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P G Jonker - One of the best experts on this subject based on the ideXlab platform.
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a systematic search for near infrared counterparts of nearby ultraluminous X Ray Sources ii
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Timothy P L Roberts, M A P Torres, P G Jonker, M Heida, K M Lopez, D J Walton, Daesik MoonAbstract:We present the results of our continued systematic search for near-infrared (NIR) candidate counterparts to ultraluminous X-Ray Sources (ULXs) within 10 Mpc. We observed 42 ULXs in 24 nearby galaXies and detected NIR candidate counterparts to 15 ULXs. Fourteen of these ULXs appear to have a single candidate counterpart in our images and the remaining ULX has two candidate counterparts. Seven ULXs have candidate counterparts with absolute magnitudes in the range between −9.26 and −11.18 mag, consistent with them being red supergiants (RSGs). The other eight ULXs have candidate counterparts with absolute magnitudes too bright to be a single stellar source. Some of these NIR Sources show eXtended morphology or colours eXpected for active galactic nuclei (AGNs), strongly suggesting that they are likely stellar clusters or background galaXies. The RSG candidate counterparts form a valuable sample for follow-up spectroscopic observations to confirm their nature, with the ultimate goal of directly measuring the mass of the compact accretor that powers the ULX using binary Doppler shifts.
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near infrared counterparts of ultraluminous X Ray Sources
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: M A P Torres, P G Jonker, M Heida, E C Kool, Mathieu Servillat, Timothy P L RobertsAbstract:In this paper, we present the results of the first systematic search for counterparts to nearby ultraluminous X-Ray Sources (ULXs) in the near-infrared (NIR). We observed 62 ULXs in 37 galaXies within 10 Mpc and discovered 17 candidate NIR counterparts. The detection of 17 out of 62 ULX candidates points to intrinsic differences between systems that show and those that do not show infrared emission. For siX counterparts, we conclude from the absolute magnitudes and – in some cases – additional information such as morphology and previously reported photometric or spectroscopic observations, that they are likely background active galactic nuclei or ULXs residing in star clusters. 11 counterparts have absolute magnitudes consistent with them being single red supergiant stars. Alternatively, these systems may have larger accretion discs that emit more NIR light than the systems that we do not detect. Other scenarios such as emission from a surrounding nebula or from a compact radio jet are also possible, although for Holmberg II X-1 the NIR luminosity far eXceeds the eXpected jet contribution. The 11 possible red supergiant counterparts are eXcellent candidates for spectroscopic follow-up observations. This may enable us to measure the mass function in these systems if they are indeed red supergiant donor stars where we can observe absorption lines.
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identification of galactic bulge survey X Ray Sources with tycho 2 stars
The Astrophysical Journal, 2012Co-Authors: R I Hynes, P G Jonker, N J Wright, Thomas J Maccarone, S Greiss, D Steeghs, M A P TorresAbstract:We identify 69 X-Ray Sources discovered by the Galactic Bulge Survey (GBS) that are coincident with or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS Sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-Rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-Ray-to-optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also eXamine Two Micron All Sky Survey colors, variability information from the All-Sky Automated Survey, and X-Ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very miXed selection, ranging in spectral class from O9 to M3. In some cases, the X-Ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-Ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these eXhibit redder near-IR colors than eXpected for their spectral type and/or variability, and it is likely that the X-Rays originate from a late-type companion star in most or all of these objects.
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identification of galactic bulge survey X Ray Sources with tycho 2 stars
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: R I Hynes, M A P Torres, P G Jonker, N J Wright, Thomas J Maccarone, S Greiss, D SteeghsAbstract:We identify 69 X-Ray Sources discovered by the Galactic Bulge Survey (GBS) that are coincident with, or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS Sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-Rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-Ray to optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also eXamine 2MASS colors, variability information from the All-Sky Automated Survey (ASAS), and X-Ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very miXed selection, ranging in spectral class from O9 to M3. In some cases the X-Ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-Ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these eXhibit redder near-IR colors than eXpected for their spectral type and/or variability, and it is likely that the X-Rays originate from a late-type companion star in most or all of these objects.
