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Register a new userMAGIC observations and multifrequency properties of the Flat Spectrum Radio Quasar 3C 279 in 2011
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J. Aleksic
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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 measurements 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.
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Among more than fifty blazars detected in very high energy (VHE, E>100GeV) gamma-rays, only three belong to the subclass of Flat Spectrum Radio Quasars (FSRQs). MAGIC observed FSRQ PKS 1510-089 in February-April 2012 during a high activity state in the high energy (HE, E>100 MeV) gamma-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 sigma. In agreement with the previous VHE observations of the source, we find no statistically significant variability during the MAGIC observations in daily, weekly or monthly time scales. The other two known VHE FSRQs have shown daily scale to sub-hour variability. We study the multifrequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO and VLBA telescopes), X-ray (Swift satellite) and HE gamma-ray frequencies. The gamma-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multifrequency light curves suggest a common origin for the millimeter radio and HE gamma-ray emission and the HE gamma-ray flaring starts when the new component is ejected from the 43GHz VLBA core. The quasi-simultaneous multifrequency SED is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infra-red torus and a slow sheath surrounding the jet around the VLBA core. Both models fit the data well. However, the fast HE gamma-ray variability requires that within the modelled large emitting region, there must exist more compact regions. We suggest that these observed signatures would be most naturally explained by a turbulent plasma flowing at a relativistic speed down the jet and crossing a standing conical shock.
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The flat spectrum radio quasar CTA 102 ($z = 1.032$) went through a tremendous phase of variability. Since early 2016 the gamma-ray flux level has been significantly higher than in previous years. It was topped by a four month long giant outburst, where peak fluxes were more than 100 times higher than the quiescence level. Similar trends are observable in optical and X-ray energies. We have explained the giant outburst as the ablation of a gas cloud by the relativistic jet that injects additional matter into the jet and can self-consistently explain the long-term light curve. Here, we argue that the cloud responsible for the giant outburst is part of a larger system that collides with the jet and is responsible for the years-long activity in CTA 102.
We report first observational results of multifrequency campaigns on the prominent Virgo blazars 3C 273 and 3C 279 which were carried out in January and February 1999. Both blazars are detected from radio to gamma-ray energies. We present the measured X- to gamma-ray spectra of both sources, and for 3C 279 we compare the 1999 broad-band (radio to gamma-ray) spectrum to measured previous ones.
We report the AGILE detection and the results of the multifrequency follow-up observations of a bright $gamma$-ray flare of the blazar 3C 279 in June 2015. We use AGILE-GRID and Fermi-LAT $gamma$-ray data, together with Swift-XRT, Swift-UVOT, and ground-based GASP-WEBT optical observations, including polarization information, to study the source variability and the overall spectral energy distribution during the $gamma$-ray flare. The $gamma$-ray flaring data, compared with as yet unpublished simultaneous optical data which allow to set constraints on the big blue bump disk luminosity, show very high Compton dominance values of $sim 100$, with a ratio of $gamma$-ray to optical emission rising by a factor of three in a few hours. The multi-wavelength behavior of the source during the flare challenges one-zone leptonic theoretical models. The new observations during the June 2015 flare are also compared with already published data and non-simultaneous historical 3C 279 archival data.
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