- ID:
- ivo://CDS.VizieR/J/ApJS/232/7
- Title:
- 8yr R-band photopolarimetric data of blazar Mrk 421
- Short Name:
- J/ApJS/232/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of 8yr R-band photopolarimetric data of blazar Mrk 421 collected from 2008 February to 2016 May are presented, along with extensive multiwavelength observations covering radio to TeV {gamma}-rays around the flares observed in 2008 May, 2010 March, and 2013 April. The most important results are found in 2013, when the source displayed in the R band a very high brightness state of 11.29+/-0.03mag (93.60+/-1.53mJy) on April 10 and a polarization degree of 11.00%+/-0.44% on May 13. The analysis of the optical data shows that the polarization variability is due to the superposition of two polarized components that might be produced in two distinct emitting regions. An intranight photopolarimetric variability study carried out over seven nights after the 2013 April maximum found flux and polarization variations on the nights of April 14, 15, 16, and 19. In addition, the flux shows a minimum variability timescale of {Delta}t=2.34+/-0.12hr, and the polarization degree presents variations of~1%-2% on a timescale of {Delta}t~minutes. Also, a detailed analysis of the intranight data shows a coherence length of the large-scale magnetic field of l_B_~0.3pc, which is the same order of magnitude as the distance traveled by the relativistic shocks. This result suggests that there is a connection between the intranight polarimetric variations and spatial changes of the magnetic field. Analysis of the complete R-band data along with the historical optical light curve found for this object shows that Mrk 421 varies with a period of 16.26+/-1.78yr.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/245/18
- Title:
- 9yr R-band photopolarimetric data of 3C 279
- Short Name:
- J/ApJS/245/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An exhaustive analysis of 9yr optical R-band photopolarimetric data of the flat-spectrum radio quasar 3C 279 from 2008 February 27 to 2017 May 25 is presented, along with multiwavelength observing campaigns performed during the flaring activity exhibited in 2009 February/March, 2011 June, 2014 March/April, 2015 June, and 2017 February. In the R band, this source showed the maximum brightness state of 13.68+/-0.11mag (1.36+/-0.20mJy) on 2017 March 2 and the lowest brightness state ever recorded of 18.20+/-0.87 mag (0.16+/-0.03mJy) on 2010 June 17. During the entire period of observations, the polarization degree varied between 0.48%+/-0.17% and 31.65%+/-0.77%, and the electric vector position angle (EVPA) exhibited large rotations between 82.98+/-0.92{deg} and 446.32+/-1.95{deg}. Optical polarization data show that this source has a stable polarized component that varied from~6% (before the 2009 flare) to~13% after the flare. The overall behavior of our polarized variability data supports the scenario of jet precessions as responsible for the observed large rotations of the EVPA. Discrete correlation function analysis shows that the lags between gamma-rays and X-rays compared to the optical R-band fluxes are {Delta}t~31 days and 1 day in 2009. Lags were also found among gamma-rays compared with X-rays and radio of {Delta}t~30 and 43 days in 2011, and among radio and optical R band of {Delta}t~10 days in 2014. A very intense flare in 2017 was observed in optical bands, with a dramatic variation in the polarization degree (from~6% to 20%) in 90 days without exhibiting flaring activity in other wavelengths.
- 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.
- 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.
- 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^.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/124
- Title:
- 2yrs of eclipse data & precise RVs for LP661-13
- Short Name:
- J/ApJ/836/124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of stellar eclipses in the LP 661-13 system. We present the discovery and characterization of this system, including high-resolution spectroscopic radial velocities and a photometric solution spanning two observing seasons. LP 661-13 is a low-mass binary system with an orbital period of 4.7043512_-0.0000010_^+0.0000013^d at a distance of 24.9+/-1.3pc. LP661-13A is a 0.30795+/-0.00084M_{sun}_ star, while LP661-13B is a 0.19400+/-0.00034M_{sun}_ star. The radius of each component is 0.3226+/-0.0033R_{sun}_ and 0.2174+/-0.0023R_{sun}_, respectively. We detect out-of-eclipse modulations at a period slightly shorter than the orbital period, implying that at least one of the components is not rotating synchronously. We find that each component is slightly inflated compared to stellar models, and that this cannot be reconciled through age or metallicity effects. As a nearby eclipsing binary system, where both components are near or below the full-convection limit, LP 661-13 will be a valuable test of models for the structure of cool dwarf stars.