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chandra localization and optical near infrared follow up of galactic X Ray Sources
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: E M Ratti, C G Bassa, M A P Torres, L Kuiper, J C A Millerjones, P G JonkerAbstract:We investigate a sample of 11 Galactic X-Ray Sources recently discovered with INTEGRAL or RXTE with the goal of identifying their optical and/or near-infrared (NIR) counterpart. For this purpose, new Chandra positions of nine objects are presented together with follow-up observations of all the targets in the optical and NIR. For the four Sources IGR J16194-2810, IGR J 16479-4514, IGR J 16500-3307 and IGR J 19308+0530, the Chandra position confirms an eXisting association with an optical/NIR object, while for two Sources, XTE J1716-389 and IGR J18490-0000, it rules out previously proposed counterparts indicating new ones. In the case of IGR J17597-220, a counterpart is selected out of the several possibilities proposed in the literature, and we present the first association with an optical/NIR source for IGR J16293-4603 and XTE J1743-363. Moreover, optical/NIR observations are reported for XTE J1710-281 and IGR J17254-3257; we investigate the counterpart to the X-Ray Sources based on their XMM-Newton positions. We discuss the nature of each system considering its optical/NIR and X-Ray properties.
G P Garmire - One of the best experts on this subject based on the ideXlab platform.
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a naive bayes source classifier for X Ray Sources
Astrophysical Journal Supplement Series, 2011Co-Authors: P S Broos, Eric D Feigelson, Konstantin V Getman, Matthew S Povich, L K Townsley, G P GarmireAbstract:The Chandra Carina CompleX Project (CCCP) provides a sensitive X-Ray survey of a nearby starburst region over >1 deg2 in eXtent. Thousands of faint X-Ray Sources are found, many concentrated into rich young stellar clusters. However, significant contamination from unrelated Galactic and eXtragalactic Sources is present in the X-Ray catalog. We describe the use of a naive Bayes classifier to assign membership probabilities to individual Sources, based on source location, X-Ray properties, and visual/infrared properties. For the particular membership decision rule adopted, 75% of CCCP Sources are classified as members, 11% are classified as contaminants, and 14% remain unclassified. The resulting sample of stars likely to be Carina members is used in several other studies, which appear in this special issue devoted to the CCCP.
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a catalog of chandra X Ray Sources in the carina nebula
Astrophysical Journal Supplement Series, 2011Co-Authors: Patrick S Broos, Leisa K Townsley, Eric D Feigelson, Konstantin V Getman, G P Garmire, Thomas Preibisch, Nathan Smith, B L Babler, S T Hodgkin, Remy IndebetouwAbstract:We present a catalog of ~14,000 X-Ray Sources observed by the ACIS instrument on the Chandra X-Ray Observatory within a 1.42?deg2 survey of the Great Nebula in Carina, known as the Chandra Carina CompleX Project (CCCP). This study appears in a special issue devoted to the CCCP. Here, we describe the data reduction and analysis procedures performed on the X-Ray observations, including calibration and cleaning of the X-Ray event data, point-source detection, and source eXtraction. The catalog appears to be complete across most of the field to an absorption-corrected total-band luminosity of ~1030.7?erg?s?1 for a typical low-mass pre-main-sequence star. Counterparts to the X-Ray Sources are identified in a variety of visual, near-infrared, and mid-infrared surveys. The X-Ray and infrared source properties presented here form the basis of many CCCP studies of the young stellar populations in Carina.
