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17951. 8yr INTEGRAL/IBIS soft gamma-ray source obs.
ID:
ivo://CDS.VizieR/J/ApJS/223/15
Title:
8yr INTEGRAL/IBIS soft gamma-ray source obs.
Short Name:
J/ApJS/223/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
Here we report an all-sky soft gamma-ray source catalog based on IBIS observations performed during the first 1000 orbits of INTEGRAL. The database for the construction of the source list consists of all good-quality data available, from the launch in 2002, up to the end of 2010. This corresponds to ~110Ms of scientific public observations, with a concentrated coverage on the Galactic Plane and extragalactic deep exposures. This new catalog includes 939 sources above a 4.5{sigma} significance threshold detected in the 17-100keV energy band, of which 120 sources represent previously undiscovered soft gamma-ray emitters. The source positions are determined, mean fluxes are provided in two main energy bands, and these are both reported together with the overall source exposure. Indicative levels of variability are provided, and outburst times and durations are given for transient sources. A comparison is made with previous IBIS catalogs and catalogs from other similar missions.
17952. 6-yr light curves of 10 blazars
ID:
ivo://CDS.VizieR/J/ApJS/237/30
Title:
6-yr light curves of 10 blazars
Short Name:
J/ApJS/237/30
Date:
21 Oct 2021
Publisher:
CDS
Description:
We carried out multi-color optical monitoring of a sample of 10 blazars from 2005 to 2011. The sample contains 3 LBLs, 2 IBLs, 4 HBLs, and 1 FSRQ. Our monitoring focused on the long-term variability and the sample included nine BL Lac objects and one flat-spectrum radio quasar (FSRQ). A total of 14,799 data points were collected. This is one of the largest optical databases for a sample of 10 blazars. All objects showed significant variability except for OT 546. Because of the low sampling on each single night, only BL Lacertae were observed to have intraday variability on 2006 November 6. Most BL Lac objects showed a bluer-when-brighter (BWB) chromatism, while the FSRQ, 3C 454.3, displayed a redder-when-brighter trend. The BWB color behaviors of most BL Lacs can be at least partly attributed to the trend of increasing variation amplitude with increasing frequency observed in these objects. The average spectral index of LBLs is around 1.5, as expected from the model dominated by synchrotron self-Compton loss. The optical emission of HBL is probably contaminated by the thermal emission from the host galaxies. Correlation analysis did not reveal any time delay between variations at different wavelengths.
17953. 2yr obs. of JHK variability of stars in Tr37
ID:
ivo://CDS.VizieR/J/ApJ/878/7
Title:
2yr obs. of JHK variability of stars in Tr37
Short Name:
J/ApJ/878/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have monitored nearly a square degree in IC 1396A/Tr 37 over 21 epochs extending over 2014-2016 for sources variable in the JHK bands. In our data, 65%+/-8% of previously identified cluster members show variations, compared with <=0.3% of field stars. We identify 119 members of Tr 37 on the basis of variability, forming an unbiased sample down to the brown dwarf regime. The K-band luminosity function in Tr 37 is similar to that of IC 348 but shifted to somewhat brighter values, implying that the K- and M-type members of Tr 37 are younger than those in IC 348. We introduce methods to classify the causes of variability, based on behavior in the color-color and color-magnitude diagrams. Accretion hot spots cause larger variations at J than at K with substantial scatter in the diagrams; there are at least a dozen, with the most active resembling EXors. Eleven sources are probably dominated by intervention of dust clumps in their circumstellar disks, with color behavior indicating the presence of grains larger than for interstellar dust, presumably due to grain growth in their disks. Thirteen sources have larger variations at K than at J or H. For 11 of them, the temperature fitted to the variable component is very close to 2000K, suggesting that the changes in output are caused by turbulence at the inner rim of the circumstellar disk exposing previously protected populations of grains.
