Intrinsic X-ray Research Articles

Probing the heating of the neutral atomic interstellar medium in the Dwarf Galaxy Survey through infrared cooling lines

Star formation in galaxies is regulated by dynamical and thermal processes. In the Milky Way and star-forming galaxies with similar metallicity, the photoelectric effect on small dust grains usually dominates the heating of the neutral atomic gas, which constitutes the main star-forming gas reservoir. In more metal-poor galaxies, the lower dust-to-gas mass ratio together with the higher occurrence and luminosity of X-ray sources suggest that other heating mechanisms may be at play. We aim to determine the contribution of the photoelectric effect, photoionization by UV and X-ray photons, and ionization by cosmic rays to the total heating of the neutral gas in a sample of 37 low-metallicity galaxies. In particular, we wish to assess whether X-ray sources can be a significant source of heating. We also attempt to recover the intrinsic X-ray fluxes and compare them with observations when available. We used the statistical code MULTIGRIS together with a photoionization grid of Cloudy models propagating radiation from stellar clusters and potential X-ray sources to the ionized and neutral gas. This grid includes physical parameters such as metallicity, gas density, ionization parameter, and radiative source properties. We describe a galaxy as a combination of many 1D components linked by a few physical hyperparameters. We used infrared cooling lines as constraints to evaluate the most likely combinations and parameters. We constrained the heating fractions for the main mechanisms for the first time in a low-metallicity galaxy sample. We show that for the higher metallicity galaxies, the photoelectric effect dominates the neutral gas heating. At metallicities below $1/8$ the Milky Way value, cosmic rays and photoionization can become predominant. We computed an observational proxy for the photoelectric effect heating efficiency on polycyclic aromatic hydrocarbons (PAHs) using the total cooling traced by We show that this proxy can match theoretical expectations when accounting for the fraction of the heating due to the photoelectric effect according to our models. Finally, we show that it is possible to predict the X-ray fluxes reasonably well in the $0.3-8$\,keV band from the gas cooling lines for most of the galaxies observed in this band. With the current grid and assumptions, determining the exact heating fraction due to cosmic rays remains difficult, but we speculate that heating from X-ray sources is more important. As expected from the low abundance of dust and PAHs in metal-poor galaxies, heating mechanisms other than the photoelectric effect heating must be accounted for. Bright X-ray sources may deposit their energy on large scales in such transparent, dust-poor interstellar medium, and thus they represent promising avenues to understand the physical properties of the main star-forming gas reservoir in galaxies. The modeling strategy adopted here makes it possible to recover the global intrinsic radiation field properties when X-ray observations are unavailable, such as in early universe galaxies.

A cascade X-ray energy converting approach toward radio-afterglow cancer theranostics.

Leveraging X-rays to initiate prolonged luminescence (radio-afterglow) and stimulate radiodynamic 1O2 production from optical agents provides opportunities for diagnosis and therapy at tissue depths inaccessible to light. However, X-ray-responsive organic luminescent materials are rare due to their intrinsic low X-ray conversion efficiency. Here we report a cascade X-ray energy converting approach to develop organic radio-afterglow nanoprobes (RANPs) for cancer theranostics. RANPs comprise a radiowave absorber that down-converts X-ray energy to emit radioluminescence, which is transferred to a radiosensitizer to produce singlet oxygen (1O2). 1O2 then reacts with a radio-afterglow substrate to generate an active intermediate that simultaneously decomposes to emit radio-afterglow. Through finetuning such a cascade, intraparticle radioluminescence energy transfer and the 1O2 transfer process, RANPs possess tunable wavelengths and long half-lives, and generate radio-afterglow and 1O2 at tissue depths of up to 15 cm. Moreover, we developed a biomarker-activatable nanoprobe (tRANP) that produces a tumour-specific radio-afterglow signal, leading to ultrasensitive detection and the possibility of surgical removal of diminutive tumours (1 mm3) under an X-ray dosage 20 times lower than inorganic materials. The efficient radiodynamic 1O2 generation of tRANP permits complete tumour eradication at an X-ray dosage lower than clinical radiotherapy and a drug dosage one to two orders of magnitude lower than most existing inorganic agents, leading to prolonged survival rates with minimized radiation-related adverse effects. Thus, our work reveals a generic approach to address the lack of organic radiotheranostic materials and provides molecular design towards precision cancer radiotherapy.