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a catalog of chandra X Ray Sources in the carina nebula
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Patrick S Broos, Leisa K Townsley, Eric D Feigelson, Konstantin V Getman, G P Garmire, Thomas Preibisch, Nathan Smith, B L Babler, S T Hodgkin, Remy IndebetouwAbstract:We present a catalog of ~14,000 X-Ray Sources observed by the ACIS instrument on the Chandra X-Ray Observatory within a 1.42 square degree survey of the Great Nebula in Carina, known as the Chandra Carina CompleX Project (CCCP). This study appears in a Special Issue of the ApJS devoted to the CCCP. Here, we describe the data reduction and analysis procedures performed on the X-Ray observations, including calibration and cleaning of the X-Ray event data, point source detection, and source eXtraction. The catalog appears to be complete across most of the field to an absorption-corrected total-band luminosity of ~10^{30.7} erg/s for a typical low-mass pre-main sequence star. Counterparts to the X-Ray Sources are identified in a variety of visual, near-infrared, and mid-infrared surveys. The X-Ray and infrared source properties presented here form the basis of many CCCP studies of the young stellar populations in Carina.
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a naive bayes source classifier for X Ray Sources
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: Patrick S Broos, Leisa K Townsley, Eric D Feigelson, Konstantin V Getman, Matthew S Povich, G P GarmireAbstract:The Chandra Carina CompleX Project (CCCP) provides a sensitive X-Ray survey of a nearby starburst region over >1 square degree in eXtent. Thousands of faint X-Ray Sources are found, many concentrated into rich young stellar clusters. However, significant contamination from unrelated Galactic and eXtragalactic Sources is present in the X-Ray catalog. We describe the use of a naive Bayes classifier to assign membership probabilities to individual Sources, based on source location, X-Ray properties, and visual/infrared properties. For the particular membership decision rule adopted, 75% of CCCP Sources are classified as members, 11% are classified as contaminants, and 14% remain unclassified. The resulting sample of stars likely to be Carina members is used in several other studies, which appear in a Special Issue of the ApJS devoted to the CCCP.
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optical and infrared properties of the 2 ms chandra deep field north X Ray Sources
The Astronomical Journal, 2003Co-Authors: P Capak, A J Barger, Lennox L Cowie, D M Alexander, F E Bauer, E Fernandez, W N Brandt, G P GarmireAbstract:We present an optical and near-infrared catalog for the X-Ray Sources in the ?2 Ms Chandra observation of the Hubble Deep Field North region. We have high-quality multicolor imaging data for all 503 X-Ray point Sources in the X-Ray?selected catalog and reliable spectroscopic redshifts for 284. We spectroscopically identify siX high-redshift (z > 1) type II quasars (L2?8keV > 1044 ergs s-1) in our sample. Our spectroscopic completeness for the R ? 24 Sources is 87%. The spectroscopic redshift distribution shows two broad redshift spikes that have clearly grown over those originally seen in the ?1 Ms eXposure. The spectroscopically identified eXtragalactic Sources already comprise 75% of the measured 2?8 keV light. Redshift slices versus 2?8 keV fluX show that an impressive 54% of the measured 2?8 keV light arises from Sources at z 5.7 that would classify them as eXtremely red objects (EROs). The photometric redshifts of these EROs are all between z ~ 1.5 and z ~ 2.5. We use our wide wavelength coverage to determine rest-frame colors for the X-Ray Sources with spectroscopic or photometric redshifts. We find that many of the X-Ray Sources have the rest-frame colors of evolved red galaXies and that there is very little evolution in these colors with redshift. We also determine absolute magnitudes and find that many of the non?broad-line Sources are more luminous than M, even at high redshifts. We therefore infer that deep X-Ray observations may provide an effective way of locating M* galaXies with colors similar to present-day early-type galaXies to high redshifts.
Timothy P L Roberts - One of the best experts on this subject based on the ideXlab platform.
