 Gyr) ago. We show also that some wind-fed ULXs (up to 6%) may evolve into merging double compact objects (DCOs). We demonstrate that the exclusion of wind-fed ULXs from population studies of ULXs might have lead to systematic errors in their conclusions. [ABSTRACT FROM AUTHOR]

We present the results of a joint analysis of Chandra X-ray and South Pole Telescope (SPT) Sunyaev–Zel'dovich (SZ) observations targeting the first sample of galaxy clusters at 0.3 < z < 1.3, selected to be the progenitors of well-studied nearby clusters based on their expected accretion rate. We develop a new procedure in order to tackle the analysis challenge that is estimating the intracluster medium (ICM) properties of low-mass and high-redshift clusters with ∼150 X-ray counts. One of the dominant sources of uncertainty on the ICM density profile estimated with a standard X-ray analysis with such shallow X-ray data is due to the systematic uncertainty associated with the ICM temperature obtained through the analysis of the background-dominated X-ray spectrum. We show that we can decrease the uncertainty on the density profile by a factor varying between 2 and 8 with a joint deprojection of the X-ray surface brightness profile measured by Chandra and the SZ-integrated Compton parameter available in the SPT cluster catalog. We apply this technique to the whole sample of 67 clusters in order to track the evolution of the ICM core density during cluster growth. We confirm that the evolution of the gas density profile is well modeled by the combination of a fixed core and a self-similarly evolving non-cool-core profile. We show that the fraction of cool cores in this sample is remarkably stable with redshift although clusters have gained a factor of ∼4 in total mass over the past ∼9 Gyr. [ABSTRACT FROM AUTHOR]

30 Doradus C is a superbubble that emits the brightest non-thermal X- and TeV gamma-rays in the Local Group. To explore the detailed connection between the high-energy radiation and the interstellar medium, we have carried out new CO and H i observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope Compact Array with resolutions of up to 3 pc. The ALMA data of 12CO(J = 1–0) emission revealed 23 molecular clouds, with typical diameters of ∼6–12 pc and masses of ∼600–10,000 M⊙. A comparison with the X-rays of XMM–Newton at ∼3 pc resolution shows that X-rays are enhanced toward these clouds. The CO data were combined with the H i to estimate the total interstellar protons. A comparison of the interstellar proton column density and the X-rays revealed that the X-rays are enhanced with the total proton column density. These are most likely to be caused by the shock-cloud interaction, which is modeled by magnetohydrodynamical simulations (Inoue et al. 2012). We also note a trend for the X-ray photon index to vary with distance from the center of the high-mass star cluster. This suggests that the cosmic-ray electrons are accelerated by one or multiple supernovae in the cluster. Based on these results, we discuss the role of the interstellar medium in cosmic-ray particle acceleration. [ABSTRACT FROM AUTHOR]

We report a detailed analysis of the hard X-ray and GeV gamma-ray spectra of LS 5039, one of the brightest gamma-ray binary system in the Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) observation covering its entire orbit in 2016 allowed us for the first time to study the orbital variability of the spectrum above 10 keV. The hard X-ray spectrum is well described with a single power-law component up to 78 keV. The X-ray flux showed a slight deviation from those observed previously with Suzaku in 2007. The fast X-ray brightening observed with Suzaku, around the inferior conjunction, was not observed in this observation. We also analyzed 11 yr of Fermi Large Area Telescope data of LS 5039. The GeV spectrum around the inferior conjunction was well described with two nonthermal components: a power law with a photon index of ∼3 and a cutoff power law with a cutoff energy of ∼2 GeV. The orbital flux variability also changed gradually around a few GeV. These results indicate that there are two emission components in the GeV band, and the dominant component above ∼1 GeV does not depend on the orbital phase. By combining these results, we update the spectral energy distribution of LS 5039 with the highest available statistics. Theoretical models proposed so far cannot explain the obtained multiwavelength spectrum, especially the emission from ∼1 to ∼400 MeV, and we discuss the possibility that particle acceleration in LS 5039 is different from the shock acceleration. [ABSTRACT FROM AUTHOR]

We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV γ-ray source 4FGL J0540.0–7552. The source shows the persistent presence of an optical accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-ray to γ-ray flux. Together, these properties are consistent with the classification of the binary as a transitional millisecond pulsar (tMSP) in the subluminous disk state. Uniquely among the candidate tMSPs, 4FGL J0540.0–7552 shows consistent optical, X-ray, and γ-ray evidence for having undergone a state change, becoming substantially brighter in the optical and X-rays and fainter in GeV γ-rays sometime in mid-2013. In its current subluminous disk state, and like one other candidate tMSP in the Galactic field, 4FGL J0540.0–7552 appears to always be in an X-ray "flare mode," indicating that this could be common phenomenology for tMSPs. [ABSTRACT FROM AUTHOR]

We use a Chandra X-ray observation of the gravitationally lensed system MG B2016+112 at z = 3.273 to elucidate the presence of at least two X-ray sources. We find that these sources are consistent with the very long baseline interferometry (VLBI) components measured by Spingola, which are separated by ∼200 pc. Their intrinsic 0.5–7 keV source frame luminosities are 1.5 × 1043 and 1.8 × 1044 erg s−1, respectively. Most likely this system contains a dual active galactic nucleus (AGN), but we are possibly detecting an AGN plus a parsec-scale X-ray jet, the latter lying in a region at very high magnification. The quadruply lensed X-ray source is within ±40 pc (1σ) of its VLBI counterpart. Using a gravitational lens as a telescope, and a novel statistical application, we have achieved unprecedented accuracy for measuring metric distances at such large redshifts in X-ray astronomy. This is tens of mas if the source is located close to the caustics, while it is of hundreds of mas if the source is in a region at lower amplification. The present demonstration of this approach has implications for future X-ray investigations of large numbers of lensed systems. [ABSTRACT FROM AUTHOR]

The variable source OGLE-UCXB-01 is the first OGLE-discovered ultracompact X-ray binary (UCXB). The 12 yr long-term OGLE optical photometry of this source shows a period of and a fast period-decreasing rate s s−1. At a luminosity of erg s−1, its X-ray emission is also variable and correlated with the optical variability. To determine the nature of this variable source, specifically the masses and types of its binary components, we first consider an attractive possibility that the optical variation is due to the secondary's ellipsoidal variation and a strong gravitational wave emission drives the orbital decay. However, we cannot find an allowable solution to the secondary that simultaneously satisfies the three constraints: an ultratight orbit, the bright absolute magnitude, and the large-amplitude brightness variation. Moreover, the inferred mass-transfer rate is too high. This scenario is therefore ruled out. We then find the system is fully consistent with an "intermediate polar" model, in which the optical and X-ray emission comes from a magnetized white dwarf (WD) accreting from a low-mass (≲) main-sequence secondary. The observed period decay is the accretion-driven spin-up of the WD. The WD spin period is 12.8 minutes and the orbital period is shorter than 10 hr. The method presented here can be applied to other UCXB candidates or impostors with only time-domain data available. [ABSTRACT FROM AUTHOR]

