- ID:
- ivo://CDS.VizieR/J/ApJ/740/98
- Title:
- Synchroton peak for blazars and radio galaxies
- Short Name:
- J/ApJ/740/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the concept of a blazar sequence that relates the synchrotron peak frequency ({nu}_peak_) in blazars with synchrotron peak luminosity (L_peak_, in {nu}L_{nu}_) using a large sample of radio-loud active galactic nuclei. We present observational evidence that the blazar sequence is formed from two populations in the synchrotron {nu}_peak_-L_peak_ plane, each forming an upper edge to an envelope of progressively misaligned blazars, and connecting to an adjacent group of radio galaxies having jets viewed at much larger angles to the line of sight. When binned by jet kinetic power (L_kin_; as measured through a scaling relationship with extended radio power), we find that radio core dominance decreases with decreasing synchrotron L_peak_, revealing that sources in the envelope are generally more misaligned. We find population-based evidence of velocity gradients in jets at low kinetic powers (~10^42^-10^44.5^erg/s), corresponding to Fanaroff-Riley (FR) I radio galaxies and most BL Lac objects. These low jet power "weak-jet" sources, thought to exhibit radiatively inefficient accretion, are distinguished from the population of non-decelerating, low synchrotron-peaking (LSP) blazars and FR II radio galaxies ("strong" jets) which are thought to exhibit radiatively efficient accretion. The two-population interpretation explains the apparent contradiction of the existence of highly core-dominated, low-power blazars at both low and high synchrotron peak frequencies, and further implies that most intermediate synchrotron peak sources are not intermediate in intrinsic jet power between LSP and high synchrotron-peaking (HSP) sources, but are more misaligned versions of HSP sources with similar jet powers.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/458/56
- Title:
- TeV gamma-ray blazar X-ray spectral studies
- Short Name:
- J/MNRAS/458/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work is a summary of the X-ray spectral studies of 29TeV (10^12^eV, tera-electron-volt) {gamma}-ray emitting blazars observed with Swift/XRT, especially focusing on sources for which the X-ray regime allows us to study the low- and the high-energy ends of the particle distribution function. Variability studies require simultaneous coverage, ideally sampling different flux states of each source. This is achieved using X-ray observations by disentangling the high-energy end of the synchrotron emission and the low-energy end of the Compton emission, which are produced by the same electron population. We focused on a sample of 29 TeV {gamma}-ray emitting blazars with the best signal-to-noise X-ray observations collected with Swift/XRT in the energy range 0.3-10keV during 10yr of Swift/XRT operations. We investigate the X-ray spectral shapes and the effects of different corrections for neutral hydrogen absorption and decompose the synchrotron and inverse Compton components. For five sources (3C 66A, S5 0716+714, W Comae, 4C +21.35 and BL Lacertae) a superposition of both components is observed in the X-ray band, permitting simultaneous, time-resolved studies of both ends of the electron distribution. The analysis of multi-epoch observations revealed that the break energy of the X-ray spectrum varies only by a small factor with flux changes. Flux variability is more pronounced in the synchrotron domain (high-energy end of the electron distribution) than in the Compton domain (low-energy end of the electron distribution). The spectral shape of the Compton domain is stable, while the flux of the synchrotron domain is variable. These changes cannot be described by simple variations of the cut-off energy, suggesting that the high-energy end of the electron distribution is not generally well described by cooling only.
