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Register a new userMulti-wavelength Temporal Variability of the Blazar 3C 454.3 during 2014 Activity Phase
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We present a multi-wavelength temporal analysis of the blazar 3C 454.3 during the high $gamma$-ray active period from May-December, 2014. Except for X-rays, the period is well sampled at near-infrared (NIR)-optical by the emph{SMARTS} facility and the source is detected continuously on daily timescale in the emph{Fermi}-LAT $gamma$-ray band. The source exhibits diverse levels of variability with many flaring/active states in the continuously sampled $gamma$-ray light curve which are also reflected in the NIR-optical light curves and the sparsely sampled X-ray light curve by the emph{Swift}-XRT. Multi-band correlation analysis of this continuous segment during different activity periods shows a change of state from no lags between IR and $gamma$-ray, optical and $gamma$-ray, and IR and optical to a state where $gamma$-ray lags the IR/optical by $sim$3 days. The results are consistent with the previous studies of the same during various $gamma$-ray flaring and active episodes of the source. This consistency, in turn, suggests an extended localized emission region with almost similar conditions during various $gamma$-ray activity states. On the other hand, the delay of $gamma$-ray with respect to IR/optical and a trend similar to IR/optical in X-rays along with strong broadband correlations favor magnetic field related origin with X-ray and $gamma$-ray being inverse Comptonized of IR/optical photons and external radiation field, respectively.
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The blazar 3C454.3 exhibited a strong flare seen in gamma-rays, X-rays, and optical/NIR bands during 3--12 December 2009. Emission in the V and J bands rose more gradually than did the gamma-rays and soft X-rays, though all peaked at nearly the same time. Optical polarization measurements showed dramatic changes during the flare, with a strong anti-correlation between optical flux and degree of polarization (which rose from ~ 3% to ~ 20%) during the declining phase of the flare. The flare was accompanied by large rapid swings in polarization angle of ~ 170 degree. This combination of behaviors appear to be unique. We have cm-band radio data during the same period but they show no correlation with variations at higher frequencies. Such peculiar behavior may be explained using jet models incorporating fully relativistic effects with a dominant source region moving along a helical path or by a shock-in-jet model incorporating three-dimensional radiation transfer if there is a dominant helical magnetic field. We find that spectral energy distributions at different times during the flare can be fit using modified one-zone models where only the magnetic field strength and particle break frequencies and normalizations need change. An optical spectrum taken at nearly the same time provides an estimate for the central black hole mass of ~ 2.3 * 10^9 M_sun. We also consider two weaker flares seen during the $sim 200$ d span over which multi-band data are available. In one of them, the V and J bands appear to lead the $gamma$-ray and X-ray bands by a few days; in the other, all variations are simultaneous.
We report the results of a multi-band observing campaign on the famous blazar 3C 279 conducted during a phase of increased activity from 2013 December to 2014 April, including first observations of it with NuSTAR. The $gamma$-ray emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level measured in this object since the beginning of the Fermi mission, with $F(E > 100,{rm MeV})$ of $10^{-5}$ photons cm$^{-2}$ s$^{-1}$, and with a flux doubling time scale as short as 2 hours. The $gamma$-ray spectrum during one of the flares was very hard, with an index of $Gamma_gamma = 1.7 pm 0.1$, which is rarely seen in flat spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter $L_gamma/L_{rm syn} > 300$. Two 1-day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5$-$70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by $DeltaGamma_{rm X} simeq 0.4$ at $sim$4 keV. Modeling the broad-band SED during this flare with the standard synchrotron plus inverse Compton model requires: (1) the location of the $gamma$-ray emitting region is comparable with the broad line region radius, (2) a very hard electron energy distribution index $p simeq 1$, (3) total jet power significantly exceeding the accretion disk luminosity $L_{rm j}/L_{rm d} gtrsim 10$, and (4) extremely low jet magnetization with $L_{rm B}/L_{rm j} lesssim 10^{-4}$. We also find that single-zone models that match the observed $gamma$-ray and optical spectra cannot satisfactorily explain the production of X-ray emission.
In May - July 2014, the flat spectrum radio quasar 3C 454.3 exhibited strong flaring behaviour. Observations with the Large Area Telescope detector on-board the Fermi Gamma-ray Space Telescope captured the $gamma$-ray flux at energies 0.1 $leq E_{gamma}leq$ 300 GeV increasing fivefold during this period, with two distinct peaks in emission. The $gamma$-ray emission is analysed in detail, in order to study the emission characteristics and put constraints on the location of the emission region. We explore variability in the spectral shape of 3C 454.3, search for evidence of a spectral cutoff, quantify the significance of VHE emission and investigate whether or not an energy-dependence of the emitting electron cooling exists. $gamma$-ray intrinsic doubling timescales as small as $tau_{int} = 0.68$ $pm$ 0.01 h at a significance of > 5$sigma$ are found, providing evidence of a compact emission region. Significant $E_{gamma, emitted}geq$ 35 GeV and $E_{gamma, emitted}geq$ 50 GeV emission is also observed. The location of the emission region can be constrained to $rgeq1.3$ $times$ $R_{BLR}^{out}$, a location outside the broad-line region. The spectral variation of 3C 454.3 also suggests that these flares may be originating further downstream of the supermassive black hole than the emission before and after the flares.
Context. 3C 454.3 is a very active flat spectrum radio quasar (blazar) that has undergone a recent outburst in all observed bands, including the optical. Aims. In this work we explore the short-term optical variability of 3C 454.3 during its outburst by searching for time delays between different optical bands. Finding one would be important for understanding the evolution of the spectrum of the relativistic electrons, which generate the synchrotron jet emission. Methods. We performed photometric monitoring of the object by repeating exposures in different optical bands (BVRI). Occasionally, different telescopes were used to monitor the object in the same band to verify the reliability of the smallest variations we observed. Results. Except on one occasion, where we found indications of a lag of the blue wavelengths behind the red ones, the results are inconclusive for most of the other cases. There were either no structures in the light curves to be able to search for patterns, or else different approaches led to different conclusions.
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.
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