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Start Over Subject gamma-ray astronomy Subject quasars
1. AGN Fermi/LAT {gamma}-ray and 37GHz fluxes
ID:
ivo://CDS.VizieR/J/A+A/535/A69
Title:
AGN Fermi/LAT {gamma}-ray and 37GHz fluxes
Short Name:
J/A+A/535/A69
Date:
21 Oct 2021
Publisher:
CDS
Description:
Although the Fermi mission has increased our knowledge of {gamma}-ray AGN, many questions remain, such as the site of {gamma}-ray production, the emission mechanism, and the factors that govern the strength of the emission. Using data from a high radio band, 37GHz, uncontaminated by other radiation components besides the jet emission, we study these questions with averaged flux densities over the the first year of Fermi operations. We look for possible correlations between the 100MeV-100GeV band used by the Fermi satellite and 37GHz radio band observed at the Aalto University Metsahovi Radio Telescope, as well as for differences between the {gamma}-ray emission of different AGN subsamples. We use data averaged over the 1FGL period. Our sample includes 249 northern AGN, including a complete sample of 68 northern AGN with a measured average flux density exceeding 1Jy.
2. Bimodal radio variability in OVRO blazars
ID:
ivo://CDS.VizieR/J/MNRAS/467/4565
Title:
Bimodal radio variability in OVRO blazars
Short Name:
J/MNRAS/467/4565
Date:
21 Oct 2021
Publisher:
CDS
Description:
Blazars are known to show periods of quiescence followed by outbursts visible throughout the electromagnetic spectrum. We present a novel maximum likelihood approach to capturing this bimodal behavior by examining blazar radio variability in the flux-density domain. We separate quiescent and flaring components of a source's light curve by modeling its flux-density distribution as a series of "off" and "on" states. Our modeling allows us to extract information regarding the flaring ratio, duty cycle, and the modulation index in the "off"-state, in the "on"-state, as well as throughout the monitoring period of each blazar. We apply our method to a flux-density-limited subsample from the Owens Valley Radio observatory's 15 GHz blazar monitoring program, and explore differences in the variability characteristics between BL Lacs and FSRQs as well as between {gamma}-ray detected and non-detected sources. We find that: (1) BL Lacs are more variable and have relatively larger outbursts than the FSRQs; (2) unclassified blazar candidates in our sample show similar variability characteristics as the FSRQs; and (3) {gamma}-ray detected differ from the {gamma}-ray non-detected sources in all their variability properties, suggesting a link between the production of {gamma}-rays and the mechanism responsible for the radio variability. Finally, we fit distributions for blazar flaring ratios, duty cycles, and on- and off- modulation indices that can be used in population studies of variability-dependent blazar properties.
3. Blazar 0836+710 long-term multiwavelength studies
ID:
ivo://CDS.VizieR/J/A+A/556/A71
Title:
Blazar 0836+710 long-term multiwavelength studies
Short Name:
J/A+A/556/A71
Date:
21 Oct 2021
Publisher:
CDS
Description:
The observation of gamma-ray flares from blazar 0836+710 in 2011, following a period of quiescence, offered an opportunity to study correlated activity at different wavelengths for a high-redshift (z=2.218) active galactic nucleus. Optical and radio monitoring, plus Fermi-LAT gamma-ray monitoring provided 2008-2012 coverage, while Swift offered auxiliary optical, ultraviolet, and X-ray information. Other contemporaneous observations were used to construct a broad-band spectral energy distribution.
4. Blazar sequence
ID:
ivo://CDS.VizieR/J/MNRAS/451/2750
Title:
Blazar sequence
Short Name:
J/MNRAS/451/2750
Date:
21 Oct 2021
Publisher:
CDS
Description:
Based on a large Fermi blazar sample, the blazar sequence (synchrotron peak frequency {nu}_peak_ versus synchrotron peak luminosity L_peak_) is revisited. It is found that there is significant anticorrelation between {nu}_peak_ and L_peak_ for blazars. However, after Doppler correction the anticorrelation disappears. The jet cavity power (P_jet_) is estimated from the extended radio luminosity so that it is free of beaming effects. We find that there are significant anticorrelations between P_jet_ and the beam-corrected {nu}_peak_' for both blazars and radio galaxies, which supports the blazar sequence and the unification of blazars and radio galaxies (an alternative relationship is the correlation between jet power and {gamma}-ray photon index).
5. Blazars in unidentified {gamma}-ray sources
ID:
ivo://CDS.VizieR/J/ApJ/752/61
Title:
Blazars in unidentified {gamma}-ray sources
Short Name:
J/ApJ/752/61
Date:
21 Oct 2021
Publisher:
CDS
Description:
One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of unidentified {gamma}-ray sources (UGSs). Despite the major improvements of Fermi in the localization of {gamma}-ray sources with respect to the past {gamma}-ray missions, about one-third of the Fermi-detected objects are still not associated with low-energy counterparts. Recently, using the Wide-field Infrared Survey Explorer survey, we discovered that blazars, the rarest class of active galactic nuclei and the largest population of {gamma}-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Based on this result, we designed an association method for the {gamma}-ray sources to recognize if there is a blazar candidate within the positional uncertainty region of a generic {gamma}-ray source. With this new IR diagnostic tool, we searched for {gamma}-ray blazar candidates associated with the UGS sample of the second Fermi {gamma}-ray LAT catalog (2FGL). We found that our method associates at least one {gamma}-ray blazar candidate as a counterpart to each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated with {gamma}-ray sources in the 2FGL catalog.
