- ID:
- ivo://CDS.VizieR/J/ApJ/757/25
- Title:
- Fermi/LAT AGN at 5GHz
- Short Name:
- J/ApJ/757/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The parsec-scale radio properties of 232 active galactic nuclei, most of which are blazars, detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA) at 5GHz. Data from both the first 11 months (1FGL) and the first 2 years (2FGL) of the Fermi mission were used to investigate these sources' {gamma}-ray properties. We use the ratio of the {gamma}-ray-to-radio luminosity as a measure of {gamma}-ray loudness. We investigate the relationship of several radio properties to {gamma}-ray loudness and to the synchrotron peak frequency. There is a tentative correlation between {gamma}-ray loudness and synchrotron peak frequency for BL Lac objects in both 1FGL and 2FGL, and for flat-spectrum radio quasars (FSRQs) in 2FGL. We find that the apparent opening angle tentatively correlates with {gamma}-ray loudness for FSRQs, but only when we use the 2FGL data. We also find that the total VLBA flux density correlates with the synchrotron peak frequency for BL Lac objects and FSRQs. The core brightness temperature also correlates with synchrotron peak frequency, but only for the BL Lac objects. The low-synchrotron-peaked (LSP) BL Lac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BL Lac objects are more strongly beamed than the rest of the BL Lac object population.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/1060
- Title:
- Fermi/LAT broad emission line blazars
- Short Name:
- J/MNRAS/448/1060
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the broad emission line blazars detected in the {gamma}-ray band by the Large Area Telescope onboard the Fermi satellite and with the optical spectrum studied by Shaw et al. (2012, Cat. J/ApJ/748/49, hereafter S12, and 2013, Cat. J/ApJ/764/135, hereafter S13). The observed broad line strength provides a measure of the ionizing luminosity of the accretion disc, while the {gamma}-luminosity is a proxy for the bolometric non-thermal beamed jet emission. The resulting sample, composed by 217 blazars, is the best suited to study the connection between accretion and jet properties. We compare the broad emission line properties of these blazars with those of radio-quiet and radio-loud quasars present in the Sloan Digital Sky Survey, to asses differences and similarities of the disc luminosity and the virial black hole mass. For most sources, we could derive the black hole mass by reproducing the IR-optical-UV data with a standard accretion disc spectrum, and we compared the black hole masses derived with the two methods. The distributions of the masses estimated in the two ways agree satisfactorily. We then apply a simple, one-zone, leptonic model to all the 217 objects of our sample. The knowledge of the black hole mass and disc luminosity helps to constrain the jet parameters. On average, they are similar to what found by previous studies of smaller samples of sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/597
- Title:
- FERMI LAT detected blazars
- Short Name:
- J/ApJ/700/597
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b|>10{deg} with test statistic greater than 100 (corresponding to about 10{sigma}). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b|<10{deg}, were previously detected with Energetic Gamma-Ray Experiment Telescope (EGRET), probably due to variability.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A103
- Title:
- Fermi-LATi sources low-energy counterparts
- Short Name:
- J/A+A/643/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A significant fraction of all gamma-ray sources detected by the Large Area Telescope aboard the Fermi satellite is still lacking a low-energy counterpart. In addition, there is still a large population of gamma-ray sources with associated low-energy counterparts that lack firm classifications. In the last 10 years we have undertaken an optical spectroscopic campaign to address the problem of unassociated or unidentified gamma-ray sources (UGSs), mainly devoted to observing blazars and blazar candidates because they are the largest population of gamma-ray sources associated to date. Here we describe the overall impact of our optical spectroscopic campaign on sources associated in Fermi-LAT catalogs, coupled with objects found in the literature. In the literature search we kept track of efforts by different teams that presented optical spectra of counterparts or potential counterparts of Fermi-LAT catalog sources. Our summary includes an analysis of additional 30 newly collected optical spectra of counterparts or potential counterparts of Fermi-LAT sources of a previously unknown nature. Methods. New spectra were acquired at the Blanco 4m and OAN-SPM 2.1m telescopes, and those available in the Sloan Digital Sky Survey (data release 15) archive. All new sources with optical spectra analyzed here are classified as blazars. Thanks to our campaign, altogether we discovered and classified 394 targets with an additional 123 objects collected from a literature search. We began our optical spectroscopic campaign between the release of the second and third Fermi-LAT source catalogs (2FGL and 3FGL, respectively), classified about 25% of the sources that had uncertain nature and discovered a blazar-like potential counterpart for ~10% of UGSs listed therein. In the 4FGL catalog, about 350 Fermi-LAT sources have been classified to date thanks to our campaign. The most elusive class of blazars are found to be BL Lacs since the largest fraction of Fermi-LAT sources targeted in our observations showed a featureless optical spectrum. The same conclusion applied to the literature spectra. Finally, we confirm the high reliability of mid-IR color-based methods to select blazar-like candidate counterparts of unassociated or unidentified gamma-ray sources.
