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Ensemble X-Ray Variability of AGN in 2XMMi-DR3
The X-ray variability of active galactic nuclei (AGN) has been most often investigated with studies of individual, nearby sources, and only a few ensemble analyses have been applied to large samples in wide ranges of luminosity and redshift. In their study, the authors aimed to determine the ensemble variability properties of two serendipitously selected AGN samples extracted from the catalogs of XMM-Newton and Swift (the latter is not included in this table, notice), with redshift between ~ 0.2 and ~ 4.5, and X-ray luminosities, in the 0.5 - 4.5 keV band, between ~ 10<sup>43</sup> erg/s and ~ 10<sup>46</sup> erg/s. They used the structure function (SF), which operates in the time domain, and allows for an ensemble analysis even when only a few observations are available for individual sources and the power spectral density (PSD) cannot be derived. The SF is also more appropriate than fractional variability and excess variance, because these parameters are biased by the duration of the monitoring time interval in the rest-frame, and therefore by cosmological time dilation. The authors find statistically consistent results for the two samples, with the SF described by a power law of the time lag tau, approximately as SF ~ tau<sup>0.1</sup>. They do not find evidence of the break in the SF, at variance with the case of lower luminosity AGNs. They confirm a strong anti-correlation of the variability with X-ray luminosity, accompanied by a change of the slope of the SF. They also find evidence in support of a weak, intrinsic, average increase of X-ray variability with redshift. For XMM, the authors used the version of the Serendipitous Source Catalog then available, namely 2XMMi-DR3, the latest incremental update of the second version of the catalogue, with observations made between 2000 February 3 and 2008 October 08; all datasets were publicly available by 2009 October 31, but not all public observations are included in this catalog. The total area of the catalog fields is ~ 814 deg<sup>2</sup>, but taking account of the substantial overlaps between observations, the net sky area covered independently is ~ 504 deg<sup>2</sup>. The 2XMMi-DR3 catalogue contains 353,191 detections (above the processing likelihood threshold of 6), related to 262,902 unique X-ray sources, therefore a significant number of sources (41,979) have more than one record within the catalog. The selected sources were cross-correlated with the DR7 edition of the SDSS Quasar Catalog (Schneider et al. 2010, AJ, 139, 2360) to obtain redshifts and spectral classifications for the sources. The authors used a maximum distance of 1.5 arcseconds, corresponding to the uncertainty in the X-ray positions, resulting in 412 quasars that were observed by XMM-Newton from 2 to 25 epochs each for a total of 1376 observations. The authors refer to these sources as the XMM-Newton sample. This table was created by the HEASARC in April 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/536/A84">CDS Catalog J/A+A/536/A84</a> file table1.dat. This is a service provided by NASA HEASARC .
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Chandra Serendipitous Extragalactic X-Ray Source ID (SEXSI)/Spitzer AGN Catalog
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The authors compare the relative merits of active galactic nuclei (AGN) selection at X-ray and mid-infrared wavelengths using data from moderately deep fields observed by both Chandra and Spitzer. The X-ray-selected AGN sample and associated photometric and spectroscopic optical follow-up are drawn from a subset of fields studied as part of the Serendipitous Extragalactic X-ray Source Identification (SEXSI) program. Mid-infrared data in these fields are derived from targeted and archival Spitzer imaging, and mid-infrared AGN selection is accomplished primarily through application of the Infrared Array Camera (IRAC) color-color AGN "wedge" selection technique. Nearly all X-ray sources in these fields which exhibit clear spectroscopic signatures of AGN activity have mid-infrared