- 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.
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- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/79
- Title:
- 10yr of GJ176 radial velocities & VR photometry
- Short Name:
- J/ApJ/801/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an in-depth analysis of stellar activity and its effects on radial velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10yr from the High Resolution Spectrograph on the Hobby-Eberly Telescope. These data are supplemented with spectra from previous observations with the HIRES and HARPS spectrographs, and V- and R-band photometry taken over six years at the Dyer and Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth exoplanet in an 8.8-day orbit. However, the velocities of this star are also known to be contaminated by activity, particularly at the 39-day stellar rotation period. We have examined the magnetic activity of GJ 176 using the sodium I D lines, which have been shown to be a sensitive activity tracer in cool stars. In addition to rotational modulation, we see evidence of a long-term trend in our Na I D index, which may be part of a long-period activity cycle. The sodium index is well correlated with our RVs, and we show that this activity trend drives a corresponding slope in RV. Interestingly, the rotation signal remains in phase in photometry, but not in the spectral activity indicators. We interpret this phenomenon as the result of one or more large spot complexes or active regions which dominate the photometric variability, while the spectral indices are driven by the overall magnetic activity across the stellar surface. In light of these results, we discuss the potential for correcting activity signals in the RVs of M dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/132
- Title:
- ~30yr of opt. spectroscopy & Vmag obs. of GW Ori
- Short Name:
- J/ApJ/851/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the pre-main-sequence hierarchical triple-star system GW Ori. A forward modeling of the ^13^CO and C^18^O J=2-1 transitions permits a measurement of the total stellar mass in this system, 5.29+/-0.09M_{sun}_, and the circumtriple disk inclination, 137.6{deg}+/-2.0{deg}. Optical spectra spanning a 35yr period were used to derive new radial velocities and, coupled with a spectroscopic disentangling technique, revealed that the A and B components of GW Ori form a double-lined spectroscopic binary with a period of 241.50+/-0.05d; a tertiary companion orbits that inner pair with a period of 4218+/-50d. Combining the results from the ALMA data and the optical spectra with three epochs of astrometry in the literature, we constrain the individual stellar masses in the system (M_A_~2.7M_{sun}_, M_B_~1.7M_{sun}_, M_C_~0.9M_{sun}_) and find strong evidence that at least one of the stellar orbital planes (and likely both) is misaligned with the disk plane by as much as 45{deg}. A V-band light curve spanning 30yr reveals several new ~30-day eclipse events 0.1-0.7mag in depth and a 0.2mag sinusoidal oscillation that is clearly phased with the AB-C orbital period. Taken together, these features suggest that the A-B pair may be partially obscured by material in the inner disk as the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude that stellar evolutionary models are consistent with our measurements of the masses and basic photospheric properties if the GW Ori system is ~1Myr old.
- ID:
- ivo://CDS.VizieR/J/ApJ/874/13
- Title:
- 24yr of radio observations of V404 Cygni
- Short Name:
- J/ApJ/874/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Relativistic outflows are believed to be a common feature of black hole X-ray binaries (BHXBs) at the lowest accretion rates, when they are in their "quiescent" spectral state. However, we still lack a detailed understanding of how quiescent jet emission varies with time. Here we present 24yr of archival radio observations (from the Very Large Array and the Very Long Baseline Array) of the BHXB V404 Cygni in quiescence (totaling 150 observations from 1.4 to 22GHz). The observed flux densities follow lognormal distributions with means and standard deviations of (<logf{nu}>,{sigma}_logf{nu}_)=(-0.53,0.19) and (-0.53,0.30) at 4.9 and 8.4GHz, respectively (where f{nu} is the flux density in units of mJy). As expected, the average radio spectrum is flat with a mean and standard deviation of (<{alpha}_r_,{sigma}_{alpha}r_)=(0.02,0.65), where f{nu}{propto}{nu}^{alpha}_r_^. We find that radio flares that increase the flux density by factors of 2-4 over timescales as short as <10 minutes are commonplace, and that long-term variations (over 10-4000 day timescales) are consistent with shot-noise impulses that decay to stochastic variations on timescales <~10 days (and perhaps as short as tens of minutes to several hr). We briefly compare the variability characteristics of V404 Cygni to jetted active galactic nuclei, and we conclude with recommendations on how to account for variability when placing quiescent BHXB candidates with radio luminosities comparable to V404 Cygni (L_R_~10^28^erg/s) onto the radio/X-ray luminosity plane.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/170
- Title:
- 10yr of radio-to-gamma-ray obs. of 1ES 1215+30.3
- Short Name:
- J/ApJ/891/170
- Date:
- 19 Jan 2022 09:02:08
- Publisher:
- CDS
- Description:
- Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100MeV to 30TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/74
- Title:
- 27yr of RV observations of HD 219134
- Short Name:
- J/ApJ/821/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nearby (6.5pc) star HD219134 was recently shown by Motalebi+ (2015, J/A+A/584/A72) and Vogt+ (2015ApJ...814...12V) to host several planets, the innermost of which is transiting. We present 27yr of radial velocity (RV) observations of this star from the McDonald Observatory Planet Search program, and 19yr of stellar activity data. We detect a long-period activity cycle measured in the CaII SHK index, with a period of 4230+/-100d (11.7yr), very similar to the 11yr solar activity cycle. Although the period of the Saturn-mass planet HD219134h is close to half that of the activity cycle, we argue that it is not an artifact due to stellar activity. We also find a significant periodicity in the SHK data due to stellar rotation with a period of 22.8d. This is identical to the period of planet f identified by Vogt+ (2015ApJ...814...12V), suggesting that this RV signal might be caused by rotational modulation of stellar activity rather than a planet. Analysis of our RVs allows us to detect the long-period planet HD219134h and the transiting super-Earth HD219134b. Finally, we use our long time baseline to constrain the presence of longer period planets in the system, excluding to 1{sigma} objects with Msini>0.36M_J_ at 12yr (corresponding to the orbital period of Jupiter) and Msini>0.72M_J_ at a period of 16.4yr (assuming a circular orbit for an outer companion).
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/80
- Title:
- 6-yr optical monitoring of the FSRQ 3C 454.3
- Short Name:
- J/ApJ/856/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our photometric monitoring of a flat spectrum radio quasar 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows an obvious redder-when-brighter trend, which reaches a saturation stage when the source is brighter than 15.15mag at V band. We perform a simulation with multiple values of disk luminosity and spectral index to reproduce the magnitude-color diagram. The results show that the contamination caused by the disk radiation alone is difficult to produce the observed color variability. The variability properties during the outburst in 2009 December are also compared with {gamma}-ray data derived from the Fermi {gamma}-ray space telescope. The flux variation of these two bands follows a linear relation with F_{gamma}_{propto}F_R_^1.14+/-0.07^, which provides observational evidence for the external Compton process in 3C 454.3. Meanwhile, this flux correlation indicates that electron injection is the main mechanism for the variability origin. We also explore the variation of the flux ratio F{gamma}/FR and the detailed structures in the light curves, and discuss some possible origins for the detailed variability behaviors.
- 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.