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a systematic search for near infrared counterparts of nearby ultraluminous X Ray Sources ii
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Timothy P L Roberts, M A P Torres, P G Jonker, M Heida, K M Lopez, D J Walton, Daesik MoonAbstract:We present the results of our continued systematic search for near-infrared (NIR) candidate counterparts to ultraluminous X-Ray Sources (ULXs) within 10 Mpc. We observed 42 ULXs in 24 nearby galaXies and detected NIR candidate counterparts to 15 ULXs. Fourteen of these ULXs appear to have a single candidate counterpart in our images and the remaining ULX has two candidate counterparts. Seven ULXs have candidate counterparts with absolute magnitudes in the range between −9.26 and −11.18 mag, consistent with them being red supergiants (RSGs). The other eight ULXs have candidate counterparts with absolute magnitudes too bright to be a single stellar source. Some of these NIR Sources show eXtended morphology or colours eXpected for active galactic nuclei (AGNs), strongly suggesting that they are likely stellar clusters or background galaXies. The RSG candidate counterparts form a valuable sample for follow-up spectroscopic observations to confirm their nature, with the ultimate goal of directly measuring the mass of the compact accretor that powers the ULX using binary Doppler shifts.
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ultraluminous X Ray Sources
arXiv: High Energy Astrophysical Phenomena, 2017Co-Authors: Philip Kaaret, Hua Feng, Timothy P L RobertsAbstract:We review observations of ultraluminous X-Ray Sources (ULXs). X-Ray spectroscopic and timing studies of ULXs suggest a new accretion state distinct from those seen in Galactic stellar-mass black hole binaries. The detection of coherent pulsations indicates the presence of neutron-star accretors in three ULXs and therefore apparently super-Eddington luminosities. Optical and X-Ray line profiles of ULXs and the properties of associated radio and optical nebulae suggest that ULXs produce powerful outflows, also indicative of super-Eddington accretion. We discuss models of super-Eddington accretion and their relation to the observed behaviors of ULXs. We review the evidence for intermediate mass black holes in ULXs. We consider the implications of ULXs for super-Eddington accretion in active galactic nuclei, heating of the early universe, and the origin of the black hole binary recently detected via gravitational waves.
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diagnosing the accretion flow in ultraluminous X Ray Sources using soft X Ray atomic features
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: M J Middleton, Timothy P L Roberts, D J Walton, A C Fabian, Lucy Heil, Ciro Pinto, G E Anderson, A D SuttonAbstract:The lack of unambiguous detections of atomic features in the X-Ray spectra of ultraluminous X-Ray Sources (ULXs) has proven a hindrance in diagnosing the nature of the accretion flow. The possible association of spectral residuals at soft energies with atomic features seen in absorption and/or emission and potentially broadened by velocity dispersion could therefore hold the key to understanding much about these enigmatic Sources. Here we show for the first time that such residuals are seen in several Sources and appear eXtremely similar in shape, implying a common origin. Via simple arguments we assert that emission from eXtreme colliding winds, absorption in a shell of material associated with the ULX nebula and thermal plasma emission associated with star formation are all highly unlikely to provide an origin. Whilst CCD spectra lack the energy resolution necessary to directly determine the nature of the features (i.e. formed of a compleX of narrow lines or intrinsically broad lines), studying the evolution of the residuals with underlying spectral shape allows for an important, indirect test for their origin. The ULX NGC 1313 X-1 provides the best opportunity to perform such a test due to the dynamic range in spectral hardness provided by archival observations. We show through highly simplified spectral modelling that the strength of the features (in either absorption or emission) appears to anticorrelate with spectral hardness, which would rule out an origin via reflection of a primary continuum and instead supports a picture of atomic transitions in a wind or nearby material associated with such an outflow.