The importance of stochasticity in determining galaxy emissivities and UV LFs during cosmic dawn and reionization

The stochastic nature of star formation and photon propagation in high-redshift galaxies can result in sizable galaxy-to-galaxy scatter in their properties. Ignoring this scatter by assuming mean quantities can bias estimates of their emissivity and corresponding observables. We constructed a flexible, semi-empirical model, sampling scatter around the following mean relations: (i) the conditional halo mass function (CHMF); (ii) the stellar-to-halo mass relation (SHMR); (iii) the galaxy star formation main sequence (SFMS); (iv) the fundamental metallicity relation (FMR); (v) the conditional intrinsic luminosity; and (vi) the photon escape fraction. In our fiducial model, ignoring scatter in these galaxy properties overestimates the duration of the Epoch of Reionization (EoR), delaying its completion by $ z 1--2. We quantified the relative importance of each of the above sources of scatter in determining the ionizing, soft-band X-ray, and Lyman Werner (LW) emissivities as a function of scale and redshift. We find that scatter around the SFMS is important for all bands, especially at the highest redshifts where the emissivity is dominated by the faintest, most "bursty" galaxies. Ignoring this scatter would underestimate the mean emissivity and its standard deviation computed over 5 cMpc regions by factors of up to sim 2--10 at $5 z 15$. The scatter around the X-ray luminosity to star formation rate and metallicity relation is important for determining X-ray emissivity, accounting for roughly half of its mean and standard deviation. The importance of scatter in the ionizing escape fraction depends on its functional form, while scatter around the SHMR contributes at the level of sim 10--20<!PCT!>. Other sources of scatter have a negligible contribution to the emissivities. Although scatter does flatten the UV luminosity functions, shifting the bright end by 1--2 magnitudes, the level of scatter in our fiducial model is insufficient to fully explain recent estimates from JWST photometry (consistent with previous studies). We conclude that models of the EoR should account for the burstiness of star formation, while models for the cosmic 21cm signal should additionally account for scatter in intrinsic X-ray production.

Characterizing the luminosity components of luminous infrared galaxies in multi-wavelength from the X-ray to the far-infrared

We characterize luminosity components of Ultra/Luminous Infrared Galaxies (U/LIRGs) in multi-wavelength from the X-ray to far-infrared. A set of 63 AGN U/LIRGs was selected where these galaxies are powered by a central active galactic nucleus (AGN). Utilizing the X-CIGALE code, SEDs for these galaxies are carried out where their SEDs are fitted with observations. Accordingly, the physical parameters such as the stellar mass, the dust-to-gas mass ratio, and the star formation rate are calculated. The total luminosity and its decomposed components (stellar, AGN, X-ray) are also calculated. We characterized these luminosities in relative to the intrinsic luminosity and in relative to each other. As a function of the stellar mass, these luminosities reveal an increase with different correlation coefficients, showing a strong correlation. In correlation with the intrinsic AGN power, the stellar, AGN, and X-ray luminosities are strongly correlates in their variation to the intrinsic AGN luminosity, showing stronger correlations of AGN, and X-ray luminosities than those of the stellar one. In relationships between various luminosity components, both the stellar and X-ray luminosities reveal strong correlations with the AGN luminosity. On the other hand, the X-ray luminosity varies strongly with the stellar luminosity and moderately with IR luminosity. Compared to obscured AGN galaxies, both the stellar and AGN luminosities similarly vary with increasing the intrinsic power of the active nucleus but for obscured AGN they are faster in their variation than that of U/LIRG. These correlations may offer valuable insights to understand the physical properties and their relationships through the evolution of U/LIRGs.

