- ID:
- ivo://CDS.VizieR/J/AJ/134/799
- Title:
- Multiwaveband polarimetry of 15 AGN
- Short Name:
- J/AJ/134/799
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on multifrequency linear polarization monitoring of 15 active galactic nuclei containing highly relativistic jets with apparent speeds from ~4c to >40c. The measurements were obtained at optical, 1mm, and 3mm wavelengths, and at 7mm with the Very Long Baseline Array. The data show a wide range in degree of linear polarization among the sources, from <1% to >30%, and interday polarization variability in individual sources. The polarization properties suggest separation of the sample into three groups with low, intermediate, and high variability of polarization in the core at 7mm (LVP, IVP, and HVP, respectively).
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/816/53
- Title:
- Multiwavelength obs. of BL Lac in 2012-2013
- Short Name:
- J/ApJ/816/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012-2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse Compton emission from nonthermal seed photons originating from within the jet. The passage of four new superluminal very long baseline interferometry knots through the core and two stationary knots about 4 pc downstream accompanied the high flaring in 2012-2013. The seed photons for inverse Compton scattering may arise from the stationary knots and from a Mach disk near the core where relatively slow-moving plasma generates intense nonthermal radiation. The 95 spectral energy distributions obtained on consecutive days form the most densely sampled, broad wavelength coverage for any blazar. The observed spectral energy distributions and multi-waveband light curves are similar to simulated spectral energy distributions and light curves generated with a model in which turbulent plasma crosses a conical shock with a Mach disk.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A88
- Title:
- Multi-wavelength variability of Mrk 421
- Short Name:
- J/A+A/647/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of the gamma-ray emission of the blazar Mrk 421 is still a matter of debate. We used 5.5 years of unbiased observing campaign data, obtained using the FACT telescope and the Fermi LAT detector at TeV and GeV energies, the longest and densest so far, together with contemporaneous multi-wavelength observations, to characterise the variability of Mrk 421 and to constrain the underlying physical mechanisms. We studied and correlated light curves obtained by ten different instruments and found two significant results. The TeV and X-ray light curves are very well correlated with a lag of <0.6 days. The GeV and radio (15GHz band) light curves are widely and strongly correlated. Variations of the GeV light curve lead those in the radio. Lepto-hadronic and purely hadronic models in the frame of shock acceleration predict proton acceleration or cooling timescales that are ruled out by the short variability timescales and delays observed in Mrk 421. Instead the observations match the predictions of leptonic models.
- ID:
- ivo://CDS.VizieR/J/A+A/539/A149
- Title:
- Multiwavelength view of blazar PKS 2155-304
- Short Name:
- J/A+A/539/A149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E>=100GeV) occurred, provide a detailed picture of the evolution of its emission. The complete data set from this campaign is presented, including observations in VHE gamma-rays (H.E.S.S.), X-rays (RXTE, CHANDRA, SWIFT XRT), optical (SWIFT UVOT, Bronberg, Watcher, ROTSE), and in the radio band (NRT, HartRAO, ATCA). Optical and radio light curves from 2004 to 2008 are compared to the available VHE data from this period, to put the 2006 campaign into the context of the long-term evolution of the source. The data set offers a close view of the evolution of the source on different time scales and yields new insights into the properties of the emission process. The predictions of synchrotron self-Compton (SSC) scenarios are compared to the MWL data, with the aim of describing the dominant features in the data down to the hour time scale. The spectral variability in the X-ray and VHE bands is explored and correlations between the integral fluxes at different wavelengths are evaluated. SSC modelling is used to interpret the general trends of the varying spectral energy distribution.
- ID:
- ivo://CDS.VizieR/J/ApJS/206/17
- Title:
- New gamma-ray blazar candidates in the 3PBC
- Short Name:
- J/ApJS/206/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We searched for {gamma}-ray blazar candidates among the 382 unidentified hard X-ray sources of the third Palermo BAT Catalog (3PBC) obtained from the analysis of 66 months of Swift Burst Alert Telescope (BAT) survey data and listing 1586 sources. We adopted a recently developed association method based on the peculiar infrared colors that characterize the {gamma}-ray blazars included in the second catalog of active galactic nuclei detected by the Fermi Large Area Telescope. We used this method exploiting the data of the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) to establish correspondences between unidentified 3PBC sources and WISE {gamma}-ray blazar candidates located within the BAT positional uncertainty region at a 99% confidence level. We obtained a preliminary list of candidates for which we analyzed all the available data in the Swift archive to complement the information in the literature and in the radio, infrared, and optical catalogs with the information on their optical-UV and soft X-ray emission. Requiring the presence of radio and soft X-ray counterparts consistent with the infrared positions of the selected WISE sources, as well as a blazar-like radio morphology, we finally obtained a list of 24 {gamma}-ray blazar candidates.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/3568
- Title:
- Non-Fermi blazar sample
- Short Name:
- J/MNRAS/450/3568
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By statistically analysing a large sample that includes Fermi-detected blazars (FBs) and non-Fermi-detected blazars (NFBs), we find that there are significant differences between FBs and NFBs in redshift, black hole mass, jet kinetic power from cavity power, broad-line luminosity and the ratio of core luminosity to absolute V-band magnitude (Rv), but not in the ratio of the radio core to extended flux (Rc) and the Eddington ratio. Compared with NFBs, FBs have larger mean jet power, Rc and Rv, while having smaller mean redshift, black hole mass and broad-line luminosity. These results support the fact that the beaming effect is the main reason for differences between FBs and NFBs, and that FBs are likely to have a more powerful jet. For both FBs and NFBs, there are significant correlations between the jet power and the accretion rate (traced by the broad-emission line luminosity), and between the jet power and the black hole mass. For FBs, the black hole mass does not have a significant influence on jet power, while for NFBs, both the accretion rate and black hole mass contribute to the jet power. Our results support the 'blazar sequence' and show that the synchrotron peak frequency ({nu}peak) is associated with the accretion rate but not with the black hole mass.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/99