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a deficit of ultraluminous X Ray Sources in luminous infrared galaXies
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: W Luangtip, Timothy P L Roberts, D M Alexander, S Mineo, Bret Lehmer, F Jackson, Andy D Goulding, J L FischerAbstract:We present results from a Chandra study of ultraluminous X-Ray Sources (ULXs) in a sample of 17 nearby (DL < 60 Mpc) luminous infrared galaXies (LIRGs), selected to have star formation rates (SFRs) in eXcess of 7 M⊙ yr −1 and low foreground Galactic column densities (NH � 5 × 10 20 cm −2 ). A total of 53 ULXs were detected and we confirm that this is a complete catalogue of ULXs for the LIRG sample. We eXamine the evolution of ULX spectra with luminosity in these galaXies by stacking the spectra of individual objects in three luminosity bins, finding a distinct change in spectral indeX at luminosity � 2 × 10 39 erg s −1 . This may be a change in spectrum as 10 M⊙ black holes transit from aEddington to a super-Eddington accretion regime, and is supported by a plausible detection of partially-ionised absorption imprinted on the spectrum of the luminous ULX (LX � 5 × 10 39 erg s −1 ) CXOU J024238.9-000055 in NGC 1068, consistent with the highly ionised massive wind that we would eXpect to see driven by a super-Eddington accretion flow. This sample shows a large deficit in the number of ULXs detected per unit SFR (0.2 versus 2 ULXs, per M⊙ yr −1 ) compared to the detection rate in nearby (DL < 14.5 Mpc) normal star forming galaXies. This deficit also manifests itself as a lower differential X-Ray luminosity function normalisation for the LIRG sample than for samples of other star forming galaXies. We show that it is unlikely that this deficit is a purely observational effect. Part of this deficit might be attributable to the high metallicity of the LIRGs impeding the production efficiency of ULXs and/or a lag between the star formation starting and the production of ULXs; however, we argue that the evidence - including very low NULX/LFIR, and an even lower ULX incidence in the central regions of the LIRGs - shows that the main culprit for this deficit is likely to be the high column of gas and dust in these galaXies, that fuels the high SFR but also acts to obscure many ULXs from our view.
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near infrared counterparts of ultraluminous X Ray Sources
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: M A P Torres, P G Jonker, M Heida, E C Kool, Mathieu Servillat, Timothy P L RobertsAbstract:In this paper, we present the results of the first systematic search for counterparts to nearby ultraluminous X-Ray Sources (ULXs) in the near-infrared (NIR). We observed 62 ULXs in 37 galaXies within 10 Mpc and discovered 17 candidate NIR counterparts. The detection of 17 out of 62 ULX candidates points to intrinsic differences between systems that show and those that do not show infrared emission. For siX counterparts, we conclude from the absolute magnitudes and – in some cases – additional information such as morphology and previously reported photometric or spectroscopic observations, that they are likely background active galactic nuclei or ULXs residing in star clusters. 11 counterparts have absolute magnitudes consistent with them being single red supergiant stars. Alternatively, these systems may have larger accretion discs that emit more NIR light than the systems that we do not detect. Other scenarios such as emission from a surrounding nebula or from a compact radio jet are also possible, although for Holmberg II X-1 the NIR luminosity far eXceeds the eXpected jet contribution. The 11 possible red supergiant counterparts are eXcellent candidates for spectroscopic follow-up observations. This may enable us to measure the mass function in these systems if they are indeed red supergiant donor stars where we can observe absorption lines.
P Rosati - One of the best experts on this subject based on the ideXlab platform.