JADES – the Rosetta stone of JWST-discovered AGN: deciphering the intriguing nature of early AGN

ABSTRACT JWST has discovered a large population of active galactic nuclei (AGN) at high redshift, which are weak in the X-rays. Here we present the NIRSpec spectrum of the most extreme of these objects, GN-28074, an AGN at $z=2.26$ with prominent hydrogen and He i broad lines, and with the highest limit on the bolometric to X-ray luminosity ratio among all spectroscopically confirmed AGN in GOODS. This source is also characterized by a mid-IR excess, likely associated with the AGN torus’ hot dust. The high bolometric luminosity and moderate redshift of this AGN allow us to explore its properties more in depth relative to other JWST-discovered AGN. The NIRSpec spectrum reveals prominent, slightly blueshifted absorption of H$\alpha$, H$\beta$, and He i $\lambda$10830. The Balmer absorption lines require gas with densities of $n_{\rm H}\gt 10^8~{\rm cm}^{-3}$, consistent with clouds in the broad-line region (BLR). This finding suggests that part of the X-ray weakness is due to high (Compton-thick) X-ray absorption by clouds in the BLR, or in its outer regions. GN-28074 is also extremely radio-weak. The radio weakness can also be explained in terms of absorption, as the inferred density of the BLR clouds makes them attenuate the radio emission through free–free absorption. Alternatively, the nuclear magnetic field may be underdeveloped, resulting both in intrinsically weak radio emission and lack of hot corona, hence intrinsic X-ray weakness. Finally, we show that recently proposed scenarios, invoking hyper-dense outflows or Raman scattering to explain the broad H$\alpha$, are ruled out.

Evidence for Intrinsic X-Ray Weakness among Red Quasars at Cosmic Noon

Quasar feedback is a key ingredient in shaping galaxy evolution. A rare population of extremely red quasars (ERQs) at z = 2−3 are often associated with high-velocity [O iii]λ5008 outflows and may represent sites of strong feedback. In this paper, we present an X-ray study of 50 ERQs to investigate the link between the X-ray and outflow properties of these intriguing objects. Using hardness ratio analysis, we confirm that the ERQs are heavily obscured systems with gas column density reaching N H = 1023−24 cm−2. We identify 20 X-ray-nondetected ERQs at high mid-infrared (MIR) luminosities of ν L ν,6 μm ≳ 3 × 1046 erg s−1. By stacking the X-ray observations, we find that the nondetected ERQs are on average underluminous in X-rays by a factor of ∼10 for their MIR luminosities. We consider such X-ray weakness to be due to both heavy gas absorption and intrinsic factors. Moreover, we find that the X-ray-weak sources also display higher-velocity outflows. One option to explain this trend is that weaker X-rays facilitate more vigorous line-driven winds, which then accelerate the [O iii]-emitting gas to kiloparsec scales. Alternatively, super-Eddington accretion could also lead to intrinsic X-ray weakness and more powerful continuum-driven outflow.

The Remarkable X-Ray Spectra and Variability of the Ultraluminous Weak-line Quasar SDSS J1521+5202

We present a focused X-ray and multiwavelength study of the ultraluminous weak-line quasar (WLQ) SDSS J1521+5202, one of the few X-ray weak WLQs that is amenable to basic X-ray spectral and variability investigations. J1521+5202 shows striking X-ray variability during 2006–2023, by up to a factor of ≈32 in 0.5–2 keV flux, and our new 2023 Chandra observation caught it in its brightest X-ray flux state to date. Concurrent infrared/optical observations show only mild variability. The 2023 Chandra spectrum can be acceptably described by a power law with intrinsic X-ray absorption, and it reveals a nominal intrinsic level of X-ray emission relative to its optical/ultraviolet emission. In contrast, an earlier Chandra spectrum from 2013 shows apparent spectral complexity that is not well fit by a variety of models, including ionized absorption or standard Compton-reflection models. Overall, the observations are consistent with the thick-disk plus outflow model previously advanced for WLQs, where a nominal level of underlying X-ray emission plus variable absorption leads to the remarkable observed X-ray variability. In the case of J1521+5202, it appears likely that the outflow, and not the thick disk itself, lies along our line of sight and causes the X-ray absorption.

