- ID:
- ivo://CDS.VizieR/J/ApJ/722/L7
- Title:
- Fermi/LAT detected MOJAVE AGNs
- Short Name:
- J/ApJ/722/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of a non-zero time delay between radio emission measured by the VLBA at 15.4GHz and {gamma}-ray radiation ({gamma}-ray leads radio) registered by the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope for a sample of 183 radio and {gamma}-ray bright active galactic nuclei. For the correlation analysis, we used 0.1-100GeV {gamma}-ray photon fluxes, taken from monthly binned measurements from the first Fermi LAT catalog (1FGL; Abdo et al. 2010, Cat. J/ApJS/188/405), and 15.4GHz radio flux densities from the MOJAVE VLBA program (Lister et al. 2009, Cat. J/AJ/137/3718). The correlation is most pronounced if the core flux density is used, strongly indicating that the {gamma}-ray emission is generated within the compact region of the 15GHz VLBA core. Determining the Pearson's r and Kendall's {tau} correlation coefficients for different time lags, we find that for the majority of sources the radio/{gamma}-ray delay ranges from 1 to 8 months in the observer's frame and peaks at approximately 1.2 months in the source's frame. We interpret the primary source of the time delay to be synchrotron opacity in the nuclear region.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/626/A60
- Title:
- F-GAMMA 2.64-43GHz radio data over 2007-2015
- Short Name:
- J/A+A/626/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The advent of the Fermi gamma-ray space telescope with its superb sensitivity, energy range, and unprecedented capability to monitor the entire 4{pi} sky within less than 2-3 h, introduced a new standard in time domain gamma-ray astronomy. Among several breakthroughs, Fermi has - for the first time - made it possible to investigate, with high cadence, the variability of the broadband spectral energy distribution (SED), especially for active galactic nuclei (AGN). This is necessary for understanding the emission and variability mechanisms in such systems. To explore this new avenue of extragalactic physics the Fermi-GST AGN Multi-frequency Monitoring Alliance (F-GAMMA) programme undertook the task of conducting nearly monthly, broadband radio monitoring of selected blazars, which is the dominant population of the extragalactic gamma-ray sky, from January 2007 to January 2015. In this work we release all the multi-frequency light curves from 2.64 to 43 GHz and first order derivative data products after all necessary post-measurement corrections and quality checks. Along with the demanding task to provide the radio part of the broadband SED in monthly intervals, the F-GAMMA programme was also driven by a series of well-defined fundamental questions immediately relevant to blazar physics. On the basis of the monthly sampled radio SEDs, the F-GAMMA aimed at quantifying and understanding the possible multiband correlation and multi-frequency radio variability, spectral evolution and the associated emission, absorption and variability mechanisms. The location of the gamma-ray production site and the correspondence of structural evolution to radio variability have been among the fundamental aims of the programme. Finally, the programme sought to explore the characteristics and dynamics of the multi-frequency radio linear and circular polarisation. The F-GAMMA ran two main and tightly coordinated observing programmes. The Effelsberg 100 m telescope programme monitoring 2.64, 4.85, 8.35, 10.45, 14.6, 23.05, 32, and 43 GHz, and the IRAM 30 m telescope programme observing at 86.2, 142.3, and 228.9 GHz. The nominal cadence was one month for a total of roughly 60 blazars and targets of opportunity. In a less regular manner the F-GAMMA programme also ran an occasional monitoring with the APEX 12 m telescope at 345 GHz. We only present the Effelsberg dataset in this paper. The higher frequencies data are released elsewhere. The current release includes 155 sources that have been observed at least once by the F-GAMMA programme. That is, the initial sample, the revised sample after the first Fermi release, targets of opportunity, and sources observed in collaboration with a monitoring programme following up on Planck satellite observations. For all these sources we release all the quality-checked Effelsberg multi-frequency light curves. The suite of post-measurement corrections and flagging and a thorough system diagnostic study and error analysis is discussed as an assessment of the data reliability. We also release data products such as flux density moments and spectral indices. The effective cadence after the quality flagging is around one radio SED every 1.3 months. The coherence of each radio SED is around 40 min. The released dataset includes more than 3x104 measurements for some 155 sources over a broad range of frequencies from 2.64 GHz to 43 GHz obtained between 2007 and 2015. The median fractional error at the lowest frequencies (2.64-10.45 GHz) is below 2%. At the highest frequencies (14.6-43 GHz) with limiting factor of the atmospheric conditions, the errors range from 3% to 9%, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJS/217/4
