Abstract
We present multi-epoch optical spectra of the
γ
-ray bright blazar 1156+295 (4C +29.45, Ton 599) obtained with the 4.3 m Lowell Discovery Telescope. During a multiwavelength outburst in late ...2017, when the
γ
-ray flux increased to 2.5 × 10
−6
phot cm
−2
s
−1
and the quasar was first detected at energies ≥100 GeV, the flux of the Mg
ii
λ
2798 emission line changed, as did that of the Fe emission complex at shorter wavelengths. These emission-line fluxes increased along with the highly polarized optical continuum flux, which is presumably synchrotron radiation from the relativistic jet, with a relative time delay of ≲2 weeks. This implies that the line-emitting clouds lie near the jet, which points almost directly toward the line of sight. The emission-line radiation from such clouds, which are located outside the canonical accretion-disk related broad-line region, may be a primary source of seed photons that are up-scattered to
γ
-ray energies by relativistic electrons in the jet.
We present gamma-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 gamma-ray bright blazars over 4 years that we have been monitoring since 2008 August with multiple optical, ...ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma-ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their gamma-ray behavior. We derive gamma-ray, X-ray, and optical spectral indices, alpha sub(gamma), alpha sub(X), and alpha sub(0) respectively (F sub(v) is proportional to v super(alpha)), and construct spectral energy distributions during quiescent and active states. We analyze the relationships between different special indices, blazar classes, and activity states. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.
Large and variable polarization is an inherent property of a majority of blazars. Systematic rotations of the polarization vector have been claimed for several blazars. In some cases, however, the ...reality of these rotations may be questionable. We suggest an additional method for the verification of the reality of polarization position angle rotations based on the correlation of the normalized Stokes parameters.
We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and gamma -ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband ...variations in the flux and linear polarization, as well as changes in Very Long Baseline Array images at lambda = 7 mm with similar to 0.15 milliarcsec resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary 'core' and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long timescales (months/years), but the correspondence is poorer on shorter timescales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.
Blazar CTA 102 underwent exceptional optical and high-energy outbursts in 2012 and 2016–2017. We analyze its behaviour during these events, focusing on polarimetry as a tool that allows us to trace ...changes in the physical conditions and geometric configuration of the emission source close to the central black hole. We also use Fermi γ -ray data in conjunction with optical photometry in an effort to localize the origin of the outbursts.
The blazar 1156+295 was active at ...-ray energies, exhibiting three prominent flares during the year 2010. Here, we present results using the combination of broad-band (X-ray through mm single-dish) ...monitoring data and radio-band imaging data at 43 GHz on the connection of ...-ray events to the ejections of superluminal components and other changes in the jet of 1156+295. The kinematics of the jet over the interval 2007.0-2012.5 using 43 GHz Very Long Baseline Array observations reveal the presence of four moving and one stationary component in the inner region of the blazar jet. The propagation of the third and fourth components in the jet corresponds closely in time to the active phase of the source in ...-rays. We briefly discuss the implications of the structural changes in the jet for the mechanism of ...-ray production during bright flares. To localize the ...-ray emission site in the blazar, we performed the correlation analysis between the 43. GHz radio core and the ...-ray light curve. The time lag obtained from the correlation constrains the ...-ray emitting region in the parsec-scale jet. (ProQuest: ... denotes formulae/symbols omitted.)
We explore the variability and cross-frequency correlation of the flux density and polarization of the blazar OJ287, using imaging at 43 GHz with the Very Long Baseline Array, as well as optical and ...near-infrared (near-IR) polarimetry. The polarization and flux density in both the optical waveband and the 43 GHz compact core increased by a small amount in late 2005, and increased significantly along with the near-IR polarization and flux density over the course of 10 days in early 2006. Furthermore, the values of the electric vector position angle (EVPA) at the three wavebands are similar. At 43 GHz, the EVPA of the blazar core is perpendicular to the flow of the jet, while the EVPAs of emerging superluminal knots are aligned parallel to the jet axis. The core polarization is that expected if shear aligns the magnetic field at the boundary between flows of disparate velocities within the jet. Using variations in flux density, percentage polarization, and EVPA, we model the inner jet as a spine-sheath system. The model jet contains a turbulent spine of half-width 12 and maximum Lorentz factor of 16.5, a turbulent sheath with Lorentz factor of 5, and a boundary region of sheared field between the spine and sheath. Transverse shocks propagating along the fast, turbulent spine can explain the superluminal knots. The observed flux density and polarization variations are then compatible with changes in the direction of the inner jet caused by a temporary change in the position of the core if the spine contains wiggles owing to an instability. In addition, we can explain a stable offset of optical and near-IR percentage polarization by a steepening of spectral index with frequency, as supported by the data.
We investigate the multiwavelength behaviour of the high-energy peaked BL Lac object (HBL) Mrk 421 at redshift z = 0 . 031 in the period 2007-2015. We use optical photometric, spectroscopic, and ...polarimetric data and near-infrared data obtained by 35 observatories participating in the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT), as well as by the Steward Observatory Support of the Fermi Mission. We also employ high-energy data from the Swift (UV and X-rays) satellite to study correlations among emission in different bands.
Multi-Waveband Emission Maps of Blazars Marscher, Alan; Jorstad, Svetlana G.; Larionov, Valeri M. ...
Journal of astrophysics and astronomy,
06/2011, Letnik:
32, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
We are leading a comprehensive multi-waveband monitoring program of 34
γ
-ray bright blazars designed to locate the emission regions of blazars from radio to
γ
-ray frequencies. The ‘maps’ are ...anchored by sequences of images in both total and polarized intensity obtained with the VLBA at an angular resolution of ∼0.1 milliarcseconds. The time-variable linear polarization at radio to optical wavelengths and radio to
γ
-ray light curves allow us to specify the locations of flares relative to bright stationary features seen in the images and to infer the geometry of the magnetic field in different regions of the jet. Our data reveal that some flares occur simultaneously at different wavebands and others are only seen at some of the frequencies. The flares are often triggered by a superluminal knot passing through the stationary ‘core’ on the VLBA images. Other flares occur upstream or even parsecs downstream of the core.
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