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the eXtended chandra deep field south survey optical spectroscopy of faint X Ray Sources with the vlt and keck
Astrophysical Journal Supplement Series, 2010Co-Authors: J D Silverman, V Mainieri, M Salvato, G Hasinger, J Bergeron, P Capak, G Szokoly, A Finoguenov, R Gilli, P RosatiAbstract:We present the results of a program to acquire high-quality optical spectra of X-Ray Sources detected in the EXtended-Chandra Deep Field-South (E-CDF-S) and its central 2 Ms area. New spectroscopic redshifts, up to z = 4, are measured for 283 counterparts to Chandra Sources with deep eXposures (t ~ 2-9 hr per pointing) using multi-slit facilities on both VLT (VIMOS) and Keck (DEIMOS), thus bringing the total number of spectroscopically identified X-Ray Sources to over 500 in this survey field. Since our new spectroscopic identifications are mainly associated with X-Ray Sources in the shallower 250 ks coverage, we provide a comprehensive catalog of X-Ray Sources detected in the E-CDF-S including the optical and near-infrared counterparts, determined by a likelihood routine, and redshifts (both spectroscopic and photometric), that incorporate published spectroscopic catalogs, thus resulting in a final sample with a high fraction (80%) of X-Ray Sources having secure identifications. We demonstrate the remarkable coverage of the luminosity-redshift plane now accessible from our data while emphasizing the detection of active galactic nuclei (AGNs) that contribute to the faint end of the luminosity function (L_(0.5-8 keV) ~ 10^(43)-10^(44) erg s^(–1)) at 1.5 ≲ z ≲ 3 including those with and without broad emission lines. Our redshift catalog includes 17 type-2 QSOs at 1 ≲ z ≲ 3.5 that significantly increases such samples (2×). Based on our deepest (9 hr) VLT/VIMOS observation, we identify "elusive" optically faint galaXies (R_(mag) ~ 25) at z ~ 2-3 based upon the detection of interstellar absorption lines (e.g., O II+Si IV, C II], C IV); we highlight one such case, an absorption-line galaXy at z = 3.208 having no obvious signs of an AGN in its optical spectrum. In addition, we determine accurate distances to eight galaXy groups with eXtended X-Ray emission detected both by Chandra and XMM-Newton. Finally, we measure the physical eXtent of known large-scale structures (z ~ 0.7) evident in the CDF-S. While a thick sheet (a radial size of 67.7 Mpc) at z ~ 0.67 eXtends over the full field, the z ~ 0.73 structure is thin (18.8 Mpc) and filamentary as traced by both AGNs and galaXy groups. In the AppendiX, we provide spectroscopic redshifts for 49 counterparts to fainter X-Ray Sources detected only in the 1 and 2 Ms catalogs, and 48 Very Large ArRay radio Sources not detected in X-Rays.
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the eXtended chandra deep field south survey optical spectroscopy of faint X Ray Sources with the vlt and keck
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: J D Silverman, V Mainieri, M Salvato, G Hasinger, J Bergeron, P Capak, G Szokoly, A Finoguenov, R Gilli, P RosatiAbstract:We present the results of a program to acquire high-quality optical spectra of X-Ray Sources detected in the E-CDF-S and its central area. New spectroscopic redshifts are measured for 283 counterparts to Chandra Sources with deep eXposures (t~2-9 hr per pointing) using multi-slit facilities on both the VLT and Keck thus bringing the total number of spectroscopically-identified X-Ray Sources to over 500 in this survey field. We provide a comprehensive catalog of X-Ray Sources detected in the E-CDF-S including the optical and near-infrared counterparts, and redshifts (both spectroscopic and photometric) that incorporate published spectroscopic catalogs thus resulting in a final sample with a high fraction (80%) of X-Ray Sources having secure identifications. We demonstrate the remarkable coverage of the LX-z plane now accessible from our data while emphasizing the detection of AGNs that contribute to the faint end of the luminosity function at 1.5
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the northern rosat all sky noras galaXy cluster survey i X Ray properties of clusters detected as eXtended X Ray Sources
Astrophysical Journal Supplement Series, 2000Co-Authors: H Bohringer, P Rosati, W Voges, J P Huchra, B Mclean, R Giacconi, R Burg, J Mader, P Schuecker, D SimicAbstract:In the construction of an X-Ray-selected sample of galaXy clusters for cosmological studies, we have assembled a sample of 495 X-Ray Sources found to show eXtended X-Ray emission in the first processing of the ROSAT All-Sky Survey. The sample covers the celestial region with declination ? ? 0? and Galactic latitude |bII| ? 20? and comprises Sources with a count rate ?0.06 counts s-1 and a source eXtent likelihood of L ? 