colors consistent with IRAC AGN selection. These are predominantly the most luminous X-ray sources. X-ray sources that lack high-ionization and/or broad lines in their optical spectra are far less likely to be selected as AGNs by mid-infrared color selection techniques. The fraction of X-ray sources identified as AGN in the mid-infrared increases monotonically as the X-ray luminosity increases. Conversely, only 22% of mid-infrared-selected AGN are detected at X-ray energies in the moderately deep (t_exp_n~ 100 ks) SEXSI Chandra data. The authors have expanded the multi-wavelength data available for six SEXSI fields by obtaining Spitzer imaging observations. All six fields have deep Chandra X-ray images, optical imaging, and extensive, deep optical spectroscopy -- all of which has been published in Harrison et al. (2003, ApJ, 596, 944), Eckart et al. (2005, ApJS, 156, 35), and Eckart et al. (2006, ApJS, 165, 19). The authors obtained mid-infrared imaging through both archival and targeted Spitzer programs which include imaging at 3.6, 4.5, 5.8, and 8 micron (µm) from IRAC (PID 00017, 00064, 20694 and 20808), and imaging at 24 um from MIPS (PID 20808 and 00083). This table contains mid-IR photometric data for 290 hard X-ray-selected SEXSI sources. Each of the four IRAC catalogs as well as the MIPS catalog was individually matched to the SEXSI X-ray source positions using a 2.5 arcseconds search radius. To calculate a false match rate, the authors shifted the X-ray source catalog by 1' and matched to the IRAC and MIPS catalogs; this entire procedure was repeated 6 times using different 1' shifts. The resulting false match rates were 10.1% (3.6 um), 7.2% (4.5 um), 3.7% (5.8 um), 2.6% (8.0 um), 1% (24 um), and <1% for four-band-detected IRAC sources. This table was created by the HEASARC in Match 2012 based on CDS Catalog J/ApJ/708/584 file table2.dat. This is a service provided by NASA HEASARC .
XMM-Newton Bright Serendipitous Survey: AGN X-Ray Spectral Properties
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X-ray surveys are a key instrument in the study of active galactic nuclei (AGN). Thanks to their penetrating ability, X-rays are able to map the innermost regions close to the central super massive black hole (SMBH) as well as to detect and characterize its emission up to high redshift. This table contains results from a detailed X-ray spectral analysis of the AGN belonging to the XMM-Newton Bright Serendipitous Survey (XBS, the HEASARC Browse XMMBSS table, CDS Cat. IX/41). The XBS is composed of two flux-limited samples selected in the complementary 0.5 to 4.5 and 4.5 to 7.5 keV energy bands and comprising more than 300 AGN up to redshift ~2.4. The authors have performed an X-ray analysis following two different approaches: by analyzing individually each AGN X-ray spectrum and by constructing average spectra for different AGN types. From the individual analysis, the authors find that there seems to be an anticorrelation between the spectral index and the sources' hard X-ray luminosity, such that the average photon index for the higher luminosity sources (>1044 erg s-1) is significantly (>2 sigma) flatter than the average for the lower luminosity sources. They also find that the intrinsic column density distribution agrees with AGN unified schemes, although a number of exceptions are found (3% of the whole sample), which are much more common among optically classified type 2 AGN. The authors also find that the so-called "soft-excess", apart from the intrinsic absorption, constitutes the principal deviation from a power-law shape in AGN X-ray spectra and it clearly displays different characteristics, and likely a different origin, for unabsorbed and absorbed AGN. Regarding the shape of the average spectra, they find that it is best reproduced by a combination of an unabsorbed (absorbed) power law, a narrow Fe K-alpha emission line and a small (large) amount of reflection for unabsorbed (absorbed) sources. This table was created by the HEASARC in November 2011 based on CDS Catalog J/A+A/530/A42 files table2.dat and table3.dat. This is a service provided by NASA HEASARC .