- Title:
- 2FGL sources observed between 5-9GHz
- Short Name:
- J/ApJS/217/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an all-sky radio survey between 5 and 9GHz of sky areas surrounding all unassociated {gamma}-ray objects listed in the Fermi Large Area Telescope Second Source Catalog (2FGL). The goal of these observations is to find all new {gamma}-ray active galactic nucleus (AGN) associations with radio sources >10mJy at 8GHz. We observed with the Very Large Array and the Australia Telescope Compact Array the areas around unassociated sources, providing localizations of weak radio point sources found in 2FGL fields at arcmin scales. Then we followed-up a subset of those with the Very Long Baseline and the Long Baseline Arrays to confirm detections of radio emission on parsec-scales. We quantified association probabilities based on known statistics of source counts and assuming a uniform distribution of background sources. In total we found 865 radio sources at arcsec scales as candidates for association and detected 95 of 170 selected for follow-up observations at milliarcsecond resolution. Based on this we obtained firm associations for 76 previously unknown {gamma}-ray AGNs. Comparison of these new AGN associations with the predictions from using the Wide-field Infrared Survey Explorer color-color diagram shows that half of the associations are missed. We found that 129 out of 588 observed {gamma}-ray sources at arcmin scales not a single radio continuum source was detected above our sensitivity limit within the 3{sigma} {gamma}-ray localization. These "empty" fields were found to be particularly concentrated at low Galactic latitudes. The nature of these Galactic {gamma}-ray emitters is not yet determined.
- ID:
- ivo://CDS.VizieR/J/ApJS/248/23
- Title:
- 4FGL sources with IR/Rad associations
- Short Name:
- J/ApJS/248/23
- Date:
- 09 Nov 2021 09:30:22
- Publisher:
- CDS
- Description:
- Associating {gamma}-ray sources to their low-energy counterparts is one of the major challenges of modern {gamma}-ray astronomy. In the context of the Fourth Fermi Large Area Telescope Source Catalog (4FGL), the associations rely mainly on parameters such as apparent magnitude, integrated flux, and angular separation between the {gamma}-ray source and its low-energy candidate counterpart. In this work, we propose a new use of the likelihood ratio (LR) and a complementary supervised learning technique to associate {gamma}-ray blazars in 4FGL, based only on spectral parameters such as the {gamma}-ray photon index, mid-infrared colors, and radio-loudness. In the LR approach, we crossmatch the Wide-field Infrared Survey Explorer Blazar-Like Radio-Loud Sources catalog with 4FGL and compare the resulting candidate counterparts with the sources listed in the {gamma}-ray blazar locus to compute an association probability (AP) for 1138 counterparts. In the supervised learning approach, we train a random forest algorithm with 869 high-confidence blazar associations and 711 fake associations and then compute an AP for 1311 candidate counterparts. A list with all 4FGL blazar candidates of uncertain type associated by our method is provided to guide future optical spectroscopic follow-up observations.
- ID:
- ivo://CDS.VizieR/J/AJ/138/1032
- Title:
- Filling in the gaps in the 4.85GHz sky
- Short Name:
- J/AJ/138/1032
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a 4.85GHz survey of bright, flat-spectrum radio sources conducted with the Effelsberg 100m telescope in an attempt to improve the completeness of existing surveys, such as CRATES. We report the results of these observations and of follow-up 8.4GHz observations with the VLA of a subset of the sample. We comment on the connection to the Wilkinson Microwave Anisotropy Probe point source catalog and on the survey's effectiveness at supplementing the CRATES sky coverage.