- 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%.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/12
- Title:
- 16yrs of radial velocity measurements of S0-2
- Short Name:
- J/ApJ/854/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The star S0-2, which orbits the supermassive black hole (SMBH) in our Galaxy with a period of 16 years, provides the strongest constraint on both the mass of the SMBH and the distance to the Galactic center. S0-2 will soon provide the first measurement of relativistic effects near a SMBH. We report the first limits on the binarity of S0-2 from radial velocity (RV) monitoring, which has implications for both understanding its origin and robustness as a probe of the central gravitational field. With 87 RV measurements, which include 12 new observations that we present, we have the requisite data set to look for RV variations from S0-2's orbital model. Using a Lomb-Scargle analysis and orbit- fitting for potential binaries, we detect no RV variation beyond S0-2's orbital motion and do not find any significant periodic signal. The lack of a binary companion does not currently distinguish different formation scenarios for S0-2. The upper limit on the mass of a companion star (M_comp_) still allowed by our results has a median upper limit of M_comp_ sin i <=1.6M_{sun}_ for periods between 1 and 150 days, the longest period to avoid tidal break-up of the binary. We also investigate the impact of the remaining allowed binary system on the measurement of the relativistic redshift at S0-2's closest approach in 2018. While binary star systems are important to consider for this experiment, we find that plausible binaries for S0-2 will not alter a 5{sigma} detection of the relativistic redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/89
- Title:
- 12yrs of radial velocity obs. of exoplanet systems
- Short Name:
- J/ApJ/821/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted a Doppler survey at Keck combined with NIRC2 K-band adaptive optics (AO) imaging to search for massive, long-period companions to 123 known exoplanet systems with one or two planets detected using the radial velocity (RV) method. Our survey is sensitive to Jupiter-mass planets out to 20au for a majority of stars in our sample, and we report the discovery of eight new long-period planets, in addition to 20 systems with statistically significant RV trends that indicate the presence of an outer companion beyond 5AU. We combine our RV observations with AO imaging to determine the range of allowed masses and orbital separations for these companions, and account for variations in our sensitivity to companions among stars in our sample. We estimate the total occurrence rate of companions in our sample to be 52+/-5% over the range 1-20M_Jup_ and 5-20AU. Our data also suggest a declining frequency for gas giant planets in these systems beyond 3-10AU, in contrast to earlier studies that found a rising frequency for giant planets in the range 0.01-3AU. This suggests either that the frequency of gas giant planets peaks between 3 and 10 AU, or that outer companions in these systems have a different semi-major axis distribution than the overall population of gas giant planets. Our results also suggest that hot gas giants may be more likely to have an outer companion than cold gas giants. We find that planets with an outer companion have higher average eccentricities than their single counterparts, suggesting that dynamical interactions between planets may play an important role in these systems.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/10
- Title:
- 12yrs of R-band photometry of the quasar 3C 454.3
- Short Name:
- J/ApJS/253/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present 8523 pairs of R-band optical photometry observations for the quasar 3C 454.3 made during the period of 2006 October - 2018 February on the 70cm meniscus telescope at Abastumani Observatory, Georgia, to study its intraday variabilities (IDVs) and long-term variations, and we have come to the following results. (1) We detected 10 outbursts, a {Delta}R=3.825mag variation, and some IDVs. The IDV timescales are from 4.1 to 285 minutes, with the corresponding variability amplitude being A=2.9%-43.67%. The amplitude increases with IDV timescale. (2) The largest variation over a 1 day timescale is {Delta}R=1.38mag. (3) The IDV timescales suggest that the emission sizes are from 8.9x10^13^cm to 6.20x10^15^cm, and the magnetic field strengths are B=0.18-0.79G. (4) Period analysis results show three possible long-term periods, p=3.04+/-0.02yr, p=1.66+/-0.06yr, and p=1.20+/-0.03yr in the optical light curve. We adopted the accretion disk models and the lighthouse models to period p=3.04+/-0.02yr: in the accretion disk models, the binary black holes have masses M=1.17x10^9^M_{sun}_; in the lighthouse models, we used two boosted jet flux densities to fit the observational light curve. (5) WWZ analysis gives some short-period (high-frequency) signals associated with strong bursts (JD2454302 and JD2454521) with variable frequencies and lasting for the entire observation time span (11.3yr).
