A Photo-Hadronic Model of the Large Scale Jet of PKS 0637-752

Abstract

Strong X-ray emission from large scale jets of radio loud quasars still remains an open problem. Models based on inverse Compton scattering off CMB photons by relativistically beamed jets have recently been ruled out, since Fermi LAT observations for 3C 273 and PKS 0637-752 give the upper limit far below the model prediction. Synchrotron emission from a separate electron population with multi-hundred TeV energies remains a possibility although its origin is not well known. We examine a photo-hadronic origin of such high energy electrons/positrons, assuming that protons are accelerated up to $10^{19}$ eV and produce electrons/positrons through Bethe-Heitler process and photo-pion production. These secondary electrons/positrons are injected at sufficiently high energies and produce X-rays and $\gamma$-rays by synchrotron radiation without conflicting with the Fermi LAT upper limits. We find that the resultant spectrum well reproduces the X-ray observations from PKS 0637-752, if the proton power is at least $10^{49}\text{erg}{\text{s}}^{-1}$, which is highly super-Eddington. It is noted that the X-ray emission originates primarily from leptons through Bethe-Heitler process, while leptons from photo-pion origin lose energy directly through synchrotron emission of multi-TeV photons rather than cascading. To avoid the overproduction of the optical flux, optical emission is primarily due to synchrotron emission of secondary leptons rather than primary electrons, or a mild degree of beaming of the jet is needed, if it is owing to the primary electrons. Proton synchrotron luminosity is a few orders of magnitude smaller.

10 pages, 5 figures, 1 table. To be published in the Astrophysical Journal

References in corpus (4)

• Energy spectra of gamma-rays, electrons and neutrinos produced at interactions of relativistic protons with low energy radiation
• Bethe-Heitler emission in BL Lacs: filling the gap between X-rays and $\gamma$-rays
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• Investigation of the Gamma-ray Spectrum of CTA 102 During the Exceptional Flaring State in 2016-2017
• XMM-Newton observation of the ultraluminous quasar SDSS J010013.02+280225.8 at redshift 6.326
• A Multi-Wavelength Study of Multiple Spectral Component Jets in AGN: Testing the IC/CMB Model for the Large-Scale-Jet X-ray Emission
• Constraints on Proton Synchrotron Origin of Very High Energy Gamma Rays from the Extended Jet of AP Librae