7. In an optical follow-up identification program we find 378 (76%) of these Sources to be clusters of galaXies.?????It was necessary to reanalyze the Sources in this sample with a new X-Ray source characterization technique to provide more precise values for the X-Ray fluX and source eXtent than obtained from the standard processing. This new method, termed growth curve analysis (GCA), has the advantage over previous methods in its ability to be robust, to be easy to model and to integrate into simulations, to provide diagnostic plots for visual inspection, and to make eXtensive use of the X-Ray data. The source parameters obtained assist the source identification and provide more precise X-Ray fluXes. This reanalysis is based on data from the more recent second processing of the ROSAT Survey. We present a catalog of the cluster Sources with the X-Ray properties obtained as well as a list of the previously flagged eXtended Sources that are found to have a noncluster counterpart. We discuss the process of source identification from the combination of optical and X-Ray data.?????To investigate the overall completeness of the cluster sample as a function of the X-Ray fluX limit, we eXtend the search for X-Ray cluster Sources to the data of the second processing of the ROSAT Survey for the northern sky region between 9h and 14h in right ascension. We include the search for X-Ray emission of known clusters as well as a new investigation of eXtended X-Ray Sources. In the course of this search we find X-Ray emission from 85 additional Abell clusters and 56 very probable cluster candidates among the newly found eXtended Sources. A comparison of the X-Ray cluster number counts of the NORAS sample with the ROSAT-ESO FluX-limited X-Ray (REFLEX) Cluster Survey results leads to an estimate of the completeness of the NORAS sample of ROSAT All-Sky Survey (RASS) I eXtended clusters of about 50% at an X-Ray fluX of FX(0.1-2.4 keV) = 3 ? 10-12 ergs s-1 cm-2. The estimated completeness achieved by adding the supplementary sample in the study area amounts to about 82% in comparison to REFLEX. The low completeness introduces an uncertainty in the use of the sample for cosmological statistical studies that will be cured with the completion of the continuing Northern ROSAT All-Sky (NORAS) Cluster Survey project.
M A P Torres - One of the best experts on this subject based on the ideXlab platform.
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a systematic search for near infrared counterparts of nearby ultraluminous X Ray Sources ii
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Timothy P L Roberts, M A P Torres, P G Jonker, M Heida, K M Lopez, D J Walton, Daesik MoonAbstract:We present the results of our continued systematic search for near-infrared (NIR) candidate counterparts to ultraluminous X-Ray Sources (ULXs) within 10 Mpc. We observed 42 ULXs in 24 nearby galaXies and detected NIR candidate counterparts to 15 ULXs. Fourteen of these ULXs appear to have a single candidate counterpart in our images and the remaining ULX has two candidate counterparts. Seven ULXs have candidate counterparts with absolute magnitudes in the range between −9.26 and −11.18 mag, consistent with them being red supergiants (RSGs). The other eight ULXs have candidate counterparts with absolute magnitudes too bright to be a single stellar source. Some of these NIR Sources show eXtended morphology or colours eXpected for active galactic nuclei (AGNs), strongly suggesting that they are likely stellar clusters or background galaXies. The RSG candidate counterparts form a valuable sample for follow-up spectroscopic observations to confirm their nature, with the ultimate goal of directly measuring the mass of the compact accretor that powers the ULX using binary Doppler shifts.
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near infrared counterparts of ultraluminous X Ray Sources
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: M A P Torres, P G Jonker, M Heida, E C Kool, Mathieu Servillat, Timothy P L RobertsAbstract:In this paper, we present the results of the first systematic search for counterparts to nearby ultraluminous X-Ray Sources (ULXs) in the near-infrared (NIR). We observed 62 ULXs in 37 galaXies within 10 Mpc and discovered 17 candidate NIR counterparts. The detection of 17 out of 62 ULX candidates points to intrinsic differences between systems that show and those that do not show infrared emission. For siX counterparts, we conclude from the absolute magnitudes and – in some cases – additional information such as morphology and previously reported photometric or spectroscopic observations, that they are likely background active galactic nuclei or ULXs residing in star clusters. 11 counterparts have absolute magnitudes consistent with them being single red supergiant stars. Alternatively, these systems may have larger accretion discs that emit more NIR light than the systems that we do not detect. Other scenarios such as emission from a surrounding nebula or from a compact radio jet are also possible, although for Holmberg II X-1 the NIR luminosity far eXceeds the eXpected jet contribution. The 11 possible red supergiant counterparts are eXcellent candidates for spectroscopic follow-up observations. This may enable us to measure the mass function in these systems if they are indeed red supergiant donor stars where we can observe absorption lines.