Accretion properties of X-ray AGN: evidence for radiation-regulated obscuration with redshift-dependent host galaxy contribution

ABSTRACT We adopt a Bayesian X-ray spectral approach to investigate the accretion properties of unobscured ($20\lt \log (N_{\rm H}/{\rm cm}^{-2}\lt 22$) and obscured ($22\lt \log (N_{\rm H}/{\rm cm}^{-2}\lt 24$) active galactic nuclei (AGNs) to shed light on the orientation versus evolution scenarios for the origin of the obscuring material. For a sample of 3882 X-ray-selected AGN from the Chandra COSMOS Legacy, AEGIS, and CDFS extragalactic surveys, we constrain their stellar masses, $M_\star$, intrinsic X-ray luminosities, $L_{\rm X}$, obscuring column densities, $N_{\rm H}$, and specific accretion rates $\lambda \propto L_{\rm X}/M_\star$. By combining these observables within a Bayesian non-parametric approach, we infer, for the first time, the specific accretion rate distribution (SARD) of obscured and unobscured AGN to $z\approx 3$, i.e. the probability of a galaxy with mass $M_\star$ at redshift z hosting an AGN with column density $N_{\rm H}$ and specific accretion rate $\lambda$. Our findings indicate that (1) both obscured and unobscured SARDs share similar shapes, shifting towards higher accretion rates with redshift, (2) unobscured SARDs exhibit a systematic offset towards higher $\lambda$ compared to obscured SARD for all redshift intervals, (3) the obscured AGN fraction declines sharply at $\log \lambda _{\rm break} \sim -2$ for $z \lt 0.5$, but shifts to higher $\lambda$ values with increasing redshift, (4) the incidence of AGN within the theoretically unstable blow-out region of the $\lambda -N_{\rm H}$ plane increases with redshift. These observations provide compelling evidence for AGN ‘downsizing’ and radiation-regulated nuclear-scale obscuration with an increasing host galaxy contribution towards higher redshifts.

Ups and downs in the X-ray emission of the colliding wind binaries HD 168112 and HD 167971

Context. The long-period O-star binary system HD 168112 and the triple O-star system HD 167971 are well-known sources of non-thermal radio emission that arises from a colliding wind interaction. The wind-wind collisions in these systems should result in phase-dependent X-ray emissions. The presence of a population of relativistic electrons in the wind interaction zone could affect the properties of the X-ray emission and make it deviate from the behaviour expected for adiabatic shocks. Aims. We investigate the X-ray emission of these systems with the goals of quantifying the fraction of the X-ray flux arising from wind interactions and determining whether these emissions follow the predictions for adiabatic wind-wind collisions. Methods. Six X-ray observations were collected with XMM-Newton. Three observations were scheduled around the most recent peri-astron passage of HD 168112. Spectra and light curves were analysed and compared with simple predictions of model calculations for X-ray emission from colliding wind systems. Results. The X-ray emission of HD 168112 varies as the inverse of the orbital separation, as expected for an adiabatic wind interaction zone. The relative contribution of intrinsic X-ray emission from wind-embedded shocks varies between 38% at periastron to 81% at apastron. The wind-wind collision zone remains adiabatic even around periastron passage. The X-ray emission of HD 167971 displays variations on the orbital timescale of the inner eclipsing binary. The existing data of this system do not allow us to probe variations on the timescale of the outer orbit. Conclusions. Shock modification due to the action of relativistic electrons does not seem to be efficiently operating in the HD 168112 system. In the existing observations, a significant part of the emission of HD 167971 must arise in the inner eclipsing binary. The origin of this emission is as yet unclear.

