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Register a new userA hadronic minute-scale GeV flare from quasar 3C 279?
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The flat spectrum radio quasar 3C 279 is a known $gamma$-ray variable source that has recently exhibited minute-scale variability at energies $>100$ MeV. One-zone leptonic models for blazar emission are severely constrained by the short timescale variability that implies a very compact emission region at a distance of hundreds of Schwarzschild radii from the central black hole. Here, we investigate a hadronic scenario where GeV $gamma$-rays are produced via proton synchrotron radiation. We also take into account the effects of the hadronically initiated electromagnetic cascades (EMC). For a $gamma$-ray emitting region in rough equipartition between particles and kG magnetic fields, located within the broad-line region (BLR), the development of EMC redistributes the $gamma$-ray luminosity to softer energy bands and eventually leads to broad-band spectra that differ from the observed ones. Suppression of EMC and energy equipartition are still possible, if the $gamma$-ray emitting region is located beyond the BLR, is fast moving with Doppler factor ($>70$), and contains strong magnetic fields ($>100$ G). Yet, these conditions cannot be easily met in parsec-scale jets, thus disfavouring a proton synchrotron origin of the Fermi-LAT flare.
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We report results from 5-day VLBI observations of the well-known quasar 3C 279 at 1.3 mm (230 GHz) in 2011. The measured nonzero closure phases on triangles including stations in Arizona, California and Hawaii indicate that the source structure is spatially resolved. We find an unusual inner jet direction at scales of $sim$1 parsec extending along the northwest-southeast direction (PA = $127^{circ}pm3^{circ}$), as opposed to other (previously) reported measurements on scales of a few parsecs showing inner jet direction extending to the southwest. The 1.3 mm structure corresponds closely with that observed in the central region of quasi-simultaneous super-resolution VLBA images at 7 mm. The closure phase changed significantly on the last day when compared with the rest of observations, indicating that the inner jet structure may be variable on daily timescales. The observed new direction of the inner jet shows inconsistency with the prediction of a class of jet precession models. Our observations indicate a brightness temperature of $sim 8times10^{10}$ K in the 1.3 mm core, much lower than that at centimeter wavelengths. Observations with better uv coverage and sensitivity in the coming years will allow the discrimination between different structure models and will provide direct images of the inner regions of the jet with 20--30 $mu$as (5--7 light months) resolution.
On 2015 June 16, Fermi-LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with a peak $>100$ MeV flux of $sim3.6times10^{-5};{rm photons};{rm cm}^{-2};{rm s}^{-1}$ averaged over orbital period intervals. It is the historically highest $gamma$-ray flux observed from the source including past EGRET observations, with the $gamma$-ray isotropic luminosity reaching $sim10^{49};{rm erg};{rm s}^{-1}$. During the outburst, the Fermi spacecraft, which has an orbital period of 95.4 min, was operated in a special pointing mode to optimize the exposure for 3C 279. For the first time, significant flux variability at sub-orbital timescales was found in blazar observations by Fermi-LAT. The source flux variability was resolved down to 2-min binned timescales, with flux doubling times less than 5 min. The observed minute-scale variability suggests a very compact emission region at hundreds of Schwarzschild radii from the central engine in conical jet models. A minimum bulk jet Lorentz factor ($Gamma$) of 35 is necessary to avoid both internal $gamma$-ray absorption and super-Eddington jet power. In the standard external-radiation-Comptonization scenario, $Gamma$ should be at least 50 to avoid overproducing the synchrotron-self-Compton component. However, this predicts extremely low magnetization ($sim5times10^{-4}$). Equipartition requires $Gamma$ as high as 120, unless the emitting region is a small fraction of the dissipation region. Alternatively, we consider $gamma$ rays originating as synchrotron radiation of $gamma_{rm e}sim1.6times10^6$ electrons, in magnetic field $Bsim1.3$ kG, accelerated by strong electric fields $Esim B$ in the process of magnetoluminescence. At such short distance scales, one cannot immediately exclude production of $gamma$ rays in hadronic processes.
Context. We report the detection by the AGILE satellite of an intense gamma-ray flare from the gamma-ray source 3EG J1255-0549, associated to the Flat Spectrum Radio Quasar 3C 279, during the AGILE pointings towards the Virgo Region on 2007 July 9-13. Aims. The simultaneous optical, X-ray and gamma-ray covering allows us to study the spectral energy distribution (SED) and the theoretical models relative to the flaring episode of mid-July. Methods. AGILE observed the source during its Science Performance Verification Phase with its two co-aligned imagers: the Gamma- Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE) sensitive in the 30 MeV - 50 GeV and 18 - 60 keV respectively. During the AGILE observation the source was monitored simultaneously in optical band by the REM telescope and in the X-ray band by the Swift satellite through 4 ToO observations. Results. During 2007 July 9-13 July 2007, AGILE-GRID detected gamma-ray emission from 3C 279, with the source at ~2 deg from the center of the Field of View, with an average flux of (210+-38) 10^-8 ph cm^-2 s^-1 for energy above 100 MeV. No emission was detected by Super-AGILE, with a 3-sigma upper limit of 10 mCrab. During the observation lasted about 4 days no significative gamma-ray flux variation was observed. Conclusions. The Spectral Energy Distribution is modelled with a homogeneous one-zone Synchrotron Self Compton emission plus the contributions by external Compton scattering of direct disk radiation and, to a lesser extent, by external Compton scattering of photons from the Broad Line Region.
A multiwavelength temporal and spectral analysis of flares of 3C 279 during November 2017--July 2018 are presented in this work. Three bright gamma-ray flares were observed simultaneously in X-ray and Optical/UV along with a prolonged quiescent state. A harder-when-brighter trend is observed in both gamma-rays and X-rays during the flaring period. The gamma-ray light curve for all the flares are binned in one-day time bins and a day scale variability is observed. Variability time constrains the size and location of the emission region to 2.1$times$10$^{16}$ cm and 4.4$times$10$^{17}$ cm, respectively. The fractional variability reveals that the source is more than 100% variable in gamma-rays and it decreases towards the lower energy. A cross-correlation study of the emission from different wavebands is done using the textit{DCF} method, which shows a strong correlation between them without any time lags. The zero time lag between different wavebands suggest their co-spatial origin. This is the first time 3C 279 has shown a strong correlation between gamma-rays and X-rays emission with zero time lag. A single zone emission model was adopted to model the multiwavelength SEDs by using the publicly available code GAMERA. The study reveals that a higher jet power in electrons is required to explain the gamma-ray flux during the flaring state, as much as, ten times of that required for the quiescent state. However, more jet power in magnetic field has been observed during the quiescent state compared to the flaring state.
We present the first FIR polarisation results of the OVV quasar 3C 279 obtained with ISOPHOT for two epochs in 1996 and 1997. We describe its integral polarisation properties at a wavelength of 170 micron where the source shows a maximum in its energy distribution. After a gamma-ray flare in January 1996, a polarisation of 23 % closely aligned with the radio jet axis was measured in July 1996. In June 1997, the polarisation degree had decreased to 6.5 % with a less good alignment. On the other hand, the total 170 micron flux is the same for both epochs. Our measurements provide additional constraints for the multi-wavelength properties of synchrotron emission in radio jets and the temporal evolution of these properties: they show that the FIR radiation of 3C 279 is optically thin and that its origin is very close to the core. The variability of the FIR polarisation without any change of the total FIR flux can be explained by a disordering of the magnetic field in between the core and the first stationary VLBI radio knot.
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