Jet precession is considered to universally exist in different-scale astronomical phenomena, including gamma-ray bursts (GRBs). For the long-lived GRB central engine, the relativistic precessing jets will periodically inject kinetic energy into the external shocks, then significantly modulate the shapes of the light curves (LCs) in GRB afterglows. In this paper, we adopt the standard external shock model to investigate the effects of jet precession on GRB X-ray afterglows in cases with different parameters, i.e., the steady or time-dependent jet powers, precession periods, precession angles, and viewing angles. In the case where the jet powers are in steady or slow decay and the jet can sweep across the line of sight, shallow decay (or plateau) segments should appear; otherwise, a giant bump will emerge in the GRB afterglow LCs. We show that jet precession is a new plausible mechanism of the energy injection in GRBs. Moreover, some observed X-ray transients without GRB associations might be powered by the precessing jets. [ABSTRACT FROM AUTHOR]

We report on the search for very-high-energy gamma-ray emission from the regions around three nearby supersonic pulsars (PSR B0355+54, PSR J0357+3205, and PSR J1740+1000) that exhibit long X-ray tails. To date there is no clear detection of TeV emission from any pulsar tail that is prominent in X-ray or radio. We provide upper limits on the TeV flux, and luminosity, and also compare these limits with other pulsar wind nebulae detected in X-rays and the tail emission model predictions. We find that at least one of the three tails is likely to be detected in observations that are a factor of 2–3 more sensitive. The analysis presented here also has implications for deriving the properties of pulsar tails, for those pulsars whose tails could be detected in TeV. [ABSTRACT FROM AUTHOR]

Since 2018 July, the black hole X-ray binary GRS 1915+105 has been in an X-ray low luminous state (XLLS), which is the faintest period ever observed in a soft X-ray band. We present here the results of near-infrared (NIR) observations from 2019 April–December in the XLLS using HONIR attached to the Kanata telescope, together with radio data obtained by the Yamaguchi Interferometer and archival X-ray data. We found the historical NIR brightening in the XLLS. For several tens of days in the XLLS, NIR flux showed a positive correlation with radio flux and negative correlation with X-ray flux. This result suggests that at least a jet contributes to the NIR bands in the NIR-bright XLLS period. An accretion disk is not likely a candidate for the NIR emission because of the decrease of X-ray flux. In contrast to the NIR band, there was no historical radio brightening in the XLLS. This implies that the NIR emission in the NIR-bright period cannot be explained by the jet alone. The X-ray obscuration suggested by X-ray data is another possible candidate for the nonjet emission component in the NIR band. [ABSTRACT FROM AUTHOR]

Solar-type stars exhibit their highest levels of magnetic activity during their early convective pre-main-sequence (PMS) phase of evolution. The most powerful PMS flares, superflares and megaflares, have peak X-ray luminosities of erg s−1 and total energies erg. Among >24,000 X-ray-selected young (t ≲ 5 Myr) members of 40 nearby star-forming regions from our earlier Chandra MYStIX and SFiNCs surveys, we identify and analyze a well-defined sample of 1086 X-ray superflares and megaflares, the largest sample ever studied. Most are considerably more powerful than optical/X-ray superflares detected on main-sequence stars. This study presents energy estimates of these X-ray flares and the properties of their host stars. These events are produced by young stars of all masses over evolutionary stages ranging from protostars to diskless stars, with the occurrence rate positively correlated with stellar mass. Flare properties are indistinguishable for disk-bearing and diskless stars indicating star–disk magnetic fields are not involved. A slope of α ≃ 2 in the flare energy distributions is consistent with that of optical/X-ray flaring from older stars and the Sun. Megaflares (erg) from solar-mass stars have an occurrence rate of flares/star/year and contribute at least 10%–20% to the total PMS X-ray energetics. These explosive events may have important astrophysical effects on protoplanetary disk photoevaporation, ionization of disk gas, production of spallogenic radionuclides in disk solids, and hydrodynamic escape of young planetary atmospheres. Our following paper details plasma and magnetic loop modeling of the >50 brightest X-ray megaflares. [ABSTRACT FROM AUTHOR]

The high-redshift quasar PMN J0909+0354 (z = 3.288) is known to have a parsec-scale compact jet structure, based on global 5 GHz very long baseline interferometry (VLBI) observations performed in 1992. Its kiloparsec-scale structure was studied with the Karl G. Jansky Very Large Array (VLA) in the radio and the Chandra space telescope in X-rays. Apart from the north-northwestern jet component seen in both the VLA and Chandra images at 2.″3 separation from the core, there is another X-ray feature at 6.″48 in the northeastern (NE) direction. To uncover more details and possible structural changes in the inner jet, we conducted new observations at 5 GHz using the European VLBI Network in 2019. These data confirm the northward direction of the one-sided inner jet already suspected from the 1992 observations. A compact core and multiple jet components were identified that can be traced up to ∼0.25 kpc projected distance toward the north, where the structure becomes more and more diffuse. A comparison with arcsecond-resolution imaging with the VLA shows that the radio jet bends by ∼30° between the two scales. The direction of the parsec-scale jet as well as the faint optical counterpart found for the newly detected X-ray point source (NE) favors the nature of the latter as being a background or foreground object in the field of view. However, the extended (∼160 kpc) emission around the positions of the quasar core and NE detected by the Wide-field Infrared Survey Explorer in the mid-infrared might suggest a physical interaction of the two objects. [ABSTRACT FROM AUTHOR]

WR 25 is a colliding-wind binary star system comprising a very massive O2.5If*/WN6 primary and an O-star secondary in an eccentric orbit with a 208 day period. These hot stars have strong, highly supersonic winds that interact to form a bright X-ray source from wind-collision shocks whose conditions change with stellar separation. Different views through the winds of Wolf–Rayet and O stars are afforded with orbital phase as the stars move about their orbits, allowing for exploration of wind structure in ways not easy or even possible for single stars. We have analyzed an on-axis Chandra/HETGS spectrum of WR 25 obtained shortly before periastron when the X-rays emanating from the system are the brightest. From the on-axis observations, we constrain the line fluxes, centroids, and widths of various emission lines, including He triplets of Si xiii and Mg xi. We have also been able to include several serendipitous off-axis HETG spectra from the archive and study their flux variation with phase. This is the first report on high-resolution spectral studies of WR 25 in X-rays. [ABSTRACT FROM AUTHOR]

