High Lx Research Articles

X-ray emission from hot gas in galaxy groups and clusters in simba

ABSTRACT We examine X-ray scaling relations for massive haloes ($M_{500}\gt 10^{12.3}\, \mathrm{M}_\odot$) in the simba galaxy formation simulation. The X-ray luminosity, LX versus M500 has power-law slopes ${\approx }\frac{5}{3}$ and ${\approx }\frac{8}{3}$ above and below $10^{13.5} \, \mathrm{M}_{\odot }$, deviating from the self-similarity increasingly to low masses. TX − M500 is self-similar above this mass, and slightly shallower below it. Comparing simba to observed TX scalings, we find that LX, LX-weighted [Fe/H], and entropies at 0.1R200 (S0.1) and R500 (S500) all match reasonably well. S500 − TX is consistent with self-similar expectations, but S0.1 − TX is shallower at lower TX, suggesting the dominant form of heating moves from gravitational shocks in the outskirts to non-gravitational feedback in the cores of smaller groups. simba matches observations of LX versus central galaxy stellar mass M*, predicting the additional trend that star-forming galaxies have higher LX(M*). Electron density profiles for $M_{500}\gt 10^{14}\, \mathrm{M}_\odot$ haloes show a ∼0.1R200 core, but the core is larger at lower masses. TX are reasonably matched to observations, but entropy profiles are too flat versus observations for intermediate-mass haloes, with Score ≈ 200–400 keV cm2. simba’s [Fe/H] profile matches observations in the core but overenriches larger radii. We demonstrate that Simba’s bipolar jet AGN feedback is most responsible for increasingly evacuating lower-mass haloes, but the profile comparisons suggest this may be too drastic in the inner regions.

A Comparison of the X-Ray Properties of FU Ori-type Stars to Generic Young Stellar Objects

Abstract Like other young stellar objects (YSOs), FU Ori-type stars have been detected as strong X-ray emitters. However, little is known about how the outbursts of these stars affect their X-ray properties. We assemble available X-ray data from XMM-Newton and Chandra observations of 16 FU Ori stars, including a new XMM-Newton observation of Gaia 17bpi during its optical rise phase. Of these stars, six were detected at least once, while 10 were non-detections, for which we calculate upper limits on intrinsic X-ray luminosity (L X) as a function of plasma temperature (kT) and column density (N H). The detected FU Ori stars tend to be more X-ray luminous than is typical for non-outbursting YSOs, based on comparison to a sample of low-mass stars in the Orion Nebula Cluster. FU Ori stars with high L X have been observed both at the onset of their outbursts and decades later. We use the Kaplan–Meier estimator to investigate whether the higher X-ray luminosities for FU Ori stars are characteristic or a result of selection effects, and we find the difference to be statistically significant (p < 0.01) even when non-detections are taken into account. The additional X-ray luminosity of FU Ori stars relative to non-outbursting YSOs cannot be explained by accretion shocks, given the high observed plasma temperatures. This suggests that, for many FU Ori stars, either (1) the outburst leads to a restructuring of the magnetosphere in a way that enhances X-ray emission, or (2) FU Ori outbursts are more likely to occur among YSOs with the highest quiescent X-ray luminosity.

Hot, dense He iioutflows during the 2017 outburst of the X-ray transientSwift J1357.2−0933

AbstractTime-resolved SALT spectra of the short-period, dipping X-ray transient, Swift J1357.2−0933, during its 2017 outburst has revealed broad Balmer and He ii λ4686 absorption features, blueshifted by ∼600 km s−1. Remarkably these features are also variable on the ∼500 s dipping period, indicating their likely association with structure in the inner accretion disc. We interpret this as arising in a dense, hot (≳30 000 K) outflowing wind seen at very high inclination, and draw comparisons with other accretion disc corona sources. We argue against previous distance estimates of 1.5 kpc and favour a value ≳6 kpc, implying an X-ray luminosity LX ≳ 4 × 1036 erg s−1. Hence it is not a very faint X-ray transient. Our preliminary 1D Monte Carlo radiative transfer and photoionization calculations support this interpretation, as they imply a high intrinsic LX, a column density NH ≳ 1024 cm−2, and a low covering factor for the wind. Our study shows that Swift J1357.2−0933 is truly remarkable amongst the cohort of luminous, Galactic X-ray binaries, showing the first example of He ii λ4686 absorption, the first (and only) variable dip period and is possibly the first black hole ‘accretion disc corona’ candidate.