On the Origin of the X-Ray Emission in Heavily Obscured Compact Radio Sources

X-ray continuum emission of active galactic nuclei (AGNs) may be reflected by circumnuclear dusty tori, producing prominent fluorescence iron lines at X-ray frequencies. Here, we discuss the broadband emission of three radio-loud AGNs belonging to the class of compact symmetric objects (CSOs), with detected narrow Fe Kα lines. CSOs have newly born radio jets, forming compact radio lobes with projected linear sizes of the order of a few to hundreds of parsecs. We model the radio-to-γ-ray spectra of compact lobes in J1407+2827, J1511+0518, and J2022+6137, which are among the nearest and the youngest CSOs known to date, and are characterized by an intrinsic X-ray absorbing column density of N H > 1023 cm−2. In addition to the archival data, we analyze the newly acquired Chandra X-ray Observatory and Submillimeter Array (SMA) observations, and also refine the γ-ray upper limits from Fermi Large Area Telescope monitoring. The new Chandra data exclude the presence of the extended X-ray emission components on scales larger than 1.″5. The SMA data unveil a correlation between the spectral index of the electron distribution in the lobes and N H, which can explain the γ-ray quietness of heavily obscured CSOs. Based on our modeling, we argue that the inverse-Compton emission of compact radio lobes may account for the intrinsic X-ray continuum in all these sources. Furthermore, we propose that the observed iron lines may be produced by a reflection of the lobes’ continuum from the surrounding cold dust.

Investigating Model Dependencies for Obscured Active Galactic Nuclei: A Case Study of NGC 3982

Abstract X-ray spectroscopy of heavily obscured active galactic nuclei (AGN) offers a unique opportunity to study the circumnuclear environment of accreting supermassive black holes. However, individual models describing the obscurer have unique parameter spaces that give distinct parameter posterior distributions when fit to the same data. To assess the impact of model-specific parameter dependencies, we present a case study of the nearby heavily obscured low-luminosity AGN NGC 3982, which has a variety of column density estimations reported in the literature. We fit the same broadband XMM-Newton+NuSTAR spectra of the source with five unique obscuration models and generate posterior parameter distributions for each. By using global parameter exploration, we traverse the full prior-defined parameter space to accurately reproduce complex posterior shapes and inter-parameter degeneracies. The unique model posteriors for the line-of-sight column density are broadly consistent, predicting Compton-thick N H > 1.5 × 1024 cm−2 at the 3σ confidence level. The posterior median intrinsic X-ray luminosity in the 2–10 keV band was found to differ substantially, however, with values in the range log L 2–10 keV/ erg s−1 = 40.9–42.1 for the individual models. We additionally show that the posterior distributions for each model occupy unique regions of their respective multidimensional parameter spaces and how such differences can propagate into the inferred properties of the central engine. We conclude by showcasing the improvement in parameter inference attainable with the High Energy X-ray Probe, with its uniquely broad, simultaneous, and high-sensitivity bandpass of 0.2–80 keV.

Comparative analysis of the SFR of AGN and non-AGN galaxies, as a function of stellar mass, AGN power, cosmic time, and obscuration