- ID:
- ivo://CDS.VizieR/J/AJ/130/2473
- Title:
- Fine-scale structure in 250 sources at 15GHz
- Short Name:
- J/AJ/130/2473
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have examined the compact structure in 250 flat-spectrum extragalactic radio sources using interferometric fringe visibilities obtained with the Very Long Baseline Array (VLBA) at 15GHz. With projected baselines out to 440M{lambda}, we are able to investigate source structure on typical angular scales as small as 0.05mas.
- ID:
- ivo://CDS.VizieR/J/A+AS/106/29
- Title:
- Flat-spectrum radio sources at 327 MHz
- Short Name:
- J/A+AS/106/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/AN/338/700
- Title:
- Flux densities for 290 blazars
- Short Name:
- J/AN/338/700
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of nine years of the blazar observing programme at the RATAN-600 radio telescope (2005-2014). The data were obtained at six frequency bands (1.1, 2.3, 4.8, 7.7, 11.2, 21.7GHz) for 290 blazars, mostly BL Lacs. In addition, we used data at 37GHz obtained quasi-simultaneously with the Metsahovi radio observatory for some sources. For each source NVSS name (RA (hhmmss) and DEC (ddmmss) for the J2000.0 epoch), and flux densities at seven frequencies are presented (1.1-37GHz).
- ID:
- ivo://CDS.VizieR/J/ApJ/892/105
- Title:
- Fourth catalog of Fermi LAT-detected AGNs (4LAC)
- Short Name:
- J/ApJ/892/105
- Date:
- 17 Jan 2022 00:31:09
- Publisher:
- CDS
- Description:
- The fourth catalog of active galactic nuclei (AGNs) detected by the Fermi Gamma-ray Space Telescope Large Area Telescope (4LAC) between 2008 August 4 and 2016 August 2 contains 2863 objects located at high Galactic latitudes (|b|>10{deg}). It includes 85% more sources than the previous 3LAC catalog based on 4yr of data. AGNs represent at least 79% of the high-latitude sources in the fourth Fermi-Large Area Telescope Source Catalog (4FGL), which covers the energy range from 50MeV to 1TeV. In addition, 344 gamma-ray AGNs are found at low Galactic latitudes. Most of the 4LAC AGNs are blazars (98%), while the remainder are other types of AGNs. The blazar population consists of 24% Flat Spectrum Radio Quasars (FSRQs), 38% BL Lac-type objects, and 38% blazar candidates of unknown types (BCUs). On average, FSRQs display softer spectra and stronger variability in the gamma-ray band than BL Lacs do, confirming previous findings. All AGNs detected by ground-based atmospheric Cerenkov telescopes are also found in the 4LAC.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/22
- Title:
- FRII radio sources dynamical models
- Short Name:
- J/ApJS/255/22
- Date:
- 03 Dec 2021 13:25:10
- Publisher:
- CDS
- Description:
- Dynamical evolution models of 361 extragalactic Fanaroff-Riley type II radio sources selected from the Cambridge 3CRR, 6CE, 5C6, and 5C7 Sky Surveys, as well as the Bologna B2, Green Bank GB, and GB2 Surveys, are presented. Their spectra, compiled mostly from the recent catalogs of radio sources and the available NASA/IPAC and Astrophysical Catalogs Support System databases, along with morphological characteristics of the sources determined from their radio maps, have been modeled using the DYNAGE algorithm and/or its extension (KDA EXT) for the hypothetical case of further evolution after the jet's termination. The best-fit models provide estimates of a number of important physical parameters of the sources, as (i) the jet power, (ii) the density distribution of the external gaseous medium surrounding the radio core and the jet propagating through it, (iii) the initial energy distribution of the relativistic particles accelerated at the shock fronts, and (iv) the age of the observed radio structure. Additionally, estimates of some derivative parameters are provided, e.g., the radio lobes' pressure, their longitudinal expansion velocity, the magnetic field strength, and the total energy deposited in the lobes. The observed spectra and their best-fit models are included. Finally, one of the useful applications of the above models is presented, namely a strong correlation between the ambient medium density and the rest-frame two-point spectral index available directly from the observed spectra.