Soft excess in the quiescent Be/X-ray pulsar RX J0812.4–3114

Abstract We report a 72 ks XMM–Newton observation of the Be/X-ray pulsar (BeXRP) RX J0812.4–3114 in quiescence ($L_X \approx 1.6\times 10^{33}\, \mathrm{erg\, s^{-1}}$). Intriguingly, we find a two-component spectrum, with a hard power-law (Γ ≈ 1.5) and a soft blackbody-like excess below ≈1 keV. The blackbody component is consistent in kT with a prior quiescent Chandra observation reported by Tsygankov et al. and has an inferred blackbody radius of ≈10 km, consistent with emission from the entire neutron star (NS) surface. There is also mild evidence for an absorption line at $\approx 1$ and/or $\approx 1.4\, \mathrm{keV}$. The hard component shows pulsations at P ≈ 31.908 s (pulsed fraction 0.84 ± 0.10), agreeing with the pulse period seen previously in outbursts, but no pulsations were found in the soft excess (pulsed fraction $\lesssim \!31\, {\rm per\, cent}$). We conclude that the pulsed hard component suggests low-level accretion on to the NS poles, while the soft excess seems to originate from the entire NS surface. We speculate that, in quiescence, the source switches between a soft thermal-dominated state (when the propeller effect is at work) and a relatively hard state with low-level accretion, and use the propeller cut-off to estimate the magnetic field of the system to be $\lesssim\! 8.4\times 10^{11}\, \mathrm{G}$. We compare the quiescent thermal LX predicted by the standard deep crustal heating model to our observations and find that RX J0812.4–3114 has a high thermal LX, at or above the prediction for minimum cooling mechanisms. This suggests that RX J0812.4–3114 either contains a relatively low-mass NS with minimum cooling, or that the system may be young enough that the NS has not fully cooled from the supernova explosion.

Luminosity functions of cluster galaxies

We derive NUV luminosity functions for 6471 NUV detected galaxies in 28 0.02 < z < 0.08 clusters and consider their dependence on cluster properties. We consider optically red and blue galaxies and explore how their NUV LFs vary in several cluster subsamples, selected to best show the influence of environment. Our composite LF is well fit by the Schechter form with M*NUV = −18.98 ± 0.07 and α = −1.87 ± 0.03 in good agreement with values for the Coma centre and the Shapley supercluster, but with a steeper slope and brighter L* than in Virgo. The steep slope is due to the contribution of massive quiescent galaxies that are faint in the NUV. There are significant differences in the NUV LFs for clusters having low and high X-ray luminosities and for sparse and dense clusters, though none are particularly well fitted by the Schechter form, making a physical interpretation of the parameters difficult. When splitting clusters into two subsamples by X-ray luminosity, the ratio of low to high NUV luminosity galaxies is higher in the high X-ray luminosity subsample (i.e., the luminosity function is steeper across the sampled luminosity range). In subsamples split by surface density, when characterised by Schechter functions the dense clusters have an M* about a magnitude fainter than that of the sparse clusters and α is steeper (−1.9 vs. −1.6, respectively). The differences in the data appear to be driven by changes in the LF of blue (star-forming) galaxies. This appears to be related to interactions with the cluster gas. For the blue galaxies alone, the luminosity distributions indicate that for high LX and high velocity dispersion cluster subsamples (i.e., the higher mass clusters), there are relatively fewer high UV luminosity galaxies (or correspondingly a relative excess of low UV luminosity galaxies) in comparison the lower mass cluster subsamples.

EXPLORING X-RAY BINARY POPULATIONS IN COMPACT GROUP GALAXIES WITH CHANDRA

ABSTRACT We obtain total galaxy X-ray luminosities, L X, originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the ±1σ scatter of the Mineo et al. L X–star formation rate (SFR) correlation or have higher L X than predicted by this correlation for their SFR. We discuss how these “excesses” may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. L X–stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low- or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme L X values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high L X values can be observed due to strong XRB variability.

Do the spectral energy distributions of type 1 active galactic nuclei show diversity?