- Title:
- NuSTAR serendipitous survey: the 40-month catalog
- Short Name:
- J/ApJ/836/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first full catalog and science results for the Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey. The catalog incorporates data taken during the first 40 months of NuSTAR operation, which provide ~20Ms of effective exposure time over 331 fields, with an areal coverage of 13deg^2^, and 497 sources detected in total over the 3-24keV energy range. There are 276 sources with spectroscopic redshifts and classifications, largely resulting from our extensive campaign of ground-based spectroscopic follow-up. We characterize the overall sample in terms of the X-ray, optical, and infrared source properties. The sample is primarily composed of active galactic nuclei (AGNs), detected over a large range in redshift from z=0.002 to 3.4 (median of <z>=0.56), but also includes 16 spectroscopically confirmed Galactic sources. There is a large range in X-ray flux, from log(f_3-24keV_/erg/s/cm^2^)~-14 to -11, and in rest-frame 10-40keV luminosity, from log(L_10-40keV_/erg/s)~39 to 46, with a median of 44.1. Approximately 79% of the NuSTAR sources have lower-energy (<10keV) X-ray counterparts from XMM-Newton, Chandra, and Swift XRT. The mid-infrared (MIR) analysis, using WISE all-sky survey data, shows that MIR AGN color selections miss a large fraction of the NuSTAR-selected AGN population, from ~15% at the highest luminosities (L_X_>10^44^erg/s) to ~80% at the lowest luminosities (L_X_<10^43^erg/s). Our optical spectroscopic analysis finds that the observed fraction of optically obscured AGNs (i.e., the type 2 fraction) is F_Type2_=53_-15_^+14^% , for a well-defined subset of the 8-24keV selected sample. This is higher, albeit at a low significance level, than the type 2 fraction measured for redshift- and luminosity-matched AGNs selected by <10keV X-ray missions.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A74
- Title:
- OJ 287 far-infrared photometry
- Short Name:
- J/A+A/610/A74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The blazar OJ 287 has shown a ~~12 year quasi-periodicity over more than a century, in addition to the common properties of violent variability in all frequency ranges. It is the strongest known candidate to have a binary singularity in its central engine. We aim to better understand the different emission components by searching for correlated variability in the flux over four decades of frequency measurements. We combined data at frequencies from the millimetric to the visible to characterise the multifrequency light curve in April and May 2010. This includes the only photometric observations of OJ 287 made with the Herschel Space Observatory: five epochs of data obtained over 33 days at 250, 350, and 500um with Herschel-SPIRE. Although we find that the variability at 37GHz on timescales of a few weeks correlates with the visible to near-IR spectral energy distribution (SED), there is a small degree of reddening in the continuum at lower flux levels that is revealed by the decreasing rate of decline in the light curve at lower frequencies. However, we see no clear evidence that a rapid flare detected in the light curve during our monitoring in the visible to near-IR light curve is seen either in the Herschel data or at 37GHz, suggesting a low-frequency cut-off in the spectrum of such flares. We see only marginal evidence of variability in the observations with Herschel over a month, although this may be principally due to the poor sampling. The spectral energy distribution between 37 GHz and the visible can be characterised by two components of approximately constant spectral index: a visible to far-IR component of spectral index {alpha}=-0.95, and a far-IR to millimetric spectral index of {alpha}=0.43. There is no evidence of an excess of emission that would be consistent with the 60um dust bump found in many active galactic nuclei.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/275
- Title:
- OJ 287 flux & polarization during 2016 outburst
- Short Name:
- J/ApJ/835/275
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The gamma-ray blazar OJ 287 was in a high activity state during 2015 December-2016 February. Coinciding with this high brightness state, we observed this source for photometry on 40 nights in R-band and for polarimetry on nine epochs in UBV RI bands. During the period of our observations, the source brightness varied from 13.20+/-0.04 mag to 14.98+/-0.04mag and the degree of polarization (P) fluctuated between 6.0%+/-0.3% and 28.3%+/-0.8% in R-band. Focusing on intranight optical variability (INOV), we find a duty cycle of about 71% using {chi}^2^-statistics, similar to that known for blazars. From INOV data, the shortest variability timescale is estimated to be 142+/-38min, yielding a lower limit of the observed Doppler factor {delta}_0_=1.17, the magnetic field strength B<=3.8G, and the size of the emitting region R_s_<2.28x10^14^cm. On internight timescales, a significant anticorrelation between R-band flux and P is found. The observed P at U-band is generally larger than that observed at longer-wavelength bands, suggesting a wavelength-dependent polarization. Using V-band photometric and polarimetric data from Steward Observatory obtained during our monitoring period, we find a varied correlation between P and V-band brightness. While an anticorrelation is sometimes seen between P and V-band magnitude, no correlation is seen at other times, thereby suggesting the presence of more than one short-lived shock component in the jet of OJ 287.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/1861
- Title:
- OJ287 polarization and VLBI jet direction
- Short Name:
- J/MNRAS/421/1861
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the variation of the optical polarization angle in the blazar OJ287 and compare it with the precessing binary black hole model with a "live" accretion disc. First, a model of the variation of the jet direction is calculated, and the main parameters of the model are fixed by the long-term optical brightness evolution. Then this model is compared with the variation of the parsec-scale radio jet position angle in the sky. Finally, the variation of the polarization angle is calculated using the same model, but using a magnetic field configuration which is at a constant angle relative to the optical jet. It is found that the model fits the data reasonably well if the field is almost parallel to the jet axis. This may imply a steady magnetic field geometry, such as a large-scale helical field.