6. Blazar (sub-)mm & {gamma}-ray luminosities
ID:
ivo://CDS.VizieR/J/ApJ/754/23
Title:
Blazar (sub-)mm & {gamma}-ray luminosities
Short Name:
J/ApJ/754/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
The coexistence of Planck and Fermi satellites in orbit has enabled the exploration of the connection between the (sub-)millimeter and {gamma}-ray emission in a large sample of blazars. We find that the {gamma}-ray emission and the (sub-)mm luminosities are correlated over five orders of magnitude, L_{gamma}_{prop.to}L_(sub-)mm_. However, this correlation is not significant at some frequency bands when simultaneous observations are considered. The most significant statistical correlations, on the other hand, arise when observations are quasi-simultaneous within two months. Moreover, we find that sources with an approximate spectral turnover in the middle of the mm-wave regime are more likely to be strong {gamma}-ray emitters. These results suggest a physical relation between the newly injected plasma components in the jet and the high levels of {gamma}-ray emission.
7. Blazars with {gamma}-ray counterparts. I.
ID:
ivo://CDS.VizieR/J/ApJS/206/12
Title:
Blazars with {gamma}-ray counterparts. I.
Short Name:
J/ApJS/206/12
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new method for identifying blazar candidates by examining the locus, i.e., the region occupied by the Fermi {gamma}-ray blazars in the three-dimensional color space defined by the WISE infrared colors. This method is a refinement of our previous approach that made use of the two-dimensional projection of the distribution of WISE {gamma}-ray-emitting blazars (the Strip) in the three WISE color-color planes. In this paper, we define the three-dimensional locus by means of a principal component analysis of the color distribution of a large sample of blazars composed of all the ROMA-BZCAT sources with counterparts in the WISE All-Sky Catalog associated with {gamma}-ray sources in the second Fermi-LAT catalog (2FGL; the WISE Fermi blazars sample, WFB). Our new procedure yields a total completeness of c_tot_~81% and a total efficiency of e_tot_~97%. We also obtain local estimates of the efficiency and completeness as functions of the WISE colors and galactic coordinates of the candidate blazars. The catalog of all WISE candidate blazars associated with the WFB sample is also presented, complemented by archival multi-frequency information for the alternative associations. Finally, we apply the new association procedure to all {gamma}-ray blazars in the 2FGL and provide a catalog containing all the {gamma}-ray candidate blazars selected according to our procedure.
8. Blazars with {gamma}-ray counterparts. II.
ID:
ivo://CDS.VizieR/J/ApJS/206/13
Title:
Blazars with {gamma}-ray counterparts. II.
Short Name:
J/ApJS/206/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
A significant fraction (~30%) of the high-energy gamma-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) are still of unknown origin, being not yet associated with counterparts at low energies. We recently developed a new association method to identify if there is a {gamma}-ray blazar candidate within the positional uncertainty region of a generic 2FGL source. This method is entirely based on the discovery that blazars have distinct infrared colors with respect to other extragalactic sources found, thanks to the Wide-field Infrared Survey Explorer (WISE) all-sky observations. Several improvements have also been performed to increase the efficiency of our method in recognizing {gamma}-ray blazar candidates. In this paper we applied our method to two different samples, the first constituted by unidentified {gamma}-ray sources (UGSs), and the second by active galaxies of uncertain type, both listed in the 2FGL. We present a catalog of IR counterparts for ~20% of the UGSs investigated. Then, we also compare our results for the associated sources with those present in the literature. In addition, we illustrate the extensive archival research carried out to identify the radio, infrared, optical, and X-ray counterparts of the WISE-selected, {gamma}-ray blazar candidates. Finally, we discuss the future developments of our method based on ground-based follow-up observations.
9. Classification of Fermi blazar cand. from the 4FGL
ID:
ivo://CDS.VizieR/J/ApJ/887/134
Title:
Classification of Fermi blazar cand. from the 4FGL
Short Name:
J/ApJ/887/134
Date:
21 Oct 2021
Publisher:
CDS
Description:
The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the active galactic nuclei (AGNs), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine-learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine-learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy ~91.8%, or ~92.9%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction.
10. EGRET blazar gamma-ray spectrum
ID:
ivo://CDS.VizieR/J/ApJ/657/706
Title:
EGRET blazar gamma-ray spectrum
Short Name:
J/ApJ/657/706
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO) discovered gamma-ray emission from more than 67 blazars during its 9yr lifetime. We conducted an exhaustive search of the EGRET archives and selected all the blazars that were observed multiple times and were bright enough to enable a spectral analysis using standard power-law models. The sample consists of 18 flat-spectrum radio quasars (FSRQs), 6 low-frequency peaked BL Lac objects (LBLs) and 2 high-frequency peaked BL Lac objects (HBLs). We do not detect any clear pattern in the variation of spectral index with flux. Some of the blazars do not show any statistical evidence for spectral variability.

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