We create broadband SEDs of 761 type 1 AGN. The Scott et al. sample, created by a cross-correlation of the optical SDSS DR5 quasar catalogue and the 2XMMi catalogue of serendipitous X-ray sources, is further matched with the FIRST catalogue of radio sources, the WISE MIR all-sky data release, the 2MASS NIR point source catalogue, the UKIDSS DR9 Large Area Survey and the GALEX all-sky and medium UV imaging surveys. This allows broadband SEDs covering log(nu)~9.2-18.1 to be created. We investigate variations in the SED shape by binning a subsample of 237 AGN with the best quality SEDs according to their X-ray spectral parameters, their AGN sub-type and their luminosity, black hole mass and Eddington ratio. The AGN sub-populations show some significant differences in their SEDs; X-ray absorbed AGN show a deficit of emission at X-ray/UV frequencies and an excess in the MIR consistent with absorption and re-emission, radio-loud AGN show increased radio and X-ray emission, consistent with the presence of a jet component in addition to the emission seen from radio-quiet AGN and the SEDs of NLS1s only differ from other type 1s in the X-ray regime, suggesting any physical differences are limited to their X-ray emitting region. Binning the AGN according to underlying physical parameters reveals more subtle differences in the SEDs. The X-ray spectral slope does not appear to have any influence or dependence on the multiwavelength emission in the rest of the SED. The contribution of X-rays to Lbol is lower in higher luminosity sources, and relatively more emission in the optical/UV is seen in AGN with higher Lx. Variations in the relative flux and peak frequency of the BBB are observed and may suggest higher inner disc temperatures with increasing accretion rates. Overall, we find that the diversity in the SED shapes is relatively small, and we find no apparent single driver for the variations.

Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genusInga

Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga, Lx levels were high in shade leaves (mostly above 20 mmol mol(-1) chlorophyll) and low in sun leaves. In Virola surinamensis, both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol(-1) chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, Q(A), and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection.

X-ray pulsar radiation from polar caps heated by back-flow bombardment

Abstract We consider the problem of the thermal X-ray radiation from the hot polar caps of radio pulsars that show evidence of E×B subpulse drift in radio band. In our recent Paper I, using the partially screened gap (PSG) model of inner acceleration region we derived a simple relationship between the drift rate of subpulses observed in a radio-band and the thermal X-ray luminosity from polar caps heated by the back-flow particle bombardment. This relationship can be tested for pulsars in which the so-called carousel rotation time P4, reflecting the E×B plasma drift, and the thermal X-ray luminosity Lx from the hot polar cap are known. To test the model we used only two available pulsars: PSRs B0943+10 and B1133+16. They both satisfied the model prediction, although due to low photon statistics the thermal component could not be firmly identified from the X-ray data. Nevertheless, these pulsars were at least consistent with PSG pulsar model. In this Letter we consider two more pulsars: PSRs B0656+14 and B0628−28, the data for which have recently become available. In PSR B0656+14 the thermal radiation from the hot polar cap was clearly detected, and PSR B0628−28 also seems to have such a component. In all cases for which both P4 and Lx are presently known, the PSG pulsar model seems to be fully confirmed. Other available models of inner acceleration region fail to explain the observed relationship between radio and X-ray data. The pure vacuum gap model predicts too high Lx and too low P4, while the space charge limited model predicts too low Lx and the origin of the subpulse drift has no natural explanation.

The Density of Coronal Plasma in Active Stellar Coronae

We have analyzed high-resolution X-ray spectra of a sample of 22 active stars observed with the High Energy Transmission Grating Spectrometer on Chandra in order to investigate their coronal plasma density. Densities were investigated using the lines of the He-like ions O VII, Mg XI, and Si XIII. Si XIII lines in all stars of the sample are compatible with the low-density limit (i.e., ne ≲ 1013 cm-3), casting some doubt on results based on lower resolution Extreme Ultraviolet Explorer (EUVE) spectra finding densities ne > 1013 cm-3. Mg XI lines betray the presence of high plasma densities up to a few times 1012 cm-3 for most of the sources with higher X-ray luminosity (≳1030 ergs s-1); stars with higher LX and LX/Lbol tend to have higher densities at high temperatures. Ratios of O VII lines yield much lower densities of a few times 1010 cm-3, indicating that the "hot" and "cool" plasma resides in physically different structures. In the cases of EV Lac, HD 223460, Canopus, μ Vel, TY Pyx, and IM Peg, our results represent the first spectroscopic estimates of coronal density. No trends in density-sensitive line ratios with stellar parameters effective temperature and surface gravity were found, indicating that plasma densities are remarkably similar for stars with pressure scale heights differing by up to 3 orders of magnitude. Our findings imply remarkably compact coronal structures, especially for the hotter (~7 MK) plasma emitting the Mg XI lines characterized by the coronal surface filling factor, f, ranging from 10-4 to 10-1, while we find f values from a few times 10-3 up to ~1 for the cooler (~2 MK) plasma emitting the O VII lines. We find that f approaches unity at the same stellar surface X-ray flux level as characterizes solar active regions, suggesting that these stars become completely covered by active regions. At the same surface flux level, f is seen to increase more sharply with increasing surface flux. These results appear to support earlier suggestions that hot 107 K plasma in active coronae arises from flaring activity and that this flaring activity increases markedly once the stellar surface becomes covered with active regions. Comparison of our measured line fluxes with theoretical models suggests that significant residual model inaccuracies might be present and, in particular, that cascade contributions to forbidden and intercombination lines resulting from dielectronic recombination might be to blame.