Selected Area 57 XMM-Newton X-Ray Source Catalog
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The maximum number density of Active Galactic Nuclei (AGNs), as deduced from X-ray studies, occurs at z >= 1, with lower luminosity objects peaking at smaller redshifts. Optical studies lead to a different evolutionary behaviour, with a number density peaking at z ~ 2 independently of the intrinsic luminosity, but this result is limited to active nuclei brighter than the host galaxy. A selection based on optical variability can detect low luminosity AGNs (LLAGNs), where the host galaxy light prevents the identification by non-stellar colours. The authors collected X-ray data in a field where there existed an optically-selected sample of "variable galaxies", i.e. variable objects with diffuse appearance, in order to investigate the X-ray and optical properties of the population of AGNs, particularly of low luminosity ones, where the host galaxy is visible. They observed a field of ~ 0.2 deg2 in the Selected Area 57, for 67 ks with XMM-Newton. They correlated the list of detected X-ray sources with a photographic survey of SA 57, complete to B_J ~ 23 and with the available spectroscopic data. They obtained a catalog of 140 X-ray sources to limiting fluxes of 5 x 10-16 and 2 x 10-15 erg/cm2/s in the 0.5 - 2 keV and 2 - 10 keV bands, respectively, 98 of which are identified in the optical bands. The X-ray detection of part of the variability-selected candidates confirms their AGN nature. Diffuse variable objects populate the low luminosity side of the sample. Only 25/44 optically-selected QSOs are detected in X-rays. 15% of all QSOs in the field have X/O < 0.1. Additional information on the likely optical counterparts of 98 of the X-ray sources is available in the reference paper, e.g., in Table 3. This table was created by the HEASARC in September 2007 based on CDS table J/A+A/469/1211 file table2.dat. This is a service provided by NASA HEASARC .
X-Ray Selected High-z AGN Catalog
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This table contains the results from an analysis of the largest high-redshift (z > 3) X-ray-selected active galactic nucleus (AGN) sample to date, combining the Chandra Cosmological Evolution Survey and Chandra Multi-wavelength Project surveys and doubling the previous samples. The sample comprises 209 X-ray-detected AGNs, over a wide range of rest-frame 2-10 keV luminosities log LX = 43.3 - 46.0 erg/s. X-ray hardness ratios show that ~39 per cent of the sources are highly obscured, NH > 1022 cm-2, in agreement with the ~37 per cent of type-2 AGNs found in this sample based on their optical classification. For ~26 per cent of objects, there are mismatched optical and X-ray classifications. Utilizing the 1/Vmax method, the authors confirm that the comoving space density of all luminosity ranges of AGNs decreases with redshift above z > 3 and up to z ~ 7. With a significant sample of AGNs (N = 27) at z > 4, it is found that both source number counts in the 0.5-2 keV band and comoving space density are consistent with the expectation of a luminosity-dependent density evolution (LDDE) model at all redshifts, while they exclude the luminosity and density evolution (LADE) model. The measured comoving space density of type-1 and type-2 AGNs shows a constant ratio between the two types at z > 3. These results for both AGN types at these redshifts are consistent with the expectations of LDDE model. The high-redshift AGN sample used in this work has been selected from the C-COSMOS X-ray catalog, combining the spectroscopic and photometric information available from the identification catalogue of X-ray C-COSMOS sources (Civano et al. 2011, ApJ, 741, 91; 2012, ApJS, 201, 30) and the ChaMP (Chandra Multi-wavelength Project) X-ray catalog using only the 323 ChaMP ObsIDs overlapping with Sloan Digital Sky Survey (SDSS; Richards et al. 2006, AJ, 131, 2766) DR5 imaging. This table was created by the HEASARC in March 2016 based on the CDS catalog J/MNRAS/445/1430 file tablea1.dat. This is a service provided by NASA HEASARC .
