- ID:
- ivo://CDS.VizieR/J/AJ/126/2740
- Title:
- X-ray emission of RASS Abell clusters
- Short Name:
- J/AJ/126/2740
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the X-ray emission for a complete sample of 288 Abell clusters spanning the redshift range 0.016<=z<=0.09 from the ROSAT All-Sky Survey. This sample is based on our 20cm VLA survey of nearby Abell clusters. We find an X-ray detection rate of 83%. We report cluster X-ray fluxes and luminosities and two different flux ratios indicative of the concentration and extent of the emission. We examine correlations between the X-ray luminosity, Abell richness, and Bautz-Morgan and Rood-Sastry cluster morphologies. We find a strong correlation between LX and cluster richness coupled with a dependence on the optical morphological type. These results are consistent with the observed scatter between X-ray luminosity and temperature and a large fraction of cooling flows. For each cluster field, we also report the positions, peak X-ray fluxes, and flux ratios of all X-ray peaks above 3{sigma} significance within a box of 2x2(h_75_)^-1^Mpc centered on Abell's position.
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- ID:
- ivo://CDS.VizieR/J/A+A/454/595
- Title:
- X-ray emission of T Tau stars in Lupus 3
- Short Name:
- J/A+A/454/595
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present analysis results of an XMM-Newton observation of the Lupus 3 region that contains a high proportion of young low mass T Tauri stars in the Lupus star-forming complex. The detection of X-ray sources in 0.5 to 4.5-keV images of the Lupus 3 core was performed using the standard source detection method of the XMM-Newton Science Analysis Software. One hundred and two candidate X-ray sources were detected in the 30-arcmin diameter field-of-view of the EPIC cameras, of which 25 have visible or near-IR counterparts that are known as pre-main sequence stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/706/810
- Title:
- X-ray emitters in the Groth-Westphal strip
- Short Name:
- J/ApJ/706/810
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Groth field is one of the sky regions that will be targeted by the OSIRIS Tunable Filter Emission Line Object survey in the optical 820nm and 920nm atmospheric windows. In the present paper, public Chandra X-ray data with total exposure time of 200ks are analyzed and combined with optical broadband data of the Groth field, in order to study a set of optical structural parameters of the X-ray emitters and its relation with X-ray properties. To this aim, we processed the raw, public X-ray data using the Chandra Interactive Analysis of Observations, and determined and analyzed different structural parameters, in order to produce a morphological classification of X-ray sources. We present the morphology of 340 X-ray emitters with optical counterpart detected. Objects have been classified by X-ray type using a diagnostic diagram relating X-ray-to-optical ratio (X/O) to hardness ratio. We did not find any clear correlation between X-ray and morphological types. We analyzed the angular clustering of X-ray sources with optical counterpart using two-point correlation functions. A significant positive angular clustering was obtained from a preliminary analysis of four subsamples of the X-ray sources catalog. The clustering signal of the optically extended counterparts is similar to that of strongly clustered populations like red and very red galaxies, suggesting that the environment plays an important role in active galactic nuclei phenomena. Finally, we combined optical structural parameters with other X-ray and optical properties, and we confirmed an anticorrelation between the X/O ratio and the Abraham concentration index, which might suggest that early-type galaxies have lower Eddington rates than those of late-type galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/435/799
- Title:
- X-ray emitting normal galaxies from BMW-HRI
- Short Name:
- J/A+A/435/799
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtained a sample of 143 normal galaxies with X-ray luminosity in the range 10^38^-10^43^erg/s from the cross-correlation of the ROSAT HRI Brera Multi-scale Wavelet (BMW-HRI) Catalogue with the Lyon-Meudon Extragalactic Database (LEDA). We find that the average X-ray properties of this sample are in good agreement with those of other samples of galaxies in the literature. We selected a complete flux limited serendipitous sample of 32 galaxies from which we derived the logN-logS distribution of normal galaxies in the flux range 1.1-110x10^-14^erg/cm^2^/s. The resulting distribution is consistent with the Euclidean -1.5 slope. Comparisons with other samples, such as the Extended Medium Sensitivity Survey, the ROSAT All Sky Survey, the XMM-Newton/2dF survey, and the Chandra Deep Field Survey indicate that the logN-logS distribution of normal galaxies is consistent with a Euclidean slope over a flux range of about 6 decades. Description:
- ID:
- ivo://CDS.VizieR/J/ApJ/574/258
- Title:
- X-ray-emitting young stars in the Orion nebula
- Short Name:
- J/ApJ/574/258
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Orion Nebula Cluster (ONC) and the molecular cloud (OMC) in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23hr exposure in two observations, on 1999 October 12 and 2000 April 1. We detect 1075 X-ray sources, most with sub-arcsecond positional accuracy. Ninety-one percent of the sources are spatially associated with known stellar members of the cluster, and an additional 7% are newly identified deeply embedded cloud members.
