- ID:
- ivo://CDS.VizieR/J/ApJ/457/L99
- Title:
- 25yr CaII-HK observations of F-K nearby stars
- Short Name:
- J/ApJ/457/L99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We find a significant correlation between the magnetic and rotational moments for a sample of 112 lower main-sequence stars. The rotational moment is calculated from measurements of the rotation period in most of the stars (not from the projected rotational velocity inferred from Doppler broadening). The magnetic moment is computed from a database of homogeneous measurements of the mean level of Ca II H and K emission fluxes sampled for most of the stars over an interval of 25yr. The slope connecting the logarithm of the magnetic moment and the logarithm of the rotational moment is about +0.5-0.6, with a Pearson correlation coefficient of about +0.9. The scatter of points from the mean relation has a component that is natural and caused by decade-long surface variability.
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- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/896/L19
- Title:
- 16yr LC of TXS 0506+056 from MASTER networks
- Short Name:
- J/ApJ/896/L19
- Date:
- 07 Dec 2021
- Publisher:
- CDS
- Description:
- We present the earliest astronomical observation of a high-energy neutrino error box of which the variability was discovered after high-energy-neutrino detection. The one robotic telescope of the MASTER global international networks automatically imaged the error box of the very high-energy-neutrino event IceCube-170922A. Observations were carried out in minutes after the IceCube-170922A neutrino event was detected by the IceCube observatory at the South Pole. MASTER found the blazar TXS 0506+056 to be in the off-state after one minute and then switched to the on-state no later than two hours after the event. The effect is observed at a 50{sigma} significance level. We also present own a unique 16yr light curve of blazar TXS 0506+056 (518 data set).
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/90
- Title:
- 4yr 1.3mm VLBI observations of SgrA* with EHT
- Short Name:
- J/ApJ/820/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over four years. Closure phases, which are the sum of visibility phases along a closed triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180{deg} rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/6
- Title:
- 4.5yr obs. of Mrk421 with ARGO-YBJ & Fermi
- Short Name:
- J/ApJS/222/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to {gamma}-rays, during the 4.5yr period of ARGO-YBJ and Fermi common operation time, from 2008 August to 2013 February. These long-term observations, extending over an energy range of 18 orders of magnitude, provide a unique chance to study the variable emission of Mrk 421. In particular, due to the ARGO-YBJ and Fermi data, the entire energy range from 100MeV to 10TeV is covered without any gap. In the observation period, Mrk 421 showed both low- and high-activity states at all wavebands. The correlations among flux variations in different wavebands were analyzed. The X-ray flux is clearly correlated with the TeV {gamma}-ray flux, while the GeV {gamma}-rays only show a partial correlation with the TeV {gamma}-rays. Radio and UV fluxes seem to be weakly or not correlated with the X-ray and {gamma}-ray fluxes. Seven large flares, including five X-ray flares and two GeV {gamma}-ray flares with variable durations (3-58d), and one X-ray outburst phase were identified and used to investigate the variation of the spectral energy distribution with respect to a relative quiescent phase. During the outburst phase and the seven flaring episodes, the peak energy in X-rays is observed to increase from sub-keV to a few keV. The TeV {gamma}-ray flux increases up to 0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV {gamma}-rays is found to vary depending on the flare, a feature that leads us to classify flares into three groups according to the GeV flux variation. Finally, the one-zone synchrotron self-Compton model was adopted to describe the emission spectra. Two out of three groups can be satisfactorily described using injected electrons with a power-law spectral index around 2.2, as expected from relativistic diffuse shock acceleration, whereas the remaining group requires a harder injected spectrum. The underlying physical mechanisms responsible for different groups may be related to the acceleration process or to the environment properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/145
- Title:
- 20yr obs. of the spectroscopic binary EC 20117-4014
- Short Name:
- J/ApJ/859/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC 20117-4014 (=V4640 Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion; however, the period and the orbit semimajor axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic observed minus calculated (O-C) variations were detected in the two highest-amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P=792.3d) and the light-travel-time amplitude (A=468.9s). This binary shows no significant orbital eccentricity, and the upper limit of the eccentricity is 0.025 (using 3{sigma} as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was dP/dt=5.4(+/-0.7)x10^-14^d.d^-1^, which shows that the sdB is just before the end of the core helium-burning phase.
- ID:
- ivo://CDS.VizieR/J/ApJS/248/8
- Title:
- 9-yr of Fermi-LAT & Swift obs. of 3C 454.3 flares
- Short Name:
- J/ApJS/248/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 3C 454.3 is frequently observed in the flaring state. The long-term light curve of this source has been analyzed with 9yr (2008 August - 2017 July) of data from the Fermi-LAT detector. We have identified five flares and one quiescent state. The flares have substructures with many peaks during the flaring phase. We have estimated the rise and decay time of the flares and compared with flares of other similar sources. The modeling of gamma-ray spectral energy distributions shows in most cases that a log-parabola function gives the best fit to the data. We have done time-dependent leptonic modeling of two of the flares, for which simultaneous multiwavelength data are available. These two long-lasting flares, Flare-2A and Flare-2D, continued for 95 and 133 days, respectively. We have used the average values of Doppler factor, injected luminosity in electrons, size of the emission region, and the magnetic field in the emission region in modeling these flares. The emission region is assumed to be in the broad-line region in our single-zone model. The energy losses (synchrotron, synchrotron self-Compton, external Compton) and escape of electrons from the emission region have been included while doing the modeling. Although the total jet powers required to model these flares with the leptonic model are higher compared to other sources, they are always found to be lower than the Eddington luminosity of 3C 454.3. We also select some flaring peaks and show that the time variation of the Doppler factor or the injected luminosity in electrons over short timescales can explain their light curves.
- 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.
