The impact of variability

I have reason to claim that the non-simultaneity of my broadband data does not strongly affect my results and conclusions. The XMM-Newton optical/UV photo- metry and X-ray spectra are truly simultaneous and sample the outer and inner accretion flows, respectively. The high-frequency end of the XMM-Newton spectra and low-frequency end of the NuSTAR spectra are of very similar flux levels despite the seventeen-month gap between observations. As noted in Section 4.5.1.1, the ap- parent discrepancy in spectral shape may be due to a calibration issue. Considering the higher frequencies, the flux levels of the NuSTAR and Swift BAT X-ray spectra are consistent in their region of overlap and the Fermi γ-ray data was chosen to sample the period covering the XMM-Newton observation. Turning to lower fre- quencies, the XMM-Newton optical photometry (simultaneous with the X-rays) are consistent with points sampling the continuum determined from the Keck optical spectrum. The GNIRS spectrum was flux-scaled to match the Keck data, because I suspect that the apparent difference in flux is due to a shift resulting from the un- certain absolute flux calibration of the near-IR spectrum rather than genuine source variability (as described inLandt et al. 2017). After this correction has been applied, the near-IR data then appears to connect with the mid- and far-IR bands sampled by

Spitzer and WISE. As I commented in Section 4.6.2, the WISE photometry agrees

very well with the Spitzer data even though the observations were separated by more than a year.

With regards to the Effelsberg and IRAM radio data,Angelakis et al.(2015) reported flux density variability magnitudes on average ≈ 30 % and up to 63 %, with the variability being more pronounced at higher frequencies. Whilst the flux densities at lower frequencies were generally stable, frequencies 14.6 GHz and above exhibited occasional flaring. However, the mean values from which I used in my analysis are not strongly affected by the flaring episodes and are broadly consistent with the stable, baseline level.

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I noted in Section 4.4.1.2 and Section 4.2.3.3 that the X-ray and γ-ray data were obtained during periods of low activity. Given the constancy in flux betweeen neighbouring frequency bands, it is therefore reasonable to conclude that all of my multiwavelength data is appropriate to describe this source in a low state. Although my data are mostly not simultaneous, for the reasons given above I do not expect that this impairs my overall conclusions.

4.6.5

The origin of the γ-ray emission

It is generally accepted that in the case of a high-accretion rate blazar, such as 1H 0323+342, the γ-ray emission results from the EC process. Here I compare my general findings with those from other similar studies. BothAbdo et al.(2009b) and

Paliya et al. (2014) (for the quiescent state) found that the dissipation region must

be relatively near to the SMBH, with Z_diss ≈ 1300 R_g, very similar to the value I used in the EC-disc model here, which adopts the mean FSRQ Z_diss of G10. Yao

et al. (2015a) were unable to constrain the location so well, since models with a

dissipation region located inside or outside of the BLR both reasonably reproduced their broadband SED. In my preferred EC-disc model, the jet emission region appears to be relatively near the accretion disc, with EC-disc photons producing the hard X-rays and the γ-rays. This is different to the findings of Paliya et al. (2014) where EC-BLR photons were dominant in all states (both quiescent and flaring). This is also different to Yao et al. (2015a) who considered only EC-BLR and EC-torus situations. Here, both the EC-BLR and EC-tor models are shown to overpredict the observed radio emission.

In many jet models, such as mine, it is assumed that R_diss = φZ_diss, therefore a compact emission region (with small R_diss) must be relatively near to the core of the AGN. However, other geometries have been proposed such as the ‘spine-sheath’ (e.g.Sol et al. 1989, Ghisellini et al. 2005,Sikora et al. 2016) or ‘turbulent cell’ (e.g.

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its entire cross-section so a compact emission region does not necessarily imply one that is close to the SMBH. For simplicity, and for the ease of comparison with the work of other authors, I have not considered alternative jet geometries here.

Overall, my EC-disc model has a set of parameters that best match the broadband SED, across an exceptionally wide range of frequencies, from the radio to γ-rays. This model has the added attraction that is very close to an energy equipartition solution with U_e/UB = 1.1. The parameters of the accelerated electron distribution

for this model are the same as those for the scaled-down FSRQ model, with the exception of the slope s₁ which is 1.5 in the former and 1.0 in the latter. It differs from the scaled FSRQ model mainly in that its magnetic field and power injected into the electrons are much lower than predicted.

The jet parameters determined from the fit to the SED are model-dependent. The parameter space is large and complex, so it cannot be claimed that one set of parameters represents a unique solution. I have attempted to restrict the various parameters through observational or theoretical considerations, using the modelling

of G&T09 and G10 as a framework; Table 4.7 lists these parameters and their

determined values or ranges. The external photon field parameters are very well determined from the multiwavelength data. Jet parameters such as the inclination angle are determined observationally and (under the assumption Γ_BLF ≈ 1/i) this sets a reasonable range for Γ_BLF. The parameters of the accelerated electron distribution are also likely to be relatively well determined; Table4.8 shows that I do not have to alter these greatly from the mean FSRQ values to achieve a reasonable fit to the data. It was necessary to adjust the slope s₁ of the distribution. Since the shape of the electron distribution is directly related to the (observed) shape of the synchrotron and EC humps, this minor alteration is justified by the data. The similarity of the injected electron distribution parameters to the mean FSRQ values implies that the electron acceleration mechanism in 1H 0323+342 is very similar to that in a typical FSRQ. Less well-determined quantities include the precise values of B and P_relwhich in turn influence the jet power. However, as described in Section 4.5.3it is possible

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to tune B and P_rel and Γ_BLF together to find a near-equipartition solution.