The metastable helium (He*) lines near 10830 Å are ideal probes of atmospheric erosion—a common phenomenon of close-in exoplanet evolution. A handful of exoplanet observations yielded well-resolved He* absorption features in transits, yet they were mostly analyzed with 1D isothermal models prescribing mass-loss rates. This work devises 3D hydrodynamics coevolved with ray-tracing radiative transfer and nonequilibrium thermochemistry. Starting from the observed stellar/planetary properties with reasonable assumptions about the host's high-energy irradiation, we predict from first principles the mass-loss rate, the temperature and ionization profiles, and 3D outflow kinematics. Our simulations well reproduce the observed He* line profiles and light curves of WASP-69b. We further investigate the dependence of He* observables on simulation conditions and host radiation. The key findings are as follows: (1) Simulations reveal a photoevaporative outflow (∼0.55 M⊕ Gyr−1 ≃ 1011 g s−1) for WASP-69b without a prominent comet-like tail, consistent with the symmetric transit shape. (2) 3D simulations are mandatory for hydrodynamic features, including Coriolis force, advection, and kinematic line broadening. (3) EUV (>13.6 eV) photons dominate photoevaporative outflows and populate He* via recombination; FUV is also detrimental by destroying He*; X-ray plays a secondary role. (4) K stars hit the sweet spot of EUV/far-UV balance for He* line observation, while G and M stars are also worthy targets. (5) Stellar flares create characteristic responses in the He* line profiles. [ABSTRACT FROM AUTHOR]

X-ray emission from the surface of isolated neutron stars (NSs) has been now observed in a variety of sources. The ubiquitous presence of pulsations clearly indicates that thermal photons either come from a limited area, possibly heated by some external mechanism, or from the entire (cooling) surface but with an inhomogeneous temperature distribution. In an NS the thermal map is shaped by the magnetic field topology since heat flows in the crust mostly along the magnetic field lines. Self-consistent surface thermal maps can hence be produced by simulating the coupled magnetic and thermal evolution of the star. We compute the evolution of the NS crust in three dimensions for different initial configurations of the magnetic field and use the ensuing thermal surface maps to derive the spectrum and the pulse profile as seen by an observer at infinity, accounting for general-relativistic effects. In particular, we compare cases with a high degree of symmetry with inherently 3D ones, obtained by adding a quadrupole to the initial dipolar field. Axially symmetric fields result in rather small pulsed fractions (≲5%), while more complex configurations produce higher pulsed fractions, up to ∼25%. We find that the spectral properties of our axisymmetric model are close to those of the bright isolated NS RX J1856.5-3754 at an evolutionary time comparable with the inferred dynamical age of the source. [ABSTRACT FROM AUTHOR]

We present Chandra X-ray observations of 14 radio-loud quasars at redshifts 3 < z < 4, selected from a well-defined sample. All quasars are detected in the 0.5–7.0 keV energy band, and resolved X-ray features are detected in five of the objects at distances of 1″–12″ from the quasar core. The X-ray features are spatially coincident with known radio features for four of the five quasars. This indicates that these systems contain X-ray jets. X-ray fluxes and luminosities are measured, and jet-to-core X-ray flux ratios are estimated. The flux ratios are consistent with those observed for nearby jet systems, suggesting that the observed X-ray emission mechanism is independent of redshift. For quasars with undetected jets, an upper limit on the average X-ray jet intensity is estimated using a stacked image analysis. Emission spectra of the quasar cores are extracted and modeled to obtain best-fit photon indices, and an Fe K emission line is detected from one quasar in our sample. We compare X-ray spectral properties with optical and radio emission in the context of both our sample and other quasar surveys. [ABSTRACT FROM AUTHOR]

Transients powered by interaction with the circumstellar medium (CSM) are often observed in wavelengths other than the optical, and multiwavelength modeling can be important when inferring the properties of the explosion and CSM, or for distinguishing from other powering mechanisms. We develop a model calculating the time-dependent emission spectrum of interaction-powered transients. We solve the energy equations of electron–proton plasma in the shocked supernova ejecta and CSM and the radiation transfer equation out to the outer edge of the CSM, incorporating collisional relaxation and the Comptonization of bremsstrahlung radiation. We compare our model to observations of Type IIn supernovae covering a frequency range from the optical to X-rays. For SN 2010jl the observed optical and X-ray light curves can be consistently explained if a clumpy or asymmetric structure in the CSM is assumed, in agreement with previous studies. For SN 2014C our model successfully reproduces the X-ray bremsstrahlung component and the emergence of Hα emission at 400 days after explosion. Finally we find a parameter space where the supernova is extremely X-ray bright, reaching 1043–1044 erg s−1, for up to 100 days. Such X-ray transients are likely to be detectable with all-sky surveys by, e.g., eROSITA. [ABSTRACT FROM AUTHOR]

Using Chandra observations, we derive the YX proxy and associated total mass measurement, , for 147 clusters with z < 0.35 from the Planck early Sunyaev–Zeldovich catalog, and for 80 clusters with z < 0.22 from an X-ray flux-limited sample. We reextract the Planck YSZ measurements and obtain the corresponding mass proxy, , from the full Planck mission maps, minimizing Malmquist bias due to observational scatter. The masses reextracted using the more precise X-ray position and characteristic size agree with the published PSZ2 values, but yield a significant reduction in the scatter (by a factor of two) in the – relation. The slope is 0.93 ± 0.03, and the median ratio, , is within the expectations from known X-ray calibration systematics. YSZ/YX is 0.88 ± 0.02, in good agreement with predictions from cluster structure, and implying a low level of clumpiness. In agreement with the findings of the Planck Collaboration, the slope of the YSZ– flux relation is significantly less than unity (0.89 ± 0.01). Using extensive simulations, we show that this result is not due to selection effects, intrinsic scatter, or covariance between quantities. We demonstrate analytically that changing the YSZ–YX relation from apparent flux to intrinsic properties results in a best-fit slope that is closer to unity and increases the dispersion about the relation. The redistribution resulting from this transformation implies that the best-fit parameters of the – relation will be sample-dependent. [ABSTRACT FROM AUTHOR]