17954. 40yr of geodetic/astrometric VLBI obs. of ICRF sources
ID:
ivo://CDS.VizieR/J/ApJS/242/5
Title:
40yr of geodetic/astrometric VLBI obs. of ICRF sources
Short Name:
J/ApJS/242/5
Date:
21 Oct 2021
Publisher:
CDS
Description:
Geodetic/astrometric very long baseline interferometry (VLBI) has been routinely observing using various global networks for 40yr, and it has produced more than 10 million baseline group delay, phase, and amplitude observables. These group delay observables are analyzed worldwide for geodetic and astrometric applications, for instance, to create the International Celestial Reference Frame (ICRF). The phase and amplitude observables are used in this paper, by means of closure analysis, to study intrinsic source structures and their evolution over time. The closure amplitude rms, CARMS, indicating how far away a source is from being compact in terms of morphology, is calculated for each individual source. The overall structure-effect magnitudes for 3417 ICRF radio sources are quantified. CARMS values larger than 0.3 suggest significant source structures and those larger than 0.4 indicate very extended source structures. The 30 most frequently observed sources, which constitute 40% of current geodetic VLBI observables, are studied in detail. The quality of ICRF sources for astrometry is evaluated by examining the CARMS values. It is confirmed that sources with CARMS values larger than 0.30 can contribute residual errors of about 15ps to geodetic VLBI data analysis and those with the CARMS values larger than 0.4 generally can contribute more than 20ps. We recommend CARMS values as an indicator of the astrometric quality for the ICRF sources and the continuous monitoring of the ICRF sources to update CARMS values with new VLBI observations as they become available.
17955. 10yr of Swift/XRT obs. of GRBs
ID:
ivo://CDS.VizieR/J/ApJS/224/20
Title:
10yr of Swift/XRT obs. of GRBs
Short Name:
J/ApJS/224/20
Date:
21 Oct 2021
Publisher:
CDS
Description:
X-ray flares are generally supposed to be produced by later activities of the central engine, and may share a similar physical origin with the prompt emission of gamma-ray bursts (GRBs). In this paper, we have analyzed all significant X-ray flares from the GRBs observed by Swift from 2005 April to 2015 March. The catalog contains 468 bright X-ray flares, including 200 flares with redshifts. We obtain the fitting results of X-ray flares, such as start time, peak time, duration, peak flux, fluence, peak luminosity, and mean luminosity. The peak luminosity decreases with peak time, following a power-law behavior L_p_{propto}T_peak,z_^-1.27^. The flare duration increases with peak time. The 0.3-10keV isotropic energy of the distribution of X-ray flares is a log-normal peaked at 10^51.2^erg. We also study the frequency distributions of flare parameters, including energies, durations, peak fluxes, rise times, decay times, and waiting times. Power-law distributions of energies, durations, peak fluxes, and waiting times are found in GRB X-ray flares and solar flares. These distributions could be well explained by a fractal-diffusive, self-organized criticality model. Some theoretical models based on magnetic reconnection have been proposed to explain X-ray flares. Our result shows that the relativistic jets of GRBs may be dominated by Poynting flux.
17956. 5yr radial velocity measurements of 19 Cepheids
ID:
ivo://CDS.VizieR/J/ApJS/226/18
Title:
5yr radial velocity measurements of 19 Cepheids
Short Name:
J/ApJS/226/18
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the radial velocity (RV) variability and spectroscopic binarity of 19 Galactic long-period (P_puls_>~10d) classical Cepheid variable stars whose trigonometric parallaxes are being measured using the Hubble Space Telescope and Gaia. Our primary objective is to constrain possible parallax error due to undetected orbital motion. Using over 1600 high-precision RVs measured between 2011 and 2016, we find no indication of orbital motion on <~5yr timescales for 18 Cepheids and determine upper limits on allowed configurations for a range of input orbital periods. The results constrain the unsigned parallax error due to orbital motion to <2% for 16 stars, and <4% for 18. We improve the orbital solution of the known binary YZ Carinae and show that the astrometric model must take into account orbital motion to avoid significant error (~+/-100{mu}arcsec). We further investigate long-timescale (P_orb_>10yr) variations in pulsation-averaged velocity v_{gamma}_ via a template fitting approach using both new and literature RVs. We discover the spectroscopic binarity of XZ Car and CD Cyg, find first tentative evidence for AQ Car, and reveal KN Cen's orbital signature. Further (mostly tentative) evidence of time-variable v_{gamma}_ is found for SS CMa, VY Car, SZ Cyg, and X Pup. We briefly discuss considerations regarding a vetting process of Galactic Leavitt law calibrators and show that light contributions by companions are insignificant for most distance scale applications.