X-Ray Properties of Pre-Main-Sequence Stars in the Orion Nebula Cluster with Known Rotation Periods

We re-analyze all archival Chandra/ACIS observations of the Orion Nebula Cluster (ONC) to study the X-ray properties of a large sample of pre--main-sequence (PMS) stars with optically determined rotation periods. Our goal is to elucidate the origins of X-rays in PMS stars by seeking out connections between the X-rays and the mechanisms most likely driving their production--rotation and accretion. In our sample X-ray luminosity is significantly correlated with stellar rotation, in the sense of decreasing Lx/Lbol with more rapid rotation, suggesting that these stars are in the super-saturated regime of the rotation-activity relationship. However, we also find that stars with optical rotation periods are significantly biased to high Lx. This is not the result of magnitude bias in the optical rotation-period sample but rather to the diminishingly small amplitude of optical variations in stars with low Lx. Evidently, there exists in the ONC a population of stars whose rotation periods are unknown and that possess lower average X-ray luminosities than those of stars with known rotation periods. These stars may sample the linear regime of the rotation-activity relationship. Accretion also manifests itself in X-rays, though in a somewhat counterintuitive fashion: While stars with spectroscopic signatures of accretion show harder X-ray spectra than non-accretors, they show lower X-ray luminosities and no enhancement of X-ray variability. We interpret these findings in terms of a common origin for the X-ray emission observed from both accreting and non-accreting stars, with the X-rays from accreting stars simply being attenuated by magnetospheric accretion columns. This suggests that X-rays from PMS stars have their origins primarily in chromospheres, not accretion.

The operation of the lutein epoxide cycle correlates with energy dissipation.

A new xanthophyll cycle involving de-epoxidation of lutein epoxide (Lx) into lutein in the light and epoxidation back in the dark has been recently described in parasitic plants and in trees from the genus Quercus. To explore the role of the Lx cycle in photoprotection, shade leaves of red oak (Q. rubra), with a relatively high Lx pool, were exposed to different light intensities. Both violaxanthin and Lx were de-epoxidised to the same extent, although the initial kinetics differed, with a rate proportional to the light intensity. De-epoxidation of violaxanthin and Lx was inhibited by dithiothreitol, suggesting that the same enzyme, violaxanthin de-epoxidase (VDE), catalyses both reactions. Dark recovery lagged in the case of Lx, and after 5 h in darkness, the Lx cycle was much more de-epoxidised than the violaxanthin cycle. The different rates of epoxidation of the violaxanthin and Lx cycles were used to study the role of the Lx cycle in photoprotection. Statistical approaches (partial correlation and multiple regression) indicate that in these leaves, maximal photochemical efficiency of PSII (Fv/Fm) and non-photochemical quenching are correlated with the level of Lx de-epoxidation. The potential implications of this finding for the understanding of the photosynthetic process in shaded and understorey leaves are discussed.

New X‐Ray Clusters in theEinsteinExtended Medium‐Sensitivity Survey. I. Modifications to the X‐Ray Luminosity Function

The complete ensemble of Einstein Imaging Proportional Counter (IPC) X-ray images has been reprocessed and reanalyzed using a multiaperture source detection algorithm. A catalog of 772 new source candidates detected within the 38' diameter central regions of the 1435 IPC fields comprising the Extended Medium-Sensitivity Survey (EMSS) has been compiled. By comparison, 478 EMSS sources fall within the same area of sky. A randomly selected subsample of 133 fields was examined; 73 sources were detected and compared with 49 original EMSS sources in the same region of sky. We expect, on the basis of confusion statistics, that most of these sources either are the summation of two or more lower count-rate point sources that fall within the larger detection apertures or are single point sources. An optical imaging study discovered one possible cluster of galaxies among 43 identified sources, suggesting that ≤2.3% of the full catalog of sources are extrapolated to be actual distant (z ≥ 0.14) clusters whose extended X-ray structure kept them from being detected in the EMSS despite having sufficient total flux. We have constructed other subsamples specifically selected to contain those X-ray sources most likely to be clusters based upon additional X-ray and optical criteria. Both a database search and an optical imaging study of these subsamples have found several new distant clusters, setting a firm lower limit on the number of new clusters in the entire catalog. Given both the numbers of new EMSS clusters and their spectroscopic or photometric redshifts, we estimate that the original EMSS cluster sample is 72%-83% complete. We update the Henry et al. EMSS distant (z ≥ 0.14) cluster sample with more recent information and use the redshifts and X-ray luminosities for these new EMSS clusters to compute revised X-ray luminosity functions (XLFs) in the three redshift shells defined by Henry et al. The addition of these new high-z, high-LX clusters to the EMSS is sufficient to remove the requirement for negative evolution at high LX out to z ~ 0.5. Although the best estimate of the EMSS XLF at z = 0.3-0.6 and log LX = 44.9-45.2 ergs s-1 falls 1 σ below the low-z (<0.3) XLF, the optical identification of the full 772 source catalog remains incomplete. We conclude that the EMSS has systematically missed clusters of low surface brightness. Since all X-ray cluster surveys are less sensitive to low surface brightness emission, they may also be affected.