This study involves a comparative analysis of the star formation rates (SFRs) of active galactic nucleus (AGN) galaxies and non-AGN galaxies and of the SFRs of type 1 and 2 AGNs. To carry out this investigation, we assembled a dataset consisting of 2677 X-ray AGNs detected by the XMM-Newton observatory and a control sample of 64 556 galaxies devoid of AGNs. We generated spectral energy distributions (SEDs) for these objects using photometric data from the DES, VHS, and AllWISE surveys, and we harnessed the CIGALE code to extract measurements for the (host) galaxy properties. Our dataset encompasses a diverse parameter space, with objects spanning a range of stellar masses from 9.5 < log [M*(M⊙)] < 12.0, intrinsic X-ray luminosities within 42 < log[LX,2−10 keV(erg s−1)] < 45.5, and redshifts between 0.3 < z < 2.5. To compare SFRs, we calculated the SFRnorm parameter, which signifies the ratio of the SFR of an AGN galaxy to the SFR of non-AGN galaxies sharing similar M* and redshift. Our analysis reveals that systems hosting an AGN tend to exhibit elevated SFRs compared to non-AGN galaxies, particularly beyond a certain threshold in LX. Notably, this threshold increases as we move toward more massive galaxies. Additionally, for AGN systems with the same LX, the magnitude of the SFRnorm decreases as we consider more massive galaxies. This suggests that in galaxies with an AGN, the increase in SFR as a function of stellar mass is not as prominent as in galaxies without an AGN. This interpretation finds support in the shallower slope that we identify in the X-ray star-forming main sequence in contrast to the galaxy main sequence. Employing CIGALE’s measurements, we classified AGNs into type 1 and type 2. In our investigation, we focused on a subset of 652 type 1 AGNs and 293 type 2 AGNs within the stellar mass range of 10.5 < log[M (M⊙)] < 11.5. Based on our results, type 1 AGNs display higher SFRs than type 2 AGNs, at redshifts below z < 1. However, at higher redshifts, the SFRs of the two AGN populations tend to be similar. At redshifts z < 1, type 1 AGNs show augmented SFRs in comparison to non-AGN galaxies. In contrast, type 2 AGNs exhibit lower SFRs when compared to galaxies that do not host an AGN, at least up to log[LX,2−10 keV(erg s−1)] < 45.

Sample Preparation for X-Ray Fluorescence Microscopy of Iron Distribution in Biological Specimen.

Characterizing the two- and three-dimensional distribution of trace metals in biological specimens is key to better understand their role in biological processes. Iron (Fe) is of particular interest in these trace metals due to its widespread role in maintaining cellular health and preventing disease. X-ray fluorescence microscopy (XFM) is emerging as the method of choice for investigators to interrogate the cellular and subcellular distribution of Fe. XFM utilizes the intrinsic X-ray fluorescence properties of each element to produce quantitative 2D and 3D distributions of trace metals within a sample. Herein, methods for sample preparation of cells and tissue for the determination of Fe distribution by XFM are described.

Glycosylation with different saccharides on the gelling, rheological and structural properties of fish gelatin

In this study, the influence of glycosylation with κ-Carrageenan (κC), high methoxyl pectin (HMP), d-Galactose (Gal) on the gelling, rheological properties and mechanisms of fish gelatin (FG) were comparatively investigated. Results showed that κC was easiest to glycosylated with FG in comparison to HMP and Gal, also had the most significant improvement on the gelling properties and viscosity of FG. HMP was most difficult to glycosylated FG, but still had an excellent enhancement on viscosity. The results of intrinsic fluorescence, FTIR, X-Ray and SEM indicated that proper glycosylation changed the conformation structure and improved the contents of hydrogen bonds and α-helix, stabilizing the gels network. LC-MS/MS results showed that the main glycosylation sites were lysine and arginine amino groups, which was regarded as N-terminal glycosylation. In conclusion, proper N- glycosylation could significantly improve the gelling and rheological properties of FG. This study may provide a new guideline for modification FG to expand its application.