The massive binary system Eta Carinae is characterized by intense colliding winds that form shocks and emit X-rays. The system is highly eccentric (e ≃ 0.9), resulting in modulated X-ray emission during its 5.54 yr orbit. The X-ray flux increases in the months prior to periastron passage, exhibiting strong flares, then rapidly declines to a flat minimum lasting a few weeks, followed by a gradual recovery. We present the Neutron Star Interior Composition Explorer telescope spectra obtained before, during, and after the 2020 X-ray minimum, and perform spectral analysis to establish the temporal behavior of the X-ray flux and X-ray-absorbing column density (NH(t)) for the 2–10 keV and 5–10 keV energy ranges. The latter range is dominated by the stellar wind-collision region and, therefore, these spectral parameters—in particular, NH(t)—serve as potentially stringent constraints on the binary orientation. We compare the observed NH(t) results to the behavior predicted by a simple geometrical model in an attempt to ascertain which star is closer to us at periastron: the more massive primary (ω ≃ 240°–270°) or the secondary (ω ≃ 90°). We find that the variations in column density, both far from periastron and around periastron passage, support the latter configuration (ω ≃ 90°). The 2020 X-ray minimum showed the fastest recovery among the last five minima, providing additional evidence for a recent weakening of the primary star's wind. [ABSTRACT FROM AUTHOR]

Flat-spectrum radio quasars (FSRQs) are a subclass of blazars characterized by prominent optical emission lines and a collimated large-scale jet along the observer's line of sight. An X-ray spectral flattening has been reported in FSRQs (at relatively high redshifts) that is attributable either to absorption from gas along the line of sight or to intrinsic jet-based radiative processes. We study a sample of 16 high-redshift FSRQs (z of 1.1–4.7; rest-frame energy up to 50 keV) observed with the XMM-Newton and Swift satellites spanning 29 epochs. The X-ray spectra are fit with a power law including free excess absorption and one multiplied by an exponential roll-off to account for the intrinsic jet-based processes. A statistical analysis is used to distinguish between these models to understand the origin of the spectral flattening. The model selection is unable to distinguish between them in 10 of the 16 FSRQs. Intrinsic jet-based radiative processes are indicated in 4 FSRQs, where we infer energy breaks consistent with their expectation from the external Compton-scattering of low-energy ambient photons. Two of the FSRQs indicate mixed results, supportive of either scenario, illustrating the difficulty of identifying X-ray absorption signatures. A clear detection can be employed to disentangle the relative contributions from the intergalactic medium and the intracluster medium, the method of which is outlined and applied to the latter two sources. [ABSTRACT FROM AUTHOR]

We report measurements of electron-impact excitation cross sections for the strong K-shell n = 2 → 1 transitions in S xv, using the LLNL EBIT-I electron beam ion trap, two crystal spectrometers, and the EBIT Calorimeter Spectrometer. The cross sections are determined by direct normalization to the well-known cross sections of radiative electron capture, measured simultaneously. Using contemporaneous polarization measurements with the two crystal spectrometers, whose dispersion planes are oriented parallel and perpendicular to the electron beam direction, the polarization of the direct excitation line emission is determined, and in turn the isotropic total cross sections are extracted. We further experimentally investigate various line-formation mechanisms, finding that radiative cascades and collisional inner-shell ionization dominate the degree of linear polarization and total line-emission cross sections of the forbidden line, z. [ABSTRACT FROM AUTHOR]

Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz–selected, and so orientation-unbiased, sample of 44 0.5 < z < 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with unification, intrinsic obscuration (measured by NH, X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-z 3CRR sources: NLRGs viewed at intermediate inclination angles with NH < 1022 cm−2. Multiwavelength analysis suggests that these objects have lower L/LEdd than typical NLRGs at similar orientation. Thus, both orientation and L/LEdd are important, and a "radiation-regulated unification" provides a better explanation of the sample's observed properties. In comparison with the 3CRR sample at 1 < z < 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% versus 29%) but a similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and thus a more "puffed-up" torus atmosphere. We posit that this is due to a range of L/LEdd extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high L/LEdd values allowed orientation (and so simple unification) to dominate the sample's observed properties. [ABSTRACT FROM AUTHOR]

We present theoretical predictions for the free–free emission at centimeter wavelengths obtained from photoevaporation and magnetohydrodynamic (MHD) wind disk models adjusted to the case of the TW Hydrae young stellar object. For this system, disk photoevaporation with heating due to the high-energy photons from the star has been proposed as a possible mechanism to open the gap observed in the dust emission with the Atacama Large Millimeter/submillimeter Array. We show that the photoevaporation disk model predicts a radial profile for the free–free emission that is made of two main spatial components, one originated from the bound disk atmosphere at 0.5–1 au from the star, and another more extended component from the photoevaporative wind at larger disk radii. We also show that the stellar X-ray luminosity has a significant impact on both these components. The predicted radio emission from the MHD wind model has a smoother radial distribution which extends to closer distances to the star than the photoevaporation case. We also show that a future radio telescope such as the Next Generation Very Large Array would have enough sensitivity and angular resolution to spatially resolve the main structures predicted by these models. [ABSTRACT FROM AUTHOR]

The location of the obscuring "torus" in an active galactic nucleus (AGN) is still an unresolved issue. The line widths of X-ray fluorescence lines originating from the torus, particularly Fe Kα, carry key information on the radii of line-emitting regions. Utilizing XCLUMPY, an X-ray clumpy torus model, we develop a realistic model of emission line profiles from an AGN torus where we take into account line broadening due to the Keplerian motion around the black hole. Then, we apply the updated model to the best available broadband spectra (3–100 keV) of the Circinus galaxy observed with Suzaku, XMM-Newton, Nuclear Spectroscopic Telescope Array, and Chandra, including 0.62 Ms Chandra/HETG data. We confirm that the torus is Compton-thick (hydrogen column density along the equatorial plane is), geometrically thin (torus angular width), viewed edge-on (inclination), and has supersolar abundance (times solar). Simultaneously analyzing the Chandra/HETG first-, second-, and third-order spectra with consideration of the spatial extent of the Fe Kα line-emitting region, we constrain the inner radius of the torus to be times the gravitational radius, or for a black hole mass of (1.7 ± 0.3) × 106M⊙. This is about three times smaller than that estimated from the dust sublimation radius, suggesting that the inner side of the dusty region of the torus is composed of dust-free gas. [ABSTRACT FROM AUTHOR]

