- ID:
- ivo://CDS.VizieR/J/other/RAA/13.259
- Title:
- {gamma}-ray Doppler factor for Fermi blazars
- Short Name:
- J/other/RAA/13.2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations suggest that gamma-ray loud blazars are strongly beamed. The Fermi mission has detected many of blazars, which provide us with a good opportunity to investigate the emission mechanism and the beaming effect in the gamma-ray region. We compiled the X-ray observations for 138 Fermi blazars (54 flat spectrum radio quasars, 36 low-peaked BL Lacertae objects, and 48 high-peaked BL Lacertae objects) and calculated their Doppler factors, {delta}_{gamma}. It is interesting that the calculated Doppler factors, {delta}_{gamma}, are strongly correlated with the gamma-ray luminosity.
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- ID:
- ivo://CDS.VizieR/J/ApJ/722/520
- Title:
- Gamma-ray light curves of Fermi blazars
- Short Name:
- J/ApJ/722/520
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents light curves as well as the first systematic characterization of variability of the 106 objects in the high-confidence Fermi Large Area Telescope Bright AGN Sample (LBAS). Weekly light curves of this sample, obtained during the first 11 months of the Fermi survey (2008 August 4-2009 July 4), are tested for variability and their properties are quantified through autocorrelation function and structure function analysis. For the brightest sources, 3 or 4 day binned light curves are extracted in order to determine power density spectra (PDSs) and to fit the temporal structure of major flares. More than 50% of the sources are found to be variable with high significance, where high states do not exceed 1/4 of the total observation range. Variation amplitudes are larger for flat spectrum radio quasars and low/intermediate synchrotron frequency peaked BL Lac objects. Autocorrelation timescales derived from weekly light curves vary from four to a dozen of weeks.
- ID:
- ivo://CDS.VizieR/J/ApJ/726/16
- Title:
- {gamma}-ray loud blazars
- Short Name:
- J/ApJ/726/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. At lower flux levels, radio flux density does not directly correlate with {gamma}-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the {gamma}-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the {gamma}-ray loud FSRQs are fundamentally different from the {gamma}-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for {gamma}-ray loud AGNs.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/445
- Title:
- Gamma-ray loud blazars optical monitoring. II.
- Short Name:
- J/A+AS/127/445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New data from the optical monitoring of gamma-ray loud blazars at the Torino Astronomical Observatory are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A134
- Title:
- {gamma}-ray signature in WHSP blazars (1BIGB)
- Short Name:
- J/A+A/598/A134
- Date:
- 04 Feb 2022 00:00:12
- Publisher:
- CDS
- Description:
- A direct search of {gamma}-ray emission centered on multifrequency selected candidates is a valuable complementary approach to the standard search adopted in current {gamma}-ray Fermi-LAT catalogs. Our sources are part of the 2WHSP sample that was assembled with the aim of providing targets for Imaging Atmospheric Cherenkov Telescopes (IACT). A likelihood analysis based on their known position enabled us to detect 150 {gamma}-ray excess signals that have not yet been reported in previous {gamma}-ray catalogs (1FGL, 2FGL, 3FGL). By identifying new sources, we solve a fraction of the extragalactic isotropic {gamma}-ray background (IGRB) composition, improving the description of the {gamma}-ray sky. We perform data reduction with the Fermi Science Tools using positions from 400 high synchrotron peaked (HSP) blazars as seeds of tentative {gamma}-ray sources; none of them have counterparts from previous 1FGL, 2FGL and 3FGL catalogs. Our candidates are part of the 2WHSP sample (currently the largest set of HSP blazars). We focus on HSPs characterized by bright synchrotron component with peak flux {nu}f_({nu})_>=10^-12.1^erg/cm^2^/s, testing the hypothesis of having a {gamma}-ray source in correspondence to the WHSP positions. Our likelihood analysis considers the 0.3-500GeV energy band, integrating over 7.2yr of Fermi-LAT observation and making use of the Pass 8 data release. From the 400 candidates tested, a total of 150 2WHSPs showed excess {gamma}-ray signature: 85 high-significance detections with test statistic (TS)>25, and 65 lower-significance detections with TS between 10 to 25. We assume a power law spectrum in the 0.3-500GeV band and list the spectrum parameters describing all 150 new {gamma}-ray sources. We study the {gamma}-ray photon spectral index distribution, the likelihood of detection according to the synchrotron peak brightness (figure of merit parameter), and plot the measured {gamma}-ray LogN-LogS of HSP blazars, also discussing the portion of the IGRB that has been resolved by the present work. We also report on four cases where we could resolve source confusion and find counterparts for unassociated 3FGL sources with the help of high-energy TS maps together with multifrequency data. The 150 new {gamma}-ray sources are named with the acronym 1BIGB for the first version of the Brazil ICRANet Gamma-ray Blazar catalog, in reference to the cooperation agreement supporting this work.