Ultrasonic pretreatment and epigallocatechin gallate incorporation enhance the formation, apparent viscosity, and antioxidant activity of pea protein amyloid-like fibrils

Research on the application of plant protein-based carrier in the field of food is increasing in recent years. Pea protein, a critical plant protein source in food processing, has the advantages of high nutritional value, low price and low allergy. In this study, the effects of pre-ultrasonic treatment on the fibrillation behavior of pea protein, the microstructure, rheological property and antioxidant activity of pea protein amyloid-like fibrils as well as the interaction between epigallocatechin gallate and pea protein amyloid-like fibrils were examined. Thioflavin T fluorescence illuminated pre-ultrasonic treatment could dramatically facilitate the formation of β-sheet structure. Interaction between epigallocatechin gallate and pea protein fibrils was mainly through hydrophobic interaction, evidenced by intrinsic fluorescence spectroscopy, X-ray diffraction and surface hydrophobicity analysis. Antioxidant properties and apparent viscosity of pea protein fibrils were remarkably enhanced with both ultrasound and epigallocatechin gallate addition. The pre-ultrasound treated amyloid-like fibrils were more slender than those without treatment in terms of morphology. It was found that pre-ultrasound treated pea protein fibrils-epigallocatechin gallate composites exhibited the highest stability, viscosity and antioxidant activities, which showed great promising as excellent carriers of bioactive substances. The results obtained in this study could enable the utilization of pea protein fibrils-based hydrogel for stabilizing, encapsulating, and delivering bioactive compounds in food processing.

The intrinsic X-ray luminosity distribution of an optically selected SDSS quasar population

ABSTRACT In active galactic nuclei, the relationship between UV and X-ray luminosity is well studied (often characterised by αox) but often with heterogeneous samples. We have parametrized the intrinsic distribution of X-ray luminosity, LX, for the optically selected sample of SDSS quasars in the Stripe 82 and XXL fields across redshifts 0.5–3.5. We make use of the available XMM observations and a custom pipeline to produce Bayesian sensitivity curves that are used to derive the intrinsic X-ray distribution in a hierarchical Bayesian framework. We find that the X-ray luminosity distribution is well described by a Gaussian function in log10 LX space with a mean that is dependent on the monochromatic 2500 Å UV luminosity, L2500. We also observe some redshift dependence of the distribution. The mean of the LX distribution increases with redshift while the width decreases. This weak but significant redshift dependence leads to L2500–LX and L2500–αox relations that evolve with redshift, and we produce a redshift- and L2500-dependent αox equation. Neither black hole mass nor Eddington ratio appear to be potential drivers of the redshift evolution.

X-Ray Spectral Characterization of the Young Cygnus OB2 Population

We analyze the X-ray spectra of the ∼8000 sources detected in the Cygnus OB2 Chandra Legacy Survey (this focus issue), with the goals of characterizing the coronal plasma of the young low-mass stars in the region and estimating their intrinsic X-ray luminosities. We adopt two different strategies for X-ray sources for which more or less than 20 photons were detected. For the brighter sample we fit the spectra with absorbed isothermal models. In order to limit uncertainties, for most of the fainter Cygnus OB2 members in this sample we constrain the spectral parameters to characteristic ranges defined from the brightest stars. For X-ray sources with <20 net photons we adopt a conversion factor from detected photon flux to intrinsic flux. This was defined, building on the results for the previous sample, as a function of the 20% quantile of the detected photon energy distributions, which we prove to also correlate well with extinction. We then use the X-ray extinction from the spectral fits to constrain the ratio between optical and X-ray extinction toward Cyg OB2, finding it consistent with standard “Galactic” values, when properly accounting for systematics. Finally, we exploit the large number of sources to constrain the average coronal abundances of several elements, through two different ensemble analyses of the X-ray spectra of low-mass Cyg OB2 members. We find the pattern of abundances to be largely consistent with that derived for the young stellar coronae in the Orion Nebula Cluster.

