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Register a new userParsec-Scale Jet Behavior of the Quasar 3C 454.3 during the High Gamma-Ray States in 2009 and 2010
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We analyze total and polarized intensity images of the quasar 3C 454.3 obtained monthly with the VLBA at 43 GHz within the ongoing Boston U. monitoring program of gamma-ray blazars started in June 2007. The data are supplemented by VLBA observations performed during intense campaigns of 2 week duration when the quasar was observed 3 times per campaign. We find a strong increase of activity in the parsec-scale jet of the quasar during high gamma-ray states in December 2009, April 2010, and November 2010. We detect new superluminal knots, K09 and K10, associated with the autumn 2009 and 2010 outbursts, respectively, and compare their kinematic parameters. We analyze optical polarimetric behavior along with polarization parameters of the parsec-scale jet and outline similarities and differences in polarization properties across wavelengths. The results of the analysis support the conclusions that the optical polarized emission is produced in a region located in the vicinity of the mm-wave core of the jet of the quasar, and that the gamma-ray outbursts occur when a superluminal disturbance passes through the core.
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We analyze the multifrequency behavior of the quasar 3C 454.3 during three prominent gamma-ray outbursts: 2009 Autumn, 2010 Spring, and 2010 Autumn. The data reveal a repeating pattern, including a triple flare structure, in the properties of each gamma-ray outburst, which implies similar mechanism(s) and location for all three events. The multi-frequency behavior indicates that the lower frequency events are co-spatial with the gamma-ray outbursts, although the gamma-ray emission varies on the shortest timescales. We determine that the variability from UV to IR wavelengths during an outburst results from a single synchrotron component whose properties do not change significantly over the different outbursts. Despite a general increase in the degree of optical linear polarization during an outburst, the polarization drops significantly at the peak of the gamma-ray event, which suggests that both shocks and turbulent processes are involved. We detect two disturbances (knots) with superluminal apparent speeds in the parsec-scale jet associated with the outbursts in 2009 Autumn and 2010 Autumn. The kinematic properties of the knots can explain the difference in amplitudes of the gamma-ray events, while their millimeter-wave polarization is related to the optical polarization during the outbursts. We interpret the multi-frequency behavior within models involving either a system of standing conical shocks or magnetic reconnection events located in the parsec-scale millimeter-wave core of the jet. We argue that gamma-ray outbursts with variability timescales as short as ~ 3 hr can occur on parsec scales if flares take place in localized regions such as turbulent cells.
We compare the gamma-ray light curves of the blazars, constructed with data provided by the Fermi Large Area Telescope, with flux and polarization variations in the VLBI core and bright superluminal knots obtained via monthly monitoring with the Very Long Baseline Array at 43 GHz. For all blazars in the sample that exhibit a high gamma-ray state on time scales from several weeks to several months, an increase of the total flux in the mm-wave core is contemporaneous with the gamma-ray activity (more than a third of the sample). Here we present the results for quasars with the most extreme gamma-ray behavior (3C 454.3, 3C 273, 3C 279, 1222+216, and 1633+382). The sources show that in addition to the total flux intensity behavior, a maximum in the degree of polarization in the core or bright superluminal knot nearest to the core coincides with the time of a gamma-ray peak to within the accuracy of the sampling of the radio data. These argue in favor of location of many of gamma-ray outbursts in blazars outside of the broad line region, either in the vicinity or downstream of the mm-wave VLBI core.
The quasar 3C~286 is one of two compact steep spectrum sources detected by the {it Fermi}/LAT. Here, we investigate the radio properties of the parsec(pc)-scale jet and its (possible) association with the $gamma$-ray emission in 3C~286. The Very Long Baseline Interferometry (VLBI) images at various frequencies reveal a one-sided core--jet structure extending to the southwest at a projected distance of $sim$1 kpc. The component at the jet base showing an inverted spectrum is identified as the core, with a mean brightness temperature of $2.8times 10^{9}$~K. The jet bends at about 600 pc (in projection) away from the core, from a position angle of $-135^circ$ to $-115^circ$. Based on the available VLBI data, we inferred the proper motion speed of the inner jet as $0.013 pm 0.011$ mas yr$^{-1}$ ($beta_{rm app} = 0.6 pm 0.5$), corresponding to a jet speed of about $0.5,c$ at an inclination angle of $48^circ$ between the jet and the line of sight of the observer. The brightness temperature, jet speed and Lorentz factor are much lower than those of $gamma$-ray-emitting blazars, implying that the pc-scale jet in 3C~286 is mildly relativistic. Unlike blazars in which $gamma$-ray emission is in general thought to originate from the beamed innermost jet, the location and mechanism of $gamma$-ray emission in 3C~286 may be different as indicated by the current radio data. Multi-band spectrum fitting may offer a complementary diagnostic clue of the $gamma$-ray production mechanism in this source.
Since 2005, the blazar 3C 454.3 has shown remarkable flaring activity at all frequencies, and during the last four years it has exhibited more than one gamma-ray flare per year, becoming the most active gamma-ray blazar in the sky. We present for the first time the multi-wavelength AGILE, SWIFT, INTEGRAL, and GASP-WEBT data collected in order to explain the extraordinary gamma-ray flare of 3C 454.3 which occurred in November 2010. On 2010 November 20 (MJD 55520), 3C 454.3 reached a peak flux (E>100 MeV) of F_gamma(p) = (6.8+-1.0)E-5 ph/cm2/s on a time scale of about 12 hours, more than a factor of 6 higher than the flux of the brightest steady gamma-ray source, the Vela pulsar, and more than a factor of 3 brighter than its previous super-flare on 2009 December 2-3. The multi-wavelength data make a thorough study of the present event possible: the comparison with the previous outbursts indicates a close similarity to the one that occurred in 2009. By comparing the broadband emission before, during, and after the gamma-ray flare, we find that the radio, optical and X-ray emission varies within a factor 2-3, whereas the gamma-ray flux by a factor of 10. This remarkable behavior is modeled by an external Compton component driven by a substantial local enhancement of soft seed photons.
During the month of December, 2009 the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F ~2000E-8 ph/cm2/s for E > 100 MeV. Starting in November, 2009 intensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here we report the results of a 2-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, RossiXTE for the high-energy observations, and Swift/UVOT, KANATA, GRT, REM for the near-IR/optical/UV data. The GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting ~1 month at all wavelengths: in the gamma-ray band, peak emission was reached on December 2-3, 2009. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broad-band spectral evolution severely constrain the theoretical modelling. We find that the pre- and post-flare broad-band behavior can be explained by a one-zone model involving SSC plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the Dec. 2-3, 2009 super-flare and of the secondary peak emission on Dec. 9, 2009 cannot be satisfactorily modelled by a simple one-zone model. An additional particle component is most likely active during these states.
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