- ID:
- ivo://CDS.VizieR/J/A+A/406/L9
- Title:
- TeV Gamma-Rays from 1ES1959+650
- Short Name:
- J/A+A/406/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- TeV gamma-rays from the BL Lac object 1ES1959+650 have been measured during the years 2000 and 2001 with a significance of 5.2{sigma} at a value of 5.3% of the Crab flux and in May 2002 during strong outbursts with >23{sigma} at a flux level of up to 2.2Crab, making 1ES1959+650 the TeV Blazar with the third best event statistics. The deep observation of 197.4h has been performed with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes (IACT system). 1ES1959+650 is located at a redshift of z=0.047, providing an intermediate distance between the nearby Blazars Mkn 421 and Mkn 501, and the much more distant object H1426+428. This makes 1ES1959+650 an important candidate of the class of TeV Blazars in view of the absorption of TeV photons by the diffuse extragalactic background radiation (DEBRA). The differential energy spectrum of 1ES1959+650 during the flares can be well described by a power law with an exponential cut-off at (4.2(+0.8-0.6)_stat_+/-0.9_sys_) TeV and a spectral index of 1.83+/-0.15_stat_+/-0.08_sys_, while the low state spectrum can be fitted by a pure power law with a spectral index of 3.18+/-0.17_stat_+/-0.08_sys_.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A68
- Title:
- TeV/non-TeV BL Lacs multi-lambda fluxes
- Short Name:
- J/A+A/608/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have collected the most complete multi-wavelength (6.0-6.0E^-18^cm) dataset of very high energy (VHE) gamma-ray emitting (TeV) BL Lacs, which are the most numerous extragalactic VHE sources. Using significant correlations between different bands, we aim to identify the best TeV BL Lac candidates that can be discovered by the current and next generation of imaging air Cherenkovtelescopes. We formed five datasets from lower energy data, i.e. radio, mid-infrared, optical, X-rays, and GeV gamma-ray, and five VHE gamma-ray datasets to perform a correlation study between different bands and to construct the prediction method. The low energy datasets were averaged for individual sources, while the VHE gamma-ray data were divided into subsets according to the flux state of the source. We then looked for significant correlations and determined their best-fit parameters. Using the best-fit parameters we predicted the level of VHE gamma-ray flux for a sample of 182 BL Lacs, which have not been detected at TeV energies. We identified the most promising TeV BL Lac candidates based on the predicted VHE gamma-ray flux for each source. We found 14 significant correlations between radio, mid-infrared, optical, gamma-ray, and VHE gamma-ray bands. The correlation between optical and VHE gamma-ray luminosity is established for the first time. We attribute this to the more complete sample and more accurate handling of host galaxy flux in our work. We found nine BL Lac candidates whose predicted VHE gamma-ray flux is high enough for detection in less than 25 hours with current imaging air Cherenkov telescopes.
- ID:
- ivo://CDS.VizieR/J/MNRAS/493/2438
- Title:
- The 2BIGB gamma-ray blazars catalog
- Short Name:
- J/MNRAS/493/2438
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the results of a {gamma}-ray likelihood analysis over all the extreme and high synchrotron peak blazars (EHSP and HSP) from the 3HSP catalogue. We investigate 2013 multifrequency positions under the eyes of Fermi Large Area Telescope, considering 11yr of observations in the energy range between 500MeV and 500GeV, which results in 1160 {gamma}-ray signatures detected down to the TS=9 threshold. The detections include 235 additional sources concerning the Fermi Large Area Telescope Fourth Source Catalog (4FGL), all confirmed via high-energy TS (Test Statistic) maps, and represent an improvement of ~25% for the number of EHSP and HSP currently described in {gamma}-rays. We build the {gamma}-ray spectral energy distribution (SED) for all the 1160 2BIGB sources, plot the corresponding {gamma}-ray logN-logS, and measure their total contribution to the extragalactic gamma-ray background, which reaches up to ~33% at 100GeV. Also, we show that the {gamma}-ray detectability improves according to the synchrotron peak flux as represented by the figure of merit parameter, and note that the search for TeV peaked blazars may benefit from considering HSP and EHSP as a whole, instead of EHSPs only. The 2BIGB acronym stands for 'Second Brazil-ICRANet Gamma-ray Blazars' catalogue.
- ID:
- ivo://CDS.VizieR/J/MNRAS/326/1455
- Title:
- The CLASS blazar survey. I.