Probing the Origin of Changing-look Quasar Transitions with Chandra

Extremely variable quasars can also show strong changes in broad-line emission strength and are known as changing-look quasars (CLQs). To study the CLQ transition mechanism, we present a pilot sample of CLQs with X-ray observations in both the bright and faint states. From a sample of quasars with bright-state archival SDSS spectra and (Chandra or XMM-Newton) X-ray data, we identified five new CLQs via optical spectroscopic follow-up and then obtained new target-of-opportunity X-ray observations with Chandra. No strong absorption is detected in either the bright- or the faint-state X-ray spectra. The intrinsic X-ray flux generally changes along with the optical variability, and the X-ray power-law slope becomes harder in the faint state. Large-amplitude mid-infrared variability is detected in all five CLQs, and it echoes the variability in the optical with a time lag expected from the light-crossing time of the dusty torus for CLQs with robust lag measurements. The changing-obscuration model is not consistent with the observed X-ray spectra and spectral energy distribution changes seen in these CLQs. It is highly likely that the observed changes are due to the changing accretion rate of the supermassive black hole, so the multiwavelength emission varies accordingly, with promising analogies to the accretion states of X-ray binaries.

A Tight Correlation between Millimeter and X-Ray Emission in Accreting Massive Black Holes from

Recent studies have proposed that the nuclear millimeter continuum emission observed in nearby active galactic nuclei (AGNs) could be created by the same population of electrons that gives rise to the X-ray emission that is ubiquitously observed in accreting black holes. We present the results of a dedicated high-spatial-resolution (∼60–100 mas) Atacama Large Millimeter/submillimeter Array (ALMA) campaign on a volume-limited (<50 Mpc) sample of 26 hard X-ray (>10 keV) selected radio-quiet AGNs. We find an extremely high detection rate (25/26 or ), which shows that nuclear emission at millimeter wavelengths is nearly ubiquitous in accreting SMBHs. Our high-resolution observations show a tight correlation between the nuclear (1–23 pc) 100 GHz and the intrinsic X-ray emission (1σ scatter of 0.22 dex). The ratio between the 100 GHz continuum and the X-ray emission does not show any correlation with column density, black hole mass, Eddington ratio, or star formation rate, which suggests that the 100 GHz emission can be used as a proxy of SMBH accretion over a very broad range of these parameters. The strong correlation between 100 GHz and X-ray emission in radio-quiet AGNs could be used to estimate the column density based on the ratio between the observed 2–10 keV () and 100 GHz (F 100 GHz) fluxes. Specifically, a ratio strongly suggests that a source is heavily obscured (). Our work shows the potential of ALMA continuum observations to detect heavily obscured AGNs (up to an optical depth of one at 100 GHz, i.e., N H ≃ 1027 cm−2), and to identify binary SMBHs with separations <100 pc, which cannot be probed by current X-ray facilities.

Hydrothermal crystal growth of tetralithium octafluoridozirconate (Li4ZrF8) and its physicochemical properties

A single crystal of tetralithium octafluridozirconate (Li4ZrF8) has been obtained by using a hydrothermal process. The crystal phase was analyzed using a powder X-ray diffraction pattern and matched with standard reference data. The high-resolution X-ray diffraction curve indicates that the crystal has good crystalline perfection. The thermal behavior of the crystal sample was investigated by TGA/DSC analysis. The optical bandgap of the crystal sample was calculated from the Tauc plot and found to be 5.8 eV. The crystal sample exhibits intrinsic X-ray excited luminescence with a peak maximum of 265 nm. The thermoluminescence measurement shows two peaks, one is at the high-temperature region of 545 K and another one is at the low-temperature region at 383 K. TL kinetic parameters such as activation energy (E) and frequency factor (s) for the peak at 545 K was estimated as 1.20 eV and 2.06 × 10−10 respectively. The sample has good TL sensitivity to the neutron dose in the order of µsv. The low-temperature thermoluminescence measurements were carried out to study the trap levels and found two major glow peaks at 108 and 130 K. Scintillation properties were analyzed under α-rays from a 241Am source. The decay time profile was well fitted with three components and the fitted values show the fast component of 500 ns (9 %), the medium component of 2.4 μs (24 %), and a slow component of 12.8 μs (67 %).