Chandra ACIS Survey for X-Ray AGN in Nearby Galaxies
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The authors searched the public archive of the Chandra X-ray Observatory as of 2016 March and assembled a sample of 719 galaxies within 50 Mpc with available Advanced CCD Imaging Spectrometer observations. By cross-correlation with the optical or near-infrared nuclei of these galaxies, 314 of them are identified to have an X-ray active galactic nucleus (AGN). The majority of them are low-luminosity AGNs and are unlikely X-ray binaries based upon their spatial distribution and luminosity functions. The AGN fraction is around 60% for elliptical galaxies and early-type spirals, but drops to roughly 20% for Sc and later types, consistent with previous findings in the optical. However, the X-ray survey is more powerful in finding weak AGNs, especially from regions with active star formation that may mask the optical AGN signature. For example, 31% of the H II nuclei are found to harbor an X-ray AGN. For most objects, a single power-law model subject to interstellar absorption is adequate to fit the spectrum, and the typical photon index is found to be around 1.8. For galaxies with a non-detection, their stacked Chandra image shows an X-ray excess with a luminosity of a few times 1037 erg/s on average around the nuclear region, possibly composed of faint X-ray binaries. This paper reports on the technique and results of the survey; in-depth analysis and discussion of the results were to be reported in forthcoming papers, e.g., She et al. (2017, ApJ, 842, 131). The sample was assembled based on Chandra/ACIS observations that were publicly available as of 2016 March. The authors first generated a full list of ACIS observations, and then searched in the NASA/IPAC Extragalactic Database (NED) for galaxies within 50 Mpc whose nuclear positions were less than 8 arcminutes from the aim point of any Chandra observation. The adopted distances were taken from NED, in the following order of priority: surface brightness fluctuations, Cepheid variables, tip of the red giant branch, Type Ia supernovae, the fundamental plane, Faber-Jackson relation, Tully-Fisher relation. If more than one reference is available for the distance by the same means, the latest one is selected, unless otherwise specified. Whenever possible, the authors obtain positions of the galaxy nuclei based on measurements from near-infrared images, which suffer from less obscuration by dust or confusion from young star-forming regions. Most of the data come from the Two-Micron All Sky Survey (2MASS) extended source catalog (Skrutskie et al. 2006, AJ, 131, 1163), or NED otherwise. In a few cases, the NED positions come from radio observations. The authors discarded galaxies whose nuclear positions in NED were obtained from X-ray observations. This table was created by the HEASARC in September 2017 based upon the CDS Catalog J/ApJ/835/223 files table1.dat, table2.dat and table4.dat. This is a service provided by NASA HEASARC .
CHAMP (Chandra Multiwavelength Project) Hard X-Ray Emitting AGN
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This table contains the results from an X-ray and optical analysis of 188 active galactic nuclei (AGN) identified from 497 hard X-ray (observed flux in the (2.0 - 8.0 keV) band > 2.7 x 10-15 erg/cm2/s) sources in 20 Chandra fields (1.5 square degrees) forming part of the Chandra Multiwavelength Project (ChaMP). These medium-depth X-ray observations enable the detection of a representative subset of those sources responsible for the bulk of the 2 - 8 keV cosmic X-ray background. Brighter than the survey's optical spectroscopic limit, the authors achieve a reasonable degree of completeness (77% of X-ray sources with counterparts r' < 22.5 have been classified): broad emission-line AGNs (62%), narrow emission-line galaxies (24%), absorption-line galaxies (7%), stars (5%), or clusters (2%). To construct a pure AGN sample, the authors required the rest-frame 2.0-8.0 keV luminosity (uncorrected for intrinsic absorption) to exceed 1042 erg s-1, thereby excluding any sources that may contain a significant stellar or hot ISM component. The most luminous known star-forming or elliptical galaxies attain at most LX = 1042 erg s-1. Since many of the traditional optical AGN signatures are not present in obscured sources, high X-ray luminosity becomes the authors' single discriminant for supermassive black hole accretion. They believe that almost all of the NELGs and ALGs harbor accreting SMBHs based on their X-ray luminosity. They find that 90% of the identified ChaMP sources have luminosities above this threshold. These selection criteria yield a sample of 188 AGNs from 20 Chandra fields with f(2-8 keV) > 2.7 x 10-15 erg cm-2 s-1, r' < 22.5, and LX > 1042 erg s-1. The authors removed five objects identified as clusters based on their extended X-ray emission. This table was created by the HEASARC in March 2007 based on the CDS table J/ApJ/618/123, file table4.dat. This is a service provided by NASA HEASARC .
