- ID:
- ivo://CDS.VizieR/J/ApJ/892/16
- Title:
- X-ray mass segregation effect in GCs. III. M28
- Short Name:
- J/ApJ/892/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using archival Chandra observations with a total effective exposure of 323ks, we derive an updated catalog of point sources in the bulge globular cluster M28. The catalog contains 502 X-ray sources within an area of ~475arcmin^2^, and more than 90% of these sources are first detected in this cluster. We find significant dips in the radial distribution profiles of X-ray sources in M28, and the projected distance and width of the distribution dip for bright (L_X_>~4.5x10^30^erg/s) X-ray sources are larger than for faint (L_X_<~4.5x10^30^erg/s) sources. Fitting with the "generalized King model" gives a slightly larger average mass for the bright sources (1.30+/-0.15M_{sun}_) than for the faint ones (1.09+/-0.14M_{sun}_), which supports a universal delay in mass segregation between heavy objects in globular clusters. We show that the dynamical age of M28 is comparable to that of Terzan 5 and much smaller than that of 47 Tuc, but M28 is evolving faster (i.e., with a shorter two-body relaxation timescale) than 47 Tuc. These features may suggest an acceleration effect of cluster dynamical evolution by tidal shock in M28. Besides, we find an abnormal deficiency of X-ray sources in the central region (R<~1.5') of M28 compared with its outskirts, which indicates that M28 may have suffered an early phase of primordial binary disruption within its central region, and the mass segregation effect will erase such a phenomenon as clusters evolve to an older dynamical age.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/705/1336
- Title:
- X-ray measurements of ChaMP-SDSS galaxies
- Short Name:
- J/ApJ/705/1336
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The combination of the Sloan Digital Sky Survey (SDSS) and the Chandra Multiwavelength Project (ChaMP; Green et al. 2004ApJS..150...43G) currently offers the largest and most homogeneously selected sample of nearby galaxies for investigating the relation between X-ray nuclear emission, nebular line emission, black hole masses, and properties of the associated stellar populations. We provide X-ray spectral fits and valid uncertainties for all the galaxies with counts ranging from 2 to 1325 (mean 76, median 19). We present here novel constraints that both X-ray luminosity L_X_ and X-ray spectral energy distribution bring to the galaxy evolutionary sequence HII->Seyfert/Transition Object->LINER->Passive suggested by optical data.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/50
- Title:
- X-ray & MIR AGNs in Stripe 82 with eBOSS spectra
- Short Name:
- J/ApJ/876/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a Sloan Digital Sky Survey IV eBOSS program to target X-ray sources and mid-infrared-selected Wide-field Infrared Survey Explorer (WISE) active galactic nucleus (AGN) candidates in a 36.8deg^2^ region of Stripe 82. About half this survey (15.6deg^2^) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGNs in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r~22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGNs, with a median sample redshift of z~1. About 30% of the AGNs are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGNs at z<0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGNs or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGNs are not selected as mid-infrared AGNs, with 22% of X-ray AGNs undetected by WISE. Most of these latter AGNs have high X-ray luminosities (Lx>10^44^erg/s), indicating that mid-infrared selection misses a sizable fraction of the highest luminosity AGNs, as well as lower luminosity sources where AGN-heated dust is not dominating the mid-infrared emission. Conversely, ~58% of WISE AGNs are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray-detected WISE AGNs.
- ID:
- ivo://CDS.VizieR/J/ApJ/892/18
- Title:
- X-ray & MIR luminosities of the GBT galaxies
- Short Name:
- J/ApJ/892/18
- Date:
- 19 Jan 2022 08:55:44
- Publisher:
- CDS
- Description:
- We present an investigation of the dependence of H_2_O maser detection rates and properties on the mid-IR active galactic nucleus (AGN) luminosity, L_AGN_, and the obscuring column density, N_H_, based on mid-IR and hard X-ray photometry. Based on spectral energy distribution fitting that allows for decomposition of the black hole accretion and star formation components in the mid-infrared, we show that the megamaser (disk maser) detection rate increases sharply for galaxies with 12{mu}m AGN luminosity L_12um_^AGN^ greater than 10^42^erg/s, from <~3% (<~2%) to ~12% (~5%). By using the ratio of the observed X-ray to mid-IR AGN luminosity as an indicator of N_H_, we also find that megamaser (disk maser) detection rates are boosted to 15% (7%) and 20% (9%) for galaxies with N_H_>=10^23^/cm^2^ and N_H_>=10^24^cm^-2^, respectively. Combining these column density cuts with a constraint for high L_12um_^AGN^ (>=10^42^erg/s) predicts further increases in the megamaser (disk maser) detection rates to 19% (8%) and 27% (14%), revealing unprecedented potential increases of the megamaser and disk maser detection rates by a factor of 7-15 relative to the current rates, depending on the chosen sample selection criteria. A noteworthy aspect of these new predictions is that the completeness rates are only compromised mildly, with the rates remaining at the level of ~95% (~50%) for sources with N_H_>=10^23^/cm^2^ (N_H_>=10^24^/cm^2^). Applying these selection methods to current X-ray AGN surveys predicts the detection of >~15 new megamaser disks.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/7
- Title:
- X-ray monitoring of 1ES 1927+654
- Short Name:
- J/ApJS/255/7
- Date:
- 06 Dec 2021 19:56:23
- Publisher:
- CDS
- Description:
