Constraints on the emission region of 3C 279 during strong flares in 2014 and 2015 through VHE γ-ray observations with H.E.S.S.

Abstract

The flat spectrum radio quasar 3C 279 is known to exhibit pronounced variability in the high-energy (100 MeV < E < 100 GeV) γ-ray band, which is continuously monitored with Fermi-LAT. During two periods of high activity in April 2014 and June 2015 target-of-opportunity observations were undertaken with the High Energy Stereoscopic System (H.E.S.S.) in the very-high-energy (VHE, E > 100 GeV) γ-ray domain. While the observation in 2014 provides an upper limit, the observation in 2015 results in a signal with 8.7σ significance above an energy threshold of 66 GeV. No VHE variability was detected during the 2015 observations. The VHE photon spectrum is soft and described by a power-law index of 4.2 ± 0.3. The H.E.S.S. data along with a detailed and contemporaneous multiwavelength data set provide constraints on the physical parameters of the emission region. The minimum distance of the emission region from the central black hole was estimated using two plausible geometries of the broad-line region and three potential intrinsic spectra. The emission region is confidently placed at r ≳ 1.7 × 1017 cm from the black hole, that is beyond the assumed distance of the broad-line region. Time-dependent leptonic and lepto-hadronic one-zone models were used to describe the evolution of the 2015 flare. Neither model can fully reproduce the observations, despite testing various parameter sets. Furthermore, the H.E.S.S. data were used to derive constraints on Lorentz invariance violation given the large redshift of 3C 279.

Neutrino production in blazar radio cores

“…For the target photon spectrum, we use the 3C 279 synchrotron SC spectrum model from ref. [53] (figure 7 of that work, low state), presented here in figure 2.…”

“…The simulation is performed in the core frame, so the spectrum of SSC photons of ref. [53] is converted to the photon density using eq. (2.1), and the resulting neutrino flux is converted back to the observer's frame using the inverse of eq.…”

Leptonic and Hadronic Radiative Processes in Supermassive-Black-Hole Jets

“…Detailed calculations including all relevant BLR lines and the thermal continuum from the disk scattered by the BLR [114,[142][143][144][145] show that the very detection of γ-ray photons with energies greater than 100 GeV from FSRQs is enough to put the location of the emitting region beyond the BLR. Observations of FSRQs at E > 100 GeV confirmed this scenario and proved that, at least for the sources that have been detected at high energies, the emitting region is at or beyond r BLR [146][147][148][149][150][151][152].…”

Studying the influence of external photon fields on blazar spectra using a one-zone hadro-leptonic time-dependent model

“…While the radius of the emission region may not expand as rapidly as the larger jet structure that surrounds it, it expands nonetheless while it travels through the jet [33] given the high energy densities in the emission region. While recent observational results [30,34] indicate compact emission regions beyond the BLR, and maybe even at tens of parsecs from the black hole, it is not clear whether these are indeed moving emission regions originating close to the black hole or turbulent cells within a larger flaring region. Similarly, while a high magnetic field can be expected close to the black hole, the expansion of the emission region causes a drop of the magnetic field with increasing distance.…”

“…The given parameter values are a toy model, which we use to perform a small parameter study. The parameters are based upon the flat spectrum radio quasar 3C 279 [30], however a direct data comparison is beyond the scope of this paper. Instead, we wish to analyze the influence of the external fields on the SED and the particle distributions.…”