- ID:
- ivo://CDS.VizieR/J/other/RAA/18.56
- Title:
- gamma-ray spectrum for Fermi blazars
- Short Name:
- J/other/RAA/18.5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The curvature of the {gamma}-ray spectrum in blazars may reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The {gamma}-ray spectra of Fermi blazars are normally fitted either by a single power-law (PL) or a log-normal (call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3LAC Clean Sample.We find that the {gamma}-ray flux (100MeV-100GeV) and variability index follow bimodal distributions for PL and LP blazars, where the {gamma}-ray flux and variability index show a positive correlation. However, the distributions of {gamma}-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of {gamma}-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved {gamma}-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.
- ID:
- ivo://CDS.VizieR/J/ApJ/742/27
- Title:
- 15GHz and jet properties of MOJAVE blazars
- Short Name:
- J/ApJ/742/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the Fermi Large Area Telescope {gamma}-ray and 15GHz Very Long Baseline Array radio properties of a joint {gamma}-ray and radio-selected sample of active galactic nuclei (AGNs) obtained during the first 11 months of the Fermi mission (2008 August 4-2009 July 5). Our sample contains the brightest 173 AGNs in these bands above declination -30{deg} during this period, and thus probes the full range of {gamma}-ray loudness ({gamma}-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least 4 orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing {gamma}-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class.
- ID:
- ivo://CDS.VizieR/J/AJ/137/3718
- Title:
- 15GHz monitoring of AGN jets with VLBA
- Short Name:
- J/AJ/137/3718
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present images from a long-term program (MOJAVE: Monitoring of Jets in active galactic nuclei (AGNs) with VLBA Experiments) to survey the structure and evolution of parsec-scale jet phenomena associated with bright radio-loud active galaxies in the northern sky. The observations consist of 2424 15GHz Very Long Baseline Array (VLBA) images of a complete flux-density-limited sample of 135 AGNs above declination -20{deg}, spanning the period 1994 August to 2007 September. These data were acquired as part of the MOJAVE and 2cm Survey programs, and from the VLBA archive. The sample-selection criteria are based on multi-epoch parsec-scale (VLBA) flux density, and heavily favor highly variable and compact blazars. The sample includes nearly all the most prominent blazars in the northern sky, and is well suited for statistical analysis and comparison with studies at other wavelengths. Our multi-epoch and stacked-epoch images show 94% of the sample to have apparent one-sided jet morphologies, most likely due to the effects of relativistic beaming. Of the remaining sources, five have two-sided parsec-scale jets, and three are effectively unresolved by the VLBA at 15GHz, with essentially all of the flux density contained within a few tenths of a milliarcsecond.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A75
- Title:
- 43GHz observation of the blazar Mrk 421
- Short Name:
- J/A+A/559/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results obtained for the AGN Markarian 421 by model-fitting the data in the visibility plane, studing the proper motion of jet components, the light curve, and the spectral index of the jet features. We compare the radio data with optical light curves obtained at the Steward Observatory, considering also the optical polarization information. Mrk 421 has a bright nucleus and a one-sided jet extending towards the north-west for a few parsecs. The model-fits show that brightness distribution is well described using 6-7 circular Gaussian components, four of which are reliably identified at all epochs; all components are effectively stationary except for component D, at ~0.4mas from the core, whose motion is however subluminal. The analysis of the light curve shows two different states, with the source being brighter and more variable in the first half of 2011 than in the second half. The highest flux density is reached in February. A comparison with the optical data reveals an increase of the V magnitude and of the fractional polarization simultaneous with the enhancement of the radio activity.
- ID:
- ivo://CDS.VizieR/J/AJ/133/1947
- Title:
- 37GHz observations of BL Lac objects
- Short Name:
- J/AJ/133/1947
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 37GHz data obtained at Metsahovi Radio Observatory in 2001 December-2005 April for a large sample of BL Lacertae objects. Metsahovi radio telescope is a radome enclosed antenna with a diameter of 13.7 metres. The 37 GHz receiver is a dual horn, Dicke-switched receiver with a HEMT preamplifier, and is operated at room temperature. The observations are ON-ON observations, alternating the source and the sky in each feed horn. A typical integration time to obtain one flux density data point is 1200-1600s, and the detection limit under optimal weather conditions is about 0.2Jy.