- 1ES 1927+654 is a nearby active galactic nucleus (AGN) that underwent a changing-look event in early 2018, developing prominent broad Balmer lines that were absent in previous observations. We have followed up this object in the X-rays with an ongoing campaign that started in 2018 May and that includes 265 NICER (for a total of 678ks) and 14 Swift/XRT (26ks) observations, as well as three simultaneous XMM-Newton/NuSTAR (158/169ks) exposures. In the X-rays, 1ES 1927+654 shows a behavior unlike any previously known AGN. The source is extremely variable both in spectral shape and flux and does not show any correlation between X-ray and UV flux on timescales of hours or weeks/months. After the outburst, the power-law component almost completely disappeared, and the source showed an extremely soft continuum dominated by a blackbody component. The temperature of the blackbody increases with the luminosity, going from kT~80eV (for a 0.3-2keV luminosity of L_0.3-2_~10^41.5^erg/s) to ~200eV (for L_0.3-2_~10^44^erg/s). The spectra show evidence of ionized outflows and of a prominent feature at ~1keV, which can be reproduced by a broad emission line. The unique characteristics of 1ES 1927+654 in the X-ray band suggest that it belongs to a new type of changing-look AGN. Future X-ray surveys might detect several more objects with similar properties.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A52
- Title:
- X-ray monitoring of M31 novae
- Short Name:
- J/A+A/533/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Context. Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of the galaxy M31. We performed a dedicated monitoring of the M31 central region with XMM-Newton and Chandra between Nov 2007 and Feb 2008 and between Nov 2008 and Feb 2009, respectively, to find SSS counterparts of CNe, determine the duration of their SSS phase, and derive physical outburst parameters. We systematically searched our data for X-ray counterparts of CNe, determined their X-ray light curves and characterised their spectra using blackbody fits and white dwarf (WD) atmosphere models. Additionally, we determined luminosity upper limits for all previously known X-ray emitting novae that are not detected any more and for all CNe in our field of view with optical outbursts between one year before the start of the X-ray monitoring (Oct 2006) and its end (Feb 2009).
- ID:
- ivo://CDS.VizieR/J/A+A/563/A2
- Title:
- X-ray monitoring of M31 novae
- Short Name:
- J/A+A/563/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical novae (CNe) represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbouring galaxy M 31. We performed a dedicated monitoring of the M 31 central region, which aimed to detect SSS counterparts of CNe, with XMM-Newton and Chandra between Nov and Mar of the years 2009/10, 2010/11, and 2011/12. We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and also their spectral properties in the case of XMM-Newton data. Additionally, we determined luminosity upper limits for all previously known X-ray emitting novae, which are not detected anymore, and for all CNe in our field of view with recent optical outbursts.
- ID:
- ivo://CDS.VizieR/J/A+A/465/375
- Title:
- X-ray monitoring of optical novae in M31
- Short Name:
- J/A+A/465/375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical novae have recently been identified as the major class of supersoft X-ray sources in M 31 based on ROSAT and early XMM-Newton and Chandra observations. This paper reports on a search for X-ray counterparts of optical novae in M 31 based on archival Chandra HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brightnesses for counterparts of four novae with earlier outbursts. For comparison with the X-ray data we created a catalogue of optical novae in M 31 based on our own nova search programs and on all novae reported in the literature. We collected all known properties and named the novae consistently following the CBAT scheme. We detect eleven out of 34 novae within a year after the optical outburst in X-rays. While for eleven novae we detect the end of the supersoft source phase, seven novae are still bright more than 1200, 1600, 1950, 2650, 3100, 3370 and 3380d after outburst. One nova is detected to turn on 50d, another 200d after outburst. Three novae unexpectedly showed short X-ray outbursts starting within 50d after the optical outburst and lasting only two to three months. The X-ray emission of several of the novae can be characterized as supersoft from hardness ratios and/or X-ray spectra or by comparing HRC-I count rates with ACIS-I count rates or upper limits. The number of detected optical novae at supersoft X-rays is much higher than previously estimated (>30%). We use the X-ray light curves to estimate the burned masses of the White Dwarf and of the ejecta.
- ID:
- ivo://CDS.VizieR/J/MNRAS/367/627
- Title:
- X-ray/NIR correlation for early-type galaxies
- Short Name:
- J/MNRAS/367/627
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relation between X-ray luminosity and near-infrared (NIR) luminosity for early-type galaxies has been examined. NIR luminosities should provide a superior measure of stellar mass compared to optical luminosities used in previous studies, especially if there is significant star formation or dust present in the galaxies. However, we show that the X-ray-NIR relations are remarkably consistent with the X-ray-optical relations. This indicates that the large scatter of the relations is dominated by scatter in the X-ray properties of early-type galaxies, and is consistent with early-types consisting of old, quiescent stellar populations. We have investigated scatter in terms of environment, surface brightness profile, Mg2, H{beta}, H{gamma} line strength indices, spectroscopic age and nuclear H{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/161
- Title:
- X-ray obs. and membership probabilities of M37
- Short Name:
- J/ApJ/809/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods (P_rot_). M37 was observed almost continuously for five days, for a total of 440.5ks, to measure stellar X-ray luminosities (L_X_), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with P_rot_, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, R_0_=P_rot_/{tau}, where {tau} is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L_X_/L_bol_, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500Myr. We find that fast rotators, for which R_0_<0.09+/-0.01, show saturated levels of activity, with log(L_X_/L_bol_)=-3.06+/-0.04. For R_0_>=0.09+/-0.01, activity is unsaturated and follows a power law of the form R_0_^{beta}^, where {beta}=-2.03^+0.17^_-1.14_. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3M_{sun}_, P_rot_ in the range 0.4-12.8 days, and L_X_ in the range 10^28.4-30.5^erg/s. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ~500Myr.