Single AGB stars are not normally expected to be X-ray emitters due to the lack of a corona capable of powering a hot plasma. Therefore, the detection of X-ray emission in AGB stars by the ROSAT, Chandra, and XMM-Newton observatories has been interpreted as evidence for binarity. The number of X-ray-emitting AGB stars is, however, very small, and statistically sound conclusions shall be considered tentative. In this paper we aim at increasing the number of X-ray-emitting AGB stars and at providing a consistent analysis of their X-ray emission to be compared to their UV and optical properties. The XMM-Newton 4XMM-DR9 catalog has been searched for X-ray counterparts of various types of AGB stars: nearby (i.e., listed in Hipparcos), mass-losing, and S- and C-types. Seventeen X-ray counterparts of AGB stars have been found in the 4XMM-DR9. Nine of them have pointed XMM-Newton observations, whereas eight are genuine serendipitous discoveries. Together with the AGB stars detected by ROSAT, this increases the number of X-ray AGB stars to 26. Most of their X-ray spectra can be fit by the emission from an optically thin single-temperature thermal plasma with temperatures typically larger than 107 K. There is no obvious correlation between the X-ray and bolometric luminosity of these stars, but the X-ray luminosity generally increases with the amount of far-UV excess. The high temperature of some X-ray-emitting plasma in AGB stars and the correlation of their X-ray luminosity with the far-UV emission supports the origin of this X-ray emission from accretion disks around unseen companions. [ABSTRACT FROM AUTHOR]

This paper studied the faint, diffuse extended X-ray emission associated with the radio lobes and the hot gas in the intracluster medium (ICM) environment for a sample of radio galaxies. We used shallow (∼10 ks) archival Chandra observations for 60 radio galaxies (7 FR I and 53 FR II) with 0.0222 ≤ z ≤ 1.785 selected from the 298 extragalactic radio sources identified in the 3CR catalog. We used Bayesian statistics to look for any asymmetry in the extended X-ray emission between regions that contain the radio lobes and regions that contain the hot gas in the ICM. In the Chandra broad band (0.5–7.0 keV), which has the highest detected X-ray flux and the highest signal-to-noise ratio, we found that the nonthermal X-ray emission from the radio lobes dominates the thermal X-ray emission from the environment for ∼77% of the sources in our sample. We also found that the relative amount of on-jet axis nonthermal emission from the radio lobes tends to increase with redshift compared to the off-jet axis thermal emission from the environment. This suggests that the dominant X-ray mechanism for the nonthermal X-ray emission in the radio lobes is due to the inverse Compton upscattering of cosmic microwave background (CMB) seed photons by relativistic electrons in the radio lobes, a process for which the observed flux is roughly redshift independent due to the increasing CMB energy density with increasing redshift. [ABSTRACT FROM AUTHOR]

There are only a few very-high-energy sources in our Galaxy that might accelerate particles up to the knee of the cosmic-ray spectrum. To understand the mechanisms of particle acceleration in these PeVatron candidates, Fermi-Large Area Telescope (LAT) and High-Energy Stereoscopic System (H.E.S.S.) observations are essential to characterize their γ-ray emission. HESS J1640–465 and the PeVatron candidate HESS J1641–463 are two neighboring (0.25°) γ-ray sources, spatially coincident with the radio supernova remnants (SNRs) G338.3–0.0 and G338.5+0.1. Detected both by H.E.S.S. and the Fermi-LAT, we present here a morphological and spectral analysis of these two sources using 8 yr of Fermi-LAT data between 200 MeV and 1 TeV with multiwavelength observations to assess their nature. The morphology of HESS J1640–465 is described by a 2D Gaussian (σ = 0.053° ± 0.011°stat ± 0.03°syst) and its spectrum is modeled by a power law with a spectral index Γ = 1.8 ± 0.1stat ± 0.2syst. HESS J1641–463 is detected as a point-like source and its GeV emission is described by a logarithmic-parabola spectrum with α = 2.7 ± 0.1stat ± 0.2syst and significant curvature of β = 0.11 ± 0.03stat ± 0.05syst. Radio and X-ray flux upper limits were derived. We investigated scenarios to explain their emission, namely, the emission from accelerated particles within the SNRs spatially coincident with each source, molecular clouds illuminated by cosmic rays from the close-by SNRs, and a pulsar/pulsar wind nebula origin. Our new Fermi-LAT results and the radio and flux X-ray upper limits pose severe constraints on some of these models. [ABSTRACT FROM AUTHOR]

Heating of neutral gas by energetic sources is crucial for the prediction of the 21 cm signal during the epoch of reionization. To investigate differences induced on the statistics of the 21 cm signal by various source types, we use five radiative transfer simulations that have the same stellar UV emission model and varying combinations of more energetic sources, such as X-ray binaries (XRBs), accreting nuclear black holes (BHs), and hot interstellar medium emission (ISM). We find that the efficient heating from the ISM increases the average global 21 cm signal while reducing its fluctuations and thus power spectrum. A clear impact is also observed in the bispectrum in terms of scale and timing of the transition between a positive and a negative value. The impact of XRBs is similar to that of the ISM, although it is delayed in time and reduced in intensity because of the less efficient heating. Due to the paucity of nuclear BHs, the behavior of the 21 cm statistics in their presence is very similar to that of a case when only stars are considered, with the exception of the latest stages of reionization, when the effect of BHs is clearly visible. We find that differences between the source scenarios investigated here are larger than the instrumental noise of SKA1-low at z ≳ 7–8, suggesting that in the future it might be possible to constrain the spectral energy distribution of the sources contributing to the reionization process. [ABSTRACT FROM AUTHOR]

We present an analysis of 745.8 ks of archival Chandra X-Ray Observatory Advanced CCD Imaging Spectrometer data accumulated between 2000 and 2016 of the millisecond pulsar (MSP) population in the rich Galactic globular cluster Terzan 5. Eight of the 38 MSPs with precise positions are found to have plausible X-ray source matches. Despite the deep exposure, the remaining MSPs are either marginally detected or have no obvious X-ray counterparts, which can be attributed to the typically soft thermal spectra of rotation-powered MSPs, which are strongly attenuated by the high intervening absorbing column (∼1022 cm−2) toward the cluster, and in some instances to severe source crowding/blending. For the "redback" MSP binaries PSR J1748−2446P and PSR J1748−2446ad and the "black widow" binary system PSR J1748−2446O, we find clear evidence for large-amplitude X-ray variability at the orbital period consistent with an intrabinary shock origin. The third redback MSP in the cluster, PSR J1748−2446A, shows order-of-magnitude variations in flux on timescales of years, possibly due to state transitions or intense flaring episodes from a magnetically active secondary star. [ABSTRACT FROM AUTHOR]