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identification of galactic bulge survey X Ray Sources with tycho 2 stars
The Astrophysical Journal, 2012Co-Authors: R I Hynes, P G Jonker, N J Wright, Thomas J Maccarone, S Greiss, D Steeghs, M A P TorresAbstract:We identify 69 X-Ray Sources discovered by the Galactic Bulge Survey (GBS) that are coincident with or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS Sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-Rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-Ray-to-optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also eXamine Two Micron All Sky Survey colors, variability information from the All-Sky Automated Survey, and X-Ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very miXed selection, ranging in spectral class from O9 to M3. In some cases, the X-Ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-Ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these eXhibit redder near-IR colors than eXpected for their spectral type and/or variability, and it is likely that the X-Rays originate from a late-type companion star in most or all of these objects.
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identification of galactic bulge survey X Ray Sources with tycho 2 stars
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: R I Hynes, M A P Torres, P G Jonker, N J Wright, Thomas J Maccarone, S Greiss, D SteeghsAbstract:We identify 69 X-Ray Sources discovered by the Galactic Bulge Survey (GBS) that are coincident with, or very close to bright stars in the Tycho-2 catalog. Additionally, two other GBS Sources are resolved binary companions to Tycho-2 stars where both components are separately detected in X-Rays. Most of these are likely to be real matches, but we identify nine objects with large and significant X-Ray to optical offsets as either detections of resolved binary companions or chance alignments. We collate known spectral types for these objects, and also eXamine 2MASS colors, variability information from the All-Sky Automated Survey (ASAS), and X-Ray hardness ratios for the brightest objects. Nearly a third of the stars are found to be optically variable, divided roughly evenly between irregular variations and periodic modulations. All fall among the softest objects identified by the GBS. The sample forms a very miXed selection, ranging in spectral class from O9 to M3. In some cases the X-Ray emission appears consistent with normal coronal emission from late-type stars, or wind emission from early-types, but the sample also includes one known Algol, one W UMa system, two Be stars, and several X-Ray bright objects likely to be coronally active stars or binaries. Surprisingly, a substantial fraction of the spectroscopically classified, non-coincidental sample (12 out of 38 objects) have late B or A type counterparts. Many of these eXhibit redder near-IR colors than eXpected for their spectral type and/or variability, and it is likely that the X-Rays originate from a late-type companion star in most or all of these objects.
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chandra localization and optical near infrared follow up of galactic X Ray Sources
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: E M Ratti, C G Bassa, M A P Torres, L Kuiper, J C A Millerjones, P G JonkerAbstract:We investigate a sample of 11 Galactic X-Ray Sources recently discovered with INTEGRAL or RXTE with the goal of identifying their optical and/or near-infrared (NIR) counterpart. For this purpose, new Chandra positions of nine objects are presented together with follow-up observations of all the targets in the optical and NIR. For the four Sources IGR J16194-2810, IGR J 16479-4514, IGR J 16500-3307 and IGR J 19308+0530, the Chandra position confirms an eXisting association with an optical/NIR object, while for two Sources, XTE J1716-389 and IGR J18490-0000, it rules out previously proposed counterparts indicating new ones. In the case of IGR J17597-220, a counterpart is selected out of the several possibilities proposed in the literature, and we present the first association with an optical/NIR source for IGR J16293-4603 and XTE J1743-363. Moreover, optical/NIR observations are reported for XTE J1710-281 and IGR J17254-3257; we investigate the counterpart to the X-Ray Sources based on their XMM-Newton positions. We discuss the nature of each system considering its optical/NIR and X-Ray properties.