Investigation of Reactive Shear Localization in Energetic Solids

The behavior of an energetic solid subjected to shear is modelled. Data from torsional splitHopkinson bar (TSHB) experiments are first reduced to calibrate a constitutive model for stress, accounting for the effects of strain and strain rate hardening, in an inert simulant, Mock 900–20, of the high explosive LX–14. This stress model is employed in a transient one dimensional model which includes effects of thermal softening, thermal diffusion, plastic heating, and exothermic reaction. For an event with an average strain rate of 2.8×103S-1, reactive shear localization with local strain rates and temperatures in excess of 5×104s-1 and 5000K, respectively, is predicted. It is predicted that within a domain of length comparable to that of the largest heterogeneities, around 250 µm, reaction evolves over sub-nanosecond times scales. Localization and ignition are found to be sensitive to changes in mechanical properties, specific heat. and activation energy, and insensitive to changes in kinetic rate constant, heat release, and thermal conductivity.

Evidence for environmental effects on early-type galaxy X-ray halos

Possible causes for the large dispersion in the X-ray luminosities (Lx) of early-type galaxies are discussed. It is shown that early-type galaxies with relatively low values of Lx for a given optical luminosity L(B) have about 50 percent more neighbors than galaxies with relatively high Lx, suggesting that low-Lx galaxies tend to be in denser environments. It is concluded that the large dispersion in X-ray luminosity, for a given L(B) might be caused either by ram-pressure stripping of the gaseous halos or by mergers.

The X-ray Spectra of High Redshift Quasars

We present mean spectral parameters for various ensembles of quasars observed with the Einstein Observatory Imaging Proportional Counter (IPC). Our sample contains 71 optically or radio selected quasars with 0.1 &lt; z &lt; 3.5, Galactic NH &lt; 1021 cm−2, total counts of 30 −500, and IPC gain &lt; 19. Quasars are grouped into ensembles according to radio properties (Flat Radio Spectrum [FRS], Steep Radio Spectrum [SRS] or Radio Quiet [RQ]), and either redshift or X-ray luminosity, lx. We find a clear correlation between radio properties and α. FRS quasars have α∼0.4, SRS quasars have α∼0.7 and RQ quasars have α ∼1–1.4. There is no evidence for a dependence of α on z nor, for the FRS and SRS ensembles, on lx over nearly three decades. FRS quasars with 2.0 &lt; z &lt; 3.5 have just as flat mean spectra as those with low z, implying that a single power law, which is flatter than the canonical one with α ∼ 0.65, continues into the 1–10 keV band (in which the observed softer X-rays were emitted). Unfortunately, the results for high redshift and high lx RQ quasars are ambiguous because of systematic uncertainties in the ensemble means. Thus we cannot test the two-component spectral hypothesis of Wilkes and Elvis for these objects. SRS X-ray spectra could be steeper than FRS spectra because of the mixing of two components, although a single intrinsically steeper spectrum is easier to reconcile with the absence of z dependence. The uncertainty in a for RQ quasars with high z leaves open the important question of their contribution to the cosmic X-ray background.

A statistical study of the relationship between X-ray, optical and radio luminosity for a sample of QSOs

Our statistical study finds that the X-ray luminosity, lx for an average QSO of given optical luminosity, lo is an increasing function of radio luminosity, lr. An average QSO of given lo and lr has higher lx if the radio spectrum is flat than if it is steep. The correlation between lx, lo and lr appears to be improved if lr refers only to core emission, lrcore. Assuming an average radio-loud QSO is a radio-quiet QSO with a separate component which produces lrcore and Ixcore, lxcore/lrcore is larger if the core is that of a QSO with extended radio structure than if that of a compact flat-spectrum QSO.