Relativistic magnetic reconnection is a potential particle acceleration mechanism for high-frequency BL Lac objects (HBLs). The Imaging X-ray Polarimetry Explorer (IXPE) scheduled to launch in 2021 has the capability to probe the evolution of magnetic field in HBLs, examining the magnetic reconnection scenario for the HBL flares. In this paper, we make the first attempt to self-consistently predict HBL X-ray polarization signatures arising from relativistic magnetic reconnection via combined particle-in-cell and polarized radiation transfer simulations. We find that although the intrinsic optical and X-ray polarization degrees are similar on average, the X-ray polarization is much more variable in both the polarization degree and angle (PD and PA). Given the sensitivity of the IXPE, it may obtain one to a few polarization data points for one flaring event of nearby bright HBLs Mrk 421 and 501. However, it may not fully resolve the highly variable X-ray polarization. Due to temporal depolarization, where the integration of photons with variable polarization states over a finite period of time can lower the detected PD, the measured X-ray PD can be considerably lower than the optical counterpart or even undetectable. The lower X-ray PD than the optical thus can be a characteristic signature of relativistic magnetic reconnection. For very bright flares where the X-ray polarization is well resolved, relativistic magnetic reconnection predicts smooth X-ray PA swings, which originate from large plasmoid mergers in the reconnection region. [ABSTRACT FROM AUTHOR]

We report the discovery of diffuse X-ray emission around the supernova remnant (SNR) G106.3+2.7, which is associated with VER J2227+608 and HAWC J2227+610 and is known as a candidate for a PeV cosmic-ray accelerator (PeVatron). We analyze observational data of Suzaku around the SNR and the adjacent pulsar PSR J2229+6114. We find diffuse X-ray emission that is represented by either thermal or nonthermal processes. However, the metal abundance for the thermal emission is <0.13 Z⊙, which may be too small in the Milky Way and suggests that the emission is nonthermal. The intensity of the diffuse emission increases toward PSR J2229+6114 in the same way as radio emission, and it is in contrast with gamma-ray emission concentrated on a molecular cloud. The X-ray photon index does not change with the distance from the pulsar and it indicates that radiative cooling is ineffective and particle diffusion is not extremely slow. The X-ray and radio emissions seem to be of leptonic origin and the parent electrons may originate from the pulsar. The gamma-ray emission appears to be of hadronic origin because of its spatial distribution. The parent protons may be tightly confined in the cloud separately from the diffusing electrons. [ABSTRACT FROM AUTHOR]

"Changing-look" quasars are a new class of highly variable active galactic nuclei that have changed their spectral type over surprisingly short timescales of just a few years. The origin of this phenomenon is debated, but is likely to reflect some change in the accretion flow. To investigate the disk–corona systems in these objects, we measure optical/UV–X-ray spectral indices () and Eddington ratios () of 10 previously discovered changing-look quasars at two or more epochs. By comparing these data with simulated results based on the behavior of X-ray binaries, we find possible similarities in spectral indices below the 1% Eddington ratio. We further investigate the Eddington ratios of changing-look quasars before and after their spectral type changes, and find that changing-look quasars cross the 1% Eddington ratio boundary when their broad emission lines disappear/emerge. This is consistent with the disk-wind model as the origin of broad emission lines. [ABSTRACT FROM AUTHOR]

We report results of the first broadband observation of the transient X-ray pulsar GRO J1008−57 performed in the quiescent state. Observations were conducted quasi-simultaneously with NuSTAR and the Mikhail Pavlinsky ART-XC telescope on board SRG right before the beginning of a Type I outburst. GRO J1008−57 was detected in the state with the lowest observed luminosity around several ×1034 erg s−1 and consequently accreting from the cold disk. Timing analysis allowed us to detect pulsations during this state for the first time. The observed pulsed fraction of about 20% is, however, almost three times lower than in brighter states when the accretion proceeds through the standard disk. We traced the evolution of the broadband spectrum of the source on a scale of three orders of magnitude in luminosity and found that at the lowest luminosities the spectrum transforms into the double-hump structure similarly to other X-ray pulsars accreting at low luminosities (X Persei, GX 304–1, and A 0535+262) reinforcing the conclusion that this spectral shape is typical for these objects. [ABSTRACT FROM AUTHOR]

We report on the discovery of a promising candidate for a black widow (BW) millisecond pulsar binary, 4FGL J0336.0+7502, which shows many pulsar-like properties in the 4FGL-DR2 catalog. Within the 95% error region of the LAT source, we identified an optical counterpart with a clear periodicity at Porb = 3.718178(9) hr using the Bohyunsan 1.8 m Telescope, the Lulin One-meter Telescope, the Canada–France–Hawaii Telescope, and Gemini-North. At the optical position, an X-ray source was marginally detected in the Swift/X-Ray Telescope archival data, and the detection was confirmed by our Chandra/ACIS DDT observation. The spectrum of the X-ray source can be described by a power-law model of Γx = 1.6 ± 0.7 and erg cm−2 s−1. The X-ray photon index and the low X-ray-to-γ-ray flux ratio (i.e., <1%) are both consistent with that of many known BW pulsars. There is also a hint of an X-ray orbital modulation in the Chandra data, although the significance is very low (1.3σ). If the pulsar identity and the X-ray modulation are confirmed, it would be the fifth BW millisecond pulsar binary that showed an orbitally modulated emission in X-rays. [ABSTRACT FROM AUTHOR]

As the central engine of gamma-ray bursts (GRBs), a nascent magnetar can release its rotational energy by magnetic dipole radiation. This energy is injected into the outflow of the GRB jet. With the rapid evolution of the magnetic inclination angle, the perpendicular component of the magnetar's surface magnetic field decreases rapidly. The energy loss rate of the magnetar is characterized by two different timescales. This peculiar two-stage energy injection model will affect the shape of the X-ray afterglow light curve. It is shown that a new shallow decay phase will emerge following the initial shallow decay phase. As a result, there could be two plateaus in the X-ray light curve. The effects of various physical parameters on the light curves are studied in detail. It is found that the observed afterglows of GRB 161217A and GRB 190114A, both having two plateaus in the light curve, can be well fitted in our framework. [ABSTRACT FROM AUTHOR]

An appearance or disappearance of quasi-periodic oscillations (QPOs) associated with the variation of X-ray flux can be used to decipher the accretion–ejection mechanism of black hole X-ray sources. We searched for and studied such rapid transitions in H1743-322 using archival data from the Rossi X-ray Timing Explorer and found eight such events, where a QPO vanishes suddenly along with the variation of X-ray flux. The appearance/disappearance of QPOs was associated with four events exhibiting type-B QPOs at ∼4.5 Hz: one was a type-A QPO at ν ∼ 3.5 Hz, and the other three were connected to type-C QPOs at ∼9.5 Hz. Spectral studies of the data revealed that the inner disk radius remained at the same location around 2–9 rg, depending on the model used, but power-law indices were varying, indicating that either a corona or a jet is responsible for the events. The probable ejection radii of coronas were estimated to be around 4.2–15.4 rg based on the plasma ejection model. Our X-ray and quasi-simultaneous radio correlation studies suggest that the type-B QPOs are probably related to the precession of a weak jet, though a small and weak corona is present at its base, and the type-C QPOs are associated with the base of a relatively strong jet, which is acting like a corona. [ABSTRACT FROM AUTHOR]