17957. 4-yr RV survey of red giant in eclipsing binaries
ID:
ivo://CDS.VizieR/J/ApJ/832/121
Title:
4-yr RV survey of red giant in eclipsing binaries
Short Name:
J/ApJ/832/121
Date:
21 Oct 2021
Publisher:
CDS
Description:
Given the potential of ensemble asteroseismology for understanding fundamental properties of large numbers of stars, it is critical to determine the accuracy of the scaling relations on which these measurements are based. From several powerful validation techniques, all indications so far show that stellar radius estimates from the asteroseismic scaling relations are accurate to within a few percent. Eclipsing binary systems hosting at least one star with detectable solar-like oscillations constitute the ideal test objects for validating asteroseismic radius and mass inferences. By combining radial velocity (RV) measurements and photometric time series of eclipses, it is possible to determine the masses and radii of each component of a double-lined spectroscopic binary. We report the results of a four-year RV survey performed with the echelle spectrometer of the Astrophysical Research Consortium's 3.5m telescope and the APOGEE spectrometer at Apache Point Observatory. We compare the masses and radii of 10 red giants (RGs) obtained by combining radial velocities and eclipse photometry with the estimates from the asteroseismic scaling relations. We find that the asteroseismic scaling relations overestimate RG radii by about 5% on average and masses by about 15% for stars at various stages of RG evolution. Systematic overestimation of mass leads to underestimation of stellar age, which can have important implications for ensemble asteroseismology used for Galactic studies. As part of a second objective, where asteroseismology is used for understanding binary systems, we confirm that oscillations of RGs in close binaries can be suppressed enough to be undetectable, a hypothesis that was proposed in a previous work.
17958. 25yrs monitoring of stellar orbits in the GC
ID:
ivo://CDS.VizieR/J/ApJ/837/30
Title:
25yrs monitoring of stellar orbits in the GC
Short Name:
J/ApJ/837/30
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center (GC), we present an update of the main results from this unique data set: a measurement of mass and distance to SgrA*. Our progress is not only due to the eight-year increase in time base, but also to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to Sgr A*; the statistical errors of 0.13x10^6^M_{sun}_ and 0.12kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, the star S1 also yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M=4.28+/-0.10|_stat._+/-0.21|_sys_x10^6^M_{sun}_ and R_0_=8.32+/-0.07|_stat._+/-0.14|_sys_kpc. These numbers are in agreement with the recent determination of R_0_ from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from Sgr A*, and of the radio source Sgr A* agree to within 1mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars that we can explicitly show are members of the clockwise disk of young stars, and which have lower-eccentricity orbits.
17959. 16yrs of AGNs X-ray spectral analyses from 7Ms CDF-S
ID:
ivo://CDS.VizieR/J/ApJS/232/8
Title:
16yrs of AGNs X-ray spectral analyses from 7Ms CDF-S
Short Name:
J/ApJS/232/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) identified in the 7Ms Chandra Deep Field-South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe K{alpha} line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2-21 months. With this approach, we not only present the power-law slopes, column densities N_H_, observed fluxes, and absorption-corrected 2-10keV luminosities L_X_ for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the N_H_ variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and N_H_ can be well explained by the continuum suppression with increasing N_H_. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of N_H_ for the CDF-S AGN population and present reselected subsamples that are complete with respect to N_H_. The N_H_-complete subsamples enable us to decouple the dependences of N_H_ on L_X_ and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average N_H_ and L_X_ of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as f_obscured_~0.42(1+z)^0.60^.
17960. >20yrs of HST obs. of Cepheids in SNIa host gal.
ID:
ivo://CDS.VizieR/J/ApJ/830/10
Title:
>20yrs of HST obs. of Cepheids in SNIa host gal.
Short Name:
J/ApJ/830/10
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of an optical search conducted as part of the SH0ES project (Supernovae and H_0_ for the Equation of State of dark energy) for Cepheid variable stars using the Hubble Space Telescope (HST) in 19 hosts of Type Ia supernovae (SNe Ia) and the maser-host galaxy NGC4258. The targets include nine newly imaged SN Ia hosts using a novel strategy based on a long-pass filter that minimizes the number of HST orbits required to detect and accurately determine Cepheid properties. We carried out a homogeneous reduction and analysis of all observations, including new universal variability searches in all SNIa hosts, which yielded a total of 2200 variables with well-defined selection criteria, the largest such sample identified outside the Local Group. These objects are used in a companion paper to determine the local value of H_0_ with a total uncertainty of 2.4%.

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