XMM-COSMOS Catalog of X-Ray Selected Type 1 AGN
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This table contains the results from a study of the X-ray to optical properties of a sample of 545 X-ray selected Type 1 AGN, from the XMM-Newton Cosmic Evolution (XMM-COSMOS) survey, over a wide range of redshifts (0.04 < z < 4.25) and X-ray luminosities (40.6 <= log(L2-10keV) <= 45.3). About 60% of them are spectroscopically identified Type 1 AGN, while the others have a reliable photometric redshift and are classified as Type 1 AGN on the basis of their multi-band Spectral Energy Distributions (SEDs). In the reference, the authors discuss the relationship between UV and X-ray luminosity, as parametrized by the X-ray to optical-UX alphaox spectral slope, and its dependence on redshift and luminosity. Herein optical and X-ray properties for 545 Type 1 AGN in XMM-COSMOS are presented. For each source, X-ray ID, spectroscopic redshift, photometric redshift, upper error on the photometric redshift, lower error on the photometric redshift, logarithm of the monochromatic luminosity at 2500 Angstroms, logarithm of the monochromatic luminosity at 2 keV, alphaox, logarithm of the 2-10 keV luminosity, logarithm of the bolometric luminosity in solar units, bolometric correction, photometric classification, logarithm of the Eddington ratio, logarithm of the black hole mass in solar masses, and a flag for the 2-10 keV detection (flag = 1 [343 entries] means a detection in the 2-10 keV band, while flag = 0 is for 2-10 keV upper limits) are given. This table was created by the HEASARC in May 2010 based on CDS catalog J/A+A/512/A34 file table2.dat. This is a service provided by NASA HEASARC .
Chandra COSMOS Radio-Selected Star-Forming Galaxies and AGN Catalog
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X-ray surveys contain sizable numbers of star-forming galaxies, beyond the AGN which usually make up the majority of detections. Many methods to separate the two populations are used in the literature, based on X-ray and multi-wavelength properties. The authors aim at a detailed test of the classification schemes and to study the X-ray properties of the resulting samples. They build on a sample of galaxies selected at 1.4 GHz in the VLA-COSMOS survey, classified by Smolcic et al. (2008, ApJS, 177, 14) according to their optical colors and also observed by Chandra. A similarly selected control sample of AGN is also used for comparison. The authors review some X-ray based classification criteria and check how they affect the sample composition. The efficiency of the classification scheme devised by Smolcic et al. (2008) is such that ~30% of composite/misclassified objects are expected because of the higher X-ray brightness of AGN with respect to galaxies. The latter fraction is actually 50% in the X-ray detected sources, while it is expected to be much lower among X-ray undetected sources. Indeed, the analysis of the stacked spectrum of undetected sources shows, consistently, strongly different properties between the AGN and galaxy samples. X-ray based selection criteria are then used to refine both samples. The radio/X-ray luminosity correlation for star-forming (SF) galaxies is found to hold with the same X-ray/radio ratio valid for nearby galaxies. Some evolution of the ratio may be possible for sources at high redshift or high luminosity, though it is likely explained by a bias arising from the radio selection. Finally, in their paper the authors discuss the X-ray number counts of star-forming galaxies from the VLA- and C-COSMOS surveys according to different selection criteria, and compare them to the similar determination from the Chandra Deep Fields. The classification scheme proposed here may find application in future works and surveys. This table contains the catalogs of radio-selected SF- and AGN-candidate sources with an X-ray detection in C-COSMOS which were contained in Tables 2 and 3 of the reference paper, respectively. The HEASARC has merged these into a single table, adding a new parameter sample which is set to 'SFG' for radio-selected SF-candidate sources from Table 2 and to 'AGN' for the AGN-candidate sources from Table 3. This table was created by the HEASARC in June 2012 based on CDS table J/A+A/542/A16 files table2.dat and table3.dat. This is a service provided by NASA HEASARC .