We present deep (265 ks) Chandra X-ray observations of PSO J352.4034−15.3373, a quasar at z = 5.831 that, with a radio-to-optical flux ratio of R > 1000, is one of the radio-loudest quasars in the early universe and is the only quasar with observed extended radio jets of kiloparsec scale at z ≳ 6. Modeling the X-ray spectrum of the quasar with a power law, we find a best fit of , leading to an X-ray luminosity of and an X-ray to UV brightness ratio of αOX = −1.45 ± −0.11. We identify a diffuse structure 50 kpc (∼8″) to the NW of the quasar along the jet axis that corresponds to a 3σ enhancement in the angular density of emission and can be ruled out as a background fluctuation with a probability of P = 0.9985. While with few detected photons the spectral fit of the structure is uncertain, we find that it has a luminosity of L2–10 ∼ 1044 erg s−1. These observations therefore potentially represent the most distant quasar jet yet seen in X-rays. We find no evidence for excess X-ray emission where the previously reported radio jets are seen (which have an overall linear extent of 0.″28), and a bright X-ray point source located along the jet axis to the SE is revealed by optical and NIR imaging to not be associated with the quasar. [ABSTRACT FROM AUTHOR]

We present a multiwavelength analysis of the cluster A1668, performed by means of new EVLA and Chandra observations and archival Hα data. The radio images exhibit a small central source (∼14 kpc at 1.4 GHz) with L1.4GHz ∼ 6 · 1023 W Hz−1. The mean spectral index between 1.4 GHz and 5 GHz is ∼−1, consistent with the usual indices found in BCGs. The cooling region extends for 40 kpc, with bolometric X-ray luminosity Lcool = 1.9 ± 0.1 · 1043 erg s−1. We detect an offset of ∼6 kpc between the cluster BCG and the X-ray peak, and another offset of ∼7.6 kpc between the Hα and the X-ray peaks. We discuss possible causes for these offsets, which suggest that the coolest gas is not condensing directly from the lowest-entropy gas. In particular, we argue that the cool ICM was drawn out from the core by sloshing, whereas the Hα filaments were pushed aside from the expanding radio galaxy lobes. We detect two putative X-ray cavities, spatially associated with the west radio lobe (cavity A) and the east radio lobe (cavity B). The cavity power and age of the system are Pcav ∼ 9 × 1042 erg s−1 and tage ∼ 5.2 Myr, respectively. Evaluating the position of A1668 in the cooling luminosity–cavity power parameter space, we find that the AGN energy injection is currently consistent within the scatter of the relationship, suggesting that offset cooling is likely not breaking the AGN feedback cycle. [ABSTRACT FROM AUTHOR]

We examine a sample of 21 gamma-ray burst (GRB) afterglow light curves at radio frequencies and compare them to the X-ray and/or optical properties of the afterglows and to the predictions of the standard jet/fireball model. Our sample includes every Swift GRB with an X-ray light curve indicating a jet break and with a published radio light curve, as well as several other targets with observed X-ray or and/optical jet breaks. We examine the late-time decline of each burst and attempt to fit an analytical model based on the standard GRB afterglow equations to each data set. We show that most of the events in our Swift GRB sample are incompatible with the radio light-curve behavior predicted by conventional afterglow theory. Many exhibit a late-time radio decline incompatible with the post-break X-ray or optical afterglow. Only one radio afterglow in this sample, at any time, shows the eventually expected decline of ∼t−2, although two others show it in their millimeter light curve. Several others remain consistent with the standard model if such a decline began after the observations. The radio behavior alone does not, however, indicate whether a GRB can be fit by our modeling code. Indeed, several of the well-fit GRBs may only appear so due to a lack of multiwavelength data. While a second source of emission can account for some of the anomalous radio behavior, our tests indicate this is often not the case unless the main jet component is simultaneously suppressed. [ABSTRACT FROM AUTHOR]

We report on the X-ray properties of the new transient Swift J0840.7−3516, discovered with Swift/BAT in 2020 February, using extensive data from Swift, MAXI, NICER, and NuSTAR. The source flux increased for ∼103 s after the discovery, decayed rapidly over ∼5 orders of magnitude in five days, and then remained almost constant over nine months. Large-amplitude short-term variations on timescales of 1–104 s were observed throughout the decay. In the initial flux rise, the source showed a hard power-law-shaped spectrum with a photon index of ∼1.0 extending up to ∼30 keV, above which an exponential cutoff was present. The photon index increased in the following rapid decay and became ∼2 at the end of the decay. A spectral absorption feature at 3–4 keV was detected in the decay. It is not straightforward to explain all the observed properties by any known class of X-ray sources. We discuss the possible nature of the source, including a Galactic low-mass X-ray binary with multiple extreme properties and a tidal disruption event by a supermassive black hole or a Galactic neutron star. [ABSTRACT FROM AUTHOR]

The detection of GeV γ-ray emission from Galactic novae by the Fermi-Large Area Telescope has become routine since 2010, and is generally associated with shocks internal to the nova ejecta. These shocks are also expected to heat plasma to ∼107 K, resulting in detectable X-ray emission. In this paper, we investigate 13 γ-ray emitting novae observed with the Neil Gehrels Swift Observatory, searching for 1–10 keV X-ray emission concurrent with γ-ray detections. We also analyze γ-ray observations of novae V407 Lup (2016) and V357 Mus (2018). We find that most novae do eventually show X-ray evidence of hot shocked plasma, but not until the γ-rays have faded below detectability. We suggest that the delayed rise of the X-ray emission is due to large absorbing columns and/or X-ray suppression by corrugated shock fronts. The only nova in our sample with a concurrent X-ray/γ-ray detection is also the only embedded nova (V407 Cyg). This exception supports a scenario where novae with giant companions produce shocks with external circumbinary material and are characterized by lower density environments, in comparison with novae with dwarf companions where shocks occur internal to the dense ejecta. [ABSTRACT FROM AUTHOR]