- Short Name:
- J/MNRAS/326/1455
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents a new complete and well-defined sample of flat-spectrum radio sources (FSRS) selected from the Cosmic Lens All-Sky Survey (CLASS), with the further constraint of a bright (mag<=17.5) optical counterpart. The sample has been designed to produce a large number of low-luminosity blazars in order to test the current unifying models in the low-luminosity regime. In this first paper the new sample is presented and the radio properties of the 325 sources contained therein are discussed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/329/877
- Title:
- The CLASS blazar survey. II.
- Short Name:
- J/MNRAS/329/877
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the optical properties of the objects selected in the CLASS blazar survey. Because an optical spectrum is now available for 70 per cent of the 325 sources present in the sample, a spectral classification, based on the appearance of the emission/absorption lines, is possible. A wide variety of optical spectral types is found. Besides `classical' BL Lacs (42), BL Lac candidates (5) and high-power (P_5GHz_>10^26^W/Hz) flat spectrum radio quasars (67), a significant number of `passive' elliptical galaxies (41) is also found. Moreover, 33 broad emission line objects with a low radio power (P(5GHz)>10^26^W/Hz) are discovered, suggesting that at least a fraction (~24-30 per cent) of low-power blazars have a broad line region. Finally, 34 objects showing only narrow emission lines, either as a result of some starburst activity in the host galaxy or as a result of the presence of an active galactic nucleus, appear in the sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/348/937
- Title:
- The CLASS blazar survey. III.
- Short Name:
- J/MNRAS/348/937
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the properties of the sources in the CLASS blazar survey, which aims at the selection of low radio power (P_5GHz_<10^25^W/Hz) blazars. We use Very Large Array (VLA) data from available catalogues and from our own observations to constrain the radio core-dominance of the sample which, together with the flat radio spectral index, is a signature of the blazar activity. X-ray data from the ROSAT All Sky Survey were also collected in order to constrain the radio-to-X-ray luminosity ratio of the sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/2464
- Title:
- The CLASS BL Lac sample
- Short Name:
- J/MNRAS/430/2464
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents a new sample of BL Lac objects selected from a deep (30mJy) radio survey of flat spectrum radio sources (the CLASS blazar survey). The sample is one of the largest well-defined samples in the low-power regime with a total of 130 sources of which 55 satisfy the 'classical' optical BL Lac selection criteria, and the rest have indistinguishable radio properties. The primary goal of this study is to establish the radio luminosity function (RLF) on firm statistical ground at low radio luminosities where previous samples have not been able to investigate. The gain of taking a peek at lower powers is the possibility to search for the flattening of the luminosity function which is a feature predicted by the beaming model but which has remained elusive to observational confirmation. In this study, we extend for the first time the BL Lac RLF down to very low radio powers ~10^22^W/Hz, i.e. two orders of magnitude below the RLF currently available in the literature. In the process, we confirm the importance of adopting a broader, and more physically meaningful set of classification criteria to avoid the systematic missing of low-luminosity BL Lacs. Thanks to the good statistics we confirm the existence of weak but significant positive cosmological evolution for the BL Lac population, and we detect, for the first time the flattening of the RLF at L~10^25^W/Hz in agreement with the predictions of the beaming model.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/33
- Title:
- The Fermi LAT fourth source catalog (4FGL)
- Short Name:
- J/ApJS/247/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the fourth Fermi Large Area Telescope catalog (4FGL) of {gamma}-ray sources. Based on the first eight years of science data from the Fermi Gamma-ray Space Telescope mission in the energy range from 50MeV to 1TeV, it is the deepest yet in this energy range. Relative to the 3FGL catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for the Galactic diffuse {gamma}-ray emission, and two sets of light curves (one-year and two-month intervals). The 4FGL catalog includes 5064 sources above 4{sigma} significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall, 358 sources are considered as identified based on angular extent, periodicity, or correlated variability observed at other wavelengths. For 1336 sources, we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, and 239 are pulsars.