- ID:
- ivo://CDS.VizieR/J/ApJS/199/31
- Title:
- Fermi LAT second source catalog (2FGL)
- Short Name:
- J/ApJS/199/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the second catalog of high-energy {gamma}-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100MeV to 100GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely {gamma}-ray-producing source classes.
- ID:
- ivo://CDS.VizieR/J/ApJS/218/23
- Title:
- Fermi LAT third source catalog (3FGL)
- Short Name:
- J/ApJS/218/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100MeV-300GeV range. Based on the first 4yr of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse {gamma}-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources above 4{sigma} significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ~3% at 1GeV.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/4193
- Title:
- Fermi/non-Fermi blazars jet power and accretion
- Short Name:
- J/MNRAS/451/4193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the relationship between jet power and accretion for Fermi and non-Fermi blazars. We also compare the relevant parameter. Our main results are: (i) Fermi and non-Fermi blazars have significant differences in red shift, black hole mass and broad line luminosity. (ii) Fermi blazars have a higher average core-dominance parameter than non-Fermi blazars, which suggests that Fermi blazars have a strong beaming effect. (iii) We find a significant correlation between broad line emission and jet power for Fermi and non-Fermi blazars, which suggests a direct tight connection between jet and accretion. (iv) The accretion and black hole mass may have a different contribution to jet power for Fermi and non-Fermi blazars.
- 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/MNRAS/493/1926
- Title:
- 4FGL blazar classification neural network
- Short Name:
- J/MNRAS/493/1926
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fermi Large Area Telescope (LAT) has detected more than 5000 gamma-ray sources in its first 8 years of operation. More than 3000 of them are blazars. About 60 per cent of the Fermi-LAT blazars are classified as BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the rest remain of uncertain type. The goal of this study was to classify those blazars of uncertain type, using a supervised machine learning method based on an artificial neural network, by comparing their properties to those of known gamma-ray sources. Probabilities for each of 1329 uncertain blazars to be a BL Lac or FSRQ are obtained. Using 90 per cent precision metric, 801 can be classified as BL Lacs and 406 as FSRQs while 122 still remain unclassified. This approach is of interest because it gives a fast preliminary classification of uncertain blazars. We also explored how different selections of training and testing samples affect the classification and discuss the meaning of network outputs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/3180
- Title:
- 3FGL Blazar of Unknown Type classification
- Short Name:
- J/MNRAS/462/3180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fermi-Large Area Telescope (LAT) is currently the most important facility for investigating the GeV {gamma}-ray sky. With Fermi-LAT, more than three thousand {gamma}-ray sources have been discovered so far. 1144 (~40 per cent) of the sources are active galaxies of the blazar class, and 573 (~20 per cent) are listed as blazar candidate of uncertain type (BCU), or sources without a conclusive classification. We use the empirical cumulative distribution functions and the artificial neural networks for a fast method of screening and classification for BCUs based on data collected at {gamma}-ray energies only, when rigorous multiwavelength analysis is not available. Based on our method, we classify 342 BCUs as BL Lacs and 154 as flat-spectrum radio quasars, while 77 objects remain uncertain. Moreover, radio analysis and direct observations in ground-based optical observatories are used as counterparts to the statistical classifications to validate the method. This approach is of interest because of the increasing number of unclassified sources in Fermi catalogues and because blazars and in particular their subclass high synchrotron peak objects are the main targets of atmospheric Cherenkov telescopes.