We present optical follow-up observations for candidate clusters in the Clusters Hiding in Plain Sight survey, which is designed to find new galaxy clusters with extreme central galaxies that were misidentified as bright isolated sources in the ROSAT All-Sky Survey catalog. We identify 11 cluster candidates around X-ray, radio, and mid-IR-bright sources, including six well-known clusters, two false associations of foreground and background clusters, and three new candidates, which are observed further with Chandra. Of the three new candidates, we confirm two newly discovered galaxy clusters: CHIPS 1356-3421 and CHIPS 1911+4455. Both clusters are luminous enough to be detected in the ROSAT All-Sky Survey data if not because of their bright central cores. CHIPS 1911+4455 is similar in many ways to the Phoenix cluster, but with a highly disturbed X-ray morphology on large scales. We find the occurrence rate for clusters that would appear to be X-ray-bright point sources in the ROSAT All-Sky Survey (and any surveys with similar angular resolution) to be 2% ± 1%, and the occurrence rate of clusters with runaway cooling in their cores to be <1%, consistent with predictions of chaotic cold accretion. With the number of new groups and clusters predicted to be found with eROSITA, the population of clusters that appear to be point sources (due to a central QSO or a dense cool core) could be around 2000. Finally, this survey demonstrates that the Phoenix cluster is likely the strongest cool core at z < 0.7—anything more extreme would have been found in this survey. [ABSTRACT FROM AUTHOR]

We report that the RS CVn–type star GT Mus (HR 4492, HD 101379+HD 101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. We detected 11 flares from GT Mus in 8 yr of observations with the Monitor of All-sky X-ray Image (MAXI) from 2009 August to 2017 August. The detected flare peak luminosities were 1–4 × 1033 erg s−1 in the 2.0–20.0 keV band for its distance of 109.6 pc. Our timing analysis showed long durations (τr + τd) of 2–6 days with long decay times (τd) of 1–4 days. The released energies during the decay phases of the flares in the 0.1–100 keV band were in the range of 1–11 × 1038 erg, which are at the upper end of the observed stellar flare. The released energies during the whole duration were in the range of 2–13 × 1038 erg in the same band. We carried out X-ray follow-up observations for one of the 11 flares with the Neutron star Interior Composition Explorer (NICER) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4 × 1012 cm (or 60 R☉). The electron density is derived to be 1 × 1010 cm−3, which is consistent with the typical value of solar and stellar flares (1010–13 cm−3). The ratio of the cooling timescales between radiative (τrad) and conductive (τcond) cooling is estimated to be τrad ∼ 0.1 τcond from the temperature; thus, radiative cooling was dominant in this flare. [ABSTRACT FROM AUTHOR]

We present the spatial analysis of five Compton thick (CT) active galactic nuclei (AGNs), including MKN 573, NGC 1386, NGC 3393, NGC 5643, and NGC 7212, for which high-resolution Chandra observations are available. For each source, we find hard X-ray emission (>3 keV) extending to ∼kiloparsec scales along the ionization cone, and for some sources, in the cross-cone region. This collection represents the first, high-signal sample of CT AGN with extended hard X-ray emission for which we can begin to build a more complete picture of this new population of AGN. We investigate the energy dependence of the extended X-ray emission, including possible dependencies on host galaxy and AGN properties, and find a correlation between the excess emission and obscuration, suggesting a connection between the nuclear obscuring material and the galactic molecular clouds. Furthermore, we find that the soft X-ray emission extends farther than the hard X-rays along the ionization cone, which may be explained by a galactocentric radial dependence on the density of molecular clouds due to the orientation of the ionization cone with respect to the galactic disk. These results are consistent with other CT AGN with observed extended hard X-ray emission (e.g., ESO 428-G014 and the Ma et al. CT AGN sample), further demonstrating the ubiquity of extended hard X-ray emission in CT AGN. [ABSTRACT FROM AUTHOR]

We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with archival Chandra observations. With ∼20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ∼2 and ∼8 days via the Bayesian block technique. A phase-dispersion minimization and a test suggest that the dip is likely recurrent with a period of ∼2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream–disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ∼60°. Given that the magnetic field of M51 ULX-7 is moderately high, B ∼ 1013 G, a low geometric beaming with is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required. [ABSTRACT FROM AUTHOR]

We report on the temporal properties of the ultraluminous X-ray (ULX) pulsar M51 ULX-7 inferred from the analysis of the 2018–2020 Swift/X-ray Telescope monitoring data and archival Chandra data obtained over a period of 33 days in 2012. We find an extended low flux state, which might be indicative of propeller transition, lending further support to the interpretation that the neutron star is rotating near equilibrium. Alternatively, this off-state could be related to a variable superorbital period. Moreover, we report the discovery of periodic dips in the X-ray light curve that are associated with the binary orbital period. The presence of the dips implies a configuration where the orbital plane of the binary is closer to an edge-on orientation, and thus demonstrates that favorable geometries are not necessary in order to observe ULX pulsars. These characteristics are similar to those seen in prototypical X-ray pulsars such as Her X-1 and SMC X-1 or other ULX pulsars such as NGC 5907 ULX1. [ABSTRACT FROM AUTHOR]

Tidal disruption events (TDEs) occurring in active galactic nuclei (AGNs) are a special class of sources with outstanding scientific significance. TDEs can generate ultrafast winds, which should almost inevitably collide with the preexisting AGN dusty tori. We perform analytical calculations and simulations on the wind–torus interactions and find such a process can generate considerable X-ray afterglow radiation several years or decades later after the TDE outburst. This provides a new origin for the years delayed X-rays in TDEs. The X-ray luminosity can reach 1041−42 erg s−1, and the light curve characteristics depend on the parameters of winds and tori. We apply the model to two TDE candidates, and provide lower limits on the masses of the disrupted stars, as well as rigorous constraints on the gas densities of tori. Our results suggest that the observations of the time delay, spectral shape, luminosity, and the light curve of the X-ray afterglow can be used to constrain the physical parameters of both TDE winds and tori, including the wind velocity, wind density, cloud density, and cloud size. [ABSTRACT FROM AUTHOR]

The reprocessed X-ray emission from active galactic nuclei is an important diagnostic tool to study the dynamics and geometry of the matter surrounding supermassive black holes (SMBHs). We present a broadband (optical-UV to hard X-ray) spectral study of the bare Seyfert 1 galaxy, ESO 511–G030, using multi-epoch Suzaku and XMM-Newton data from 2012 and 2007, respectively. The broadband spectra of ESO 511–G030 exhibit a UV bump, a prominent soft excess below , a relatively broad () Fe emission line at , and a weak Compton hump at. The soft X-ray excess in ESO 511–G030 can be described either as the thermal Comptonization of disk seed photons by a warm (), optically thick (), and compact () corona or as the blurred reflection from an untruncated and moderate to highly ionized accretion disk. However, for the blurred reflection, the model requires some extreme configuration of the disk and corona. Both these models prefer a rapidly spinning black hole () and a compact corona, indicating a relativistic origin of the broad Fe emission line. We found an inner disk temperature of that characterizes the UV bump and the SMBH accretes at a sub-Eddington rate (). [ABSTRACT FROM AUTHOR]