- 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:
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Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/PAZh/29/571
- Title:
- X-ray fluxes of radio pulsars
- Short Name:
- J/PAZh/29/571
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the correlations between the luminosities of radio pulsars in various frequency ranges and the magnetic fields of the light cylinder.
- ID:
- ivo://CDS.VizieR/J/MNRAS/466/3309
- Title:
- X-ray flux variability of AGN
- Short Name:
- J/MNRAS/466/3309
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a systematic study of flux variability on hourly time-scales in a large sample of active galactic nuclei (AGN) in the 3-79keV band using data from Nuclear Spectroscopic Telescope Array. Our sample consists of four BL Lac objects (BL Lacs), three flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 Seyfert 2 and eight narrow line Seyfert 1 (NLSy1) galaxies. We find that in the 3-79keV band, about 65 per cent of the sources in our sample show significant variations on hourly time-scales. Using the Mann-Whitney U-test and the Kolmogorov-Smirnov test, we find no difference in the variability behaviour between Seyfert 1 and 2 galaxies. The blazar sources (FSRQs and BL Lacs) in our sample are more variable than Seyfert galaxies that include Seyfert 1 and Seyfert 2 in the soft (3-10keV), hard (10-79keV) and total (3-79keV) bands. NLSy1 galaxies show the highest duty cycle of variability (87 per cent), followed by BL Lacs (82 per cent), Seyfert galaxies (56 per cent) and FSRQs (23 per cent). We obtained flux doubling/halving time in the hard X-ray band less than 10 min in 11 sources. The flux variations between the hard and soft bands in all the sources in our sample are consistent with zero lag.
21740. X-ray galaxy cluster sample
- ID:
- ivo://CDS.VizieR/J/A+A/636/A15
- Title:
- X-ray galaxy cluster sample
- Short Name:
- J/A+A/636/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The isotropy of the late Universe and consequently of the X-ray galaxy cluster scaling relations is an assumption greatly used in astronomy. However, within the last decade, many studies have reported deviations from isotropy when using various cosmological probes; a definitive conclusion has yet to be made. New, effective and independent methods to robustly test the cosmic isotropy are of crucial importance. In this work, we use such a method. Specifically, we investigate the directional behavior of the X-ray luminosity-temperature (L_X_-T) relation of galaxy clusters. A tight correlation is known to exist between the luminosity and temperature of the X-ray-emitting intracluster medium of galaxy clusters. While the measured luminosity depends on the underlying cosmology through the luminosity distance D_L_, the temperature can be determined without any cosmological assumptions. By exploiting this property and the homogeneous sky coverage of X-ray galaxy cluster samples, one can effectively test the isotropy of cosmological parameters over the full extragalactic sky, which is perfectly mirrored in the behavior of the normalization A of the L_X_-T relation. To do so, we used 313 homogeneously selected X-ray galaxy clusters from the Meta-Catalogue of X-ray detected Clusters of galaxies. We thoroughly performed additional cleaning in the measured parameters and obtain core-excised temperature measurements for all of the 313 clusters. The behavior of the L_X_-T relation heavily depends on the direction of the sky, which is consistent with previous studies. Strong anisotropies are detected at a>=4{sigma} confidence level toward the Galactic coordinates (l, b)~(280{deg}, -20{deg}), which is roughly consistent with the results of other probes, such as Supernovae Ia. Several effects that could potentially explain these strong anisotropies were examined. Such effects are, for example, the X-ray absorption treatment, the effect of galaxy groups and low redshift clusters, core metallicities, and apparent correlations with other cluster properties, but none is able to explain the obtained results. Analyzing 10^5^ bootstrap realizations confirms the large statistical significance of the anisotropic behavior of this sky region. Interestingly, the two cluster samples previously used in the literature for this test appear to have a similar behavior throughout the sky, while being fully independent of each other and of our sample. Combining all three samples results in 842 different galaxy clusters with luminosity and temperature measurements. Performing a joint analysis, the final anisotropy is further intensified (~5{sigma}), toward (l, b)~(303{deg}, -27{deg}), which is in very good agreement with other cosmological probes. The maximum variation of D_L_ seems to be ~16+/-3% for different regions in the sky. This result demonstrates that X-ray studies that assume perfect isotropy in the properties of galaxy clusters and their scaling relations can produce strongly biased results whether the underlying reason is cosmological or related to X-rays. The identification of the exact nature of these anisotropies is therefore crucial for any statistical cluster physics or cosmology study.