INTEGRAL IBIS AGN Catalog
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In this work, the authors present the most comprehensive INTEGRAL active galactic nucleus (AGN) sample. It lists 272 AGN for which they have secure optical identifications, precise optical spectroscopy and measured redshift values plus X-ray spectral information, i.e. 2-10 and 20-100 keV fluxes plus column densities. In their paper, the authors mainly use this sample to study the absorption properties of active galaxies, to probe new AGN classes and to test the AGN unification scheme. The authors find that half (48%) of the sample is absorbed, while the fraction of Compton-thick AGN is small (~7%). In line with their previous analysis, they have however shown that when the bias towards heavily absorbed objects which are lost if weak and at large distance is removed, as is possible in the local Universe, the above fractions increase to become 80% and 17%, respectively. The authors also find that absorption is a function of source luminosity, which implies some evolution in the obscuration properties of AGN. A few peculiar classes, so far poorly studied in the hard X-ray band, have been detected and studied for the first time such as 5 X-ray bright optically normal galaxies (XBONGs), 5 type 2 QSOs and 11 low-ionization nuclear emission regions. In terms of optical classification, this sample contains 57% type 1 and 43% type 2 AGN; this subdivision is similar to that found in X-rays if unabsorbed versus absorbed objects are considered, suggesting that the match between optical and X-ray classifications is on the whole good. Only a small percentage of sources (12%) does not fulfill the expectation of the unified theory as the authors find 22 type 1 AGN which are absorbed and 10 type 2 AGN which are unabsorbed. Studying in depth these outliers they found that most of the absorbed type 1 AGN have X-ray spectra characterized by either complex or warm/ionized absorption more likely due to ionized gas located in an accretion disc wind or in the bi-conical structure associated with the central nucleus, therefore unrelated to the toroidal structure. Among the 10 type 2 AGN which are unabsorbed, at most 3-4% are still eligible to be classified as 'true' type 2 AGN. In the fourth INTEGRAL/IBIS survey (Bird et al. 2010, ApJS, 186, 1, available in the HEASARC database as the IBISCAT4 table), there are 234 objects which have been identified with AGN. To this set of sources, the present authors then added 38 galaxies listed in the INTEGRAL all-sky survey by Krivonos et al. (2007, A&A, 475, 775, available in the HEASARC database as the INTIBISASS table) updated on the website (http://hea.iki.rssi.ru/integral/survey/catalog.php) but not included in the Bird et al. catalog due to the different sky coverage (these latter sources are indicated with hard_flag = 'h' values in this HEASARC table). The final data set presented and discussed in the reference paper and constituting this table therefore comprises 272 AGN and was last updated in March 2011 March. It represents the most complete view of the INTEGRAL extragalactic sky as of the date of publication in 2012. This table was created by the HEASARC in October 2014 based on CDS Catalog J/MNRAS/426/1750 files tablea1.dat and refs.dat. This is a service provided by NASA HEASARC .
M 33 XMM-Newton X-Ray Variability Source Catalog
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This table contains the summary results of an analysis of the individual observations (24 archival raster observations) of a deep XMM-Newton survey of the Local Group spiral galaxy M 33. The authors detected a total of 350 sources with fluxes (in the 0.2 - 4.5 keV energy band) in the range from 6.7 x 10-16 to 1.5 x 10-11 erg/cm2/s. This comprehensive study considered flux variability, spectral characteristics, and classification of the detected objects. Thirty-nine objects in the catalog are new sources, while 311 were already detected in a previous analysis of most of the same data using combined images. The authors present improved positions of these sources, ans also systematically searched for flux variability on time scales of hours to months or years. The detected variability was then used to classify 8 new X-ray binary candidates in M 33. Together with the hardness ratio method and cross-correlation with optical, infrared, and radio data, the authors also classified or confirmed previous classification of 25 supernova remnants and candidates, 2 X-ray binaries, and 11 super-soft source candidates (7 of which are new SSS candidates). In addition, they classified 13 active galactic nuclei and background galaxies, 6 stars, and 23 foreground star candidates in the direction of M 33. A further 206 objects are classified as 'hard', approximately half of which are sources intrinsic to M 33. The relative contribution of the classified XRB and SSS in M 33 is now comparable to M 31. The luminosity distribution of SNRs in both spiral galaxies is almost the same, although the number of the detected SNRs in M 33 remains much higher. This table was created by the HEASARC in March 2007 based on the CDS table J/A+A/448/1247 file table4.dat. The CDS has another table which lists the properties of the sources detected on an observation-by-observation basis which is not included as part of this Browse table but is available at https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/448/1247/table5.dat.gz This is a service provided by NASA HEASARC .
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