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تسجيل مستخدم جديدExploring the Variability of the Flat Spectrum Radio Source 1633+382. II: Physical Properties
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The flat spectrum radio quasar 1633+382 (4C~38.41) showed a significant increase of its radio flux density during the period 2012 March - 2015 August which correlates with gamma-ray flaring activity. Multi-frequency simultaneous VLBI observations were conducted as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program and supplemented with additional radio monitoring observations with the OVRO 40m telescope, the Boston University VLBI program, and the Submillimeter Array. The epochs of the maxima for the two largest gamma-ray flares coincide with the ejection of two respective new VLBI components. Analysis of the spectral energy distribution indicates a higher turnover frequency after the flaring events. The evolution of the flare in the turnover frequency - turnover flux density plane probes the adiabatic losses in agreement with the shock-in-jet model. Derived synchrotron self absorption magnetic fields, of the order of 0.1mG, do not seem to dramatically change during the flares, and are much smaller, by a factor $10^4$, than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle dominated emitting region.
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We present multi-frequency simultaneous VLBI radio observations of the flat spectrum radio quasar 1633+382 (4C~38.41) as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program combined with additional obse
rvations in radio, optical, X-rays and $gamma-$rays carried out between the period 2012 March - 2015 August. The monitoring of this source reveals a significant long-lived increase in its activity since approximately two years in the radio bands, which correlates with a similar increase on all other bands from sub-millimeter to $gamma-$rays. A significant correlation is also found between radio fluxes and simultaneous spectral indices during this period. The study of the discrete correlation function (DCF) indicates time lags smaller than the $sim40$ days uncertainties among both radio bands and also high-energy bands, and a time lag of $sim$70 days, with $gamma-$rays leading radio. We interpret that the high-energy and radio fluxes are arising from different emitting regions, located at $1pm12$ and $40pm13$ pc from the central engine respectively.
The quasar-type blazar 4C 38.41 (B3 1633+382) experienced a large outburst in 2011, which was detected throughout the entire electromagnetic spectrum. We present the results of low-energy multifrequency monitoring by the GASP project of the WEBT cons
ortium and collaborators, as well as those of spectropolarimetric/spectrophotometric monitoring at the Steward Observatory. We also analyse high-energy observations of the Swift and Fermi satellites. In the optical-UV band, several results indicate that there is a contribution from a QSO-like emission component, in addition to both variable and polarised jet emission. The unpolarised emission component is likely thermal radiation from the accretion disc that dilutes the jet polarisation. We estimate its brightness to be R(QSO) ~ 17.85 - 18 and derive the intrinsic jet polarisation degree. We find no clear correlation between the optical and radio light curves, while the correlation between the optical and gamma-ray flux apparently fades in time, likely because of an increasing optical to gamma-ray flux ratio. As suggested for other blazars, the long-term variability of 4C 38.41 can be interpreted in terms of an inhomogeneous bent jet, where different emitting regions can change their alignment with respect to the line of sight, leading to variations in the Doppler factor delta. Under the hypothesis that in the period 2008-2011 all the gamma-ray and optical variability on a one-week timescale were due to changes in delta, this would range between ~ 7 and ~ 21. If the variability were caused by changes in the viewing angle theta only, then theta would go from ~ 2.6 degr to ~ 5 degr. Variations in the viewing angle would also account for the dependence of the polarisation degree on the source brightness in the framework of a shock-in-jet model.
Almost 10 yr of $gamma$-ray observations with the Fermi Large Area Telescope (LAT) have revealed extreme $gamma$-ray outbursts from flat spectrum radio quasars (FSRQs), temporarily making these objects the brightest $gamma$-ray emitters in the sky. Y
et, the location and mechanisms of the $gamma$-ray emission remain elusive. We characterize long-term $gamma$-ray variability and the brightest $gamma$-ray flares of six FSRQs. Consecutively zooming in on the brightest flares, which we identify in an objective way through Bayesian blocks and a hill-climbing algorithm, we find variability on subhour time scales and as short as minutes for two sources in our sample (3C279, CTA102) and weak evidence for variability at time scales less than the Fermi satellites orbit of 95 minutes for PKS1510-089 and 3C454.3. This suggests extremely compact emission regions in the jet. We do not find any signs for $gamma$-ray absorption in the broad-line region (BLR), which indicates that $gamma$-rays are produced at distances greater than hundreds of gravitational radii from the central black hole. This is further supported by a cross-correlation analysis between $gamma$-ray and radio/millimeter light curves, which is consistent with $gamma$-ray production at the same location as the millimeter core for 3C273, CTA102, and 3C454.3. The inferred locations of the $gamma$-ray production zones are still consistent with the observed decay times of the brightest flares if the decay is caused by external Compton scattering with BLR photons. However, the minute-scale variability is challenging to explain in such scenarios.
We study the multifrequency emission and spectral properties of the quasar 3C 279. We observed 3C 279 in very high energy (VHE, E>100GeV) gamma rays, with the MAGIC telescopes during 2011, for the first time in stereoscopic mode. We combine these mea
surements with observations at other energy bands: in high energy (HE, E>100MeV) gamma rays from Fermi-LAT, in X-rays from RXTE, in the optical from the KVA telescope and in the radio at 43GHz, 37GHz and 15GHz from the VLBA, Metsahovi and OVRO radio telescopes and optical polarisation measurements from the KVA and Liverpool telescopes. During the MAGIC observations (February to April 2011) 3C 279 was in a low state in optical, X-ray and gamma rays. The MAGIC observations did not yield a significant detection. These upper limits are in agreement with the extrapolation of the HE gamma-ray spectrum, corrected for extragalactic background light absorption, from Fermi-LAT. The second part of the MAGIC observations in 2011 was triggered by a high activity state in the optical and gamma-ray bands. During the optical outburst the optical electric vector position angle rotatated of about 180 degrees. There was no simultaneous rotation of the 43GHz radio polarisation angle. No VHE gamma rays were detected by MAGIC, and the derived upper limits suggest the presence of a spectral break or curvature between the Fermi-LAT and MAGIC bands. The combined upper limits are the strongest derived to date for the source at VHE and below the level of the previously detected flux by a factor 2. Radiation models that include synchrotron and inverse Compton emissions match the optical to gamma-ray data, assuming an emission component inside the broad line region (BLR) responsible for the high-energy emission and one outside the BLR and the infrared torus causing optical and low-energy emission. We interpreted the optical polarisation with a bent trajectory model.
The flat spectrum radio quasar 4C 38.41 showed a significant increase of its radio flux density during the period 2012 March - 2015 August which correlates with gamma-ray flaring activity. Multi-frequency simultaneous VLBI observations were conducted
as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program and supplemented with additional monitoring observations at various bands across the electromagnetic spectrum. The epochs of the maxima for the two largest gamma-ray flares coincide with the ejection of two respective new VLBI components and the evolution of the physical properties seem to be in agreement with the shock-in-jet model. Derived synchrotron self absorption magnetic fields, of the order of 0.1 mG, do not seem to dramatically change during the flares, and are much smaller, by a factor 10,000, than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle dominated emitting region.
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