- ID:
- ivo://CDS.VizieR/J/ApJ/790/16
- Title:
- X-ray ETGs properties in the Chandra COSMOS survey
- Short Name:
- J/ApJ/790/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study a sample of 69 X-ray detected early-type galaxies (ETGs), selected from the Chandra COSMOS survey, to explore the relation between the X-ray luminosity of hot gaseous halos (L_X, gas_) and the integrated stellar luminosity (L_K_) of the galaxies, in a range of redshift extending out to z = 1.5. In the local universe, a tight, steep relationship has been established between these two quantities (L_x.gas_ ~ L_K_^4.5^), suggesting the presence of largely virialized halos in X-ray luminous systems. We use well-established relations from the study of local universe ETGs, together with the expected evolution of the X-ray emission, to subtract the contribution of low-mass X-ray binary populations from the X-ray luminosity of our sample. Our selection minimizes the presence of active galactic nuclei (AGNs), yielding a sample representative of normal passive COSMOS ETGs; therefore, the resulting luminosity should be representative of gaseous halos, although we cannot exclude other sources such as obscured AGNs or enhanced X-ray emission connected with embedded star formation in the higher-z galaxies. We find that most of the galaxies with estimated L_X_< 10^42^ erg/s and z < 0.55 follow the L_X, gas_-L_K_ relation of local universe ETGs. For these galaxies, the gravitational mass can be estimated with a certain degree of confidence from the local virial relation. However, the more luminous (10^42^ erg/s <L_X_< 10^43.5^ erg/s) and distant galaxies present significantly larger scatter; these galaxies also tend to have younger stellar ages. The divergence from the local L_X, gas_-L_K_relation in these galaxies implies significantly enhanced X-ray emission up to a factor of 100 larger than predicted from the local relation. We discuss the implications of this result for the presence of hidden AGNs, and the evolution of hot halos, in nuclear and star formation feedback.
- ID:
- ivo://CDS.VizieR/J/ApJ/775/121
- Title:
- X-ray events in Earth's magnetosphere
- Short Name:
- J/ApJ/775/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We found 217 X-ray brightening events in Earth's magnetosphere. These events occur in the high-energy band (0.5-4{AA}) of the Geostationary Operational Environmental Satellite (GOES) X-ray light curves, although GOES X-ray light curves are frequently used as indices of solar flare magnitudes. We found that (1) brightening events are absent in the low-energy band (1-8{AA}), unlike those associated with solar flares; and (2) the peak fluxes, durations, and onset times of these events depend on the magnetic local time (MLT). The events were detected in 2006, 2010, and 2011 at around 19-10MLT, that is, from night to morning. They typically lasted for 2-3hr. Their peak fluxes are less than 3x10^-8^W/m^2^ in the 0.5-4{AA} band and are maximized around 0-5MLT. From these MLT dependencies, we constructed an MLT time profile of X-ray brightening events. Because 0.5-4 and 1-8{AA} fluxes were observed and had the same order of magnitude when GOES 14 passed through Earth's shadow, we expected that X-ray brightening events in the 1-8{AA} band are obscured by high-background X-ray fluxes coming from the Sun. We also found coincidence between X-ray brightening events and aurora substorms. In the majority of our events, the minimum geomagnetic field values (AL index) are below -400nT. From these results and consideration of the GOES satellite orbit, we expect that these X-ray brightening events occur in the magnetosphere. We cannot, however, clarify the radiative process of the observed X-ray brightening events.
- ID:
- ivo://CDS.VizieR/J/A+A/311/211
- Title:
- X-ray flare of CF Tuc (=HD 5303)
- Short Name:
- J/A+A/311/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Solar abundance fits to the quiescent spectra 1-3 and 20-35 were made with a two-component thermal plasma (model 1a) whereas sub-solar abundance fits to the quiescent spectra were made with a one-component thermal plasma (model 2a). Modifications of these models were used for the flare spectra 4-19 in order to account for the `quiescent background'. Thus solar abundance fits to the flare spectra were made with a thermal plasma of two variable components plus two components kept constant at the average quiescent values T_qu,cool=2.46*10^6K, EM_qu,cool=0.49*10^53cm^-3, T_qu,hot =17.8*10^6K, EM_qu,hot=1.95*10^53cm^-3, and z=1.00 (model 1b). Sub-solar abundance fits to the flare spectra were made with a plasma of one variable component plus one component kept constant at the average quiescent values T_qu=13.0*10^6K, EM_qu=5.20*10^53cm^-3, and z=0.10 (model 2b). In both cases the mean values of spectra 3, and 20-35 were used to account for the quiescent emission.
- ID:
- ivo://CDS.VizieR/J/A+A/474/495
- Title:
- X-ray flares from Cygnus OB2 young stars
- Short Name:
- J/A+A/474/495
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We characterize individual and ensemble properties of X-ray flares from stars in the Cygnus OB2 and ONC star-forming regions. We analyzed X-ray light-curves of 1003 Cygnus OB2 sources observed with Chandra for 100ks and of 1616 ONC sources detected in the "Chandra Orion Ultra-deep Project" 850ks observation. We employed a binning-free maximum likelihood method to segment the light-curves into intervals of constants signal and identified flares on the basis of both the amplitude and the time-derivative of the source luminosity. We then derived and compared the flare frequency and energy distribution of Cygnus OB2 and ONC sources. The effect of the length of the observation on these results was investigated by repeating the statistical analysis on five 100ks-long segments extracted from the ONC data.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/418
- Title:
- X-ray flares in Orion young stars. I.
- Short Name:
- J/ApJ/688/418
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Pre-main-sequence (PMS) stars are known to produce powerful X-ray flares, which resemble magnetic reconnection solar flares scaled by factors up to 104. However, there are numerous puzzles, including the structure of X-ray-emitting coronae and magnetospheres, the effects of protoplanetary disks, and the effects of stellar rotation. To investigate these issues in detail, we examine 216 of the brightest flares from 161 PMS stars observed in the Chandra Orion Ultradeep Project (COUP, Getman et al. Cat. J/ApJS/160/319). The current study (Paper I) examines the flare morphologies, and provides a general comparison of COUP flare characteristics with those of other active X-ray stars and the Sun.
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